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Zenith Grant Awardee

Dr. Sara Seager

Carnegie Institution of Washington


George Cody, <i>Carnegie Institution of Washington</i><br>Matthew Schrenk, <i>Carnegie Institution of Washington</i><br>Drake Deming, <i>NASA Goddard Space Flight Center</i><br>Marc Kuchner, <i>NASA Goddard Space Flight Center</i>

Project Title

The Characterization & Search for Life on Hot Rocky Exoplanets

Project Summary

Are we alone? Astronomers have made progress towards answering this question by discovering almost 200 planets around other stars. Most of these newly discovered planets, however, are strikingly different from Earth. A new class of exoplanets known as "hot super Earths" has recently been discovered. These exoplanets are likely the only exoplanets to consist substantially of rock, making them the best analogs we have for Earth. We propose to investigate whether life can exist on these hot rocky planets – and if it exists – whether we could detect it.

The definition of life is controversial. We will bypass this controversy and focus on what life does, rather than what life is. One thing life does is extract energy from its environment; this process is called "metabolism." Humans, for example, extract energy from the environment by metabolizing food. We will theoretically evaluate the possible metabolisms, which could be operative on a hot super Earth, then determine which chemical signatures will be generated in the process. We will then study how we can detect these chemicals using current or already-planned telescopes. The method we propose to develop to identify metabolic products on exoplanets will enable a key advancement towards finding signs of extraterrestrial life.

Technical Abstract

Conventional ideas for the search for extraterrestrial life focus upon finding extra-solar analogs for life as we know it. Because of this bias, mainstream studies lean heavily on Earth-mass planets within a range of semi-major axes compatible with surface liquid water, the so-called habitable zone. The hot rocky exoplanets are a recently discovered class of exoplanets with masses ranging from 7.5 to 21 Earth masses. These ?super Earths? are very close to their host stars (Mercury?s orbit or 10 times closer) – so close that their exteriors are heated to temperatures of 300 to 1500 K. Since these planets have low masses, they are the first known exoplanets that likely consist substantially of rock making them analogs of the terrestrial planets that support life in our solar system.

We propose an unconventional study of life on hot rocky exoplanets. We circumvent the controversial definition of what life is, and instead focus on what life does: its metabolism and byproducts. We plan to: map out the energetic landscape on the surface and subsurface of specific super Earths and predict metabolic strategies based on planetary resources and limits to life. We will then investigate if potential byproducts are detectable by space-borne telescopes.

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