Jupiter’s twin found… 60 light years away!

By Phil Plait | February 15, 2008 7:17 pm

Astronomers have just announced that they have found a near twin of Jupiter orbiting the star HD 154345, a fairly sunlike star about 60 light years away. This is very cool news, and has some pretty big implications for finding another Earth around some distant star.

Artist’s impression of an extrasolar planet. Courtesy NASA.

Finding a planet like this isn’t as easy as it sounds! Finding planets with the same mass as Jupiter isn’t hard; many have been found with even lower mass. The hard part is finding one that is orbiting a sun-like star at the same distance Jupiter orbits our Sun. The closer in a planet is to its star, the easier it is to find: the method used measures how hard the planet’s gravity tugs on its parent star as it orbits; the planet pulls the star around just like the star pulls the planet, and we see this as a change in the velocity of the star toward and away from us (called the radial velocity; Wikipedia has a nice animated GIF for this), and that effect gets bigger with bigger planets, and the closer they orbit.

So we see lots of superjupiters orbiting close in, and some lighter planets also close to their parent stars. But finding a Jupiter-like planet on an orbit like Jupiter’s, well, that takes a long time to do. Jupiter takes 12 years to orbit the Sun, so it would take many observations over many years to detect a planet like that.

But they’ve done it! The team (Jason Wright, Geoff Marcy, Paul Butler, and Steven Vogt) have been using the monster 10-meter Keck telescope for ten years, observing HD 154345. This star is a lot like the Sun (it’s a G8, and the Sun is a G0 G2, meaning it’s a little smaller, lower mass, and cooler than the Sun). The planet (called HD 154345b) has a mass of no less than 0.95 times that of Jupiter, and orbits the star 4.2 AU out — 1 AU is the Earth-Sun distance, and Jupiter’s orbit is about 5.2 AU from the Sun. The planet takes a little over 9 years to orbit the star, and the orbit is circular.

As the planet orbits the star, the star’s velocity relative to us changes very slightly in a periodic fashion. In the case of HD 154345, the change in velocity over the course of several years is just 30 meters per second… about the speed of a car on a highway!

This makes HD 154345b the first true Jupiter analog discovered. It’s a tremendous achievement!

So why is this important?

The superjupiters in tight orbits that have been discovered probably didn’t form that close to their stars; it’s a tough environment to form a big planet. The commonly accepted theory is that a planet like that forms farther out from the star and migrates closer in over millions of years, probably due to friction from the disk of gas and dust from which it formed.

Now imagine: you’re a planet that’s about the size of Earth, orbiting your star at about the same distance Earth is from the Sun. You’re pretty happy, thinking that in a few hundred million years, things’ll cool off, you’ll form oceans, and continents, and life. But then, hey, what’s that? Oh, it’s a planet with 500 times your mass, headed right for you! When it passes you by, its tremendous gravity either drops you into the star, or ejects you right out of the system!

Bummer.

So we don’t think that the stars that have close-in massive planets will have Earth-like planets. It may be that the only solar systems with planets like Earth will have their Jupiter analogs orbiting farther out, where they can’t hurt the smaller planets.

And hey, that’s just what we have here!

So, does HD 154345 have a blue-green ball orbiting it as well? These observations can’t say; they are only sensitive enough to find the Jupiter-like planet (and they can’t rule out planets farther out either). It might, or it might not. But here’s an interesting point: the system is probably about 2 billion years old. By that age, the Earth was already teeming with microscopic life. Provocative, eh?

I expect that future missions will spend quite a bit of time peering at this system. As of right now, it holds a lot of promise for those of us hoping that one day we’ll find another Earth.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (39)

  1. Yoshi_3up

    That looks great. Another Solar System twin? Hmm… Maybe we’ll never know v^_^v

  2. Darth Lunchbox

    This is really cool stuff, it’s what got me to major in astronomy a couple years ago. I can’t wait to see more explorations of this system.

  3. DTdNav

    BA Said:

    “Now imagine: you’re a planet that’s about the size of Earth, orbiting your star at about the same distance Earth is from the Sun. You’re pretty happy, thinking that in a few hundred million years, things’ll cool off, you’ll form oceans, and continents, and life. But then, hey, what’s that? Oh, it’s a planet with 5000 times your mass, headed right for you! When it passes you by, its tremendous gravity either drops you into the star, or ejects you right out of the system!”

