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Browsing the Exoplanet Catalog

We now have on the order of 335 confirmed exoplanets, with an ongoing race between the CoRoT and Kepler teams to find the first Earth analog in the habitable zone around another star. CoRoT’s shorter observation cycles make finding a terrestrial world around a G-class star problematic — the orbit would necessarily be on the order of a year, and the transit would then have to be confirmed with additional transits and whatever radial velocity observations could be mustered. But CoRoT just might find an Earth-class planet in the habitable zone of a K-class star, so we shouldn’t assume Kepler is necessarily going to win the ‘habitable Earth’ race.

I mentioned a few days back that the Planetary Society has unveiled its new Catalog of Exoplanets, a fine resource with the basics on detection methods and a glossary that complements a catalog filled with helpful orbital animations. If you want to get a quick read on a given exoplanet, take a look here. Some of these planets have gone beyond the stage of being purely numerical designations to emerge as places in their own right, with our deepening knowledge making them come alive. How long will it be before we start naming these worlds?

Consider HD 189733 b, some 62 light years from us, a hot Jupiter orbiting at a distance of some 5 million kilometers from its star. Because we found this one (four years ago) by radial velocity methods and then were able to pull off a transit detection, HD 189733b has become one of the best understood exoplanets we’ve studied. Who would have thought, back in 1995 when Michel Mayor and Didier Queloz identified 51 Pegasi b, that within fifteen years we would be creating an absorption spectrum of an exoplanetary atmosphere, revealing gases like water vapor, methane and carbon dioxide, mixing with potassium, sodium and ammonia?

The Catalog of Exoplanets has a section that runs through the most notable finds thus far, including the 55 Cancri system, where five planets, all of them gas giants, orbit the star with the most exoplanet detections. Here we’re in interesting territory in terms of the habitable zone, because 55 Cancri f is a Saturn-sized planet near the zone where water could exist on a planetary surface, leading to inevitable speculation about rocky moons and their potential for life. And then there’s Gliese 581 c, well known because of its nearness to the habitable zone and the media attention that followed its discovery, along with icy ‘super-Earth’ Gl 581 d.


Image: The system around 55 Cancri in comparison to our own. Credit: NASA/JPL-Caltech.

What I’m thinking is that a browse through the Catalog of Exoplanets now is going to be memorable when you consider what will be in the catalog within a decade or so. Sort of like jumping from site to site back in the early days of the Web, when the explosive growth of commerce and search engines and personal pages had yet to occur. How fascinating and yet sparse the Web was then, and how much richer it has become. Will the Catalog of Exoplanets a decade hence list hundreds of terrestrial planets, many in the habitable zone of their stars? The odds seem to favor it, though our planet hunter spacecraft will have the next word.

And a final thought: Given the budgetary problems that have beset the Space Interferometry Mission (now known as SIM Lite, a change of name that speaks volumes) and the mutating Terrestrial Planet Finder concepts, Kepler has emerged as the NASA planet hunter with the most to prove. If it turns out that we find few terrestrial worlds where we think there should be many, the impetus for more advanced missions to characterize planetary atmospheres, for example, is bound to be weakened no matter when the economy begins to recover. Let’s hope Kepler and CoRoT both yield a continuing harvest of small new worlds.

Comments on this entry are closed.

  • philw1776 March 10, 2009, 12:27

    One concern I had about the original full featured imagined TPF was that it was limited to spectroscopy to something under 50LY. If Earth analogs (terrestrial planets in HZs) are few and far statisticly then we may need a larger optics TFP capable of asy 100LY analysis, nearly a factor of 10 more stars.

  • andy March 10, 2009, 15:09

    Any list of most notable exoplanets which doesn’t include the terrestrial-mass pulsar planets (which STILL blast all these claims for “least massive extrasolar planet” out of the water) or the HW Virginis circumbinary planetary system is deeply flawed IMHO. Bunch of fusion-chauvinists. Still promoting the Gliese 581c = habitable viewpoint I see.


  • Administrator March 10, 2009, 16:07

    Yes, and incautiously at that, as witness this statement from the site re Gl 581c:

    A small rocky planet with a mild climate where water can flow? Sounds a lot like our own world…

    I like that ‘fusion chauvinist’ term, by the way.

  • Ross March 10, 2009, 17:46

    Why “they” (for example those in charge of Kepler) aren’t even mentioning jupiter sized or larger planets in the habitable zone of stars as great potential sources of habitable worlds continues to amaze me. We can detect these gas giants easier than we can smaller rocky worlds, and the potential for mars or larger sized moons with liquid water on them could be high.

    We have already spotted some of these giants, for example check out http://www.planetary.org/exoplanets/list.php?exo=HD+28185+b, a planet orbiting a 1.24 mass star every 383 days. This planet is 5 x Jupiter and could have moons bigger than mars, covered with liguid water … in the habitable zone of the star. Take look at it’s almost circular orbit, then tell me that is not a very interesting target for more powerful telescopes (when/if we get them).

    Why does nobody get excited about these planets and why do they get almost no press or interest?

    I ask myself that question every time someone talks about kepler finding exact duplicates of single earth type planets at 1 AU of sunlike stars, and then mentions that if we don’t find them we may be alone.

