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An asteroid about the size of a refrigerator shot past Earth last week, and astronomers didn't know the object existed until hours after it was gone.
It was a close call (from a cosmic perspective); the space rock's trajectory on Oct. 24 carried it over Antarctica within 1,800 miles (3,000 kilometers) of Earth — closer than some satellites — making it the third-closest asteroid to approach the planet without actually hitting it, CNET reported.
Scientists were unaware of the object, dubbed Asteroid 2021 UA1, because it approached Earth's daytime side from the direction of the sun, so the comparatively dim and small visitor went undetected until about 4 hours after passing by at its closest point, according to CNET.
OK, this one is very small and probably would not have made much of a mess on Earth, and may even have burnt up on entry. However, how large do these things have to be to be detected prior to their arrival?
The reason it wasn't seen until after it had passed by earth was because it came from the direction of the sun which made it too dim to detect easily. Had it come from a different direction it probably would have been seen.
OK, this one is very small and probably would not have made much of a mess on Earth, and may even have burnt up on entry. However, how large do these things have to be to be detected prior to their arrival?
There's no criteria.
There's work underway to improve space surveillance, but there will always be some % chance of us missing the "big one". The idea is to get us to a high % chance of detecting city-killers and larger space rocks several years before they'd cross our orbit.
DART is launching soon, to test out our ability to redirect them.
If we were to detect a big one that had a high chance of impacting us within a year or two, right now, it would be a really tough question of what to even do. We can't be sure we wouldn't knock it into an orbit that made it a guaranteed impact, and--even if we started planning/building interceptor spacecraft the second we detected it, it would be a crap-shoot that we could even hit the thing.
I guess if it were a surprise dinosaur killer a year or two out, we'd probably throw everything we had at it. Right now, there's about 30 medium and heavy launch vehicles (mostly Falcon 9's, with Some Atlas, Vega, Falcon Heavy, and Soyuz) ready to go in the next 6 months. That's quite a bit lifting power, but the actual interceptors would be a big problem.
Most of those payloads are Earth-orbiters and they don't have the guidance systems to intercept an asteroid in deep space. As well, the upper stages on those vehicles might not have the capability to put their payload on an intercept course.
I imagine we'd make a lot of scientists, soldiers, and companies unhappy by pulling off delicate instruments, batteries, and transmitters and strapping modified (yield turned WAAAAY up into the megatons) nukes to anything we thought could get close, like the JWST, some GEO telecom birds, and probably a classified milsat or two. We might also co-opt some more under-construction deep space probes or space tug demonstrators (and anything else with a robust AVCS system), accelerate their completion and stack 'em on what LV's are ready to roll.
Then we'd have to kludge together some sort of proximity fusing system, and also figure how the heck we're going to guide the birds to the target. Every telescope, and most of the transmitters we have would need to be pointed at the rock and we'd have to time the interceptor launches and contact intervals to avoid RFI (confusing the interceptors with each other's instructions). Then we'd just keep shooting and praying until all the chambers were empty and we see if we knocked the thing far enough off course.
I think it's reasonable that we could probably put 3-5 or so spacecraft into the target.
Whether they'd move it enough or not, is another question. Thus, DART. A year from now, we'll have a much better idea of how to shift potentially dangerous space rocks.
When the Vera Rubin Observatory goes online in 2023, it will become the world’s largest astronomical all-sky survey telescope. An important result of our work is to confirm that within just the first year of operation, the Vera Rubin Observatory will discover more than 9,000 Near-Earth-Asteroids larger than the Tunguska asteroid (diameter approximately 50 meters), as well as thousands of smaller asteroids. This will roughly double the total number of “city killer” asteroids that have been discovered to date by all previous observatories. However, the most significant part of this work is that many of these newly discovered asteroids will have a possibility of hitting the Earth which cannot immediately be ruled out.
You need a big telescope to detect small objects. The LSST has a primary mirror diameter of 8.4 m (27 ft. 6.7 in.).
It was the size of a refrigerator. It clearly wasn't detected because it was very dim and left a small radar signature. Scaling up, potential impactors are easier to spot (in the same way that a Cessna is easier to see than a bird, a regional airliner even easier, and a widebody easier still) and less numerous (usually by something of an order of magnitude with each doubling in size). Comparing this to a dangerous impactor is literally akin to say "Oh my God! A robin just flew into my window! What if it had been a 737?".
The sole point of interest in the article is our ability to detect such small objects at any point in their journeys throughout the solar system. Otherwise, it's just click-bait.
The problem may well be that IF we managed to hit one coming in, then there are going to be many pieces each of which could be a potential impact asteroid.
Some are going to miss Earth as a result of the initial attempt to divert the large asteroid, but the many smaller pieces may have consequences of their own if they hit Earth somewhere. Yes, they will be smaller, but after a certain size, it doesn't matter - you are still going have mass destruction and develop a sunlight blackout with years of cold weather, maybe tectonic Earth changes too.
The problem may well be that IF we managed to hit one coming in, then there are going to be many pieces each of which could be a potential impact asteroid.
Some are going to miss Earth as a result of the initial attempt to divert the large asteroid, but the many smaller pieces may have consequences of their own if they hit Earth somewhere. Yes, they will be smaller, but after a certain size, it doesn't matter - you are still going have mass destruction and develop a sunlight blackout with years of cold weather, maybe tectonic Earth changes too.
I doubt any such future system wold be trying to disintegrate the asteroid. Much more likely it would be trying to change the trajectory to miss Earth.
See the DART thread in this forum for a proof of concept test.
Space rocks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth's atmosphere and cause little or no damage.
This may well be the case however, there have been several captured on windscreen cameras (recently in Russia and other places) which have exploded above the ground causing windows to be blown in, etc. If this happens in the countryside then it will not cause much trouble, but over cities may be another matter. Then we have the flattened trees at Tunguska which was caused by an air burst and no crater was ever found. Although the scientists reckon this one was much larger than 25 metres, an air burst could still knock out some ground infrastructure.
Quote:
The explosion happened over the sparsely populated northern forestland above the Podkamennaya Tunguska River in what is present-day Krasnoyarsk Krai.
The blast released enough energy to kill reindeer and flatten an estimated 80 million trees over an area of 830 square miles (2,150 square km). Witnesses reported seeing a fireball – a bluish light, nearly as bright as the sun – moving across the sky. A flash and a sound similar to artillery fire was said to follow it. A powerful shockwave broke windows hundreds of miles away and knocked people off their feet.
I wonder how scientists will gently push the meteorite off its present course without knocking pieces off it? Particularly if it is a large one, it will need a huge amount of force at just the correct angle just to deflect it a very small amount to miss Earth. I am sure there is a whole science to this and I just hope they have some science and mathematical wizards on the case. I suspect that all the deep bunkers in the world will not save governments from an event which will kill the rest of us.
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