FRANKFURT, Germany (AP) - Scientists at the European Space Agency are preparing for the first fly-by of an asteroid by their deep-space explorer, Rosetta, on a mission to solve the mystery of the birth of the solar system.

Rosetta is set to rendezvous with the Steins asteroid, also known as Asteroid 2867, just before 3 p.m. EDT Friday at a distance of just less than 500 miles. The craft, launched in March 2005, is some 250 million miles away from Earth.

Once it flies by the irregularly shaped asteroid, it will begin taking images and measurements.

The data and pictures will be sent to ESA's Darmstadt control room and laboratories. They will be analyzed and unveiled to the world on Saturday.

"Once we learn more about asteroids and comets, we have reached another big step in understanding how planets are formed too," said Gerhard Schwehm, the Rosetta mission manager at ESA.

The timing of the flyby means that the asteroid will be illuminated by the sun, making it likely the transmitted images will be clear and concise.

Astronomers have had to work with limited data from brief flybys, such as when ESA's Giotto probe swept by Halley's Comet in 1986, photographing long canyons, broad craters and 3,000-foot hills.

Steins is Rosetta's first scientific target as it makes its incursion into the asteroid belt located between the orbits of Mars and Jupiter en route to its destination, the comet 67/P Churyumov-Gerasimenko, which is scheduled for 2014.

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