Dehydrating Venus

By Phil Plait | December 18, 2008 10:09 am

Why is Venus so dry?

The atmosphere of Venus has almost no water in it at all, whereas water is everywhere on Earth. This has been a long standing mystery about out sister planet. Where did all the water go? The culprit may be the magnetic field of Venus, or, more accurately, its lack of one.

The Sun spews out subatomic particles in its solar wind. When they reach the Earth, these particles are snagged by our magnetic field tens of thousands of miles above the surface of our planet, where they are slowed and trapped. But Venus has no such field, so these particles slam directly into the atmosphere. They can impart so much energy to the atoms there that they can escape the planet entirely, like shrapnel accelerated by a bullet.

Venus Express sees water being ripped from the atmosphere of Venus.
Venus is losing water from its air due to the solar wind.
Click to see a very cool animation.

Venus Express, an ESA probe orbiting Venus now, has finally detected this directly. As it rounds Venus on its elliptical orbit, it can detect particles in space around the planet. Venus Express has found that hydrogen on the day side of Venus — the side facing the Sun — is flowing out of the atmosphere. Last year the probe detected both hydrogen and oxygen coming off the night side of Venus like a comet tail, indicating water was being stripped apart and ripped out of the atmosphere. This new day side finding is important in that it gives scientists a better look at the actual mechanism at work.

It’s not clear if this is the main process that has stripped the water from Venus over the past few billion years or not. We’re seeing the tail end of a very long series of events, and there are other factors. For example, the atmosphere of Venus is pretty different than ours; for some reason Venus’ carbon budget is all in its air, while ours is mostly locked up in sediment in the ocean floor. Venus suffered a runaway greenhouse effect, so it’s incredibly hot on the surface (400 C or about 900 F) and its atmospheric density is absurdly high. Any ocean on Venus would have boiled away long ago, putting all that water into the atmosphere, where possibly its lack of magnetic field left that water at the mercy of the solar wind.

So Venus may be dry because of its greenhouse effect coupled with having no magnetic field (and who knows, maybe those two things are related as well). But why does Venus have no magnetic field, and we do? Venus and Earth are roughly the same size and density, so why should we enjoy a strong field, and Venus has none?

And there is a remaining question: why has no oxygen been seen escaping the day side of Venus? They found hydrogen, but no oxygen. If it’s the last remaining water in the atmosphere of Venus providing the hydrogen, then oxygen should be there too. If it’s not, that means we still need to figure out what’s going on over there.

And, of course, all this points directly back at us. We know our planet is simultaneously stable (it’s had life on it for billions of years) as well as fragile (a lot of things have to be balanced pretty well for complex life to maintain itself).

When we look at Venus, there but for the grace of magnetic fields go us. It’s important we understand that, and so it’s critical that we continue to study the solar system and the Universe around us. Our water and our lives may depend on it.

Tip o’ the Faraday cage to Carl Zimmer.

CATEGORIZED UNDER: Astronomy

Comments (82)

Links to this Post

  1. A Second Hand Conjecture » Cool Image of Venus | December 19, 2008
  1. Robbie

    Why don’t Venus and Mars have magnetic fields? Or is the question, why are their magnetic fields so weak? Is the element and mineral composition of those planets drastically different than Earth’s? What about the other planets in the Solar system’s magnetic fields?

  2. IVAN3MAN

    Off topic, Phil, but is it just me or is everyone else getting the same error message when attempting to establish a connection with DiscoverMagazine/BadAstronomy?:

    WordPress

    Error establishing a database connection

    This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at localhost. This could mean your host’s database server is down.

    * Are you sure you have the correct username and password?

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    * Are you sure that the database server is running?

    If you’re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.

  3. Venus is also known for having the longest “day” of all the planets in the Solar System. It takes 243 days for Venus to rotate just once on it’s axis (which makes a day on Venus longer than a year on Venus). IF Venus ever had an ocean I wonder what part the planet’s achingly slow rotation might have played in the disappearance of it’s ocean. I would imagine that if the Earth rotated that slowly the day side would get pretty darn hot (but how hot, I don’t know). And I also have to wonder if Venus’s slow rotation and it’s lack of magnetic field have a common origin?

    Hmm, all I do know is I won’t be turning to Immanuel Velikovsky’s “Worlds In Collision” for the answer to those questions.

  4. IVAN3MAN, I got the same thing. I imagine it was some server dropping the ball.

  5. Todd W.

    @IVAN3MAN

    I’ve been getting that error intermittently, too.

  6. Todd W.

    @Imrryr

    I was thinking the same thing about Venus’ rotation speed being linked to the magnetic field.

    And, as a tribute to OilIsMastery, since Venus has no magnetic field to speak of, any matter on the planet has long since drifted off its surface and into space. You know, since gravity doesn’t exist, and all. :P

  7. Taking into account purely thermal effects it should take Venus more than 1.0E159 years to lose its Carbon dioxide atmosphere:

    Program to compute atmospheric loss from a planet

    Atmospheric gas = CO2 (carbon dioxide)
    Molecular weight of gas = 44.010 gm/mole
    Boiling point of gas = -78.0 deg C
    Molecular diameter of gas = 3.340 angstroms
    Surface temperature of planet = 462.0 deg C
    Mass of the planet = 8.15E-1 earth masses
    Radius of the planet = 9.50E-1 earth radii
    Surface pressure of the planet’s atmosphere = 9.20E1 atm

    Surface gravity of planet = 0.903 g’s
    Average density of planet = 5.242 gm/cm^3
    Escape velocity at surface of planet = 10.362 km/sec
    Surface density of the planet’s atmosphere = 6.71E-2 gm/cm^3
    Surface particle density of the planet’s atmosphere = 9.18E20 molecules/cm^3
    Mean free path of gas molecules at surface = 1.474 nanometers
    Isothermal scale height of the planet’s atmosphere = 15.617 km
    Minimum altitude of the exosphere = 434.738 km
    Fraction of total atmosphere comprised by exosphere = 8.14E-13
    Initial mass of planetary atmosphere = 4.83E20 kg
    Initial number of molecules in planetary atmosphere = 6.60E45

    RMS velocity of gas molecules = 645.5 m/sec
    Mean velocity of gas molecules = 594.7 m/sec
    = 1/17.424 * v-escape
    Most probable velocity of gas molecules = 527.0 m/sec
    Speed of sound at the surface of the planet = 421.8 m/sec

    Velocity of the peak of the distribution = 527.0 m/sec
    Fraction of gas moving at greater than escape velocity = 2.77E-167
    Average velocity of molecules above escape velocity = 10.376 km/sec
    Average time for a molecule to escape from atmosphere = 1.51E0 sec
    Fraction of total atmosphere lost per year = 2.91E-160
    Time for planetary atmosphere to lose 1% of its mass = 3.44E157 years
    Time for planetary atmosphere to lose half its mass = 2.37E159 years

    There is no significant loss of atmosphere over the age of the solar system

  8. Todd W.
  9. Changing the atmospheric component to water vapor reduces the time for atmospheric loss from ~1.0E159 years to ~1.0E60 years but it is still much longer than the age of the solar system. Of course, this is not taking into account the solar wind effects which may be quite significant.

    Program to compute atmospheric loss from a planet

    Atmospheric gas = H2O (water vapor)
    Molecular weight of gas = 18.015 gm/mole
    Boiling point of gas = 100.0 deg C
    Molecular diameter of gas = 3.770 angstroms
    Surface temperature of planet = 462.0 deg C
    Mass of the planet = 8.15E-1 earth masses
    Radius of the planet = 9.50E-1 earth radii
    Surface pressure of the planet’s atmosphere = 9.20E1 atm

    Surface gravity of planet = 0.903 g’s
    Average density of planet = 5.242 gm/cm^3
    Escape velocity at surface of planet = 10.362 km/sec
    Surface density of the planet’s atmosphere = 2.75E-2 gm/cm^3
    Surface particle density of the planet’s atmosphere = 9.18E20 molecules/cm^3
    Mean free path of gas molecules at surface = 1.157 nanometers
    Isothermal scale height of the planet’s atmosphere = 38.010 km
    Minimum altitude of the exosphere = 989.563 km
    Fraction of total atmosphere comprised by exosphere = 4.94E-12
    Initial mass of planetary atmosphere = 4.81E20 kg
    Initial number of molecules in planetary atmosphere = 1.61E46

    RMS velocity of gas molecules = 1008.9 m/sec
    Mean velocity of gas molecules = 929.5 m/sec
    = 1/11.148 * v-escape
    Most probable velocity of gas molecules = 823.8 m/sec
    Speed of sound at the surface of the planet = 670.2 m/sec

    Velocity of the peak of the distribution = 824.0 m/sec
    Fraction of gas moving at greater than escape velocity = 2.64E-68
    Average velocity of molecules above escape velocity = 10.395 km/sec
    Average time for a molecule to escape from atmosphere = 3.66E0 sec
    Fraction of total atmosphere lost per year = 1.14E-61
    Time for planetary atmosphere to lose 1% of its mass = 8.77E58 years
    Time for planetary atmosphere to lose half its mass = 6.05E60 years

    There is no significant loss of atmosphere over the age of the solar system

  10. @Todd W., IVAN3MAN, et al

    Yep, I’m getting that error intermittently too. It really sucks when the Discover blog software is worse than Blogspot’s free version.

