does liquid water flow on the night side of this exoplanet?

Astronomers have found an Earth-sized exoplanet where many volcanoes may be active. Volcanic eruptions are as common on the exoplanet LP 791-18 d as on Jupiter’s pizza moon Io.

The scientists used data from the Spitzer Space Telescope and TESS (Transiting Exoplanet Survey Satellite) to find and examine the exoplanet. Several observatories on Earth were also deployed. The paper can be read in the scientific journal Nature.

Synchronous rotation
LP 791-18 d orbits a small red dwarf star about 90 light-years distant from its parent star. The exoplanet has a synchronous rotation. This means that the rotation period is equal to the orbital period, which in turn ensures that the same side of the exoplanet always faces the red dwarf star. It also means that it is always day on one side and always night on the other side. Many objects in our solar system have a synchronous rotation, such as the moon around the earth. Hence, the Moon always looks the same from the Earth’s surface. Dwarf planet Pluto and its moon Charon take it a step further: they both have a synchronous rotation, so that both celestial bodies always have the same side facing each other.

“The day side of LP 791-18 d is probably too hot and therefore no liquid water exists on the surface,” concludes co-author and professor Björn Benneke. “But since there may be a lot of volcanic activity, we expect the exoplanet could have an atmosphere, and that means water could condense on the night side.”

This may lead to volcanic activity
LP 791-18 d is not the only planet near the star LP 791-18. Previously LP 791-18 b and LP 791-18 c have been found. LP 791-18 c is a hefty planet: about 2.5 times larger than Earth and more than seven times more massive. The elliptical orbits of planets c and d are close together at certain points, so these alien worlds sometimes brush past each other. Every time the bigger brother – LP 791-18 c – flies past LP 791-18 d, this planet tugs at its little brother. The interior of planet d is kneaded by this, the temperature rises and volcanic activity occurs on the surface. We see the same thing happening with Jupiter’s moon Io, only Jupiter is the one that warms Io.

It’s James Webb’s turn now
For example, LP 791-18 d seems an interesting exoplanet to study further. There is probably volcanic activity, the exoplanet is in the habitable zone around the star and there is a chance of liquid water on the surface. Planet c will soon be examined more closely by the James Webb telescope, but the researchers hope that the space telescope will also take a look at planet d. If James Webb “smells” the atmosphere, the telescope may detect elements that hint at volcanic activity. This will no doubt be continued.