ESO/L. Calçada

ScienceShot: Birth of a Planet

Observations of a nearby star at infrared wavelengths may capture the ongoing birth of a planet. The star, known as HD 100546, lies about 335 light-years from Earth in the southern constellation Musca ("The Fly") and is surrounded by a thick disk of gas and dust. Structures in the disk indicate that the purported protoplanet hasn't cleared its neighborhood of gas and dust, making the new observations the first of such an object so early in its formation. Previous analyses of the star's spectra suggest the object, which is about 2.5 times the mass of our sun, formed only a few million years ago. The protoplanet, which orbits about 10 billion kilometers from its parent star—about 68 times the distance between Earth and our sun—shows up as a bright spot embedded in the much-cooler gas in its neighborhood (artist's concept). The protoplanet is now between one-half and three times the mass of Jupiter but will undoubtedly continue to grow as it accumulates dust and gas from the disk. It's possible, but not likely, that the bright spot represents an object located far beyond but directly behind the disc surrounding HD 100546, researchers report online today in The Astrophysical Journal Letters. It's also possible but unlikely that the protoplanet is an object recently ejected from a closer orbit around its star, the researchers say. Further observations of the object—which, if really a protoplanet, orbits its parent star about once every 360 years—will reveal its true nature.

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