The latest on the asteroid approaching Mars, with potentially Tunguska-like dangers, is that it will likely pass a safe 48,000 kilometers from the surface at about 1100 UTC on January 30. This news release describes the possibility of an impact as ‘unlikely,’ but goes on to say that if it does occur, the best view of the event will come from the Mars Reconnaissance Orbiter, whose High Resolution Imaging Experiment (HiRISE) would provide an unprecedented look at the crater.

While the size of asteroid 2007 WD5 approximates the object whose impact formed Meteor Crater (northern Arizona) some 50,000 years ago, the latter is thought to have been a metallic asteroid, while the one approaching Mars is probably stony. Current estimates of 2007 WD5 make it out to be 50 meters wide, traveling at some 13 kilometers per second. That’s enough to carry quite a punch, as the Tunguska impact proved in 1908, and as we may conceivably see at the end of January.

As we watch for updates, ponder the Catalina Sky Survey, which discovered the asteroid on November 20. The job of the CSS is to add to our inventory of near-Earth objects (NEOs), working under a congressional directive to NASA to identify objects one kilometer or larger to a confidence level of 90 percent or better. A later mandate brings that size down to 140 meters or larger. You can see the problem for objects in what we might call the ‘Tunguska-class.’ 2007 WD5 is almost three times smaller than our current programs are designed to track, though the CSS work on it proves that such identifications can be made.

2007 was a banner year for this particular survey. The Catalina team found 450 NEOs during the year, and that’s not the final count. Moreover, the number is growing: 400 were found in 2006, 310 in 2005. Even so, this is tricky work. The threat an object represents depends upon its impact energy, a quantity that demands knowledge of its size, density and velocity. That makes characterizing the objects that threaten our planet a major goal of observing programs, and an important objective for an early mission to an asteroid to further refine this information.