* Astronomy

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20:00 UT, 25th December, 2007.

Rocky terrestrial planets, perhaps like Earth, Mars or Venus, appear to be forming or to have recently formed around a star in the Pleiades ("seven sisters") star cluster, the result of "monster collisions" of planets or planetary embryos.
 Astronomers using the Gemini Observatory in Hawaii and the Spitzer Space Telescope report their findings in an upcoming issue of the Astrophysical Journal, the premier journal in astronomy.
 
"This is the first clear evidence for planet formation in the Pleiades, and the results we are presenting may well be the first observational evidence that terrestrial planets like those in our solar system are quite common" - Joseph Rhee, a UCLA postdoctoral scholar in astronomy and lead author of the research.
 
Although referred to as the "seven sisters," "the cluster actually contains some 1,400 stars" - co-author Inseok Song, a staff scientist at NASA's Spitzer Science Centre at the California Institute of Technology and a former astronomer with the Gemini Observatory.
 
Located about 400 light-years away, the Pleiades is one of the closest star clusters to Earth. One of the cluster's stars, known as HD 23514, which has a mass and luminosity a bit greater than those of the sun, is surrounded by an extraordinary number of hot dust particles.

"hundreds of thousands of times as much dust as around our sun. The dust must be the debris from a monster collision, a cosmic catastrophe" - Benjamin Zuckerman.
 
The astronomers analysed emissions from countless microscopic dust particles and concluded that the most likely explanation is that the particles are debris from the violent collision of planets or planetary embryos.

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The Pleiades


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Exposure: 10 sec
Time: 3:46 GMT, 23 August, 2007.

Title: A wide deep infrared look at the Pleiades with UKIDSS: new constraints on the substellar binary fraction and the low mass IMF
Authors: N. Lodieu (1 and 2), P. D. Dobbie (3 and 2), N. R. Deacon (4), S. T. Hodgkin (5), N. C. Hambly (6), R. F. Jameson (2) ((1) IAC, Tenerife, (2) Leicester, UK, (3) AAO, Australia, (4) Radboud University Nijmegen, (5) IoA, Cambridge, UK, (6) SUPA, ROE, Edinburgh, UK)

We present the results of a deep wide-field near-infrared survey of 12 square degrees of the Pleiades conducted as part of the UKIDSS Deep Infrared Sky Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high probability proper motion members down to 0.03 solar masses using a combination of UKIDSS photometry and proper motion measurements obtained by cross-correlating the GCS with data from the Two Micron All Sky Survey (2MASS), the Isaac Newton (INT) and the Canada-France-Hawai'i (CFHT) telescopes. Additionally, we have unearthed 73 new candidate brown dwarf members on the basis of five band UKIDSS photometry alone. We have identified 23 substellar multiple system candidates out of 63 candidate brown dwarfs from the (Y-K,Y) and (J-K,J) colour-magnitude diagrams, yielding a binary frequency of 28-44% in the 0.075-0.030 Msun mass range. Our estimate is three times larger than the binary fractions reported from high-resolution imaging surveys of field ultracool dwarfs and Pleiades brown dwarfs. However, it is marginally consistent with our earlier ``peculiar'' photometric binary fraction of 50+/-10% presented in Pinfield et al. (2003), in good agreement with the 32-45% binary fraction derived from the recent Monte-Carlo simulations of Maxted & Jeffries (2005) and compatible with the 26+/-10% frequency recently estimated by Basri & Reiners (2006). A tentative estimate of the mass ratios from photometry alone seems to support the hypothesis that binary brown dwarfs tend to reside in near equal-mass ratio systems.

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