The Earthiest planets in the universe (that we know of)

Last week, Rob told you how scientists announced that they'd found two Earth-like planets orbiting the star Kepler-62. One of those, Kepler-62e, now ranks as the most Earth-like exoplanet we've ever found. Of course, all of this is relative.

What I like about this chart is that it kind of shows you how "Earth-like" doesn't really mean, "Man, that is totally exactly like Earth." Instead, you should translate it more as, "Welp, this is about the closest to Earth that we've found so far." Even Kepler-62e, as you can see, is much larger than the Earth and Mars. And size matters when it comes to actual habitability. As does density — and we don't know what Kepler-62e is made of yet. It's also worth noting that #2 on this list, the infamous Gleise 581g, is really a planet candidate, rather than a planet. We aren't actually certain it exists, just yet.

Popular Science has a neat little breakdown explaining what life might be like on Kepler-62e, if we could go there. But it's worth keeping the context in mind on these Earth-like planets. Don't pack your bags just yet.



  1. “It’s also worth noting that #2 on this list, the infamous Gleise 581g, is really a planet candidate, rather than a planet. We aren’t actually certain it exists, just yet.”

    Don’t bother me with details.  START THE INVASION!!

  2. Here’s a link to the math on the  Earth Similarity Index ESI (a haphazard look at that suggests the need for the left absolute value to move to cover the “1 -” but, even if it did go negative a fractional exponent would quickly show the error of one’s ways)
    interesting set of properties considered; nothing considering the atmosphere at all?  (“most of these planets are too far away to get any atmosphere data you @#$!!!”)

    1. They’re all artists’ renditions anyway, without actual data. For the most part, all we’ve seen of these planets have been variations in their stars’ light outputs.  (If we’ve seen anything more than that, it’s been a “one dark pixel in front of the star” for a hot Jupiter.)

  3. Although, honestly, the graph is just as good a reminder of how un-Earthlike Mars is.  

    It hadn’t occurred to me, but I suppose a huge but low-density planet could actually be habitable.  And real-estate would be a lot cheaper!  But also I suppose it wouldn’t have a rotating metal core.

    1.  -This is the kitchen and there is the backyard, 200 acres of free space available for any kind of project for garden to a F1 circuit!
      -Mmmm yessss… but does it have a rotating iron core? I’m not much into cosmic radiation… you know?
      -Well, window shutters are plated in lead!

  4. Something that strikes me about a lot of these extrasolar planets is how CLOSE they are to their stars.  

    1. A lot of that is to do with the method used to detect them. One of the main methods involves seeing the wobble produced in a star by the gravitational influence of a planet. You get more wobble with more gravitational influence and you get more gravitational influence when a planet is bigger or closer to a star. That’s why the first extrasolar planets detected were gas giants orbiting ridiculously close to their stars.

  5. “Now you must decide how many people you wish to save from death, and what supplies will be required to support them. Any mistake at this point will doom you and your colonists to certain death. Have a nice day.” 

  6. The numbers on the chart look wrong. If Mars is roughly two-thirds the size of Earth and is 0.62 ESI, then how can No. 6, Kepler-62f, be about two-thirds bigger than Earth and only 0.69 ESI? Assuming the Earth:Mars ratio is correct, then Kepler-62f should be 1.69 ESI, no? That, or the drawings are all wrong.

    1.  Diameter is not the only factor that goes into the ESI. Otherwise it wouldn’t be ESI, it would be “earth standard diameters” and we’d have Venus on that list despite it being insanely lethal.

      Among other critical things, distance from the star, and the stars own output would be pretty damn important. As mentioned, we can’t judge atmosphere, density, or magnetosphere from here – but in reality you’d want those numbers for any “practical” evaluation.

      For certain values of practical, it’s not like we’re going to hop around for a visit any time soon.

  7. “It’s a great big Universe, and we are really puny:
     Just tiny little dots, about the size of Mickey Rooney…”

  8. If anyone cares:
    HD 40307 g appears to be confirmed. 
    If you are going to include unconfirmed planets like Gliese 581 g and Tau Ceti e, the current champ would anyway  seem to be KOI-1686.01, which if you go with their numbers (and why wouldn’t you?), the Planetary Habitability lab shows as a .89. 
    For the stars they include, Pop Sci’s numbers all seem to be taken from the PHL’s, except for Kepler-62 e, which is shown in the lab’s database as .83

  9. If it weren’t for the fact that greater than 90% of all North Korean rocket launches fail, I’d be genuinely worried that they would try to colonize one of those planets.

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