May 15, 2017 - Last week, NASA announced that its flying observatory, SOFIA (short for Stratospheric Observatory for Infrared Astronomy) completed a study of a nearby planetary system that is very much like our Solar System, centered on the star Epsilon Eridani, also known as Eps Eri.

SOFIA is the world’s largest airborne observatory and flies at altitudes between 39,000 and 45,000 feet, above more than 99% of the water vapor in the atmosphere, making it possible to obtain astronomical data that are impossible to access from telescopes on the ground.

Eps Eri is 10.5 light-years away, and is one of the closest stars to Earth that is of a similar type as Earth’s sun. It’s a little smaller and a little dimmer, but is comparable in terms of temperature, luminosity, and mass.

Interestingly, Eps Eri is one of two stars (the other was Tau Ceti) that were examined by Frank Drake in 1960 as his first radio astronomy observation, using the Tatel Telescope in West Virginia. Eps Eri and Tau Ceti were selected because of their proximity to Earth’s Solar System, because of their similarities to Earth’s sun, and because they are single stars thought likelier to be able to host a potentially habitable planet in a stable orbit.

Although Frank Drake did not observe a signal from Eps Eri during that first SETI observation, it continues to be the subject of various types of observations, including from SOFIA, focusing on Eps Eri ‘s circumstellar debris disk.

Debris disks are comprised of rocky or icy material orbiting a star that can be left behind after a planet has been formed. In Earth’s Solar System, we have two debris disks: the asteroid belt between Mars and Jupiter, and the Kuiper Belt which is located beyond Neptune and includes Pluto, now reclassified as being part of the debris remaining after planetary formation.

In 1983, astronomer Fred Gillett found evidence for a Kuiper Belt-like debris disk around Eps Eri using data from the Infrared Astronomy Satellite, IRAS.  In 2009, SETI Institute scientist Dana Backman, who worked with Gillett on analyzing the IRAS data and now manages SOFIA mission Outreach for the Institute, discovered a debris disk similar to the asteroid belt around Eps Eri using the NASA’s Spitzer Space Telescope. In fact, the Spitzer data indicated two asteroid belts around Eps Eri, one in approximately the same position as in Earth’s Solar System, and a second between the first belt and the comet ring, at about where Uranus’s orbit would be in our system.

"The Eps Eri system probably looks a lot like ours did when life first took root on Earth," said Backman at the time. "The main difference we know of so far is that it has an additional, third, ring of leftover planet construction material."

Other observations of Eps Eri had previously revealed a planet similar in size to Jupiter at a similar distance from its parent star. Backman’s Spitzer observations indicated that the innermost debris belt around Eps Eri is made of silicate material, like our asteroid belt, and is located just inward of the Jupiter-like planet’s orbit, also like our asteroid belt.  Subsequently, an alternative theory was put forth, suggesting that the planetary debris around Eps Eri wasn’t configured in two belts, but rather in a broad sheet, which would not correlate with the positions of planets.

Now, new observations from SOFIA, which has a larger telescope diameter than Spitzer – 100 inches vs. 33.5 inches and thus 3x better spatial resolution – confirmed that Eps Eri’s debris disk is concentrated into at least one narrow belt of debris, similar to our Solar System’s asteroid belt.  This confirms Dana’s hypothesis that in the Eps Eri system, as in our Solar System, the formation of large planets results in adjacent debris belts.

Full details about NASA’s announcement can be found here.

To learn about the SETI Institute’s other activities with SOFIA through its Airborne Astronomy Ambassadors (AAA) program, click here.