New simulations that describe how the moons, incl The Earthown munformed strongly suggest that exomoons they are more likely to be found around rocks exoplanets.
Our moon is believed to have formed when Marsa Theia-sized planetesimal slammed into Earth, gouging a huge gash into our planet and melting its entire surface. It is believed that the moon then coalesced from debris that settled into a ring around our planet.
These are the generally accepted details, but the specifics are still hotly debated. The angle and speed at which Theia hit Earth could change the scenario significantly, for example. A more energetic impact would result in a moon-forming disk dominated by vapor, while a less energetic impact would result in a disk dominated by silicate rock. And any of those cases will have a big impact on whether moons can form around a given planet at all, according to new research that examines the consequences 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 tiny particles in a vapor-rich disk around a planet are able to accumulate in concentrations that quickly form moons ranging in size from 10 yards (100 meters) to 62 miles (100 kilometers).
Connected: Are they exoluns or not? Scientists are debating the existence of the first moons observed outside our solar system
Flow instabilities are thus important in models of planet formation, but in simulations carried out 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 the flow instability produces are not large enough to be trapped in a disk around a planet and begin to experience drag from vapor friction in the region. This drag slows their orbital speed and reduces the size of their orbit until they collide with their parent planet.
Therefore, these results suggest that a vapor-rich disk could not build a natural satellite as large as our moon, which is 2,159 miles (3,475 kilometers) wide. Instead, the various models, which depict a more silicate-rich, vapor-poor disk full of pebbles and chunks of rock ejected by a “gentler” impact, are more likely to lead to the formation of a large moon.
This leads to a prediction of 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 cause a less energetic collision.
“Relatively small planets similar in size to Earth are more difficult to observe, and they have not been the main focus of the search for moons,” Nakajima said in a statement. “However, we predict that these planets are actually better candidates for hosting moons.”
To date, no exomoons have been discovered for sure. There are a few contenders, but these are it hotly debated and I’m really stretching the definition of “moon”. They are more like twin planets, like a gas giant it’s bigger than Jupiter in partnership with a “satellite” the size of Neptune. The latter would be “the moon” in this case.
It should also be said that the large moons of the gas and ice giants in ours solar system — namely of Jupiter, Saturn, Uranus and Neptune — are formed by giant-like objects comets which came too close to each respective planet and were torn apart by the gravity of those planets before reassembling into multiple smaller objects. Moons around gas giants cannot form from collisions because, as we saw in 1994 with the impact of fragments from Comet Shoemaker–Levy 9 in Jupiter, any impactors would simply be swallowed up by the gas world.
Although moons are not necessary for life, our moon has undoubtedly had an impact on life on Earth. Its presence stabilizes our axial tilt and therefore our climate, while the tides it generates could help provide an environment for the origin of life, which some theories suggest occurred in tidal basins.
The findings were published on June 17 in Planetary Science Journal.
