The Search for Habitable Planets around Red Giant Stars -New Discovery Announced

A planet orbiting a giant red star in the constellation Perseus (the Greek hero who slew Medusa) has been discovered by an astronomy team led by Penn State's Alex Wolszczan, who in 1992 discovered the first planets ever found outside our solar system. The new planet circles the giant star every 360 days and is located about 300 light years from Earth.

"After astronomers have spent more than 10 years searching for planets around Sun-like stars and discovering over 250 planets elsewhere in our galactic neighborhood, we still do not know whether our solar system's properties, including life-supporting conditions on our planet, are typical or exceptional among solar systems throughout the Galaxy," Wolszczan says. "The picture for now, based on the searches for planets around stars like our Sun, is that our planetary system appears to be unusual in a number of ways."

The discovery resulted from an ongoing effort that the research team -a collaboration between astronomers at Penn State, Nicholas Copernicus University in Poland, the McDonald Observatory, and the California Institute of Technology- began three years ago to find Jupiter-mass planets around red-giant stars that are typically farther from Earth than those included in most other planet searches.

"This planet is the first one discovered by Penn State astronomers with the Hobby-Eberly Telescope, and it is in one of the most distant of the ten published solar systems discovered around red-giant stars," according to Lawrence Ramsey, a member of the discovery team and the head of the Department of Astronomy and Astrophysics at Penn State.

Astronomers now are branching out with different strategies for searching for planets, with the hope of more quickly detecting life elsewhere in the universe, of discovering all the possible kinds of solar systems, and of learning how they form around different kinds of stars. The Penn State team used one of these new strategies -- searching for planets around giant stars, which have evolved to a later stage of life than our Sun's.

"We have compiled a catalog of nearly a thousand giant stars that are candidates for hosting solar systems," Wolszczan says. Because the method for discovering planets involves repeated measurements of their gravitational effect on the star they circle, and because planets around red giants can take years to make one orbit around the star, the research team is just now beginning to reap discoveries from years of systematic observations.

"It took us 3 years to gather enough data on over 300 stars to start identifying those that are good candidates for having planetary companions," Wolszczan said. "This planet is just the first of a number of planet discoveries that this research program is likely to produce."

One reason for studying red-giant stars is to understand how their habitable zones move farther out as the star's radiating surface becomes bigger. Based on how long it took for life to develop on Earth, scientists speculate that there is more than enough time during a star's giant phase for life to get a start somewhere in the evolving habitable zones. "In our solar system, places like Europa – a satellite of Jupiter that now is covered by a thick layer of water ice -- might warm up enough to support life for more than a billion years or so, over the time when our Sun begins to evolve into a red giant, making life on Earth impossible," Wolszczan said.

Another reason astronomers are trying to discover planets around different kinds of stars at different stages of stellar evolution is to find out how different kinds of planetary systems change when their stars become red giants and how they ultimately end their lives as burnt-out, shrunken white-dwarfs.

"We really are at the very beginning of this effort and it is going to take time to get a consistent picture of planetary formation and evolution," Wolszczan says. "The more we learn, the greater the chance will be that sooner or later we will discover how ordinary or extraordinary is our home -- the Earth's solar system."

Posted by Casey Kazan

Adapted from a Pennsylvania State University news release
"Planet Orbiting a Giant Red Star Discovered with Hobby-Eberly Telescope"