Arsenic-based life and Astrobiology

3 07 2012

File:Arsenate.png

It’s been some time since the controvertial announcement that “arsenic-based life” had been discovered on planet Earth.  With time, however, the less-sensational reality of the discovery has been made more clear, and I think it is sensible to review the current state of the research as it relates to the biochemistry of life and the idea of “alternative” biochemistries.

An Imminent Announcement

NASA "meatball" insignia 1959–82 and 1992–presentThe recap: Making some serious waves back in November of 2010, NASA released a media advisory stating that a news conference would be held days later that would reveal “an astrobiology finding” that would “impact the search for extraterrestrial life.”

The journal Science strictly embargoed details until the news conference was held.

Of course, the internet went bezerk.  NASA’s announcement, the first of its kind since the announcement of potential bacterial fossils in Mars meteoriete ALS-84001, seemed to hint to many that a rover had finally hit paydirt.  Signs of extraterrestrial biology had finally been found!

However, the rampant speculation that followed only fueled an initial spike of disappointment with the actual announcement: that young biogeochemist and astrobiologist Felisa Wolfe-Simon led a research team that discovered, as was popularly-reported, “arsenic-based” life here on Earth.

Wolfe-Simon’s discovery was  published in the journal Science and was actually met with a fair degree of sensationalism right out of the gate, followed by sharp criticism that survives to this day.

File:GFAJ-1 (grown on arsenic).jpg

Magnified cells of bacterium GFAJ-1 grown in a medium containing arsenate. (Credit: NASA)

GFAJ-1: The Arsenic Experiment

A critical question of astrobiology is whether or not life is required to take advange of the same chemistry we do, i.e., that our biochemistry is the only biochemistry that works.  If other types of chemistry were available to life, (such as silicon-based life hypothesized on Saturn’s moon Titan,) then this implies that opportunities for life elsewhere in the universe are great in number.

If not, then life may be more rare; waiting for the perfect “goldilocks” conditions before it can arise.

Testing this hypothesis, astrobiology researchers have been pressing for evidence of so-called “shadow biospheres,” or examples of life taking advantage of different or exotic chemistries right under our own noses.  In other words, seeking out environments where life might have evolved out of necessity to take advantage of different, ordinarily toxic chemical elements is one strategy to investigate the question here at home.

With this objective in mind, Wolfe-Simon (and colleagues) proposed that instead of phosphate (PO4), life might find a way to substitute arsenate (AsO4, depicted in the header)  into its DNA.  Specifically, by isolating an extremophile (an exotic bacterium) from the bizarre ecosystem at work in the alakaline, salt-ridden, and arsenic-laden Mono Lake, Wolfe-Simon’s research team claimed success: the identification of an organism that was capable of substituting arsenic for a small percentage of its phosphorus!

Clarifying “Arsenic-based” 

Wolfe-Simon’s findings, which were obtained when the GFAJ-1 bacteria were grown in a culture doped with arsenate, are more accurately described as identifying a potential “arsenic-utilizing” as opposed to “arsenic-based” form of life.  Even so, the results were considered a boon for those proposing widening the technical search for extraterrestrial life.  In this view, should life be utilizing very different biochemistry than what we’re accustomed to, it is possible that the instruments on our rovers, etc., might not even detect it (or recognize what it was that was being detected).

However, the results have been hotly-debated since, and more recently, have been outright cast into doubt when researchers just this year used a separate analytical method and failed to detect arsenic in the GFAJ-1 bacteria.

The Take-Home

The jury is still out considering whether or not we’ve actually detected so-called “alien” biochemistry or hard evidence of a shadow biosphere.  That having been said, the justification and approach is still in my opinion a solid one.

It remains within the realm of possibility that extraterrestrial life (or terrestrial life under extreme conditions) might, due to opportunity or necessity, be chemically different from our own.

Food for thought.





Liberating Ares in commercial rocket fray

10 02 2011

Rendering of the Liberty Launch Vehicle. (Credit: ATK)

The NewSpace rocket environment is growing from a band of determined forerunners to a healthy platoon.  Salvaging what they could from NASA’s cancelled Ares I rocket, industry giant ATK (responsible for building Space Shuttle’s solid rocket boosters, a critical component in the Ares rocket design,) has teamed up with Eurpoean company Astrium (of Ariane 5 fame) to develop a new vehicle: Liberty.

Maiden launch of NASA's Ares I-X rocket in 2009. (Credit: NASA)

The vehicle, which will marry ATK’s bottom booster stages with an updated version of Ariane’s second stage and fairing, is the latest in an increasingly-heated competition for NASA contacts to ferry crew and cargo to the International Space Station after the retirement of the Space Shuttle.  Highly reminiscent of the Ares I design, Liberty joins the competetive ranks of commercial rockets such as SpaceX’s Falcon IX, Boeing’s Delta IV, the Russian Proton, and Lockheed’s Atlas V.

I am personally glad to see the Ares expertise utilized in a commercial design, and we who hope for widening access to space couldn’t hope for a better situation – one increasingly likely to stimulate competetive rocket vehicle pricing, innovation, and development.





