BY DR EMILY BALDWIN
Posted: 06 January, 2009
According to a new study of planet formation around young stars, gas giants have to form in under five million years, or they probably won’t form at all.
Just like the festive period for Earthlings can be a time of putting on a few pounds, the first few million years of Jupiter’s life also saw it gaining weight in a hurry, before essential planetary building ingredients were exhausted.
This photograph from NASA's Spitzer Space Telescope shows the young star cluster NGC 2362. By studying it, astronomers found that gas giant planet formation happens very rapidly and efficiently, within less than 5 million years, meaning that Jupiter-like worlds experience a growth spurt in their infancy. Image: NASA/JPL-Caltech/T. Currie (CfA).
Smithsonian astronomers examined a five million year old star cluster known as NGC 2362 with NASA's Spitzer Space Telescope, which can detect the signatures of actively forming planets in infrared light. They found that all stars with the mass of the Sun or greater had lost their planet-forming discs, with only a few stars less massive than the Sun retaining their discs. These proto-planetary discs provide the raw materials for forming gas giants like Jupiter.
"Even though astronomers have detected hundreds of Jupiter-mass planets around other stars, our results suggest that such planets must form extremely fast,” says lead researcher Thayne Currie of the Harvard-Smithsonian Center for Astrophysics. “Whatever process is responsible for forming Jupiters has to be incredibly efficient."
Even though nearly all gas giant-forming discs in NGC 2362 have disappeared, several stars in the cluster have debris discs, which indicates that smaller rocky or icy bodies such as Earth, Mars, or Pluto may still be forming. "The Earth got going sooner, but Jupiter finished first, thanks to a big growth spurt," says co-author Scott Kenyon. The astronomers say that while Earth took about 20 to 30 million years to reach its final mass, Jupiter was fully grown in only 2 to 3 million years.
Previous studies indicated that protoplanetary discs disappear within 10 million years and so the new findings put even tighter constraints on the time available to create gas giant planets around stars of various masses.
The research was presented at the American Astronomical Society meeting in Long Beach, California, this week.