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2 hours ago
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Asteroid 2024 YR4 caused quite a stir last year when it was discovered and originally calculated to have a 3% chance of hitting Earth. Since then models have been refined and while it no longer has a chance of hitting Earth, it does have a 4% chance of hitting the Moon in December 2032. As that time gets closer, we’ll have a better idea of the probability, but engineers and scientists are also planning for what we would need to do in order to ensure it doesn’t hit our only natural satellite at all. A new paper from NASA and a bunch of other researchers details potential missions and timelines that could make sure the Moon isn’t pummeled with a decent-sized asteroid in less than a decade.
A good first question is - why do we care? There are no definitive plans to have a permanent human presence on the Moon by that point, so it wouldn’t directly affect any human activities. Except an asteroid this large could create a huge debris field that would increase the micrometeoroids hitting the Earth by up to 1,000 times the normal background average for a few days. While that would make for one of the best meteor shows of the last few hundred years, it would also pose a danger to Earth-orbiting satellites and even astronauts on the ISS and other space stations - assuming they’re still there in 2032.
Really, there are only two options to stop that eventuality, if 2024 YR4 is indeed going to hit the Moon - which to be honest is still very unlikely. One option is to deflect it. The other is to destroy it.
NASA video explaining the details of asteroid 2024 YR4
Deflection would be preferred - simply moving its orbital path slightly would ensure it would miss both the Earth and the Moon. The earlier we could do it the smaller nudge would be needed, so it’s better to do it sooner rather than later. However, in order to accurately deflect 2024 YR4, we need to know how much it weighs.
We have a relatively good estimate of its diameter - around 60m give or take 10%. But estimates of its mass depend on its density, which is hard to calculate from so far away. The asteroid’s weight could range from between 51 million kg to over 711 million kg - and the amount of energy needed to move either of those weights a very precise amount is massively different. If a mission to deflect it is based on the wrong mass calculation, it could potentially accidentally change its trajectory to make the problem even worse - including potentially redirecting it towards Earth.
Engineers could design a reconnaissance mission to try to get a better estimate of 2024 YR4’s mass, but the best time to do so would be in 2028 - only three years away. Designing and launching a purpose built mission in that tight timeframe has never been done before, and while it could be for a mission to solve something that’s a high enough threat level, 2024 YR4 probably isn’t it.
Fraser's video on how we stop asteroids from hitting Earth - or in this case the Moon.
That being said, we could repurpose existing missions that are already in space or in development. OSIRIS-APEX, the name for the extended mission for the OSIRIS-Rex mission that is currently on its way to Apophis, another near-Earth asteroid. Psyche could also be commandeered on its way to its main-belt target. But in either case, those missions would have to give up their intended targets in order to get close enough to 2024 YR4. Another option is Janus, which is currently sitting in storage, but it’s unclear how well they would do in defining its weight.
Given the uncertainties around the deflection option, the paper notes the other option is at least feasible. Destruction of an asteroid can come in one of two forms. The first is “kinetic” - basically hitting it with something big and heavy enough to break it into smaller 10m chunks. DART recently proved the idea of redirecting an asteroid by doing the same thing - but hitting it with the intention to destroy it would be a different level of difficulty, though certainly one that we could design and build in time for a launch window of sometime between April 2030 and April 2032.
The other option to destroy it will stir a feeling in the hearts of nineties kids - we could nuke it. It might not involve Bruce Willis sacrificing himself, but setting off a nuclear explosion at some height off the surface of 2024 YR4. Known as the “height of burst”, we would still need some reconnaissance to try to tailor the explosion. But, the paper calculates that a 1 megaton nuke would be enough to “disrupt” 2024 YR4 no matter what size it is - and that is well within our current nuclear arsenal.
To be fair, we’ve never tested a nuclear explosion in space before, but physics certainly says it’s possible. It's as much a political decision as a technical one as to whether that would be a viable option for this particular threat to our planetary system. We’re not even sure if 2024 YR4 is actually going to hit the Moon yet, and we won't find out until 2028. But if we find out it is, it’s best to at least have the ability to disrupt it if we want. That decision will have to be made in the next few years as the window to get missions off the ground is growing smaller every day - whether they’re nuclear or not.
Learn More:
B. W. Barbee et al - Space Mission Options for Reconnaissance and Mitigation of Asteroid 2024 YR4
UT - Will YR4 Hit the Moon? We Won't Know Until 2028
UT - The Mother of All Meteor Showers Could Threaten Satellites
UT - Remember that Asteroid That Isn't Going to Hit Earth? We Could Send A Mission to Explore it!