    “And, as a tribute to OilIsMastery, since Venus has no magnetic field to speak of, any matter on the planet has long since drifted off its surface and into space. You know, since gravity doesn’t exist, and all.”

    I wasn’t sure if that guy was an Electric Universe guy or what. His web site had stuff on it like “Abiogenic Petroleum” which is actually not such an unreasonable idea – Thomas Gold promotes that theory in his 1999 book “The Deep Hot Biosphere”. I thought his web site was at least readable and nicely layed out. I didn’t see too much EU stuff on it but I guess I didn’t look too hard.

    At least it wasn’t like that guy who was promoting “Pan Theory”. What was his name? Forest Gump or something? He wanted to overturn all of modern physics with a 300-page PDF file that had like 3 equations in it. LOL.

  11. JoeSmithCA

    @Tom Marking
    *blink* *blink* *blink* *blink*
    [pause and then switches jumping up and down]
    Oh! Oh! Pretty green light in sky! Oh! Pretty! :)

  12. Andrew

    On a related note, does anyone know why Venus has such a slow rotation (to say nothing of being retrograde)?

    I assume that it must be because of a primordial collision, but has there been any research into this?

  13. Didn’t Birkeland once theorize that there is a large voltage potential between the hot plasma of the sun and the charges on the planetsary plates?

  14. IVAN3MAN

    Imrryr: “IVAN3MAN, I got the same thing. I imagine it was some server dropping the ball.”

    I imagine it is OilIsMastery and his friends mounting a “denial-of-service attack” on BadAstronomy out of spite for being labelled “a troll” and having his comments “spammed” by Phil.

  15. Cheyenne

    It’s not like this would ever keep me up at night but we know what Mars had plate tectonics at one point right? That it had a hot interior, and probably had a magnetic field? Do we know if Venus had a magnetic field at one point? I would guess it must have in its early years. So one planet farther away from the sun than us lost its field, and another one closer in lost it as well (and they are both fairly similar in make up to us).

    So I guess what I’m wondering is – will Earth loose it’s magnetic field in some unknown future date down the road? The radioactive isotopes in the mantle/core will run down, the interior will ultimately cool, and the field will shut down? That would be pretty bad for life on the surface.

    As you can tell, I have a PhD in geology. Particularly that kind that studies the other, um, planetary bodies and such.

  16. Imrryr:

    Venus’s temperature can easily be explained by it’s proximity to the Sun, coupled with its atmosphere. (Venus is hotter than Mercury thanks to a rampant greenhouse effect.) No need to invoke the spin rate on that particular point. However, you’re right, the lack of any significant spin probably is at least partially responsible for the lack of magnetic intrinsic magnetic field, as it is believed that the dynamos that generate the fields in the planets require a conducting, spinning fluid.

  17. The server issues were because the Top Ten list is getting a month’s worth of traffic in one day! The servers are being hammered, but the problems appear to be getting better.

    Tom Marking, the thermal loss of an atmosphere is probably not the dominating effect, so that calculation (if it’s correct) only goes to show that other processes are are at work here.

  18. Cheyenne:
    Where have you seen reference to Mars having plate tectonics? As of when I was in grad school (~ ten years ago), there were no bodies other than the Earth that showed evidence of plate tectonics. (Tectonics, yes. Plate tectonics, no.)

    I know of no evidence that Venus ever had a notable magnetic field, but you’re right that Earth will likely lose its eventually, assuming we aren’t vaporized by the expanding Sun first. It’d be the same cause as the death of Mars’s field: as the interior cools, the fluid slows and solidifies so it cannot work the dynamo process.

    That said, it’s probably (guessing, can’t recall the cooling timescale for Earth accurately) billions of years on, when we’d have other issues. And the amount of harm the lack of field would directly do isn’t as clear as the media often claims. Our atmosphere seems capable to stopping most dangerous radiation. On the other hand, the magnetic field may be protecting the atmosphere, so there’s a secondary effect to worry about.

  19. @Phil Plait “Tom Marking, the thermal loss of an atmosphere is probably not the dominating effect, so that calculation (if it’s correct) only goes to show that other processes are are at work here.”

    Phil, you are quite right. That calculation I provided only computes atmospheric loss due to the tail of the Maxwell-Boltzmann distribution being over the escape velocity of the planet. Doing a full-blown simulation involving solar wind/magnetospheric effects is way beyond the abilities of an amateur such as myself. It would probably require quite a bit of supercomputer time to do it correctly. I included my data for illustrative purposes only (i.e., it shows that it is much easier to lose H2O from an atmosphere than CO2 due to the difference in molecular weight). So it goes to support the idea that water may be preferentially lost from the Venusian atmosphere which is what your original post is all about.

  20. Gary Ansorge

    As has been noted before, Earth is the only planet in the solar system
    1)with known plate tectonics
    2) that is a binary system

    Plate tectonics is a known recycler of minerals, which brings calcium to the surface where it can interact with CO2 and sequester it.

    Wondering if the binary system is the probable cause of all that?
    Consequence of a binary planetary system:
    1) Luna flexes and drags, thru gravitational interaction on mass concentrations under earths mantle.
    2) this stirs the core resulting in:
    3) core electrical currents and resultant magnetic field generation

    If this is a viable proposition, it is interesting to consider the Fermi Paradox:
    What are the odds that a large enough impact with Earth from a body just the right mass, angle of impact and velocity to eject just the right mass to form our kind of binary system, early enough to generate a consistent magnetic field to protect H2O from solar wind degradation and allow life to prosper?

    I’m in a hurry to get to work, so I leave this as an exercise in frustration.

    GAry 7

  21. Dang, the animation is Quicktime. Is there a MOV player available that doesn’t involve submitting to the Borg Apple?

  22. @Cheyenne “we know what Mars had plate tectonics at one point right?”

    Actually, the presence of Olympus Mons on the Tharsis plateau of Mars is pretty good evidence that there is no plate tectonics acting on Mars now or during the last 2 billion years. Imagine for a moment what would happen to Hawaii if plate tectonics were to shut off on the Earth. The mantle plume would continue to shove magma upward only now the plate isn’t moving relative to the mantle. Hawaii would grow into a massive volcano, much bigger than it is now. You wouldn’t get a chain of islands, but just one gigantic one with a peak probably well over 50,000 feet in altitude. So having that gigantic volcano on Mars is pretty good evidence that the plates are not moving relative to the mantle.

  23. What are the odds that a large enough impact with Earth from a body just the right mass, angle of impact and velocity to eject just the right mass to form our kind of binary system, early enough to generate a consistent magnetic field to protect H2O from solar wind degradation and allow life to prosper?

    Evidently: p=1.0

    A better query might be: What is the probability that Gary’s query is a thinly veiled attempt to propose an argument in support of a mystical sky fairy that set everything up?

    Unfortunately, your query is unanswerable within current knowledge since we don’t know how much life prospers elsewhere under different conditions. Observation through the history of science to date would indicate that life prospers here because life has evolved to fit the conditions that are already here. Observation of life even on this planet where conditions are wildly different (abyssal vents, volcanoes, polar ice, etc.) would indicate that life CAN prosper under conditions quite different than are normally found here. Thus, there is no reason to think that there is now, nor was there ever “just the right…” anything that allows life to prosper.

    It’s probably fairer to say that the life that prospers here is just the right life for the ambient conditions.

  24. Cheyenne

    John- The “plate tectonics” on Mars bit was based solely on my thinking that they have a couple of huge canyons and a monster mountain. So I thought they formed from plate tectonics. But again, I obviously don’t really know.

    Do you know how fast it takes to “flip” the polarity of the field on Earth? Apparently this has happened many times in the past. Even though the media/Hollywood might play up the harm of that a bit (“The Core”) it would seem to be a little dangerous when that transition period is occurring.

  25. Cheyenne

    Tom – Ah, that seems to make sense.

    Science- learn something new every day!

  26. Jeffersonian

    I have the same question: where did Venus’ magnetic field go?
    How was it created in the 1st place and what changed?
    (ironically I was listening to the latest Magnetic Fields LP as I read this article)

    @EvoSquid
    There are tons that play .mov
    check at download.com
    There i s also a codex plug-in that allows Windows Media Player to decompress .mov
    However that site gave me a still picture, not anything animated

  27. @John Weiss “However, you’re right, the lack of any significant spin probably is at least partially responsible for the lack of magnetic intrinsic magnetic field, as it is believed that the dynamos that generate the fields in the planets require a conducting, spinning fluid.”

