Make us your home page
Instagram

Today’s top headlines delivered to you daily.

(View our Privacy Policy)

An alien solar system with two Earth-sized worlds

Scanning the heavens, you might very well miss the star Kepler-62. It's a rather typical star, slightly smaller, cooler, and more orange than the Sun, much like tens of billions of other stars in our galaxy. But it holds a surprise: It's orbited by at least five planets . . . and two of them are Earth-sized and orbit the star in its habitable zone.

The two planets, called Kepler-62e and Kepler-62f, are both bigger than Earth, but not by much; they are 1.6 and 1.4 times the Earth's diameter, respectively. Kepler-62e orbits the star every 122 days, while Kepler-62f, farther out, takes about 267 days.

Given the temperature and size of the parent star, this means that both planets are inside the zone around the star where water on the surface could be a liquid. Now, to be clear, this depends on a lot of factors we don't know yet: the masses of the planets, their compositions, whether they have atmospheres or not, and what those putative atmospheres are made of. For example, Kepler-62e could have a thick CO2-laden blanket of air, making its surface temperature completely uninhabitable, like Venus.

Or it might not. We just don't know yet, and won't for quite some time - both planets are too small to get a measurement of their masses. It's worth noting, though, that we do have size and mass determinations for a few planets like this around other stars, and they look rocky, like Earth. That makes it likelier these two planets are as well.

Also, the best computer models we have, based on what we know about how planets form and change over time, indicate that these planets could very well have water on them (it is, after all, incredibly common both in our solar system and in the Universe at large). We've already seen at least one planet with indications of the presence of water.

That's pretty exciting. For years we didn't know if any planets existed around other stars at all. When we started finding them all we could see were ones that were huge and hot, as unlike Earth as you can imagine. But as time went on, and our technology and techniques got better, we started finding smaller, less massive worlds. Now we are finding ones that look achingly like home.

These planets were found using the transit method: The Kepler spacecraft stares at one region of the sky, observing about 150,000 stars all the time. If a planet orbits a star, and the orbit is oriented edge-on from our point of view, we see the planet pass directly in front of the star once per orbit. This is called a transit, and it blocks a teeny bit of the star's light. The amount of light blocked depends on the size of the star (which we can determine) and the size of the planet. A big planet blocks more light, and a small one less.

That's what makes finding Earth-sized planets hard; they only block about 0.01 percent of the star's light. Kepler was designed to be sensitive enough to detect that meager dimming, though, and has actually found several planets in this size range now.

The other problem is timing. For a planet to be in the star's habitable zone, it may take months or even years for it to pass in front of the star several times (multiple transits are needed to make sure we're not seeing some other event, like a starspot). That takes time, but Kepler has been observing these stars for years now, which is why we're seeing more and more smaller planets now.

And to find two orbiting the same star is very cool indeed. Assuming they're made up of the same materials as Earth (metal and rock) and therefore have about the same density, you'd weigh 60 percent more on Kepler-62e, and 40 percent more on Kepler-62f. I'll note that all things considered, neither would be paradise: Kepler-62e gets about 20 percent more sunlight than we do on Earth, and Kepler-62f gets about half; a bit hot and cold for my taste. But again, we don't know the conditions on these planets. Give Kepler-62e a thin atmosphere, and Kepler-62f a thick one, and they might look a lot like Earth.

What an amazing thing that would be: two inhabitable worlds around one star. It's fun to imagine it being like a Victorian science fiction novel, spurring interplanetary travel and trade between alien races . . . or war. I guess that depends on which writer you read.

Of course, the habitability of these two newly found planets is all supposition, but consider this: We think there are tens of billions of Earth-sized planets orbiting other stars. Even if a fraction of them are the right distance to be in their stars' habitable zones, that still leaves tens or hundreds of millions of planets. That's a lot of planets to play with. Sure, some will be too hot, too cold, have too much air or not enough, or have toxic atmospheres. But still, statistically speaking, it seems very likely indeed that there are plenty of planets out there that will look an awful lot like Earth.

Phil Plait, the creator of Bad Astronomy, is author of "Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax' " and "Death from the Skies! These Are the Ways the Universe Will End."

An alien solar system with two Earth-sized worlds 04/18/13 [Last modified: Thursday, April 18, 2013 5:01pm]
Photo reprints | Article reprints

Copyright: For copyright information, please check with the distributor of this item, Slate.
    

Join the discussion: Click to view comments, add yours

Loading...
  1. Rays set to activate Tommy Hunter from DL

    Blogs

    The Rays plan to activate RHP Tommy Hunter from the DL for Thursday's series finale against the Angels.

  2. Reporter says Republican candidate in Montana body-slammed him (w/video)

    Nation

    HELENA, Mont. — Witnesses said the Republican candidate for Montana's sole congressional seat body-slammed a reporter Wednesday, the day before the polls close in the nationally watched special election. Authorities said late Wednesday that Greg Gianforte has been cited for misdemeanor assault over incident with …

    Greg Gianforte, right, receives congratulations from a supporter in Helena, Mont., in March. [Associated Press]
  3. Culpepper falls just short on 'Survivor' finale

    Human Interest

    In the end, Tampa lawyer Brad Culpepper fell just short, and the ex-Tampa Bay Buccaneer lost Survivor: Game Changers and the $1 million prize to Sarah Lacina, a police officer from Iowa.

  4. Families dispute claims that slain Tampa Palms roommates shared neo-Nazi beliefs

    Crime

    TAMPA — Andrew Oneschuk never liked making small talk on the phone, his father said, but the last time the two spoke, something seemed off.

    Andrew Oneschuk and Jeremy Himmelman lived in a Tampa Palms apartment with Devon Arthurs and Brandon Russell. Oneschuk and Himmelman reportedly planned to move out.
  5. Brad Culpepper makes it to final 3 on Survivor, but jury picks Sarah

    The Feed

    UPDATE, WEDNESDAY NIGHT: Tampa's Brad Culpepper make it to the final 3 on Survivor, but jurors chose Sarah as the winner of the $1 million.

    Original report follows:

    "The Tables Have Turned" - Brad Culpepper, Tai Trang and Hali Ford on the fourth episode of SURVIVOR: Game Changers on the CBS Television Network. Photo: Jeffrey Neira/CBS Entertainment