Nearby "earth-like" planet: not so much

By Phil Plait | July 20, 2011 7:06 am

There’s some chatter on the web right now over a new scientific paper about a nearby exoplanet, and what I’m seeing are people speculating that it might be earth-like. Technology Review even titled their article "Astronomers Discover Habitable ExoEarth Orbiting Binary Star".

The problem with that is that the planet’s not terribly earth-like, and it may not be habitable*.

So what’s the deal? I read the journal article (PDF), and this really is a good story, just not the one I’m seeing the chatter about.

55 Cancri is a nearby binary star at a distance of about 40 light years. One star is a dinky red dwarf, and the other is a fairly Sun-like star, though somewhat smaller and cooler. It’s also much older, roughly 10 billion years old, more than twice the age of the Sun. It’s actually at the point where it’s starting to evolve into a red giant, and is called a sub-giant.

Back in 2007 it was announced that at least five planets orbit the bigger of the two stars (called 55 Cancri A; confusingly the red dwarf is 55 Cancri B (note the capital letter), while the planets are called b-f (lower case)). They range in mass from 0.026 to 3.84 times that of Jupiter (8.3 to 1200 times the mass of the Earth). 55 Cancri e is the lowest mass of these, but is extremely dense and hot, so not at all earth-like.

55 Cancri f is the interesting planet, though. The astronomers in question observed the star using an interferometer, allowing extremely precise measurements of the star’s size, which in turn yielded very accurate numbers for its temperature and mass. All these together can be used to figure out its "habitable zone", the region around it where an orbiting planet would have liquid water on its surface.

Now right away, I’ll say that finding the HZ (as we in the know call it) is not really straightforward. For example, a planet that has a thick atmosphere can be farther from its star and still have water due to the greenhouse effect; in fact, without air the average surface temperature of the Earth would be below freezing! And the greenhouse effect depends on what’s in the atmosphere, its density, and so on. So I am wary of any declarations of planets being habitable based on this alone.

Still, let’s see what we get. The authors published this diagram of the orbit of planet f:

The orbit of the planet is the solid black line, the grey area is the habitable zone of 55 Cancri A, and the dotted lines represent the orbits to scale of planets in our solar system (Mercury, Venus, Earth, and part of Mars) — the red dwarf binary companion is way, way off the scale here. As you can see, due to its highly elliptical orbit, planet f spends about 3/4 of its time inside the star’s HZ! That’s pretty interesting. But what does it mean?

Specifically, with the new, more accurate numbers for the star, some assumptions about the planet’s temperature can be made. For example, if it has no air at all and has no way to redistribute heat from the star, it has a temperature range of -10° to 86° C (18° to 187° F) as it swings around its star. That’s quite a range!

As far as I can tell, it’s unknown if this planet has an atmosphere or not. But if it can redistribute heat (as our atmosphere does for Earth), then those temperatures become -52° to 29° C (-60° to 84° F). These ranges of temperature, remember, are due to the changing distance of the planet to the star. If the planet is tilted, then you get seasonal changes too which can make these temperatures either more extreme or more moderate. But we can’t know.

So clearly, the planet isn’t exactly a garden spot. If it has air, the weather must be fierce!

But we’re not done. What about the planet itself? Turns out it has over eight about 50 times the Earth’s mass! and twice the radius (it’s a hefty planet, actually roughly the same mass and size as its sister 55 Cancri e), giving it a surface gravity about twice that of Earth. Trying to lose weight? Stay away from 55 Cancri f! You’d weigh twice what you do now if you were there. [My apologies. Somehow I misread the planetary parameters for the planet e as the ones for f. Ironically, the reality makes my point even more strongly: at 50 Earth masses, 55 Cancri f is heftier than I thought, and so is not earth-like at all. It is far more likely to be a gas giant of some kind. It doesn’t transit the star, so its actual size is unknown. My thanks to astronomer David Spiegel at Princeton for pointing out my error.]

Even though this planet may not remind us all that much of home, there are still mysteries to be pondered. How did two planets of nearly equal mass and size form in this system? Why is this one on such a highly elliptical orbit? Mind you, that planet is ten billion years old, twice as old as Earth! Did it get kicked into that orbit by some gravitational encounter with another planet? And how long has it been that way? Is this sort of configuration stable over billions of years?

And aside from all that, of course, the search for a truly earth-like planet will continue. My money is still on Kepler, but it’ll be another year or so before we’ll see anything. Patience can be a virtue; we’ve waited thousands of years to know if another Earth exists Out There, and we’ll get our answer soon enough.

