Snowball, or “slushball” Earths have occurred several times in our planet’s history, covering large swaths — and perhaps at times all of the planet — in glacial ice and snow. (NSF)

Some two billion years ago, all of Earth may well have been covered in snow and ice.  Oceans, continents, everything, and for many millions of years.  Observed from afar, the planet would be pretty low on the list of planets that might conceivably support life.  But we know that it did.

Five hundred to seven hundred million years ago, our planet had what scientists have determined to be another severe period of cold, with the global mean temperature somewhere around 10 degrees F.   Again, hardly a good candidate planet for life.  But in fact, the tropics were ice-free and Earth’s biosphere was preparing for its biggest explosion of life ever.

These kinds of insights and conclusions are part of the work now underway to use the earth and its climate history as a way to understand exoplanets, and some day to predict the best targets for examination.

Illustrations of exoplanets that orbit their suns within a habitable zone. Left to right: Kepler-22b, Kepler-69c, Kepler-62e, and Kepler-62f, compared with Earth at far right. (NASA/Ames/JPL-Caltech)

It is a field with numerous players, but perhaps none so deeply engaged as NASA’s Goddard Institute for Space Studies (GISS) in New York City.

Using the same 3D modeling that it produces to understand our currently changing climate,  GISS and its collaborators is pushing further into the study of ancient Earth and solar system climates as a way to better understand exoplanets and someday identify potentially inhabited, or at least habitable, candidates.

Anthony Del Genio, a senior climate scientist at GISS, is the team leader for this novel effort, which includes some 30 scientists from a variety of institutions.

Anthony Del Genio, leader of GISS team using cutting edge Earth climate models to better understand conditions on exoplanets.

Undergirding the effort is the conviction that it would be a mistake to see exoplanets as static entities rather than as evolving bodies, with pasts and futures that can be as changeable as our own mutable planet.

“The beauty of Earth’s climate history for this project is that we have so many well studied fluctuations, and they give some tantalizing clues for a deeper understanding of other planets,”  said Del Genio, whose team is sponsored by both the NASA Planetary Atmospheres, Exobiology, and Habitable Worlds Programs  and the Nexus for Exoplanet System Science (NExSS,) a NASA initiative. … Read more