Why is the Moon without an atmosphere, though the Earth has one?
I believe it's to do with the mass of the moon relative to the earth. We have a much greater mass which means the effect of our gravity is greater which in turn can hold an atmosphere in place.
The Moon does have an atmosphere, just much less dense than that of the earth, so much so that it's pretty much negligible. MisterH is right in saying that this is due to it's low mass. This leads to a small escape velocity - the speed at which objects have to be travelling to escape a body. So compared to earth, the escape velocity of the moon is low, and hence its atmosphere is negligibly dense.
The escape velocity at the surface of the moon is only 2.38 km/sec, compared with 11.19 km/sec for Earth. That's a factor of about 4.7.
Earth has trouble holding onto its hydrogen and helium, because in the upper atmosphere, it gets hit my sunlight and cosmic rays, and gets going faster than the escape velocity, and goes flying off into space. So we are slowly losing our hydrogen and helium.
Kinetic energy is proportional to velocity squared, so the Moon can only hold onto molecules with speed less than Earth can, by a factor of 4.7 squared, which is about 22. Now if an oxygen atom, with mass 16 times that of a hydrogen atom, got as much energy from photons as hydrogen atoms do in Earth's atmosphere, they would be even harder for the Moon to hold onto than hydrogen is for Earth to hold onto.
Because, owing to its small size, the moon had not sufficient attractive power to retain the atmosphere which once enveloped it. The atoms of this gradually escaped into space. The earth, being much larger than the moon, and having a greater pull, has been able to prevent its atmosphere leaving it.
The moon has no atmosphere because, due to its small mass, does not have enough gravity to retain gases. Even if gravity were sufficient to retain the atmosphere, due to total absence of magnetic field the solar wind would have direct access to the atmosphere and due to its effects of erosion, the atmosphere would be slowly taken away.
by Rafini 15 months ago
My son thinks so, and now I'm beginning to think it could be true - has this theory already been considered? I mean, it's impossible to know what the sun is really made of...all we know for sure, is that its still burning. It could have a solid mass at its core....I'm thinking that when...
by ii3rittles 6 years ago
I ask because this was brought to my attention...The moon does not spin, as it simply orbits around the Earth. There is nothing pulling on its axis to cause it to spin. So say we did not have a moon, would the Earth then not spin? Wouldn't this cause steady climate all over the world and no storms?...
by the_legend 7 years ago
what would the world be without a moon?
by Kartik ahir 6 years ago
A body of mass 9Kg is taken to moon what is the mass of body on moon?..........Take time to ans and ans with proper reason.
by Joan Veronica Robertson 6 years ago
How did the expression "a blue moon" originate? What does it mean?Please explain in detail and add different ways in which this expressionis can be used.
by sibtain bukhari 5 years ago
. ''Do ye not see that Allah has subjected to your (use) all things in the heavens and on earth, and has made his bounties flow to you in exceeding measure, (both) seen and unseen? Yet there are among men those who dispute about Allah, without knowledge and without guidance, and without a Book to...
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