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  • “Exploration is in our nature.” - Carl Sagan

NEOWISE, studying near-Earth asteroids

Highlights

  • NEOWISE is a NASA space telescope that detects, tracks, and studies near-Earth asteroids.
  • The threat from asteroid impacts is small, but real — and preventable. Missions like NEOWISE are essential to help us understand how to stop dangerous asteroids.
  • NEOWISE originally launched as the WISE astrophysics mission in 2009. Its replacement mission, NEO Surveyor, is scheduled to launch in 2028.

What is NEOWISE?

In order to stop asteroids from hitting Earth, we must find, track and study them. Because near-Earth asteroids reflect very little light, they can be hard to spot against the darkness of space. Fortunately, there's another way: asteroids heat up in the Sun and radiate that heat back into space, making them glow in infrared light. Space telescopes — particularly, space telescopes that can see infrared light — are ideal asteroid-hunting tools.

NEOWISE, NASA's Near-Earth Object Wide-field Infrared Survey Explorer, orbits the Earth and sweeps the sky looking for asteroids. As of early 2021 it has surveyed the entire sky 15 times, observing roughly 40,000 solar system objects, including 1,200 near-Earth asteroids. These observations help us understand the different sizes and types of near-Earth asteroids, their trajectories through the solar system, and what to do if we find one on course to hit Earth.

NEOWISE's past, present, and future

NEOWISE is the only space mission currently dedicated to planetary defense, yet it was never built explicitly for that purpose. It originally launched as an astrophysics mission called WISE, the Wide-field Infrared Survey Explorer. WISE's job was to scan the sky for the nearest and coolest stars, the most luminous galaxies in the universe, and asteroids.

The telescope and its four infrared detectors were kept chilled inside a tank with frozen hydrogen-filled walls to prevent WISE from detecting its own heat. The hydrogen supply ran out as expected in 2010, rendering two of WISE's four detectors useless. After a 30-month hibernation, NASA reactivated the spacecraft as NEOWISE in 2013 and gave it its current mission to study near-Earth objects.

Atmospheric drag is slowly shifting NEOWISE's orbit to the point where it will be unable to make observations without sunlight or reflected Earth light entering the telescope. It is expected to reenter Earth's atmosphere in 2025. A replacement telescope called NEO Surveyor is scheduled to launch in 2028.

Asteroid Apophis
Asteroid Apophis NEOWISE searches for potentially hazardous near-Earth asteroids like Apophis, which in 2029 will pass closer to Earth than some geostationary satellites. Apophis is 450 meters (1500 feet) wide and would cause widespread regional destruction if it were to hit Earth.Image: The Planetary Society

How does NEOWISE work?

NEOWISE is essentially a 40-centimeter-diameter telescope with four infrared detectors, two of which are still functional without the spacecraft's supply of frozen hydrogen ran out. NEOWISE is relatively small and compact, measuring less than 3 meters along its longest axis.

NEOWISE operates in low-Earth orbit, at an altitude slightly higher than the International Space Station. It orbits Earth pole-pole along the planet's terminator, the dividing line between day and night. This allows it to say in continual sunlight with its solar arrays face-on to the Sun and the telescope barrel pointing away into space. As atmospheric drag alters its orbit, it will eventually drift into a position where it will eventually be unable to observe the sky without sunlight or reflected Earthlight entering the telescope. This will effectively end its mission.

NEOWISE artist's concept
NEOWISE artist's concept NASA's NEOWISE spacecraft (formerly WISE).Image: NASA

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