Image credit: NASA/JPL/Caltech

* And, to be nit-picky, it only orbits one of the stars in a binary pair.

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Dense exoplanet gets the lead out and in
Astronomers find 5 planet system
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Does Gliese 581g exist?

CATEGORIZED UNDER: Astronomy, Piece of mind, Science, Top Post

Comments (43)

  1. Gonçalo Aguiar

    “Trying to lose weight? Stay away from 55 Cancri f! You’d weigh twice what you do now if you were there.”

    I don’t say lose weight, but if you’re trying to lose mass, 55 Cancri f would be a good place to exercise your muscles 😀

  2. Patrick

    Even though all those changes from earth that you noted, I did not see you contradict the fact that the planet could be habitable. It may not be a good place for humans to live, but its proven that there are things on earth that could survive those temps, yes, your right, there are alot of unknowns, and it is not an earthlike planet, but still could be habitable, and if it has air, and the oxygen content was right, even a human could live there.

  3. Patrick

    @goncalo aguiar hell yeah, good place to go exercise huh, could you imagine landing on that planet and then trying to take off again! You would need twice as much fuel! Which would weigh twice as much, and your ship would weigh twice as much, seems like it should be a one way trip!

  4. Apu Illapu

    I don’t care about weight, it’s mass I’m trying to loose. 55 Cancri f is exactly what I’d need.

    D’oh. It figures, all the extra mass slows me down.

  5. Tony

    I think in those temperature ranges, it could have oceans…and that would give life some additional protection from the surface weather and environment.

    Its all conjecture, but if the planet has really had 10 billion years of that kind of environment…it’s hard not to let the imagination run a little wild. Our planet has been around just slightly less than half that time, and look what we got?

  6. Gary

    I’m a little confused by the numbers for the temperature ranges. Could someone with a stronger physics background explain why the lower bound for the model with atmosphere is lower than without?

  7. Grizzly

    Just a minor petulant complaint here… it rubs me the wrong way when I read comments like “we in the know”. There’s not some super secret double nought spy club with beanies and secret decoder rings.

    Wait a minute, you mean there is and I haven’t been invited?


    Seriously though, I know it’s not your intent, but it does come off as a tad… smug? superior? elitist? Dunno.

    As I said, I am a tad petulant today so take it with more than a grain of salt.

  8. Jason Dick

    Well, it’s so hard with current observational equipment to detect habitable-zone planets, I’d be willing to bet that there are a huge number of them out there that we just can’t see yet. In the mean time, with such small numbers of potential habitable-zone planets trickling in, it makes perfect sense that a large number of them turn out not to be actually that habitable.

  9. Stuff like this makes me miss science fiction writer, Hal Clement. Now he could come up with a nifty form of life that would love all those variables you mention.

  10. Tuttle

    I always thought the naming convention for planets used numbers (ie, that our planet would be “Sol-3” and that this one would be “55 Cancri A-5”) and that the lower-case letters were for moons (Luna would be Sol-3a, Titan Sol-6f). Then again, wiki tells me Titan is also known as Saturn VI and not as Sol-something-anything.

    Astronomy seems to be a bit wishy-washy when it comes to taxonomy.

    Also, why no ‘a’ planet? Empty orbit (in which case “55 Cancri A-6″… and “Sol-4” IIRC), or just not wanting a “55 Cancri A a”?

  11. magetoo

    This bit seems odd to me:

    if it has no air at all and has no way to redistribute heat from the star, it has a temperature range of -10° to 86° C
    But if it can redistribute heat … then those temperatures become -52° to 29° C

    Both extremes move in the same direction, down. That can’t be right for just moving the same amount of heat around, can it? (Should it be -52 to 86, and -10 to 29?)

  12. A planet that size is likely to have a hefty atmosphere from volcanic outgassing, and a strong greenhouse effect. Maybe just too dang hot.

    Why would an atmosphere decrease the minimum temp? Is that a typo?

    An aside on Kepler – they were supposed to release more data 4 months after the February release, and haven’t. They’ve been stingy on the data releases. Someone should use the bully pulpit to get the info out.