    But that explanation doesn’t explain why Mercury, which also has a very slow rotation period of 59 days, has a dynamo-induced magnetic field (~300 nanoteslas = 3 milligauss at the equator). Mercury rotates 4 times faster than Venus, but Venus is larger and should have more material in its core to generate a magnetic field. So it looks like rotation is not necessarily the deciding factor. Perhaps the chemical composition of the core has something to do with it.

  28. “The Sun spews out subatomic particles in its solar wind. When they reach the Earth, these particles are snagged by our magnetic field tens of thousands of miles above the surface of our planet, where they are slowed and trapped.”

    Where do these particles go once they are snagged by our magnetic field? I assume some of the matter converts to light (e.g. aurorae).

  29. DrFlimmer

    “However that site gave me a still picture, not anything animated”

    Under the picture on that site is a link to the “highres mov”

  30. dkary

    One quick comment on the thermal escape calculations: molecules like CO2 and H2O will be broken up by the high energy end of the solar UV flux, so you really need to look at the escape times for atomic hydrogen, carbon, and oxygen. These still may not come down to reasonable solar system times, but they will be lower than 10^60 years.

    I agree with Tom’s question about Mercury: it’s the really odd case in the whole geo-dynamo model: why should anything that small and that slowly rotating have an active dynamo? My last course on the topic was decades ago and I really didn’t follow much of it (partially my weakness in the material and partially a prof who was almost impossible to understand even when he wasn’t talking about Alfen waves). So I’d love to hear what the current thinking is on the Mercury dynamo, especially with the new Messenger results.

  31. @Gary Ansorge “Wondering if the binary system is the probable cause of all that? Consequence of a binary planetary system:
    1) Luna flexes and drags, thru gravitational interaction on mass concentrations under earths mantle.
    2) this stirs the core resulting in:
    3) core electrical currents and resultant magnetic field generation”

    Well, just in terms of the magnetic field it is NOT necessary to have a double planet (i.e., two masses in orbit of one another whose mass ratio is less than two orgers of magnitude). Jupiter’s moon Ganymede has a dipole generated magnetic field of 700 nanoteslas (7 milligauss) at the equator:

    http://en.wikipedia.org/wiki/Ganymede_(moon)#Magnetosphere

    “The Galileo craft made six close flybys of Ganymede from 1995–2000 (G1, G2, G7, G8, G28 and G29) and discovered that Ganymede has a permanent (intrinsic) magnetic moment independent of the Jovian magnetic field. The value of the moment is about 1.3E13 tesla-m^3, which is three times larger than the magnetic moment of Mercury. The magnetic dipole is tilted with respect to the rotational axis of Ganymede by 176°, which means that it is directed against the Jovian magnetic moment. Its north pole lies below the orbital plane. The dipole magnetic field created by this permanent moment has a strength of 719 nanoteslas at the equator of the moon, which should be compared with the Jovian magnetic field at the distance of Ganymede – about 120 nanoteslas. The equatorial field of Ganymede is directed against the Jovian field, meaning reconnection is possible. The intrinsic field strength at the poles is two times that at the equator — 1440 nanoteslas.”

    There is some evidence that Jupiter’s moon Io also has an intrinsic dynamo-generated magnetic field with a surface strength of 1,300 nanoteslas (13 milligauss) at the equator. Presumably both of these dyanamoes are caused by tidal flexing via Jupiter’s gravitational field. No double planet is needed.

  32. Elmar_M

    I always thought that earth magnetic field was due a spin- rotation of the the iron core inside the mantle. From what I understand that is supposed to cause electrostatic charging due to it “rubbing” against the core?
    I think there are also some plasma effects going on in the core (like electrons moving freely due to the iron being super hot and super pressurized?
    Maybe I am mixing something up though…
    Anyway, both Mars and venus are smaller than earth which means a smaller core, that most certainly has cooled off already in the case of Mars. Not so sure about Venus, but I doubt that the proximity to the sun really has that much effect on the temperature of the core.

    On the hydrogen escaping Venus on the dayside…
    Maybe this hydrogen is not actually from Venus, but hydrogen from the solar- wind. If it is ionic hydrogen (protons), then it might most likely be just that. I could imagine that the ions hitting Venus are (at least many of them) being slowed down in the atmosphere, maybe they are also reacting with the atmosphere?

    One question I have: I always thought that Venus’ atmosphere was rather dense (the cause of the greenhouse effect there). But if Venus, like Mars does not have a magnetic field, why is it not completely gone now, like Mars’ atmosphere is? Is Venus’ gravitation so much stronger for it to retain more atmosphere than Mars?
    But then the solar wind hitting Mars is much weaker. I always assumed that Mars atmosphere was “ripped” apart by the solar wind (and its water too).

  33. IVAN3MAN

    Evolving Squid, what’s your problem? QuickTime 7 Player is free!

  34. @dkary “One quick comment on the thermal escape calculations: molecules like CO2 and H2O will be broken up by the high energy end of the solar UV flux, so you really need to look at the escape times for atomic hydrogen, carbon, and oxygen. These still may not come down to reasonable solar system times, but they will be lower than 10^60 years.”

    Same parameters (i.e., Venus mass, temperature, etc.) but different atmosphere… Monatomic oxygen will still be retained over the life of the solar system. Helium (if there is any to begin with) will all be gone in a couple hundred million years. Diatomic hydrogen will all be gone in a few decades. And monatomic hydrogen will all be gone in only a few days. So yes, UV photodissociation of H2O will speed up the process tremendously, especially for the hydrogen, but not so much for the oxygen.

    Monatomic oxygen (molecular weight = 16):
    Time for planetary atmosphere to lose 1% of its mass = 2.13E51 years
    Time for planetary atmosphere to lose half its mass = 1.47E53 years

    Helium (molecular weight = 4):
    Time for planetary atmosphere to lose 1% of its mass = 2.77E6 years
    Time for planetary atmosphere to lose half its mass = 1.91E8 years

    Diatomic hydrogen (molecular weight = 2):
    Time for planetary atmosphere to lose 1% of its mass = 1.94E-1 years
    Time for planetary atmosphere to lose half its mass = 1.34E1 years

    Monatomic hydrogen (molecular weight = 1):
    Time for planetary atmosphere to lose 1% of its mass = 7.04E-5 years
    Time for planetary atmosphere to lose half its mass = 4.86E-3 years

  35. Tom Marking:

    Mercury is a bit of a mystery, last I knew, by dynamo theory isn’t simple either. It’s a weird little planet in many regards, though. For one thing, it has more metal in its interior than you’d expect. Also, remember Mercury’s field is fairly weak. (Stronger than you’d expect, but weak.)

    Another possible problem may be the requirement (I forgot to point out) of convection. I suppose it’s possible the Venus lacks convection inside, though I think I’d be rather surprised if it were the case. (I suppose material near the surface may not cool effectively, surpressing convection, but I can’t recall off hand hearing anyone suggest this.)

    Also, you can pretty easily rule out needing a “double planet” for a magnetic field. All four giant planets have womping fields, after all, to say nothing of the Sun. So either they all have a different mechanism, or the “double planet” hypothesis needs work. Furthermore, while Venus and Mercury lack moons (certainly large moons), they do have the Sun. Even at Earth’s distance, the Sun provides about half the tidal effect that the Moon does. At Venus’s position, should be up by a factor of about three from what we experience; at Mercury’s orbit, 16 times here. (So eight times more significant than the Moon’s tides on Earth.)

    Cheyenne:

    Valles Marineris is tectonic, but it’s due to the weight of the Tharsis bulge cracking the crust of Mars, almost certainly. The location and orientation of the canyon and the cracking around it are fairly suggestive of that.

    It takes around a few hundred to a thousand or so years for the field to switch. It’s a surprisingly fast process.

  36. @Elmar_M “Is Venus’ gravitation so much stronger for it to retain more atmosphere than Mars?”

    We actually don’t have any evidence on how thick Venus’ atmosphere was in the past. We know that it has a surface pressure of 92 atmospheres now but we have no data for the past. It could have been 9,200 atmospheres 4.5 billion years ago in which case it has lost 99 percent of its atmosphere into outer space. We just don’t know. We can rely on computer models like the one I presented which tell us that there should not have been any significant loss of a CO2 atmosphere over the age of the solar system via thermal effects alone. What the loss was via solar wind is pretty iffy since we don’t know what the strength of the solar wind has been during the past 4.5 billion years. So this is not an area where anyone can draw very precise conclusions.

  37. Helioprogenus

    One possible reason for Venus’ retrograde orbit and lack of magnetic field can be tied to an immense planetary collision early during the formation of our solar system. We’re rather certain that Earth was smacked by a mars sized object and in a trajectory that was able to eject enough material to form the moon. Now imagine if you will an object that strikes Venus in such a way that it alters its orbit. The energy involved in this must be unbelievably large. Compared to Earth’s early collision, Venus’ collision must have been a monster.

