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Detecting (and Understanding) Life Signals

A symposium celebrating the first fifty years of NASA’ exobiology program takes place on October 14 in Arlington, Virginia. ‘Seeking Signs of Life’ looks all the way back to 1959, when NASA funded its first exobiology investigation, an experiment for a future spacecraft to detect life on Mars. The actual exobiology program was established in 1960, and led to the three Viking experiments that eventually flew. Exobiology has these days morphed into ‘astrobiology,’ as we look at topics as diverse as chemical evolution in interstellar space and planetary formation.

For those in range of Arlington, more information is available here. Be aware as well of a workshop on SETI that is now taking place at the National Radio Astronomy Observatory in Green Bank, WV, marking the 50th anniversary of Frank Drake’s first search for extraterrestrial signals. Webcasts begin at 0830 EDT (1230 UTC), and will include Drake’s views on ‘SETI in 2061 and Beyond’ at that time on September 15. Further information is available from NRAO.

Thinking about astrobiology has me turning to an interesting notion put forward by Caleb Scharf last week on his Life, Unbounded site. It has to do with what we mean by habitability, a necessary term in searching for life on other worlds that has to be defined to help us narrow our search, but one that may be misleading. Scharf (Columbia University) is wondering whether habitability is only part of a template that may be just a bit too tidy to be truly descriptive:

If there is one inevitable thing about life it is that particular variants, species, modes of existence, are all prone to extinction. A new work by Drake & Griffen in Nature this week makes this point rather succinctly. They show, by subjecting water flea populations to a series of unfortunate events, how the population dynamics of a species can fundamentally shift due to environmental changes. Fluctuations in population numbers occur even in stable environments, but the character and size of these fluctuations changes in degrading environments, and beyond a certain point there is no recovery. Long before it all goes down the tube there are clear statistical indicators that things are not well – population sizes drop as the tree begins to fall.

We do indeed know that extinction events are an unfortunate fact of life on planets like ours — at least, they have been on this one. Right now we’re looking to a near-term future when we can go to work on planetary atmospheres, eventually subjecting terrestrial planets to scrutiny with space-based spectroscopy. But if we do find biomarkers in an alien atmosphere, what will they mean? Scharf argues that any planet we find with these methods will most likely be one in which life is moving toward instability, a fertile but dangerous period pointing to catastrophe:

We are most likely to be able to sniff out the signs of life on a terrestrial-type planet when it’s in full swing. Suppose a world is having a particularly fertile episode, chock-a-block with organisms, but not a stable situation. It’s prime for collapse. Relative populations will swing high and swing low. At the high point for some, a planet may show the greatest bio-signatures, and make itself far more tasty for our prying telescopic eyes. Without running the numbers it’s impossible to give a precise answer, but it would seem that the odds will be shifted. We may be most likely to find not the signs of normality, but the signs of a system approaching some kind of biological collapse – just like the stock market, it’s all about the fluctuations.

Evolutionary success may wind up creating all the conditions for sudden, catastrophic change, a delicate balance that, once put out of whack, quickly degrades. We may detect, then, signs of planets overrun by particular kinds of life, with populations in a state of fluctuation over timescales as low as thousands or even hundreds of years. Must it always be so? Of course not, but what Scharf is saying is that our limited detection sensitivity will hamper us in the early going, and we’d better be careful about the kind of conclusions we draw from the evidence.

Which brings me to the closing panel at the upcoming astrobiology conference in Arlington. It’s titled “Homing in on ET Life: Where, and How, To Look.” With our one example of planetary life to go on, the ‘how’ gets increasingly important. We aim for the most recognizable life scenarios but must keep in mind that what Scharf calls ‘convenient truths’ can mislead us. Stable, long-term life may not show as strong a signal as biological collapse, so that as is the case with ‘hot Jupiters,’ we start off by seeing extreme examples of a much more evenly distributed phenomenon. We’ll want to learn from that lesson if it’s one we observe in spectroscopy, and avoid drawing too many conclusions from the outliers that our early instrumentation may reveal.


Comments on this entry are closed.

  • Ron S September 13, 2010, 21:54

    “We’ll want to learn from that lesson if it’s one we observe in spectroscopy, and avoid drawing too many conclusions from the outliers that our early instrumentation may reveal.”

    The scientists involved will almost always be careful in what they say or conclude after releasing their results. The danger comes more from the promotional press releases by their host institutions and the journalists who then dress up the story even further in an effort to draw attention. I think we will just have to accept that exo-planet atmospheric observations will be widely misrepresented and misconstrued, at least until they become routine and therefore uninteresting to most people.

    I’d be happy enough to see the unmistakable signature of a substantial quantity of oxygen, which could be a strong indicator of an active biosphere.

  • James M Essig September 13, 2010, 22:41

    Hi Paul;

    This is some really good news.

    I live about 10 miles West of Arlington about 1/2 mile off of Route-50. I will have to check the local newspapers and new-broadcasts while the conference is in session.

    Thanks for this late day posting.