  13. Robert E

    @Tuttle: “55 Cancri A a” is the star itself

  14. It could be a great source of inspiration for SciFi! Think about how Earth’s colonist life could be on such planet! As often happens reality is more interesting than fiction! :)

  15. Jearley

    Or Poul Anderson.
    Anyway, given that life may have first evolved in the oceans, and that water has a great deal of thermal inertia, along with the benefits of bouyancy, IF this world has water and IF it has a stable history, then it MIGHT have life in its oceans. Any life on the land above the level of insects had better be tough, by our standards, or be able to hide out during the hot times.

  16. Dean

    For comparison, does anyone know the base temperature range for Earth? Since Earth’s orbit is nearly circular, I’d expect something like 24.9° C to 25.1° C.

  17. Gary Ansorge

    16. Dean

    From Yahoo answers;

    Coldest: -129 degrees (F) in Antarctica
    Warmest: 136 degrees in Libya

    Of course, that’s just weather,,,which requires an atmosphere,,,

    Gary 7

  18. John Miller

    Something that big could have lots of moons, any one of which could support life.

  19. M

    6 (Gary) and 11 (magetoo): I agree. The reduction in minimum temperature with the addition of an atmosphere seems odd to me. In fact, everything about the temperature change seems a little odd to me. And in fact, I have found Phil’s error by actually reading the paper: what the paper did is make two assumptions: either f=2, there is no heat redistribution, or f=4, there is perfect heat redistribution. f=2 means 263K to 359K. f=4 means 221K to 302K (pg 4 of the paper). Note that BOTH temperatures are lower in the latter case. Also note that this is a magic atmosphere that redistributes heat but has no greenhouse effect.

    My understanding of the effects of adding an atmosphere to a planet involve a number of issues:
    1) balancing nightside and daytime temperatures, and polar and equatorial temperatures. This one is important for looking at the instantaneous range of temperature (see 17 – Gary Ansorge – and the range from Antarctica to Libya). However, for the purposes of this question, we actually care about the orbital range in temperature (see 16 – Dean – eg, what’s the Earth’s average temperature at Northern Hemisphere midsummer vs. Southern Hemisphere midsummer, which I believe dominates over the average temperature change due to perigee vs. apogee). Here, the paper claims that the effect is to reduce the average temperature. This is counter to my intuition, which says that Stefan-Boltzmann tells us that radiation is related to temperature to the fourth power: therefore, I’d think that if you concentrated N Watts of heating power on 1 square meter of a 10 square meter surface, the average temperature across the full surface would be lower than if you spread the heating evenly…

    2) the greenhouse effect: this can increase a planet’s temperature over a temperature in the absence of an atmosphere. This would _add_ temperature to both the bottom and top of the range.

    3) clouds: if the atmosphere can hold clouds, then we might expect a change in albedo, which means more reflectivity, which means a cooler planet. On Earth and Venus the GHG effect dominates the cloud reflectivity effect.

    along with indirect effects:
    a) land-ice: because of the GHG effect, Earth is warmer and therefore has less land-ice than it would otherwise, which helps it stay warm.

    And a last important effect: does the planet have an ocean? This would help a lot in reducing temperature swings between perigee and apogee because it would add a lot of thermal inertia to the system (especially when coupled to an atmosphere).


  20. JaberwokWSA

    First, does the existence of 55 Cancri B have any impact on the HZ either in the past or now that it is going sub-giant, or is it too far away?

    Second, @7, I agree with you. It like a SRCTYCX (as those of us in the know say).

  21. Jim Johnson

    They keep publishing these stories where an “earthlike planet in the habitable zone” has been found, with headlines implying the planet could support human life (the old “M type planet” in Star Trek parlance). But the likelihood that this is so is vanishingly small.

    Our own solar system has 3 earthlike planets in the habitable zone. Of the three of them, two are not only not habitable, they are drastically uninhabitable. Going by atmospheric pressure alone:

    Earth Sea level 101.325 kPa
    habitable lower limit (Mt Everest) 4 kPa
    habitable upper limit (oxygen toxicity) 161 kPa

    Mars 0.6 kPa
    Venus 9500 kPa

    If atmospheric pressure for all such “earthlike planets in the habitable zone” fall between those of Mars and Venus (they probably don’t – many might fall outside that range and we wouldn’t know, but let’s be generous) and if the density levels were evenly distributed amongst such planets (again, not likely – a bell curve distribution is more likely than a linear one, but since the peak of that curve is unlikely to fall within the habitable 4 – 161 kPa, let’s again be generous and call it a linear distribution ) then only 1 out of 60 such planets would have an atmosphere we could survive – even if the air is the same composition as earth’s.

