Sign of 'Embryonic Planets' Forming in Nearby Stellar SystemsOctober 02, 2007Astronomers at the University of Rochester are pointing to three nearby stars they say may hold "embryonic planets"-a missing link in planet-formation theories. As scientists try to piece together how our own planet came to be, they look to the forming planets of other star systems for clues. But astronomers have been unable to find evidence for one of the key stages of planet development, a period early in the planet's formation when it is only as large as tiny Pluto. In an attempt to reveal this hidden phase of a planet's life, Alice Quillen, associate professor of astronomy at the University of Rochester, employed new Hubble Space Telescope imagery to measure the thickness of the dust disks that surround forming stars, and to calculate the size of the planets growing within. The results help paint a picture of a planet's earliest years, and tell us how our own small planet probably began its life, says Quillen. Scientists have inferred the presence of nearly 250 planets in the last decade, but Quillen's method focuses on a unique aspect: the proto-planetary disk's thickness. Quillen explains that a disk of gritty dust usually surrounds forming stars, and provides the raw material for planet building. The cloud of dust thins as the system ages, but if enough dust has clumped together, the "embryonic planet," as Quillen calls it, will knock the dust and grit into ever-more eccentric orbits. Over time, this will cause an otherwise razor-thin disk to appear puffed up. "We're able to determine for the first time how large the bodies must be in a disk to scatter the dust the way we've observed," says Quillen, one of the world's leading experts on the interaction between planets and stellar dust disks. Using new Hubble images, Quillen measured the "puffiness" of AU Microscopii, Beta Pictoris, and Fomalhaut-three nearby stars with young disks positioned edge-on toward Earth. All three stars displayed a thicker disk than conventional models anticipated, so Quillen stepped beyond those models. Dust disks have a lifespan determined by a balance of how quickly the solar wind blows the dust away, and how quickly the largest "grit clumps" replenish the dust through their collisions, says Quillen. Based on this balance, the size and age of a disk reveal how large the clumps inside must be. But the conventional theory doesn't take a disk's thickness into account because until the Hubble images, astronomers had no way to measure it. Thus, the largest "clump" the model could predict was about a kilometer wide-a far cry from the fully grown planets that emerge from such disks. Armed with the new images and her own models of dust dynamics, Quillen estimated how much mass was required to gravitationally scatter the dust to the thicknesses she observed. "Those calculations pushed us into Pluto-sized bodies," says Quillen. At roughly 1,000 kilometers in size-and owing to Pluto's recent demotion from planethood-Quillen dubbed these new bodies, embryonic planets. Quillen is now looking for more young star systems to investigate with her model, but the criteria for candidates is quite strict. The systems have to be young enough to still have their protostellar disks, but old enough to be forming the embryonic planets. The systems must also appear edge-on from Earth and be near enough that Hubble can accurately discern the thickness of their disks. At the moment, the three stars Quillen has already observed appear to be the only candidates that meet all the standards. This research was funded in part by the National Science Foundation. The University of Rochester |
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| Related Planet Formation Current Events and Planet Formation News Articles 32 new exoplanets found The latest batch of exoplanets announced today comprises no less than 32 new discoveries. Including these new results, data from HARPS have led to the discovery of more than 75 exoplanets in 30 different planetary systems. Dirty stars make good solar system hosts Some stars are lonely behemoths, with no surrounding planets or asteroids, while others sport a skirt of attendant planetary bodies. New research published this week in The Astrophysical Journal Letters explains why the composition of the stars often indicates whether their light shines into deep space, or whether a small fraction shines onto orbiting planets. Twin Keck Telescopes Probe Dual Dust Disks Astronomers using the twin 10-meter telescopes at the W. M. Keck Observatory in Hawaii have explored one of the most compact dust disks ever resolved around another star. James Webb Space Telescope Begins to Take Shape at Goddard NASA's James Webb Space Telescope is starting to come together. A major component of the telescope, the Integrated Science Instrument Module structure, recently arrived at NASA Goddard Space Flight Center in Greenbelt, Md. for testing in the Spacecraft Systems Development and Integration Facility. Trigger-happy star formation A new study from two of NASA's Great Observatories provides fresh insight into how some stars are born, along with a beautiful new image of a stellar nursery in our Galaxy. Primitive asteroids in the main asteroid belt may have formed far from the sun Many of the objects found today in the asteroid belt located between the orbits of Mars and Jupiter may have formed in the outermost reaches of the solar system. University of Hawaii at Manoa astronomers discover pair of solar systems in the making Two University of Hawai'i at Mānoa astronomers have found a binary star-disk system in which each star is surrounded by the kind of dust disk that is frequently the precursor of a planetary system. Radio telescope images reveal planet-forming disk orbiting twin suns Astronomers are announcing today that a sequence of images collected with the Smithsonian's Submillimeter Array (SMA) clearly reveals the presence of a rotating molecular disk orbiting the young binary star system V4046 Sagittarii. AAAS, leading Texas scientists urge state board to reject anti-evolution effort Leading members of the Texas scientific community, in collaboration with the American Association for the Advancement of Science (AAAS), have urged the Texas State Board of Education to reject amendments to the state's draft science standards that would undermine sound science teaching. Jupiter-like Planets Could Form Around Twin Suns Life on a planet ruled by two suns might be a little complicated. Two sunrises, two sunsets. Twice the radiation field. More Planet Formation Current Events and Planet Formation News Articles |
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