Hunt for Earth-like Planets with Alien Life is Too Narrow: Exoplanets Could Hold the Key

Are there duplicate Earths in the Universe? There definitely are. Already, astronomers have discovered Earth-like planets located light years away. The real question is, though, if they actually possess extraterrestrial life. Now, one researcher has announced that we may have to broaden our search a bit when it comes to discovering alien life.

Currently, researchers are focusing on discovering Earth-like planets in our Universe. In fact, NASA is deploying its James Webb Space Telescope (JWST) by the end of this decade; the telescope should give scientists the opportunity to find out what gases exist on alien worlds and should be able to pick out Earth-like planets using a transit search.

Although it may seem like a good idea to look at "second" Earths for the promise of life, this narrow focus could hinder the search for life rather than help it. Sara Seager of the Massachusetts Institute of Technology, a pioneer  in the study of exoplanet atmospheres, has pointed out that searching only for Earth-like planets would exclude a host of potentially life-supporting exoplanets.

"Our basic premise is that to be habitable, a planet has to have liquid water," said Seager in an interview with National Geographic. "In addition, planets with thin atmospheres are mostly heated by their stars. But what primarily controls surface temperature is the greenhouse effect, what types of gases are in the atmosphere and how massive a planet's atmosphere is. That's what we really have to understand."

Exoplanets are planets located outside of our Solar System. While some of them are certainly Earth-like, others are truly alien. Scientists discovered the first of these planets around a sun-like star in 1995. Since then, the number of discovered planets has grown to more than 700, according to Space.com.  These planets can include enormous, hot "Jupiters" that whirl around their star at an extremely close range, or "rogue planets" that actually cruise through space without any parent star.

While some of these exoplanets probably couldn't support life, others that are not typically defined as "Earth-like" may be able to. Some of these alien worlds could conceivably hang onto their gaseous hydrogen, which long ago escaped from smaller planets such as Earth, Venus and Mars. While they may not be in the traditionally described "habitable zone," the powerful greenhouse gas could make liquid water possible.

It's not just cold planets that that could support life, though. Dry, rocky planets with atmospheres that have much less water vapor than Earth's could also potentially support life, despite being closer to their host star than Earth is.

"I hope it gets people to realize that so many types of worlds could be habitable, and that our chance of finding one is higher when we accept that," said Seager in an interview with Space.com.

The details of this theory are written in a paper published in the journal Science.