    Or… you drop into orbit around it an continue on your merry evolving way!

    Couldn’t this be one of the possibilities? Maybe we shouldn’t write those systems off so quickly.

  4. Christian X Burnham

    The post title did remind me of the Linda Smith joke about Erith where she grew up:

    “It’s not twinned with anywhere, but it does have a suicide pact with Dagenham”

  5. Uhhh Phil…Sol’s a G2, not a G0!

  6. davidlpf

    one word “cool”

  7. Wayne, you’re right. I wrote G0, then made a note to myself to look it up because I knew that wasn’t right… and then forgot to look it up. D’oh!

  8. MandyDax

    Also, on the life front, it might be a “vacuum cleaner” and stabilizer for a debris ring between it and the habitable zone, much like Jupiter cleared out a lot of debris from the early Solar system and now is a stabilizing factor in maintaining the asteroid belt and the Trojans. This could give any HZ terrestrial planets a better chance for life to take hold and start to diversify by reducing the number of extinction-level collisions. I’m very excited about this news, and am hopeful of what the Terrestrial Planet Finder might see there.

  9. tacitus

    Or… you drop into orbit around it an continue on your merry evolving way!

    Couldn’t this be one of the possibilities? Maybe we shouldn’t write those systems off so quickly.

    I suspect that the mechanics of such an encounter would make being captured by the incoming gas giant well nigh impossible. In any case, the gas giants BA is talking about end up very (very) close to the star. It would probably be a little too toasty for anything to survive, let alone evolve.

  10. tacitus

    By the way, this is a simple, but very cool chart showing the number of extrasolar planets discovered in every year since 1989.

    http://en.wikipedia.org/wiki/Image:Number_of_extrasolar_planet_discoveries_by_year.svg

    Fat and happy times ahead in the planet hunting business.

  11. “Oh, it’s a planet with 5000 times your mass”

    Jupiter is only 318 times more massive than Earth. A 5000 Earth mass planet would be 15 times bigger than Jupiter, which would put it over the 13Mj brown dwarf limit.

    So it wouldn’t be a planet. It would be a star.

  12. Hi, Phil! Thanks for plugging our paper. It’s a great write-up in the style only the Bad Astronomer can deliver. Only one quibble: it’s WRIGHT, not White.

    cheers!

  13. pfc

    Wow x2. I’ve also seen this other one in a couple places today, it was submitted 14 Feb: http://arxiv.org/pdf/0802.1920v1

    Abstract: … We report the detection of a multiple-planet system with [gravitational] microlensing. We identify two planets with masses of ? 0.71 and ? 0.27 times the mass of Jupiter and orbital separations of ? 2.3 and ? 4.6 astronomical units orbiting a primary star of mass ? 0.50 solar masses at a distance of ?1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn.

    Is it just me, or does the exoplanet search really seem to be heating up?

    I can’t resist one more quote, from from my well-thumbed copy of Burnham’s Celestial Handbook: “.. There may, in fact, be millions of other planetary systems. But, because of the vastness of space, we shall never be able to observe them directly. Even at the distance of the nearest star – a mere four light years – a planetary system such as ours would be completely beyond the range of the greatest telescope in the world; which is in the nature of a comment on both the incredible immensity of our Universe and the almost microscopic insignificance of our home in space.”

    I guess persistence and ingenuity does pay off. Or said another way: Science. It works, Bad Word Deleted.

  14. andy

    So we don’t think that the stars that have close-in massive planets will have Earth-like planets.

    That’s not actually correct – simulations suggest that there is still enough material left behind after the gas giant goes charging through to build Earth-mass planets.

  15. Victor Bogado

    Hi, just a quick question, Does those migrating planets have moons, like our Jovian planets? I know that since thay are detected indirectly it is probably impossible, or at least very hard, to detect moon orbiting a planet, but they could have moons, right?

    Maybe a moon of a planet could have the conditions to hold and nurture life.

