* Astronomy

New observations made with the Spitzer Space Telescope of a young star show that it is like our own solar system when it was forming.

The star is surrounded by a disk of dust, the sort of "protoplanetary" disk from which planets formed around our Sun, according to theory. In the disk is a gap that astronomers say likely was formed by one or more giant gas planets.

The thinking is that when giant planets develop, they gather the dust from their orbital path, sweeping clean a region of space around the star.
Excess emissions at near-IR wavelengths detected by the Spitzer Space Telescope can be explained with a 300 AU, 0.047 solar mass disk that is cleared of material out to 4AU from the star. Dynamical models of planets interacting with disks show that such a gap may be formed by a 2 Jupiter mass planet orbiting at 2.5 AU.
The planets have not been imaged.

Similar star systems have been seen around other stars, but few have been so young. This is the first evidence for a planet around a star so young that is also Sun-like.
The star, GM Aurigae is 1.05 times as massive as the Sun, and about 420 light-years away.


Image source
Position (2000): RA = 04 55 10.2 DEC = +30 21 58

The K5V:e T Tau-type star is just a million years old.

If the system were overlaid onto our own solar system, the newly discovered gap would extend roughly from the orbit of Jupiter to the orbit of Uranus.

"GM Aurigae is essentially a much younger version of our Sun, and the gap in its disk is about the same size as the space occupied by our own giant planets. Looking at it is like looking at baby pictures of our Sun and outer solar system" - Dan Watson, professor of physics and astronomy at the University of Rochester.

The finding, along with a similar one last year, has astronomers puzzled that large planets could form so quickly.
Conventional theory holds that all planets form first as a rocky core. Earth and the other three terrestrial planets stopped there. But the gas giants then use an ever-building core to begin to attract an vast envelope of gas and dust.
An alternative theory says that rocky planets form in the conventional way, but gas giants don't. Instead, they collapse, over a few thousand years, out of a knot in the ring of gas and dust.

"The results pose a challenge to existing theories of giant-planet formation, especially those in which planets build up gradually over millions of years. Studies like this one will ultimately help us better understand how our outer planets, as well as others in the universe, form" - Nuria Calvet, professor of astronomy at the University of Michigan and lead author of a paper on the results in the Sept. 10 issue of Astrophysical Journal Letters.

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