Fifth-graders making Styrofoam solar system models may have the right idea. A team of astronomers from Vanderbilt, Lehigh and Ohio State universities have discovered a new planet orbiting a star 320 light years from Earth with the same density as Styrofoam. This “puffy planet” may provide opportunities for testing atmospheres that will be useful when assessing future planets beyond our solar system for signs of life.
“It is highly inflated, so that while it’s only one fifth the mass of Jupiter, it is nearly 40 percent larger, making it about as dense as Styrofoam, with an extraordinarily large atmosphere,” said Joshua Pepper, assistant professor of physics at Lehigh University, who led the study in collaboration with Vanderbilt’s Stevenson Professor of Physics Keivan Stassun and Associate Professor Scott Gaudi from Ohio State University, which included contributions from a number of amateur astronomers and researchers at universities and observatories around the world.
Astronomers have only found two other exoplanets with precisely measured masses and radii that have lower densities than the newly discovered planet, which has been designated KELT-11b. The paper describing the discovery, titled “KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V+8 Subgiant HD 93396,” was published online April 18 in The Astronomical Journal.
The planet’s host star is extremely bright, allowing precise measurement of the properties of the planet’s atmosphere making it “an excellent test-bed for measuring the atmospheres of other planets,” Pepper said. Such observations help astronomers develop tools to see the types of gases in atmospheres, which will be necessary in the next 10 years when they apply similar techniques to Earthlike exoplanets with next-generation telescopes now under construction.
KELT-11b is an extreme version of a gas planet, like Jupiter or Saturn, but is orbiting very close to its host star with an orbital period less than five days. Its host star, KELT-11, has started using up its nuclear fuel and is evolving into a red giant, so the planet will be engulfed by its star in the next hundred million years and so will not survive.
The unusual exoplanet was discovered by the KELT (Kilodegree Extremely Little Telescope) survey, which uses two small robotic telescopes, one in Arizona and the other in South Africa. The low-cost telescopes scan the sky night after night, measuring the brightness of about five million stars. Researchers search for stars that seem to dim slightly at regular intervals, which can indicate a planet is orbiting that star and eclipsing it. Researchers then use other telescopes to measure the gravitational “wobble” of the star–the slight tug a planet exerts on the star as it orbits – to verify that the dimming is due to a planet and to measure the planet’s mass.