In Centauri Dreams‘ imagination, the name Epsilon Eridani is magic. Like many of us, my earliest speculations about life on other worlds always came back to the nearby, Sun-like stars like Tau Ceti, Epsilon Eridani and Centauri A and B. Frank Drake used the first two as his targets for Project Ozma in 1960, an effort that continues to inspire SETI work today. And Epsilon Eridani is joined by Vega, Fomalhaut and Beta Pictoris as the first stars found by the Infrared Astronomical Satellite (IRAS) to have a cool debris disk somewhat analogous to our own Kuiper Belt.

The fact that this K2 star is likely to be orbited by the closest exoplanet to our Sun is also exciting. Its planet seems to be slightly larger than Jupiter, with estimates ranging from 0.8 to 1.6 Jupiter masses, and an eccentric orbit varying from 5.3 to 1.3 AU (here again we see how important it is to establish the effect of gas giants on terrestrial worlds in the habitable zone). At 10.5 light years from us, Epsilon Eridani offers an unusual close look at the final phases of planetary formation.

Epsilon Eridani is, moreover, a young star (less than a billion years old) with a disk featuring interesting clumpy structures suggestive of planetary interactions with the dust. Some computer models, still inconclusive, make the case for a Neptune-class planet as the cause. Using the Spitzer Space Telescope to study the debris disk for more planetary companions in the system’s outer regions is thus fruitful science, as a team led by Massimo Marengo (Harvard-Smithsonian Center for Astrophysics) has demonstrated.

Spitzer is one of our most productive instruments, the source of the only three detections of thermal radiation from exoplanets (all three are eclipsing ‘hot Jupiters’). Brown dwarfs and Jupiter-sized planets can be investigated since they are characterized by strong molecular absorptions in the mid-infrared range. They become accessible targets thanks to the sensitivity of Spitzer’s InfraRed Array Camera (IRAC). What we still lack is what this team would like to provide, a direct detection of gas giants orbiting their star at Jupiter-like distances and beyond.

No new planets here, but Marengo’s team was able to establish limits on planetary detection using the IRAC instrument. Spitzer, they find, can detect young gas giants with a mass as low as several Jupiters when they are orbiting their star at distances comparable to the Kuiper belt. Moreover, planets in highly elliptical orbits during the era of planetary formation can be detected down to a single Jupiter mass. These are useful boundaries for future work, and although the data at the time of publication were insufficient to verify the existence of any new planets around Epsilon Eridani, some infrared sources need further study to determine their nature by measuring if they have a common proper motion with Epsilon Eridani.

Expect more work on Epsilon Eridani, including an upcoming paper from the same team based on results from Spitzer’s InfraRed Spectrograph and Multiband Imaging Photometer, to be published soon. The paper above is Marengo, Megeath, Fazio et al., “A Spitzer/IRAC Search for Substellar Companions of the Debris Disk Star Epsilon Eridani,” available here.