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introduction
The search for life beyond Earth is only just beginning, but science has an encouraging initial answer: There are many planets in the galaxy, many with similarities to ours. But what we don’t know fills the volumes.
Observations from the ground and space have confirmed thousands of planets beyond our solar system. Our galaxy probably contains trillions of them. But so far we have no evidence of life beyond Earth. Is life in the cosmos easy and mundane? Or is it incredibly rare?
How big is the Milky Way galaxy? Make the leap to light years as we navigate our galaxy. Video credit: NASA / JPL-Caltech
More questions than answers
More questions than answers
In the thousands of years that humanity has contemplated the cosmos, we are the first people to know for sure one thing: the stars beyond our sun are teeming with planets. They come in many varieties, and a good portion of them are Earth-sized. Like most scientific questions, however, getting this one answered only generates more questions: Which, if any, of these exoplanets hosts any life form? How fast does life start? And how long does it last?
This artist’s concept allows us to imagine what it would be like to stay on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius, as of February 2017.
Where is everyone?
Where is everyone?
The disturbing silence of the universe has its name: the “Fermi paradox”. Physicist Enrico Fermi asked the famous question: “Where is everyone?” Even at low travel speeds, the billions of years of the universe’s existence leave plenty of time for intelligent and technological life forms to traverse the galaxy. Why, then, is the cosmos so silent?
Meanwhile, exoplanet discoveries over the past two decades have filled some of the terms of the much-discussed Drake equation, a chain of numbers that may one day tell us how many intelligent civilizations we can expect to find. Most of its terms remain empty – the fraction of planets with life, with intelligent life, with detectable technology – but the equation itself suggests that one day we may arrive at an answer. It seems at least a little more hopeful than Fermi’s silence.
We are at a crossroads in the search for life. We have found thousands of planets in our galaxy, the Milky Way, a large fraction of them in the size range of the Earth and orbiting in the “habitable zones” of their stars – the distance from the star. he could exist on the surface. We know that the galaxy probably contains trillions of planets. Our telescopes in space and on earth and our remote sensing technology are becoming more and more powerful. Yet, so far, the only life we know of is right here at home. For the moment, we’re staring into space, hoping someone is staring at us.
Revised Drake’s equation. Image credit: University of Rochester
Next: We don’t have a universally accepted definition of life itself, so can we find life?
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