Astro News Briefs: August 2–8

MARSIS Delayed

August 4, 2004 | Europe's Mars Express orbiter completed its formal scientific commissioning on June 3rd, but the mission has run into a problem with one of its main science instruments. The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) was set to use long radio waves to penetrate deep below the Martian surface to search for buried water or ice. The deployment of its 40-meter-long (130-foot) antenna has been put on hold, however, because of a possible design flaw. Although prelaunch studies indicated that the two spring-loaded antennas would lock into place smoothly, in March engineers raised new concerns that the flexible rods might whip back with enough force to damage other parts of the spacecraft. Several months of simulations have failed to resolve the issue, and for now the deployment is on hold.

Lunar Rock Pinpointed

August 3, 2004 | When Apollo 15 landed on the outskirts of the Mare Imbrium basin, astronauts gathered buckets full of rocks that later turned out to be quite strange. The lander, it seemed, touched down in an anomalous region of the Moon, one with a uniquely large concentration of radioactive thorium, uranium, and potassium. Now astronomers on the ground have identified a meteorite on Earth that they can trace directly to Imbrium. As reported in the July 30th issue of Science, scientists deduced the history of the 206-gram rock named Sayh al Uhaymir (SaU) 169 from its radioactive markers. According to Edwin Gnos (Institute for Geological Sciences, Bern, Switzerland) and colleagues, the makeup of the rock suggests that it was involved in four different impact events that explain the layered nature of the layered basin:

  • First was the Imbrium formation event 3.9 billion years ago. This was the origin of the rock material.
  • 2.8 billion years ago an impact south of Imbrium sent debris into the basin, including SaU 169.
  • A third impact at least 200 million years ago brought SaU 169 to the surface (within a half meter).
  • An impact less than 340,000 years ago launched SaU 169 on a course to Earth. Its travel time was about 300,000 years.