  16. D’oh! An extra 0 slipped in to that number. Glad I have so many editors. :-)

    And Jason, my apologies. I’m getting a sneaking suspicion my spell check changes names; that’s not the first time something like that has happened. Or I may just be a bonehead sometimes.

  17. Bill Nettles

    G…(pun intended), couldn’t all these periodic fluctuations be explained by either 1) periodic fluctuations in the universal gravitational non-constant or 2) waves in the ether that Michelson couldn’t detect because he was looking at terrestrial and near terrestrial objects, not stars 60 light years away.

    Just kidding, but these would be interesting objections to eliminate. I especially like the ether possibility.

  18. Cusp

    The timing is interesting – just before the Gaudi Microlensing Science paper…

    The Gaudi paper was embargoed so could not appear on astro-ph until it actually appeared – whereas the Wright paper (being in ApJL) could.

    Would be nice if BA covered both :)

  19. Gary Ansorge

    We’re all there is. We’re all alone.

    Now, go populate the universe with complex life forms,,,

    GAry 7

  20. Aeryn

    I say we start broadcasting prime numbers at them and see what happens. ::grin::

    (Ok, ok, I know – no evidence one way or the other for a terrestrial life-bearing planet, and even if it’s there, the system’s not old enough, etc. etc. But I can dream, can’t I?)

  21. I say we start broadcasting prime numbers at them and see what happens.

    They will say “We really thought they had potential with Star Trek, but this? Enough with the post-modernist art. Let’s not bother.”

  22. Tom Marking

    I’m not sure what all the fuss is about.

    Planet 55 Cancri Ad orbits its star every 12.4 years at a distance of 5.26 AU. It has a mass of at least 3.9 Jupiters and it was discovered in 2002.

    Planet 47 Ursae Majoris c orbits its star every 7.1 years at a distance of 3.8 AU. It has a mass of at least 0.8 Jupiters, an eccentricity of close to zero, and was discovered in 2002.

    Planet Mu Arae c orbits its star every 11.5 years at a distance of 5.24 AU. It has a mass of at least 1.8 Jupiters, an eccentricity of 10 percent, and was discovered in 2004.

    So several close analogs to Jupiter have been known for several years. On another subject, using the theory of orbital resonances I constructed a computer program to produce 10,000 random solar systems. 21 percent of them contained a hot Jupiter. 21 percent of them had some type of planet in the habitable zone (defined as going from 0.77 to 1.13 AU). 4 percent of them contained an earth-like planet in the habitable zone. Here are some more detailed results:

    **********************************************************

    Generating 10000 random star systems

    Luminosity of star relative to the sun = 1.0
    Mass of star relative to the sun = 1.0
    Minimum radius of innermost planet from star = 0.1 A.U.
    Maximum radius of innermost planet from star = 0.6 A.U.
    Maximum radius of outermost planet from star = 40.0 A.U.

    Albedo (i.e., reflectivity) of planet = 0.3
    Increase in temperature at planet’s surface due to greenhouse effect = 33.0 deg C
    Minimum surface temperature of habitable zone = 0.0 deg C
    Maximum surface temperature of habitable zone = 50.0 deg C
    Minimum radius of habitable zone = 0.771 A.U.
    Maximum radius of habitable zone = 1.126 A.U.
    Minimum mass of planet = 0.05 Earth masses
    An Earth-like planet is defined as a planet with a mass >= 0.5 Earth masses
    and = 100.0 Earth masses
    and a distance from its star < 0.771 A.U.
    Minimum total mass of planets: 3.423 Earth masses
    Maximum total mass of planets: 1476.849 Earth masses
    Average total mass of planets: 452.733 Earth masses

    Random star system: index = 9135
    Total mass of planets = 257.994 Earth masses
    Planet Radius Period Mass Within Habitable
    Index (A.U.) (years) (Earth=1) Zone
    —— —— ——- ——— —————-
    1 0.164 0.066 4.744 false
    2 0.556 0.415 1.274 false
    3 1.887 2.593 29.825 false
    4 3.476 6.482 19.293 false
    5 6.404 16.204 22.289 false
    6 10.165 32.409 0.495 false
    7 21.144 97.227 9.841 false
    8 38.948 243.067 170.233 false

