* Astronomy

Blobrana · L

Comet 67P/Churyumov-Gerasimenko

Blobrana · L

Rosetta's first glimpse of the comet

Three years before its arrival the camera system on board the space probe Rosetta renders the first images of its destination.

Approximately 163 million kilometres still separate ESA's spacecraft Rosetta from comet Churyumov-Gerasimenko, its 2014 target. Despite this remarkable distance, scientists from the Max Planck Institute for Solar System Research (MPS) in Germany have succeeded in obtaining the first images of the remote destination using the onboard camera system OSIRIS. These pictures were generated during the tests performed by the team during the last weeks. After the successful completion of these tests, Rosetta will now start its almost three year hibernation period: In order to save energy on the last part of the way offering only little sunlight, all systems will be powered down.

Blobrana · L

Surface illumination model of the nucleus of comet Churyumov-Gerasimenko approximately 3 AU from the Sun.

Blobrana · L

Title: The Dust Trail of Comet 67P/Churyumov-Gerasimenko between 2004 and 2006
Authors: Jessica Agarwal, Michael Mueller, William T. Reach, Mark V. Sykes, Hermann Boehnhardt, Eberhard Gruen

We report on observations of the dust trail of comet 67P/Churyumov-Gerasimenko (CG) in visible light with the Wide Field Imager at the ESO/MPG 2.2m telescope at 4.7 AU before aphelion, and at 24 micron with the MIPS instrument on board the Spitzer Space Telescope at 5.7 AU both before and after aphelion. The comet did not appear to be active during our observations. Our images probe large dust grains emitted from the comet that have a radiation pressure parameter beta<0.01. We compare our observations with simulated images generated with a dynamical model of the cometary dust and constrain the emission speeds, size distribution, production rate and geometric albedo of the dust. We achieve the best fit to our data with a differential size distribution exponent of -4.1, and emission speeds for a beta=0.01 particle of 25 m/s at perihelion and 2 m/s at 3 AU. The dust production rate in our model is on the order of 1000 kg/s at perihelion and 1 kg/s at 3 AU, and we require a dust geometric albedo between 0.022 and 0.044. The production rates of large (>10 micron) particles required to reproduce the brightness of the trail are sufficient to also account for the coma brightness observed while the comet was inside 3 AU, and we infer that the cross-section in the coma of CG may be dominated by grains of the order of 60-600 micron.

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Blobrana · L

Title: The Dust Trail of Comet 67P/Churyumov-Gerasimenko
Authors: Michael S. Kelley, William T. Reach, David J. Lien

We report the detection of comet 67P/Churyumov-Gerasimenko's dust trail and nucleus in 24 micron Spitzer Space Telescope images taken February 2004. The dust trail is not found in optical Palomar images taken June 2003. Both the optical and infrared images show a distinct neck-line tail structure, offset from the projected orbit of the comet. We compare our observations to simulated images using a Monte Carlo approach and a dynamical model for comet dust. We estimate the trail to be at least one orbit old (6.6 years) and consist of particles of size >~100 micron. The neck-line is composed of similar sized particles, particles of size but younger in age. Together, our observations and simulations suggest grains 100 micron and larger in size dominate the total mass ejected from the comet. The radiometric effective radius of the nucleus is 1.87 ± 0.08 km, derived from the Spitzer observation. The Rosetta spacecraft is expected to arrive at and orbit this comet in 2014. Assuming the trail is comprised solely of 1 mm radius grains, we compute a low probability (~10^-3) of a trail grain impacting with Rosetta during approach and orbit insertion.

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