by Brian on September 3, 2003

The Age is running a story today headed Asteroid Heads for Earth. Which sounds fairly scary I guess. The article then says that the best estimate is that it has a 1 in 909,000 chance of hitting the earth. I guess Asteroid might be heading for earth, like you might win the lottery this week was too long to fit above the story.



chris 09.03.03 at 4:52 pm

But how about “Asteroid 15 times more likely to hit earth than you are to win the lottery this week!” ?

(Which is roughly right, at least for the UK’s national lottery).


Jon 09.03.03 at 5:29 pm

Msnbc.com reports that after further review, the probability is 1 in 2.2 million. Funny thing is they headlined their story about this change: “Asteroid strike ruled out for 2014” – <http://www.msnbc.com/news/960340.asp?0dm=C13LT> I’m guessing that their threshold for declaring something “ruled out” is 1 in a million.


JNelsonW 09.03.03 at 5:30 pm

Well, heading towards something isn’t the same as colliding with it. When I say I’m heading to grandma’s house, that doesn’t mean I’m going to necessarily run into and destroy it.


Chris Lepore 09.03.03 at 6:27 pm

It seems highly unlikely we’re going to be wiped out by this particular asteroid come 2014, but not as unlikely as we might wish it to be. After all, even using MSNBC’s 1:2.2 million forecast, one could say that odds like that pay off 4 times a day in New York City.


Matthew 09.03.03 at 6:55 pm

Well yes, but we are concerned with 8-9m New Yorkers, and so the comparison would only be relevant if there were 8-9m earths we were worried about. In which case 4 would be zapped. But as we are worrying about only one earth, it is like saying i’m worried about a 1 in 2.2m chance thing happening to a Mr G.A.XYZ from New York, i.e. it’s highly unlikely.

My favourite example of low probability odds was a UK lottery statistic in the LRB, where it noted that to have a higher chance of winning the jackpot than dying before it is drawn you must buy the ticket only 3 1/2 mins beforehand. If you are 16 you get an hour, if you are 75 just 24 seconds.


michael 09.03.03 at 8:32 pm

Matthew has pre-empted me.

Calculating the probability of someone winning a particular lottery is straight forward, and the result — 1 to 13.98 million against in the UK’s national lottery, for example — is meaningful. There are only so many permutations of possible input, and the output will certainly be one of them.

Calculating the chances of an asteroid hitting us is far from trivial.

The “probability” in this case is a function of the uncertainty in our knowledge of the asteroid’s orbital trajectory and speed. And in the case of long-period bodies, which are the most difficult to spot and hence the most dangerous, it is also a function of our estimation of how the presence of other bodies will affect its orbit.

When I see astronomers smiling at television cameras, happily quoting precise odds on our survival, I can’t help thinking that they would be happier running Wall Street hedge funds.


Loren 09.03.03 at 10:06 pm

While we’re on the topic of odds and perdition: you don’t need to calculate the likelihood of an asteroid collision to know that the world is going to end soon.


… no, I don’t really believe in doom soon (near-flying asteroids be damned — http://web.mit.edu/www/writing/doom.html)


Matt McIrvin 09.03.03 at 11:06 pm

Jon: Actually, the phrase “ruled out” does make sense. The distinction is one that the original news story failed to make, because they were misreading the probabilities on the NASA NEO Current Impact Risks page.

These potentially hazardous asteroids often have several possible collisions with Earth. The probability listed on the front page is the cumulative probability for all possible collisions, not the probability for the earliest one, which can be seen by going to the page for the individual asteroid. The initially listed probability for 2003 QQ47’s 2014 collision with Earth was about 1 in 1.75 million; the “1 in 909,000” number cited on the wires was the cumulative probability. As you can see, now the 2014 collision’s probability is nil and it is not listed, but there are still impact possibilities for 2003 QQ47 in the late 21st century.

That NASA page is the go-to place for analysis on giant asteroid scare stories, but you have to know how to read it.


Matt McIrvin 09.03.03 at 11:14 pm

And, actually, I should qualify what I said above: by “all possible collisions” I meant “all possible collisions within the range of interest of the NASA SENTRY program”, namely the next 100 years. Beyond that, asteroid impact predictions usually get too uncertain to bother with, with some oddball exceptions.

I’m actually not sure where MSNBC’s “1 in 2.2 million” number comes from; the cumulative probability for 2003 QQ47 on the NASA site is higher now, more like 1 in 500,000, mostly because of possibilities in 2058, 2067, 2069, 2087, and 2096. Maybe it went up after the story was written.


Brett Bellmore 09.04.03 at 12:04 am

Let’s keep in mind that, while the odds of a major asteriod strike in any given year are pretty low, when it does happen so many people will be killed, that asteroid impacts are, on average anyway, a major cause of death. Theoretically. In the long run.


Geoff Pynn 09.04.03 at 3:38 am


In the VERY long run. The sum of the impact probabilities (from NASA NEO Current Impact Risks) over the next 100 years is 3.28 x 10^-3, or 0.00328. Which, if the risks remain roughly consistent over the long run, means we have a 6.56% chance of impact over the next 200,000 years (I think I’m doing this math right), or roughly the same amount of time since the speciation of homo sapiens. So chances are excellent that we’ll get an impact within the next 3,051,000 years or so.

But GOSH that’s a long time! Hopefully long enough to figure out how to deal with the risk. (Hey, it’s roughly 61,000 times as long as it took from Watson and Crick’s discovery of DNA to the sequencing of the human genome, which I have to regard as a problem of similar difficulty.)


Chris 09.04.03 at 6:22 am

NEO uses the phrase ‘ruled out’: “The new data have enabled astronomers to refine the orbit of asteroid 2003 QQ47, and so rule out 13 of the 31 potential impacts originally listed on the JPL Current Impact Risk table. Among those ‘virtual orbits’ to be ruled out was the one for 21 March 2014, which gave the asteroid its Torino 1 rating.”


bryan 09.04.03 at 10:08 pm

HEY, I just won the lottery! Wow, this is my lucky day, I wish everyone a happy life!

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