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Astro Bob: NASA's NEO Surveyor to hunt down killer asteroids from space

Bad-boy space rocks take note. There will soon be a new cop on the block.

NEO Surveryor NASA JPL Caltech.jpg
In this NASA illustration, the NEO (Near-Earth Object) Surveyor is pictured against a star field photographed in infrared light by a previous mission. The new spacecraft will look for asteroids in infrared light from orbit that would otherwise escape detection from the ground.
Contributed / NASA, JPL-Caltech, University of Arizona
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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.

Near-Earth asteroid census
This chart shows how data from NASA's Wide-field Infrared Survey Explorer, or WISE, has led to recent revisions in the estimated number of near-Earth asteroids. As the graphic reveals, only a small difference was observed in the estimated total numbers of the largest asteroids — the ones with the potential for global consequences should they impact Earth. For medium-sized asteroids, which could still destroy a metropolitan area, new estimates predict fewer space rocks than previously thought. One-thousand meters (1,000 m) equals one kilometer or 0.6 mile. Notice that that there are A LOT more small asteroids than large ones. Though far less dangerous, we've discovered relatively few of them.
Contributed / NASA, JPL-Caltech

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%.

Chelyabinsk glass
Glass from windows shattered by the meteor shock wave litters the floor of the Chelyabinsk Drama Theater on Feb. 13, 2015.
Contributed / Nikita Plekhanov, CC BY-SA 3.0

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.

Lagrange points
The L1 Lagrange point, located a million miles ahead of Earth in the sun's direction, is one of five sun-Earth Lagrange points, positions in space where an object placed there tends to stay put. NASA will launch the NEO Surveyor to L1 sometime in 2028. From there it will be able to spot asteroids approaching Earth from the direction of the sun that would otherwise be impossible to see from the ground because of solar glare and skyglow.
Contributed / NASA, STScI

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 asteroids bright and dark infrared.jpg
This chart illustrates why infrared-sensing telescopes are better suited to finding small, dark asteroids than telescopes that detect visible light. The top of the chart shows how three asteroids of the same size but differing compositions would appear in visible light. An asteroid that has a shinier surface, or higher albedo, will appear brighter than a dark asteroid, even though they're the same size because it reflects more visible light from the sun. The bottom of the chart shows the same three asteroids when viewed in infrared light. They appear to be the same brightness, regardless of how much visible light they reflect. Objects of the same size will radiate about the same amount of infrared light when heated by the sun, making them easier to spot with an infrared telescope.
Contributed / NASA, JPL-Caltech

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.

Read more from Astro Bob
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Related Topics: SCIENCE AND NATURE
"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at nightsky55@gmail.com.
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