European Spacecraft Has Weekend Date With Asteroid
ESA’s Rosetta spacecraft flew by asteroid (2867) Steins on 5 September 2008. Steins was Rosetta’s first nominal scientific target. The spacecraft encountered the asteroid in the course of its first incursion into the main asteroid belt located between the orbits of Mars and Jupiter, while on its way to Comet 67P/Churyumov-Gerasimenko.
Credit: ESA, image by C.Carreau

A comet-chasing European space probe has a blind date with an asteroid on Saturday, and will snap the first ever close-up photos of the space rock in a landmark flyby.

The European Space Agency's Rosetta spacecraft is currently on a path to its main target, comet 67P/Churyumov-Gerasimenko. It is expected to arrive at the comet in 2014. But, on July 10, the probe will swoop past a different cosmic object ? the asteroid Lutetia.

On Saturday, Rosetta is expected to fly by Lutetia at a distance of about 1,900 miles (about 3,100 km) at a relative speed of 9 miles per second (15 km/s). The encounter is expected to occur at approximately 3:45 p.m. GMT (11:45 a.m. EDT).

Asteroid pit stop

The Lutetia flyby is an important milestone in Rosetta's long voyage, which began in 2004, and marks a rare chance to observe a primitive asteroid up close, ESA officials said in a statement. [More asteroid photos.]

The close pass will allow Rosetta about two hours of observation time to study the asteroid. Rosetta will rapidly beam this data to Earth, and the first pictures from the quick visit are expected to be released later that evening.

"Little is known about asteroid Lutetia other than it is about 100 kilometers (62 miles) wide," said Claudia Alexander, project scientist for the U.S. role in the Rosetta mission, from NASA's Jet Propulsion Laboratory in Pasadena, Calif.  "Allowing Rosetta's suite of science instruments to focus on this target of opportunity should greatly expand our knowledge of this huge space rock, while at the same time giving the mission's science instruments a real out-of-this-world workout." 

The enigmatic space rock, which is from the main asteroid belt that orbits between Mars and Jupiter, simply appears as little more than a single point of light to ground-based telescopes.

Preliminary observations suggest that Lutetia's continuous variation in brightness indicate that it is rotating and has an uneven surface. These observations have allowed astronomers to estimate the asteroid's shape and size, but their determinations are still varied.

Rosetta could provide more conclusive evidence about the asteroid's dimensions and composition ? another area with more questions than answers.

Next stop: a comet

After encountering Lutetia, Rosetta will not perform scientific activities until it reaches Churyumov-Gerasimenko in May 2014. Once there, it will observe the comet for 18 months, releasing a lander to further explore the comet in November of that year.

Rosetta previously flew by a different asteroid, called Steins, on Sept. 5, 2008, approaching the space rock to within close to 500 miles (800 km). But Lutetia is a much larger asteroid, which is why the spacecraft will glide past at a greater distance. Any closer, and the probe would not be able to fit the entire asteroid into the onboard camera's field of view.

ESA scientists are hoping that the observations from the Lutetia flyby will contribute to the relatively small body of knowledge about asteroids.

The data collected from the Rosetta flyby will provide valuable observations for asteroid science, and will at least give scientists preliminary information that can then be corroborated through ground-based observations. And, the findings will not only apply for Lutetia, but for other asteroids as well.

One hundred and fifteen elementary school students will be at JPL during the flyby. The students will view close-up images of Lutetia, talk to the U.S. Rosetta project manager and participate in educational activities.

The U.S. Rosetta project leaders hope to use this event as a kickoff of more coordinated activities with selected schools around the United States.