NASA/JPL-Caltech/R. Hurt (SSC)

ScienceShot: 'Super-Earths' May Not Be So Super for Life

A nice neighborhood doesn’t necessarily guarantee that your house is livable. Likewise, even if a planet orbits within the so-called Goldilocks zone surrounding its parent star where conditions are neither too hot nor too cold, its atmosphere may be hostile to life, a new study suggests. Even “super-Earths,” orbs with masses that fall between one and 10 times that of our planet (depicted at right in the artist’s concept above) and therefore offer some semblance of similarity to Earth, might be uninhabitable. Using computer simulations, researchers modeled the growth and evolution of a variety of planets as they and their sunlike parent star coalesced from a cloud of whirling gas and dust. In most scenarios, planets that started with a rocky core between one-tenth and one times the mass of Earth lost their hydrogen-rich protoatmospheres 100 million years or less after the dust and gas surrounding the nascent star had dissipated, researchers report online this week in the Monthly Notices of the Royal Astronomical Society. That forfeiture, driven by the intense ultraviolet radiation streaming from the young parent star, offered those planets the chance to develop a more hospitable atmosphere later in their lives (either from gases later emitted from the planet itself or gained via the impacts of comets and asteroids), the researchers note. But in many instances, the simulations show, even planets starting with rocky cores as little as 1.5 Earth’s mass may trap and hold atmospheres containing between 100 and 1000 times the amount of hydrogen found in the water in Earth’s oceans—thick, dense envelopes exerting pressures so hellish that life on the planets’ surfaces might be almost impossible.

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