So we have a very nice planet with liquid water, and that is because it's at the right distance from the Sun, so it's warm enough, and we have an atmosphere, we have air that keeps a nice pressure on the planet, so that we can have big oceans. That's not so easy to find. We also believe that the possibility of having life is very highly connected to having liquid water.
We don't know how life started on the Earth, but we know very much that life is very old. As soon as the planet "calmed down", life started to exist here.
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I can't tell you if there's other life out in the Universe. If I ever happen to tell anybody that I'm an astronomer, the first question I get is is there life out there? But what I hope we can do rather soon is to tell you something about are there other Earth-like planets out there, where the conditions are the same. Looking at our neighbor Mars, it is today a cold, dry, desert planet. It's smaller than the Earth. But during the time that life arose on Earth, originated here, Mars was very different. It had a huge ocean on the northern hemisphere.
It had an atmosphere. So conditions were rather similar on Mars and on the Earth.
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Perhaps life started on Mars as well. We don't know that as yet, but the conditions were very similar. If we talk about life in the Universe, people usually want the big spaceship landing right outside there, so we can, you know, try to communicate and stuff. But I would be almost just as intrigued if I'd found a dead bacteria or something very small life-like on Mars, because that could give us the key to the question of whether life originates if you have a place where the conditions are favorable.
The reason why Mars has changed too much is that it's smaller than the Earth. The lesser gravity means that Mars has been unable to keep its atmosphere. So, it's a very low pressure on the surface. If you were to pour out a glass of water on the surface of Mars, it would just evaporate instantly. But there has been lots of water there, and this picture shows an old river delta on Mars. So just imagine this neighbor planet - it has had oceans, it has had rivers; it's been a very different world.
So worlds can change.
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This means that Mars is not a very good candidate perhaps for life today, because there's no liquid water on the surface, and there's no protecting ozone layer there. Perhaps there could be some very simple life forms below the surface. We might find out, or perhaps they are not there. But there's one place in our Solar System where liquid water might exist that's not the Earth. It's this small moon. The moon is called Europa. It's one of Jupiter's moons. If you look at Europa, it looks like a big ice ball. Why would you have liquid water out in the outer regions of the Solar System? Well, Jupiter has approximately 60 moons; we have one.
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If you combine the gravity working on Europa from the big Jupiter - Jupiter is so much bigger than the Earth - and the 60 other moons, you have different forces acting on Europa all the time, heating it. There's one moon that's even closer to Jupiter that's called Io. It has constant volcanoes because there's so many forces acting on it.
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Europa is a little bit further from Jupiter, and it looks like a big ice ball with cracks in it. We have had a few probes out there, taking pictures of the surface of Europa. The people who are looking at the ice claim that the surface of Europa, it looks more like the Arctic than the Antarctic. The difference, of course, is that on the Arctic, at the North Pole, you have ice floating on water.
If you look at the Antarctic, you have ice lying on a continent. They say that Europa shows more features that look like ice floating on water. So perhaps, out on this small moon, could be a very… several kilometers thick crust of ice, but there may be a huge subsurface ocean there, and in that case, it's the only other place than the Earth in our Solar System where you have liquid water. The conditions are probably quite similar to the conditions very deep in our own oceans. You have some heat from the interior of the moon. It's dark, of course, but you have liquid water, you have carbon, all the other elements that life is formed from here on the Earth, and you have energy.
So, it's a very interesting place, and I hope that you will have the chance to learn more about it. Several expeditions to this moon are planned. The first thing is to try to find out is there an ocean there. And we'll see if somebody is swimming in it. If we are to leave our own Solar System - I hope we don't have to, actually - in about a billion years, the Sun is constantly increasing its luminosity, its output, its power, so actually, in about a billion years, the Earth will be too hot to have liquid water.
A billion years is a very long time. Human history is quite short, actually. Sometimes when you talk about astronomy, people think that, "Oh, we are so small and insignificant, just living on this very small planet, and having to repress things and not to think about it. But I believe we are quite remarkable.
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We have a very short history of science, of thinking like that, but we constantly keep asking ourselves those questions: where do we come from? Why does everything look like it is and what can we do?
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What are those things shining up there? I don't say that we have all the answers as yet, but at least we know something about the And also, a little bit into the future. I hope that mankind's future will be very long; I sincerely hope so. So we have at least a billion years to solve our problems, but I think it's important to start today, but then we have to travel outwards, perhaps to Mars, perhaps to Europa.
But is there some place else to go to? In , we started to find the first planets around other stars. This is not a photo; this is a drawing by an artist.
We can't take any pictures of these other planets as yet. So finding planets around other stars is a fairly new kind of science. About one year ago, we had discovered , which means that we can start to make some statistics. The fun thing is that we found so many planets that nobody has ever said that there was going to be out there, and the question was really could there be another Earth or is this the only one? There are so many really strange things out there: super Earths, hot Jupiters, ice giants.
We are trying to keep up with the nomenclature right now. With new telescopes, during , the number of discovered planets is now exceeding 2,, and we are finally getting some reports on perhaps Earth-sized planets at least. There actually seems to be quite a good chance of finding ocean planets or water worlds out there, that is planets that have no continents; just very, very deep oceans.
You have some variations of these. If you move them a little bit further from their star, you get big icy planets, ice giants. If you move them a little bit towards the stars, you get steam, some kind of sauna planets. I really want to impress upon you that Universe is always stranger than we can imagine, but it is a support of our thinking from a very long time: how common are we and our kind of planet?
I mean, you are students, most of you; you can try to find out this, what's out there. Some of them might be Earth-like also. The problem is that they are very small compared to a star, so they are hard to find. We have some different methods of trying to find them. So far, the Earth-like planets are very few, but I believe that in five years, we will know very much more about this. If we have to leave our home in a billion years, perhaps we will know where to go. Applause Translation - Italian Grazie. Mi chiamo Maria Sundin, e sono un'astrofisica.
Ci sono altri mondi come il nostro pianeta? Bene, la storia dell'acqua risale a E' iniziata col Big Bang. E quando le stelle esplodono, questo ossigeno si sparge nell'Universo. Nella foto vedete una stella esplosa.
Parecchie stelle dovettero esplodere prima che fosse creato il nostro sole. Da quando un po' di stelle sono esplose, questi detriti intorno, che avrebbero formato il sole, avevano dell'ossigeno dentro, e molto idrogeno, e questi elementi insieme si sono uniti per formare l'acqua. Nei primi tempi della terra, essa era bombardata da comete.
follow url Le comete sono Durante il primo mezzo miliardo di anni dell'esistenza della terra, era bombardata continuamente dalle comete. Ma durante il periodo in cui la vita nasceva sulla terra, Marte era molto diverso. Aveva un oceano enorme nell'emisfero nordico. Aveva un'atmosfera. Le condizioni su Marte erano simili a quelle sulla terra.
Noi non lo sappiamo ancora, ma le condizioni erano molto simili.