In a few weeks’ time, a rocket launched in 2015 is expected to crash into the Moon. The fast-moving piece of space junk is the upper stage of a SpaceX Falcon 9 rocket that hoisted the Deep Space Climate Observatory satellite off our planet. It has been chaotically looping around Earth and the Moon ever since.
Asteroid-hunter Bill Gray has been keeping tabs on the 4-tonne booster since its launch. This month he realised his orbit-tracking software projected the booster will slam into the lunar surface on March 4 moving at more than 9,000 km/hr. The booster is tumbling wildly as it travels, which adds some uncertainty to the timing and location of the predicted impact. It is likely to occur on the far side of the Moon, so it will not be visible from Earth. Some astronomers say the collision is “not a big deal”, but to a space archaeologist like me it is quite exciting. It will be the Moon’s newest archaeological site, joining more than 100 other locations that document human activity on the Moon.
Lunar crash landing
The impact will leave a new crater on the dark side of the Moon.
The very first human-made artefact to make contact with the Moon was the Soviet Luna 2 in 1959 – an extraordinary feat, as it was only two years after the launch of Sputnik 1, the first artificial Earth satellite. The mission consisted of a rocket, a probe, and three “bombs”. One released a cloud of sodium gas to enable the crash to be seen from Earth. The Soviet Union did not want the groundbreaking mission to be called a hoax.
he other two “bombs” were spheres of pentagonal medallions inscribed with the date and Soviet symbols. If they exploded as planned, they would have scattered 144 medallions over the lunar surface. Other crashes have been missions gone wrong, like the Israeli Beresheet lander in 2019. This was especially controversial as the lander carried a secret cargo of dried tardigrades, tiny creatures that could be revived in the presence of water.
Various spacecraft have naturally decayed and fallen out of orbit, like the Japanese relay satellite Okina in 2009. Others have been intentionally crashed at the end of their mission life.
The NASA Ebb and Flow spacecraft were deliberately crashed into the lunar south pole in 2012, specifically to avoid any risk of damaging the Apollo landing sites. Impacting at a speed of 6,000 km per hour, they left craters 6 metres across.
Environmental impacts
The Falcon 9 rocket stage is significantly larger than the tiny Ebb and Flow spacecraft and is travelling faster. The crash will make a much larger crater, which will kick up chunks of rock and dust. On this airless world, the dust could travel a fair way before settling down.
The only other spacecraft on the Moon’s far side are the US Ranger 4 probe, which crashed in 1962, and China’s Chang-e 4 lander and Yutu-2 rover. Yutu-2 is still trundling along the lunar surface on its six wheels.
Yutu’s latest results show that “soil” on the far side may be stickier than the near side, and there is a higher density of small craters.
The rocket stage could potentially cause damage to these historic spacecraft if it lands on or near them. However, this is statistically unlikely. Current predictions have it landing in Hertzsprung crater, a long way from the Aitken basin where the Chinese spacecraft are operating.
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