After months of carefully examining photos of the lunar surface, scientists have finally found the site of the crash of a forgotten rocket that hit the far side of the moon in March.
They still do not know for sure from which rocket the wayward debris originated. And they are puzzled as to why the impact dug two craters, not just one.
“It’s cool because it’s an unexpected result,” said Mark Robinson, a professor of geology at Arizona State University who serves as chief camera researcher aboard NASA’s Lunar Reconnaissance Orbiter, which has been filming the moon since 2009. ” is always a lot more fun than if the forecast for the crater, its depth and diameter were exactly correct.
Robinson announced the discovery on Friday on a website that stores images taken by the lunar orbiter.
The intrigue of the rocket crash began in January when Bill Gray, developer of Project Pluto, a package of astronomical software used to calculate the orbits of asteroids and comets, traced what looked like a rocket’s top-up. He realized that he was on a course of collision with the far side of the moon.
The crash was certain, around 7:25 a.m. Eastern Time on March 4. 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 was the second phase of the SpaceX Falcon 9, which launched the Deep Space Climate Observatory or DSCOVR for the National Oceanic and Atmospheric Administration in February 2015.
He was wrong.
A NASA engineer said the DSCOVR’s launch trajectory was incompatible with the orbit of the object Gray was tracking. After some more digging, Gray concluded that the most likely candidate was the Long March 3C missile, which was launched from China a few months earlier, on October 23, 2014.
Students at the University of Arizona said analysis of the light reflected from the object found that the mixture of wavelengths matched similar Chinese missiles, not the Falcon 9.
But a Chinese official denied that it was part of a Chinese rocket, saying that the rocket stage of this mission, which launched the Chang’e-5 T1 spacecraft, re-entered the Earth’s atmosphere and burned.
No matter which rocket it was part of, the object continued to follow a spiral path dictated by gravity. At the scheduled time, he crashed into the far side of the moon in the 350-mile-wide Herzsprung crater, out of sight of anyone on Earth.
The Lunar Reconnaissance Orbiter was unable to observe the impact, but the hope was that a freshly carved crater would appear in a photo the spacecraft later took.
Gray’s software made a prediction of the location of the impact. Experts from NASA’s Jet Engine Laboratory calculated a location a few miles to the east, while members of the Massachusetts Institute of Technology’s Lincoln Laboratory expected the crash to happen tens of miles to the west.
This meant that researchers had to look for a section about 50 miles long for a crater several 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 images to fill the box.”
While the Lunar Reconnaissance Orbiter has photographed most of the Moon several times in the last 13 years, there are places it has missed. It turned out that some of the gaps were close to the expected location of the crash.
Robinson remembered thinking about Murphy’s Law and joked, “I know exactly where it’s going to hit.”
Since 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 makes the comparison, but this works best if the photos before and after 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 made a few people manually go through millions of pixels,” Robinson said.
Alexander Sonke, a senior geologist in Arizona, contributed to the effort. He estimated that he had spent about 50 hours in a few weeks doing the tedious task.
Sonke finished in May. He got married. He went on his honeymoon. A week and a half ago was his first day back at work – he was about to start his postgraduate studies with Robinson as his adviser – and he resumed his search for the crash site.
He found it.
Sonke said he saw “a group of pixels that looked significantly different in brightness” as the images before and after flashed back and forth.
“I was pretty confident when I saw that this was a new geological feature,” Sonke said. “I certainly jumped a little out of my seat, I had the feeling it was definitely this, and then I tried to control my excitement.”
The eastern crater, about 20 yards in diameter, is superimposed on the slightly smaller western crater, which most likely formed several thousandths of a second before the eastern one, Robinson said.
This is not the first time a part of a spaceship has hit the moon. For example, pieces of the Saturn 5 rockets that took astronauts to the moon in the 1970s also carved craters. But none of these strikes created a double crater.
The reason for this may point to his mysterious identity. The Chinese mission from October 2014 carried the Chang’e-5 T1 spacecraft, the predecessor of another mission, Chang’e-5, which landed on the moon and brought rock samples back to Earth.
The predecessor of the T1 spacecraft did not include a lander, but Robinson suggested that it had a heavy mass at the top of the step to simulate the presence of one. If so, then the rocket engines below and the landing simulator above could create the two craters.
“This is pure speculation on my part,” Robinson said.
The other parts of the rocket would be thin, light aluminum, unlikely to make a large indentation on the lunar surface.
The actual crash site was located between Gray’s sites and NASA’s Jet Propulsion Laboratory, close to NASA’s. “It was within the limits of the error we had calculated,” Gray said.
It was also lucky that the Lunar Reconnaissance Orbiter team had filled in the gaps – called blood, in the language of cartographers – in the images. “As Murphy would have liked, this thing was reflected in what was one of the curses,” Robinson said. “If I hadn’t been warned, we wouldn’t have had a previous image.”
Eventually, scientists may have found the crash site. Dirt ejected from a carved crater is usually brighter, becoming darker over time. Thus, scientists have identified craters caused by Saturn 5 degrees.
But they would still be looking for a small bright spot in a haystack on the moon.
This article originally appeared in The New York Times.
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