New simulations describing how moons, including Soil‘s own mohformed strongly implies that exomons are more likely to be found around rocky exoplanets.
Our moon is thought to have that formed when a Mars-size planetesimal called Theia smashed into Earth, cutting a huge wound in our planet and melting its entire surface. It is believed that the moon subsequently coalesced from debris that settled in a ring around our planet.
Those are the generally accepted details, but the details are still hotly debated. For example, the angle and speed at which Theia hit Earth could significantly change the scenario. A more energetic impact would have resulted in a moon-forming disk dominated by vapor, while a less energetic impact would have produced a disk dominated by silicate rock. Furthermore, whichever of these is the case would have a major impact on whether moons can form around a given planet at all, according to new research examining the consequences of something called “streaming instability.”
Before you ask, no, streaming instability has nothing to do with when a show on your favorite streaming channel starts to buffer. Instead, a flow instability describes how small particles in a vapor-rich disk around a planet can build up into concentrations that quickly form moons ranging in size from 100 meters to 100 kilometers.
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Streaming instabilities are thus important in models of planet formation, but in simulations conducted by a team led by Miki Nakajima of the University of Rochester, they could spell bad news for the survival of moons. According to the team’s calculations, the moons created by flow instabilities are not large enough to hold their own in a disk around a planet, and they begin to feel drag from friction with vapor 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 cannot build a natural satellite as large as our moon, which is 3,475 kilometers wide. Instead, the various models that depict a more silicate-rich, vapor-poor satellite disk, full of pebbles and chunks of rock ejected by a “softer” impact, would likely result in the formation of a large moon.
This leads to a prediction about where we can find exomoons.
Collisions involving very large super-Earths or mini-Neptunes would likely be more energetic because of the stronger gravitational field associated with these worlds. However, planets less than 1.6 times the size of Earth would be more likely to have a less energetic collision.
“Relatively small planets comparable to Earth’s size are more difficult to observe and have not been the main focus of the moon hunt,” Nakajima said in a statement. “However, we predict that these planets are actually better candidates to host moons.”
To date, no exomoons have been found with certainty. There are a few candidates, but these are out there hotly debated and really stretch the definition of ‘moon’. They look more like binary planets, such as a gas giant bigger than Jupiter along with a ‘satellite’ the size of Neptune. The last in this case would be the “moon”.
It should also be said that the large moons of the gas and ice giants in our solar system – namely from Jupiter, Saturn, Uranus And Neptune – were formed from objects such as giants Come eat which came too close to each respective planet and were torn apart by those planets’ gravity before being reassembled into a host of smaller objects. Moons around gas giants cannot form from impacts because, as we saw in 1994 with the impact of the fragments of Comet Shoemaker-Levy 9 in Jupiter, all the impactors would simply be swallowed up by the gaseous world.
Although moons are not necessary for life, our moon has undoubtedly influenced life on Earth. Its presence stabilizes our axial tilt and thus our climate, while the tides it generates could have helped create an environment for the origin of life, which some theories propose took place in tidal pools.
The findings were published on June 17 in Planetary Science Journal.