Astronomers have found a planet just 87 light-years from Earth, nearly the same size as Earth, orbiting its star at a distance neither fried nor frozen. Looks perfect for Earth 2.0, right? It’s not very fast. Known as LP 791-18d, the exoplanet was pulled so far from its flat circular orbit by another planet that its interior was probably a violent hot mess erupting from its surface in the form of violent volcanoes.

While not exactly a native discovery, it could help astronomers better understand how habitable conditions arise on Earth-like planets.

“The LP 791-18d is tidally locked, which means it’s always the same side facing the star,” says astronomer Bjorn Benneke of the University of Montreal in Canada.

“The day side will likely be too hot to have liquid water on the surface. But the amount of volcanic activity we suspect is happening around the planet could support an atmosphere that could allow water to condense on the night side.”

LP 791-18 is a small, cool red dwarf star with only 14 percent of the Sun’s mass and 17 percent of its radius. In 2019, astronomers discovered two exoplanets here; A super-Earth called LP 791-18b, which is 1.46 times the mass of the Earth and rotates in 0.94 days, and a mini-Neptune named LP 791-18c, which is thought to be about 6 times the mass of Earth and is thought to be about 6 times that of Earth. 4.99 days.

Because this star is one of the coolest exoplanets known, a team led by University of Montreal astronomer Merrin Peterson used the Spitzer Infrared Space Telescope to make nearly continuous observations of the star for 127 hours. There, as they orbited between us and the star, they saw faint dips in starlight, called transits, not caused by LP 791-18b or Lp 791-18c.

This suggested the existence of a previously unknown third world. Continuing their observations with ground-based telescopes, the researchers confirmed that LP 791-18d, an exoplanet with a radius of 1.03 times the Earth and a mass of 0.9 times the Earth, revolves around the star for 2,753 days. That’s much closer than Earth is to the Sun, but LP 791-18 is also much cooler, meaning the newly discovered exoplanet is still in the star’s habitable zone, in the space zone far from the star where liquid is theoretically allowed. water on the surface. The water is not hot enough to boil and not cold enough to freeze.

However, this closeness brings with it another problem. The exoplanet’s rotation is “fixed” to the same period as its orbit; in fact, just as one side of the moon always faces the Earth, the same side of the earth always faces the star. In the case of the LP 791-18d, this “tidal lock” means that one side is always in warm daylight and the other in eternal night.

The team recorded a total of 72 passes, including 43 passes with the LP 791-18d and 29 passes with the mini-Neptune LP 791-18c. This enabled them to measure transit time variations that occur when gravitational interaction between exoplanets causes minor changes in transit times. In contrast, the researchers were able to calculate the mass of mini Neptune with greater accuracy and determined that it was equivalent to 7.1 Earth masses. They also learned that the two exoplanets pass so close together in their orbital paths that mini-Neptune pulls the smaller Earth into a distinctly elliptical orbit. This means that as LP 791-18d approaches and moves away from the star, the changing gravity stretches and compresses the planet, warming it from the inside.

This internal heating can occur as volcanic activity, which can be seen as a thick atmosphere. Measurements from an observatory like the James Webb Space Telescope can give an idea of ​​what planets like Earth or Venus, both of which are volcanically active, but have very different evolutionary paths.

“A big question in astrobiology, a field that broadly studies the origins of life on Earth and beyond, is whether tectonic or volcanic activity is necessary for life,” says astrophysicist Jesse Christiansen of the Cal Institute of Technology.

“In addition to potentially creating an atmosphere, these processes can capture materials that would otherwise sink into the crust, including things we think are important to life, such as carbon.”

The discovery shows how complex life can be and the importance of studying each planetary system holistically. Finding an Earth-sized world in the temperate zone of its star is no longer enough. The effects of other worlds on the system should also be carefully considered.

It is important to continue to find and characterize these worlds, livable or not. They show us how wide a range of outcomes are possible for presumed Earth-like exoplanets and predict the likelihood of habitable conditions in the wider galaxy.

“This discovery is just the first step,” says astronomer Karen Collins of the Harvard-Smithsonian Center for Astrophysics.

“With the potential to continue studying this planet with the James Webb Space Telescope, we will be able to fine-tune our observations and learn more about the planet’s possible volcanic atmosphere. Future discoveries will help us understand how the components of life might have arisen. To find ourselves on worlds other than our own.”