It is not often that a fresh impact crater on the Moon appears out of nowhere, but that will happen on March 4 when a derelict SpaceX Falcon 9 rocket collides with it.
Nasa’s Deep Space Climate Observatory (DSCOVR) probe was launched into a position 1.5 million kilometers from Earth, facing the Sun, by the rocket in 2015.
However, the rocket’s spent upper stage was unable to escape into an independent orbit around the Sun, and it was abandoned without the ability to guide back into the Earth’s atmosphere.
That would be standard procedure, enabling stages to burn up on re-entry, lowering the amount of harmful debris in near-Earth space.
The derelict upper stage, which is 14 meters long and weighs roughly four tonnes, has been in a broad orbit above the Earth since February 2015. Because it was impacted by lunar and solar gravity as well as the Earth’s, its exact motions were difficult to predict.
However, we now know that it will strike the Moon on March 4 at a speed of 2.6 kilometers per second. This will result in a 19-meter-wide crater, a potential that has sparked indignation on social media among those who are outraged that human irresponsibility would deface the Moon in this manner.
A Concern that is misplaced
A dead rocket landing on the Moon, on the other hand, is unquestionably more ecologically benign than being spread across Earth’s upper atmosphere as metal oxide particles during a re-entry burn up.
Because the Moon lacks an atmosphere to protect it from space debris, it is constantly acquiring naturally occurring impact craters.
The Lunar Reconnaissance Orbiter has previously captured images of a 19-meter crater created in March 2013 when a half-tonne chunk of asteroid rock flying 10 times faster than the Falcon 9 collided with the surface.
Nasa’s lunar impact monitoring program has detected hundreds of smaller impacts involving bits of rock weighing as little as half a kilogram during the last decade.
We will not be able to view the next collision since it will occur on the far side of the moon. After that, though, satellites circling the Moon will be able to photograph the impact crater.
Will we be able to learn anything new? We have seen numerous purposeful impacts on the Moon before, so we know what to anticipate.
The much bigger upper stages of the rockets used in the Apollo landing missions, for example, were crashed so that vibrations measured by seismometers on the surface could be utilized to probe the lunar interior.
The seismometers on the Apollo spacecraft were shut off a long time ago, and it is unclear if the seismometer aboard China’s Chang’e 4 far side lunar lander will produce any relevant data this time.
In 2009, Nasa’s LCROSS mission sent a projectile into a permanently shadowed polar crater, creating a smaller crater on its ice bottom and ejecting a plume that included the hoped-for water vapor.
Contamination by biological agents
So I am not worried by another crater on the Moon. It already contains around a half-billion craters with a diameter of 10 meters or more. What we should be concerned about is contaminating the Moon with live bacteria or compounds that may be misconstrued as proof of previous life on the Moon in the future.
The majority of countries have agreed to planetary protection guidelines, which aim to reduce the possibility of biological contamination from Earth to another body (and also from another body back to Earth). The guidelines are in place for ethical and scientific reasons.
The ethical issue is that bringing creatures from Earth that may flourish on another body would jeopardize any ecosystem that may exist there. The scientific argument is that we want to study and understand the natural conditions on each other’s bodies, thus we should not risk contaminating or damaging them.
In 2019, the privately sponsored Israeli lunar lander Beresheet crashed on the Moon, bringing DNA samples and hundreds of tardigrades. This was the most recent infringement of the COSPAR rules.
These are half-millimeter-long creatures that can survive, but not thrive, in space’s vacuum. These, as well as the bacteria that dwelt in their intestines, are now strewn over the crash site at Beresheet.
Most of them will most likely not wind up in a niche with enough water to revive and become active, but that is not a chance we should take. The DSCOVR Falcon 9 was not sterile when it launched, but it did not have any biological cargo either.
It has already been seven years in space, so the danger of biocontamination is nil – but the more we send to the Moon, the more cautious we must be, and the more difficult it will be to enforce any standards.