    Further, if such a powerful collision can alter the orbital rotation, the effects on the magnetic field can probably be likewise severe. Perhaps the collision effected the dynamo operating in the core, early in Venus’ formation, resulting in a loss of the magnetic field.

    I’m no planetary physicist, but I wonder whether the scenario is plausible.

  38. # Evolving Squid Says:
    Dang, the animation is Quicktime. Is there a MOV player available that doesn’t involve submitting to the Borg Apple?

    Try my favorite ‘universal’ player: VLC Player, available from videolan.org. Straight install it runs pretty much all video and audio, even has a version for ‘streaming’ video from my DVR (ReplayTV and DVArchive on the computer).

    # Cheyenne Says:
    Do you know how fast it takes to “flip” the polarity of the field on Earth? Apparently this has happened many times in the past. Even though the media/Hollywood might play up the harm of that a bit (”The Core”) it would seem to be a little dangerous when that transition period is occurring.

    An interesting SF series that deals with that, as well as ‘parallel universes’ is from Robert Sawyer – The Neanderthal Parallax: Hominids, Humans, Hybrids.
    (OT: Sawyer’s FlashForward is being developed as a TV series, involved the LHC startup in the original)

    J/P=?

  39. @Evolving Squid “What is the probability that Gary’s query is a thinly veiled attempt to propose an argument in support of a mystical sky fairy that set everything up?”

    Nah, would Gary do that to us? It’s more likely to be caused by a underworld deity similar to Hades but with better hair. No mystical sky fairies needed here. :)

    “Thus, there is no reason to think that there is now, nor was there ever “just the right…” anything that allows life to prosper.”

    Except that life has never been conclusively shown to exist anywhere else except on Earth (Chandra Wickramasinghe, Gilbert Levin, George Adamski, etc. notwithstanding). If life adapts itself to the ambient conditions then Mars should have life, Venus should have life, Mercury should have life, the sun should have life, etc., etc.

  40. john hart

    Is that animation what the scientists think it looks like or is that from real data?

  41. @Cheyenne “Do you know how fast it takes to “flip” the polarity of the field on Earth? Apparently this has happened many times in the past.”

    Nova on PBS had a good show on this subject a few years ago. Apparently a time period of from several hundred years to several thousand years is what it takes for a magnetic reversal. The last time it happened was 780,000 years ago but there is good evidence that it’s about to happen in the near future. Apparently once the magnetic field intensity gets weak enough the direction of magnetic north can change several degrees per day. This might cause us to include a daily magnetic report along with our daily weather report to predict where the 8 magnetic poles will be located tomorrow. Reading a compass will be quite fun during this period, I might add.

    http://www.pbs.org/wgbh/nova/transcripts/3016_magnetic.html

    “NARRATOR: No one has ever experienced a magnetic reversal. If this is really the beginning of a flip, what exactly will happen next?

    One man who may know, is geologist Rob Coe. For 25 years, he’s been coming to Steens Mountain in Oregon, a vast heap of hundreds of ancient lava flows.

    ROB COE (University of California, Santa Cruz): Sixteen million years ago there was a huge series of eruptions here. You can pick out literally hundreds of lava flows over on that wall. Each line delineates a different lava flow. It’s over 3,000 feet of overlying flows.

    NARRATOR: What makes Steens special, is that 16 million years ago, when this lava was erupted, the magnetic field was in the middle of a flip. Taking samples from dozens of flows all the way up the mountain, Rob and his colleagues have pieced together a detailed record of this magnetic reversal, although it’s so surprising that not everyone accepts it.

    ROB COE: What we found as it started to reverse was the strength of the Earth’s field decreased dramatically, by 80 or 90 percent.

    NARRATOR: The field started out pointing south, but as it weakened the direction of the field began to change erratically. After 300 years, it had swung a full 180 degrees to point north, and the field strength started to recover.

    ROB COE: But it couldn’t hold that polarity, and it fell back to…reversed and the intensity crashed again.

    NARRATOR: Once more the Earth’s magnetic shield practically disappeared, this time for 3,000 years. What was left was changing so fast that Rob found a flow that captured these wild gyrations even as the lava cooled.

    ROB COE: And what we found was even harder to believe. The quickly chilled margins in the bottom and the top had one direction, like that of the underlying flow, and the middle portion had a direction that was sixty degrees farther away. It was just as though, while the flow cooled, the field had moved sixty degrees, which if you calculate it out, that comes to about six degrees of movement per day. If we were observing this with a compass, you would be able almost to see the motion with your eye. It was truly astonishing and extraordinary.

    NARRATOR: The lava layers of Steens Mountain suggest we could be in for magnetic chaos, with magnetic north changing from day to day. More seriously, for perhaps thousands of years, the Earth’s magnetic shield will be weakened, something that will affect every person on the planet.

    GARY GLATZMAIER: The intensity of the magnetic field will be weaker, maybe ten, maybe a hundred times weaker than it is today, which means that more cosmic radiation will get through.

    ANDREW COATES: This basically opens our defenses so that solar and galactic radiation can hit the atmosphere directly. And this means that the radiation at ground level increases as well.

    NARRATOR: One estimate is that our overall exposure to cosmic radiation will double. And in some places it could be even worse.

    Today, the magnetic field focuses space radiation towards the far north and south where few people live. But as the main field collapses, the weak field that’s left will have a more complex structure. Instead of just two magnetic poles, there may be four or even eight, slowly moving across the Earth’s surface.”

  42. Law Mom

    Evolving Squid–

    Just last night I spent (wasted) 90 minutes trying to play .mov files from my new camera and kept getting a stupid Quicktime error about missing compressors or whatever. Even after downloading a couple of codec packages that should have worked, nothing. So finally I downloaded VLC for free and it worked like a charm. http://www.videolan.org/vlc/

  43. Aidan Karley (FGS)

    Mars and it’s (putative) plate tectonics : John Weiss, Cheyenne, Gary Ansorge, and I think Tom Marking were commenting on the suggested evidence ofr plate tectonics in some period of Mars’ history.
    Without checking my file of references (because they’re on a different continent, assuming that I’m currently floating above the African or Asian plate), about 1998 or 1999 a paper was published in Nature showing the results of magnetometry over large parts of the Martian surface, by satellite. (I forget which satellite, sorry) Over a significant portion of the southern hemisphere, IIRC 10s of degrees of latitude and considerably more in longitude, was a reasonably well-defined pattern of sub-parallel stripes of high-low magnetig field intensity alternations. While reminiscent of the classic map of the Reyjkanes Ridge, several elements we’re familiar with from terrestrial present-day tectonics were [b]not[/b] observed, including — no central feature (ridge) ; — no reflection of pattern across the central ridge; no noticeable topographic development.

    The favoured interpretation (then) was that this was evidence of a deep convection system operating long ago in Martian history, and that this resulted in an analogue of sea-floor spreading ; however with time, the core cooled, the convection shut down, any topographic expression died away … and Mars started to die.
    It is by no means clear cut evidence for Mars having once had processes like Earth’s plate tectonics, but it is significantly suggestive ; other proposals for Mars’ thermal and geological (“Areological”, surely) history will have to take this datum into account.

    Tectonics on Venus? Hmm, I’d have to go to read up on that. Certainly there have been proposed schemes that are very different to Earth’s history, but I haven’t got those in my head at the moment.

  44. IVAN3MAN

    @ Helioprogenus,

    I think that the two links in the following abstract of two articles will be of interest to you:

    According to Alex Alemi and David Stevenson of the California Institute of Technology, their recent study of models of the early solar system shows that it is very likely that, billions of years ago, Venus had at least one moon, created by a huge impact event. About 10 million years later, according to Alemi and Stevenson, another impact reversed the planet’s spin direction. The reversed spin direction caused the Venusian moon to gradually spiral inwards until it collided and merged with Venus. If later impacts created moons, those moons also were absorbed the same way the first one was. The Alemi/Stevenson study is recent, and it remains to be seen what sort of acceptance it will achieve in the scientific community.

  45. Torbjörn Larsson, OM

    Hydrogen escaping from the day side sounds like preferential sputtering by the solar wind protons to me. I should check if it’s feasible, but don’t know how to get the sputter yield out of that situation, so instead I ask what the current ideas are?

    Wondering if the binary system is the probable cause of all that?

    It was my understanding that the Earth-Moon system could be responsible, at least in part, but due to a different mechanism.

    AFAIU models of super-Earths put Earth sizes down as probably marginally plate tectonic, pending better understanding of the mechanisms perhaps.

    But, also AFAIU, a known consequence of the impact event that created the Moon was a preferential launching of crust material from both original bodies. (Seems atmospheres and cores mostly were retained by Earth.) IIRC evidenced by Moon rocks, heterogeneity of Moon composition, simulations, possibly more.

    So maybe Earth got a lucky last grazing great hit, while the last great impactor that putatively retrograded Venus didn’t make a large enough splash after all. (And the same for the last great impactor that thinned northern Mars, which I presume was too small for individual plates anyway.)

