Astronomers have recently detected a planet that is about the same size as Earth but vastly different in appearance. The planet’s surface is split between perpetual daylight on one side and perpetual nighttime on the other, and it is covered with numerous active volcanoes.
A new planet has been discovered by astronomers named LP 791-18d, which orbits a small red dwarf star about 90 light years away. This planet is not at all like Earth, with half the planet being permanently daytime and the other half in permanent night, and is carpeted with active volcanoes. The discovery of volcanic activity on this planet is especially important for astronomers, as it helps in the interaction between a planet’s interior and exterior, and contributes to the planetary atmosphere. UC Riverside astrophysicist Stephen Kane explains that volcanism is important because it is the major source contributing to a planetary atmosphere, which is a requirement for sustaining life as we know it.
The planet’s outer planet, LP 791-18c, is about 2.5 times Earth’s size and nearly nine times its mass, and is already known to astronomers. During each orbit around the star, planets c and d pass very close to each other. As they do, c’s massive size produces a gravitational tug that makes planet d’s orbit more elliptical, rather than perfectly circular. These deformations to the orbit create friction that heats the planet’s interior, producing volcanic activity at the surface.
The planet was discovered using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and the retired Spitzer Space Telescope. TESS observations were conducted by UC Riverside astrophysicist Stephen Kane, who co-authored a paper about the newly discovered planet published in the scientific journal Nature.
Another notable feature of LP 791-18d is that it does not rotate. As Björn Benneke, co-author of the paper and astronomy professor at the Trottier Institute for Research on Exoplanets, based at the University of Montreal, explains, the planet is tidally locked, which means the same side constantly faces its star. The day side would likely be too hot for liquid water to exist on the surface, but the amount of volcanic activity occurring all over the planet could sustain an atmosphere, which may allow water to condense on the night side.
Though LP 791-18d is likely uninhabitable due to the presence of constantly erupting volcanoes, its discovery provides new information about evolution. For instance, it helps in answering a big question in astrobiology, which is whether tectonic or volcanic activity is necessary for life. These processes could churn up materials that would otherwise sink down and get trapped in the crust, including those that are important for life, like carbon.
Finally, the discovery of active volcanoes on Venus and planets like LP 791-18d can shed important insights into how volcanoes shape planetary environments with time, including those of Venus and Earth. Volcanic emissions, such as carbon dioxide and water vapor, are greenhouse gases that can help keep a planet warm, as seen on Venus.
