In our pursuit to understand the cosmos and our place within it, one question often rises above all others:
Are we alone in the universe?
It could be decades or even centuries before we learn the answer — if we ever do.
For now, we must take on slightly simpler, more manageable questions. For example, could any of the other planets discovered so far have the potential to support life? Do they have the stuff life needs?
However, that raises another question: What would life on other worlds need?
We don’t completely know the answer to that, either. But based on the needs of life on Earth, we can make some educated guesses.
Unfortunately for those in search of habitable worlds, none of the planets whose atmospheres have been investigated so far could host any kind of life as we know it. They are “hot Jupiters,” giant planets of gas that lie so close to their stars that they are heated to unbearable temperatures, sometimes reaching thousands of degrees Fahrenheit. So the search for habitable planets continues on.
However, the Hubble Space Telescope opened up new realms of discovery when it detected sodium in the atmosphere of exoplanet HD 209458 b. Hubble's achievement showed not only that we can learn whether a planet light-years away has an atmosphere but also what that atmosphere contains.
Hubble's observation of water, carbon, oxygen, carbon dioxide, and methane in those atmospheres proves that we can hunt down some of the ingredients and byproducts of life when we do find potentially habitable planets. Additionally, Hubble's detection of life's ingredients on multiple exoplanets hints that these constituents might be common.
Until we pick up a signal that could only come from an intelligent civilization elsewhere in the cosmos, we might never know for sure whether there is life out there. But perhaps one day, future telescopes like the James Webb Space Telescope will employ today's atmosphere-probing techniques to pick up some chemical beacon on a far-off world that could only be produced by living organisms, providing the first compelling evidence that we are not alone.