Monday, March 30, 2009

Asteroid 2008TC3 is now the Almahata Sitta meteorite For decades, geologists have classified meteorites based on their geochemistry, and astronomers have classified asteroids based on their reflectance spectra. Until now, these have been difficult to cross-correlate. To do so requires one of two methods. The first is to build a robotic spacecraft to land on an asteroid, pick up a piece, and safely return it to the Earth. The second is to find an asteroid on a collision course with Earth, and then pick up the pieces after the impact. This paper uses the latter approach.

Emily and Amir over at the Planetary Society have excellent write ups. Have a look if you haven't seen them. The smoke trail pics are particularly cool.

For long time fans of the lounge, this result shows that my estimate was 22 km NW of the main debris field, and 12 km NNE of the closest fragment. Had I remembered to move south by tan(latitude) x altitude from the apparent fireball location, I might have actually picked it. Now you know why I'm not a structural geologist.

I think it's fantastic that three of the Sudanese are high in the authorship list, and that they involved their undergrads on the project. Opportunities to do cutting edge science don't come along all that often for undergrads at African universities, and it is great that these young people were able to make a genuine contribution to Earth and planetary science. The nature paper is a fairly easy read, for those with access.

The paper briefly mentions that some of the carbonaceous matter in this meteorite was diamond. I referenced a couple of ureilite diamond papers in my thesis; they are considered classic examples of impact-formed diamonds.

Of course, the wonder of this discovery inevitably brings in discussion of missiles in space to deflect future impactors. I would like to go on the record as against such projects.

First of all, they would deprive us of great science, like this.

Secondly, the missiles and bombs inevitably nominated as the tools of choice for asteroid deflection are way more dangerous than asteroids are.

Thirdly, any technology which can deflect an asteroid away from the Earth can deflect an asteroid from one part of the Earth to another. We have enough ways of killing each other already.

And finally, bolide's don't kill people. Volcanoes do. And nobody wants to blow them up.

We don't blow up tsunamis, or hurricanes, or river floods either. We predict when and where they are going to happen, tell people to get out of the way, and then fix the damage after the event. There is no reason the same procedure can't be used for impactors, once early detection and prediction becomes commonplace. Given any sort of discount rate at all, a warning system will be far cheaper, safer, and saner than building a multi-zillion dollar doomsday bomb to deflect the asteroid.

Meteorite detection will only improve with time. In fact, I suspect that within my lifetime, an Earth-impacting object on a collision course with an accessible part of the developed world will be detected at least 24 hours in advance. I am even prepared to make a prediction about the first such event. That is this:

Once the orbit is calculated, and the target and time is announced, more people will travel into the target zone than away from it. I might even be one of them.

Jenniskens, P., Shaddad, M., Numan, D., Elsir, S., Kudoda, A., Zolensky, M., Le, L., Robinson, G., Friedrich, J., Rumble, D., Steele, A., Chesley, S., Fitzsimmons, A., Duddy, S., Hsieh, H., Ramsay, G., Brown, P., Edwards, W., Tagliaferri, E., Boslough, M., Spalding, R., Dantowitz, R., Kozubal, M., Pravec, P., Borovicka, J., Charvat, Z., Vaubaillon, J., Kuiper, J., Albers, J., Bishop, J., Mancinelli, R., Sandford, S., Milam, S., Nuevo, M., & Worden, S. (2009). The impact and recovery of asteroid 2008 TC3 Nature, 458 (7237), 485-488 DOI: 10.1038/nature07920


Chris Phoenix said...

You're arguing against a strawman. No one is proposing that we send up a multi-billion-dollar rocket against a rock that would do, at most, a few million dollars in damage. Your science is safe.

What people are worried about is a "dinosaur killer" asteroid, or its slightly smaller cousins. The kind that comes along only once every few thousand years, but can devastate a whole continent or change the climate.

Others can argue about the frequency and relative risk of such things. They may or may not be worth spending money on. But the arguments you give here simply don't apply.

Even the argument about directing asteroids to another point on earth - it's much harder to hit a specific target than to make it miss us entirely, when "anything that's not the planet" is the target.


C W Magee said...

Given that the dinosaurs lived 150 million years, I don't think dinosaur killers come along every few thousand years. There is a five order of magnitude disconnect there.

Humans have a natural tendency to overemphasize unique catastrophes over chronic problems already. Scientists have a duty to correct this misplaced prioritization, not take advantage of it. Fluvial flooding or air pollution will kill far, far more people than meteorites ever will, and can probably be mitigated more cheaply.

Chris Phoenix said...

Um, it's the slightly smaller cousins of the dinosaur killer that come along every few thousand years.

There's a theory that around 12,000 years ago, an asteroid grazed the atmosphere over North America and torched the place, killing every human on the continent.

Others have done the math on risk vs. cost of risk reduction. I agree there are lots of tangible risks that we should be working to reduce, such as coal power and automobile accidents. But my impression is that the risks from asteroids are actually noticeable, for reasonable estimates of size vs. collision frequency.


Chris said...

"There's a theory that around 12,000 years ago, an asteroid grazed the atmosphere over North America and torched the place, killing every human on the continent."

That is by no means the scientific consensus. Have a look at this blog post by Steven Novella for a quick overview of the current debate:

Chris Phoenix said...

As I said, it's a theory, not a fact.

But at the moment, there's good evidence that a continent-killing meteorite may have hit less than 15,000 years ago.

Such an event today would be unimaginably catastrophic. (It would have been back then also, but the people who actually knew about it would have all died.)

I find it interesting that no one is arguing against the meteorite hypothesis on the grounds of implausibility...

If there's a one in ten thousand chance of something similar happening next year, times 100 million deaths, times $100,000 per death, then we should spend $1 billion per year on prevention (assuming it can be prevented - which it probably can, if we spend that much).

Feel free to debate any of my numbers. As Winston Churchill said, at this point we're just arguing about the price.



C W Magee said...

What is the mechanism by which a bolide wipes out a continent without having a global scale atmospheric effect?

Chris Phoenix said...

What I remember is that it was thought to graze the atmosphere, dumping lots of (I guess) radiant energy overhead, without creating a massive impact that would throw up enough particulates to disrupt things worldwide.

Remember that whatever-it-was might have broken up, either high in the atmosphere or due to previous gravitational stress, so there might have been lots of smaller fireballs instead of one massive one. Think multiple Tunguska's.