    The universe could be full of habitable moons, have almost no other earthlike planets and still be teeming with life …

    Yes it would be great if we find hundreds of rocky planets, 1 x the mass of earth at exactly 1 AU around stars 1 x the mass of the sun with exactly the same metallicty. But it we don’t find them, there are other options for life to take hold of/on, and we don’t have to retreat into our old “we are alone” shell and stop funding planet finding telescopes … as was mentioned by someone in one of the articles I just recently read.

    My apologies for the rant …

  • John Hunt March 10, 2009, 22:24

    While looking at the Catalogue of Exoplanets and looking at a particular system I noticed that one description line I noticed that it said “Male Enhancement”. But, of course, on closer inspection it actually said “Metal Enhancement”. I’m afraid to ask what this might imply about my subconscious!

  • Ronald March 11, 2009, 4:44

    @Ross: “The universe could be full of habitable moons, have almost no other earthlike planets and still be teeming with life”.

    True, but I wonder: how feasible would it be for Kepler, or any telescope, to detect an earthlike moon near a giant gas planet?

    And for the TPF, or Darwin, or any telescope, to spectroscopically analyze its atmosphere for biosignatures?

  • ljk March 11, 2009, 9:01

    Ross said:

    “Why does nobody get excited about these planets and why do they get almost no press or interest?”

    My thoughts exactly and no need to apologize. While I can understand
    why people are interested in finding Earthlike worlds, it also strikes me
    as showing a lack of imagination. That’s why pre-Pegasi 51 reports of
    massive exoplanets very near their suns were dismissed, because we
    *knew* that Jovian worlds only orbited way out in their solar systems.

    Hopefully this latest paradigm will be broken and we will start looking
    in new places. Even if we don’t find life, we may find something else
    we did not expect.

  • Ronald March 11, 2009, 11:02

    Now that we are on it, are there any studies with regard to:
    1) detectability of large moons of gas giants
    2) habitability (i.e. chances for biological life in general) of large moons of gas giants, in comparison with ‘regular’ terrestrial planets

  • Administrator March 11, 2009, 13:13

    Ronald, with regard to exomoons, check David Kipping’s work on the subject. I wrote it up here:


    To my knowledge, Kipping’s team is more involved in exomoon studies than any other.

  • James M. Essig March 11, 2009, 13:38

    Hi Folks;

    The presense of human habitable biospheres on exomoons in orbit around large gas giant planet, or even gas giant planets on the scale of Neptune and Uranus gives one the mental imagery of the various moons depected in the Star Wars series of movies. I can imagine a planet rise on some beautiful exomoon surface wherein the planet might have an angular diameter of perhaps 3 to 10 degrees. Factor in moom rises of sibling exomoons and the night sky could be fantastically beautiful.

    The beautiful mental imagery and real artistic depictions of such moon and planet based night skies almost makes me want to try my hand at painting such imaginary scenes. An ensemble of such unique scenes must play out in terms of real environments throughtout our universe.



  • Ronald March 11, 2009, 18:28

    Paul, thank you for reminding me; I noticed, while checking the CD article you mention, that I had posted the following comment there myself (allow me to repeat it here):

    a quick scan of the Extrasolar Planets Encyclopedia showed me that of the 294 extrasolar planets in the main table, some 50 are of at least 1 Jupiter mass (up to 18 Mj) at between 0.7 and 1.5 AU semi-major axis, orbiting a roughly sunlike star (from F6 – K2, main sequence V and subgiant IV; excluding a few M dwarfs and KIII giants).

    That means that just over 1 in 6 extrasolar planets discovered so far is a giant planet (>= 1Mj) roughly in or near the habitable zone.

    Gives relevance to the issue of exomoons.

  • andy March 11, 2009, 18:56

    As for actual detections of exomoons, various curious properties of the directly-imaged planet Fomalhaut b led to the suggestion that it is surrounded by a moon-forming disc. Furthermore, there is a suggestion that a transit of the planet of Beta Pictoris was detected in 1981 (if confirmed, this would presumably be the earliest detection of an exoplanetary transit), and that the inferred size of the planet was much larger than predicted by evolutionary models – an indication that it too may be surrounded by a large ring system or moon-forming disc.

    Observations of exomoons seem to have begun in a similar way to the observational history of detecting exoplanets: the first results are detections of the discs from which the objects form.

  • ljk April 29, 2011, 22:31

    Press Release Release No.: 2011-12

    For Release: Friday, April 29, 2011

    Student’s Prediction Points the Way to Hot, Dense Super-Earth

    Cambridge, MA – A planet that we thought we knew turns out to be rather different than first suspected. Our revised view comes from new data released today by an international team of astronomers. They made their observations of the planet “55 Cancri e” based on calculations by Harvard graduate student Rebekah Dawson (Harvard-Smithsonian Center for Astrophysics), who worked with Daniel Fabrycky (now at the University of California, Santa Cruz) to predict when the planet crosses in front of its star as seen from Earth. Such transits give crucial information about a planet’s size and orbit.

    The team found that 55 Cancri e is 60 percent larger in diameter than Earth but eight times as massive. (A super-Earth has one to 10 times the mass of Earth.) It’s the densest solid planet known, almost as dense as lead. Even better, the star it orbits is so close and bright that it’s visible to the naked eye in the constellation Cancer the Crab. This makes it an excellent target for follow-up studies.

    Full article here: