There are more than 200 moons in our solar system. Most major planets except Mercury and Venus have moons. Pluto and some other dwarf planets and many asteroids have small moons. Saturn and Jupiter have the largest number of moons, orbiting two dozen giant planets each. Only one moon orbits our planet.

The planets in our solar system come in two forms, some rocks and some gases. But all the moons in our solar system revolve around rocks and gas giants. Why are some moons in the solar system not created by gas? Are there gas moons anywhere in the universe?

Good reasons

Jonathan Lunin, head of the Department of Astronomy at Cornell University, told the website:Direct science(Live Science) There are some good reasons for the absence of gas moons nearby.

But even if we did not find any gaseous moons outside our solar system, under the right circumstances it would be possible. In particular, it depends on the mass of the Moon, the effect of ambient temperature and wave forces, and the gravitational pull of a nearby object such as the host planet orbiting the Moon.

To illustrate how these conditions can affect the gas moon, imagine that our moon’s rock formation has been replaced by pure hydrogen. Hydrogen gas is much less dense than rock, so immediately, the Moon will grow to the size of Earth. That means the “gas moon” is likely to be about the size of its parent planet, so it would be more appropriate to call it a “binary planet”.

Gas binary planets may be possible, but they are very rare because planetary formation usually leads to two planets merging or separating from each other. Therefore, no gas satellite has been detected so far.

Large size and temperature

In fact, the sheer size of Jupiter-like gas giants is one reason for their existence. Because if it is so small, the force of gravity will not be strong enough to hold those light elements together.

Like gaseous planets, a gas must be larger than its rock counterparts because if it were so small it would not have enough gravity to hold lighter gases such as hydrogen and helium.

But size is not the only factor, temperature is also. “Let’s just take the moon as a rock,” says Lunin. “Then we’ve put the atmosphere of hydrogen around it. We know that the hydrogen atmosphere will leave very quickly due to the effects of heat.” Hydrogen evaporates due to the heat of the sun.

What this tells us is that if our moon were made entirely of hydrogen, it would not be stable. But even if our imaginary gas moon were the size of Earth and the temperature around it was too cold, the host planet would tear it up.

“Earth’s moon is subject to tidal forces from Earth, but it does not decompose because it is combined with some physical force,” says Lunin. “But the hypothetical gas is not like that on the moon because it is made of gas.

How is the gas moon possible?

The moon’s host planet must be very far and cold for a gas moon to be possible.

And if a gas moon were the same size as ours and located somewhere in our solar system, it would not run stable. But if the gas moon were approximately the size of Neptune and orbited Jupiter, the gravitational forces holding these massive objects together would prevent wave forces from destroying the Neptune-sized moon. It can be very stable.