Mar 13 2023

New Asteroid Probably Won’t Hit Earth

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NASA recently discovered a 50 meter wide asteroid whose orbit will come close to Earth. They estimate a close approach in 2046, which will likely bring the asteroid within 1.1 million miles of the Earth, about four times the distance of the moon. However, there is always uncertainty in calculating orbits, and the farther into the future you try to project their path, the more uncertainty there is. At this point in time NASA estimates a one in 560 chance that the asteroid, dubbed 2023 DW, will hit the Earth in 2046.

Orbits are calculated through multiple observations of the object along its orbit. We have to see how it is moving, and the longer the observation the greater the precision. For recently discovered objects, like this asteroid, there is more uncertainty in the orbital calculations, which is why NASA cannot completely rule out an impact. Because it is a near-Earth object, however, they will continue to make observations, refining their calculated orbit, and reducing the uncertainty.

Interestingly, the current scale for designating the risk of an object hitting the Earth, the Palermo scale, is not based on a simple percentage probability, but on the probability relative to the background rate of impacts. A Palermo scale of 0 means that the chance of a particular object hitting the Earth is no different than the background rate of impacts. The scale is also logarithmic, so a Palermo rating of 1 means a chance of impact 10 times the background rate, 2 is 100 times. 2023 DW has a Palermo rating of -2.17.

What would an asteroid of this size do on impact? That also depends of velocity. Objects coming in from the outer solar system can be going pretty fast when they cross Earth’s orbit – often compared to the speed of a bullet. But the fastest objects would be interstellar, and even an object of this size hitting at interstellar velocities could be catastrophic. But this object is in a 271 day orbit, and its speed relative to the Earth is not very fast. It would only pose a danger if it scored a direct hit on a city or high population density area. So there is a low chance of a hit, and if it did there is a low chance of significant damage.

But what would we do if this object had a much higher chance of hitting the Earth? What if, after further orbital calculations, NASA determines that this is a Palermo 2 or 3 object? What if the probability of an impact is >10% or so, or even a near certainty? The question is – what is our current threshold for deciding that we should do something about it? One of the biggest science news items of last year was the successful DART mission, which tested our ability to slam a rocket into an asteroid and deflect its trajectory. This is the most likely method we would use to deflect an object away from the Earth. So now we have the luxury of asking the question – should we try to deflect this asteroid?

There are a few parameters that determine how feasible such a mission would be. The biggest is time – how long until the asteroid hits. The longer we have then the more time we have to plan, build, and execute a mission. This asteroid won’t have close approach until 2046, so we have 23 years to act. Also, the more time we have then the easier it is to deflect asteroids, because smaller changes to their orbit are necessary to avoid collision. If we have a couple of decades, a slight nudge might do it. If we only had a few months, there might be nothing we could do about it. Also the vector of the orbit would also be a factor.

Perhaps 2023 DW is a good opportunity for a follow up test to DART. It seems like a good candidate and we have plenty of time. It would be good to see how quickly we could plan and execute such a mission, and what the results would be. This might be a great opportunity for a dry run in case we ever really need to divert an asteroid. Such a mission, however, would not be risk free. If we are not careful it is theoretically possible that we could alter 2023 DW’s orbit to accidentally make it more likely to hit Earth. But if we did it early enough we could still have time to correct the mistake.

We are essentially living in the first moments of human history when we are not helpless before the prospect of being hit by a large asteroid. While the technology, surveillance system, and response capability have not yet been perfected and fully developed, DART confirms that we do have the technology to deflect incoming asteroids. Detecting such objects now comes with a decision of whether or not we are going to act. I don’t see any evidence this is being discussed for 2023 DW, and it wouldn’t be until we make further observations of it’s orbit. There is no reason not to observe a full 271 day orbital period to get the most precise calculations we can, before even raising the prospect of a DART-like mission, whether for practice or need. And there will be other asteroids, perhaps better candidates. This is likely not a rare opportunity – but it could be a good one.

Probably there will not be much follow up that hits the mainstream media, unless the probability of impact is upgraded rather than downgraded, which is far more likely. But it can be fun to follow asteroid tracking, and might get more interesting the more we have an active program to deflect potential threats to the Earth.

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