Asteroid Terrestrial-impact Last Alert System

A project to patrol the entire night sky
every night in search of incoming asteroids

(and other interesting astronomical events!)

We are a small project with an ambitious goal: early warning of asteroid impact on Earth.

We think it's possible to provide a useful degree of warning for most impacts, meaning a day for a 30 kiloton "town killer", a week for a 5 megaton, "city killer", three weeks for a 100 megaton "county killer". (Yes, those are the same kilotons and megatons of TNT used to describe nuclear explosions because a serious asteroid impact is very similar to a nuclear explosion, complete with mushrooom cloud, except there is no radioactivity or fallout.) We also think it's possible to build and operate the system for a relatively small amount of money ($3M construction and $0.5M per year for operations).

On this site we describe the ATLAS Project, and then tell you something about why people think that asteroids can actually be dangerous to your health. Part of this stems from calculations, part comes from the fact that Earth has been subjected to many historical impacts . We also have a list of some of the other projects and efforts going on to help reduce the risk of being whacked by surprise.

Asteroid Impacts

We hope to persuade you that there really is a danger and that the computer revolution finally offers us the means to do something about it - ATLAS.

Although 'Killer Asteroids' have been dramatized in movies that focus on infrequent but civilization-ending impacts, the vastly more numerous and frequent town-, county-, state-, or country- 'killers' are out there and they will hit us again and again as they have since the origin of the earth. ATLAS is designed to find them before they find us.

Artist's conception of the Chicxulub impact.

On the left is an artist's conception of what the meteor impact at Chicxulub, Mexico might have looked like 65 million years ago. This is the one that may have killed the dinosaurs. People speculate that this asteroid was 10km (6 miles) in diameter, and the explosion released a million times more energy than a 100 megaton nuclear bomb.

The arrival of such an asteroid would have been far more sudden than is depicted in the movies. It's coming in at 50 times the speed of an airliner, so it would only take a few seconds from the moment that you might notice it until you were vaporized. One-one-thousand, two-one-thousand, three-one-thou... The explosion was so big that it would have blasted a huge amount of super-hot material out of the atmosphere on ballistic trajectories at the same time it created a 1000 ft tsunami (tidal wave) across the Caribbean and a circular shock front through the atmosphere that would have knocked down everything in its path. The explosion would have been hot, hotter than the surface of the sun, and the glare from it as well as the falling molten rock would have started vast fires. It is possible that the entire ecology of the Earth was ruined for years, causing the downfall of specialized creatures such as dinosaurs everywhere.

Civilization-ending impacts like the one that killed the dinosaurs occur on average every 100 million years or so but impacts causing major damage to an area the size of a major metropolitan area occur about once every 100 years. The last impact of this scale occurred (surprise!) about 103 years ago - the Tunguska impact in Siberia. Nobody saw it coming. Had this impact taken place over New York City, London or Tokyo it would have killed millions of people. While most impacts will occur over the water or over remote and uninhabited areas we think it is a good idea to know in advance where and when they are going to hit. That's why we want to build ATLAS.

Asteroids and Comets

So what is an asteroid anyway? It's a piece of rock left over from the very early days of the Solar System. If it is loaded with ice and other volatiles it's called a comet, but comets tend to live most of their lives far away from the Sun where it's so cold that these volatiles have not evaporated over the lifetime of the Solar System. When a comet's orbit gets jostled so that it plunges close to the Sun, it can put on a spectacular show for a little while as it evaporates.

Approximately three fourths of asteroids are called "chondrites" (C-type). These consist of small chunks of gravel pasted together. Of the remaining quarter, about two thirds are called "stony asteroids" (S-type) and the final third "metal asteroids" (M-type). These are blasted-off chunks from the middle of a larger body that was hot enough to melt and for iron elements to settle to the center. Chondrites are fragile and are much less likely to survive intact when they strike as a meteor than are stony or metal meteors. Since the atmosphere puts up a fairly good barrier to an incoming asteroid, the size of the explosion an impacting asteroid can create on the ground depends on its composition as well as its size and velocity.

Remnants from Solar System Formation

The Solar System was formed about 4.5 billion years ago out of a cloud that condensed into the Sun and also formed a disk of gas and dust. This disk itself condensed and clumped into bodies of all sizes, and these in turn tended to clump into bigger and bigger bodies because collisions tend to be sticky. The young Earth, for example, was probably ripped apart by a massive collision, but most of the ejecta recondensed into the Moon. In the early days of the Solar System all planets were subjected to heavy, frequent bombardment that only let up when all the junk near the orbit of a planet had been consumed. The remains of this bombardment are evident in the massive cratering of the airless Moon. Earth was smashed even more badly, but the evidence has been erased over the eons by plate tectonics and weather.

Not all the left over junk was eliminated. The presence of Jupiter interfered with the overall stickiness of collisions inside of its orbit, and so we have an asteroid belt of relatively small fragments of rock instead of a planet between Mars and Jupiter. These too can be jostled onto new orbits that take them far from their safe haven of 4 billion years, and in many cases it is only a matter of time before they collide with some other planet, sometimes Earth.

You can find out a lot more about close-passing asteroids at the Near Earth Object (NEO) site at the Jet Propulsion Laboratory (JPL). There are lots of images of historical impact craters at the Lunar and Planetary Institute. There is a wealth of information on you can search for on Wikipedia and elsewhere on the web, such as the nice introduction written by Nick Strobel.