    1 out of 60. And that ignores planets made uninhabitable by atmospheric toxicity and/or acidity, deadly temperatures, radiation exposure, and probably many other factors I can’t think of.

    I just have a hard time getting excited about those odds.

  22. Gary

    19 (M) Ok–found the equation. Thanks for the explanation! That’s a much more simple model than I was assuming. Out of curiosity, what would happen if you plugged in the constants for Earth? Or Venus?

  23. andy

    55 Cancri is definitely one of the premier exoplanetary systems, especially given the fact the innermost planet is transiting. Despite the initial announcement, 55 Cnc e actually seems to be less dense than initially thought – how such a low-mass, volatile-rich planet could survive in such an intensely-irradiated environment should prove to be a challenge to the theorists (especially given the age of the star).

    The architecture of the system is also somewhat perplexing: the second (55 Cnc b) and fifth (55 Cnc d) planets are both massive gas giants, but why they should have accreted enough material to become full-fledged jovians while the planets inbetween (55 Cnc c and f) did not is a mystery. There’s also a large gap between planets f and d which may be occupied by more planets that are not massive enough to have been detected yet: apparently the current observational data and stability constraints still allow for a couple of Saturn-mass planets to be lurking there. Certainly the high eccentricity of planet f seems to be at odds with the rest of the system, it leads me to be suspicious that this might arise from contamination of the signal with that arising from an undetected (and hence unmodelled) planet.

    It would also be interesting to find out what (if anything) is orbiting the secondary star, unfortunately it seems it is probably too faint for the current instruments to make sufficiently-accurate radial velocity measurements. Hopefully when infrared RV techniques are further developed we will find out!

    As for habitability I’m not holding my breath: certainly the scaling relationships derived from the solar system for gas giant satellite systems would suggest that the moons orbiting 55 Cnc f would probably be too small to be habitable. However given the current absence of any detected exomoons it is not clear how well this would apply to other solar systems and other satellite-formation processes (e.g. capture) may produce massive satellites of gas giants under some circumstances. Temperature ranges quoted by BA seem to assume the absence of any kind of thermal inertia in the planet, there have been numerous studies which indicate that orbital eccentricities less than about 0.6 are compatible with habitability.

  24. Sam H

    Merci bien pour vos éditions, Phil!! :)

    I was puzzled when I first read this, because I was under the impression that 55 Cancri f was a gas giant – so the image I received reading this was “okay, we revised the data, so if it’s habitable it’s probably a Neptune-sized ocean planet (probably with one well over 100 miles deep – God, I can’t even begin to imagine the pressure of depths like that on any ocean world – hopefully the Europa sub isn’t a fantasy for that reason. Is there an equation for calculating that?) Fortunately my previous guess was correct, so given that life is likely impossible on even water-cloud gas giants now we should turn our speculation to the possibility of moons. So what might the chances be of a sufficiently large (Mars-Earth sized), atmosphered moon with surface liquid water and the possibility for an Earthlike climate? (I hope for something like Pandora, but that’s probably much less likely. :))

    Now, back to distance learning French…:roll:

  25. M

    Ah, reading the paper further, the reason why inclusion of an atmosphere lowers the planets temperature, is that in the no-atmosphere scenario the paper is only reporting the dayside temperature:
    “Note that the temperature given for the f = 2 scenario is the planet dayside temperature.”

    So, of course the temperature goes down when if you only average in the nightside temperature when there’s an atmosphere!

  26. M

    22-Gary: The two papers that this paper cite do a better job of thinking about what an atmosphere might mean: see and

    The simplest thing to do is note that Earth’s GHG effect is worth about 33 degrees C of temperature – if the paper is assuming that the planet has an Earth-like albedo, it makes sense to assume an earth-like GHG effect to go along with it.

    A good planetary scientist could probably make a good guess as to what the atmosphere might be like on an unknown planet based on the weight and distance from the sun… eg, if you are too light, you lose all the good bits, if you are too close you bake out the water which means that you turn into Venus, if you are too far your gases liquify and never have a chance to be GHGs, but if you are just right, you hold onto the gases and they warm stuff up.

    Of course, Earth’s atmosphere would have been hard to predict apriori, because it is totally dependent on life: if life had never arisen, there would probably be no oxygen and a lot more methane. I think CO2 would be similar without life – the major sources on the geologic timescale is volcanoes (not life dependent) and the major sink is weathering… hmm… weathering has probably increased because of life… so maybe CO2 would be higher without life? Also, life does a good job of sinking carbonates into the deep ocean. So I’m not sure, but if I had to guess, a no-life Earth atmosphere would have more methane, more CO2, and less oxygen. So probably a bunch warmer. (which was important in the old days, because the sun was about 30% cooler back in the day!)