    Number of star systems with 1 Earth-like planet in habitable zone = 430
    Random star system with 1 Earth-like planet in habitable zone: index = 9987
    Total mass of planets = 291.621 Earth masses
    Planet Radius Period Mass Within Habitable
    Index (A.U.) (years) (Earth=1) Zone
    —— —— ——- ——— —————-
    1 0.332 0.191 0.100 false
    2 0.527 0.383 0.052 false
    3 1.096 1.148 0.776 true
    4 2.019 2.870 0.365 false
    5 3.720 7.174 0.217 false
    6 6.852 17.936 2.316 false
    7 12.621 44.839 286.871 false
    8 23.249 112.097 0.755 false
    9 36.905 224.195 0.170 false

    Number of star systems with 2 Earth-like planets in habitable zone = 1
    Random star system with 2 Earth-like planets in habitable zone: index = 6436
    Total mass of planets = 200.081 Earth masses
    Planet Radius Period Mass Within Habitable
    Index (A.U.) (years) (Earth=1) Zone
    —— —— ——- ——— —————-
    1 0.419 0.271 0.053 false
    2 0.772 0.678 0.586 true
    3 1.011 1.017 1.551 true
    4 3.431 6.355 123.516 false
    5 6.320 15.888 10.733 false
    6 11.642 39.721 60.089 false
    7 21.444 99.302 3.554 false

    Number of star systems with 3 Earth-like planets in habitable zone = 0

    Number of star systems with 1 planet of any type in habitable zone = 2107
    Random star system with 1 planet of any type in habitable zone: index = 9998
    Total mass of planets = 696.904 Earth masses
    Planet Radius Period Mass Within Habitable
    Index (A.U.) (years) (Earth=1) Zone
    —— —— ——- ——— —————-
    1 0.251 0.126 4.199 false
    2 0.851 0.785 2.513 true
    3 5.320 12.271 686.864 false
    4 9.800 30.679 2.022 false
    5 13.776 51.131 0.280 false
    6 21.868 102.262 0.319 false
    7 30.740 170.437 0.707 false

    Number of star systems with 2 planets of any type in habitable zone = 27
    Random star system with 2 planets of any type in habitable zone: index = 9994
    Total mass of planets = 69.862 Earth masses
    Planet Radius Period Mass Within Habitable
    Index (A.U.) (years) (Earth=1) Zone
    —— —— ——- ——— —————-
    1 0.126 0.045 0.598 false
    2 0.786 0.697 8.772 true
    3 1.105 1.162 4.576 true
    4 2.299 3.485 0.369 false
    5 4.234 8.713 55.171 false
    6 7.800 21.783 0.110 false
    7 14.367 54.457 0.210 false
    8 22.806 108.914 0.057 false

    Number of star systems with 3 planets of any type in habitable zone = 0

    Number of star systems with at least 1 hot Jupiter = 2125
    Random star system with at least 1 hot Jupiter: index = 9988
    Total mass of planets = 244.455 Earth masses
    Planet Radius Period Mass Within Habitable
    Index (A.U.) (years) (Earth=1) Zone
    —— —— ——- ——— —————-
    1 0.192 0.084 216.925 false
    2 2.207 3.279 0.160 false
    3 4.065 8.196 0.745 false
    4 6.453 16.393 2.841 false
    5 11.887 40.982 23.634 false
    6 21.896 102.456 0.150 false

  23. Tom Marking

    Looks like HTML has reared its ugly head and clobbered my less than sign and greater than sign. The gibberish in the previous post should have said:

    An Earth-like planet is defined as a planet with a mass greater than or equal to 0.5 Earth masses and less than or equal to 2.0 Earth masses

    A hot Jupiter is defined as a planet with a mass greater than or equal to
    100.0 Earth masses and a distance from its star less than 0.771 A.U.

  24. StevoR

    Awesome news! 8)

  25. StevoR

    Adding to the list of Jupiter-like exoplanets from Tom Marking is

    HD7046 b

    A planet about 2-3 times the mass of Jove with a circular orbit at 2.3 AU from a star the same mass and age of our Sun.

    This one was found back in July 2003 by the Anglo-Australian telescope and was published about in the ‘Astrophysical Journal’ -lead author Dr Brad Carter.

