The December 26 tsunami was a deadly reminder that even exceedingly rare natural events can happen, and can have devastating results. The tragedy was compounded by the fact that warnings could have been issued and responded to, but the systems to do so weren't available. But around the same time, we came very close to having a second reminder, one which could have led to an even more terrible result.
On December 23, astronomers noted that asteroid 2004 MN4, which orbits the Sun near the Earth, had a 1-in-300 chance of hitting the Earth in April of 2029. This corresponded to a rating on the Torino Scale of 2 -- a slight chance of impact, with widespread regional damage if it happened. The Torino Scale was developed as a way of putting asteroid strike possibility announcements in context, to make sure that the level of risk -- so far, always quite low -- was clear. Every time a possible asteroid hit has been announced, refined study of the rock's orbit over the subsequent few days eliminated the possibility, lowering the Torino Scale rating to 0.
Late on December 24, the Torino Scale rating of 2004 MN4 was upped to 4, with a 1-in-60 chance of hitting the Earth. On December 26, the 1-in-60 chance was quietly increased to 1-in-37. While still a 97% chance of missing the Earth, the Torino 4 rating was by far the highest level ever given to a potential impact. Finally, on December 27, astronomers were able to refine the asteroid's orbit sufficiently to determine that 2004 MN4 will miss the Earth in 2029, albeit only by a few tens of thousands of miles.
We got lucky with 2004 MN4 -- it won't hit us. But in a way, we were also unlucky, as once again asteroid impacts will largely be the concern of bad moviemakers and obsessive astronomy buffs. The characteristics of 2004 MN4 would have been close to ideal for an impact prevention effort. At 440 meters in diameter, it was big but not planet-killer big; and at 24 years to impact, we would have had sufficient time to develop the tools and mission to shift its orbit. Apollo astronaut Rusty Schweickart has been thinking about the Earth-impacting asteroid problem for awhile now, and I attended a talk he gave a few months ago spelling out our choices. I wrote a lengthy post for WorldChanging going into the details of his talk, and what we can do to prevent an impact if we get sufficient warning.
We may not get that kind of warning next time. One of the closest near-Earth asteroids in awhile zipped past us on December 24, coming to within 1.2 million miles from hitting the Earth -- a clean miss, but alarmingly close by astronomical standards. The big problem was that we only first noticed it on November 3; if its orbit had been slightly different, we would have had no time to do anything but watch it approach and hit. Depending upon where it impacted, the results could have orders of magnitude worse than the December 26 tsunami. While there are global efforts to identify and track near-Earth asteroids, funding is tight, and much work remains to be done.
Complicating matters is that as we spot and track more asteroids, the possibility of false alarms increases. Calculating an asteroid's orbit is difficult, especially when it's a recent discovery with too few observations to get good numbers. Getting it wrong either way can be a costly mistake. In early 2004, astronomers discovered a small (~30 meter) asteroid seemingly heading right towards Earth, with a northern hemisphere impact possible within days; the data were spotty, however. Astronomers were set to notify the White House, but better numbers came in; the asteroid missed us by over 8 million miles.
False alarms are the inevitable result of any kind of disaster monitoring system. As many as 75% of the tsunami alerts issued by the International Tsunami Information Center since 1948 turned out to be false alarms -- the tsunami appeared, but were far smaller than feared (sometimes just a few inches in height). Although newer technology makes false alarms much less likely, they can't be ruled out completely. The new tsunami warning systems likely to be installed in the Indian Ocean may well lead to numerous frightening warnings which come to nothing long before they raise a useful alarm. The main danger arising from false alarms isn't just the expense of unnecessary evacuations, or even the risk of panic -- it's complacency. Relying upon warning systems that people don't listen to because they're almost always wrong are as bad as not having warning systems at all.
The more we understand our planet (and planetary system), the more opportunities we'll have for seeing dangers before they arrive. On balance, this is a good thing. But along with improving our abilities to measure and monitor our world, we'll need to improve our abilities to evaluate the risks we face.
