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.

Rocket body impact
A rocket body impacted the Moon on March 4, near Hertzsprung crater, creating a double crater roughly 92 feet (28 meters) wide in the long dimension. This photo is enlarged 3x.
Contributed / NASA/Goddard/Arizona State University
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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 .

Lunar far side impact
The wayward rocket stage struck the moon's far side within the crater Hertzsprung, an enormous impact basin 350 miles (570 km) across.
Contributed / NASA, Goddard, Arizona State University

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.

Rocket stages
Many space missions are launched on multi-stage rockets. Once the fuel in the first stage is used up, it falls back to Earth. This reduces the weight of the rising rocket, so later stages have to do less work, conserving fuel. The final stage enters orbit with the spacecraft.
Contributed / NASA

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.

Impact before and after
NASA's Lunar Reconnaissance Orbit took the before image, left, on Feb. 28. The after image is from May 21. The width of the frame is about 1,200 feet (367 meters). The bright material to the right of the pair is likely fresh rock and dust excavated by the impact.
Contributed / NASA, Goddard, Arizona State University

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.


Apollo rocket body impacts
These four images show craters formed by impacts of the Apollo S-IVB stages — the third stages of the Saturn V rockets that took six crews of astronauts to the moon. Crater diameters range from about 115 to 131 feet (35 to 40 meters) in the longest dimension.
Contributed / NASA, Goddard, Arizona State University

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.

Spent Saturn S-IVB
A spent Saturn S-IVB rocket stage from the Apollo era is seen floating in space. A similar spent booster of uncertain origin slammed into the moon to form the double-crater.
Contributed / NASA

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.

Read more from Astro Bob
Here's something you don't see very often: the moon eclipsing the Earth! We also preview a new, multi-part lunar mission launching Wednesday, Nov. 30.

"Astro" Bob King is a freelance writer for the Duluth News Tribune.

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at
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