Studying a planet that’s orbiting a star is like studying a firefly in a headlight.

Katelyn Allers

PSO J318.5-22 is a free-floating planet with six times the mass of Jupiter. It wanders through space, approximately 80 light years from Earth, without a star to tether it to its orbit. Professor Katelyn Allers, physics & astronomy, was on the team that discovered PSO J318.5-22, and now, she and her students are on the lookout for other "lonely planets" like it.

"Studying a planet that's orbiting a star is like studying a firefly in a headlight," says Allers. "Finding a free-floating planet, or a brown dwarf, gives us a chance to examine a planetary body without interference from a parent star. This allows us to determine the age and composition of planetary-mass objects."

Brown dwarfs are larger than planets but smaller than stars. Stars form when a cloud of gas and dust collapses. With enough mass, the collapse triggers nuclear fusion, which emits heat and light. Without nuclear fusion, the result is a brown dwarf. Allers and her team use infrared filters to hunt for potential brown dwarfs. Once a free-floating planet is identified as a candidate, spectroscopic observations can confirm its cool temperature and determine its age and composition.

Bucknell leases time on a 3.5-meter diameter telescope at Apache Point Observatory in New Mexico using funds provided by the Isaac J. Tressler Fund for Astronomy. "This gives my students access to some of the most sophisticated equipment available and lets them view distant areas of space in real time right from their computers," Allers says. She has also taken students to large observatories in Hawaii and Chile. "There's nothing like having hands-on access — and in such beautiful locations," she says.

On campus, Allers teaches classes that range from general courses for non-science majors to advanced courses geared toward physics majors and engineers. "My upper-level courses are very project-based," she says. "My Modern Optics students build a working spectrometer by the end of the semester."

Will one of Allers' students discover the next PSO J318.5-22? "It's estimated that there are about a dozen free-floating planets within 100 light years of us," she says. "So yes, it's a possibility."

Posted Sept. 30, 2015


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