Archive for June, 2010
I just mentioned this on our email list (http://lists.jhu.edu, seach for “astrobioclub”): yesterday Greg showed me JournalFire, an online journal club website and suggested we use it for online sharing and discussion of research papers. I just set up a journal club for us. If you’re interested, register at the site and join the club. I just added a bunch of papers from the “hydrogen-eating microbes on titan” controversy.
Here’s a list of scientific writing tips from a science journalist that are good to follow regardless of whether you’re writing a journal article or an email to a friend. They dissect a famous human genome paper from Nature to address points about using jargon, long and short sentences, subjective and objective clauses, active verbs, and speculative voice. My favorite piece of advice is “you should be able to read a sentence out loud in one breath.”
Today’s XKCD comic:
We’ve got another lecture in the STSci Astrobiology Lecture Series coming up tomorrow! This month the lecture will be by Wes Traub from the Jet Propulsion Laboratory at Caltech. It’ll be in Mudd 100 at 12:30pm tomorrow. The lecture is entitled “Astrobiological Factors in Exoplanet Exploration Strategies.” The abstract:
What is the best strategy for finding signs of life beyond the Solar System? Until recent years this was a purely philosophical question, but today we have the technical ability to search for signs of life on exoplanets around nearby stars, so the question is now a practical one. To start, we ask what kind of signs of life should we be looking for, and where should we be looking? Next we might ask about the methods we could use for such a search, and the kinds of evidence that we expect to obtain. Finally we can ask about the prospects for starting this search in the coming decade.
After the lecture, the Astrobiology Club gets to meet with Traub at 3pm in Mudd 128. Don’t miss out!
This week, the Kepler team released much (but not all) of their data including 306 possible planet candidates. The team published two papers on the results.
The upshot is that, contrary to our current inventory of planets, the Kepler data is implying that small planets do indeed far outnumber the larger Jovian planets. This has been expected but never observed up until now. Kepler’s released candidates show approximately a 1/r^2 relationship between frequency of planets and planet radius. The second paper goes into greater detail on 5 systems that appear to have multiple planet candidates, including one with 3 planets transiting! As for the planet candidates that Kepler has withheld, they have 400 of the most promising (read “most dramatic” and “Earthlike”) to do another 9 months of radial velocity analysis and observing. The smallest released candidates are at 1.5 Earth-radius and they mention that they have smaller candidates in the list of 400. One caveat for astrobiology…all of the released candidates are in close orbits of their stars (inside Mercury’s orbit). Perhaps longer period candidates are in the list of 400.
COROT, the French planet-finding satellite, announced another 6 planets (one of which is a probable brown dwarf) to increase their total to 15. They also hinted that they have several hundred candidates that they are sifting through. http://www.nature.com/news/2010/100414/full/news.2010.182.html
Expect to see the number of confirmed extrasolar planets double (and more!) in the next year!
We had a great meeting today with another large turnout. Judit Szulágyi gave a presentation about habitability zones. We discussed a recent article on arxiv.org about detecting life with microbial fuel cells. Then we capped off the hour with a lengthy review of the recent papers that lend evidence to Titan having methane-based life.
Here is the original press release, “What is Consuming Hydrogen and Acetylene on Titan?” and Chris McKay’s response from earlier this week to the furor it kicked up. And here are the four papers referenced in the discussion today:
- The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe
- Possibilities for methanogenic life in liquid methane on the surface of Titan
- Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions
- Detection and Mapping of Hydrocarbon Deposits on Titan
A recent paper by Johns Hopkins own Darrell Strobel has been making the rounds. His paper, “Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions,” in conjunction with results from a VIMS study soon to be published in the Journal of Geophysical Research, has renewed interest in a 2005 paper by Chris McKay and Heather Smith about methane-based life. From a JPL press release:
One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan’s atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.
This lack of acetylene is important because that chemical would likely be the best energy source for a methane-based life on Titan, said Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, Calif., who proposed a set of conditions necessary for this kind of methane-based life on Titan in 2005. One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen.
“We suggested hydrogen consumption because it’s the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth,” McKay said. “If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth.”
Cheers to Johns Hopkins for being on the cutting edge of astrobiology research!
I’ve been a little slow getting this posted, but here’s the paper we discussed in the second half of last month’s meeting: A formal test of the theory of universal common ancestry
Universal common ancestry (UCA) is a central pillar of modern evolutionary theory. As first suggested by Darwin, the theory of UCA posits that all extant terrestrial organisms share a common genetic heritage, each being the genealogical descendant of a single species from the distant past. The classic evidence for UCA, although massive, is largely restricted to ‘local’ common ancestry—for example, of specific phyla rather than the entirety of life—and has yet to fully integrate the recent advances from modern phylogenetics and probability theory. Although UCA is widely assumed, it has rarely been subjected to formal quantitative testing, and this has led to critical commentary emphasizing the intrinsic technical difficulties in empirically evaluating a theory of such broad scope. Furthermore, several researchers have proposed that early life was characterized by rampant horizontal gene transfer, leading some to question the monophyly of life. Here I provide the first, to my knowledge, formal, fundamental test of UCA, without assuming that sequence similarity implies genetic kinship. I test UCA by applying model selection theory to molecular phylogenies, focusing on a set of ubiquitously conserved proteins that are proposed to be orthologous. Among a wide range of biological models involving the independent ancestry of major taxonomic groups, the model selection tests are found to overwhelmingly support UCA irrespective of the presence of horizontal gene transfer and symbiotic fusion events. These results provide powerful statistical evidence corroborating the monophyly of all known life.
If you’ve got any interesting papers you’d like to discuss, bring it to the next meeting on Thursday, June 10th, at 12pm in 310 Olin Hall.