Ask the Astronaut: How likely is it that there is life in our galaxy?

Artist's concept depicting some of the Kepler telescope's planetary discoveries. (NASA/W. Stenzel)
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Q: What is the probability that there is life on planets in the Milky Way galaxy? (Cherelle Brown, Troy, Michigan)

Answer : 100%. We are living proof. [end]

OK, I think you mean on other planets in the galaxy. In early May, NASA announced that its Kepler planet-hunting space telescope had confirmed another 1,284 new planets. Scientist Paul Hertz, the Astrophysics Division director at NASA headquarters, said that “Before Kepler was launched, we did not know whether exoplanets were rare or common in the galaxy. Thanks to Kepler and the research community, we now know there could be more planets than stars.” Because the Milky Way is home to up to 400 billion stars, that means there could be at least 400 billion planets in our galaxy.

Of the new Kepler discoveries, nearly 550 could be rocky planets like Earth, based on their estimated size. Of these, nine orbit their stars in the “habitable zone,” where the planet’s surface temperatures would permit liquid water to exist (a critical factor for the evolution of life, astrobiologists think). These new discoveries bring the current count to 21 exoplanets which are thought to orbit their stars in the habitable zone.

Kepler mission scientist Natalie Batalha said in a press conference that her “back of the envelope calculation” points to “tens of billions of potentially habitable” worlds. So far, Kepler data suggest that 24 percent of stars possess potentially habitable planets around 1.6 times the size of Earth.

The bottom line is that among 10 billion candidates, I would be very surprised if life did not start on many of these. Kepler’s successors will give us the ability to detect the chemical evidence for life in the atmospheres of some of these worlds. Let’s keep looking.

Have a question of your own? Ask the Astronaut.

Ask the Astronaut: A Galaxy of Astonishing Answers to Your Questions on Spaceflight

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About Tom Jones

Former astronaut Tom Jones is a scientist, author, and pilot. In more than eleven years with NASA, Tom flew on four space shuttle missions to Earth orbit. On his last flight, he led three spacewalks to install the centerpiece of the International Space Station, the American Destiny laboratory. He has spent 53 days working and living in space. See his full bio here.

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