Asteroids: An Introduction

image of an asteroid impacting Earth

NASA Image

It’s a hot, tropical morning about 65 million years ago. Pterodactyls glide in huge, lazy circles in the humid air, looking for small teleost fish near the surface of the shallow water, while plesiosaurs play in the deeper waters beyond the reefs. Suddenly, a dark mass appears high in the sky, beginning to glow at the leading edge. It cuts quickly through the atmosphere, trailing glowing straight lines that expand away from the object’s slanted path. In only a few seconds the object soundlessly slams into the ocean at the edge of sight, disappearing in a blinding ball of light that expands in all directions from the point of impact. For a few more seconds, the wall of light silently rushes toward the startled inhabitants, until the irresistible wall of the atmospheric shock wave slams into them with unbearable heat and noise, and sweeps them from the sea and air. Near the point of impact, another wall, this time of dark water and seafloor rocks, rises cone-like into the sky, the leading edge passing overhead. The cone expands outward, lifting the boiling sea into the sky. Vaporized rock and water are thrown into space followed by cubic kilometers of rock, most of which falls back to Earth. A tidal wave many kilometers high sweeps across the shore of lands that will become North and South America, breaking on the mountains whose forests are already ablaze from the atmospheric shock wave. A thick blanket of water and rock from the widening crater crashes onto the ground. It thins with distance from the impact into a broken rain of red-hot mountain-sized boulders that gouge smaller new craters and ignite all remaining vegetation. The cloud of infalling debris extends around the entire Earth in less than an hour. Thick clouds of dust and steam from the fires and explosions quickly fill Earth’s entire atmosphere, cutting off sunlight to the surface below. It will be months before sunlight is seen at the surface again. Below the clouds, 95% of all living things, and 70% of all species are dead or dying. The age of the dinosaurs has ended.

Image of an asteroid impacting Earth while Pterodactyle fly around, oblivious

NASA Image

The collision that closed the curtain of time on the dinosaurs is the best-known example of a very physical connection between Earth and the asteroids, but not the only one. Over 150 asteroid scars — called impact craters — are known on Earth’s land surfaces, and probably many more lie on the poorly explored ocean floors (visit the Earth Impact Database for more information on craters). Most impact craters are small, only a few kilometers across, like Meteor Crater in Northern Arizona, but a few are hundreds of kilometers across. Likewise, most of the craters are tens or hundreds of millions of years old, but a few are only twenty or thirty thousand years old — and a few may be younger still (link). Impacts of large asteroids make large craters. The asteroid that ended the dinosaur era was about 10 kilometers in diameter, and it made a crater about 180 kilometers across. Its affect was world-wide. The object that made Meteor Crater was much smaller, only about 50 meters across. It made a much smaller crater 1.5 kilometers across, and affected only a part of northern Arizona. Thus our most immediate interest in asteroids is to know where asteroids are, how big they are, and what the chances are that one might hit us.

Our second main interest in asteroids relates more to the future: asteroids, depending on what they are made of, could provide us with needed mineral resources that may become important as we use up mineral deposits here on Earth.

Finally, astronomers are interested in asteroids because of what they can tell us about the origin and formation of the Solar System and our own Earth.

In this project we will learn about asteroids: their orbits, their sizes, their compositions, what kind of rocks are found on their surfaces and what geologic processes shaped them. We will use telescopes to take our own images and spectra, and we will use data that other astronomers have gathered. With those data, we will investigate asteroids in the Wilderness of Rocks.