After months of scrutinizing photographs of the lunar surface, scientists have finally found the site of the crash of a forgotten rocket stage that hit the other side of the Moon in March.
They still do not know for sure from which rocket the rebel debris originated. And they are perplexed about why the impact dug two craters and not just one.
“It’s great, because it’s an unexpected result,” said Mark Robinson, a geological science professor at Arizona State University who acts as the principal investigator of the camera aboard NASA’s Lunar Reconnaissance Orbiter, which photographs the Moon since 2009. “This is always more fun than if the crater’s prediction, its depth and diameter, had been exactly correct.”
Robinson reported Friday the discovery on the website that stores images taken by the lunar orbiter.
The intrigue of the rocket crash began in January when Bill Gray, developer of the Pluto Project, a set of astronomical software used to calculate the orbits of asteroids and comets, tracked what appeared to be the discarded upper stage of ‘a rocket. He realized he was colliding with the other side of the moon.
The accident was safe, around 7:25 a.m., Eastern Time on March 4th. But 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 part was the second stage of a SpaceX Falcon 9 that launched the Deep Space Climate Observatory, or DSCOVR, for the National Oceanic and Atmospheric Administration in February 2015.
He was wrong.
A NASA engineer noted that the DSCOVR’s launch trajectory was incompatible with the orbit of the object Gray was tracking. After digging a little deeper, Gray concluded that the most likely candidate was a Long March 3C rocket that was 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 by the object found that the mixture of wavelengths coincided with similar Chinese rockets instead of a Falcon 9.
But a Chinese official denied that he was part of a Chinese rocket, saying that the rocket stage of this mission, which launched the Chang’e-5 T1 spacecraft, had re-entered the Earth’s atmosphere and it had burned.
Regardless of the rocket of which it was a part, the object continued to follow the spiral path dictated by gravity. At the scheduled time, it collided with the end of the moon inside the 350-mile-wide Hertzsprung crater, without anyone on Earth seeing it.
The Lunar Reconnaissance Orbiter was not in a position to see the impact, but the hope was that a freshly cut crater would appear in a photograph the spacecraft later took.
Gray’s software made a prediction of the place of impact. Experts at NASA’s Jet Propulsion Laboratory calculated a location a few miles to the east, while members of the Lincoln Laboratory at the Massachusetts Institute of Technology expected the crash to occur tens of miles to the west. .
This meant that researchers had to search 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 identify recent disturbances.
Robinson said he was worried that “it would take us a year of pictures to fill the box.”
Although the Lunar Reconnaissance Orbiter has photographed the vast majority of the moon several times over the past 13 years, there are points that have been lost. It turned out that some of the gaps were near the site of the expected accident.
Robinson recalled thinking about Murphy’s Law and joking, “I know exactly where he’s going to get.”
Because the accident was predicted a month in advance, the mission team was able to fill most of the gaps.
Then the search began.
Normally, a computer program makes 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 sat down and had several people manually going through millions of pixels,” Robinson said.
Alexander Sonke, a senior in the Arizona State Department of Geological Sciences, contributed to the effort. He estimated that he had spent about 50 hours for several weeks doing the tedious task.
Sonke graduated in May. He got married. It was honeymoon. A week and a half ago it was his first day back at work – he is about to start his postgraduate studies with Robinson as his advisor – and he resumed his search for the impact site.
He found it.
Sonke said he had seen “a group of pixels that had a significantly different brightness” as the before and after images flashed back and forth.
“I was pretty sure when I saw that it was a new geological feature,” Sonke said. “I certainly jumped out of my seat a little bit. I had the feeling that this was definitely all and then I tried to contain my excitement.”
The eastern crater, about 20 meters in diameter, overlaps to the west a little smaller, which probably formed a few thousandths of a second before the east, Robinson said.
It is not the first time that a part of the spacecraft has reached the Moon. For example, pieces of the Saturn 5 rockets that brought astronauts to the moon in the 1970s also cut craters. But none of these impacts created a double crater.
The reason he did this could point to his mysterious identity. The October 2014 Chinese mission brought the Chang’e-5 T1 spacecraft, a precursor to another mission, Chang’e-5, which landed on the moon and brought rock samples back to Earth. .
The T1 precursor spacecraft did not include any landings, but Robinson assumes it had a heavy mass at the top of the stage to simulate the presence of one. If so, the rocket engines at the bottom and the landing simulator at the top could have created the two craters.
“That’s pure speculation on my part,” Robinson said.
The other parts of the rocket stage would have been thin and light aluminum, which probably would not have made a big impact on the lunar surface.
The actual impact site was between the sites predicted by Gray and NASA’s Jet Propulsion Laboratory, close to NASA’s. “It was within the margins of error we had calculated,” Gray said.
It was also fortunate that the Lunar Reconnaissance Orbiter team had filled in the gaps, called gores, in the language of cartographers, in images. “Just as Murphy would like, this thing impacted what was one of the gorges,” Robinson said. “If I hadn’t been warned, we wouldn’t have had a previous image.”
Scientists could have finally found the crash site. Dirt thrown from a pointed crater tends to be brighter and gets darker over time. This is how scientists identified the craters caused by Saturn’s 5 stages.
But they would still be looking for a little bright spot in the barn of the moon.
This article originally appeared in The New York Times.