In and around our planet there are thousands of comets and asteroids known as near-earth objects (NEOs). Multiple space agencies and government affiliates are responsible for tracking them, especially those known as potentially dangerous asteroids (PHA). These objects are so designated because they will cross Earth’s orbit and may one day even collide with it. When you consider how past impacts caused mass extinctions (like the Chicxulub impact event that killed the dinosaurs), future impact is something we want to avoid!
Monitoring PHAs is a huge responsibility that requires a global effort, including tracking, alerting and disaster preparedness. Last year, more than 100 participants from 18 countries (including NASA scientists and the NEOWISE mission) conducted an international exercise simulating an encounter with an asteroid flying close to Earth. As NASA revealed in a recently released study, the exercise was a huge success. Lessons learned can help prevent real consequences in the near future or significantly limit the devastation a person could cause.
The study, which appeared in the May 31 issue of The Planetary Science Magazine (titled “Apophis Planetary Defense Campaign”), was conducted by the Planetary Defense Exercise Working Group and led by Vishnu Reddy – an associate professor at the Lunar and Planetary Laboratory (LPI) at the University of Arizona. The working group is made up of more than 100 participants from 18 countries and includes facilities such as NASA’s Planetary Defense Coordination Office (PDCO), the ESA NEO Coordination Center, the Russian Academy of Sciences, the Korea Astronomy and Space Science Institute (KASI), and many universities. and research institutes worldwide.
Simulating a threat
As Reddy and his colleagues describe in the paper, the planetary defense exercise was the culmination of work beginning in 2017 designed to test the operational readiness of our global planetary defense capabilities. The exercise was conducted with the support of NASA’s PDCO, the Minor Planet Center (MPC) – the internationally recognized authority for monitoring the position and movement of small celestial bodies – and the International Asteroid Warning Network (IAWN). The exercise was dubbed the “Apophis Campaign” because it coincided with the approach of NEO (99942) Apophis, which flew past Earth from December 2020 to March 2021.
Apophis is one of several PHAs regularly monitored by the Defense Monitoring Planetary Database. Shortly after it was discovered in 2004, Apophis was determined to have a significant chance of hitting Earth in 2029 or later. But after years of tracking and various close-up approaches, astronomers have refined Apophis’ orbit and concluded that it poses no risk of affecting Earth for a century or more. Apophis was specially selected for this campaign because planetary defense experts knew it would be close to Earth beginning December 4, 2020.
To make the exercise more realistic, the MPC removed Apophis from the planetary defense monitoring database to see if it could again be correctly detected, tracked and characterized by the planetary defense system. Since it was not previously included in the database, astronomers had nothing to reference, making it seem as if astronomers were seeing it for the first time. Other goals included the system’s ability to perform observations, hypothetical risk assessment, risk prediction, and hazard communication.
Finding Apophis (again)
On December 4, the asteroid began to brighten in the night sky, and the NASA-funded Catalina Sky Survey in Arizona was able to detect it and report its position to the MPC. The NASA-funded Asteroid Terrestrial-impact Last at Alert System (ATLAS) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii made subsequent detections. This was followed by observations from NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission, an asteroid-hunting campaign that relies on the Wide-field Infrared Survey Explorer (WISE) space telescope.
The space-based NEOWISE provided infrared observations of Apophis that were not possible with ground-based telescopes because of atmospheric interference — that is, water vapor in our atmosphere absorbs light at these wavelengths. On December 23, the MPC announced the discovery of this “new” asteroid and added it to the list of known PHAs. During Apophis’ next close approach (in March 2021), JPL astronomers used NASA’s Goldstone Solar System Radar (GSSR) in California to take pictures (shown above) and accurately measure the asteroid’s speed and distance from Earth.
NASA engineer Davide Farnocchia, who led the orbital determination calculations for JPL’s Center for Near-Earth Object Studies (CNEOS), explained in a recent NASA press release:
“While we knew that Apophis in reality had no impact on Earth in 2029, from the outset — with just a few days of astrometric data from survey telescopes — there were major uncertainties in the object’s orbit that theoretically allowed for an impact that year. ”
What were the results? † Combined with measurements from other observatories, the exercise not only “discovered” the object, but also managed to constantly reassess its chances of hitting Earth. As Reddy pointed out, they were able to rule out the possibility of an impact in 2029 and a probability of impact for 100 years or more. “This real-world scientific input has stress-tested the entire planetary defense response chain, from initial detection to determining its orbit to measuring the asteroid’s physical features and even determining if, and where, it could hit Earth. hit,” said Reddy.
A second paper describing the results obtained by the NEOWISE mission during the exercise (entitled “NEOWISE Observations of the Potentially Hazardous Asteroid (99942) Apophis”) was also recently published in The Planetary Science Magazine† This study was led by undergraduate researcher Akash Satpathy and principal investigator of NEOWISE, Amy Mainzer, both of the University of Arizona. They were joined by researchers from Caltech, UCLA, the Astronomical Research Institute and NASA’s Jet Propulsion Laboratory. As Satpathy explained:
“The independent infrared data collected from space has benefited greatly from the results of this exercise. NEOWISE was able to confirm the rediscovery of Apophis while quickly collecting valuable information that can be used in planetary defense assessments, such as its size, shape, and even clues about its composition and surface properties.
The NEOWISE measurements also allowed for updated assessments of the asteroid’s size. As they pointed out in the study, Apophis is an elongated object with an “effective spherical diameter” of 270 to 410 meters (~885 to 1345 ft). These improved measurements allowed the research team and the participating scientists at the NASA Ames Research Center to make new estimates of the impact energy this asteroid would provide. In a series of simulations looking at impacts from different geographic locations, the team found that an impact from an Apophis-like object “would likely cause damage at a regional level, not a global one.”
This concerted effort can help disaster agencies plan for future impacts and develop potential mitigation and evacuation strategies. Michael Kelley, a program scientist at PDCO who guided the participants in the exercise, said:
“It was impressive to see the planetary defense community come together during the final close approach to Apophis. Even during a pandemic, when many of the participants in the exercise had to work remotely, we were able to detect, track and learn more about a potential hazard with great efficiency. The exercise was a resounding success.”
Last year, NASA approved the next-generation NEO Surveyor spacecraft — an asteroid-hunting space telescope and direct successor to NEOWISE — for further development. This mission will be launched no earlier than 2026 and will provide updated data that will greatly expand our knowledge of the near-Earth asteroids that populate our solar system (and pose a collision risk with Earth). On September 26, 2022, NASA’s Double Asteroid Redirection Test (DART) mission will collide with the asteroid Didymos and collide with its moon to test an important asteroid defense technique (the kinetic impact method).
As noted, a major impact (and an extinction-level event) is something that humanity would like to avoid. A significant amount of resources are currently being devoted to developing all the means to prevent that. But the best tool we have in our arsenal is regular tracking, which ensures we are prepared for any threats that could ever arise.
This article was originally published on Universe today by Matt Williams. Read the original article here.