Planets in our solar system come in two forms: some are rocky and some are gaseous. But all moons in our solar system are rocky, even those orbiting gas giants. Why aren’t some moons in the solar system made of gas? Are there gaseous moons anywhere in the universe?
There are some good reasons why there are no nearby gaseous moons. And while we didn’t find a gas moon behind us Solar SystemIt might be possible under the right conditions, said Jonathan Lunin, chair of the astronomy department at Cornell University.
Specifically, it will depend on the mass of the moon and its circumference temperature And the effect of tidal forces – that is, the gravitational pull of a nearby object, such as the host planet.
Related: Can the moon be pushed out of orbit, as in the case of “moonfall”?
To illustrate how these conditions can affect a gaseous moon, imagine that the moon’s rock formation has been replaced by a pure moon. hydrogen. Hydrogen gas is much less dense than rock, so immediately, the the moon will grow to size a landLunin said.
In fact, the sheer size of gas giants like Jupiter is one reason for their existence. If it is too small, the strength gravity It wouldn’t be strong enough to hold those lighter items together.
But size is not the only influencing factor; There is also a temperature.
“Let’s take the moon as it is – as a rock,” Lunin told Live Science. “Then let’s put an atmosphere of hydrogen around it. We know that the atmosphere of hydrogen is going to escape very quickly just because of thermal effects.” In other words, the sun’s warmth could cause the hydrogen to evaporate away.
“And that’s what it will tell me is that Earth’s moon made entirely of hydrogen at Earth’s distance from the sun will not be stable,” Lunin said. He added that this is true even with respect to the orbit of Pluto.
But even if our imaginary gaseous moon was the size of Earth and the surrounding temperature was extremely cold, it’s possible that the host planet would still shred it.
“Remember that the Earth’s moon is subject to tidal forces from the Earth,” Lunin said. “So it’s actually not a ball. It’s pulled a little bit, but it doesn’t tear because it has some physical strength attached to it.”
This is not the case with the hypothetical gaseous moon. “Because it’s a gas and not a solid — even if it’s very cold — if it’s orbiting something else, it’s going to be stripped and torn apart by the tides,” Lunin said.
So how could a gaseous moon be possible? The lunar planet system must be either very distant and cold, or very large.
“If it were the size of our moon, anywhere in our solar system, it wouldn’t function properly. Far in the depths of interstellar space? There, it’s a question mark,” Lunin said. “If you want to make something really big, like Neptune around Jupiter, you can definitely do that.”
In this case, the gravitational forces holding these massive objects together would likely prevent tidal forces from destroying a Neptune-sized moon.
“That could be quite stable,” Lunin said.
Originally published on Live Science.