The Interior of Exoplanets Could Point the Way to Finding Life

With thousands of exoplanets now known to astronomers, the search for which planets may have developed life has started. By looking at the processes that led to life on Earth, scientists at the Carnegie Institution for Science believe they are able to better define those worlds most likely to harbor living beings.

On Earth, the interior of our planet drives continental drift, producing several effects which make our world suitable for life. A strong magnetic field driven by the process blocks significant amounts of radiation which could otherwise be dangerous to life. The process also mediates climate, making Earth friendlier for life. Similar processes within the interior of exoplanets may also be needed to make them habitable, the study concludes.

An artist’s conception of Kepler 186f, an Earth-like planet in the habitable zone around its parent star. Image credit: NASA

“We need a better understanding of how a planet’s composition and interior influence its habitability, starting with Earth. This can be used to guide the search for exoplanets and star systems where life could thrive, signatures of which could be detected by telescopes,” Dr. Anat Shahar of the Carnegie Institution for Science explained.

It’s a Lovely Composition

As planets are formed from the disks of dust and gas surrounding stars, the chemical makeup of all worlds is similar — oxygen, carbon, silicon, magnesium, and hydrogen. However, the proportions of these materials, and the process by which they cool can differ. The unique properties of planets can determine the size of oceans and the makeup of their atmosphere, and with that, the chances that life may form on a world.

Researchers from Cornell University, Lehigh University and Vanderbilt University recently developed the TESS Habitable Zone Star Catalog. This study, developed for the Transiting Exoplanet Survey Satellite (TESS), described 1,822 exoplanets where life is most likely to be found. Hundreds of these are similar to Earth, but the search may need to be expanded, if we find life elsewhere in our own family of planets.

“The discovery of life elsewhere in the Solar System, for example on an icy satellite, would… radically expand the types of planets that need to be considered,” researchers described in an article published in Science Magazine.

“Do you ever wonder if — well, if there are people living on the third planet?”
“The third planet is incapable of supporting life,” stated the husband patiently. “Our scientists have said there’s far too much oxygen in their atmosphere.”
― Ray Bradbury, The Martian Chronicles (Evidently, mansplaining is a thing among aliens, as well.)

Water is necessary for life on Earth, and the most likely places to find life on other worlds are on worlds in the habitable zone of their solar system — where planets are neither too close, nor to distant, from their star for liquid water to pool on their surface.

“One of the big questions we need to ask is whether the geologic and dynamic features that make our home planet habitable can be produced on planets with different compositions,” Carnegie planetary scientist Dr. Peter Driscoll describes.

The last 200 million years of plate tectonics on Earth, condensed to two minutes. Video credit: California Academy of Sciences

The Life of the Party

Life on Earth was the result of a large number of processes on our planet, involving geology, climate, and our place in the solar system, relative to other planets, including Jupiter. Evolution on our world was altered over billions of years by global climate change, volcanic eruptions, and (at least once) by the collision of a mountain-sized asteroid with the Earth. Therefore, a thorough cross-disciplinary study of exoplanets will be needed to determine which planets are most likely to harbor life, researchers concluded.

The TRAPPIST-1 system possesses at least seven planets, and some of these could have oceans far larger than those found on Earth. This artist’s conception shows what they may look like, based on the best available data. Image credit: NASA/JPL-Caltech

“The first microscopic life forms are thought to have emerged about a billion years after Earth’s formation from the dust, globs and chunks of material that made up the infant sun’s protoplanetary disk. They might have emerged much sooner. But it took roughly another 3 billion years for multi-celled, macroscopic creatures to begin making their mark on the fossil record,” NASA describes in Exoplanet Exploration.

When (and if) life is found on other worlds, it is likely to be extremely primitive, as it was for most of the history of the Earth. However, the laws of chemistry, physics, and evolution would still apply on other worlds, suggesting what life may look like on other planets.