A new way to characterize habitable planets

For decades, science fiction writers have imagined scenarios in which life thrives on the hard surfaces of Mars or our Moon, or in the oceans beneath the icy surfaces of Saturn’s moon Enceladus, and the moon of Jupiter, Europe. But the study of habitability – the conditions required to support and maintain life – is not limited to the pages of fiction. As more planetary bodies in our solar system and beyond are studied for their potential to host conditions favorable for life, researchers debate how to characterize habitability.

While many studies have focused on information obtained by orbiting spacecraft or telescopes that provide snapshot views of ocean worlds and exoplanets, a new paper highlights the importance of studying the complex geophysical factors that can be used to predict long-term maintenance of life. These factors include how energy and nutrients flow across the planet.

“Time is a crucial factor in characterizing habitability,” says Mark Simons, the John W. and Herberta M. Miles Professor of Geophysics at Caltech. “It takes time for evolution to occur. Being habitable for a millisecond or a year is not enough. But if habitable conditions last for a million years, or a billion…? Understanding habitability “a planet requires a nuanced perspective that requires astrobiologists and geophysicists to talk to each other.”

This perspective article, published in the journal Natural astronomy Dec. 29 will see a collaboration between Caltech scientists from the Pasadena campus and JPL, which Caltech manages for NASA, as well as colleagues representing various fields.

The study highlights new directions for future missions to measure habitability on other worlds, using Saturn’s icy moon Enceladus as a primary example. Enceladus is covered in ice with a salty ocean underneath. Over the past decade, NASA’s Cassini mission has acquired chemical measurements of plumes of water vapor and ice grains bursting from cracks in Enceladus’ south pole, discovering the presence of elements like carbon and nitrogen that could be conducive to life as we know it.

These geochemical properties are sufficient to describe the “instantaneous” habitability of the Moon. However, to truly characterize the long-term habitability of Enceladus, the paper emphasizes that future planetary missions must study geophysical properties that indicate how long the ocean has been there and how heat and nutrients flow between the core, the interior ocean and the surface. These processes create important geophysical signatures that can be observed as they affect features such as the topography and thickness of Enceladus’ ice crust.

This broader framework for studying habitability is not limited to the study of Enceladus. This applies to all planets and moons where researchers are looking for the conditions necessary for life.

“This article discusses the importance of including geophysical capabilities in future missions to ocean worlds, as is currently the case with the Europa Clipper mission targeting Jupiter’s moon Europa,” explains Steven Vance, a scientist at the JPL and deputy director of the laboratory’s Planetary Sciences Section. , as well as co-author of the article.

The article is titled “Sustainable and Comparative Habitability Beyond Earth.”

The study’s lead author is Charles Cockell of the University of Edinburgh and JPL. Besides Cockell, Simons and Vance, other co-authors are Peter Higgins of the University of Toronto; Lisa Kaltenegger of Cornell University; and Julie Castillo-Rogez, James Keane, Erin Leonard, Karl Mitchell, Ryan Park and Scott Perl of JPL.