Meteorites can thrash our planet with incredible force. Arizona’s Barringer Meteor Crater, created by an iron-nickel alloy from the core of an asteroid, lies a quarter mile across and 600 feet deep. Russia’s Tunguska impact blew trees down for over 200 square miles.
The strength of the explosions from the sudden dissipation of energy during these impacts ejects the rock from the craters, throwing it up around the area in reverse order. The presence of ejecta clues geologists in to the presence of a meteorite crater, rather than a sinkhole from a drained underground aquifer.
Chabot’s own Gerald McKeegan, member of the media team and principal investigator for our asteroid tracking program, shared information about asteroids and meteorites during May’s volunteer enrichment.
Asteroids are small objects within our solar system, either the remains of planets that disintegrated or matter that never came together to form a planet. Being smaller, they can have more unpredictable orbits and get affected by the gravity of planets they pass, and on rare occasions get close enough to the Earth to hit as meteorites. Meteors, or falling stars, are objects which burn up due to the friction in our atmosphere, and land on Earth as microscopic space dust – of which we get roughly a few thousand tons per year.
Asteroids come closer to us than the moon about 20 or 30 times a year. On March 5th of this year, three asteroids were closer than the moon within a 25-hour period.
They, and a few older comets, earn the title of Near Earth Objects (NEOs) when they come within 28 million miles of Earth’s orbit. We have identified 11,000 near earth objects, and expect that more than a million remain to be catalogued.
McKeegan pointed out that scientists have only been able to predict a meteorite impact accurately twice. This happened once in 2008, and again on January 4th of this year, when a meteorite fell over the Mid-Atlantic ocean. In both of these cases, they only had less than a day’s notice.
He, and others at the Chabot Space and Science Center, hope to improve these predictions through dedicated research into NEO’s. Major goals of the work at Chabot in this area include confirming possible new objects discovered by NASA and observing the catalogued asteroids in more detail to improve or verify information about their size and orbits.
Astronomers seeking to understand NEOs pay attention to astrometry, measurements of an object’s position used to compute its orbit, and luminosity, a measure of brightness used to estimate the asteroid’s size. The basic approach to asteroid location involves taking three or more images of the same part of the sky over 10-30 minute intervals, scaling the images, flipping through them in order to identify the moving object, and then reporting it to the International Astronautical Congress, the world body which catalogs this data.
Dedicated, curious amateurs do much of this research, which always involves an element of educated guesswork. There are only about a dozen professional observatories participating in this global effort. Researchers hope to bring more people aboard, especially in the Southern Hemisphere. More information should lead to longer warning times before an asteroid impact, and McKeegan assured us that with years of advance notice, scientists should be able to deflect the oncoming asteroid.
Small errors accumulate in the timing of image snapshots, meaning that researchers might not compare exactly the same section of sky. Brightness alone also does not completely convey an object’s size, as variations in an asteroid’s color or reflectivity may make it seem brighter and closer than it is. (This is why researchers hope to use infrared telescopes in the near future.) Even accounting for these sorts of error, asteroid hunters have identified a good number of possible orbits for the known NEOs, many of which could put them on collision courses with Earth.
However, McKeegan rushed to put things in perspective. Once every ten million years or so, he said, a huge, deadly meteorite hits our planet. That gives us a 99.999 percent chance of not getting hit by a meteorite.
In the future, researchers plan to use more small, space-based telescopes for these efforts, as they can find NEOs at 10 to 100 times the rate of ground based telescopes. The geosynchronous Sentinel spacecraft, orbiting Earth at the same speed as our planet’s daily rotation, aims to locate these objects when it is launched in 2018.