Thursday, January 26, 2006

ALH84001: The claim of life in a Martian meteorite 10 years later

We had an interesting in-house seminar yesterday at the LPI (Lunar and Planetary Institute) given by Dr. Allan Treiman. The topic was the Martian meteorite ALH84001, which is the rock that gained much fame and notoriety in 1996 when a team of scientists from the Johnson Space Center announced that they had found evidence for possible relic biogenic activity (read: traces of small dead bugs from Mars) within cracks in the meteorite. Unless you've been living in a cave for the past ten years, you've probably heard about this rock. In fact, this Martian rock is without question the single most studied rock on the planet. A quick search of google scholar and the NASA Astrophysical Data System reveals several hundred subsequent studies that cite the original publication in Science. The impact of this paper was huge and cannot be understated. By how do things stand today? Has this paper been re-affirmed or disproved? McKay et al. (science-speak for McKay and co-authors) gave four lines of evidence in their initial paper of non-terrestrial biologic activity in the meteorite:
  1. Small bacteria-shaped objects.
  2. Abundant PAHs or polycyclic aromatic hydrocarbons, which are often formed from the breakdown of organic molecules.
  3. Carbonate globules.
  4. Tiny magnetite grains associated with the carbonates that are similar to those produced by known terrestrial bacteria.
Although each of these lines of evidence, taken individually, is not conclusive, the authors argues that the collective weight of the evidence supported a Martian biologic origin. In their words,
None of these observations is in itself conclusive for the existence of past life. Although there are alternative explanations for each of these phenomena taken individually, when they are considered collectively, particularly in view of their spatial association, we conclude that they are evidence for primitive life on early Mars.
Personally, I have always been bothered by this statement. Essentially, this statement is akin to Occam's Razor, a philosophic tool which states that "one should not increase, beyond what is necessary, the number of entities required to explain anything." Occam's Razor is often paraphrased as "the simplest explanation is often the best." McKay et al. are saying that although individual components may be explained by non-biologic processes, it is difficult to conceive of a single non-biologic explanation that explains all of these observations. Therefore, biology is the most likely culprit.

While this idea is not wholly without merit, I believe this is an utterly insufficient criterion in this case. Carl Sagan if often quotes as having said "extraordinary claims require extraordinary evidence." I can think few claims more extraordinary than the existence of life on another planet. The idea of accepting such a fantastic claim as true on the basis of faith in antithetical to the very nature of science. Therefore, the burden of proof lies upon those making the claim.


Treiman presented an alternative, non-biologic scenario. Partly based on his own calculations and partly based upon the work of other scientists, Treiman proposed that the carbonates and associated magnetites were formed from the relatively high temperature (~400° C) decomposition of siderate (an iron-bearing carbonate). The
features which resemble bacteria turn out to be much smaller than most terrestrial bacteria and may thus have insuffient interior volume to contain a cell wall, nucleus, and other components necessary for self-sustained operation. They may instead be parasitic, or more troubling may be artifacts of the sample preparation process. The PAHs found in ALH84001 are not terrestrial in origin, but may also be from the breakdown of organic compoundss that are not associated with once-living organisms.

So where do we stand? I think the consensus is that biologic activity does not seem to be required to have produced thefeaturess observed in ALH84001. Most, if not all, of the observed features can be plausibly explained without invoking a biologic explanation. But the same argument I raised earlier applies here: while biology is not required, neither is it entirely ruled out. No one can say for certain that biology played no role.

Was it all for naught? After all that work, the best answer we have is "we don't know for sure?" That's what NASA's been spending my tax dollars on? Before you get on the phone to your congressperson, consider the following. The study of this rock has advanced our knowledge considerably. Scientists in many different sub-disciplines to make considerable advances in analytical techniques. Our understanding of contamination procedures have been improved. I think we are better prepared as a result of this effort to study samples that we will bring from Mars and other bodies. We now have a better idea of the kinds of biomarkers and traces of life we should be looking for. In short, it was be no means a wasted effort. Sometimes science raises more questions than it answers. And believe me, that is a good thing.

Tuesday, January 17, 2006

NSA surveillance = data mining

Much has been written about the secret NSA program to illegally spy on Americans without court oversight. As discussed in numerous media accounts there is a secret court to oversee warrants for wiretaps called FISA, and such requests are almost never turned down. The government can even forge ahead with the warrantless eavesdropping so long as they return to the court to retroactively get permission within 72 hours.

So why would the NSA need to circumvent a standard that is obviously heavily slanted towards the government? Pro-administration media pundits have espoused the "need for speed" in certain situations, claiming that there just isn't time to go to the court to get these warrants. But given the fact that there is a 72-hour grace period where emergency, warrantless wiretaps can be conducted, this need for speed argument just doesn't hold water.

The real reason, rather, is likely that the scope of the program is such that obtaining warrants, which presumably must be done on an individual basis, is not feasible. So this program is really more data mining than anything else. Data mining is where a huge number of communications are electronically monitored simultaneously, and suspicious patterns are sniffed out for further scrutiny. According to the NY Times,
Although the program's public disclosure last month has generated speculation that it may have been used to monitor journalists or politicians, no evidence has emerged to support that idea. Bush administration officials point to a secret audit by the Justice Department last year that reviewed a sampling of security agency interceptions involving Americans and that they said found no documented abuses.
I don't really put too much faith in this administration's power to investigate itself. [Prisoner abuses in military prisons? What abuses? Or better yet, what prisoners?] So should you take some comfort in that it is a computer [initially] violating your privacy rather than a human operator? Absolutely not. I bet we're not talking about a few thousand privacy violations here, we're talking about hundreds of millions of privacy violations. How long before some turns this surveillance tool to another end, such as monitoring public opinion? This isn't a slippery slope we're sliding down, we just went off a cliff.

Friday, January 13, 2006

Stardust returns

The NASA mission Stardust is slated to return to Earth on Sunday, Jan. 15, at approximately 2:12 a.m PST in Utah. The cool thing about Stardust is that is used aerogel to capture particles from both a comet and interplanetary dust particles (IDPs). Aerogel, as you see here, is the least dense substance every created. Think of it like super-fluffy jello - it's over 98% empty space.

From a science standpoint, the potential results are exciting because these returned materials represent the building blocks of the solar system. Hopefully, the recovery will go smoother than the Genesis mission, which crash-landed in the desert when it's parachute failed to open. Something most media outlets have failed to report, however, it that ~85% of the sample returned by Genesis was eventually recovered. Contamination is an issue, but a remarkably large portion of the payload survived the rough ride home. I think NASA needs to do better informing the public that although the mission looked like a spectacular failure, many of the science objectives will most likely be met.