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

Thursday, March 26, 2009

Fossil skullduggery request

Just a reminder that we don't yet have any naughty paleontologists to nominate as the 2009 Dr. Bad Example. If you hear on anything, post in comments.

Saturday, March 21, 2009

A thirsty southern star

When our solar system formed, the terrestrial planets when allow the practice of geology were assembled from solid material which condensed from the solar nebula. The composition of this nebula is hypothesized to have been the same as the composition of the sun, as spectroscopic measurements of the solar photosphere yield similar elemental ratios as analysis of meteorites for condensable elements.

The most common elements in the solar nebula were H, He, O, C, and N. At high temperature, they form the molecules H2, CO, H2O, and N (or NH3), which remain gaseous until very low temperatures. The combination of CO + H2O is possible because the molar C/O ratio is less than one- it is about 0.5 in the sun. Stars where C/O is greater than one will condense carbon and carbide to form carbon planets, as explained by Kuchner and Seager 2005. No such stellar systems have been identified to date. In our solar system, the abundance of all other elements is sufficiently low that all the metals and rock forming elements condensed from the solar nebula in the presence of H2O and CO gas. A simple stoichiometry exercise will show that condensing all the metal oxides with the reaction M+H2O -> MOx + xH2 will not deplete the solar nebula’s supply of H2O, so the CO + H2O buffer will remain in place until the H2O condenses, the CO reacts with H2 to form H2O + CH4, or the solar nebula dissipates.

The first 2 conditions require fairly low temperature, and are generally confined to the outer solar system. So condensation in the presence of H2O and CO is a good first order assumption for our solar system. Not surprisingly, H2O is pretty common in the solar system, and is found everywhere from the mantle of Earth and the acids of Venus all the way out to the Kupier belt.

The bulk solar composition is not too different to that of other nearby stars. So one might be tempted to assume that all planets condense under similar conditions. Is this valid? Let’s have a look at an interesting nearby system for comparison.

HD28185 is a sun-like star 138 light years away, in the constellation Eridanus. It is orbited by a 5 jupiter mass planet in a low eccentricity orbit with a radius similar to our own. This has led some folks to believe that any moon orbiting this planet may have liquid water present, and may be suitable for life as we know it. Does the star’s bulk composition have any bearing on this hypothesis?

HD28185 has higher concentration of most metals and carbon than the sun. But the oxygen, as reported by Gonzalez and Laws (2008) is only slightly elevated. Does this matter? A simple calculation below shows something interesting.

Unlike the solar nebula, the HD 28185 nebula does not contain enough water to buffer the condensation of the refactory major elements. Somewhere around 1400K 900K, the condensation of silicate minerals will suck all of the H2O out of the nebula. What will that do? I don’t know. Figuring it out requires a complex thermodynamic model, a plasma condensation apparatus, or an interstellar spaceship to find extrasolar asteroids. But one thing is certain. It will be different than what happened here. And taking the presence of water for granted may not be a safe assumption.

Friday, March 20, 2009

The right sky

Jen over at Twisted Physics and Cocktail Party Physics has recently set up SEEx- a translation service which allows speakers of science and media to communicate with each other. In her introductory blog, she mentioned the story of Neil Tyson and the wrong sky. In short, Dr. Tyson complained that despite getting all this historical trivia about the Titanic correct- which nobody would notice, much less care about, they screwed up the starscape that was visible after the ship sank. The thing that ticks me off about this is that it is trivial to do correctly. Fifteen minutes browsing the web (even the 1996 web) would have found them a downloadable program that would inform them that the survivors of the shipwreck would have seen this:

Tuesday, March 17, 2009

The habitable planet bubble

Greg at has recently put a price on terrestrial planets, as the successful launch of the Kepler telescope has piqued various people's interest in these worlds. More recently, he has announced a prize for the first planet to exceed a million dollars on his pay scale. Just for comparison's sake, he rates the Earth at 4 quadrillion dollars on this scale, while the small, cold Mars comes in at a paltry 13 grand. No currently known exoplanet can even match this value, with Gliese 581b maxxing out at just over $500. However, there is at least one low hanging fruit.