    As of when I was in grad school (~ ten years ago), there were no bodies other than the Earth that showed evidence of plate tectonics.

    Of course, some scientists cheats and call Mars an example of tectonics by “a single plate”:

    This is not the case on Mars, which appears to have a single plate that encapsulates the entire planet like the shell of an egg. But Shijie Zhong, associate professor of physics at the University of Colorado at Boulder, thinks this shell-like plate might be moving, driven by a powerful, single plume of hot material affecting the area of the thickened crust of the Crustal Dichotomy. This would explain the migration of volcanic activity in the Tharsis Rise region of the formation of Tharsis, he said.

  46. I was always under the impression (as above a few times) that the magnetic field was a result of Earth’s core rotating. I’m not saying I have valid proof of this, but it does seem to fit – Mars and Venus have weak/no magnetic fields and they have no current plate tectonics going on.

    Maybe the reason we have one is due to the theorized impact earth had with another body which created the moon? It could be that Earths core is still cooking as a direct result of that collision – and it’s possibly kept cooking thanks to the tidal force of the mixed effect of the moon orbiting and the earth spinning.

  47. JT

    If life adapts itself to the ambient conditions then Mars should have life, Venus should have life, Mercury should have life, the sun should have life, etc., etc.

    If rain puddles conform to the holes they find themselves in. Then rain puddles should exist in the middle of the Sahara, the Pacific ocean, and floating in thin air above our heads.

  48. Helioprogenus

    @ IVAN3MAN

    Thanks for the links. I wonder if the repercussions of those particular events had anything to do with the loss of Venus’ magnetic field. Also, because of its closer distance to the sun, it probably had a greater chance of receiving blows, and those two might not be the only planetary-scale events in Venus’ history.

    I can imagine Mercury possibly had even more collisions, and one may have ripped apart the crust and mantle, leaving the proportionally much larger iron/nickel core intact.

  49. Torbjörn Larsson, OM

    If life adapts itself to the ambient conditions then Mars should have life, Venus should have life, Mercury should have life, the sun should have life, etc., etc.

    I get the impression that today abiogenesis researchers assume life is really likely as opposed to earlier ideas. Current evidence albeit controversial hints that life started early on Earth, potentially before the oldest known rocks as some suggest based on mineral inclusion isotope ratios. So AFAIU the idea that it was a lucky event is iffy, and people have to look for prebiotic evolutionary mechanisms instead.

    Btw, I assume astrobiologists would ask of your examples how we know that Mars and Venus is and was truly sterile (proposed lasting niches are underground respectively atmospheric), and how you suggest Mercury and the sun plausibly entertain complex organic chemistry? Life is an adaptive system, but not all adaptive systems are life.

    To make it out, the biological process needs to hit on efficient evolution, and that seems to mean hereditary evolution as in all the examples we know of. Earth suspiciously lacks any form of eternal (but adaptable) life.

    And which might bring that point home further, it seems that efficient genetics was hit upon through a rather complicated path. (See the bootstrap from potentially pre-RNA to RNA to DNA/protein; the current idea that evidence points to the LUCA as potentially eukaryotic, with nucleus, introns, and what not, and just later made streamlined and robust as archea and bacteria under intense selection for thermophily and related niches; and let’s not forget sexuality. ;-) )

    Hence the need for organic chemistry to make flexible enough genetics, and possibly to make it through a bottleneck of messy and clunky generalist ancestors later arriving at something efficient and hardy like bacteria (or virus, even more abundant).

  50. @Torbjorn Larsson

    “Current evidence albeit controversial hints that life started early on Earth”

    Let’s assume for the sake of argument that life really is unique to Earth and exists nowhere else in the universe. If so then it must have started at some time after the Earth formed. So the fact that this particular starting time is very early in Earth’s history does not really speak to the uniqueness of life since there is no evidence that it is anything other than a coincidence. There is also the Anthropic Principle at work here: if life had started very late on the earth, say 4 billion years after the Earth formed, there would not be enough time for complex lifeforms such as ourselves to evolve in which case we wouldn’t be here huddled around the intertoobs debating this subject. With a statistical sample size of one you can not make sweeping conclusions. To put it another way, you roll a die and you get a 1 – this is not evidence that 1 is special. You roll the same die 100 times and you get 1 each time – this is overwhelming evidence that the die is rigged.

    “Btw, I assume astrobiologists would ask of your examples how we know that Mars and Venus is and was truly sterile (proposed lasting niches are underground respectively atmospheric)”

    Go back and read what I said which was “life has never been conclusively shown to exist anywhere else except on Earth”. If you or your astrobiologist associates know of such conclusive evidence for the existence of extraterrestrial life then please provide it. Otherwise it is not up to me to prove that it doesn’t exist.

    “And how you suggest Mercury and the sun plausibly entertain complex organic chemistry?”

    I didn’t suggest it. I believe you are suggesting that life requires complex organic chemistry. I wonder what that is based on. Perhaps a single sample?

    “To make it out, the biological process needs to hit on efficient evolution, and that seems to mean hereditary evolution as in all the examples we know of.”

    Again, this is based on a statistical sample of 1 planet.

  51. BaldApe

    NARRATOR: One estimate is that our overall exposure to cosmic radiation will double. And in some places it could be even worse.

    So just what does that mean? I mean, twice an eensy weensy bit is not very threatening (think of doubling you chance of being eaten by a tyrannosaur) but twice a small but significant risk is pretty bad.

    On the magnetic field/plate tectonics/rate of revolution argument, as I understand it the collision that created the moon would have merged the cores of the proto-earth and the Mars-sized body it collided with. That give the Earth a double core, meaning lots of molten iron and nickel, compared to Venus and Mars. The thicker layer of molten magnetic metal gives a stronger magnetic field, a greater dynamo effect, better shielding from the solar wind, and all that good stuff.

    Is that close to right?

  52. Gary Ansorge

    Squid: You’re wrong!

    Tom Marking:
    Excellant comment on Mercurys mag field and the tidal drag of the Sun.

    The reason I said it was an exercise in frustration is because we have insufficient data about plate techtonics, its cause and relationship to our “unique” double planet system(if any). I expect, if Luna was the size of Venus, we’d have both planets tidally locked together. How that would affect plate tech. I have no idea, but I suspect there wouldn’t be any such activity and it appears that plate tech. are required for the recirculation of material from the planets surface. A much larger satellite(than Luna) might eliminate that effect, a much smaller sat. would have so much less drag on Earth that again, we’d have no plate subduction. This is highly suppositional of course, since we have no other heavy core planets to compare us to(I’m leaving open the binary system of Pluto and Charon). The magnetic field quandary of Venus is a real puzzle. As you pointed out, the gravitational influence of Sol is quite adequate to induce drag if Venus was rotating fast enough. Perhaps the tidal lock (with Sol)occurred early enough to prevent the rise of life and its perennial balancing act(maintaining an acceptable environment).

    Note: This is really about the rise of COMPLEX life and its environmental requirements, stable enough for life but challenging enough to impel species development. Too much volcanism and you have excessive toxic gas exudates, too little and there’s not enough recirculation. Earth is the only metal rich, binary system w/in the “life zone” we know. I really look forward to our investigation of other solar systems. After we’ve developed the ability to spot earth sized planets in various stellar systems then perhaps we can acquire enough data to estimate the probability of complex life in the galaxy.

    I’d be willing to bet a binary system is a requirement for plate tech and I expect that will be known for sure within 100 years.

    GAry 7

  53. Al Viro

    Evolving Squid: er? How does one get from “life is quite rare” to “conditions on one particular planet (out of very big number) must have been set up”? After all, the number of sentient species on Earth makes a tiny fraction of the entire number of animal species, doesn’t it? And I’m yet to see anybody trying to use that as an argument in favour of H.sap. being engineered by somebody. Granted, *any* weirdness is probably promoted by some creationist somewhere, but…

    Seriously, whether the Rare Earth stuff is true or false, “the Earth couldn’t be anything unusual, unless you propose that somebody made it so” is not a valid argument. _If_ conditions needed for life are rare enough to leave a handful of inhabitable planets in the entire MW, we are still left with tens of billions of such planets in the Universe and anybody able to have such a conversation would observe these conditions locally, no miracles required. Hell, conditions on the Earth surface *are* unusual in at least one obvious respect anyway – just compare the volume of biosphere with that of the Solar System…

    Torbjörn Larsson: references? “The methods used in to root the tree are vulnerable to and with the present data we can’t even exclude the possibility of Eukarya being paraphyletic wrt Archea and Eubacteria” != “we think that Eukarya *is* paraphyletic wrt Archea and Eubacteria”, not to mention any statements about nucleus being present in the root node…

  54. Al Viro

    Sigh… “The methods used in (paper) are vulnerable to (list of artifacts) and with the present data…”. Comment preview would be really nice to have ;-/

  55. IVAN3MAN

    @ Helioprogenus, you’re welcome!

