In and around our planet there are thousands of comets and asteroids called Earthy objects (NEOs). Several space organizations and government subsidiaries are responsible for tracking them, especially those called Potentially dangerous asteroids (PHA). These objects are so designed because they will cross the Earth’s orbit and may even collide with it one day. Given how effects in the past have caused mass extinctions (such as Chicxulub Impact Event who killed the dinosaurs), future effects are something we would like to avoid!
PHA monitoring is a huge responsibility that requires a worldwide effort, including tracking, warnings and disaster preparedness. Last year, more than 100 participants from 18 countries (including NASA researchers and the NEOWISE mission) conducted an international exercise that simulated an encounter with an asteroid which made a close flight to Earth. As NASA revealed in one recently released study, the exercise was a complete success. The lessons learned can help ward off real effects in the near future or significantly limit the devastation one can cause.
The study, which was published in the May 31 issue of The Planetary Science Journal (entitled “Apophis Planetary Defense Campaign”), Was conducted by the Planetary Defense Exercise Working Group and led by Vishnu Reddy – an associate professor at the University of Arizona’s Lunar and Planetary Laboratory (LPI). The working group consists of more than 100 participants from 18 countries and includes facilities such as NASA’s Planetary Defense Coordination Office (PDCO), den ESA NEO Coordination Centerthe Russian Academy of Sciencesthe Korea Astronomy and Space Science Institute (KASI), and many universities and research institutes around the world.
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Simulates a threat
As Reddy and his colleagues describe in the paper, the planetary defense exercise was the culmination of the work that began in 2017, which was 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 International Asteroid Warning Network (IAWN). The exercise was named “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 many PHAs that are regularly monitored by the Planetary Defense Monitoring Database. Shortly after its discovery in 2004, Apophis was determined to have a significant chance of affecting the earth in 2029 or later. But after years of tracking and several related approaches, astronomers have refined Apophis’ orbit and concluded that it poses no risk of affecting the Earth for a century or more. Apophis was specifically selected for this campaign because planetary defense experts knew it was approaching Earth near the beginning of December 4, 2020.
To make the exercise more realistic, MPC removed Apophis from the planetary defense monitoring database to see if it could be rediscovered, tracked and characterized by the planetary defense system. Without any previous information about it in the database, astronomers had nothing to refer to, which made it appear that astronomers saw it for the first time. Other objectives included the system’s ability to perform observations, hypothetical risk assessment, risk prediction and risk communication.
Find Apophis (again)
On December 4, the asteroid began to shine in the night sky, and NASA-funded Catalina Sky Survey in Arizona was able to detect it and report its position to the MPC. NASA-funded Asteroid Terrestrial Impact Last at Alert System (ATLAS) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii made subsequent discoveries. This was followed by observations from NASA Ground-based objects Wide-field Infrared Survey Explorer (NEOWISE) mission, an asteroid hunting campaign that relies on Wide-field Infrared Survey Explorer (WISE) space telescope.
The space-based NEOWISE produced infrared observations of Apophis that were not possible with ground-based telescopes due to atmospheric interference – ie 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 approach (in March 2021), JPL astronomers used NASA Goldstone Solar System Radar (GSSR) in California to take pictures (shown above) and accurately measure the asteroid’s speed and distance from Earth.
“Even though we knew that Apophis did not actually affect the Earth in 2029, from square one – with only a few days’ astrometry data from survey telescopes – there were major uncertainties in the object’s orbit that theoretically enabled a crash that year.”
In combination with measurements from other observatories, the exercise not only “discovered” the object but constantly managed to re-evaluate its chances of hitting the earth. As Reddy indicated, they could rule out the possibility of an impact in 2029 and any chance of impact for 100 years or more. “This scientific input actually tested the entire planetary defense chain, from initial detection to determining the orbit to measuring the asteroid’s physical properties and even determining if and where it could hit the Earth,” Reddy said.
A second article describing the results obtained by the NEOWISE mission during the exercise (entitled “NEOWISE Observations of the Potentially Dangerous Asteroid (99942) Apophis“) Was also recently published in The Planetary Science Journal. This study was led by a researcher Akash Satpathy and NEOWISE’s principal investigator Amy Mainzer, both from the University of Arizona. They were joined by researchers from Caltech, UCLA Astronomical Research Institute, and NASA’s Jet Propulsion Laboratory. Som Satpathy explained:
The independent infrared data collected from space greatly benefited from the results of this exercise. NEOWISE was able to confirm Apophis’ rediscovery while rapidly gathering valuable information that could be used in planetary defense assessments, such as its size, shape and even clues about its composition and surface properties. “
The NEOWISE measurements also enabled updated estimates of asteroid size. As indicated in the study, Apophis is an elongated object with an “effective spherical diameter” of 270 to 410 meters (~ 885 to 1345 feet). These improved measurements enabled the research team and participating scientists at the NASA Ames Research Center to make new estimates of the impact energy that this asteroid would deliver. In a series of simulations, which looked at effects in different geographical locations, the team found that an impact on an Apophis-like object “would probably cause damage at the regional level and not globally.”
This cooperation can help disaster organizations plan for future consequences and develop possible containment and evacuation strategies. Michael Kelley, a program researcher with PDCO who guided the training participants, sa:
“Seeing the planetary defense community gather during the recent approach of Apophis was impressive. Even during a pandemic, when many of the exercise participants were forced to work remotely, we were able to discover, track and learn more about a potential danger with great efficiency. The exercise was a great success. ”
Last year, NASA approved the next generation NEO Surveyor spacecraft – a space telescope that chases asteroids and NEOWISE’s direct successors – for further development. This mission will start no earlier than 2026 and provide updated data that will significantly expand our knowledge of the asteroids near Earth that populate our solar system (and which pose a risk of collision with Earth). September 26, 2022, NASAs Dual asteroid routing test The (DART) mission will meet with the asteroid Didymos and collide with its moon to test an important asteroid defense technique (the kinetic impact method).
As mentioned, a major impact (and an event of extinction) is something that humanity would like to prevent. A significant amount of resources are currently focused on developing all means to avoid this. But the single best tool we have in our arsenal is the regular tracking, which ensures that we are prepared for any threats that may arise one day.
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