Science Friday: A Trillion Worlds for the Taking

For thousands of years of recorded history a fragile race of bipedal apes have cast their primate eyes skyward in hope of Divine Salvation or in fear of Heavenly Apocalypse. Strangely, unbeknownst to them, those superstitious musings weren't far from the truth. Tumbling silently through the farthest reaches of our solar system are the twin potentials of untold wealth and apocalyptic peril. Great iron mountains unchained by land, hydrocarbon ice bergs floating in an endless spatial ocean, and self gravitating heaps of gravel. There are trillions of them by best estimate. All these riches are ours for the taking: Each a potential Destroyer of Worlds.

Sixty-five million years ago, a smallish one made a fateful rendezvous with our lush steamy, planet and changed the course of life on earth. And while it may have been the harbinger of doom for the dinosaurs, it was midwife to the birth of modern day furry mammals, and its many celestial cousins left behind may yet provide our deliverance or our demise.

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The date of the Last Cretaceous Day on earth was not chosen on terrestrial shores, it was awarded in the depths of interplanetary space. Tiny tweaks on the path of a nondescript, mini-world, perhaps millions of years in the making, conspired to send it careening into the inner solar system. We don't know how many circuits it may have made across the orbit of the earth. We don't know if it burned straight in on the first pass or danced in an elegant gravitational embrace for centuries before consummating the deadly union with our planet. But once it had a bead on us, models indicate that the closing velocity would have been ferocious. At these kinds of speeds, it would traverse the distance between the earth and the moon in less than half a day. Even with an array of telescopes and satellites as sophisticated as our own, odds are the warning time for a rocky object heading directly our way from the outer solar system might be at most a few hours. And that's if some bored astronomer notices the tiny speck at all.

Title: Death of the Dinosaurs by artist Lynette Cook. On the shore of an ancient sea near modern day Mexico, a T. rex has a front row seat to the end of her world as she dines on a triceratops. A smaller scavenging theropod dinosaur lurks in the background. Perched safely out of reach in the conifer tree is an early primate like mammal. Copyright © 1998-2006 Lynette R. Cook, All Rights Reserved. Used with permission

At least part of the object seems to have blasted into what was then a shallow sea on the gulf coast of present day Yucatán in Central America. To get an idea of the enormity of the impact, when the bottom of the intruder was at sea level, the top would have been higher than the peak of Mt. Everest. Today, the 200 kilometer wide crater lies buried beneath 1000 meters of limestone and is centered on the town of Chicxulub. The object would have vaporized countless billions of gallons of sea water instantly. The shock wave of wind and super heated steam would have spread from the titanic bulls-eye at supersonic speeds, followed by tsunamis measured in hundreds or thousands of meters.

Millions of tons of rocky sea bottom would have been heated to vapor, much of it thrown into suborbital trajectory. What goes up must come down: The earth would have been hit with orbital artillery for days, from missiles the size of small mountains to ones no larger than a sand grain. The streaking fragments would have glowed white hot as they tore through the thin layer of air into the land and water at several miles per second.

All over the earth today there is a telltale layer of dark material at this boundary between the Cretaceous Period and the Tertiary Period. It's composed of carbon mostly, shot through with bits of glassy spheres and rare trace elements found in asteroids and comets, all of which supports a dramatic conclusion: Our planet was on fire. Many or most of the fields and forests on the earth were ablaze after being showered with incandescent ejecta from a massive meteor strike.

The K-T Boundary shows up in this exposed strata as the border between the lighter and darker rock. Similar layers are found worldwide. The line of black contains evidence of melted and shocked rock and minerals, along with carbon, i.e. soot, and traces of meteor/cometary material

As luck would have it, the Cretaceous-Tertiary (K-T) Impacter happened to strike a relatively rare concentration of gypsum and other material containing large quantities of sulfur--along with the more common offshore ocean strata rich in carbon and calcium such as limestone. The resulting aerosols would have been highly acidic when dissolved in water, and with the atmosphere shot full of dust, and so much water vapor present from the impact, it's highly plausible the earth was pelted by acid rain strong enough to eat through solid bone for months. First fire, then a chemical deluge, followed by years of nuclear winter. 'Hellish' doesn't do it justice.

Not all scientists attribute the extinction of 70 percent of all life on earth at the K-T boundary to the impact. But the evidence is quite suggestive that a large object did indeed strike the earth around this time, so whatever additional factors may have been in play contributing to the extinction of so many diverse types of life, that event couldn't have helped. When it was all over, the intelligent Troodons, the fearsome Tyrannosaurs, the armored ankylosaurs, the grand marine reptiles, the iridescent ammonoids floating in the warm oceans; all would be gone. Except for the birds, no dinosaur, and no land animal weighing more than a few kilograms, would make it through the catastrophe.