  • Ronald September 14, 2010, 6:08

    I am slightly puzzled by this article and I think that some people, such as Scharf, are mixing up a few things, in particular biosignature, habitability, (mass) extinction.
    When I think of biosignatures, which can be detected telescopically, I think of chemical marks such as particularly oxygen (O2), ozone (O3), water en methane (CH4), maybe even more complex organic compounds such as chlorophyll.
    However, these biosignatures will not necessarily decrease or change significantly as a result of a mass extinction event. In other words, after a mass extinction event, defined as a significant loss of species, the amounts of water vapour, O2, O3 etc. and their relative abundances in the atmosphere do not necessarily change significantly.
    Furthermore, even the worst known mass extinction events do not necessarily diminish the habitability per se of a planet, in terms of temperature, water, atmosphere etc., but mainly its number of inhabitant species and even that only temporarily.
    If one thing is clearly demonstrated by the history of life on our own planet it is the fact that life, once it gets established on a planet, it is extremely persistent and resilient.
    Conclusion: extinction may hit species and civilizations, but it does not (or rarely) diminish the habitability of a planet, which is primarily determined by the physical characteristics of the star and the planet.

  • Caleb Scharf September 15, 2010, 15:02

    Ronald, my point in my piece in Life, Unbounded was that given a particular level of detection sensitivity (for example to O2, CH4) – or rather insensitivity given the extreme challenges involved in these types of spectroscopic measurements (even with instruments like NIRSpec on JWST) – we will clearly be prone to only detect chemical components associated with biospheres when a particular planet is flush with them. This therefore biases us towards highly abundant biomass. My point therefore was that it is conceivable that we would be more likely to detect life on worlds where things were – to put it crudely – running amok. We wouldn’t know a priori if extinction was imminent on these worlds, but it might be, and therefore bias our picture of ‘habitable’ planets by just revealing to us those ‘outliers’.

  • ljk September 15, 2010, 22:24

    Future of Life – The Future of SETI

    Tuesday, 14 September 2010 15:44

    Written by David Tow

    David Hunter Tow, Director of The Future of Life Research Centre, provides a possible solution to the mystery of why signals from alien civilizations have not yet been received by the SETI project.

    SETI has recently celebrated its 50th birthday. On the surface, the project still radiates optimism, driven by the possibility that a credible signal might one day herald the existence of another intelligent civilisation in the galaxy.

    Over the past 50 years SETI has focused primarily on radio frequency transmissions, while also dabbling briefly with the optical spectrum, searching for laser pulses from outer space. A number of more radical approaches have been canvassed, including infrared transmissions, gravity waves and neutrinos, but these appear to be infeasible at present.
    In the meantime the SETI Institute continues to apply its Allen Telescope Array, an array of 42 small dishes, to the search, now introducing a new project– setiQuest, designed to open up its search algorithms to the public, providing a new source of computational power and innovation.

    Over time, a number of additional powerful instruments and techniques have been deployed by the astronomical community, to probe the mysteries of other candidate star systems across the galaxy, including searching for signs of life. Discoveries of other solar systems similar to our own, including those that may harbor earth-like rocky planets are becoming increasingly likely, with some predictions of up to 100 million earths in the galaxy.
    The glittering prize therefore seems tantalizingly close.

    But something’s missing from the project. Under the invisibility cloak of eternal optimism there are growing doubts about SETI’s methodology. After 50 years there should have been something to show- some hint of intelligent life or even a reason for the lack of it – and there was. For a fleeting moment back in the seventies an unusual spike in the spectrum appeared- the Wow signal. But then disappeared just as quickly as it arrived. With hindsight however it might have provided a clue to the mindset of other civilisations.

    Full article here:


  • spaceman September 16, 2010, 16:12

    So, the main idea behind this thread is as follows: presumably a distribution of habitable planets in our galaxy exists and the ones in the distribution that we are most likely to detect are the ones where a successful species is so successful (has a high population, high energy use, high environmental footprint, etc) that its presence is writ large. It would certainly seem that Earth in the present era would be one of the planets in this distribution; therefore, the applicability of this idea to our home planet’s current situation with humans, the most successful and dominant species on the planet, is that “our” orb is part of the sub-sample of easily detectable habitable planets in the Milky Way. Is my understanding on the mark?

  • Ron S September 17, 2010, 12:59

    spaceman, there were recent experimental observations from spacecraft (was it New Horizons?) of Earth to test just what could be learned regarding bio-signatures from a moderate distance. I recall that there was some success, but I don’t know if the methods used work from an interstellar distance. You should be able to do a web search (I believe Paul has covered it here as well) to find out more.

  • Caleb Scharf September 17, 2010, 13:41

    The Earth may or may not be one of these ‘life rich’ worlds. The kind of signatures we’re talking about are at the moment limited to spectroscopic detection of atmospheric molecular species, such as H2O, CO2, and if we’re lucky rarer components like O2 and CH4. Only the latter two in this list are going to be serious contenders as ‘bio markers’, owing to their disequilibrium nature (i.e. something would have to be replenishing them on a regular/continual basis). The Earth today is arguably less full of life than it may have been during, for example, the Jurassic. More recently, about 30 million years ago there are indications of higher atmospheric O2 concentrations. Pushing back to around 280 Myr ago there is evidence that the Late Paleozoic had O2 at 30% (vs the 21% today).