    This info comes via an ABC e-news article (in my exoplanet news folder!) :

    http://www.abc.net.au/science/news/stories/s893913.htm

    Hope that link works!

    & thanks again …

    http:

  26. StevoR

    # Tom Marking on 16 Feb 2008 at 5:12 pm

    “I’m not sure what all the fuss is about.

    Planet 55 Cancri Ad orbits its star every 12.4 years at a distance of 5.26 AU. It has a mass of at least 3.9 Jupiters and it was discovered in 2002.

    Planet 47 Ursae Majoris c orbits its star every 7.1 years at a distance of 3.8 AU. It has a mass of at least 0.8 Jupiters, an eccentricity of close to zero, and was discovered in 2002.

    Planet Mu Arae c orbits its star every 11.5 years at a distance of 5.24 AU. It has a mass of at least 1.8 Jupiters, an eccentricity of 10 percent, and was discovered in 2004.

    So several close analogs to Jupiter have been known for several years.”

    Perhaps the difference is that the 55 Cancrisite & Mu Araean systems at least are full of other closer in superjovian & Hot Jovian planets?

    Not sure about how close the other planet is for 47 Ursae Majoris (must check ..) but it too may be too close and preclude the chances of an earth-like planet in the habitable zone …

    I’m guessing *that’s* the difference – here there’s just the one Jupiter-like planet in the right place to allow an earth-like world – elsewhere perhaps there’s not?

    Mind you I’ve already noted above another example that is also quite similar – unless another world or something else was found for HD 70642 that rules it out since …

  27. andy

    47 Ursae Majoris is surprisingly poorly-known for a system that has been known for such a long time. While the first planet (47 UMa b, at 2.1 AU, perilously close to the habitable zone – indeed simulations suggest that habitable planet formation around 47 UMa would have been inhibited by the presence of 47 UMa b) is well known, it is not so clear for the outer planet. 47 UMa c probably exists, but its parameters are difficult to judge. See this paper for details: that paper obtains a best orbit for 47 UMa c of 7.7 AU, rather than the value of 3.7 AU that was originally suggested. So while it likely is a Jupiter-analogue, its actual characteristics are poorly-known, plus there is an inner gas giant.

    As for HD 70642b, it’s located rather closer to its star than Jupiter is (3.3 AU versus 5.2 AU) and is at least twice as massive.

    An additional consideration is how the planet’s atmosphere works… more massive planets likely have more internal heating, which for planets more than about 2 Jupiter masses would (for a ~5 Gyr old planet, and when combined with the radiation from the star) keep the planet too warm to have Jupiter-like clouds even if located at Jupiter-like distances. Most so-called “Jupiter analogues” probably fail the atmospheric criterion due to being too close to their stars or too massive.

    So once the planets which have poorly-constrained parameters have been eliminated, and setting a cutoff of minimum mass=1.6 Jupiter masses to allow for the fact that the true mass may be significantly higher than the minimum, that leaves: Gliese 849b, OGLE-2006-BLG-109Lb (note these first two have very similar properties), Gliese 317b and HD 154345b. With the exception of HD 154345b, they are all orbiting red dwarf stars.

  28. Tom Marking

    O.K. So the criterion seems not to be “Jupiter-ness” but rather “Solar system-ness”. I detect several chauvinisms creeping into the discussion concerning extraterrestrial life including 1.) carbon chauvinism, 2.) water chauvinism, and now 3.) solar system chauvinism (i.e., a planetary system must be sufficiently similar to our solar system to have any hope of having a planet with the possibility of life). I believe that all three chauvinisms will eventually turn out to be pure bunk but it may take several centuries for this to come about.

