Giant Planets Form Quick or Not At All

For those doing extra-terrestrial projects, this is an interesting article about how other planets form. It states that planets the size of Jupiter form quickly or don't form at all. By quickly they are talking a few billion years. Earth will obviously never be as big as Jupiter. But talking about other worlds out there, just to be a little more on the scientific side, this helps out.

http://dsc.discovery.com/news/2009/01/08/jupiter-planets.html

Jupiter-Sized Planets Grow Up Fast
Irene Klotz, Discovery News

Jan. 8, 2008 -- Compared to small, rocky worlds like Earth, Jupiter-class gas giant planets form quickly or not at all, a new study shows.

The realization stems from studies of a five-million-year-old star cluster in the constellation Canis Major made with NASA's Spitzer infrared space telescope. Scientists discovered that all stars in the cluster that were as least as big as the sun had no accompanying disks of gas and dust from which to make gas giants like Jupiter.

Only a few stars in the cluster that were smaller than the sun still had protoplanetary disks, though several did still have debris remnants that could be used to build smaller rocky bodies like Earth or Mars or icy worlds like Pluto, say researchers with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Extrapolating from the data, scientists conclude that while a planet like Earth took 20 million to 30 million years to evolve, Jupiter was fully grown in a fraction of the time, just two million to three million years.

"We have an understanding of how star formation proceeds, and our own star should not be an exception to that. It is the assumption that our solar system should not be special," said lead researcher Thayne Currie, who presented the team's findings at the American Astronomical Society meeting under way this week in Long Beach, Calif.

The cluster studied by Currie and his colleagues, NGC 2362, is located about 4,500 light-years away from Earth -- too far to be probed with current technologies to determine if any of its stars harbor planets, Currie told Discovery News.

The research builds on earlier findings from a team led by University of Arizona astronomer Ilaria Pascucci that probed 15 sun-like stars, ranging in age from three million to 30 million years old, for gas that could be used to form Jupiter-like planets. They discovered that all the stars, even the very young ones, have less than 10 percent of Jupiter's mass in gas swirling around them, indicating that the giant worlds either had already formed or they were not to be.

Currie's team says the window of opportunity for stars to form Jupiter-class worlds is even smaller, less than five million years.

"Whatever process is responsible for forming Jupiters has to be incredibly efficient," Currie said.
Scientists have two leading theories for how planets like Jupiter form: by building up a solid core which gases then accrete on to or from gases that collapse in on themselves due to gravitational forces.

If the second theory is correct, Jupiter-sized worlds could form in just thousands to tens of thousands of years, said University of Washington astrophysicist Thomas Quinn, who has done computer modeling of planetary formation.

"There's still an ongoing debate about exactly what the time scale would be," he said.