Giant planets cling close to their suns, rarely forming great distances from their star. This is the conclusion of a study taking direct images of 70 stars and the planetary systems that surround them.
The Gemini Observatory's Planet-Finding Campaign, the most extensive direct-imaging survey ever performed for alien worlds, was just completed, revealing evidence that giant stars huddle close to their stars. The project used the Gemini South telescope, located in Chile.
"It seems that gas-giant exoplanets are like clinging offspring. Most tend to shun orbital zones far from their parents. In our search, we could have found gas giants beyond orbital distances corresponding to Uranus and Neptune in our own Solar System, but we didn't find any," Michael Liu of the University of Hawaii's and Gemini Planet-Finding Campaign project leader, said.
Since the distances at which various planets form are critical to theories about how star systems form, knowing that giant planets form closer to their suns can further refine models of planetary foundation.
"The two largest planets in our Solar System, Jupiter and Saturn, are huddled close to our Sun, within 10 times the distance between the Earth and Sun. We found that this lack of gas-giant planets in more distant orbits is typical for nearby stars over a wide range of masses," Eric Nielsen of the University of Hawaii, said.
Every rule needs an exception, and the finding that massive planets huddle close to their stars has its own. The star HR 8799 has a family of planets that includes gas giants that orbit between 25-70 times further away from their star than the Earth revolves around the Sun. By comparison, Neptune, the most distant planet in our solar system, lies about 30 times further away from the Sun than our home world. The worlds of HR 8799 were first imaged in 2008 using the Gemini North telescope and the Keck Observatory in Hawaii.
Liu and his team will soon be publishing a pair of papers on their study of other star systems. One will examine the formation of gaps in planetary dust rings. While most astronomers believed that gaps like these are caused by the formation of giant worlds, Liu hypothesizes that small, unseen worlds could be sweeping away the dust. The other article will detail their study of young stars near the Earth. The Gemini team believes that such young systems will have easy-to-find planets.
The study was funded in part by NASA and the National Science Foundation.