    In the meantime, concerning chauvinism numero tres let’s define the following criteria:

    A.) semi-major axis between 3.5 and 6 AU
    B.) mass greater than or equal to 0.5 Jupiters
    C.) no planets of mass greater than 0.1 Jupiters with a distance less than 4 AU (at least that has been detected)
    D.) eccentricity is less than or equal to 30 percent

    That should be a pretty good measure for “solar system-ness”. Now, looking at:
    http://en.wikipedia.org/wiki/List_of_stars_with_confirmed_extrasolar_planets
    we see the following systems meeting these criteria:

    HD72659 b
    Star: G0V, 168 light-years away, constellation Hydra
    Planet: at least 2.96 Jupiter masses, distance 4.16 AU, orbital period 8.7 years, eccentricity 20 percent, discovered 2002

    HD 89307 b
    Star: G0V, 108 light-years away, constellation Leo
    Planet: at least 2.73 Jupiter masses, distance 4.15 AU, orbital period 8.5 years, eccentricity 27 percent, discovered 2004

    HD 30177 b
    Star: G8V, 179 light-years away, constellation Dorado
    Planet: at least 9.17 Jupiter masses, distance 3.86 AU, orbital period 7.7 years, eccentricity 30 percent, discovered 2002

    HD 50499 b
    Star: G1V, 154.2 light-years away, constellation Puppis
    Planet: at least 1.71 Jupiter masses, distance 3.86 AU, orbital period 7.1 years, eccentricity 23 percent, discovered 2005

    HD 117207 b
    Star: G8VI, 108 light-years away, constellation Centaurus
    Planet: at least 2.06 Jupiter masses, distance 3.78 AU, orbital period 7.2 years, eccentricity 16 percent, discovered 2004

    So out of 221 extrasolar systems 5 of them are close solar system analogs. Now given the huge observational bias in favor of high mass, close-in planets the true percentage must be much greater than 5 out of 221 (2 percent). So I repeat my initial comment which was, what is all the fuss about concerning one more member to this club of common objects?

    (BTW, all 5 stars are of spectral class G which is the same as the sun)

  29. andy

    Tom Marking, all of the planets you list are closer to their stars than Jupiter and more massive than Jupiter. Thus they all would be too warm (from a combination of internal heating and stellar radiation) to be truly Jupiter-like – the ammonia and related compounds would not condense out into Jupiter-like clouds – the prediction is that their skies would be dominated by water clouds instead.

    So in a sense HD 154345b is the first truly Jupiter-like exoplanet (provided it isn’t an object being observed in a face-on orbit and actually is far more massive than the lower limit): it’s small and cool enough for a Jupiter-like atmosphere, and unlike the other candidates it orbits a G star. This is important in terms of photochemistry – the different spectrum of a red dwarf star means that the reactions going on in the atmosphere may well be different for planets around such stars even if they are at similar temperatures.

  30. andy

    ^ (“the other candidates” being the ones I listed in my earlier post)

  31. Jason Wright

    Hi, Tom. I agree that there have been many other long-period planets discovered. In fact, our paper lists many of them in the introduction.

    You’re right that long-period planets are not new — though this is one of the longest periods yet discovered. You’re also right that HD 154345b is not particularly low mass, though it is the smallest of all of the planets you list. You’re also right that circular orbits are not unknown outside the Solar System — though they are pretty rare and HD 154345b is by far the most circular on your list. But this system is the first to have all of those properties at once, and the first to look almost exactly like our Sun would look if we were observing it from a distant star with present technology.

    As for the charge of chauvinism, I think that all of the exoplanets are interesting. On the other hand, it has long been an outstanding problem that so few long-period exoplanets have circular orbits like our planets.
    Your cut of e=0.3 for “circular-ness” is rather generous — half of all exoplanets have e < 0.3, but the (now) eight planets in our Solar System all have eccentricities much less than that. It’s important to planet formation theory to see that there are other exceptions as well.

    Finally, as for the life thing, most astronomers will enthusiastically agree that we have very little idea what form extraterrestrial life will have if and when we eventually discover it (and we’re pretty imaginative people!). But throwing up our hands and saying “it could be anywhere!” does not lead to a plan for finding it. Building space telescopes costs billions of dollars and requires detailed specifications, so we have to have very specific targets in mind. Lacking anything else to go on, prudence dictates that we look in the most likely places first, and based on the quick development of life on Earth in water, that means oceans on rocky planets. In short, the reason we look for Earth analogs isn’t that we can’t imagine where else life would form. The reason is that we have limited resources and have to start somewhere.

  32. Tom Marking

    “Hi, Tom. I agree that there have been many other long-period planets discovered. In fact, our paper lists many of them in the introduction.”

