Earth's oceans thrive in lucky Lane 3
Does an 800-square-foot, one-bedroom, one-bath condo going for $950,000 sound like a good deal? If its back yard is a beach on Monterey Bay, it might. Only five miles inland, in Watsonville, you can move into a 1,440-square-foot, two-bedroom, two-bath single-family dwelling for a mere $189,000.
Ever wonder why oceanfront property is so expensive? Of course not; it’s self-evident: we humans love big bodies of water. The rumble and hiss of surf, the panoramic sweep of the sea, the galvanizing salt breezes all make an oceanside stroll hard to resist.
It’s no wonder the ocean soothes our spirits; we’re drawn to it as a weary wanderer is drawn home. When eons ago our aquatic ancestors dragged themselves onto the enticing strangeness of the land, did they never look back? Hardly. In a remote corner of our unconscious, we’ve never forgotten that the ocean is the womb from which we came.
We’re also drawn to the ocean by its otherness. Stand on its shore and see it recede and meld with the ocean of sky. Sail into its heart and feel lost in a vastness more featureless than outer space. Plunge into its depths and discover the cold, the crushing pressure, the creatures more outlandish than the monsters of sci-fi.
If you’re a well-adjusted Homo sapiens and love the ocean, thank your lucky star – the Sun – that it’s the right star at the right distance: 93 million miles. What makes that distance special? It falls within a range of 74 and 148 million miles, also known as HZ, the habitable zone. Of all the lanes in our solar speedway, Lane No. 3 – Earth’s lane – is the most conducive to water. Outside Lane 3, oceans boil off or freeze solid. End of life as we know it.
Luckily for us, Earth is in no danger of going off the deep (or shallow) end and wandering mindlessly out of the HZ. We’re safe for now. But how privileged is our status? In the last half century, speculation regarding the likelihood of life on extra-solar planets (exoplanets) has taken some curious turns. And the jury’s still out.
Before the era of space exploration it was assumed that planets covered by large bodies of liquid water must be common in our universe. We took our cue from the polar caps of Mars and the tropical paradise we imagined would lie cloaked beneath the clouds of Venus.
Closer inspection by interplanetary probes gave us a jolt: Mars’ polar caps consisted not of frozen H2O but frozen CO2 – dry ice. Mars was a frigid desert. Venus, we learned, was hell – a greenhouse machine radiating surface temperatures of 800 F.
But that’s only our solar system. Considering the billions of stars in our galaxy and billions of galaxies in the universe, it stood to reason that although Earth’s surface oceans are unique in our solar system, they’re common in the cosmos. With few exceptions, we imagined, all planetary systems must sustain their own HZs. Surely somewhere around the myriad stars out there must orbit millions of exoplanets adorned with life-giving oceans.
Only in the last few years have we developed the tools – such as the Kepler space observatory, launched by NASA in 2009 – to conduct a serious search for planets orbiting other stars in our neck of the galactic woods.
As of June 1, the Extrasolar Planets Encyclopaedia listed 3,422 confirmed exoplanets. Their sheer number, plus the fact that many of them reside in their star’s HZ, has led some enthusiasts to believe that Earthlike exoplanets are a dime a dozen.
Problem is, HZ is more than a matter of distance. Size matters. Large stars sustain broad HZs but are subject to short lifespans, and small stars live long but sustain narrow (or no) HZs. Were the sun less than 83 percent of its present mass, it wouldn’t radiate enough heat to counteract runaway glaciation on Earth. On the other hand, were the Sun 20 percent more massive, it would have consumed all its hydrogen fuel before it reached its billionth birthday. Earth would have gone dead 3½ billion years ago.
The same principles apply to the size of planets. Were Earth only 10 percent more massive, it would have produced a jailbreak greenhouse effect. Had it been 6 percent less massive, it wouldn’t have developed a sufficient ozone layer to shield it from the sun’s ultraviolet radiation. In either case, kiss life on Earth goodbye.
Our single-minded search for water worlds has also made us realize that too much water can be a problem. A computer modeling study suggests that two Earthlike candidates – Kepler-62e and Kepler-62f, 1,200 light years from Earth – are probably covered by seamless, global oceans. Lacking reasonable access to fire and metals – not to mention electricity – whatever life forms take hold beneath those endless seas would likely be strangers to technology as we know it.
Factors such as orbital eccentricity, axial tilt and rotation, the influence of a moon or giant planet in the vicinity, atmospheric pressure – even the density of the galactic neighborhood – also need to be finely tuned for a planet to be hospitable to our form of life. That, plus our meager understanding of the processes that govern the makeup and evolution of exoplanets’ atmospheres, have led some experts to conclude that Earth might be a special case.
Imagine the citizens of Earth, centuries in the future, on a quest to find an earthlike planet somewhere in our galaxy. Were they to visit a million worlds, their chances of finding a grand total of one world graced with oceans and continents would be remote. When our spacefaring descendants leave the nest and flutter into the cosmos, they’ll likely never again get to enjoy a simple walk by the sea.
We Californians are doubly blessed: blessed to live on the edge of the mighty Pacific Ocean and blessed to live on a blue planet. The next time you take a sunset walk on the beach, don’t leave till the stars come out. Look up, and know that in all that immensity you’ll not find many gems like our sapphire Earth. The color of water.