What Threats Do We Face from Outer Space?

No, we’re not talking about attacks from little green men in flying saucers. There are some very real threats that, while rare in occurrence, have the potential to do damage that is almost unimaginable in scale. It is theorized that large asteroid impacts have caused mass extinctions of most of the life on the planet on several occasions. Coronal Mass Ejections (CMEs) from the Sun have done massive damage to electrical grids and communications systems across the planet, and scientists warn that the next big one may be much worse because of our increased dependence on delicate microelectronics. Here are some of the potential threats we may face:

Near-Earth Objects

A great many objects orbit the sun near the earth, or periodically cross its orbit. Most of them are tiny and pose no danger. We call them “shooting stars” as they hit the earth’s atmosphere and burn up. A few are large enough to survive the passage through the atmosphere and hit the ground as meteorites. But some objects are large enough to be of serious concern. Over 800 “Potentially Hazardous Asteroids” have been identified, and more are being found all the time. Potentially Hazardous Asteroids (PHAs) are rocks larger than about 100 meters in diameter that approach within about 4,500,000 miles of the Earth. Astronomers track these objects very carefully to make sure none of them is on a collision course with our planet.

Comets

Comets are large balls of rock and ice with highly elliptical orbits that carry them far into the outer reaches of the solar system, then swing them back near the sun. A number of comets cross the earth’s orbit and could potentially collide with the planet at some point. Many of these are well known and have been watched by astronomers for centuries, but new ones appear frequently.

Solar Flares

Our Sun may look peaceful from here, but up close it is a violently seething ball of burning gas that frequently launches huge fireballs of incredibly hot, electrically charged matter and radiation into space. These are called solar flares or coronal mass ejections. Thankfully, the earth’s magnetic field repels most of this matter harmlessly. We can see our planet’s natural defenses in action when auroras appear. But a large enough mass can get through, causing power outages, damaging satellites, exposing humans to dangerous radiation, and even changing weather patterns on earth.

Supernovae

Not only our own sun, but other stars can be potentially hazardous. Every now and then a star explodes with unimaginable force in what is called a supernova, suddenly expanding to millions of times its normal size, and giving off billions of times its normal radiation. If the star were close enough the earth could be bombarded with deadly rays.

Gamma Ray Bursts

The most luminous events known in the universe are gamma ray bursts. Their cause is not clearly understood, but they occur every few days in seemingly random locations throughout the universe. A gamma ray burst lasts only a few seconds to a few minutes, but can give off as much energy as a billion trillion suns. A gamma ray burst anywhere in our part of the galaxy could produce enough radiation to destroy all life on earth. Fortunately, no gamma ray burst has ever been detected in our galaxy.