One of NASA's moon probes, the Lunar Crater Observation and Sensing Satellite (LCROSS), will complete a relatively simple mission next month: releasing a spent rocket stage toward a shadowy crater, then following it to see what the impact stirs up before crashing the mother ship itself into the crater. All the while, Earth-based and orbiting telescopes will be watching, looking for any evidence of water ice that might be hidden in the crater's depths.

Today, NASA unveiled its target of choice for LCROSS's double impact on October 9: a south-polar crater known as Cabeus A. The 48-kilometer-wide crater is named for 17th-century Italian astronomer Niccolo Cabeo. According to NASA, Cabeus A was chosen both for its potential for harboring water ice and for its location, which will allow Earth observers to track the plumes thrown up by the LCROSS impacts. For a fuller description of the LCROSS mission, see our coverage from June, just before the spacecraft launched.

The European Space Agency (ESA) successfully launched two spacecraft this morning that should shed light on some of the big questions in astronomy and cosmology, from the origins of the universe to the formation of stars and planets.

ESA's Planck and Herschel lifted off on board an Ariane 5 rocket at 9:12 Eastern Daylight Time from the European Spaceport in French Guiana.

Less than 40 minutes later the two spacecraft radioed back to an ESA antenna in Australia to confirm that they had separated from the launcher as planned. (The video below shows an animation of Planck's separation.) They are on separate trajectories to loop around a point 930,000 miles (1.5 million kilometers) from Earth, well beyond the moon. To lend a sense of scale, ESA has a video showing Herschel's planned trajectory and orbit.

A commercial satellite collided with a Russian satellite over Siberia yesterday, yielding a cloud of fragments, according to a NASA scientist tracking space debris. The collision between the commercial satellite, belonging to the American communications firm Iridium, and the Russian satellite, believed to be defunct based on its advanced age, was the first of its kind, says Nicholas Johnson, chief scientist at the NASA Orbital Debris Program at Johnson Space Center in Houston. (A spokesperson for Iridium said a statement on the incident would be released shortly.)*

"In the past almost 20 years, there have been three other accidental collisions between objects in orbit, but they've all been very minor," Johnson says. "The most debris ever produced in an event was like four debris, and this is two intact spacecraft colliding, and we have hundreds of debris out there. We don't know exactly how many yet."

In 2011 NASA’s MESSENGER spacecraft will insert itself into Mercury’s orbit, ending a nearly seven-year journey spanning billions of miles. The real work begins, though, once MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) settles in as Mercury’s lone satellite and provides the first prolonged look at the dense little planet. Until that time, planetary scientists have to settle for tantalizing but fleeting glimpses of Mercury from MESSENGER’s three flybys, the second of which took place on October 6.

Some of the results of that up-close peek were announced at a NASA news conference today, providing a taste of what revelations will come once MESSENGER takes up residence in Mercury’s orbit. (The flybys are gravity-assist procedures to bring MESSENGER’s trajectory into line for the future orbit insertion; any scientific data collected during them are icing on the cake.) Relatively little is known about the planet, because its proximity to the sun largely precludes ground-based study; before MESSENGER’s first pass, less than half the planet had even been imaged.

NASA’s MESSENGER spacecraft, launched in 2004, completed its second flyby of Mercury early Monday morning, passing within 125 miles (200 kilometers) of the planet’s surface and snapping striking photographs of never-before-seen terrain.

MESSENGER (short for MErcury Surface, Space ENvironment, GEochemistry and Ranging) captured more than 1,200 images during its pass, filling in many of the gaps left by Mariner 10, which imaged 45 percent of Mercury’s planetary surface during three flybys in the mid-1970s. The pockmarked planet, the smallest in the solar system (following Pluto’s demotion to the minor, er, dwarf leagues), is difficult to study from ground-based observatories due to its location—it’s the closest to the sun and is often lost in its parent star’s glare.