Asteroid Steins: A diamond in the sky (Forwarded)

ESA News
http://www.esa.int

6 September 2008

Steins: A diamond in the sky

The first images from Rosetta's OSIRIS imaging system and VIRTIS infrared
spectrometer were derived from raw data this morning and have delivered
spectacular results.

"Steins looks like a diamond in the sky," said Uwe Keller, Principal
Investigator for the OSIRIS imaging system from the Max Planck Institut Fuer
Sonnensystemforschung, Lindau.

Visible in the image are several small craters on the asteroid, and two huge
ones, one of which is 2 km in diameter, indicating that the asteroid must be
very old.

The images are 50 to 60 pixels in diameter, enough to characterise the shape
and other characteristics of the body of the asteroid.

Rita Schulz, Rosetta Project Scientist, said, "In the images is a chain of
impact craters, which must have formed from recurring impact as the asteroid
rotated. The impact may have been caused by a meteoroid stream, or fragments
from a shattered small body."

The chain is composed of about 7 craters. To determine the age of the
asteroid, a count of the craters on the asteroid's surface has been started
(the more the number of craters, the older the asteroid). So far, 23 craters
have been spotted.

From the images, scientists will try and understand why the asteroid is
unusually bright, and how fine grains of the surface regolith are. This will
tell them more about how the asteroid formed.

Gerhard Schwehm, Mission Manager for Rosetta said, "It looks like a typical
asteroid, but it is really fascinating how much we can learn from just the
images. This is our first science highlight; we certainly have a lot of
promising science ahead of us. I'm already looking forward to encountering
our next diamond in the sky, the much bigger Lutetia."

The OSIRIS imaging system's Wide Angle Camera (WAC) worked perfectly through
the fly-by.

The OSIRIS team expects that the images that they will retrieve from the
Narrow Angle Camera (NAC) will be of comparable resolution. This will add to
the detailed colour information and hence to knowledge of the surface
composition.

Science team members noted that the Narrow Angle Camera (NAC) appears to
have switched to safe mode a few minutes before closest approach, but
switched back on after a few hours. The software is programmed to switch to
safe mode when certain parameter thresholds are crossed to protect the
camera. The team will concentrate investigating the reasons for this anomaly
once the science data has been analysed.

After analysis of the Rosetta data, Steins will be one of the
best-characterised asteroids so far.

[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaCP/SEMNMYO4KKF_index_1.html ]