  27. Torbjörn Larsson, OM

    Of course it is “earth-like”, since the concept isn’t well defined! (And should be avoided.) Here it is habitable terrestrial.

    Which is pretty interesting:

    1) We don’t know too many HZ planets, even less terrestrial HZ planets.

    2) The orbit extends the envelope of HZ outcomes.

    So yay the speculation, as we in the know (web users) call it.

  28. realta fuar

    The age of the system pretty much guarantees that the system is dynamically stable and not the oher way around. Large eccentricities are quite common (though initally unexpected) among exo-planets and are almost certainly left-overs from the early days of the system. The sentence “If the planet is tilted, then you get seasonal changes too which can make these temperatures either more extreme or more moderate.” is simply incorrect.
    A non-zero obliquity of the ecliptic means that the altitude of the local sun always changes as a function of the seasons and that can’t act to moderate those seasons. Aside from that, and all the crossed-out mistakes, a quite informative post and it’s certainly a very interesting system.
    As Andy above alludes to, it seems unlikely, given current theory and observations, that a planet of this mass can have a earth or Mars mass moon; one large enough to hold an atmosphere and possibly be habitable itself. An earth mass moon might eventually make its presence known through radial velocity anomalies, given enough precision and enough data.

  29. andy

    @realta fuar: regarding the prospects of RV detection of moons, I don’t think so. Problem is this is going to be a very subtle effect: to first order you can treat the planet-moon system as a single mass in orbit around the star. There will be a very small effect due to the motion of the planet and satellite around their centre-of-mass, but this is going to be far less than the activity-related intrinsic RV variations of the star. Even for the much more observationally-accessible case of a planet-moon system around a millisecond pulsar where you can rely on the precision of a rotating neutron star to make extremely accurate measurements, you would need some fairly extreme configurations for this to be detectable (such as a Saturn-size moon orbiting a Jupiter-class planet).

  30. It’s worth noting that the Dawson and Fabrycky paper (Arxiv Astro-ph 1005.4050) that they use for the orbital elements shows the eccentricity of f is quite sensitive to the model. So it could have an orbit quite a bit closer to circular than shown.

  31. realta fuar

    @Andy Well, it certainly would be very difficult, and possibly impossible in a system as complicated as 55 Cancri and probably impossible for a high mass ratio planet/ moon system (such as Jupiter and an earth mass moon). For an earth/luna type ratio, around an M dwarf, my gut feeling is it’s feasible, especially if, as many now believe, it’s possible to model out much of the activity signal. An important thing to remember is that the activity signal that really matters is the rotational period of the star, as any starspot cycle is likely to be at a very different period than either the orbital period of the planet/moon system around its center of mass or of them both around their star. Still, I haven’t modelled this situation in detail and you could be correct. It would certainly require a precison and accuracy of a few cm/sec, at least, and a data string lasting perhaps dozens of orbital periods. Such a detection is roughly 100 times harder than an rv detection of an earth mass planet in a habitable zone, I would think. Really*cubed hard! and maybe impossible.

  32. amphiox

    If the star is 10 billion years old and on the cusp of going sub-giant, then that habitable zone isn’t going to remain habitable for much longer.

    But, it is interesting to note that, the star being at the end of its main sequence life also means that it must be near the end of its main sequence luminosity increase, and that means that several billion years ago, the time period one must take into consideration when thinking about the possibility of life in a star system this old, the star would have been substantially cooler, and the habitable zone closer in.

    Of course this also depends on whether or not the planet was in the same orbit billions of years ago, and the odd ellipticity suggests the possibility that it wasn’t.

    (And if it is a gas giant, we’re back to large moon speculations!)

  33. amphiox

    Our own solar system has 3 earthlike planets in the habitable zone. Of the three of them, two are not only not habitable

    Actually, our solar system has only 2 earthlike planets in the habitable zone. Venus isn’t in the habitable zone. It may have been for a very brief period in the earliest phase of the sun’s main sequence lifespan, when the young sun was dimmer and cooler than it is today, but that period was over probably by the time the sun was a billion years old or so. (In other words, Venus isn’t in the Sun’s Continuous Habitable Zone.) Indeed, at present, the inner edge of the sun’s habitable zone is only a slight bit inwards from earth’s orbit, and even earth, arguably, isn’t in the Sun’s continuous habitable zone, as we will be moving out of it sometime in the next 1-2 billion years, and well before the end of the Sun’s life as a main sequence star.

