ASTEROID.TXT T H E A S T E R O I D S By Carolyn Collins Petersen Ever meet Hazel Stone? She's a feisty lady, who's seen it all -- and some believe -- done it all. Her stories of The Galactic Overlord thrill millions of viewers, she's a top-flight space pilot, and she can beat the pants off anybody (except her grandson, Lowell) at chess. Nobody would believe that she once took part in the uprising to liberate Luna -- and, nobody would believe that she once almost died amongst the asteroids because she forgot to check her oxy bottles. If you haven't met Hazel yet, she's one of the central figures in Robert A. Heinlein's "The Rolling Stones" -- a science fiction book about a family that roams the solar system in search of adventure. Part of Hazel's story does indeed take place amongst the asteroids -- a collection of 100,000 or so rock fragments sometimes referred to as 'the minor planets'. This belt of tiny worldlets lies mostly between the orbits of Mars and Jupiter, with a few maverick asteroid groups making their way out as far as Saturn, and inward toward the orbit of Earth. The asteroids have been the subject of many a science fiction story. Many tales postulate huge mining companies sweeping through the belt, turning the ore-ridden rocks into metal for spaceships. Others -- such as Heinlein's -- turn the Asteroid Belt into a future frontier mining camp, with feisty, grizzled old prospectors staking their claims on rotating odd lumps of rock. Lately, in a kind of "truth is stranger than fiction" turnabout, asteroids have been linked with dinosaurs and collisions with Earth. Mining seems to be a popular pastime in the asteroids of the future -- and while it may seem rather farfetched to even consider the idea, asteroid mining COULD be done. Not right now, to be sure, but in some future decade, scientists and miners could descend on a hapless asteroid for a spate of assaying. What is the fascination with these asteroids? What is it about them that makes them such a target for mining? And, why the link with dinosaurs? We have no first-hand experience in the asteroid belt, so most of the information available on the area has come from observations made here on Earth. It used to be a common belief that the asteroids were once a planet, a world which exploded sometime in the misty past of the solar system. Indeed, the asteroids do orbit an area of the solar system where a planet WAS predicted to exist by Bode's Law. (Bode's Law is a mathematical way to predict the positions of the planets in the solar system.) In fact, the search for a planet between the orbits of Mars and Jupiter led indirectly to the discovery of the asteroids. The asteroid Ceres was discovered in 1801, and its orbit was confirmed later that year. Within the next six years, Pallas, Juno and Vesta were discovered -- all by astronomers watching carefully for small specks of light that seemed to move through the sky from night to night. The discoverer of Ceres, Giuseppi Piazzi, had been asked to search for the missing planet -- but intead, was actually looking for comets! (The honor of naming the asteroids generally have fallen to their discoverers. Unfortunately, as more were discovered, hapless astronomers ran out of operatic heroines, flowers, wives and scientists after whom they could name their finds. There are now over 3000 asteroids named, some with such monickers as Gaussia, Washingtonia, and Rockefellia!) Asteroids are grouped by the characteristics of their orbits. These "families" of asteroids generally move at about the same orbital speed and inclination. Observers have identified about 100 families of asteroids. Ground-based observations of asteroids have given us some idea of their sizes and orbital characteristics. Most of them that we have been able to measure range in size from 1025 km (635 miles) down to 32 km (19 miles) in diameter. Undoubtedly there are much smaller particles in the belt. It turns out -- based on our estimates of size, and the relatively small number of asteroids -- that if you glued all the asteroids together and made them into a planet -- you'd get a world a bit smaller than Pluto! It seems that the asteroids were never a planet -- but more likely a collection of rocky worldlets that never got it together to make a planet! While most of the asteroids are so far away that we cannot see them very well, some few asteroids actually cross the path of the Earth's orbit. About 1300 of these have been identified so far, and they are grouped into three families: the Atens, Apollos and Amors. Icarus is one of these asteroids, and passed within 6.4 million kilometers (around 4 million miles) of Earth, in 1967. It is theoretically possible that an asteroid could hit the Earth. Indeed, some current theories of dinosaur extinction hinge on the actual collision of an asteroid with the earth some 65 million years ago. This collision could have kicked up a tremendous amount of dust into the atmosphere, obscuring the Sun and causing a general cooling trend in the weather. This cooling trend, if sudden, would have killed off the plant life on which the dinosaurs lived, thereby killing the dinosaurs. So goes the theory. At the heart of the theory is the element iridium -- which is known to be abundant in meteorites of asteroid-belt origin. Iridium is not too abundant on Earth -- but core samples of the Earth's rock layers show an iridium-rich layer dated back about 65 million years. Chances of another asteroid hitting the Earth are fairly slim -- some scientists put it at 3.5 per every million years. Aside from iridium, most asteroids fall into three categories: C, or carbonaceous S, or silicaceous M, or metallic. The first types are carbonacious chondrites -- stony, carbon-based bodies. The Silicaceous types are mostly silicon, with other metals in smaller amounts. These are redder and brighter than the others. The metallic asteroids are mostly iron and nickle, more massive than the others. All three types are of interest to scientists studying the origin and evolution of the solar system. But, rocky asteroids are not the sole inhabitants of the Belt. There are, scientists feel, a great many former comets in orbit out there. These icy nuclei were probably perturbed from their paths to the Sun by the gravitational pull of Jupiter. No doubt all of these different asteroids will be of interest to future geologists. Not far behind them will probably be the miners -- who, if science fiction accounts hold up -- will mine the ore that will build spaceships, space stations and all of the other tools that we will need someday to further our own adventures in the outer solar system. For now, though, the asteroids remain somewhat enigmatic -- another place to explore in the planetary neighborhood.