Bumper Crop of Habitable Worlds Discovered?

This artist illustration shows one of three super-Earth exoplanet in orbit around Gliese 667c, a red dwarf star that is a companion to two other low-mass stars, which are seen here in the distance. Credit: ESO/L. Calçada

Astronomers believe they have found an alien solar system packed with a record-breaking three potentially habitable worlds.

New observations of the star Gliese 667C—about one-third the mass of our sun—is home to between five and seven planets, three of which are classified as super-Earths. All three are larger than our own planet, but smaller than gas giants like Uranus and Neptune. (Related: “Light From a “Super Earth” Seen—A First.”)

But what makes all the difference is that these super-Earths orbit in what is known as the “Goldilocks Zone”—the region around a star where temperatures are just right for liquid water, a key ingredient in the recipe for life, to exist. (Related: “Most Earthlike Planets Found Yet: A ‘Breakthrough.'”)

“These planets are good candidates to have a solid surface and maybe an atmosphere like the Earth’s, not something like Jupiter,” said study co-author and University of Washington astronomer Rory Barnes in a statement this week.

What makes this finding so exciting is that for the first time, astronomers have three potentially rocky or ocean worlds orbiting the same star. And at 22 light-years away from Earth, Gliese 667C and it’s two companion stars are considered relatively close neighbors to our solar system, making them ideal candidates for future extraterrestrial searches for life.

“It’s exciting that we’ve found a nearby star that has so many planets in its habitable zone,” said Barnes.

Lock on Life?

Since Gliese 667C is so much smaller and cooler than our own sun, it’s habitable zone is much closer in, meaning the super-Earths take anywhere from 20 to 100 days to orbit. Astronomers suspect this indicates the planets are gravitationally more influenced by their parent star than Earth is by the sun.

“The close proximity of these planets in the habitable zone to the host star makes it likely they are ‘tidally locked,’ which in this case means the same hemisphere always faces the star,” Barnes said. “Fortunately, we know that this state can still support life.”

These finding were made possible thanks to years of radial velocity measurements of the starlight using some of the world’s largest observatories ; including the Keck  Observatory, in Hawaii, and the European Southern Observatory’s 3.6 meter telescope and Las Campanas Observatory, both in Chile. Radial velocity measures a star’s wobble caused by the gravitational tug of orbiting planets by looking for the telltale shifts in a star’s light spectrum as the planets appear to move away and towards us.  The more massive a planet, and the tighter its orbit, the higher effect it will have on its star. Since these planets were relatively small their signals were hidden in the original data and so a re-analysis and new observations helped to confirm their existence.

At least two to four other planets outside the habitable zone may exist but still need to be confirmed by further observations.

The implications of this packed planetary system on the hunt for Earth-like planets could be profound. Barnes and his team believe this discovery may indicate that low mass suns like this red dwarf—many of which populate the Milky Way—may routinely harbor multiple low-mass planets in their habitable zones. This means that there could be many more habitable planets in the Milky Way than we ever thought.

The super-Earth study will appear in the July edition of the journal Astronomy & Astrophysics.

 

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Wildlife

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.