The Age of Jupiter

Our solar system is believed to have formed from a vast cloud of primordial gas, dust and ice particles about 4.6 billion years ago. A nearby supernova may have jolted the cloud, making it swirl and condense. The sun, whose mass NASA estimates at 99.8 percent of all mass in this star system, burned at the center of a debris field called a protoplanetary disk, where planets built up as rocks and gas clumped together.

Earth started to accumulate material sooner than Jupiter and took 20 to 30 million years to reach its present size, according to the Harvard-Smithsonian Center for Astrophysics. Jupiter, that vast oblate sphere, could accommodate 1,300 Earths.

Question: How long did Jupiter take to reach its full growth? About 1,300 times 20 million years?

[A photo I took of Jupiter on the morning of March 20, 2004]

According to the center, Jupiter reached its present girth in only 2 or 3 million years. A press release dated Jan. 9 adds, “The planet Jupiter gained weight in a hurry during its infancy. It had to, since the material from which it formed probably disappeared in just a few million years, according to a new study of planet formation around young stars.”

A star cluster in the Canis Major constellation, NGC 2362, is believed to be only 5 million years old, the release says. (Some sites on the Internet give its age as 25 million years.)

Studying images collected by the orbiting Spitzer infrared telescope, center astronomers found that all of NGC 2362 stars of our sun’s mass, or greater, had lost their proplanetary disks. These disks are “the raw material for forming gas giants like Jupiter,” the release says.

“Even though astronomers have detected hundreds of Jupiter-mass planets around other stars, our results suggest that such planets must form extremely fast,” said the center’s Thayne Currie, lead researcher in the project, quoted in the press release.

“The Earth got going sooner, but Jupiter finished first, thanks to a big growth spurt,” added Scott Kenyon, co-author of the report.

[This photograph by NASA’s Spitzer Space Telescope shows the young star cluster NGC 2362. Photo credit: NASA/JPL-Caltech/T. Currie (Harvard-Smithsonian Center for Astrophysics)]

The center, located in Cambridge, Mass., is operated by the Smithsonian Astrophysical Observatory and the Harvard College Observatory. The report on formation of Jupiter-size planets was delivered at a meeting of the American Astronomical Society in Long Beach, Calif.

Europa, one of the moons that Galileo spotted circling Jupiter, is considered one of the best, if not the best, place in the solar system for extraterrestrial life. Beneath a massive ice crust is an ocean of liquid water, heated by interactions with the huge planet. If Jupiter and its attendants are older than Earth, maybe life beneath the ice has been evolving there longer than here.

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