New simulations that describe how the moon, incl Earthown mbrowncreated strongly suggest that exomoons are more likely to be found around rocky areas exoplanets.
Our moon is believed to be created when MarsA planetesimal size called Theia crashed into Earth, gouging a huge gash in our planet and melting its entire surface. The Moon is thought to have then coalesced from debris that settled into a ring around our planet.
These are the generally accepted details, but the details are still hotly debated. The angle and speed at which Theia hit Earth, for example, could change the scenario significantly. A more energetic impact would have resulted in a vapor-dominated moon-forming disk, while a lower-energy impact would have produced a disk dominated by silicate rock. Additionally, whichever is the case, it would have a big impact on whether moons can even form around a particular planet, according to new research that examines the implications of something called “flow instability.”
Before you ask, no, streaming instability has nothing to do with when a show on your favorite streaming channel starts buffering. Rather, the flow instability describes how small particles in the vapor-rich disk around the planet can clump into concentrations that quickly form moons ranging in size from 10 yards (100 meters) to 62 miles (100 kilometers).
Related: Are they exomoons or not? Scientists debate the existence of the 1st moons seen outside our solar system
Streaming instabilities are so important in models of planet formation, but in simulations by a team led by Miki Nakajima of the University of Rochester, they could offer bad news for the survival of moons. According to the team’s calculations, the moons that produce the flow-driven instabilities are not large enough to stay in the disk around the planet, and will begin to experience drag from friction against the vapor in the region. This drag slows their orbital speed and reduces the size of their orbit until they hit their parent planet.
These results therefore suggest that a vapor-rich disk cannot host a natural satellite as large as our moon, which is 2,159 miles (3,475 kilometers) wide. a disk full of pebbles and pieces of rock ejected by a “softer” impact is more likely to result in the formation of a large moon.
This leads to a prediction about where we might find exomoons.
Collisions involving very large super-Earths or mini-Neptunes would likely be more energetic due to the stronger gravitational field associated with these worlds. However, planets smaller than 1.6 times the size of Earth would be more likely to produce a less energetic collision.
“Relatively small Earth-sized planets are more difficult to observe and have not been the main target of moon hunting,” Nakajima said in a statement. “However, we predict that these planets are actually better candidates to host moons.”
To date, no exomoons have been definitively found. There are several candidates, but these are passionately debated and really expand the definition of “moon”. They are more like binary planets like a gas giant larger than Jupiter in cooperation with a “satellite” the size of Neptune. The second would be “moon” in this case.
It should also be said that the large moons of gas and ice giants in ours Solar System — namely from Jupiter, Saturn, Uranium and Neptune — were created from objects such as giant comets which came too close to each respective planet and were torn apart by the gravity of those planets before recomposing into a multitude of smaller objects. Moons around gas giants cannot be impacted because, as we saw in 1994 with the impact of debris Comet Shoemaker–Levy 9 to Jupiter, all the impactors would just be swallowed up by the gaseous world.
Although moons are not essential to life, our Moon has undoubtedly had an impact on life on Earth. Its presence stabilizes our axial tilt and thus our climate, while the tides it generates may have helped provide an environment for life to emerge, which some theories suggest occurred in tidal lakes.
The findings were published on June 17 in Planetary Science Journal.