A few weeks ago, coming home from work just after sundown, I noticed a bright terrestrial planet hanging low in the western sky. As I am a women's tennis fan, I decided to name this planet after my favorite player.

The value of Venus in the valuation is strongly dependent on its calculated blackbody temperature, which in turn depends on albedo. Using the known value of 0.75, the blackbody temperature of Venus is -40 degrees C, which is chilly, but still close enough to habitable to return a handsome 348 trillion dollars.

Assuming an albedo of zero raises the temperature by almost 100 degrees to a toasty 55 degrees C. This impacts the valuation considerably, giving a total value of only 81 trillion dollars because the planet is too hot. But 0 and 0.75 are both extreme values for albedo. What if we use something more moderate?

The purpose of the exercise is to find terrestrial planets, so assuming a terrestrial albedo (0.36) seems to be the most reasonable place to start. This assumption gives an average Venusian temperature of 20 C. That's an almost identical to the current temperature here in Canberra, and a pleasant 68 F for American readers. Plugged into the valuation formula, this model for Venus returns a staggering 1.44 quadrillion dollars. In fact, this valuation is only 20 trillion dollars short of the 1.46 quadrillion dollar value derived for the Earth using the known terrestrial albedo number. This value also puts me clear of the million dollar jackpot threshold by about nine orders of magnitude.

Of course, pedantic observers may note that Venus's blackbody behavior is tempered by the fact that the planet has a thick atmosphere, which warms the surface via the greenhouse effect. We can calculate this second order effect by substituting Teff (the model blackbody temperature- 230-330K depending on albedo) with Treal, the actual surface temperature of 737K. This drops the valuation from 1440 trillion dollars to 2.9x10-89 dollars, or 2.9x10-87 cents. But in the current financial environment, a mere 104 order of magnitude decrease is not a problem. Rather, it is a badge of honor. Who wouldn't want ten thousand googles in times like these? Were I an investment manager instead of a geologist, I could use that as a justification for a million dollar bonus paid by congressional bailout.

Compared to this planetary overvaluation, the housing bubble is imperceptible.

Here are the values for some other solar system objects:
Moon: 7x10-25 dollars. (size matters)
Europa: 7x10-47 dollars. (This makes the JIMO EJSM program 56 orders of magnitude over budget)
Ganymede: 1.2x10-37 dollars. (The European half of that mission is relatively thrifty)
Titan: 9.5x10-44 dollars. (compare this with Greg's hypothetical exomoon)

No more shots this decade.

LLLL is all done her shots until she is four. Hooray. Vaccinations are one of those things that are mildly traumatic at the time, but good for everyone in the long run. Kinda like school, and exercise. Except that shots don't just protect your kid, they protect everyone else's as well. And that's sort of what community and civilization is all about.

Friday, March 13, 2009

Wool socks have carbon footprints

There have been several insinuations that the production of beef for food is particularly problematic with regards to greenhouse gas emissions. In addition to the resource cost associated with meat in general, beef is single out because cows allegedly generate a lot of methane, as a result of being ruminant animals.

This makes me wonder, where’s the outrage against other cud chewing creatures. There are plenty of other ruminants who seems to be getting a free pass here. For example, if a juicy steak is considered by activists to be a glacier-melting extravagance, then what is a wool sweater?

As of 2002, Australia had 100 million sheep, but only 26 million cows, a ratio of 4:1*. As the cows have greater total mass, the sheep contribution is probably half to a quarter that of cows, depending on the which numbers you pick. In NZ, where the sheep/cow ratio is higher, the little bleaters account for almost half of the country’s entire weighted emissions. And hamburgers cannot be replaced by a lighter, warmer substitute synthesized from recycled plastic bottles. So if you want to get serious about the ruminant problem, phasing out wool seems to induce a much smaller decrease in standard of living than reducing the cattle herd.

Of course, there are some people who simply prefer animal-based fibres to synthetic ones, just like many people prefer meat protein to squashes and beans. The links above suggest that switching from cattle to non-ruminant meat sources like kangaroo, pork, and chicken would provide a substantial benefit. There is no reason that lovers of animal fibre clothing cannot do the same. After all, rabbits aren’t ruminants. Neither are foxes or mink. So getting all those woolen clad activists to switch to fur coats would probably reduce anthropogenic methane emissions.

