Near- Earth objects are comets and asteroids. Potentially hazardous asteroids are tracked by multiple agencies and government affiliates. These objects are designated because they are likely to collide with each other in the future. Future impacts are something we would like to avoid, considering how impacts have caused mass extinctions.
Tracking, alerts, and disaster readiness are some of the things that need to be done to monitor PHAs. Last year, over 100 participants from 18 countries, including NASA scientists and the NEOWISE mission, conducted an international exercise that mimicked an asteroid flyby to Earth. The exercise was a complete success according to NASA. Lessons learned could help limit the damage that could be done.
The study was conducted by the Planetary Defense Exercise Working Group and was published in the May 31st issue of The Planetary Science Journal. The working group is made up of more than 100 participants from 18 countries and includes facilities like NASA's Planetary Defense Coordination Office.
The planetary defense exercise was the culmination of work that began in the beginning of the year and was intended to test the readiness of our global planetary defense capabilities. The exercise was supported by the Minor Planet Center and the International Asteroid Warning Network. The exercise was called the "Apophis Campaign" because it happened to coincide with the close approach of the NEO.
ManyPHAs are regularly monitored by the planetary defense monitoring database. Apophis was determined to have a chance of impacting Earth in 2029 after it was discovered in 2004. Astronomers have concluded that Apophis does not pose a risk of impacting Earth for a long time. Apophis was chosen because planetary defense experts knew it would approach Earth in December 2020.
In order to make the exercise more realistic, Apophis was removed from the planetary defense-monitoring database. Astronomers had nothing in the database to reference it to, so it seemed like they were seeing it for the first time. The ability of the system to conduct observations was one of the goals.
The Catalina Sky Survey in Arizona was funded by the NASA and was able to detect the asteroid on December 4th. The Last at Alert System and the Panoramic Survey Telescope and Rapid Response System were funded by the NASA. The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission is an asteroid-hunting campaign that relies on the Wide-field Infrared Survey Explorer (WISE) space telescope.
Because of atmospheric interference, the ground-based telescopes were not able to observe Apophis at these wavelength levels. The new asteroid was added to the list of knownPHAs by the end of the year. The NASA Goldstone Solar System Radar was used by the JPL to take pictures and measure the asteroid's distance from Earth.
NASA engineer Davide Farnocchia led the calculations for the Center for Near- Earth Object Studies.
“Even though we knew that, in reality, Apophis was not impacting Earth in 2029, starting from square one – with only a few days of astrometric data from survey telescopes – there were large uncertainties in the object’s orbit that theoretically allowed an impact that year.”
The exercise not only discovered the object but was able to continually assess its chance of hitting Earth. They were able to rule out the possibility of an impact in 2029 and any impact for 100 years or more. This real-world scientific input stress-tested the entire planetary defense response chain, from initial detection to orbit determination to measuring the asteroid's physical characteristics.
The results of the NEOWISE mission were described in a second paper recently published in The Planetary Science Journal. Akash Satpathy is a student researcher at the University of Arizona and Amy Mainzer is the principal investigator of the study. They were joined by researchers from a number of institutions. Satpathy explained what he meant.
“The independent infrared data collected from space greatly benefited the results from this exercise. NEOWISE was able to confirm Apophis’ rediscovery while also rapidly gathering valuable information that could be used in planetary defense assessments, such as its size, shape, and even clues as to its composition and surface properties.”
The updated assessments of the asteroid's size were made possible by the NEOWISE measurement. Apophis has an effective spherical diameter of 270 to 410 meters. The scientists at NASA Ames Research Center were able to place new estimates on the impact energy of this asteroid. The team found that an impact by an Apophis-like object would cause damage at a regional level and not a global one.
Disaster agencies could benefit from this collaborative effort. Michael Kelley is a program scientist with the PDO.
“Seeing the planetary defense community come together during the latest close approach of Apophis was impressive. Even during a pandemic, when many of the exercise participants were forced 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 gave the go-ahead for the next- generation of the next- generation of the next- generation of the next- generation of the next- generation of the next- generation of the next- generation of the next- generation of the next- generation of the next- The mission will launch no earlier than 2026 and provide updated data that will greatly expand our knowledge about the asteroids that populate our Solar System. The DART mission will rendezvous with the asteroid Didymos and collide with its moon to test a key asteroid defense technique.
A major impact and an extinction-level event are things humans would like to avoid. Developing every and all means for avoiding that is the focus of a lot of resources. The most important tool we have in our arsenal is the regular tracking, which makes sure that we are prepared for any threats that may arise in the future.
The Planetary Science Journal contains further reading.
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