Mountain Views News          Saturday, June 26, 2010

8

The World Around Us

 Mountain Views News Saturday, June 26, 2010


Rosetta’s Blind Date With Asteroid Lutetia

 The European Space Agency’s comet-chaser 
Rosetta is heading for a blind date with asteroid 
Lutetia. Rosetta does not yet know what Lutetia 
looks like—but beautiful or otherwise, the two 
will meet on July 10.

 Like many first dates, Rosetta will meet Lutetia 
on a Saturday night, flying to within 2,000 
miles of the space rock. Rosetta started taking 
navigational sightings of Lutetia at the end of 
May so that ground controllers could determine 
any course corrections required to achieve their 
intended flyby distance.

 The close pass will allow around two hours of 
rendezvous (good imaging). The spacecraft will 
instantly begin beaming the data back to Earth 
and the first pictures will be released later that 
evening.

 Rosetta flew past asteroid Steins in 2008, and 
other space missions have encountered a handful 
of asteroids. Each asteroid has proven to be an 
individual, and Lutetia is expected to continue the 
trend.

 For a start, no one knows what Lutetia looks 
like. Orbiting in the main belt of asteroids 
between Mars and Jupiter, it appears as a 
single point of light to ground telescopes. The 
continuous variation in its brightness makes it 
clear that Lutetia is rotating and has an uneven 
surface. These observations allow astronomers to 
estimate its shape

and size, but their determinations all differ.

 Initially it was thought that Lutetia is around 
55 miles in diameter but only mildly elliptical. A 
more recent estimate suggests 80 miles, with a 
pronounced elongation. Rosetta will tell us for 
certain and will also investigate the composition 
of the asteroid—and herein lies another mystery.

 Planetary scientists believe that Lutetia is a 
primitive asteroid, left unchanged for billions of 
years because no planet consumed it as the Solar 
System formed. Indeed, most measurements 
appear to back this picture, making the asteroid 
out to be a “C-type,” which contains primitive 
compounds of carbon.

 However, some measurements suggest that 
Lutetia is an “M-type,” which could mean there 
are metals in its surface. “If Lutetia is a metallic 
asteroid, then we have found a real winner,” says 
Rita Schulz, Rosetta Project Scientist for the 
Paris-based European Space Agency (ESA).

 That is because although metallic asteroids 
do exist, they are thought to be fragments of the 
metallic cores of larger asteroids that have since 
been shattered into pieces. If Lutetia is made of 
metal or even contains large amounts of metal, 
Dr. Schulz says that the traditional asteroid 
classification scheme will need rethinking. 
“C-class asteroids should not have metals on their 
surfaces,” she says.

 Asteroid science stands to gain once this 
observational conundrum is resolved, because 
Rosetta’s data will provide a valuable collection 
of “ground truths” that can be used to resolve 
conflicting Earth-based observations, not just for 
Lutetia but for other asteroids as well.

 For 36 hours around the moment of closest 
approach, Rosetta will be in almost continuous 
contact with the ground. The only breaks will 
come as Earth rotates and engineers have to 
switch from one tracking station to another.

 Good contact is essential because the 
uncertainties in the asteroid’s position and shape 
may demand last minute fine-tuning to keep it 
centered in Rosetta’s instruments during the flyby. 
“The skeleton of the operation is in place, and we 
have the ability to update our plans at any time,” 
says Andrea Accomazzo, ESA Rosetta Spacecraft 
Operations Manager.

 Stay in touch with the flyby as it happens, by 
visiting the Rosetta blog: http://webservices.esa.
int/blog/blog/5/

You can contact Bob Eklund at: b.eklund@
MtnViewsNews.com.


Rosetta encountered asteroid Steins in 2008


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