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SPIE Professional April 2014

Asteroid Detectors

New sensors to detect asteroids that could hit Earth

By Scott Hauser

In the ongoing background noise of potential natural disasters vying for your attention — hurricanes, tornadoes, earthquakes, lightning strikes — the idea that a random piece of rock from outer space will cross paths with Earth is most likely a distant worry.

And if a project involving a team of University of Rochester scientists in New York and researchers at NASA’s Jet Propulsion Laboratory (JPL) in California succeeds, you may eventually be able to rest even easier when it comes to the faint possibility that an asteroid will strike Earth with catastrophic consequences. Or at least put the possibility into the same category as other hazards that can be predicted and prepared for, if not averted.

For much of the past decade, Amanda “Amy” Mainzer, the principal investigator for two JPL missions designed to survey space for asteroids and comets, and colleagues at Rochester have been collaborating in an effort to improve the ability of space telescopes to map the course of asteroids. The long-term goal is to put in place a network of detection involving both space-based and ground-based observatories that will alert observers when asteroids or comets are on a collision course with Earth. This will allow disaster professionals time to prepare a course of action to avert as much danger as possible.

In 2013, the Rochester team of Craig McMurtry, a senior engineer; Judith Pipher, professor emerita; and Bill Forrest, professor emeritus, along with Mainzer and other researchers reported an important breakthrough in that effort: a new generation of sensors appears ready to serve as the electronic eyes of a mission designed to hunt for “near-Earth objects.”

With initial funding from NASA, the group, all in the Department of Physics and Astronomy at Rochester, is proposing a new space-based telescope that would sit close to Earth’s orbit and use infrared sensors to scan the sky for asteroids on a possible collision course with Earth. Named NEOCam, or “Near-Earth Object Camera,” the mission would be able to detect objects that have a diameter of 30 to 50 meters, about the size of an office building.


Artist’s conception of a solar system with planets, a comet, and an asteroid.
Potential for destruction

While that won’t account for all the objects with potential to cause catastrophic damage, it would go a long way toward filling in a wide swath of missing information about asteroids. When such near-Earth objects are relatively small — objects the size of basketballs are estimated to enter the atmosphere once or twice a week — they dissipate harmlessly in the atmosphere.

The larger they get, of course, the greater their potential for destruction. The world was reminded of that in February 2013 when an asteroid 17 to 20 meters in diameter entered the atmosphere over the Ural region of Russia and exploded about 30 miles from the city of Chelyabinsk.

Mainzer published a detailed census in 2011 of large and midsize asteroids, reporting that the majority of objects larger than 1 kilometer in diameter and the ones measuring between 300 meters and 1 kilometer have already been spotted. Part of a project called the NEOWISE survey, the results were based on data from the Wide-field Infrared Survey Explorer, or WISE, a NASA mission launched in 2009 that was designed to scan for luminous galaxies and stars with a cooler temperature signature.

Like the WISE mission, NEOCam is based on the asteroid-hunting technology of using infrared radiation as a way to spot dark, nonreflective objects. IR radiation can be used to measure the heat emitted by an object, making it ideal for searching for objects like asteroids. Asteroids don’t emit their own light, but when warmed by the sun, emit enough IR radiation to stand out in space.

But unlike WISE, the proposed NEOCam mission will be designed to scan specifically for near-Earth objects, and where the longest wavelength detections in WISE were based in silicon, the new sensors would be made of a newly developed combination of mercury, cadmium, and tellurium. The combination allows the sensors to collect infrared wavelengths up to about 10 microns, the range at which most asteroids emit IR radiation.


The NEOCam sensor (right) in this artist’s conception is the lynchpin for the proposed NEOCam space mission (left).
Long-lasting, cool detectors

In an open-access paper published in a special section of Optical Engineering in September 2013, the Rochester team reported that the new sensors could operate comfortably at about 40 degrees above absolute zero, the temperature at which most space-based telescopes eventually live out their lives in space. The ability to operate at 40 degrees Kelvin means NEOCam would not have to carry an artificial coolant such as liquid helium or solid hydrogen, a requirement for silicon-based arrays, which operate best at 10 degrees or less above absolute zero.

“It doesn’t sound like a big difference … but to an instrument astronomer working on space telescopes, it’s night and day,” Mainzer says. “With these new detectors, we can get away with not using cryogen to keep them cold. The benefit is that they can enable the mission to have a very long life.”

The team worked with Teledyne Imaging Sensors to develop and test the new sensors. If all goes as planned, the new detectors will be capable of capturing 16 megapixels of light and will be paired with a complement of sensors at a shorter wavelength to allow for more precise measurement of asteroids.

While the mission has more NASA approvals to get through before a launch date can be set, the team envisions that the ability to make such measurements eventually could add up to a more advanced system for keeping track of asteroids that’s analogous to the National Oceanic and Atmospheric Administration’s efforts to track hurricanes and other storms.

As science gets better at detecting asteroids and tracking their orbits, a warning system could be put in place that gives people more options for dealing with potential impacts. For larger impacts, trying to divert the objects might be possible. For smaller objects, a future system could provide enough warning for people to get out of harm’s way.

The paper, “Development of sensitive long-wave infrared detector arrays for passively cooled space missions,” can be found in the SPIE Digital Library.

Read more about asteroids and near-Earth objects.

–Scott Hauser is editor of the Rochester Review of the University of Rochester. This article was excerpted and slightly edited, with permission from the Rochester Review.

Editor’s notes:

The WISE mission was renamed NEOWISE in September 2013 and became part of a new asteroid initiative in the USA to enhance NASA’s ability to find potentially hazardous asteroids. See above.

Mainzer, McMurtry, Forrest, and Pipher are among co-authors of a paper to be presented at SPIE Astronomical Telescopes + Instrumentation in June on a LWIR megapixel array developed by Teledyne for NEOCam. Paper 9154-82.


— RELATED STORIES —
Send a message to the asteroid Bennu

NASA is inviting people around the world to submit their names to be etched on a microchip aboard a spacecraft headed to the asteroid Bennu in 2016.

The “Messages to Bennu!” microchip will travel to the asteroid aboard the agency’s Origins-Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) spacecraft.

The robotic mission will spend more than two years on Bennu, which is 1760 feet (500 meters) wide. The spacecraft will collect a sample of Bennu’s surface and return it to Earth in a sample-return capsule.

Participants should submit their names online no later than 30 September.

NASA plans for planetary defense

NASA is pursuing new partnerships and collaborations in an “Asteroid Grand Challenge” to accelerate the work of finding asteroid threats to Earth and determining what to do about them.

As part of the initiative, NASA is developing an Asteroid Redirect Mission (ARM), a first-ever mission to identify, capture, and redirect an asteroid to a safe orbit of Earth’s moon for future exploration by astronauts in the 2020s.

ARM will use capabilities in development, including the new Orion spacecraft and Space Launch System rocket, as well as assets in the Near-Earth Object (NEO) program, which scans the entire celestial sky in infrared light.

NASA is combining public-private partnerships, crowdsourcing, and incentive prizes.

Find more information, including opportunities for funding and other participation.


DOI: 10.1117/2.4201404.18

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