This is another of those sensationalist doomsday stories in the red top tabloids scaring people. The stories say that we are 100% certain to be hit by an asteroid. Well, yes, for small asteroids, but we are 100% certain to be hit by lightning too, many times a year. Your chance of dying of an asteroid impact is far less than that of dying of a lightning strike, 10,000 times less likely.

  • Yes it is close to 100% certain we are hit again by a small meteorite like the Chelyabinsk one over the next few centuries and close to 100% certain for larger asteroids over thousands or millions of years
  • Yes, occasionally people die of meteorite strikes, including two reindeer herders in Siberia in 1908
  • No it is not something to worry about. It is worth doing something to detect small asteroids so we get warning of them, but it is not something to scare you. With warning we can evacuate - or - 99% certain - it doesn’t hit an urban area and we just organize tourist trips to watch the impact into the sea or a desert or ice sheet from a plane :).
  • It’s 10,000 times less likely as a personal risk than lightning, it’s also less far likely than dying by being hit by a large hail stone in freak weather conditions!
  • Within a few years we will have nearly finished the survey of 1 km and larger asteroids (95% of them already found) and have already completed it for 10 km asteroids. With the $50 million we could nearly complete it down to 45 meters in six years. We currently find one to two thousand of these a year but we could find a hundred times that many.

    Plans to launch asteroid detection telescopes keep getting shelved (most recently NASA chose two missions to visit asteroids and study them close up, Lucy for a metal asteroid and Psyche for Jupiter trojans over NeoCAM).

    However, we do have the LSST coming online in the early 2020s, a big telescope that will increase discovery of asteroids hugely, 64 times the search volume of Pan-STARRS and covers entire sky as seen from its location every 2–3 days.

IN DETAIL

Many get killed by lightning strikes every year in the US. Two reindeer herders were killed by a meteorite in 1908 and probably a few per century die of meteorite strikes.

And we have giant telescopes every night looking for asteroids. They find around a thousand a year of the ones of 140m or larger Discovery Statistics and about 1 a month of 1 km or larger.

If you see any of these stories just go here

Sentry: Earth Impact Monitoring

It looks techy but don’t be put off by that. All you need to interpret it is to be able to distinguish the colours yellow, orange or red.

Click on “use unconstrained settings”. Then look at the first row. You don’t need to look at any other rows as it is ordered with the object with the highest alert level first.

If it is white, green or blue, the usual situation, then there is nothing of any concern to the public. Yellow, orange and red are increasing levels of alert. Only red means a certain impact. With yellow, you can expect it to change to green then white as they get new observations, with a near certainty. With orange then it is also most likely to change to a lower alert level as they find out more.

If it is orange or red it would be probably the first news item in every TV story for the day. With yellow it would probably get a lot of media interest too given the interest in asteroids nowadays. You won’t need to go hunting through sensationalist press to find out about it. Just switch on your TV and listen to the news.

If the object named in the sensationalist stories isn't in the list, don't be alarmed by that. It's probably one of the removed objects - or else - most of the stories indeed - it's a harmless flyby that never had any risk of hitting Earth and you find it in the close approaches table instead.

This goes back to a story about the B612 foundation reported in news . com . au which tends to be sensationalist. The answer is that yes we are 100% certain to be hit by small asteroids, and indeed if you wait millions of years, large ones too. But they are also very rare. Once every 80 years on average for a 20 meter diameter Chelyabinsk meteorite. That makes it 99.9% certain that Earth is hit by one of these in 800 years and you might as well call it 100% certain for 8000 years. Since only 1% of Earth’s surface is urban, it’s about 8000 years on average between impacts on urban areas, with most hitting deserts, the sea, or remote rural areas with few inhabitants, which explains why our history doesn’t have accounts of asteroid impacts in the way it does of volcanic eruptions, tsunamis, earthquakes, or even hail storms.

Do you know anyone who has been killed by an asteroid? Two reindeer herders were killed in 1908 and there are various other reports suggesting that there are a few per century die of asteroid impacts worldwide. Compare that with many per year dying of lightning strikes worldwide in the US alone and you can see that you are far less likely to be hit by a small asteroid than a lightning strike.

The chance of dying of a lightning strike in your lifetime in the US is about

The chance of dying of an asteroid strike is currently estimated as

So you are more than ten thousand times less likely to die of a meteorite than a lightning strike.

Did you know hail storms are sometimes deadly in rare atmospheric conditions? A thousand English soldiers were killed by a hail storm during the hundred years war in 1360.

Black Monday hailstorm

There are many examples of deadly hailstorms, rare though they are.