    Some more information that might be of interest:

    Astronomers have postulated that, early in Mercury’s history, a giant impact with a body several hundred kilometres across stripped the planet of much of its original mantle material, resulting in the relatively thin mantle compared to the sizable core.

    Alternatively, Mercury may have formed from the solar nebula before the Sun’s energy output had stabilized. The planet would initially have had twice its present mass, but as the proto-Sun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K, and possibly even as high as 10,000 K. Much of Mercury’s surface rock could have been vaporized at such temperatures, forming an atmosphere of “rock vapor” which could have been carried away by the solar wind.

    A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material.

    As for the lack of a magnetic field around Venus, a dynamo requires three things: a conducting liquid, rotation, and convection. The core is thought to be electrically conductive, and, while its rotation is often thought to be too slow, simulations show that it is quite adequate to produce a dynamo. This implies that the dynamo is missing because of a lack of convection in Venus’ core. On Earth, convection occurs in the liquid outer layer of the core because the bottom of the liquid layer is much hotter than the top. Since Venus has no plate tectonics to let off heat, it is possible that it has no solid inner core, or that its core is not currently cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already completely solidified.

  56. Gary Ansorge

    ADDENDUM: I expect simple life will eventually be found to be ubiquitous. Anywhere it can exist, it will but COMPLEX life??? AH, that’s another story altogether.

    Well, we’ll see,,,eventually,,,

    These have been some of the most interesting/informative posts I’ve seen in quite a while. I guess the trolls were more of a distraction than I’d realized,,,

    Gary 7

  57. @Gary Ansorge “ADDENDUM: I expect simple life will eventually be found to be ubiquitous. Anywhere it can exist, it will but COMPLEX life??? AH, that’s another story altogether.”

    Gary, I see you are buying into the Rare Earth hypothesis of Ward and Brownlee, hook, line, and sinker and I’m assuming that you’ve read the book? I think it was an excellent book but it does make a number of predictions. Perhaps the most important is that microbial life exists on almost all small rocky or icy worlds, perhaps at great enough depth for the interior heat to generate temperatures within the liquid range of water. As yet, there is no experimental evidence that this prediction is true in our solar system. Perhaps we will confirm it someday soon but it has not yet been confirmed as we speak.

    I prefer to keep my powder dry until the evidence is in. No one would be happier than me if it turns out to be true (O.K. I lied – the discoverers of such extraterrestrial life would be happier since they will be getting the Nobel Prize and will thus become chick magnets for the rest of their lives but that’s a whole ‘nother story).

  58. @BaldApe “So just what does that mean? I mean, twice an eensy weensy bit is not very threatening (think of doubling you chance of being eaten by a tyrannosaur) but twice a small but significant risk is pretty bad.”

    I believe the Nova web site gave an estimate of an extra 100,000 cancer deaths caused by the increased radiation. This is small but noticeable.

    “NARRATOR: It’s impossible to know for sure, but the best guess is that every year a hundred thousand people would die from the increased levels of space radiation. But of course this would still represent only a relatively small increase in the overall incidence of cancer.”

    “That give the Earth a double core, meaning lots of molten iron and nickel, compared to Venus and Mars.”

    The average density of Earth is 5.5 gm per cm^3. The average density of Venus is 5.2 gm per cm^3 or 5 percent less than Earth’s. If Earth really had double the iron/nickel core of Venus wouldn’t it’s average density be much, much higher than Venus? Sorry, not looking good for a doubled core for Earth.

  59. @Al Viro “Seriously, whether the Rare Earth stuff is true or false, “the Earth couldn’t be anything unusual, unless you propose that somebody made it so” is not a valid argument.”

    Yes, thank you! Couldn’t have said it any better myself.

  60. Gary:

    Sometimes it’s hard to tell the players apart without a programme! :) You know how the creobots can be.

    Thanks all for the VLC references, all. I’ll download that and give it a shot.

  61. After all, the number of sentient species on Earth makes a tiny fraction of the entire number of animal species, doesn’t it? And I’m yet to see anybody trying to use that as an argument in favour of H.sap. being engineered by somebody.

    Are you kidding? That’s one of the most common creationist arguments in favour of the mighty Ghod.

  62. @Gary Ansorge “I expect, if Luna was the size of Venus, we’d have both planets tidally locked together. How that would affect plate tech. I have no idea, but I suspect there wouldn’t be any such activity and it appears that plate tech. are required for the recirculation of material from the planets surface. A much larger satellite(than Luna) might eliminate that effect, a much smaller sat. would have so much less drag on Earth that again, we’d have no plate subduction.”

    What is the purported connection between Earth’s satellite and plate tectonics? Is it that the moon causes plate tectonics due to tidal effects? Or is it strictly that the way the moon came to be formed (due to a collision with a Mars-sized object and Earth) changed the geological properties of the Earth which allowed plate tectonics to happen? And is it being alleged that if the Earth were suddenly to become tidally locked with the moon (or some other hypothetical satellite) its plate tectonics would cease?

    This seems to somewhat different than the Ward/Brownlee Rare Earth Hypothesis in which the only notable thing the moon does is to cause spin axis stabilization for the Earth. I don’t recall them claiming the moon was involved in plate tectonics in any way.

  63. bjn

    Since the Moon is a remnant of a collision of Earth and a Mars-size body, perhaps that event provided this planet with an extra helping for its radioactive core.

  64. Gary Ansorge

    Tom:
    Yes, I’ve read Rare Earth and no, they made no such proposition about the tidal drag as the source of plate tech.,,,that’s just my take on the subject and that came from the observation that satellites in Earth orbit accelerate as they pass over large masscons beneath Earths surface which set me wondering how tidal interaction from Luna would interact with them. As far as the Rare Earth proposal is concerned, it would go a long way toward explaining the Fermi Paradox but we have to wonder WHAT(besides complex life) IS so rare about Earth and the only thing I can see is that we have plate tech., which we do not observe in the other planets in Sols “life zone” (or anywhere else, for that matter).
    Thus we have:
    1) Venus: Hot, dehydrated, dead
    2)Mars: Cold, dehydrated(but with frozen or sub-surface H2O), but seemingly dead.(I’m hoping we find SOME kind of life when we get there but,,,)
    3)Earth, w/plate tech., stable, transparent atmosphere for over 4 billion years, lots of complex life.
    4)Earth has the largest satellite in proportion to the size of the primary of any Solar system planet. THAT’S “rare”. (at least in so far as our limited (Solar system)sample can show).
    5)Earth is not tidally locked, thus the core is still spinning(magnetic field production, protection from H2O degradation)
    Plate tech. allows subsurface metals(like calcium) to be recycled to the surface, where it can interact with CO2 and sequester it. What we don’t know is if that is a requirement for atmospheric stability. We’ve assumed it is life itself that creates that stability but it may be tectonic recycling that is the true rarity. SO, Europa, Ganymede, Enceladus with their H2O may show us life is capable of developing and surviving in any locale that has liquid H2O, but may need “something else”, to become really complex. That “something else” includes an energetic environment that remains stable for billions of years,,,seems almost a contradiction in terms, because “energetic” usually randomizes complex organic structures, which is why an ozone layer seems a requirement for protection from UV, a thick atmosphere to protect against energetic stellar and interstellar radiation and a strong planetary mag. field to protect H2O from dissociation by the Solar wind.
    ,,,but there also seems to be a requirement for that sequestering of hot house gasses and the only natural answer I see to that is the sequestering from recycling interior metals.

    I have a sneaking suspicion that there is a narrow range of mass/distance relationship between primary and satellite that is responsible for that but it will take some hard modeling by REAL experts in this field to show if there is, in fact, a causal relationship between Lunas mass and our plate tech. and between plate tech. and atmospheric stability. My background is in physics and computer technology, not geophysics/astrophysics. I think those are the disciplines that are needed to answer that question.
    Since I’m just a generalist, I can only propose, point at something and ask,,”DuH! Why is that like that???”
    IF it turns out that plate tech. is dependent upon a critical mass/distance relationship between primary/satellite AND that plate tech. is a requirement for long term atmospheric stability AND that this is a rare relationship, THEN we may have an explanation for why the (local) interstellar volume seems bereft of other complex life.

    AH, logic, what a wonderful two edged sword it is,,,

    Gary 7

  65. Aidan Karley (FGS):

    You’re right, the stripes are suggestive. But I also agree that it’s far from clear-cut. In fact, I don’t (personally) know of many researchers who think that those stripes really mean plate tectonics existed on Mars. If I recall right, they were pretty huge (covering a substantial fraction of the planet), which doesn’t seem right to this non-geologist. Also, aren’t they found in the southern hemisphere? The oldest terrain? You’d expect the opposite, no?

  66. @Gary Ansorge “Plate tech. allows subsurface metals(like calcium) to be recycled to the surface, where it can interact with CO2 and sequester it.”

