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NASA's first telescope specifically designed to find and track hazardous near-Earth asteroids and comets from space will soon become a reality. Called the Near-Earth Object Surveyor (NEO Surveyor), its mission is to discover 90% of asteroids 460 feet (140 meters) or larger that come within 30 million miles (48 million km) of Earth's orbit — close enough to constitute a potential future threat.
To date, about 90 percent of the larger asteroids (1 kilometer and up) that could potentially wreak planet-wide devastation have been discovered. No known asteroid poses a significant risk of impact with Earth over the next 100 years. Looking ahead, the greatest near-term threat comes from asteroid 2009 FD in 2185. A third of a mile (0.5 kilometer) across, it has a 1 in 714 chance of impact or less than 0.2%.
But there are still tens of thousands of smaller objects like 2009 FD remaining to be found, asteroids like the one the blew up in an air burst over Chelyabinsk, Russia in February 2013. While no one was struck or injured by a meteorite from the impact, the shock wave from its breakup in the atmosphere blew out thousands of windows on the ground. Flying glass shards injured some 1,200 people. Similar impacts have the potential to cause massive regional damage, adding urgency to develop new ways of detecting and deflecting potential killer asteroids.
“Ground-based telescopes remain essential for us to continually watch the skies, but a space-based infrared observatory is the ultimate high ground that will enable NASA’s planetary defense strategy,” said Lindley Johnson of NASA's Planetary Defense Coordination Office in a recent news release.
The NEO Surveyor will journey a million miles (1.5 million km) to a region of gravitational stability, called the L1 Lagrange point , between Earth and the sun. For reference, the James Webb Space Telescope orbits at the L2 Lagrange point, located about million miles in the opposite direction, where it faces into the blackness of deep space.
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From its stable perch, the NEO Surveyor's 20-inch (50 cm) telescope will view the solar system in infrared light. Earth's atmosphere blocks most incoming infrared light — which we sense as heat — from space objects, making ground-based telescopes of limited use in this slice of the electromagnetic spectrum.
NEO Surveyor’s state-of-the-art infrared detectors are designed to track the most challenging-to-find near-Earth objects, such as dark-colored asteroids and comets that reflect little visible light. Heated by the sun, these objects glow in infrared light and will give themselves up to the sensitive telescope's heat-sensing eye.
The NEO Surveyor also will be able to find asteroids that approach Earth from the direction of the Sun (like the one that entered over Chelyabinsk), as well as those that lead and trail our planet’s orbit, that are otherwise nearly impossible to find because of the glare of sunlight. While its primary mission is planetary defense, the spacecraft will study the composition, shape, rotation and orbit of near-Earth objects to further our understanding of their origin and evolution.
Large radiators will bleed away heat from the on-board electronics to help to cool the detectors so they're not swamped by infrared radiation. Additional measures include the use of low-heat-conducting, composite struts to isolate the telescope’s detectors from the warm spacecraft, as well as a sunshield to block the glare and heat of sunlight.
Astronomers have discovered about 9,000 near-Earth asteroids . Of that number, just 20-30% of the middle-sized ones NEO Surveyor is designed to spot have been found. Clearly, the mission has its work cut out. The spacecraft is expected to launch in mid-2028 and discover 90% of the total within the first five years of operation.
