OK, so I’m going to tell you about water in the universe, and the charge to you tonight is to think big, very, very big. So, why do we care about water in the universe? It’s because water is essential for life.
Where we find water, we find one of the key ingredients where we can find life. What we’re going to do tonight is a tour of the universe through the prism of water. At the top of the screen, I have a little meter for you to keep track of where we are in the universe. We’re going to start at the Earth and move out to the very early universe. So let’s start our tour, here we go.
We’re going to start here and now – here we are on the Earth – and we live in an amazing place in terms of water. You can see in this pressure-temperature diagram that there are three phases of water: solid, liquid, and gas. Every day, especially here in Colorado, we can see all three phases at once. So we see ice, we see liquid water, and we see clouds. But you can imagine if we leave the atmosphere of the Earth, the pressure drops and we can no longer have liquid water, we can only have ice or vapor.
Likewise, if we go out in the cold, cold, cold space, the pressure drops, the temperature drops as well, and we only have ice; all the water freezes out. Let’s take the next step on our tour, and we’re going to find water in a really extreme environment. You may be surprised to learn that there is water on the surface of our Sun. We can see these dark spots on the surface of the Sun; these are sunspots. They look dark because they’re slightly cooler than the rest of the Sun.
They are still very hot, about 5,000 degrees Fahrenheit, but if you look in the centers of these sunspots, it turns out that water is spontaneously forming; there is a chemistry there forming water on the surface of the Sun. It’s a gas, but it’s still water. Very hot water. We’ll see water in very extreme environments later on in our tour; this is the first spot. So let’s move further out in the solar system, let’s look at the moon of Jupiter called Europa.
Remember, when we leave the atmosphere of the Earth, can we not only have a pressure, we have water freezing, ok, so we have ice, and this moon is basically a ball of ice. But you can imagine if you burrow down into this moon, things get warmer and the pressure would go up, and in fact it’s thought that there are liquid oceans here deep inside Europa. This is one of the places where we would probably first look for life in our solar system. Likewise, for this moon of Saturn. What the Cassini probe found looking in profile at the pole of this moon, Enceladus, is water geysers shooting out of cracks at the bottom of this moon.
There are actually geysers on this object spewing water into space which tells us that in fact it is warm and wet in the interior. OK, now let’s move even further out, let’s look at other stars. In fact, over the past 15 years, astronomers have been finding planets around other stars, but an amazing discovery just last year was of a planet that is only few times the mass of the Earth, but it was of a very low density. What that density implies is that there is a lot of water here. It’s not yet known whether this is some sort of water world, or whether it’s some sort of steam planet, but we do know there must be a lot of water.
This brings us to the idea of a habitable zone. If we look around other stars, where are we going to find places where life can exist? This is really the places where we can find liquid water, and it’s indicated by the blue band here. The vertical axis here is the mass of stars, it’s how bright a star is, and the horizontal axis is the distance from stars. So you can see for lower mass stars that are dimmer, you have to be closer. But what we see at the top is our solar system, – Earth is living in that lovely, habitable zone – and you can see that it changes versus various stars.
But what we’re increasingly finding – and stay tuned for this – is planets that are actually in that habitable zone, good places to find life. All right, so let’s move further out into the universe. In order to do this, what we need to do is find a way to detect water at great distances. And what water can do – it’s an amazing molecule – it makes a natural laser; leave water to its own devices, and it shoots out a beam of light. This light is in the radiowaves, so we call them maser which stems from microwave laser, but in any case, if you happen to be looking along that beam, it’s incredibly bright.
So what we do is we use the largest telescopes on Earth to search for water at great distances. What I would need you to think about now is this equivalency between distance and time. Light takes time to travel to us from distant objects, so we see objects as they were in the past. If we want to look earlier in the universe, we just look at more distant objects. So that’s what we’re going to do.