In December 2013, astronomers reported that the Hubble Space Telescope had detected water vapor in the atmospheres of five planets outside of our solar system. Before you get too excited these are not really candidates for life. They are all hot Jupiters gas giants that orbit very close to their stars. However, you should be excited that we now have proof that water exists in atmospheres outside of our solar system.
We already have a method of detecting it. Here's how it works;
- When a planet's orbit takes it between us and its star. That stars light passes through the halo of the planet's atmosphere.
- Using an instrument called the spectrograph. Scientists can split that light into a spectrum.
- This is the same electromagnetic spectrum you seen in your whole life. Which goes from infrared light, through the colors visible light and up through ultraviolet, etc.
- Now, when nothing is between us and the star. We can see the whole spectrum as the star emits it. If something is blocking that light, we can't see any of it. However, when a planet's atmosphere is transparent. It lets some light through but not all of it.
- So, the spectrum created by the spectrograph has these dark bands running through it from where different gases in the planet's atmosphere block or absorb different frequencies of light—they called it as absorption lines.
The amazing real thing is, different chemicals create different patterns of absorption lines. So, a scientists can look at the information from the spectrograph. Figuring out which gas is the light has passed through.
At the moment, we don't have a telescope powerful enough to read the atmospheres of anything smaller and darker than those hot Jupiters. But in the future we will! Probably, as soon as 2018, when NASA launches the James Webb Space Telescope.
The time that we can read the atmospheres of terrestrial planets. Like our Earth which is made of metal and rock instead of gas. We can start looking for signs of life outside our solar system.
What will we be looking for? Well, definitely water vapor! Water in the air means there might be water on the ground. Especially, if the planet is the right distance from the Sun. Life as we know it couldn't happen without liquid water.
We'll also be looking for free-or molecular-oxygen. Molecules of oxygen (O2), oxygen atoms are relatively abundant in the universe.
- In fact, the Earth is 45% oxygen by weight and about 85% oxygen by volume. But, almost all of it is bound up in molecules with silicon, magnesium and iron—making up the rocks under our feet.
It's really friendly atom always look at to pick up an electron from any other atom that can spare one. But when it bonds with itself to form oxygen molecules. It's not particularly stable. So, it tends to get converted other molecules.
- Our atmosphere is more than 20% oxygen because it's always being made by living things. Particularly, plants and other photosynthetic organisms. Which use sunlight, water and carbon dioxide to create massive amounts of atmospheric oxygen.
So, when the astronomers get through the atmosphere of that other planet. They would see something as chemically out of balance. The planet has too much free oxygen—something is alive down there.
Once the planet have water and oxygen. The way is open for the development of cellular respiration. Which is how aerobic organisms use oxygen to fuel the metabolic processes. An aerobic metabolism is much more efficient than anaerobic metabolism—the kind that doesn't use oxygen.
Something with an aerobic metabolism can extract up to 16 times more energy out of the same amount of fuel. You need that kind of energy to support multicellular creatures such us animals, plants and eventually people type things.
So, finding water vapor in the atmosphere. These hot Jupiters is just the next step toward finding habitable and potentially inhabited planets. Identifying planets like ours isn't just the stuff of science fiction anymore. Sometime in the next ten years we're gonna be able to point the telescope in the deep space to look at a faraway planet and know if there's any chance that there might be someone out there looking back at us.