Mapping the Sky: Finding asteroids requires a combination of tools - SpaceNews
“One strike can reshape our world, and the only thing that can stop it is science.”
Those are the opening lines of “Asteroid Hunters,” an IMAX film narrated by Daisy Ridley of Star Wars fame. If the June 17 screening near NASA’s Ames Research Center is any guide, “Asteroid Hunter” achieves its goal of highlighting the threat asteroids pose and the opportunity to veer dangerously toward Earth.
At the end of the film, an audience consisting mostly of people from NASA Ames and related organizations discusses the ongoing efforts to search for near-Earth objects (NEOs), asteroids, or comets within about 45 million kilometers of Earth’s orbit. In particular, they expressed concern over the fate of NASA’s NEO Surveyor space telescope.
NASA’s 2023 budget proposal released in March called for a cut in the NEO Surveyor space telescope budget from about $143 million in 2022 to less than $40 million in 2023. The budget plan, which would delay the launch of the space telescope by two years until 2028, was opposed by National Space Society and Planetary Society.
“We urge the committee to recover funding and increase NASA’s budget to provide at least $170 million to NEO Surveyors in FY 2023,” the space outreach organization said in a June 16 letter to the House and Senate Appropriations Committees. The NEO Surveyor “is the fastest method to fulfill a congressional mandate to detect 90% of NEO 140 meters and greater. Without the NEO Surveyor, NASA would not have achieved its congressional detection mandate for another 30 years.”
Congress directed NASA in 2005 to identify 90 percent of the estimated 25,000 NEOs measuring 140 meters in diameter or larger by the end of 2020 and to analyze ways of diverting threats. Eighteen months after the deadline, less than half of the NEOs had been identified.
However, experts anticipate rapid progress in the coming decades, based on expected contributions from the NEO Surveyor and the Rubin Observatory, formerly known as the Large Synoptic Survey Telescope (LSST).
The Rubin Observatory, built on a mountaintop in Chile, “will observe about 5,000 asteroids in a single image, and hundreds of thousands every night,” said Ed Lu, a former NASA astronaut and executive director of the virtual Asteroid Institute on B612. “This is going to be a big dog, literally the most powerful machine ever built to track asteroids.”
Telescopes built to track asteroids collect multiple images of the same area every night. The Asteroid Institute and the University of Washington’s Institute for Data Intensive Research in Astrophysics and Cosmology are developing computational tools to detect NEOs in other types of astronomical imagery, as long as they provide five to six views of an area within 15 to 30 days.
An algorithm called Tracklet-less Heliocentric Orbit Recovery, running on Google Cloud, helped astronomers find 104 main belt asteroids in a search of the National Optical-Infrared Astronomy Research Laboratory’s digital archive. An upcoming search of NASA’s Near-Earth Object Wide-field Infrared Survey Explorer data will likely detect thousands.
“We want to apply this technique to the LSST data stream, but we need to practice on this existing data set,” said Lu.
SPACE-BASED TELESCOPE
Even with powerful computing tools, NASA cannot achieve its goal of detecting 90 percent of 140-meter NEO in the near future without a space-based telescope.
“Finding more than 90% of near-Earth asteroids with a diameter of more than 140 meters is a difficult problem because the objects are far away and scattered throughout the sky, but Rubin and NEO Surveyor together will get the job done,” Amy Mainzer, NEO lead researcher at the surveyor and University of Arizona professor of planetary science, said by email. “The Rubin Observatory uses visible wavelengths and is therefore sensitive to objects with more reflective surfaces, and looks up in the night sky. The NEO Surveyor operates in the thermal infrared wavelength and is therefore very sensitive to dark objects; it searches for regions near the Sun in the sky, thus enabling it to find objects with orbits that are most Earth-like (and therefore potentially dangerous).
From its orbit near Sun-Earth Lagrange point 1, the NEO Surveyor will also provide data on the size of NEOs, “which is important for knowing which ones are capable of causing severe damage,” Mainzer said. “Given the stakes, and as with monitoring for other types of natural disasters, it’s very important that we have complete coverage.”
