Astronomers have made a groundbreaking discovery of an Earth-size exoplanet that could be covered in volcanoes. The planet, named LP 791-18 d, may experience volcanic outbursts as frequently as Jupiter’s moon Io, which is the most volcanically active body in our solar system. The planet was discovered and studied using data from NASA’s TESS and retired Spitzer Space Telescope, as well as a suite of ground-based observatories. A paper about the planet, led by Merrin Peterson, a graduate of the Trottier Institute for Research on Exoplanets (iREx) based at the University of Montreal, appears in the May 17 edition of the scientific journal Nature.
LP 791-18 d orbits a small red dwarf star about 90 light-years away in the southern constellation Crater. The team estimates it’s only slightly larger and more massive than Earth. The planet is tidally locked, meaning that the same side constantly faces its star. The day side would probably be too hot for liquid water to exist on the surface. However, the amount of volcanic activity occurring all over the planet could sustain an atmosphere, which may allow water to condense on the night side.
The planet sits on the inner edge of the habitable zone, which is the traditional range of distances from a star where scientists hypothesize liquid water could exist on a planet’s surface. If the planet is as geologically active as the research team suspects, it could maintain an atmosphere. Temperatures could drop enough on the planet’s night side for water to condense on the surface.
During each orbit, planets d and c pass very close to each other. Each close pass by the more massive planet c produces a gravitational tug on planet d, making its orbit somewhat elliptical. On this elliptical path, planet d is slightly deformed every time it goes around the star. These deformations can create enough internal friction to substantially heat the planet’s interior and produce volcanic activity at its surface. Jupiter and some of its moons affect Io in a similar way.
The team thinks planet d is an exceptional candidate for atmospheric studies by the James Webb Space Telescope. Planet c has already been approved for observing time on the telescope. A big question in astrobiology is whether tectonic or volcanic activity is necessary for life. In addition to potentially providing an atmosphere, these processes could churn up materials that would otherwise sink down and get trapped in the crust, including those thought to be important for life, like carbon.
Spitzer’s observations of the system were among the last the satellite collected before it was decommissioned in January 2020. The entire body of scientific data collected by Spitzer during its lifetime is available to the public via the Spitzer data archive, housed at the Infrared Science Archive at IPAC at Caltech in Pasadena, California.
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