On Sunday, January 20, viewers across the Western Hemisphere were treated to the rusty hues of the decade's last “blood moon” eclipse. But as people across the planet watched the moon glow crimson, some lucky observers caught an unexpected delight: the flash of a space rock striking the lunar orb.
“It's a rare alignment of infrequent events,” says Justin Cowart, a Ph.D. candidate at Stony Brook University in New York. “A [meteoroid] about this size hits the moon about once a week or so,” he says. But if this event is confirmed, it may be the first time such an impact has been recorded during a lunar eclipse.
An eagle-eyed viewer on Reddit spotted the potential impact during the eclipse and reached out to the r/space community to see if others could weigh in. The news spread quickly on social media, as people from across the path of totality posted their images and video of this tiny flicker of light.
Many scientists initially approached the claims with appropriate skepticism. After spotting the buzz on Twitter, “I was wondering if it was maybe a local effect, or maybe something with the camera,” says planetary scientist Sara Mazrouei of the University of Toronto.
Flashes of light from an impact are faint and short lived, making them easy to confuse with an errant pixel. But image after image showed the same thing: At 4:41 UT, when totality was just beginning, a tiny speck of light glinted south of the crater Byrgius, a nearly 55-mile-wide pockmark in the western part of the moon.
“They all seem to see the same bright pixel,” Mazrouei says. This confluence points strongly toward the flash of light actually being an impact.
“This is something that people all around the world didn't know that they were going to sign up for” says Noah Petro, a research scientist at NASA's Goddard Space Flight Center.
Try, try again
Backyard astronomers and starstruck citizen scientists weren't the only ones watching. Jose Maria Madiedo, an astrophysicist at the University of Huelva in Spain, is co-director of the Moon Impacts Detection and Analysis System, MIDAS for short. He had been working overtime to get eight of the project's telescopes trained on the moon during the eclipse to watch for just such an event.
The MIDAS team usually scours the moon in search of faint flashes, the telltale signs of an impact, to learn about the array of space rocks that bombard our lunar companion. But most of these events are too dim to spot when the moon is full. The team does the bulk of their observing in the five days before and after a new moon. An eclipse, however, dulls the full moon's usually vibrant glow, providing one more rare opportunity to spot the tiny flashes of light.
So far, they hadn't successfully spotted an impact during an eclipse, but Madiedo didn't lose hope: “Something inside of me told me that this time would be the time.” And sure enough, his efforts paid off.
“I had a very nice reward,” he says.
Making an impact
Scientists say the next steps are gathering up the many observations to study the event in full detail, and hopefully capturing an image of the moon's new crater.
“The Earth and the moon are in such close proximity that observing the impacts on the moon can help us learn a lot more about the frequency of impacts on Earth,” explains Mazrouei, who recently authored a study detailing an ancient spike in large meteor bombardment on the moon, and thus on our planet.
Though Earth's atmosphere protects us from many of the smaller space rocks zooming through the solar system, incoming meteors can still affect the array of satellites zipping around the planet that are vital to keeping navigation, telecommunications, weather forecasting, and more humming along on the surface.
And seeing the aftermath of smaller impacts on airless worlds like the moon can help scientists learn about the effects of larger strikes on all kinds of worlds—including our own, Madiedo says.
“By knowing what happens with smaller impacts, you could know what could happen with larger impacts without really studying a large impact on Earth.”
Sweeping the moon
Finding the new crater on the already pockmarked surface of the moon will take some work, though. The spacecraft vital to this process is NASA's Lunar Reconnaissance Orbiter (LRO). Launched in 2009, the orbiter took up residence around our moon to study its surface in stunning detail. So far, it has recorded hundreds of changes to the lunar landscape, including more than two dozen new impact craters.
LRO even has history finding craters after initial reports of an impact flash. On March 17, 2013 researchers at NASA's Marshall Space Flight Center reported sighting a similar faint flicker of light on the moon. By comparing images of the moon's surface from LRO's trio of cameras before and after the event, scientists traced the debris streaks from the impact back to its associated crater.
For this latest event, the team responsible for LRO's cameras is not specifically targeting the crater in their sweeps over the moon. The orbiter essentially captures a random sampling of the moon's surface so scientists can calculate the average number of impacts over time, explains Petro, who is a project scientist for LRO. Specifically targeting the new crater would interfere with their statistical sampling.
Still, researchers can work to narrow down the new crater's location—and tease out more details about the impact itself—and then scour LRO data to see whether it passes over the right lunar section. Madiedo and his team are working to estimate the impact's energy and mass to assist in calculations of the crater's likely size and position. His initial estimates suggest that the space rock was about the size of a football, and that it left a crater between 23 and 33 feet across.
Stony Brook's Cowart is also trying to narrow down where the space rock struck using images from amateur astronomer Christian Fröschlin. He estimates that the crater lies around 29.47 south, 67.77 west. But accuracy is tricky; each pixel in the image represents an area about 2.5 miles across.
“So if I'm off by one pixel, then if we target that location, we can just totally miss the crater,” he says.
Regardless of whether the craft eventually captures the new crater, the series of events underscores the vital but often overlooked role social media can play in gathering data about natural phenomena, Petro says.
“I said going into the eclipse that this is really cool,” he adds. “This observation just reinforces how bloody cool it is.”
Editor's note: This article originally misstated the estimated size of the crater. It was between 23 and 33 feet across.