The geometry of the planetoids (Enlarge). The Kuiper Belt (Rhymes with Hyper Belt) was predicted as a consequence of gravitational interaction between large planets such as proto-Jupiter and the flotsam and jetsam making up the early solar system. It begins at the orbit of Neptune and extends for hundreds of millions of miles. The Oort Cloud is far larger in volume and may extend one-quarter of the way to the nearest star. The estimated number of objects runs in the trillions. Illustration courtesy NASA

It could happen again. We know of almost 4,000 Near Earth Objects with a diameter of over 50 meters, and we've barely begun to catalogue them. There are millions more making up the asteroid belt and not all of them are confined between the orbits of Mars and Jupiter. At the edge of our planetary neighborhood, the Kuiper Belt is thought to contain millions or billions of rocks and chunks of exotic ices in deep freeze. And the Oort Cloud could easily hold trillions, some larger than our moon.

Meteor Crater in Arizona is 1.2 kilometers (4,000 feet) across. At impact 50,000 years ago, the suspected nickel-iron meteorite was probably around 30 meters in diameter and produced an explosion equivalent to 3 megatons of TNT. In today's militarized climate, such an event could easily be mistaken for a nuclear strike and lead to Mutual Assured Destruction. Photo courtesy of the US Geological Survey

Paradoxically, as surely as these objects can lay waste to life on earth, they can provide it. It was the planetoids, large and small, that first created a simmering Hadean Earth. These interplanetary missiles then filled our oceans and peppered those early waters with the organic building blocks of life. The very elements in the air we breathe and the food we eat were delivered by astral courier to a sterile planet four and a half billion years ago.

Distant Pluto and its lonely moon Charon. Pluto is one of the nearest known Kuiper Belt Object (KBO) and the first discovered. Of the millions or billions of KBOs thought to exist, 800 have now been imaged, some equal to or larger than Pluto, but the vast majority are thought to be much, much smaller. Copyright © 1998-2006 Lynette R. Cook, All Rights Reserved. Used with permission

Today, leftover relics from that grand construction project orbit as silent reminders of our violent birth. There floating in the hard vacuum of space lays every element and compound we would need to survive and prosper. There are lodes of nickel, iron, magnesium, water, and oxygen, all free for the taking, none of which require expensive, dangerous rockets to loft into position. Just a few medium sized comets could produce more fresh water than exists in all the lakes, streams, and rivers here on earth.  One methane rich comet carries enough natural gas to power the US for a century.

They are the seeds of future industry, the base for enormous settlements. The challenge facing those who would mine them and settle them is stupendous, creating a city in the Antarctic or a giant factory deep under the sea would be a piece of cake by comparison. But the reward for success is immeasurable. Perhaps, if we continue to be lucky, in the future we or our machine hybrid descendants will cautiously colonize our solar system carried on the backs of comets and asteroids. We will cultivate these small worlds with structures of metal and plastic, creep out slowly to the Kuiper Belt, and eventually inhabit the distant Oort Cloud. Maybe in this way we will in the words of Carl Sagan "Tiptoe to the Stars" with a trillion small worlds acting as stepping stones along the way.

Left: On July 4, 2005 NASA's Deep Impact lights up Comet Tempel 1 with a slug to help reveal the composition. The accuracy required to pull that off is likened to hitting a cannon ball in mid-flight with a rifle bullet fired from a mile away. Right: Comet Wild 2 (Pronounced Vilt 2) was visited by the NASA Stardust mission which successfully returned samples of comet dust to earth on Jan 15, 2005. Objects such as these contain water, volatile gases, and minerals. Everything an organic (Or artificial) being might need. Both images courtesy of NASA

All these worlds, as best we can tell, are ours. It is part of our primeval inheritance, courtesy of the solar nebula which formed every planet including our own, and whose molecular endowment we carry in every cell of our body. We can spend that capital wisely or we can squander it, we can use these planetary riches or misuse them, we can track them or ignore them, all as we see fit. Either way, the potential locked in everyone is such that it can change our cosmic fate; treasures of metals and ice, bread crumbs leading to the stars, or portent of doom.

And the US won't be leading the way, or even capable of warding off a collision anytime soon, if the powers that be keep cutting funding for space exploration, science education, and research:

[SpaceRef Link] "One of the most inexplicable aspects of those NASA's budget request is their plan to cut between $350 to $400 million from research and analysis funding over the next five years," continued Rep. Udall.  "As you may know, that is the funding that helps develop the next generation of scientists and engineers at our nation's universities.  I am puzzled that the same Administration that announced its American Competitiveness Initiative with such fanfare would turn around and cut research funding important to our universities' educational and research missions."

There's a thousand reasons to try and utilize these worlds for our benefit and there's a thousand ways to fail at that task. But what will turn out to be the most important reason for moving from our earthly cradle is likely unknowable at this time. If we could have asked the first fish to crawl on land what the future advantages were in that revolutionary transition, given the intellectual ability it might have replied at length: But that hypothetical fish probably wouldn't have thought of Fire.

For now it's only a matter of getting to these treasure troves, once there we won't run out of new homes or sources of construction material anytime soon: There is after all a trillion worlds for the taking.