    This would be the J.T. Wright listed as an author on the paper? It’s a real pleasure communicating with you, sir. I did not mean to come off as dissing your paper. The more data we can have on exoplanets the better IMHO.

    Now that you explain the combination of parameters that HD 154345b has, I didn’t realize that nothing like that had been found before. But I do note in reading the article that you list the eccentricity as being 4.4 percent but with an error of plus or minus 4.6 percent, is that right? So the eccentricity could be as high as 9 percent and still be consistent with your data. Is that a typical error margin for the eccentricity of an exoplanet or is that higher in this case than normal?

    Regarding the search strategy for life, with only two hundred or so exoplanets being known to date (I’m sure the number might climb drastically in the future) is there really a problem with scanning them all with the new space telescopes? I would agree with the idea of starting with stellar systems similar to ours, or perhaps with planets we think are in the habitable zone (e.g., Gliese 581c) if logistical considerations are a block. On the other hand, I would also pursue a space probe to the seas of Titan (even though they are not water seas, but rather methane seas) since we know that life is a manifestation of the liquid state of matter.

  33. Jason Wright

    Tom wrote:”This would be the J.T. Wright listed as an author on the paper? ”
    Yes.

    Tom wrote: “Is that a typical error margin for the eccentricity of an exoplanet or is that higher in this case than normal?”

    These errors in the eccentricity are typical for signals as weak as this one. For more massive or more close-in planets, the errors are correspondingly smaller. Check our Catalog of Nearby Exoplanets for examples of typical eccentricity uncertainties (http://exoplanets.org).

    Tom wrote: “Regarding the search strategy for life, with only two hundred or so exoplanets being known to date (I’m sure the number might climb drastically in the future) is there really a problem with scanning them all with the new space telescopes?”

    It’s not just a problem of time (and, yes, 200 targets could easily be too many for something like TPF, depending on the design), it’s also a problem of engineering specifications. These telescopes have to be optimized to some goal. Generally, that goal is detecting a 1 earth-mass planet at 1 AU from a G star. There are trade-offs that make observing other kinds of planets more difficult (although in general, more massive planets are always easier to detect). In addition, the instruments being developed are optimized to look for water and other chemicals indicative of life on Earth. We can’t just look for “anything out of the ordinary”, we have to give the engineers very specific guidance for what sort of signals their looking for.

    Tom wrote: “I would agree with the idea of starting with stellar systems similar to ours, or perhaps with planets we think are in the habitable zone (e.g., Gliese 581c) if logistical considerations are a block. On the other hand, I would also pursue a space probe to the seas of Titan (even though they are not water seas, but rather methane seas) since we know that life is a manifestation of the liquid state of matter.”

    I, too, am excited at the possibility of looking more carefully at Titan, as well as Europa. Again, it’s a resources issue. If NASA tells us that we can look carefully at either Titan or Mars with a fixed budget (which isn’t how it actually works, but bear with me), then do you look at the closer (and thus much-cheaper-to-get-to) body with a history of liquid water, or the much more distant and costlier body with extraordinary cold ethane lakes?

    If money were no object, I think you’d see plenty of missions to find life in some very exotic places. I know several astronomers who have put in proposals to search for life in places even you might find unlikely (supermassive black holes, for instance).

  34. Chris Nelson

    I’m curious why the plotted fit is way outside the error bars for many of the measurements. Does that imply one or more inner planets? Does it have something to do with stellar jitter (which I can’t readily find a definition for on the internet)? Or does it mean that the error bars are overly optimistic?

  35. Tom Marking

    O.K. Thanks, Jason, for answering my questions. Best of luck to you in your search for more exoplanets.

  36. Jason Wright

    The error bars represent our assessment of the intrinsic measurement uncertainties. It’s not clear why some of the points are “off”. It could imply other planets, but it could also imply that there is some underlying “noise” due to the star itself. Down at these very low velocity levels, even stars as “quiet” as HD 154345 oscillate, have rotationally modulated spots, and exhibit other sources of noise that we refer to as “stellar jitter”. Some stars have more jitter than others, and we only have a rough sense of which stars are “good” and which are “bad” in terms of jitter.

    I’m surprised that HD 154345 seems to exhibit so much jitter though — we’re following it very closely to see if it is, in fact, due to inner planets.

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