A 140-meter asteroid hitting Earth would release hundreds of megatons of energy. “Never has a nuclear weapon explosion come close to that,” Lu said. (For comparison, the 40 to 60 meter asteroid that flattened an area the size of the Los Angeles basin near the Siberian Tunguska River in 1908 released about 10 to 15 megatons.)
The planetary science decade survey, published in April by a National Academy committee, supports the “development, timely launch, and subsequent operation of the NEO Surveyor” and the Multiple Asteroid Diversion Test. In September, NASA’s DART spacecraft is scheduled to collide with Dimorphos, the near-Earth-orbiting moon of the asteroid Didymos, demonstrating a technique for deflecting the asteroid’s trajectory.
The timing isn’t clear yet for the NEO Surveyor, which is “very important and needs to happen,” said Philip Christensen, Arizona State University professor of geological sciences and co-chair of the planetary science decade survey, Origins, Worlds, and Life: Decadal Strategy for Planetary Science and Astrobiology 2023- 2032.
NASA recommended the postponement of NEO Surveyor to increase funding for the Mars Sample Return and Europa Clipper.
Compared to the $7 billion Mars Sample Return and the $5 billion Clipper Europa, the NEO Surveyor is a small mission. NASA plans to spend about $811 million on the NEO Surveyor from 2022 to 2026 before the President’s budget calls for a delay.
“The more you delay a project like this, the greater the cost,” said Lindley Johnson, NASA’s planetary defense official.
Plus, NASA will need at least three to five years, and preferably 10 years, to take action if astronomers find a large asteroid that is likely to hit Earth, Johnson said.
“While a significant impact on Earth is of course a very rare event, we don’t know when the next one might occur, and the NEO Surveyor is designed to find out,” Johnson said. “The earlier we find it, the more time we have to react and the more options there are viable for dealing with it.”
Congress will ultimately decide the fate of the NEO Surveyors. In a budget document released last year, NASA anticipated spending $170 million on the space telescope by 2023. House Appropriators included $94.9 million for the NEO Surveyor in its 2023 budget and directed NASA to provide a timeline for launching the telescope before 2028.
Philip Groves, writer and producer of “Asteroid Hunters,” hopes the film will encourage congressional support from the NEO Surveyors and other efforts to detect, assess and, if necessary, divert asteroids. Asteroid Hunter, originally released in 2020 before COVID-19 reduced IMAX theater attendance, is now playing in Florida at NASA’s Kennedy Space Center visitor complex and in Los Angeles at the California Science Center.
“My hope is to get this out in front of as many members of Congress and world leaders as possible,” Groves said. “An asteroid impact is the only natural disaster we can prevent.”
THREATS AND OPPORTUNITIES
Looking ahead, the decadal survey calls for “rapid-pass flying reconnaissance missions targeted at challenging NEOs 50 to 100 meters in diameter — representing the population of objects that have the highest probability of a destructive Earth impact.”
Major asteroid strikes are relatively rare.
“In about the last century or so, the biggest impact we know of has been the Tunguska event,” Johnson said. “An event that really grabs our attention may happen once in a century or every other century on average. However, the situation we are in right now is that we don’t know when the next one will happen. But we have the know-how and technology to find out.”
NASA also has international partners.
“While the United States currently has the most significant program looking at this, we are working with a very large team around the world,” Johnson said.
The European Space Agency and the Japan Aerospace Exploration Agency have strong programs underway. In addition, dozens of countries are part of the International Asteroid Warning Network, a UN-backed forum focused on helping government agencies analyze potential impacts and mitigate their consequences.
“There has been a very significant effort to reach an understanding of how best to respond to this worldwide danger,” Johnson said.
Aside from the threat, Lu sees making detailed maps of the solar system as an opportunity.
“Why would all the great powers in the 1500s spend their treasures? Mapping the world,” said Lu. “We’re now on the cusp of opening up space, and we’re going to need a map of where things are in the solar system. With 99% of Tunguska-sized asteroids in our solar system currently untracked, we have a very incomplete map at the moment.”
This article originally appeared in the July 2022 issue of SpaceNews magazine.
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