They still do not know for sure from which rocket the strange debris came. And they are confused about why the collision dug two craters and not just one. “It’s nice, because it’s an unexpected result,” said Mark Robinson, a professor of geology at Arizona State University who has been NASA’s chief camera researcher at NASA’s Lunar Reconnaissance Orbiter, which has been photographing the moon since 2009. “It’s always a lot more fun than if the crater prediction, its depth and diameter, were just right.” Robinson reported the discovery Friday on a site that stores images taken from the lunar orbit. The anti-rocket intrigue began in January when Bill Gray, the developer of Project Pluto, an astronomical software suite used to calculate the orbits of asteroids and comets, watched what resembled the rejected upper stage of a rocket. He realized that he was in orbit colliding with the far side of the moon. The crash was certain, at about 7:25 p.m. Eastern time on March 4. However, the exact orbit of the object was not known, so there was some uncertainty about the time and place of the impact. Gray said the rocket division was the second phase of a SpaceX Falcon 9 launched by the Deep Space Climate Observatory, or DSCOVR, on behalf of the National Oceanic and Atmospheric Administration in February 2015. He made a mistake. A NASA engineer pointed out that the launch trajectory of the DSCOVR was incompatible with the trajectory of the object that Gray was watching. After a little more digging, Gray concluded that the most likely candidate was a Long March 3C rocket launched from China a few months earlier, on October 23, 2014. Students at the University of Arizona reported that an analysis of the light reflected from the object found that the mixture of wavelengths matched similar Chinese missiles rather than Falcon 9s. But a Chinese official denied being part of a Chinese rocket, saying the rocket stage from that mission, launched by the Chang’e-5 T1 spacecraft, had re-entered Earth’s atmosphere and burned. Regardless of the rocket of which he was a part, the object continued to follow the spiral path dictated by gravity. At the scheduled time, it hit the far side of the moon in the 350-mile-wide Hertzsprung crater, far from anyone on Earth. The Lunar Reconnaissance Orbiter was unable to track the impact, but the hope was that a newly carved crater would appear in a photo taken later by the spacecraft. Gray software made a prediction for the impact area. Experts at NASA’s Jet Propulsion Laboratory calculated a location a few miles east, while members of the Lincoln Laboratory at the Massachusetts Institute of Technology expected the crash to occur tens of miles west. This meant that researchers had to look in a strip about 50 miles long for a crater a few tens of feet wide, comparing the lunar landscape before and after the crash to detect recent disturbances. Robinson said he was concerned that “it would take us a while to complete the box.” While the Lunar Reconnaissance Orbiter has photographed the vast majority of the moon several times over the past 13 years, there are signs it has lost. It turned out that some of the gaps were close to the expected point of the crash. Robinson recalled thinking of Murphy’s Law and jokingly said, “I know exactly where it will strike.” Because the crash was scheduled a month earlier, the mission team was able to fill most of the gaps. Then the search began. Usually, a computer program does the comparison, but this works best if the before and after photos are taken at the same time of day. For this search, many of the images were taken at different times and the difference in shadows confused the algorithm. With all the false positives, “we just sat down and had enough people to manually switch the millions of pixels,” Robinson said. Alexander Sonke, a senior official in the Arizona State Department of Geology, contributed to the effort. He estimated that he had spent about 50 hours for several weeks performing the tedious task. Sonke graduated in May. Married. Gone is the honeymoon. A week and a half ago it was his first day back at work – he was about to start his postgraduate studies with Robinson as his mentor – and he continued to search for the crash site. He found it. Sonke said he had seen “a group of pixels that looked significantly different in brightness” as the before and after images blink back and forth. “I was pretty sure when I saw that this was a new geological feature,” Sonke said. “I definitely jumped out of my seat, I felt it was definitely that and then I tried to keep my excitement.” The eastern crater, about 20 yards in diameter, overlaps the slightly smaller western crater, which probably formed a few milliseconds before the eastern one, Robinson said. This is not the first time a spacecraft component has hit the moon. For example, fragments of Saturn 5 rockets that carried astronauts to the moon in the 1970s also carved craters. But none of these impacts created a double crater. The reason he did this may indicate his mysterious identity. The Chinese mission in October 2014 carried the Chang’e-5 T1 spacecraft, a precursor to another mission, the Chang’e-5, which landed on the moon and brought rock samples back to Earth. The T1 precursor spacecraft did not include a landing, but Robinson assumes it had a heavy mass at the top of the stage to simulate the presence of one. If so, then the rocket engines at the bottom and the landing simulator at the top could have created the two craters. “This is pure speculation on my part,” Robinson said. The other parts of the rocket stage would be thin, lightweight aluminum, which is unlikely to create a large dent on the lunar surface. The actual point of collision was between the locations projected by Gray and the NASA Jet Propulsion Laboratory, close to that of NASA. “It was within the margin of error we had calculated,” Gray said. He was also happy that the Lunar Reconnaissance Orbiter team had filled in the gaps – called gores, in the language of cartographers – in the images. “As Murphy would say, this thing had one of the causes,” Robinson said. “If I had not been notified, we would not have had a previous image.” Scientists may have finally found the crash site. Dirt thrown out of a grooved crater is usually brighter and darker over time. In this way, scientists have identified craters caused by 5 stages of Saturn. But they would still be looking for a small bright spot on the moon’s haystack. This article was originally published in the New York Times.
