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European Space Agency Rosetta Satellite Scans Asteroid

By | September 8, 2008

      The European Space Agency (ESA) spacecraft Rosetta took a close look at an asteroid called Steins, which floats in the asteroid belt, ESA announced.

      Rosetta approached asteroid 2867 Steins, coming to within a distance of only 800 kilometers (497.1 miles) from it.

      Steins is Rosetta’s first nominal scientific target in its 11-plus-years mission culminating in an exploration of the nucleus of Comet 67P/Churyumov-Gerasimenko.

      The success of the close encounter with Steins was confirmed when ESA’s ground control team at the European Space Operations Centre (ESOC) in Darmstadt, Germany, received initial telemetry from the spacecraft.

      During the flyby operations, Rosetta was out of reach from communication links because its antenna had to be turned away from Earth. At a distance of about 2.41 AU (360 million kilometers, or 223.7 million miles) from Earth, the radio signal from the probe took 20 minutes to reach the ground.

      Steins is a small asteroid of irregular shape with a diameter of only 4.6 kilometers (2.9 miles). It belongs to the rare class of E-type asteroids, which had not been directly observed by an interplanetary spacecraft before.

      Such asteroids are quite small in size and orbit and are mostly found in the inner part of the main asteroid belt located between Mars and Jupiter. They probably originate from the mantle of larger asteroids destroyed in the early history of the solar system, and are thought to be composed mainly of silicate minerals with little or no iron content.

      Data collected by Rosetta will be analysed over the coming days and weeks to finally unveil the true nature of Steins.

      Through the study of minor bodies such as asteroids, Rosetta is opening up a new window onto the early history of the solar system. It will provide a better understanding of origins and evolution of planets, and also a key to better interpreting asteroid data collected from the ground.

      This is not Rosetta’s first look at Steins. Over two years ago, in March 2006, the Osiris camera onboard Rosetta observed the brightness variations of this rotating asteroid from a distance of 159 million kilometers (98.8 million miles, or a bit more than the distance between Earth and the sun), and was able to determine that the tiny asteroid spins around its axis in about six hours.

      Together with the two navigation cameras onboard, Osiris was again pointed towards Steins last month and continued to observe the asteroid until last week, in order to assist Rosetta’s navigation by optical means – a first in the history of ESA spacecraft operations.

      A few days before the flyby, most of the Rosetta orbiter instruments, as well as the Philae lander magnetometer, were switched on to collect science data on the asteroid, with ever-increasing accuracy as the spacecraft closed in on it.

      Rosetta’s powerful instruments have initially been focusing on the asteroid’s orbital motion, rotation, shape and density. As the distance has diminished, the investigation has broadened to take in the observation of surface properties and features, and the analysis of the chemical and mineralogical composition of the terrains, as well as their relative ages and the effects of the solar wind on the surface.

      Rosetta is scheduled to conduct another flyby, this time with the much larger (21) Lutetia asteroid, on July 10, 2010. Arrival at 67P/Churyumov-Gerasimenko is due by mid- 2014.

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