An asteroid could hit the Moon: "Risks for satellites and astronauts"

Asteroid 2024 YR4, discovered late last year, made astrophysicists tremble quite a bit when its probability of hitting the Earth in 2032 reached unprecedented estimates. After refining the calculations, the alarm was then called off . However, it will pass incredibly close to us, enough to have some chance of hitting the Moon. Danger averted then? Not really, given that there could be consequences, even serious ones, for those of us who live nearby. This is the result of a new study, by Canadian astrophysicists, who have come to a conclusion: a future shield to protect the Earth, that is, ourselves, from asteroids, should also be extended to the Moon.

When we talk about planetary defense, we always refer to the possible impact of an asteroid against our planet. A massive enough one could cause significant damage to a city, a region or an entire country. And it has happened, fortunately rarely, that one of these, with a diameter of ten kilometers, triggered a mass extinction. No one lives on the Moon (yet), but a powerful event up there cannot fail to have an influence here too.

If 2024 YR4 Hits the Moon

There is a 4 in 100 chance that 2024 YR4 will hit the Moon. They may seem small, but in these contexts they are enormous. The impact would be very energetic, so much so that it would change the morphology of our natural satellite. It has an estimated diameter of about 60 meters, it is small, but falling on the Moon at a speed of about 13 kilometers per second "it would release 6.5 Megatons of energy (about 400 times the power of the bomb dropped on Hiroshima, ed .) and would produce a crater about 1 km in diameter [...] an impact of this kind could release up to 108 kg (one hundred thousand tons, ed. ) of lunar material" that could exceed escape velocity, the researchers underline. And part of this could end up in our parts.

The authors of the study, not yet peer-reviewed (the preprint, published last week on the database arXiv , has been submitted to the Astrophysical Journal Letters ), estimate that 10 percent of all these rocks, dust and fragments could reach Earth in a matter of days. And here, they could cause damage. There is already a simulation of where it could hit, along a narrow corridor that runs along much of the side of the Moon exposed to us, in the southern hemisphere.

Alert for satellites and astronauts

There is no mention of risks for us, who are protected by our atmosphere. Rather, the astronauts who work in space stations will be at risk. In 2032, the International Space Station (ISS) will probably no longer exist, whose end is scheduled for 2030, but the Chinese Tiangong should remain, there could be an Indian space station, and all those private, commercial space stations that are starting to be designed and built in these years. Not least, that of Axiom, whose environments are taking shape in Turin . And then the satellites that we have in orbit (and which in 2032 should be many thousands more than now). Satellites on which we depend for everyday life for navigation, communications, weather and land management.

Even small fragments of a few millimeters, ejected by the violent collision of the asteroid with the Moon, traveling at speeds of the order of kilometers per second, tens of thousands of kilometers per hour, would be projectiles that could create breaches in the pressurized environments and force astronauts to make an emergency reentry, or, worse, puncture the suits and vital systems of those engaged in operations outside the outposts. Management teams would have to plan extraordinary maneuvers to avoid debris, with a waste of time, money and fuel. The operational life of the satellites would be reduced. No region will be spared, "given the very large total exposed area of ​​satellites by 2032, it is possible that the entire satellite fleet will suffer hundreds or thousands of impacts from millimeter-sized debris ejected by a lunar impact of 2024 YR4 - the paper states - such impacts can damage satellites, but, generally, are small enough not to interrupt active missions or cause breakups".

More space debris

At risk are therefore geostationary satellites (such as weather satellites, for TV broadcasting and communications), in medium orbit (for geopositioning) and in low orbit where the majority of devices orbit, including space stations. Not only that. In 2032 humanity should at least have begun operations for a more or less stable presence on the Moon itself. The cloud of debris raised by the impact of 2024 YR4 could therefore affect first of all the satellites in lunar orbit, those serving the exploration of the lunar soil. But the Moon, unlike the Earth, does not have an atmosphere, a shield capable of shattering the smallest particles with air friction, as happens with the meteors that light up the show of shooting stars. Many fragments, falling back on the Moon, could damage the artificial habitats positioned to accommodate astronauts, vehicles and robots, the astronauts themselves on a mission.

It is a concern that adds to that for space debris , debris and space junk, left by human activities in orbit. Which is already a difficult problem to solve, and which, with the increase in launches and the probability of impact, is destined to worsen. The only positive aspect of the whole affair is the one concerning the swarm of shooting stars, a phenomenon that is triggered when the Earth passes through clouds of dust left by the passage of some comet. After a possible impact of 2024 YR4, the show would be guaranteed, because we would have billions of new fragments destined to become meteors that cross our sky. Too bad that, to the natural ones, "artificial fireworks" could be added, those of satellites torn to pieces as they fall into the atmosphere.

A planetary defense for the Moon too?

Wiegert and colleagues suggest something interesting, never considered before: "Our analysis highlights that planetary defense problems go beyond the effects of impacts on the Earth's surface. Impacts on the Moon can generate particles that can interfere with satellites in low Earth orbit." In 2022, Dart, a NASA probe used as a projectile, hit a small asteroid (Dimorphos, the tiny moon of the more massive Didymos) and, for the first time in human history, intentionally and measurably deviated the trajectory of a celestial body. It was the first part of a test to understand whether we have the ability to push away a possible threat before it hits us.

Having taken off in 2024, the European Space Agency's Hera probe is now on its way to study Didymos and Dimorphos up close, to measure and analyze the consequences of the impact and thus provide scientists with the parameters to study a system to avoid, as they say, the same fate as the dinosaurs. But in light of the damage that even an asteroid as small as 2024 YR4 could do, the Canadian authors of the study ultimately argue that protecting the Moon also means protecting our life, as it is now: "Considerations on planetary defense should be extended to cis-lunar space and not limited exclusively to near-Earth space."