Distant Gas-Giant Exoplanets Cling to Their Parent Stars Like Needy Children

Exoplanets are being found every day. Located far from our solar system, these planets orbit their parent stars and hold the promise for better understanding our universe. Some of these extrasolar planets, though, are distant gas-giants, massive planets similar to Jupiter and Saturn. Now, astronomers have discovered that despite being so large, these planets prefer to cling to their parent star,

Astronomers have been examining exoplanets for years now. More specifically, they're examining data from Gemini Observatory's recently completed Planet-Finding Campaign. The effort was the deepest and most extensive direct imaging survey to date--and provided scientists with quite a bit of information about gas-giant exoplanets.

"It seems that gas-giant exoplanets are like clinging offspring," said Michael Liu of the University of Hawaii's Institute for Astronomy in a news release. "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."

The scientists found that despite their size, most gas giants huddle near their stars. In our own Solar System, Jupiter and Saturn, two of the largest planets, huddle relatively close to our sun. Yet not all gas-giant exoplanets remain close to their stars.

Using the Gemini North telescope and W.M. Keck Observatory, the scientists found a family of planets around the star HR 8799. The gas-giant planets that they found were at a large orbital separation--about 25 to 70 times the Earth-Sun distance. At the time, the scientists believed that this showed gas-giants appeared at a range of distances from their parent stars. Now, though, they're realizing that this particular finding is uncommon.

"We've known for nearly 20 years that gas-giant planets exist around other stars, at least orbiting close in," said Liu in a news release. "Thanks to leaps in direct imaging methods, we can now learn how far away planets can typically reside. The answer is that they usually avoid significant areas of real estate around their host stars. The early findings, like HR 8799, probably skewed our perceptions."

The findings are huge for better understanding exoplanets and planet formation. More specifically, they show how gas-giant exoplanets are usually close to their stars rather than further away. This, in turn, reveals a little bit more about how galaxies and systems first form.