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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 573 #2
January 16, 2002
By Phillip F. Schewe, Ben Stein, and James Riordon

Looking at Extrasolar Planets By Direct Observation
Looking at extrasolar planets by direct observation will be possible soon, says UC-Berkeley astronomer Ray Jayawardhana. Because a star is so much brighter than any planet (viewed from outside our solar system, Jupiter would be only one billionth as bright as the sun), the presence of extrasolar worlds around distant stars has so far been inferred only indirectly, by the slight distortion imparted to the star's spectrum. But with new adaptive optics technology -- which, with computer-controlled flexing of secondary mirrored surfaces, can partly undo the fuzzy distortions of incoming light introduced by atmospheric air currents overhead-attached to the largest optical telescopes, such as the 8.1-m-diameter Gemini North and the 10-m Keck telescopes, the prospect of gaining the needed clarity for seeing planets has improved greatly.

(top left) A normal ground-based infrared image (from the 2MASS survey) shows a wide binary system.
(top right) Gemini adaptive optics partially corrects for blurring by the Earth's atmosphere, resolving one star in the wide binary into a close pair of stars.
(bottom left) A longer exposure with Gemini adaptive optics reveals a fainter extended object near the upper close pair.
(bottom right) A close-up of this faint object shows it to be an edge-on protoplanetary disk.
(Source)
Image Credit: UC-Berkeley/CfA/Gemini Observatory/NOAO/NSF.

At last week's meeting of the American Astronomical Society in Washington, DC, Jayawardhana reported an example of the new, sharper viewing: a picture taken with Gemini showing not yet a planet exactly but a planet in the making near the star MBM12, some 900 light years away. This protoplanetary disk (see NOAO press release) is the first such disk imaged for a four-star system and the first edge-on disk discovered with the help of adaptive optics. Furthermore, this star is still quite young and the disk itself only an estimated 2 million years along on its planet-building mission.

A close-up near-infrared image of the edge-on protoplanetary disk discovered with adaptive optics on the Gemini North telescope. The disk appears as a dark lane down the middle of the object, and the star is hidden behind it. The two nebulosities (or bright areas) on either side of the disk are produced by light from the star reflecting off dust in the top and bottom of the disk.
(Source)
Image Credit: UC-Berkeley/CfA/Gemini Observatory/NOAO/NSF.

It is young star systems like this that offer hope of seeing planets directly since the star-to-planet brightness ratio might be only as little as 100,000. With the higher angular resolution available (80 milli-arcseconds for the case of this disk, which lies at a distance of only 150 AU from the star) from adaptive optics coupled with large ground-based telescopes Jayawardhana believes planets, and not just disks, can be spotted in the next few years. Indeed he referred to some planetary candidates already glimpsed but not yet subjected to the full battery of tests needed for planetary designation-such as observing the planet candidate co-move with its star and recording a spectrum consonant with planets (methane, water, etc.).

Dan