字幕表 動画を再生する 英語字幕をプリント We're kinda destroying our lovely Earth, so can't we just go to the Moon? TERRAFORM! Yeah, that's probably not the best option… Hey guys! Moon-loving Amy with you on DNews today! We got a great question on Twitter from @atul05kumar. He asked why our Moon doesn't have an atmosphere and what would happen if we created one? When we think of a body having an atmosphere, we typically think of one like Earth's: a nice, cozy envelope of life-giving gases at pressure that keeps us alive and well. To keep an atmosphere like that, or any atmosphere, a planet needs a few things. It needs to be big enough to have enough gravity to hold on to that atmosphere, and some kind of protection from the solar wind so it doesn't get completely eroded away. Mars is a great example. The planet lost its past thicker atmosphere because it's gravity is too weak to hold on to the gasses and it doesn't have a magnetic field. Solar particles have ripped the gases away, leaving the planet with the tenuous layer of carbon dioxide it has today. Our Moon is smaller than Mars and has even lower gravity, and it's geologically inactive so has nothing to produce a magnetic field — basically a recipe for having no atmosphere…right? Well, the Moon actually does have an atmosphere! It's just super rarified, so much so that the engineers who designed the Apollo lunar module were able to completely ignore it (not to mention they didn't know it was a thing at the time but it all worked out). It's barely considered an atmosphere; properly speaking, it's called an exosphere. It's some 100 trillion times less dense than Earth's atmosphere at sea level. That's about the equivalent density as the area in space where International Space Station orbits. But still, it's there! And interestingly, the solar wind that destroys atmosphere is also one of the factors contributing to the Moon's. The Moon is constantly blasted with a stream of particles from the Sun that act as an abrasive, knocking sodium and potassium atoms off the surface to populate the exosphere. There is also gas constantly being released from the Moon's interior; the radioactive decay of potassium atoms leads to exospheric argon and helium. More material is also released after impacts of comets and meteoroids. There are still a lot of unknowns about the Moon's atmosphere, but with the discovery of water molecules trapped in the regolith (aka moon dust), scientists suspect the exosphere might play a role in a potentially dynamic lunar water cycle, moving molecules between the polar regions and the lower latitudes. As for creating an atmosphere on the Moon… well that one's a little trickier. The same conditions that have contributed to the Moon having no atmosphere mean it's unlikely to retain one we create for very long. But could we even create one? It would be really hard. Terraforming the Moon — not just building a colony or a bubble to live in but changing the Moon so it can support human life — would mean adding volatiles like hydrogen, nitrogen, and carbon, and the only place to get those elements in large enough quantities is in the distant regions of the solar system in the form of comets. We'd have to capture these comets and smash them into the Moon, allowing the frozen material to sublimate and populate the atmosphere. This would potentially liberate water in the lunar regolith at the same time, yielding natural bodies of water. Ideally, the momentum from these impacts would also get the Moon spinning faster so humans living there could have a more natural day-night cycle. But this is massively complicated and way out of our current technological capabilities! So it's unlikely to be something we'll see anytime soon, and by anytime soon I mean any century soon. But that doesn't mean there aren't reasons for us to keep researching the Moon. Because the lessons learned from Apollo — including the first ever indication of what makes up the Moon's atmosphere — really taught us that there's a lot more to learn. If you want to learn more about NASA's Moon landing on the go, check out the show When We Left Earth. You can get it now on the Discovery Go app. Check your app store or the link below in the description to find out more! And speaking of going to the Moon, the Moon's non-atmosphere helps explain why there's no flame when the Apollo lunar modules left the surface. I explain the whole story over on my channel, Vintage Space. And also, why do we only have one moon? Well, we made a video about that, here. So what other Moon mysteries - or just mysteries! - keep you guys up at night? Let us know in the comments below, be sure to like this video, and don't forget to subscribe for new episodes of DNews every single day.