Comet May Have Missed Earth By a Few hundred Kilometers

First time accepted submitter afree87 writes "A re-analysis of historical observations at a Mexican observatory suggests Earth narrowly avoided an extinction event just over a hundred years ago. On August 12th and 13th 1883, an astronomer at a small observatory in Zacatecas in Mexico made an extraordinary observation, some 450 objects, each surrounded by a kind of mist, passing across the face of the Sun. This month, Hector Manterola at the National Autonomous University of Mexico suggests these were fragments of a comet. 'If they had collided with Earth we would have had 3275 Tunguska events in two days, probably an extinction event.'"

Long-term implications

[JoshuaZ]

While we know that in practice actual asteroid and comet strikes on Earth are very rare, this sort of thing helps illustrate how we need to do a good job tracking the larger threats and preparing to deflect them if necessary. The good news is that the WISE mission http://en.wikipedia.org/wiki/Wide-field_Infrared_Survey_Explorer [wikipedia.org] has successfully tracked most of the large asteroids that have near-Earth orbits and none of them are threats in the immediate future. There are however other dangers. For example, comets that are no longer outgassing could potentially have very elliptical orbits that would not be detected by WISE. Also, there may be smaller asteroids that WISE has not detected that could make a life pretty unpleasant in a more narrow area even if they don't lead to an extinction event. An asteroid that was around a thousand feet across (300 meters) could devastate a city and could easily escape detection from WISE. Moreover, there are some real worst case scenarios. If such an asteroid landed in either Pakistan or India for example they might think that the other had launched a nuclear weapon at them.

In general, we aren't doing enough to deal with potential existential risks. At this point, we don't know if the Great Filter is in front or behind us. http://en.wikipedia.org/wiki/Great_Filter [wikipedia.org]. The basic idea of the Great Filter is that the easiest explanation of the Fermi Paradox is that there's some set of events that make life unlikely to reach the interstellar level. That could be behind us, if for example life arising is unlikely or multicellular life arising is unlikely. But at least some filtration has to be in front of us. It seems that natural events (like asteroid strikes) are not common enough to be the entire filter. But there are other potential filtration events. Learning more about these issues not only helps preserve humanity it also helps get insight into why we seem to be alone. Unfortunately, funding for these sorts of things is tiny. The WISE mission for example was only $320 million and was used not just for the asteroid work but a lot of other good astronomy for objects both inside our solar system and more distant objects. This is a tiny cost compared to what is spent on non-science issues, and is particularly tiny when one considers it as being paid for almost exclusively by a single country.

Re:Extinction level?

[dachshund]

It would probably have been calamitous but extinction level, maybe not. I mean most of those would probably have landed in the ocean anyway, with maybe a thousand or so dropping on land.

My understanding is that a major asteroid strike on the ocean could be catastrophic due to ozone depletion.* It's just a theory (because obviously we haven't tested it), but if true it would indicate that asteroid strikes are a bad thing no matter where they hit.

http://www.physorg.com/news/2010-10-asteroid-ocean-deplete-ozone-layer.html [physorg.com]

* This depends on a single very large asteroid, so a bunch of smaller ones might not be as much of an issue. Unless they're fast moving.

I'm thinking no

[The Bad Astronomer]

I'll be blunt: I'm not buying it. I give details on my blog [discovermagazine.com], but I think there are too many holes in the idea. For one thing, comets aren't that small; passing within a few thousand klicks of one would put us inside the debris field. We'd have seen vast numbers of meteors. For another, no one else saw it? At all? Comets can be visible during broad daylight - I've seen one myself - yet there's not a single other observation of a comet that close from any other person on Earth. So I am very, very, very skeptical.