In the spring of 2018, NASA’s TESS caught the first glimpse of possible planets orbiting the star LP 791-18. Located nearly 90 light-years from Earth, the star is a red dwarf. To confirm the existence of those planets, CU Boulder doctoral student William Waalkes aimed the telescopes at the Las Cumbres Observatory in the direction of LP 791-18.

At that time, scientists only knew about two planets: b and c. In a new study, a team of astrophysicists, including two researchers from CU Boulder, used NASA’s now-decommissioned Spitzer Space Telescope to get a closer look at the two planets. While doing so, they discovered a third hiding among their lanes.

This third planet, named LP 791-18d, is a small and rocky world, similar to our planet Earth, but much more chaotic. Similar in size to Earth, this newly discovered planet orbits its star LP 791-18 about once every three Earth days. Average temperatures can reach over 250 degrees Fahrenheit, and lava and gas eruptions can spew all over the planet’s surface.

William Waalkes, a co-author of the new study and a doctoral student in CU Boulder’s Department of Astrophysical and Planetary Sciences, said: “This planet can be a very turbulent environment with many volcanoes. The day side would likely get very hot, and if the planet has an atmosphere, intense winds could blow to the night side.”

Co-author Zachory Berta-Thompson, assistant professor of astrophysics at CU Boulder, is excited about the possibilities of this fiery version of Earth. In part, that’s because LP 791-18d may be a useful comparison for a planet like Venus, which has an atmosphere formed by intense heat. LP 791-18d may also be “tide-locked,” meaning that, like Earth’s moon, it doesn’t rotate. One of its hemispheres could rest in permanent daylight, while the other exists in an infinite night.

Waalkes and Berta-Thompson collected measurements from the ground of how often all three planets passed in front of their star, which helped the team calculate the mass of LP 791-18d.

The observation revealed that LP 791-18c orbits its star; it comes dangerously close to LP 791-18d. These gravitational forces can pull and push the smaller planet, resulting in a dangerous situation similar to that on Jupiter’s moon Io. There are about 150 active volcanoes on this moon.

Berta Thompson said: “Volcanoes aren’t always a bad thing for planets, though. Eruptions on the surface of LP 791-18d can litter the atmosphere with gases and even water.”

“I have no idea what it would feel like to be on the surface. But hopefully we can find out with observations in the coming decades.”

Magazine reference:

  1. Peterson, MS, Benneke, B., Collins, K. et al. An Earth-sized temperate planet with tidal heating passing an M6 star. Nature (2023). DOI: 10.1038/s41586-023-05934-8