    You can also make the argument that Mars, though in the habitable zone, isn’t earth-like. (Because we haven’t actually had the technology to reliably detect Mars-sized planets until recently, if even that, and we haven’t found any yet, the working definition of “earth-like” has always been close to earth’s size up to a around 5 times as massive, or so). By this definition, our solar system has two earth-like planets, and two planets in the habitable zone, but only one earth-like planet in the habitable zone.

  34. Gunnar

    Interesting discussion! I also find it interesting that the extra-solar planets we have so far detected have proved to be easier to detect than determining whether the nearest star system to us has planets or not, even though they are tens to hundreds of times farther from us than the Alpha Centauri System. This site: does a fairly good job of explaining why we do not yet know whether there are planets in that system, and why it could take 5 or more years of studying it with a very large telescope dedicated to that task before we can know. What will truly excite me and grab my interest would be the discovery of an earthlike planet in the HZ of Alpha Centauri A or B (with B being the more likely prospect, according to the website).

  35. chris j.

    oh, i’m sure it’s habitable – just not necessarily by us.

  36. We can terra-form any exo-planet. Just look at the success our science is having with this one.

  37. amphiox

    We can terra-form any exo-planet. Just look at the success our science is having with this one.

    Sure we can! We can terraform a habitable planet into an uninhabitable one!

    The reverse process? Still working the bugs out, I think….

    oh, i’m sure it’s habitable – just not necessarily by us.

    But not for very much longer, though, if it’s heading into the subgiant phase.

    But the thought occurs to me, if 55 Cancri is really cooler and less massive than Sol, it should be expected to have a slightly longer lifespan on the main sequence. So if Sol is projected to have a 10 billion year main sequence lifespan, at 10 billion years old, 55 Cancri ought to have a little bit more time to go….

    (According to wikipedia, 55 Cancri is a super-metal rich star (consistent with it having so many heavy planets), which makes estimation of its age and mass less accurate, though.)

  38. csrster

    “earth-like” = “Minshara Class” as any fule kno.

  39. I hate the term “Habitable Zone” because it conveys a sense of certainty about surface temps that’s completely wrong. Continuous Habitable Zone is even worse – our earth went through two or more snowball phases that might possibly have left it completely glaciated to the equator and arguably out of the Continuous Habitable Zone, which just shows how meaningless CHZ is.

    We pull lots of astronomical names out of mythic fiction, so I suggest we rename it the M-Class Habitable Zone, where a planet that is very close analog to earth and its present or past atmosphere would have surface liquid water. That would help distinguish the MHZ from other planets that could have surface liquid water in wider orbits with different atmospheres, and also for habitable bodies that haven’t yet been disproven as potential locations for water based life (Europa and gas giant/ice giant atmospheres).

  40. Ironically, the reality makes my point even more strongly: at 50 Earth masses, 55 Cancri f is heftier than I thought, and so is not earth-like at all. It is far more likely to be a gas giant of some kind.

    A “Hot Saturn” seems right – Neptune has 17 earth masses and Saturn has about 95 so think something in between those. Just withoutr the rings or with rings of dust and rock not bright ice.

    If the atmosphere of 55 Cancris f is hydrogen and helium – maybe with lots of methane – what would the likely greenhouse effect be? Anyone?

    Life in the clouds perhaps as postulated by Clarke for Jupiter – or maybe on moons? Radiation levels could be an issue there but.

    Too little info as yet to assess the chances for life really – more studies neeeded. Not likely to be fit for humans though clearly.

  41. M spotted the issue of the atmosphere vs. no atmosphere temperature ranges, which was more of a confusion between the f=2 and f=4 case.

    I have talked about this planet and the HZ in general at if anyone cares to discuss this in that forum as well.


  42. MaDeR


    “And that ignores planets made uninhabitable by atmospheric toxicity and/or acidity, deadly temperatures, radiation exposure, and probably many other factors I can’t think of.”
    You have it completely backward. Atmosphere of our planet is full of horrible toxic gas that will burn and kill anything that did not evolve to cope with it. Said gas, by the way, was not present on beginning of planet history.

  43. Matt B.

    “Patience can be a virtue; we’ve waited thousands of years to know if another Earth exists Out There, and we’ll get our answer soon enough.”

    That’s not soon enough.


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