Does oxygen necessarily mean aliens?

Astrobiologists find that the presence of oxygen in a planet's atmosphere may not necessarily mean that life exists there.

Harvard Smithsonian Center for Astrophysics/AP/File
An artist drew this representation of planets Kepler-62e and -f. Scientists using NASA's Kepler telescope found two distant planets that are in the right place and are the right size for potential life. The larger planet in the left corner, f, is somewhat covered by ice and is is farther from their shared star. The planet below it is e, which is slightly warmer, has clouds, and may be a water world.

Scientists and E.T. enthusiasts may have to rethink an allegedly telltale sign that a planet has life.

The presence of oxygen, specifically O2 , in a planet's atmosphere has long been thought to be a near-certain signal that there are, or at least were, living organisms engaging in photosynthesis on the planet. But new research suggests that oxygen can exist in large quantities without being produced by living things.

A study published Thursday in Scientific Reports found that some planets could have "abiotic" oxygen, produced through a a photocatalytic reaction of titanium oxide.

For scientists hunting for extraterrestrial life, this abiotic oxygen could create a false positive, the researchers caution.

Atmospheric oxygen, like water and complex organic molecules, have long been considered biomarkers, that is, signals that life is present.

"To search for life on extrasolar planets through astronomical observation, we need to combine the knowledge from various scientific fields and to promote astrobiology researches to establish the decisive signs of life,” study author and astrobiology professor Norio Narita said in a news release.

"Although oxygen is still one of possible biomarkers," said Dr. Narita, the new results suggest that scientists should "look for new biomarkers besides oxygen."

Water has been a popular biomarker, especially as it has been found in moons in our solar system and in atmospheres around other Earth-like planets.

This isn't the first time scientists have debunked a signifier. In 2013, astronomers found that a planet could be surrounded by atmospheric gases that suggested life, but that those gases too could be a false indication. "Beware the habitable-planet poseur," wrote the Christian Science Monitor's Pete Spotts.

It's all part of the evolving understanding of planetary processes and what they mean for extraterrestrial life. 

NASA isn't discouraged. Within 20 to 30 years, says NASA chief scientist Ellen Stofan, scientists will find clear evidence of life "out there."

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to

QR Code to Does oxygen necessarily mean aliens?
Read this article in
QR Code to Subscription page
Start your subscription today