A New Earth-like Exoplanet Discovered

[UC Irvine] A team led by astronomers at the University of California, Irvine reports the discovery of a new Earth-like exoplanet orbiting a star about 25 light-years from our solar system in our home Milky Way galaxy. The discovery adds to the growing list of exoplanets that may be hospitable to life.

“This one’s exciting,” said Paul Robertson, UC Irvine assistant professor of astronomy and lead author of the new study, published in The Astrophysical Journal. “It’s one of our closest cosmic neighbors. 25 light-years sounds like a long way, but the Milky Way is about 100,000 light-years across, so in that respect it’s our next-door neighbor.”

The planet, dubbed GJ 3378b, is roughly twice the size of Earth. It sits inside its host star’s habitable zone – the ‘goldilocks’ region around a star where a planet receives just the right amount of solar radiation such that water can exist in a liquid state on a planet’s surface.

“This super-Earth gets about 90 percent of the radiation from its host star as Earth gets from its sun, so it’s right in the sweet spot,” said Robertson, whose team made the discovery using the Habitable-zone Planet Finder on the Hobby-Eberly Telescope at McDonald Observatory in Texas, and the NEID Spectrometer on the WIYN Telescope at Kitt Peak National Observatory in Arizona.

The Habitable Zone Planet Finder instrument during installation in its clean-room enclosure in the Hobby-Eberly Telescope at McDonald Observatory. Credit: Guðmundur Stefánssonn/Penn State

One lingering mystery is the nature of the planet’s atmosphere – or if it even has an atmosphere. The planet sits right on the edge of what researchers call the cosmic shoreline – the region around a star where, if a planet sits outside it, solar radiation can strip its atmosphere away. An example from our own solar system is Mars, which astronomers think may’ve had an atmosphere like Earth’s at one time before solar radiation destroyed it.

“If you scale the Earth down to the size of an apple, its atmosphere would be about as thick as the skin of the apple,” said Robertson. “That’s just enough to maintain the kinds of surface pressures where you can have liquid water. It’s enough that there’ll be breathable air, and it provides maybe a little bit of protection from the harsh radiation environment of space.”

Angular extents of the optimistic HZ (R. K. Kopparapu et al. 2013) for nearby stars hosting exoplanets. The inner and outer HZ limits are marked with circles colored by stellar effective temperature (in kelvin), and known exoplanets are indicated as diamonds at their projected angular separations. The green shaded region indicates where planets might be accessible to imaging facilities on 30 m class telescopes, limited by the IWA and a 10−8 level contrast. The HZ of GJ 3378 is partially accessible to future imagers, but imaging GJ 3378 b will require them to achieve IWAs better than 2λ/D. – The Astrophysical Journal

The discovery of GJ 3378b adds another candidate to the list of exoplanets that may be hospitable to life. But astronomers will have to wait for the construction and deployment of future observatories before they can be sure if the planet has any kind of atmosphere.

“If a planet in the habitable zone has a proper atmosphere, we can justify further research looking for biosignatures, liquid water or other signs of life that require both an atmosphere and the right amount of heating from the host star,” said Gogod James, a UC Irvine student in Robertson’s group who worked to characterize the size of GJ 3378b.

NASA’s planned Habitable Worlds Observatory – slated to launch sometime in the 2040s – will be able to image planets like GJ 3378b to confirm whether or not they have atmospheres. If it does, astronomers will probe the planet for signs of life, which will include looking for chemicals in its atmosphere that could have biological origins.

“I think that’s just too much fun,” said Robertson.

Funding for the research came from National Science Foundation Astronomy & Astrophysics Research Grants and NASA Interdisciplinary Consortia for Astrobiology Research. Collaborators include Michael Endl & William Cochran (University of Texas at Austin/McDonald Observatory) Gudmundur Stefansson (Schmidt Sciences) and Suvrath Mahadevan (Pennsylvania State University).

A Revised Mass and Period for the Habitable Zone super-Earth GJ 3378 b: A Planet Straddling the Cosmic Shoreline, The Astrophysical Journal (open access)

Astrobiology, exoplanet,