A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus

The Trojan population consists of two swarms of asteroids following the same orbit as Jupiter and located at the L4 and L5 Lagrange points of the Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid 617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit of this double system was hitherto unknown. Here we report that the components, separated by 680 km, move around the system centre of mass, describing roughly a circular orbit. Using the orbital parameters, combined with thermal measurements to estimate the size of the components, we derive a very low density of 0.8 g/cc. The components of Patroclus are therefore very porous or composed mostly of water ice, suggesting that they could have been formed in the outer part of the solar system.Comment: 10 pages, 3 figures, 1 tabl

A URI-based approach for addressing fragments of media resources on the Web

To make media resources a prime citizen on the Web, we have to go beyond simply replicating digital media files. The Web is based on hyperlinks between Web resources, and that includes hyperlinking out of resources (e.g., from a word or an image within a Web page) as well as hyperlinking into resources (e.g., fragment URIs into Web pages). To turn video and audio into hypervideo and hyperaudio, we need to enable hyperlinking into and out of them. The W3C Media Fragments Working Group is taking on the challenge to further embrace W3C's mission to lead the World Wide Web to its full potential by developing a Media Fragment protocol and guidelines that ensure the long-term growth of the Web. The major contribution of this paper is the introduction of Media Fragments as a media-format independent, standard means of addressing media resources using URIs. Moreover, we explain how the HTTP protocol can be used and extended to serve Media Fragments and what the impact is for current Web-enabled media formats

The Orbit of 617 Patroclus Binary Trojan System from Keck LGS AO observations

International audienceWe report the results from Laser Guide Star Adaptive Optics observations in 2004-2005 of 617 Patroclus using the NIRC2 camera at the W. M. Keck Observatory. An observing campaign which focuses on this only known binary Trojan asteroid, was initiated by our group. Both components of the system were detected at 5 different epochs between Nov. 2004 and May 2005 with an angular separation between 45 and 190 mas and a Dm ˜0.17. The orbital parameters were estimated independently using two algorithms, a Monte-Carlo technique (Hestroffer and Vachier, IAU-ACM, 2005), and a visual binary method (Descamps, Cel. Mech., 2005): a= 685±40 km, e = 0.02±0.02, P = 4.287±0.002 or P= 2.391±0.003 corresponding to a total mass of 1.4 x 1018 or 4.3 x 1018 ± 0.2 kg. Considering recent radiometric measurements by Fernandez et al., (AJ, 126, 2003), the radii of components would be R1= 60.9 km and R2=56.3 km (error ˜1.6 km and with eta =0.94), leading to an averaged bulk density of 0.8 or 2.6 ±0.1 g/cm3. The factor of ˜2 uncertainty in the period will be removed using additional observations from CADC archive (in progress)

The Orbit of 617 Patroclus Binary Trojan System from Keck LGS AO observations

International audienceWe report the results from Laser Guide Star Adaptive Optics observations in 2004-2005 of 617 Patroclus using the NIRC2 camera at the W. M. Keck Observatory. An observing campaign which focuses on this only known binary Trojan asteroid, was initiated by our group. Both components of the system were detected at 5 different epochs between Nov. 2004 and May 2005 with an angular separation between 45 and 190 mas and a Dm ˜0.17. The orbital parameters were estimated independently using two algorithms, a Monte-Carlo technique (Hestroffer and Vachier, IAU-ACM, 2005), and a visual binary method (Descamps, Cel. Mech., 2005): a= 685±40 km, e = 0.02±0.02, P = 4.287±0.002 or P= 2.391±0.003 corresponding to a total mass of 1.4 x 1018 or 4.3 x 1018 ± 0.2 kg. Considering recent radiometric measurements by Fernandez et al., (AJ, 126, 2003), the radii of components would be R1= 60.9 km and R2=56.3 km (error ˜1.6 km and with eta =0.94), leading to an averaged bulk density of 0.8 or 2.6 ±0.1 g/cm3. The factor of ˜2 uncertainty in the period will be removed using additional observations from CADC archive (in progress)