So next time you see someone decrying beef stroganoff and large clunky American cars,** check out their threads. Because wool socks have big carbon footprints.

* As the current drought is more severe in sheep country than cattle country, this ratio may have dropped since then.
** Is there another kind?

Tuesday, March 10, 2009

Happy International women's day

Here's a very simple reminder of the contributions that women have made to the understanding of the Earth:

Saturday, March 07, 2009

Science by Earmark

To all those people whinging about John McCain's criticism of earmarks for scientific research:

When science funding is chosen on that basis of legislator's pet projects, and not by a peer review system, you get projects like this.

Your grandkids are going to be paying interest on that funding. Assuming that they don't die from measles first.

I'd love to see stats on citation rates comparing earmark 'science' vs competitively awarded science. Anyone with a handy link to such information?

Tuesday, March 03, 2009

Fermi paradox meets the timescale

John over at cosmic variance has been discussing extra-terrestrial life, so I figured I'd put a geologic spin on it. Specifically, look at the Fermi Paradox through the lens of deep time. The Fermi paradox states, "If advanced aliens are common in the galaxy, where are they?" More specifically, why aren't they here. As a geochronologist, I don't wonder where and why, I wonder when. So let's make a few assumptions:

Suppose that Earth has been visited by aliens 50 times since our solar system's accretion disk started to cool 4,567 million years ago. What would the aliens have seen? In order to simulate this, I generated 50 random alien arrival times in between then and now, sorted them, and put them in geologic context. They are listed below, in stratigraphic order.

Time (Ma) Time (name) My comment Alien's comments
125 Cretaceous Dinosaurs!
270 Permian Gondwanan glaciers and funky reptiles
352 Carboniferous Swamps and really big insects
668 Cryogenian Pre-Marinoan- no sponges yet
675 Cryogenian
701 Cryogenian
748 Neoproterozoic
750 Neoproterozoic
808 Neoproterozoic
925 Neoproterozoic
1021 Mesoproterozoic Grenville Big Mountains
1049 Mesoproterozoic Grenville Big Mountains
1300 Mesoproterozoic
1355 Mesoproterozoic
1533 Mesoproterozoic Mt Isa is forming If these aliens came for resources, they didn't want base metals
1684 Paleoproterozoic
1857 Paleoproterozoic
1888 Paleoproterozoic
2159 Paleoproterozoic Trans-Amazonian orogeny
2247 Paleoproterozoic Various poorly constrained glaciations in this general timeframe
2272 Paleoproterozoic Various poorly constrained glaciations in this general timeframe
2355 Paleoproterozoic
2358 Paleoproterozoic
2400 Paleoproterozoic
2459 Paleoproterozoic Oxygen just starting to leak into the atmosphere, Manganese and BIFs
2610 Neoarchean
2612 Neoarchean
2631 Neoarchean
2661 Neoarchean
2682 Neoarchean
2745 Neoarchean
2948 Mesoarchean
2956 Mesoarchean These two mesoarchean visitors missed each other by only 95,000 years.
2956 Mesoarchean These two mesoarchean visitors missed each other by only 95,000 years.
2972 Mesoarchean
2990 Mesoarchean
3152 Mesoarchean
3281 Paleoarchean
3609 Eoarchean
3614 Eoarchean
3641 Eoarchean
3647 Eoarchean
3669 Eoarchean
3828 Eoarchean
3837 Eoarchean
3875 Eoarchean LHB Dynamical instability of this system precludes the development of complex life
3947 Eoarchean LHB Dynamical instability of this system precludes the development of complex life
4011 Hadean
4266 Hadean
4425 Hadean Moon forming impact "That's not a moon, that's a battlestation"

As you can see, for aliens looking for 'Earthlike' planets, the actual Earth was easy to overlook for msot of its history. In this simulation, there was only macroscopic life for 3 of 50 visits. From another POV, three visits were eaither during the Late Heavy Bombardment, or during the moon forming impact- both of which would appear (to the casual alien visitor) to make long-term viability of life on Earth pretty unlikely.

So as we start to find 'earth-like' planets in our sky surveys, it is important to remember that Earth has only been Earthlike for a relatively short period of time.