October 24, 2017

Review: Rare Earth by Peter Ward & David Brownlee.

A controversial classic!

It is perhaps one of the greatest scientific questions of our time. How common are we? Is our existence here in time and space a widespread occurrence in the cosmos, or are we so unique that we are effectively alone? The topic of this week’s review represents a landmark paradigm shift and is an often quoted book that I’ve always wanted to get around to reading and reviewing. Rare Earth: Why Complex Life is Uncommon in the Universe by David Ward & Peter Brownlee posits that animal life in general and intelligence such as our own in particular is a rare, perhaps a singular event in our corner of the galaxy. Published in 2000, its interesting to see how the science of the day stacks up to current thinking. For example, in 2000 a handful of exoplanets were known; almost all were “hot Jupiters,” and the prospects for terrestrial planets looked slim. To date, 779 extra-solar planets have been discovered using a variety of methods, providing researchers with enough data to classify and characterize various types of planetary systems.

It should be noted that the authors do point out that while animal life may be a tough hurdle, simple bacterial life may be common in the cosmos. Our own story lends some credence to this supposition; once conditions in the early history of life on Earth stabilized about 3.5 billion years ago, simple life arose readily. For almost 90% of the span of life on Earth, however, life remained at the simple one-celled stage. It seems that at least in our own case, going to complex multi-celled life was the hard part; but yet in less than a billion years, the explosion of plant and animal life led to dogs, cats, humans, Ipads, etc. How common this tale is remains to be seen. Certainly, the discovery of bacterial life past or present within our own solar system may lend weight to the first half of the Rare Earth hypothesis.
Among the factors that the authors site as conducive to life as we know it;

-An orbit around a single relatively stable star that maintains a steady output for many billions of years, long enough for life to develop;

-A stable orbit within the habitable zone of said star, a place where water can exist in liquid state;

-Condensation from a proto-solar nebula with a high “metallicity” (remember, to an astronomer, the universe is hydrogen, helium, & metal!) full of lots of great but scarce raw materials such as carbon, silicon, nitrogen, etc.

-A single large Moon that acts to stabilize the tilt of the Earth;

-A large “goal tending” planet like Jupiter that deflects a good portion of the life extinguishing comets that come our way.

-A stable position in the galactic habitable zone, not too close to the radiation-riddled core and not in the outer metal poor ‘burbs. A good distance from any life extinguishing supernovae or gamma-ray bursters helps too, a sort of “may you live in mediocre times” curse/blessing.

-Active tectonic plates allowing for subduction and sequestration via a rock and carbon cycle.

To this end, the authors add some interesting twists to the famous Drake Equation, allowing for the events that brought us here in the mix. Certainly, if some of the scenarios such as the formation of our Moon are mandatory, chances for life are slim. One only has to look at the caveats offered by our neighboring worlds of Venus and Mars to see how different the Earth could be.

Still, a nagging hunch pulls at the back of our brain as we read Rare Earth… just how viable is a statistic of one? Are all of these happy accidents mandatory, or can life, once it’s started, make due even under drastically different conditions? One could also point out that these conditions aren’t exactly stable or permanent; the tilt of the Earth’s axis does vary, the output of the Sun is increasing and fluctuates with time, etc. It would be great to have a better understanding of the minimum and maximum criterion for life as it relates to these events. Carbon is probably crucial; no other element forms such long complex chains, although silicon is sometimes also cited as a possible alternative. Water also makes a great ‘universal solvent…” but might oxygen be poisonous to some forms of life? Would we recognize life drastically different from us if we saw it? I’m reminded of Arthur C. Clarke’s Report on Planet Three, where a Martian scientist gives a long and convincing discussion on why life on a hostile planet such as Earth couldn’t be possible.

Read Rare Earth as a very timely and still largely pertinent discussion on one of the biggest questions of our time. I would also recommend James Kasting’s How to Build a Habitable Planet as a great look at how the Earth came to be. Either conclusion has stunning implications; of course, most of us root for sentience and a cosmos teeming with diverse life with Klingons and Vulcans bickering about treaties in a Galactic Federation… but if we are truly  ”it” in our tiny niche of time and space, doesn’t that make us and the Earth all that much more precious and unique, a jewel worth safeguarding and preserving?

08.06.10: Titan and the Case of the Missing Acetylene.

Titan as imaged by Cassini in 2007. (Credit: NASA/ESA/Cassini).

Titan as imaged by Cassini in 2007. (Credit: NASA/ESA/Cassini).

  

   It started with two papers… as of late, much good and bad science journalism has been committed to the mysteries of Saturn’s largest moon, Titan.  A photochemical smog shrouded world, Titan is a dynamic place, and would easily qualify as a planet in its own right if it were in a solo orbit about the Sun. Titan has only begun giving up its secrets in the past decade; a close flyby of Voyager 1 in 1980 revealed an orange-brown disk devoid of detail. The arrival of the joint ESA-NASA Cassini Huygens mission has led to a wealth of data, as Cassini has performed a series of close mapping flybys of the moon and even deposited the successful Huygens probe on the surface in early 2005. Now, two papers from the Journal Icarus and the Journal of Astrophysical Research describe a curious anomaly; some process is consuming expected acetylene (HC2H) on the surface of Titan. Or something… but wait, let’s not got shouting, “Scientists find life on Titan!” We’re talking an indicator to a possible form of life. The studies site data gathered by Cassini’s infrared spectrometer and ion and neutral mass spectrometer as it swept by the moon. As a matter of fact, Cassini has just completed a 1,270 mile pass recently on June 5th. The process in question is the accumulation of hydrogen molecules high in the atmosphere and raining down to the lakes of methane and ethane coating the surface.  Evidence supports the idea that Titan should be coated with organic molecules, not to be confused with full fledged life itself (old school media take note!). Clearly, something is sequestering the expected acetylene that should be forming… could it be methane-based life? Keep in mind, Titan is a cold place; daytime temps reach a balmy -290 degrees Fahrenheit. Perhaps there may be warmer, as of yet undiscovered pockets of geological activity, but the very idea of methane based life is very hypothetical. Such life forms would be vastly different than what we know here on Earth, and acetylene is on the short list of oxygen-metabolism substitutes. Mark Allen at NASA’s Astrobiology Institute points out that the lack of surface hydrogen and acetylene may have a non-biological cause; “Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed.” Other processes, such as bombardment by radiation or cosmic rays (remember Titan doesn’t have an ozone layer) or the chemical action of minerals could play a role.

So, what should the man on the street take away from this? That Titan is a fascinating and dynamic place, a place in our solar system where things are happening. Clearly, there is more to Titan’s methane- fueled hydrologic cycle than we currently understand, and a spacecraft such as the proposed Titan Survey mission that would put a dirigible-based probe in the atmosphere would go a long way towards solving the “Life on Titan” puzzle. For now, it’ll just have to go on our “Mars-Europa” short-list of interesting places to visit… but don’t believe the “Aliens found on Titan!” news hype just yet!

Review: Confessions of an Alien Hunter by Seth Shostak.

Seth Shostak has a unique tale of scientific inquiry to tell. At its heart are questions that some of the greatest thinkers of our time such as Jill Tarter and Carl Sagan have pondered; are we alone? Why are we here? How common or unique are we as a species?

Only very recently has the topic and field of exobiology become a respectable science, and Confessions of an Alien Hunter by Mr. Shostak and out by Nation Geographic Press reflects on how far we’ve come in this very elusive field and where we might be headed. [Read more...]