    And, the classic Earth-observing experiment was undertaken in 1990 by the Galileo spacecraft during a swing-by prior to heading to Jupiter. Carl Sagan published a classic paper (in Nature, 1993, vol 365, p 715) in which Earth was searched for life, using the Galileo multi-band data. What was striking was that, yes, there was very good evidence for life, but it was not as clean cut as one might have supposed – and this was from up close and personal.

  • ljk October 2, 2010, 9:31

    Saturday, October 02, 2010

    Neil deGrasse Tyson and Richard Dawkins: What would aliens look like?

    Last Tuesday Howard University hosted a discussion between evolutionary biologist Richard Dawkins and astrophysicist Neil DeGrasse Tyson billed “The Poetry of Science” (a title I love). Their conversation touched on the beauty of science, life and the universe. and – among other topics – aliens.

    Full item here:


  • ljk January 19, 2011, 4:39

    Review: Talking About Life

    Astrobiology has gained traction in recent years as an interdisciplinary field seeking to answer one of the most fundamental questions: is there life elsewhere in the universe? Jeff Foust reviews a book where scientists and others talk about their work in this field.


  • ljk November 11, 2011, 16:33

    NASA needs to be more forthright about Curiousity’s mission, because otherwise it is going to be appear to be just a much more expensive and nuclear-powered version of the MERs:


    The MERs did what they were designed to do, which is find evidence of past water on Mars. NASA made it clear repeatedly that Spirit and Opportunity were not sent their to find life, having been “bitten” by the Viking lander results three decades earlier. This time they were going to start slowly towards finding native organisms, namely the main ingredient most scientists would say life needs to exist and thrive.

    The MERs did have certain capabilities to find life if they so wanted to, including a microscope. There were some objects imaged by the rovers that should have peaked the curiousity of any decent fossil hunter, but if NASA has been investigating these finds further, they are doing so far out of the public limelight.

    I am not talking the remains of a city or an alien spaceship here, I am talking small objects in the Martian ground that at least give the appearance of being the remains of creatures from the planet’s past – which scientists have said was much more friendly to life than the conditions that exist at present. Note I said friendly to life, not that there was life. But we need some serious expeditions to that planet to boldly check these things out.

    I understand that NASA does not want to make some big claim and then possibly have to retract it, but why bother sending vehicles to alien worlds if we aren’t going to explore the heck out of them in the process?

  • ljk November 14, 2011, 18:23


    Friday, November 11, 2011

    Soon…”Curiosity” will be “Up, up, and away” towards Mars…November 25th, 2011

    “NASA: New Mars rover will look for the ingredients of life”

    November 10th, 2011

    Los Angeles Times

    If you think that people who believe in the possibility of extraterrestrial life are kooks, you probably haven’t talked to a NASA space scientist in a while.

    At a news conference on Thursday, Doug McCuistion, director of the Mars program for NASA, said that when the agency’s newest Mars rover blasts off for the red planet on Nov. 25, one of its charges will be to discover if the planet contains (or contained) the ingredients of life.

    “This mission will bridge the gap scientifically from our understanding of the planet being warmer and wetter than we probably believed, to not seeking life itself, but seeking signs of life,” he said.

    He reiterated: “This is not a life-seeking mission.”

    Think about the mission this way: If NASA were going to Mars looking for signs of pancakes instead of signs of life, on this trip it would be looking for flour and eggs, not pancake crumbs — and definitely not pancakes.

    In an interview with The Times, Joy Crisp, deputy project scientist for the Mars Science Laboratory, said the rover will be looking for organic molecules and isotopic signatures that might indicate that life did exist at one time on Mars.

    “If this step pans out, if we do find organic compounds and we think that the rocks look likely to preserve evidence of life, then we will know better what to send next,” she said. “It is kind of an intermediate step.”

    Asfor the rover itself — called Curiosity — it’s 6-feet-tall, weighs roughly 2,000 pounds, and is the most complex machine to be placed on another planet, according to McCuistion.

    The rover has high-definition cameras, a laser eye, and a weather station to help scientists monitor the environment. It also has the ability to sample rocks and soils, and a drill that will allow it to capture material from inside rocks.

    “This is a Mars scientist dream machine,” said Ashwin Vasavada, Mars Science Laboratory deputy project scientist, at the news event.

    But the rover won’t be landing on the planet for a while. Curiosity is scheduled to leave Earth on Nov. 25 (the day after Thanksgiving), but it won’t be landing on Mars until August 2012.

    During the news conference, Vasavada was asked how likely he thought it was that Curiosity would find evidence of life on Mars.

    “That would be in the realm of speculation,” he said, “but the reason we are excited about Mars is that when we look into the distant past, there is evidence of rivers flowing and lakes and we are trying to find out if they are habitable environments.”

    “Of the hundreds of places we could have landed, we’ve chosen the best place to find habitable environment,” he added. “Now we’ll see if we find one.”

    The blog’s search engine really s*cks. It took me a long time to find the following.

    “Curiosity” — Clara Ma names next Mars rover