Penn State-led team discovers three new planets—and a mystery.

An international team of astronomers using the Hobby-Eberly Telescope in West Texas has discovered three new planets—each orbiting its own giant, dying star—that may provide clues about the eventual fate of our own solar system.

The team first observed the planets’ parent stars—called HD 240237, BD +48 738, and HD 96127—tens of light years away from our solar system. “Each of the three stars is swelling and has already become a red giant—a dying star that soon will gobble up any planet that happens to be orbiting too close to it,” according to team leader Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State. One of the stars—BD +48 738—is accompanied not only by an enormous, Jupiter-like planet, but also by a second, mystery object, that could be another planet, a low-mass star, or a brown dwarf, a star-like body that is intermediate in mass between the coolest stars and giant planets.

The newly found objects have already yielded insights into how dying stars behave depending on the amount of metals they contain. Giant stars, Wolszczan explains, are known to be “jittery,” oscillating much more than our own, much-younger Sun. Measuring the metal content of the stars, he says, “We found a negative correlation between a star’s metallicity and its jitteriness. It turns out that the less metal content each star had, the more noisy and jittery it was.”

As stars swell to the red-giant stage, Wolszczan adds, planetary orbits change and even intersect, and close-in planets and moons eventually get swallowed and sucked up by the dying star. It is possible that the new-found stars once had more planets in orbit, but that these planets have already been consumed. “None has a planet at a distance closer than 0.6 astronomical units—that is, 0.6 the distance of the Earth to our Sun,” Wolszczan notes. “It might be that 0.6 is the magic number at which any closer distance spells a planet's demise.”

Penn State’s Center for Exoplanets and Habitable Worlds is organizing a conference in January 2012 to discuss planets and their dying stars. The conference will be held in Puerto Rico and is scheduled to take place exactly 20 years after Wolszczan used the 1,000-foot Arecibo radiotelescope there to detect three planets orbiting a rapidly spinning neutron star—the very first discovery of planets outside our solar system.

Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics, can be reached mailto:axw5@psu.edu.

Last Updated November 30, 2011