Tau Ceti system unlikely to contain Earth 2.0

Chuck Bednar for redOrbit.com – @BednarChuck

If you’re looking to find a potentially habitable Earth-sized planet outside of our solar system, you should probably look somewhere other than the Tau Ceti system, according to a new study by researchers at Arizona State University. Sorry Star Trek fans.

While planets in the system were frequently references as being colonized worlds in the popular science-fiction universe, the ASU team explains in a recent edition of The Astrophysical Journal that the chances of that are unlikely. Their findings are based on an extensive analysis using both astronomy and geophysics to evaluate the potential habitability of Tau Ceti planets.

Can’t support life here, move along

At first glance, Tau Ceti seems like an ideal place for a potential human colony. It is located in close proximity to Earth and its star has many of the same characteristics as our sun. In addition, back in December 2012, astronomers found evidence suggesting that five planets orbited the star, including two (Tau Ceti e and f) that were potentially located in the habitable zone.

However, the ASU team’s calculations found that Tau Ceti e is only in the habitable zone “if we make very generous assumptions,” astrophysicist Michael Pagano explained. He added that Tau Ceti f, “initially looks more promising,” but modeling of the star’s evolution makes it likely that it “has only moved into the habitable zone recently as Tau Ceti has gotten more luminous.”

Based on their findings, Tau Ceti f has probably been in the habitable zone for far less than one billion years, less than half the time required for potentially detectable changes to be produced in the Earth’s biosphere. A planet that entered the habitable zone around its star this recently may be habitable and inhabited, but could lack detectable biosignatures.

Unusual composition makes life around Tau Ceti “unlikely”

Pagano said that he and his fellow researchers opted to study Tau Ceti not because they were “hoping, wanting, or thinking” that it could be a good candidate for extraterrestrial life, but for the notion that it could host completely new worlds. The star has an unusual composition, with a 1.78-to-1 magnesium-to-silicon ration, about 70 percent higher than our sun.

Mineral physicist Sang-Heon (Dan) Shim analyzed the data collected by Pagano’s team to see what this would mean for the planets in the system. He explained that the high magnesium and silicon ration could indicate that the planets around Tau Ceti have a mineraological make-up that is “significantly different” than Earth’s. They could be predominantly made up of the mineral olivine at shallow parts of the mantle, and by ferropericlase at lower depths.

Since ferropericlase is far less viscous, hot, yet solid, mantle rock may be flowing. This could have a profound effect on surface-level volcanism and tectonics – processes that have a significant impact on the habitability of Earth.

“Tau Ceti has been a popular destination for science fiction writers and everyone’s imagination as somewhere there could possibly be life,” Pagano said, “but even though life around Tau Ceti may be unlikely, it should not be seen as a letdown, but should invigorate our minds to consider what exotic planets likely orbit the star, and the new and unusual planets that may exist in this vast universe.”


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