![]() ![]() ![]() Several astronomer teams around the country operate under NASA's NEO Observations Program, helping us discover, monitor and study NEOs. Who Searches for Near-Earth Objects? In 1998, in response to a congressional directive, NASA established the Near-Earth Object Observations (NEOO) Program and has been tirelessly detecting, tracking and monitoring near-Earth objects ever since. The MPC's complete set of observations of an object from observatories around the world can be used to calculate the most accurate possible orbit around the Sun for the object to see if it could pose a risk of impact on Earth. Any time an astronomer observes an NEO using a telescope on the ground or in space, they send their measurements of the object's position to the Minor Planet Center. An NEO includes any asteroid, meteoroid or comet orbiting the Sun within 18,600,000 miles (30 million kilometers) of Earth's orbit. Located in Cambridge, Massachusetts, and operating out of the Smithsonian Astrophysical Observatory, the Minor Planet Center (MPC) is the world's repository of all observations and computed orbits of asteroids and comets in the solar system, including all the near-Earth object (NEO) data. World Asteroid Data Repository The Minor Planet Center has a modest name, but this office has a major job. Very rarely, every few decades or so, even larger objects enter the atmosphere, such as the house-sized object that streaked across the sky over Chelyabinsk, Russia, in 2013, producing a super-bright fireball and a shock wave that blasted out windows and broke down doors. Sometimes larger, chair-sized or even car-sized space objects enter Earth's atmosphere and create really bright meteors, called fireballs or bolides, which disintegrate as they explode in the atmosphere. Occasionally, Earth passes through denser streams of small debris released from comets - that's how we get meteor showers. ![]() Small planetary debris the size of grains of sand, pebbles and rocks also rain down daily into Earth's atmosphere, producing the meteors - commonly called "shooting" or "falling stars" - that you can see on any dark clear night. Frequency of Impacts Every day, roughly 100 tons of interplanetary space material rain down on our planet, most of it in the form of tiny dust particles. In 1994, the world witnessed similar-sized impacts happening in near-real time, when fragments of comet Shoemaker-Levy 9 impacted Jupiter - that's when we really started to understand that large asteroid impacts could still happen today. After scientists found the Chicxulub Crater in the Gulf of Mexico, this idea became more certain. In the 1980s, scientists discovered evidence that the demise of the dinosaurs 65 million years ago was likely caused by an asteroid impact. In fact, this realization didn't come until scientists started proving that many of the craters on Earth were caused by cosmic impacts rather than volcanic eruptions (and similarly for the craters on the Moon). A Current Hazard We didn't always know that asteroid impacts were a modern-day possibility. But even Earth is relatively small compared to the size of asteroid orbits, which is why asteroid impacts are so rare. An asteroid needs to arrive at the intersection point with Earth's orbit at the very same time Earth is crossing that point for an impact to occur. During the millennia when an asteroid is in an Earth-crossing orbit, it is possible the asteroid and Earth may find themselves in the same place at the same time. Over time, their orbits may cross Earth's path around the Sun. Why Asteroids Impact Earth Why do asteroids and meteoroids collide with Earth? These objects orbit the Sun just like the planets, as they have been doing for billions of years, but small effects such as gravitational nudges from the planets can jostle the orbits, making them gradually shift over million-year timescales or abruptly reposition if there is a close planetary encounter. ![]()
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