Yesterday, NASA announced that they had found three new exoplanets that have the potential for life. One of these planets — Kepler-62f — has the possibility of being truly 'Earth-like', with continents, oceans and polar ice caps, which is some pretty exciting news, but the other two were quite remarkable too, as they might be unlike anything we have in our solar system.
"These planets are unlike anything in our solar system," said Lisa Kaltenegger, of the Max Planck Institute for Astronomy, at the NASA press conference. "They have endless oceans."
Kepler-62e and Kepler-69c orbit around two different stars, roughly 1,500 light years apart from each other, but the two planets are fairly similar to one another. They're very close in size — being 'super-Earths' that are 1.6 and 1.7 times the size of our planet, respectively — and both orbit close to the inner edge of their star's habitable zone — the 'band' of space around the star where any planet should have the right temperature for liquid water to exist on its surface.
Even more interesting, both of these planets may be what the NASA astronomers called 'water worlds' — planets that are completely covered by a vast ocean, with no solid surface like Earth has.
Now, the astronomers don't have enough information about these planets to know this for sure (they'll need to make follow-up observations), but they're basing this conclusion on the size of the planets and what our knowledge of the planets in our solar system and planets we've already confirmed tell us.
In our solar system we have rocky planets like Mercury, Venus, Earth and Mars, we have gas giants like Jupiter and Saturn, and 'ice giants' like Uranus and Neptune. From what we've figured out about how planets form, we have a pretty good idea about how the size of the planet (and where it developed) influenced the planet's structure and what is in its atmosphere (if it has one). There's plenty of evidence that Venus, Earth and Mars all had liquid water on their surfaces, even though Earth is, apparently, the only one that still does. The size and gravity of these planets allowed the right gases to remain in their atmosphere for water to collect on the surface. For bigger planets, we only have the gas giants and and ice giants for example, and they are many times the size of Earth. Jupiter and Saturn are mostly hydrogen and helium, and Uranus and Neptune are still gas planets but made up of gases heavier than hydrogen and helium.
However, by modelling out the sizes of planets between Earth and Neptune, scientists have been able to figure out that up until a planet reaches about 1.5 times the size of Earth, it can develop into a fairly Earth-like planet. When they get bigger than about twice the size of Earth, they start to push into the realm of 'Neptune-like' planets that are mostly gases. When they're between 1.5 and 2 times the size of Earth, though, they're just in the right size category to retain an abundance of water that spreads out to form an ocean that covers the entire surface of the planet.
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Can life exist on this type of planet?
We only need to look at our own oceans to see the answer to that question, and since Earth orbits the Sun just along the inner edge of the Sun's habitable zone (based on the latest models), that makes it even more likely.
"There may be life there, but could it be technology-based like ours?" asked Kaltenegger, while speaking at the NASA press conference, and then she answered her own question by saying: "Life on these worlds would be under water with no easy access to metals, to electricity, or fire for metallurgy. Nonetheless, these worlds will still be beautiful, blue planets circling an orange star — and maybe life’s inventiveness to get to a technology stage will surprise us."
(Images courtesy: NASA Ames/JPL-Caltech)
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