There’s a bright side to every situation. In 2032, the Moon itself might have a particularly bright side if it is blasted by a 60-meter-wide asteroid. The chances of such an event are still relatively small (only around 4%), but non-negligible. And scientists are starting to prepare both for the bad (massive risks to satellites and huge meteors raining down on a large portion of the planet) and the good (a once in a lifetime chance to study the geology, seismology, and chemical makeup of our nearest neighbor). A new paper from Yifan He of Tsinghua University and co-authors, released in pre-print form on arXiv, looks at the bright side of all of the potential interesting science we can do if a collision does, indeed, happen.
On December 22nd, 2032, Asteroid 2024 YR4 has a 4% chance of actually striking the Moon. If it does, it will release enough energy to be the equivalent of smacking our nearest neighbor with a medium-sized thermonuclear weapon. It would be 6 orders of magnitude more powerful than the last major impact on the Moon, which happened back in 2013 and was caused by a much smaller meteoroid.
If it does hit the Moon, it will prove a serendipitous event for physicists who study high energy impacts. While they can simulate models of how the impact will go all they want, monitoring it as it happens will provide them with never-before collected actual data that is infeasible to get any other way. The impact will vaporize rock and plasma, and clearly be visible from the Pacific region, where it will be night during the impact.
Fraser discusses whether we should simply destroy Asteroid 2024 YR4.Even days after the impact, the melt pool of the impacted material will still be cooling, allowing infrared observers like the James Webb Space Telescope to capture plenty of data on how that cooling process works, as well as how craters are actually formed on the Moon. It should form a crater roughly 1 km wide and 150-260 m deep, with a 100m pool of molten rock at the center. Comparing it in size to other craters scattered around the Moon will help us understand its bombardment history.
The impact will also set off a global “moonquake” of magnitude 5.0. That would be the strongest moonquake yet detected by any seismometer on the Moon, and there expected to be plenty more before that impact timeline as space agencies rush back to the Moon and begin to cover it with scientific equipment. Watching the propagation of the moonquake caused by the impact will shine a light on the Moon’s interior and help researchers understand its composition without having to blast it with anything artificial.
A final piece of the scientific puzzle will be the debris field created by the blast. Up to 400kg of it is expected to survive reentry to Earth, creating essentially a free “large scale” lunar sample return mission for astronomers. Despite the fact that the samples would be charred to a crisp by their atmospheric reentry. But if you’ve ever seen the episode The Eye in the show Andor or read the book Seveneves by Neal Stephenson, then you know how spectacular such a display can be. At its peak right around Christmas of 2032, simulations expect up to 20 millions meteors per hour to hit our atmosphere, and least on the “leading edge” of the planet - most of them with naked-eye visibility. Those would include some 100-400 fireballs (i.e. larger pieces) per hour.
VideofromSpace video showing the orbits of Asteroid 2024 YR4. Credit - VideofromSpace YouTube ChannelBut there is a downside to all of this. That 400kg of meteors have to land somewhere, and it looks like the cross-hairs fall squarely on South American, North Africa, and the Arabian peninsula. Not exactly the most built up areas of the world, but a few kg of space rock falling on Dubai could certainly cause some damage. But perhaps more dangerous is the risk to the satellite mega-constellations that plan such an important role in our modern-day navigation and internet systems. Such an event could trigger “Kessler Syndrome” and bring the entire network down over the span of a few short years, while also locking us out from being able to get anything else safely into orbit for much longer.
Due to the risks, some space agencies are already considering a deflection mission that would bump Asteroid 2024 YR4 out of the way of a potential lunar collision, but that has not been set in stone yet. Neither, for that matter, has the actual impact itself. It will only have a 4% chance of happening - not the same astronomical odds as winning the lottery, but not as high as a chance of rolling a Nat 20 in a D&D game. If the odds of that increase over the coming years, eventually we as a species will have to decide whether it's worth the effort to deflect it or not. And if we do, we might miss out on a whole bunch of cool science - but we almost might save our entire orbital infrastructure and a few lives directly to boot.
Learn More:
Y. He et al. - Observation Timelines for the Potential Lunar Impact of Asteroid 2024 YR4
UT - The Mother of All Meteor Showers Could Threaten Satellites
UT - NASA Downgrades the Risk of 2024 YR4 to Below 1%
UT - Destroying Asteroid 2024 YR4 Is The Best Option To Stop It From Hitting The Moon