Titan eclipses Mars

22 08 2010

Cassini spacecraft view of Saturn's 3200-mile-wide moon, Titan, with the smaller, 698-mile-wide moon Dione actually 600,000 miles behind it. Credit: NASA/JPL/Space Science Institute

Titan has eclipsed Mars.  Not literally, mind you, but conceptually.  With active surficial geology the likes of which are known only to Earth, and considering the recent discovery of possible biochemical signatures of alien life, to me Titan has become the most interesting exploration destination in the solar system.

Take the above image, for starters.  Whereas most other rocky worlds in our solar system offer an unbridled view of craters, mountains, and ancient plains, Titan’s dynamic, hazy atmosphere betrays little.  Truly, the giant moon, which is larger than the planet Mercury itself, is a world shrouded in mystery.

-And, the more we learn about Titan, the more we have reason to believe it is the most Earth-like world this side of a few trillion miles.

(As an aside: My hat is off to the CICLOPS Cassini spacecraft imaging team for giving us real-life pictures like this.  Thanks to them, images from our science today trump the science fiction special effects of a decade ago.)

Unlike Mars, Titan offers us lakes, rivers, clouds, and rain – A full, living hydrologic cycle that is active not billions of years ago, but today.  (Yes, “hydrologic cycle” is perhaps a slight misnomer, because on Titan the active fluid is methane/ethane, not H2O, but the process appears to be the same.)  -And, perhaps most excitingly, scientists have recently discovered evidence that may indicate methane-based alien biochemistry at work.

Specifically, a flux of hydrogen molecules toward Titan’s surface, (rather than away as would be expected,) may indicate the consumption of the gas on Titan (as aerobic life on Earth consumes oxygen); A distinct lack of the hydrocarbon acetylene, one of the most potent chemical energy sources on Titan, may betray that hydrogen-breathing, methane-based life is consuming acetylene as food.

And at least hypothetically, all of the potential chemistry checks out.

If all of this together doesn’t spell impetus for further investigation, I can’t imagine what does.  To boot, because it is so cold out at Saturn’s distance from the Sun and despite Titan’s weaker gravity, the condensed atmospheric pressure on Titan is practically identical to what we experience on Earth, making human exploration all the more feasible.

Have spacesuit, will travel.  Titan or bust.





Target: Titan & Silicon-based life

18 03 2010

Move over, Mars.  According to new imagery from the Cassini spacecraft and new research recently published in the Journal of Cosmology, Saturn’s moon Titan may be the hottest exploration ticket in the Solar System.

Titan in front of Saturn. Credit: CICLOPS

Up until only five years ago, the massive moon Titan was one of the last great mysteries in our neighborhood of planets.  Itself bigger than the planet Mercury,  Titan’s freezing (-290 degrees!) smoggy, opaque, nitrogen-and-methane atmosphere was so think that we had no idea what its surface looked like.  It was only after the Cassini spacecraft settled into orbit in 2004 with advanced instruments that we were able to punch through the fog to see what was going on.

Radar images of Titan - dark areas suggest lakes/oceans of methane. Credit: CICLOPS

What we found was staggering.  Coastlines.  Erosion.  The most Earth-like environment to date.  As predicted nearly three decades ago but unproven until recently, Titan is the only other place in the solar system home to a hydrologic cycle of sorts.  I’m talking about lakes, streams, clouds, and rain.  But on Titan it isn’t water raining from the sky and running down mountainsides.  It’s far too cold, and water there is always a solid mineral, like silicon is here on Earth.  Instead, Titan’s “water” is liquid methane.

Utah? Rendering of possible Karst terrain on Titan. Credit: NASA/Malaska

While this is terribly good news for geologists interested in the processes of erosion (geomorphology), it was apparently bad news for hopeful astrobiologists.  Without liquid water, life as we know it can’t exist.  But hold that thought – Researcher Pabulo Rampelotto of Brazil’s Space Research Institute’s Exobiology and Biosphere Laboratory has identified an alternate biological chemistry that might support life on Titan…

Silicon-based Life

Our current understanding of physics, chemistry, and their roles in biology suggest that an organism could survive using an entirely non-carbon-based metabolism.  Silicon is a likely first place to look for alternatives.  Like carbon, (the chemical backbone of life as we know it,) silicon can form four bonds, stable bonds with itself and other elements, and long chemical chains known as silanes, which are very similar to the hydrocarbons essential to life on Earth.  Silicon is more reactive than carbon, which could make it optimal for extremely cold environments.

However, silanes spontaneously burn in the presence of oxygen, so an oxygen atmosphere would be deadly to any silicon-based life, and water as a solvent would be equally deadly for the same reason.  So, any environment with the potential for silicon-based life would have to be very cold, devoid of oxygen and water, but with another compatible solvent, such as liquid methane.  Sound familiar?

Of all places in the Solar System, Titan seems to be the only place active enough for life to currently exist.  -And even though Titan is definitely an alien and hostile place, it looks like we’ve identified a way for life there, as Crichton’s Ian Malcom famously put it, to “find a way.”

Tantalizing.








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