October 19, 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?

Astro-Event: The Rise of Mars & Opposition of 2012.

Mars during the 2003 opposition, nearly twice as large as this years!

(Photo by Author).

After a wintertime drought of evening planets, March and the beginning of northern hemisphere spring sees the return of the classical naked eye-planets to the PM skies, not the least of which is Mars. Currently rising low in the east at sunset in the constellation Leo, Mars reaches opposition this weekend on March 3rd at 20:00UT/15:00EST at a distance of 0.6741 Astronomical Units (A.U.s) or 62,661,510 miles from Earth. [Read more...]

14.10.09: The Earth-Moon System as viewed by HiRISE.

The image above floated through our tweet-o-sphere yesterday, thus prompting today’s news post. HiRISE, NASA’s High Resolution Imaging Science Experiment aboard the Mars Reconnaissance Orbiter(MRO) is the spacecraft that you’re probably not following, but should be. In orbit about the Red Planet since early 2006, its been transmitting some pretty mind blowing images, all definitely worth a daily peek! Housing a 0.5 meter reflecting telescope which would be the envy of any backyard astronomer, its the first true “spy satellite” quality orbiter that we’ve fielded about Mars. Able to resolve targets about 0.3 meters across, some of the highlights have included stunning views of the polar caps and dunes, snapshots of the Opportunity and Spirit landing sites, and even catching the Phoenix Lander in descent! In fact, eagle-eyed desktop amateurs may even prove successful it divining the fate of the many (more than half!) errant Mars-bound landers over the years. But as is often the case with space exploration, we travel millions of miles to find…ourselves. Some of the most memorable images are actually those of the Earth, whether its “Earth-rise” aboard Apollo 8 or the “Pale Blue Dot” as viewed from Voyager 1, images such as these and the HiRISE pic above of our tiny home remind us how special our place is. Snapped back in 2007, it shows us that the Earth is not only a pretty, but dynamic place were things are happening. Mars is tiny and cratered, and through a backyard telescope, generally yields little detail. Venus, although dazzling, is perpetually shrouded in sulfurous cloud. Not so with the Earth. Cloud cover changes, the surface shows a variation in sea, land, and seasonal growth, and at night, an experienced telescopic eye might just pick out the lights of cities, evidence of human activity. Views like this always remind me of Arthur C. Clarke’s little known but classic short story Report on Planet Three, where Martian scientists argue that life couldn’t exist on Earth! Clarke wryly points out that life elsewhere may not be remotely Earth-like. I personally can’t wait to spread my telescope tripod legs out under a night under Martian skies; and without a doubt, the slender crescent Earth-Moon duo will be my first astronomical target!