Where to find other Earths? New list narrows down the targets

New Cornell research - co-authored by an undergraduate and two recent alumni - will help exoplanet scientists pinpoint the most likely places to look for life in the universe out of more than 6,000 exoplanets.

The paper, "Probing the Limits of Habitability: a Catalogue of Rocky Exoplanets in the Habitable Zone," published March 19 in the Monthly Notices of the Royal Astronomical Society. Authors are Abigail Bohl '26, Lucas Lawrence '23, Gillis Lowry '25 and Lisa Kaltenegger,professor of astronomy and director of the Carl Sagan Institutein the College of Arts and Sciences.

The project utilizes new data from the European Space Agency's Gaia mission and the NASA Exoplanet Archive to identify planets in the habitable zone.

The paper explores how different kinds of worlds can provide fundamental information on habitability. For example, worlds near the edges of the habitable zone can shed light on where habitability ends and whether scientists' ideas about those limits are correct, Kaltenegger said. Worlds with unusual elliptical orbits around their star can offer insight on whether a planet can remain habitable when it crosses in and out of the habitable zone.

The paper also identified the planets that receive an amount of energy from their star most similar to what Earth receives from the sun.

The researchers identified 45 rocky worlds that may support life in the habitable zone, and another 24 in a narrower zone that makes a more conservative assumption of how much heat a planet can receive before it loses its habitability. The researchers also identified the best planets to observe with different techniques, to give scientists the best odds of finding signs of life if they exist on these worlds.

"While it's hard to say what makes something more likely to have life," said Lowry, now a master's student at San Francisco State University, "identifying where to look is the first key step - so the goal of our project was to say 'here are the best targets for observation.'"

"We wanted to create something that will enable other scientists to search effectively," said Lawrence, now a master's student at the University of Padua, Italy. "And we kept discovering new things about these worlds we wanted to investigate further."

The list they've created will guide astronomers who study the sky using the James Webb Space Telescope (JWST), and those using the range of new telescopes coming online in the next few decades: the Nancy Grace Roman Space Telescope (set to launch in 2027), the Extremely Large Telescope (set to see first light in 2029), the Habitable Worlds Observatory (expected to launch in the 2040s) and the proposed Large Interferometer For Exoplanets project.

Even before the paper was officially published, a preprint available online had already been cited five times by other researchers, Bohl said. "It's definitely exciting that people are already seeing it and citing it," she said. Kaltenegger said another research group already began observations a few months ago to characterize the host stars of the planets her students identified in the paper.

Lowry said she's been using the list already to take an early look at the 10 planets that receive very similar radiation to Earth, identifying two that are close enough to study: TRAPPIST-1 e and TOI-715 b.

The TRAPPIST-1 planetary system is a main focus of observation with the JWST telescope, a program led by Nikole Lewis, associate professor of astronomy in A&S. Trappist-1 and TOI-715 b are both small red stars, making it easier to see the small, Earth-sized planets orbiting around them.

Observing these small planets is the only way to confirm if they have atmospheres and liquid water. Lowry said. Thus, these planets can help set the real limits of the "habitable zone."

Where habitability starts, and ends, is a key question in the search for life in the cosmos, and these worlds will help astronomers figure it out, Kaltenegger said.

Kathy Hovis is a writer for the College of Arts and Sciences.