Lonely planet drift in 'splendid isolation.'
By Amanda Jermyn

I recently wrote about a lonely star floating in space, away from any other nearby stars. Today let me introduce you to a lonely planet floating in space without a star to orbit. Meet PSO J318.5-22, a young exoplanet, about 80 light-years from Earth, in the constellation Capricorn.

The planet was first observed two years ago by an international team of astronomers led by Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa. According to Dr. Liu, “We have never before seen an object free-floating in space that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone.”

Using the Pan-STARRS 1 wide-field survey telescope on Haleakala, Maui, the planet was inadvertently discovered during a search for brown dwarfs, star-like objects that are bigger than planets but not massive enough to become stars. With a mass about six times that of Jupiter, planet PSO J318.5-22 has similar properties to those of gas giant planets that orbit young stars. At 12 million years old, it is relatively young. It is also one of the lowest mass objects known to be free-floating in space.

Typically, exoplanets are detected by looking for the dip in brightness that indicates a planet moving in front of its star or by gravitational lensing. However, as technology improves, exoplanets are increasingly being observed directly. According to co-author of the study, Niall Deacon of the Max Planck Institute for Astronomy in Germany, “Planets found by direct imaging are incredibly hard to study, since they are right next to their much brighter host stars. PSO J318.5-22 is not orbiting a star so it will be much easier for us to study. It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth.”

After observing the lonely planet for two years the researchers established that it lies within a collection of 12 million year old stars called the Beta Pictoris moving group. While the star Beta Pictoris, for which the group is named, has a gas giant planet orbiting it, PSO J318.5-22 travels through space with this group without orbiting a star. There is speculation that the lonely planet might have originally formed in orbit around one of the stars in the Beta Pictoris group but that it was shot out of its planetary system by gravitational interactions involving one or more of the other stars in the moving group. Given that most stars form in star clusters, the interactions among nearby stars may have spawned many other rogue planets, traveling through space in splendid isolation.

Join the Springfield Stars Club on Tuesday, January 28th at 7:30pm at the Springfield Science Museum for a special showing of the planetarium show, “Stars Around the Campfire,” created by astronomy educator, Jack Megas, and curator of physical science, Richard Sanderson. Based on historical research by Megas, the show focuses on how people from different cultures and different time periods interpreted the night sky. It explores the legends surrounding the stars, constellations, planets, moon, Milky Way, comets, meteors and northern lights, all of which are visible to the unaided eye and were noticed by ancient stargazers. Megas and Sanderson will provide a brief introduction, prior to the show. The meeting will begin, as always, in the Tolman Auditorium. Refreshments will be served, and the public is welcome. The meeting is free for members, with a suggested donation of $2 per non-member.