The Case of the Disappearing Planetary Disks

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After examining the 5-million-year old star cluster NGC 2362, astronomers say that planets like Jupiter must form quickly because the material that form giant gas planets disappears in just few million years in young protoplanetary (planet forming) systems. Using NASA’s Spitzer Space Telescope, astronomers from the Smithsonian Center for Astrophysics found that all stars in this cluster with the mass of the Sun or greater have lost their protoplanetary disks, and only a few stars less massive than the Sun retain their protoplanetary disks. These disks provide the raw material for forming gas giants like Jupiter. Therefore, gas giant planets have to form in less than 5 million years or they probably won’t form at all. However, the material to form rocky terrestrial planets like Earth appears to stick around much longer.

“Even though astronomers have detected hundreds of Jupiter-mass planets around other stars, our results suggest that such planets must form extremely fast. Whatever process is responsible for forming Jupiters has to be incredibly efficient,” said lead researcher Thayne Currie of the Harvard-Smithsonian Center for Astrophysics. Currie presented the team’s findings at a meeting of the American Astronomical Society in Long Beach, California.

Even though nearly all gas giant-forming disks in NGC 2362 have disappeared, several stars in the cluster have “debris disks,” 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,” explained co-author Scott Kenyon.

Kenyon added 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 disks disappear within 10 million years. The new findings put even tighter constraints on the time available to create gas giant planets around stars of various masses.

Source: Harvard Smithsonian Center for Astrophysics