    Actually there are many types of chemical weathering that can remove CO2 from the atmosphere. The importance of plate tectonics is that it allows this CO2 to be released back into the atmosphere. This happens near subduction zones where the subducted rock becomes heated thus causing magma to rise upward towards volcanic vents where it can release its sequestered CO2 into the atmosphere.

    “What we don’t know is if that is a requirement for atmospheric stability. We’ve assumed it is life itself that creates that stability but it may be tectonic recycling that is the true rarity.”

    A stable atmosphere may not be the key ingredient. Jupiter, Saturn, Uranus, and Neptune have probably had stable atmospheres for billions of years and yet they may not contain life.

    “I have a sneaking suspicion that there is a narrow range of mass/distance relationship between primary and satellite that is responsible for that”

    Keep in mind that the Earth-Moon distance is not a constant. The moon was once much closer to the earth than it is now. Here is some data for you. It turns out that 4 billion years ago the moon was 6.6 times closer to the earth than it is now. It orbited the earth in just 1.6 days and the earth was rotating once every 6.9 hours.

    Time in Rotation Distance Revolution
    the past period of of satellite period of
    (years) primary from primary satellite
    (hours) (kilometers) (days)
    ——– ———- ————- ———–

    0.00E0 23.934 3.84E5 27.322
    1.00E8 23.382 3.80E5 26.847
    2.00E8 22.836 3.75E5 26.362
    3.00E8 22.297 3.71E5 25.865
    4.00E8 21.764 3.66E5 25.357
    5.00E8 21.238 3.61E5 24.837
    6.00E8 20.718 3.56E5 24.304
    7.00E8 20.204 3.50E5 23.760
    8.00E8 19.697 3.45E5 23.203
    9.00E8 19.196 3.39E5 22.634
    1.00E9 18.702 3.33E5 22.052
    1.20E9 17.733 3.21E5 20.850
    1.40E9 16.790 3.08E5 19.597
    1.60E9 15.872 2.94E5 18.294
    1.80E9 14.981 2.80E5 16.941
    2.00E9 14.115 2.64E5 15.542
    2.20E9 13.274 2.47E5 14.101
    2.40E9 12.460 2.30E5 12.624
    2.60E9 11.671 2.11E5 11.122
    2.80E9 10.909 1.91E5 9.606
    3.00E9 10.172 1.71E5 8.093
    3.20E9 9.460 1.49E5 6.607
    3.40E9 8.775 1.27E5 5.176
    3.60E9 8.115 1.04E5 3.835
    3.80E9 7.481 8.07E4 2.627
    4.00E9 6.873 5.80E4 1.601
    4.20E9 6.291 3.67E4 0.806
    4.40E9 5.734 1.83E4 0.283
    4.50E9 5.466 1.08E4 0.128

  67. @John Weiss “You’re right, the stripes are suggestive. But I also agree that it’s far from clear-cut. In fact, I don’t (personally) know of many researchers who think that those stripes really mean plate tectonics existed on Mars.”

    Also, from the Nova PBS web site I referenced previously, it seems that Mars lost its global magnetic field prior to 2 huge impacts: Hellas and Argyre. These are dated to 4 billion years ago or older. So if Mars ever had plate tectonics it was more than 4 billion years ago.

    “NARRATOR: Mario realized that two dramatic events in the early history of Mars might lead him to the answer.

    MARIO ACUNA: We found two very large impact basins in the southern hemisphere of Mars, which are Hellas and Argyre. There was absolutely no magnetization over them.

    NARRATOR: In these basins, formed when two huge meteorites hit Mars, the rocks were strikingly free of magnetism. And that was odd, because the huge impacts must have melted the crust, and as it cooled again, the rocks should have become magnetized by the strong Martian magnetic field. Yet there was no trace of magnetism in Hellas and Argyre.

    MARIO ACUNA: Which immediately meant that they were formed after the magnetic field of Mars had ceased to exist, and the estimate is that these impacts took place more than 4,000,000,000 years ago.”

  68. Gary Ansorge

    Tom: Your table of data isn’t particularly clear. Do you mean Luna was only 36,000 miles from Earth? Because if that is the case, it was inside Roches limit and should have been no more than a pile of rubble(ie, within 5 planetary diameters, a satellite is subject to disruptive gravity tides and would break up).

    Gary 7

  69. Gary Ansorge

    Tom: I am aware of that Luna was once closer to Earth and that Earth had a much faster rotational velocity which transferred to the “pile of rubble”, impelling it outward where it could coalesce. Only after it had become a point source gravitational influence could it have interacted in such fashion as to have initiated tidal drag.

    Jupiter, Saturn, et al, are massive and far from the disruptive influence of solar wind, so of course they have much the same atmospheres today as they had 4 plus billion years ago but they’re not in the “life zone” so I doubt we can make any qualitative comparison with our rocky, metal rich inner planets.
    Neither do they provide any data for us regarding plate tectonics or its effects on OUR atmospheric stability or lack thereof.

    GAry 7

  70. Gary, I don’t think so. The Roche limit for the Earth is around 1.5 – 3 Earth radii, depending on your definition. (That’s from just doing the calculation right now and it’s consistent with models of lunar formation I’ve seen.) For most planets, the fluid Roche limit is around 2 radii. It depends a bit on the density of the planet and the secondary, but it’s actually a surprisingly weak dependence. The Moon probably formed at the outer edge of that limit, possibly a bit inside it even.

  71. Gary Ansorge

    John:

    My data on the Roche limit was from a physics class taken about a half century ago. At that time(dark ages) it was given as a flat five times the (primary) planetary diameter, ie, about 40,000 miles for the Earth/Luna system. Obviously, that was way to simplistic.
    Thanks for the knowledge upgrade. Now I’ll just have to dump that “old” knowledge in the bit bucket. Gotta make room for the new,,,

    GAry 7

  72. @Gary Ansorge “Tom: I am aware of that Luna was once closer to Earth”

    The point is that there is no “narrow range of mass/distance relationship” for the Earth-Moon system since the distance has varied by over a factor of 30 and life has continued throughout that range of distances (unless you want to call a dynamic range of 16dB narrow :) )

    Concerning the Roche limit, I always remember it as being 1.4 times planet radius but maybe that’s from some outdated textbooks. In any case I wasn’t particularly trying to model that in my program so just disregard all distances you consider inside the Roche limit.

  73. Overall, the Roche Limit is just a rule of thumb. It’s not nearly as hard and fast as people often thing. We showed that there’s reason to think accretion has occurred within Saturn’s traditional Roche limit, for example, via simulations and data on some of the small moons.

  74. Gary Ansorge

    Tom:
    We have no way(I’m aware of) of knowing whether plate tech. has been continuous for the entire 4 plus billion years since the moon was expelled(Hah!). In the early days, Sol was 40% cooler than it is today, so hot house gasses would have been useful(at keeping H2O liquid). By the time the sun heated up enough to precipitate problems, we MAY have been up to speed with the plate tech aspect. My proposition is that plate tech is a direct outgrowth of (Lunar) tidal drag(which requires Luna to have already condensed and for there to be displaced mass concentrations w/in Earth for the tidal drag to affect)
    AND that plate tech is what’s responsible for keeping total hot house gasses at a life tolerable level but I doubt it was a significant factor 4 billion years ago. However, 4 billion years ago, Venus probably had water and maybe simple life. It’s what has occurred since then that is the puzzle.

    GAry 7

  75. @Gary Ansorge “My proposition is that plate tech is a direct outgrowth of (Lunar) tidal drag”

    I must respectfully disagree on that point. As someone has already pointed out (it may have been John) the sun also produces tides on the earth which are about half the size of the tides produced by the moon. Since tidal effects go as the inverse cube of the distance then that means the solar tides on the inner planets are something like:

    Venus: ~1.5 times Earth’s lunar tides
    Mercury: ~8 times Earth’s lunar tides

    If the lunar tides are strong enough to cause plate tectonics on Earth then the solar tides are definitely strong enough to cause plate tectonics on Venus and especially Mercury. Yet there is no evidence that either Venus or Mercury has plate tectonics.

  76. IVAN3MAN

    @ Tom Marking,

    Yes, but the Earth’s rotation period is 23h:56m:04s — equatorial rotation velocity: 1674.396 km/h — whereas Mercury’s rotation period is 58.646 (Earth) days — equatorial rotation velocity: 10.892 km/h — and Venus’ rotation period is 243.16 (Earth) days — equatorial rotation velocity: 6.52 km/h. Maybe that has something to do with plate tectonics — more rapid flexing of the Earth’s crust due to tidal force interaction from the Moon.

  77. Torbjörn Larsson, OM

    Ah, sorry I didn’t get to this yeasterday.

    @ Tom Marking:

    With a statistical sample size of one you can not make sweeping conclusions.

    True. However, science sees this as a process that can be recurrent. By your own assumption of uniqueness you can conclude that it is unique. By science assumption of an abiogenesis process that can happen if the environment is habitable, it follows that the sample tells them about the process at some likelihood.

