Astronomers discover Earth-Sized planet with active volcanoes

Astronomers discover LP 791-18d, an Earth-sized planet with active volcanoes, shedding light on planetary atmospheres and evolution.
Kavita Verma
Artist's illustration of LP 791-18d
This artist's illustration of LP 791-18d displays an Earth-sized planet located 90 light-years away. Internal heating and volcanic eruptions may be triggered by the gravitational pull of a more massive planet in the system, represented by a blue disc in t

NASA's Goddard Space Flight Center/Chris Smith/KBRwyle  

A planet called LP 791-18d, which is the size of Earth but not at all like Earth, has been discovered by astronomers. The planet is covered with active volcanoes and lies 90 light years away from a small red dwarf star in the southern constellation Crater.

Data from NASA's TESS (Transiting Exoplanet Survey Satellite), decommissioned Spitzer Space Telescope, and a number of ground-based observatories were used to discover and study the planet.

This discovery is particularly notable for astronomers since volcanism promotes interaction between a planet's interior and exterior.

Volcanism and planetary atmosphere

According to Stephen Kane, an astronomer at UC Riverside, volcanism is the primary factor in a planet's atmosphere, which is necessary for the existence of surface liquid water. Life as we know it must be sustained by liquid water. 

There are two additional planets in the LP 791-18 system that have already been detected by astronomers: LP 791-18b, which is about 20% larger than Earth, and LP 791-18c, which is almost seven times as massive and roughly 2.5 times larger than Earth. 

As a result of the planet c's gravitational influence on planet d, which causes it to have an elliptical orbit, these two planets are in close proximity to one another.

Every time planet d circles the star on this elliptical route; it gradually deviates from its original shape. Internal friction caused by these deformations has the potential to significantly heat the planet's innards and cause volcanic activity on its surface. Io experiences similar effects from Jupiter and some of its moons.

Carbon dioxide and water vapor, both greenhouse gases that can aid in maintaining a warm world, make up most of volcanic emissions. The planet LP 791-18d has so many volcanoes that they constantly erupt, making it practically uninhabitable. But the existence of these volcanoes provides fresh insights into evolution.

Because LP 791-18d is tidally locked, the same side always faces its star. Even though it would be too hot during the day for liquid water to exist on the surface, the planet's extensive volcanic activity may support an atmosphere. 

"The day side would probably be too hot for liquid water to exist on the surface. But the amount of volcanic activity we suspect occurs all over the planet could sustain an atmosphere, which may allow water to condense on the night side," said Björn Benneke, corresponding co-author of the paper and astronomy professor at the Trottier Institute for Research on Exoplanets, based at the University of Montreal.

LP 791-18d and the puzzle of Venus

Volcanoes on LP 791-18d can provide important information about the development of planetary ecosystems like Venus and Earth. Venus became uninhabitable due to a greenhouse effect caused by volcanic emissions. But researching LP 791-18d reveals vital information about the function of volcanoes in shaping planetary ecosystems across time.

Study Abstract: 

Temperate Earth-sized exoplanets around late-M dwarfs offer a rare opportunity to explore under which conditions planets can develop hospitable climate conditions. The small stellar radius amplifies the atmospheric transit signature, making even compact secondary atmospheres dominated by N2 or CO2 amenable to characterization with existing instrumentation1. Yet, despite large planet search efforts2, detection of low-temperature Earth-sized planets around late-M dwarfs has remained rare and the TRAPPIST-1 system, a resonance chain of rocky planets with seemingly identical compositions, has not yet shown any evidence of volatiles in the system3. Here we report the discovery of a temperate Earth-sized planet orbiting the cool M6 dwarf LP 791-18. The newly discovered planet, LP 791-18d, has a radius of 1.03 ± 0.04 R⊕ and an equilibrium temperature of 300–400 K, with the permanent night side plausibly allowing for water condensation. LP 791-18d is part of a coplanar system4 and provides a so-far unique opportunity to investigate a temperate exo-Earth in a system with a sub-Neptune that retained its gas or volatile envelope. On the basis of observations of transit timing variations, we find a mass of 7.1 ± 0.7 M⊕ for the sub-Neptune LP 791-18c and a mass of 0.9+0.5−0.4M⊕ for the exo-Earth LP 791-18d. The gravitational interaction with the sub-Neptune prevents the complete circularization of LP 791-18d’s orbit, resulting in continued tidal heating of LP 791-18d’s interior and probably strong volcanic activity at the surface. 

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