Rosetta before rendezvous with asteroid stones

Spacecraft investigates unusual celestial bodies

Comet probe Rosetta DLR
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The ESA Rosetta spacecraft will fly past a special "landmark" tomorrow after four and a half years in space: only about 800 kilometers will separate the probe from the asteroid stone at 20:58 Central European Summer Time (CEST). For the first time, the encounter gives researchers the opportunity to closely examine a celestial body of this type. The astronomers also expect important new insights into the nursery of the solar system.

Before, during and after the greatest rapprochement Rosetta will carry out numerous scientific experiments. The necessary images will be supplied by the OSIRIS camera system, which was developed and built under the auspices of the Max Planck Institute for Solar System Research (MPS) by a European consortium.

Since March 2, 2004 Rosetta is on her way to her real destination, the comet Churyumov-Gerasimenko. Currently, the probe brings momentum through several swing-by maneuvers for their long journey. She is now passing the still unexplored asteroid stone, the first important scientific goal of the ten-year mission.

Original components of the solar system

In particular, the composition of the body and the surface, the size and rotation, the magnetic and electrical properties and the characteristics of the environment such as gas, dust and small bodies are of interest. The meticulously prepared maneuver has been carried out by the control center of the European Space Agency ESA in Darmstadt, where the first pictures and measurements will arrive on Saturday night.

DLR is involved in the mission with numerous scientists. Especially in Berlin and Cologne, they will be active during the flyby to record the data. "Comets and asteroids are among the most primal constituents of the approximately 4.6-billion-year-old solar system, " explains Professor Tilman Spohn, director of the DLR Institute for Planetary Research in Berlin-Adlershof: "From their investigation, we expect fundamental knowledge about education the planets and moons. The sometimes very complex composition of the small bodies could also provide important clues as to how life originated on Earth ". display

Camera helps with navigation

A drawing of the spacecraft Rosetta. The two parts of the OSIRIS camera system are marked in red. ESA / AOES Medialab

In the attempt to bring Rosetta safely to the destination, the camera system OSIRIS also provides important services. Although most of the gauges on board the spacecraft will be operational shortly before the arrival of the asteroid, OSIRIS has already awakened from its sleep on 4 August 2008. Since then, the camera plays a crucial role in determining the orbit of the asteroid and adjusting its own flight path. For example, on 14 August, ESA corrected the course of the spacecraft solely on the basis of camera images. More manovers of this kind are planned.

This is a novelty for ESA. Until now, the European space agency used on-board navigation and radio signals to navigate space. "The exceptional quality of the OSIRIS camera, especially its spatial resolution, has allowed us to calculate in this precision, " says Andrea Accomazzo from the control center of the ESA in Darmstadt with regard to the course correction.

One turn around its own axis in six hours

From the 50 or so camera images available so far, the scientists have already seen some of Steins' first characteristics: The asteroid takes about six hours to turn around its own axis and has an irregular shape ige Form, says OSIRIS project manager Horst Uwe Keller. The diameter of Steins is estimated at about five kilometers.

The researchers still have to wait until September 5, 2008 for more detailed information. Then OSIRIS will also provide information about the brightness and shape of the asteroid. With a resolution of 15 meters per pixel, the camera even allows you to precisely examine the surface texture of Steins in flyby.

A rare class of asteroids

In order to fulfill their very different tasks, OSIRIS consists of two instruments: a wide-angle and a tele-camera. While one searches the surroundings of Steins for Moons, the other, thanks to its large field of view, can continuously observe the entire asteroid at high resolution.

On the ten-year path of the probe to the comet Churyumov / Gerasimenko, the camera system has already proven itself in passing by Mars and Earth. However, the upcoming task in the encounter with Steins is also new territory for OSIRIS. "Steins is a rare class of asteroids, " explains Holger Sierks, head of the OSIRIS team at the MPS.

New insights about the early solar system

Unlike most asteroids, Stein's evidence suggests that its surface contains enstatite. This mineral is composed of magnesium, silicon and oxygen. Since asteroids as well as the planets were formed about 4.6 billion years ago, the scientists hope for Stein's new insights into the early solar system.

In addition to the camera system OSIRIS, the MPS is involved in six other instruments on board Rosetta. During the upcoming encounter with Steins, a mass spectrometer and a microwave instrument will also investigate the surroundings of the asteroid.

(Max Planck Institute for Solar System Research / DLR, 04.09.2008 - DLO)