Astro Bob: Mystery rocket slams into moon, blasts 'double crater'
Two fresh craters pock the moon after a rocket booster impact. We're still trying to figure out whose it is.
Late last year, astronomers learned that a rocket body was on a collision course with the moon. First thought to be a SpaceX Falcon rocket stage that launched NASA's Deep Space Climate Observatory in 2015, they later concluded it was a rocket stage from a Chinese test run of a future lunar sampling mission .
University of Arizona students provided evidence for the fact when they studied light reflected from the booster and found it matched the paint used in Chinese Long March rockets. China's space agency disagrees, saying the rocket stage in question safely reentered and burned up in the atmosphere earlier this year.
Spacecraft launch on multi-stage rockets. The first and second stages provide the initial thrust and then separate from the rocket and fall back to Earth. The final stage boosts the payload (typically a spacecraft or satellite) into orbit. Once jettisoned, it's also in orbit and becomes yet another piece of "space junk" — unless it was designed to re-fire its engine and return to Earth or moved into an out-of-the-way orbit.
Whoever made the rocket, it certainly left an impression. On March 4, it struck the far side of the moon, blasting out a surprising pair of house-sized craters — an eastern cavity almost 59 feet (18 meters) wide superimposed on a western crater 53 feet (16 meters) across.
Spent rocket boosters have been slamming into the moon for decades. According to 2016 study by Arizona State University at least 47 NASA rocket bodies have impacted our neighbor in space. But a double crater was unexpected and may indicate that the rocket body had large masses at each end.
No other rocket body impacts to date have excavated a pair of craters. For good reason. The mass in a typical spent stage is concentrated at the engine end, with the remainder taken up by the empty fuel tank. Up till now, all human-caused impacts have resulted in single craters. A modern-day Sherlock Holmes might use this oddity as a potential clue in identifying the booster's owner.
They may be other possibilities. Did the stage somehow break into two pieces on the way down? Or could a part of the stage separate on impact and land moments later right next door? Just hunches.
None of the many human-made craters is large enough to see in a typical Earth-based telescope, the reason all these photos were taken by NASA's Lunar Reconnaissance Orbiter . The trusty orbiter, which has operated since 2009, can dip as low as 13.7 miles (22 km) above the moon's surface and reveal details as small as a meter (about 40 inches), just a little larger than the desk I sit at.
If you haven't seen the moon in a while, it will soon return — slightly more damaged — to the evening sky. On Wednesday evening, June 29, look for a super-thin crescent very low in the northwest with binoculars about 30-45 minutes after sunset. It will be considerably easier to see in the same direction about 45 minutes to an hour after sunset on Thursday evening.
"Astro" Bob King is a freelance writer for the Duluth News Tribune.