There are no examples in history at all of thousands dying of meteorites apart from a record of 10,000 Chinese people dying in Ch'ing-yang in 1490 may have been due to a large comet breaking up in the atmosphere, but could also have been a hail storm.

And - as time goes on and they map out the asteroids more and more that risk will go down, because if you can predict a small asteroid you can

  • deflect it (many ways to do it especially for small ones, can be as simple as dusting it with white material to change its thermal properties causing a gentle nudge as it spins and radiates heat that it received from the dark side)
  • evacuate the impact zone
  • or just organize tourist trips to watch the impact if it is in a remote desert or ice field or ocean, or agricultural area with few inhabitants, which is what will happen 99% of the time.

As for the larger ones, large enough to have global effects, again wait for 100 million years and you have a good chance of being hit by a 10 km diameter asteroid large enough to have major global effects. But they know all the asteroids that big that come close to Earth, and none can hit Earth in the next century.

The smallest ones with some global effects are about 1 km in diameter. We know 95% of those. Of those 1950 DA could hit us in 2880 but the chance is very small with plenty of time to deflect for future generations if needs be.

2010 AU118 needs to be monitored because it does regular close flybys of Earth with a tiny 1.8 in 100 million chance of hitting Earth this century,not a level considered enough to be significant but they keep a close eye on it of course.

Both of those are only just large enough to have some global effects - reducing global temperatures a little through all the dust thrown into the atmosphere by the impact so could affect global crops for a few years.

We have found 95% of them so far, and find one of these every month and should find most of the remaining few dozen by the mid 2020s especially with LSST coming on line with 64 times the search volume of any other telescope by around 2022. By then we will know pretty much for certain, but the risk is already pretty much retired from asteroids of 1 km or larger, it’s not very likely that any of the few remaining ones hit Earth this century.

That leaves long period comets and the chance of a large comet hitting Earth is very tiny, the closest any known long period comet has come is Lexell's comet in the seventeenth century at six times the distance to the moon. (It was a long period comet that was briefly changed to a short period comet by Jupiter, it has not been seen again and is thought that the most likely fate is that it was ejected from our solar system with a second flyby of Jupiter).

Compare this with the asteroids that fly past every day, often several to a day, and you can see the risk from a long period comet has to be very small.

The very smallest, meteoroids, hit us every year. One the size of Chelyabinsk every 80 years which means they hit an urban area every 8000 years. At that size we can evacuate the impact zone even if we have only a day or two of warning, it's most likely the sea or desert, might possibly be a remote village (maybe the villagers wake up to the sound of helicopters landing in their gardens to whisk them away to safety ). It would be more tricky if it was a city, but - that's the thing you can do with almost no warning is to evacuate everyone you can and warn the ones who are within range of a blast that could damage windows to stay away from windows and protect themselves from flying glass during the impact.

The B512 foundation want to put 8 small synthetic tracking telescopes in orbit to help find asteroids more quickly at a modest cost of $50 million. It is a charity and you can donate to support their activities. It could find more than 70% of NEOs larger than 45 meters in diameter in less than six years. With larger 30 cm telescopes they could find 95% of them in the same time period.

This is a way for smaller telescopes to track faint moving objects. They do that by assuming that they are moving and stacking the images to find the movement when they can't actually see the object in individual images. The idea is to test whether there are asteroids moving in a sequence of photos with a short exposure time taken rapidly one after another instead of using a single photograph with a longer exposure time. By stacking them with the images aligned in many different ways, if a new object pops up in one of the stacks, that’s an asteroid. It's been made possible by CCD chips that let you read off the data very quickly.

I describe this idea towards the end of this post

What can we do to retire the risk from asteroids quickly? by Robert Walker on Mars and Space

So the motivation of the B612 foundation is good. They have a way to hugely reduce even the tiny risk of an asteroid impact by using these synthetic tracking space telescopes.

Sadly it’s been reported instead as an alarmist “you are doomed” type story instead of a “any multi-millionaires, or governments, even of a small country, out there like to pay to pretty much retire the risk of even small asteroid in 6 years” story.

The original alarmist article source of all these stories is here

Anyone know an interested billionaire or multimillionaire :). $50 million is a level a which e.g. a Euromillions or Powerball lottery winner could finance it from just a fraction of their winnings. So could many small countries, it doesn’t have to be an ESA or NASA project. India, Japan, even private foundations could afford it easily.

The reason NASA never flew NeoCAM is not because of any flaws in the idea. It is because it is proposed as a science mission and you get more interesting science from a close up study of an iron asteroid or of Jupiter trojans than a telescope to find Near Earth Asteroids. If it was ring fenced for asteroid detection then it would surely have flown long ago.

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