    There is also the Anthropic Principle at work here: if life had started very late on the earth, say 4 billion years after the Earth formed, there would not be enough time for complex lifeforms such as ourselves to evolve in which case we wouldn’t be here huddled around the intertoobs debating this subject.

    Again true, by those numbers, but we are discussing tens of hundreds of million years against delays of billions. After multicellularity led to body plans (happened independently several times), complex life forms hit on us after half a billion years. We can still tell that abiogenesis is easy; easier than complex life forms such as ourselves. (Instead anthropicity is, ironically, probably luck.)

    If you or your astrobiologist associates know of such conclusive evidence for the existence of extraterrestrial life then please provide it.

    Your argument was that several locales that “should” have life has not. If you claim no evidence you have no argument.

    (To spell it out in detail, the difference is that astrobiologists doesn’t claim that all volumes of space has life, they don’t even base any science on assuming that any body except Earth is known to harbor life. They are trying to find out.]

    I believe you are suggesting that life requires complex organic chemistry. I wonder what that is based on.

    Read my previous comment for such a base; several in fact.

    Again, this is based on a statistical sample of 1 planet.

    It was based on a statistical sample of a vast biosphere under billions of years. Notably all life stems from a single LUCA that obeys evolution. Where are the vast amount of contenders that is expected if other biological processes are more efficient – or more likely, why aren’t we all such life?

    Measuring a stochastic process is not the same as making a random measurement! I see that some suggest you bone up on statistical processes. Maybe that is a good idea.

  78. Torbjörn Larsson, OM

    Again, sorry I didn’t get to this yesterday.

    @ Al Viro:

    references?

    The Last Universal Common Ancestor: emergence, constitution and genetic legacy of an elusive forerunner (Biology Direct, July 2008):

    LUCA does not appear to have been a simple, primitive, hyperthermophilic prokaryote but rather a complex community of protoeukaryotes with a RNA genome, adapted to a broad range of moderate temperatures, genetically redundant, morphologically and metabolically diverse. LUCA’s genetic redundancy predicts loss of paralogous gene copies in divergent lineages to be a significant source of phylogenetic anomalies, i.e. instances where a protein tree departs from the SSU-rRNA genealogy; consequently, horizontal gene transfer may not have the rampant character assumed by many. Examining membrane lipids suggest LUCA had sn1,2 ester fatty acid lipids from which Archaea emerged from the outset as thermophilic by “thermoreduction,” with a new type of membrane, composed of sn2,3 ether isoprenoid lipids; this occurred without major enzymatic reconversion. Bacteria emerged by reductive evolution from LUCA and some lineages further acquired extreme thermophily by convergent evolution.

    “The methods used in to root the tree are vulnerable to and with the present data we can’t even exclude the possibility of Eukarya being paraphyletic wrt Archea and Eubacteria” != “we think that Eukarya *is* paraphyletic wrt Archea and Eubacteria”,

    Thanks, now I had to get paraphyly finally.

    Yes, that claim is true if I understand correctly, but the authors seem to have some actual support for their ideas rather than claiming a possibility from undecidable data.

    not to mention any statements about nucleus being present in the root node…

    They present several potential nodes, but seem to prefer a RNA LUCA with a nucleus:

    If LUCA had a RNA genome and DNA synthesis was invented twice [11,60], we could consider the possibility that a membraneous compartment (let us call it a protonucleus) had already formed autogenously around the primeval RNA genome, so that the nucleus itself would not necessarily have emerged twice independently. Such compartmentation could very early have played a capital role in protecting RNA, in ensuring its correct partition at cell division and in separating replication and editing from protein synthesis. An interesting model [61] suggests that proteins of nuclear pores and coat vesicles (thus components of the endocytotic apparatus) could have been formed endogenously from defined protein structural modules. This model makes the emergence of the nucleus much less of a mystery than before and links nucleogenesis to the emergence of phagocytosis (see further). Moreover, as pointed out by P. Forterre in his comments on this paper, RNA “nuclei” still exist today since RNA viruses recruit host membranes elements to form compartments in which their replication apparatus is surrounded by one or two membrane layers with an opercule for communication with the cytoplasm [62].

    It seems that, on the whole, the model of a protoeukaryotic RNA LUCA is in keeping with current evidence. In particular, the antiquity of an already complex spliceosomal mechanism, appearing to have evolved before the last ancestor of living eukaryotes, is not easy to reconcile with eukaryogenesis by merging of prokaryotes. Rather, the LUCA itself may have been that ancestor, already endowed with the forerunner of the eukaryotic nucleus.

    The occurrence of nucleus-like structures in some Planctomycetes, in Poribacteria (and perhaps some Archaea as well [27] is a striking feature that must be accounted for in evolutionary scenarios centered on LUCA. The possibility of early endogenous nucleogenesis by a rather straightforward mechanism [61] places the origin of the Planctomycete nucleus in a new perspective. The nuclear body of Gemmata, with its double membrane and its pores, is presently the closest approximation of a eukaryotic nucleus outside of its traditional Domain. There may be a relationship between this eukaryotic-like structure and the capacity for sterol biosynthesis, a feature of Planctomycetes [[66] and next section]. It is however not known whether these structures are really homologous nor is it known whether TT-coupling is the rule in this bacterial group; moreover, there are ribosomes in both the cytoplasm and in the Gemmata nuclear body.

    Not being a biologist, I would like to hear any comments on the survey and its results, especially as regards “nucleus-like” vs “nucleus”. Also, the authors rely partly on papers which I’ve heard biologists elsewhere note as using unusual or unsound cladistic methods, such as forcing constraints. On the hand it is AFAIU permissible in other fields, where you want to identify possible, or enforce known, constraints and not just rely on “natural” solutions.

  79. @Torbjorn Larssen

    “However, science sees this as a process that can be recurrent.”

    There is no evidence that it can be recurrent. Scientists have not been able to reproduce abiogenesis in the laboratory, nor has life been proven to exist anywhere except on Earth.

    “By your own assumption of uniqueness you can conclude that it is unique.”

    No, you are misconstruing what I am saying. I do NOT assume that life is unique on Earth (indeed I would be very, very happy if that was not the case). I am simply saying that there is NO convincing evidence to the contrary. Those are really two vastly different positions.

    “We can still tell that abiogenesis is easy; easier than complex life forms such as ourselves. (Instead anthropicity is, ironically, probably luck.)”

    Of course, complex life forms have to follow abiogenesis in order of time. Other than timing I don’t know what evidence you are suggesting which tells us which part of the process was easy and which part of the process was difficult. If process A took twice as long as process B then was process A necessarily twice as difficult as process B?

    “Your argument was that several locales that “should” have life has not.”

    Again, complete misconstrue – I claim there is NO evidence that those locales have life, not that I have evidence that they don’t. You do see the difference there, don’t you?

    “It was based on a statistical sample of a vast biosphere under billions of years. Notably all life stems from a single LUCA that obeys evolution. Where are the vast amount of contenders that is expected if other biological processes are more efficient – or more likely, why aren’t we all such life?”

    A vast biosphere but all descended from one LUCA. I believe you’ve answered your own question – due to the Founder Effect in many ways all of life on Earth is just one data point, or as Carl Sagan might say, one voice in the Cosmic Fugue.

    “I see that some suggest you bone up on statistical processes. Maybe that is a good idea.”

    Yes, that comment came from someone who thought 35,000 data points was a statistically small sample. LOL.

  80. Sam Platts

    I think we don’t give enough attention to the fact that we are a binary system, as Gary points out. We take the moon too much for granted, without considering the total effect the moon has upon the EArth, far beyond tides and moonlight. I’m coming to the conclusion that without the moon, we would not be here. On the Earth-Moon orbit of the sun, the two bodies are only one seventh of one degree apart!

  81. amphiox

    I’ve read Rare Earth, and I think some of their arguments are pretty specious, actually. They make pretty good arguments that features like our moon and the location of Jupiter were important for the development for our specific kind of complex life, but the argument that these features have anything to do at all with the likelihood of complex life in general is not very convincing.

    I would also point out to anyone tempted by the “earth is special” arguments that earth is actually NOT optimized for our kind of complex life. Most organisms on earth can exist only in very limited regions of the planet, and would quickly die miserably if transported anywhere else. Earth is also too close to the sun, sitting on the inner edge of the habitable zone instead of the middle. As a result, our planet will go the way of Venus in 0.5 to 1.0 billion years. If it had been a little further out, it would have been habitable for several billion years more.

    It isn’t even certain that we are orbiting the right kind of star. Our sun will only spend 10 billion years on the main sequence, and its gradual warming will cook us long before then. M-dwarfs don’t warm with time, and will live ten times longer.

    We simply don’t know enough about any of the variables to say anything intelligent on this subject. All we can say is that the conditions here allow for life to occur. We might end up being in the one of the least optimized environments for life, for all we know.

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