Scientists have managed to successfully test out their asteroid warning effort in a planetary defense exercise meant to simulate recovering, tracking and characterizing an asteroid as a potential impactor.
The exercise, which was carried out in 2020-2021 and the results of which were published Tuesday in a study in the peer-reviewed academic periodical the Planetary Science Journal, used a real asteroid, 99942 Apophis, in order to simulate an encounter with a new, actual potentially hazardous asteroid to see how we would react and deal with it.
Planetary defense
Asteroid impacts are some of the most devastating possible natural disasters due to the sheer unrivaled levels of destruction they can bring.
While in theory, there are ways to prevent the impact of a Near-Earth Object (NEO), this still heavily relies on sufficient time and advanced warning.
It is for that organizations such as NASA's Planetary Defense Coordination Office (PDCO) and the International Asteroid Warning Network (IAWN) were established in order to detect, track and characterize NEOs.
This was especially important following an asteroid impact event in 2013 when a small 20 meter asteroid impacted above Chelyabinsk in Russia.
While the impact itself wasn't severe, the shockwave caused thousands of windows to shatter and saw many injured and in need of medical attention due to the shattered glass.
In 2017, a group of scientists from the PDCO and IAWN observed a Near-Earth Asteroid (NEA) designated 2012 TC4. Then in 2019, another exercise was held, this time watching the asteroid 66391 Moshup.
But this time, the exercise chose to focus on 99942 Apophis.
Apophis
The asteroid designated Apophis is very infamous.
It was first discovered on June 19, 2004 by astronomers at Arizona's Kitt Peak National Observatory. Original estimates had thought the asteroid was 450 meters in diameter. For comparison, that would make it taller than the 381-meter Empire State Building and 324-meter Eiffel Tower, and would make it around half the size of the 828-meter Burj Khalifa, the tallest manmade structure in the world.
Later estimates put it at much shorter, with scientists ultimately estimating it around 370 meters.
In terms of classification, Apophis was classified as an Aten-class asteroid, meaning its orbit crosses over with Earth's orbit around the Sun, but it spends most of its time inside it. However, it will not stay that way, and is set to be reclassified as an Apollo-class asteroid after the anticipated close flyby due to its orbit now becoming wider.
Understandably, there was a time when many people worried that it could actually hit the planet. Specifically, it was worried that it had a chance of striking the Earth in 2029 or in 2036 because it was thought it could possibly fly through a gravitational keyhole that could alter its orbit.
However, this was later found to not be an issue as further observations and calculations gave scientists a better idea of its orbit. This discovery is actually what made NASA declare that Earth was free of risk of a catastrophic asteroid impact for the next century – and make no mistake, an impact event from Apophis would have been absolutely devastating for the planet.
So why did the exercise choose Apophis?
Simply put, it was the last chance to study it before the 2029 flyby – something astronomers already know will be an incredibly close pass.
So the goal of the study was as follows: Recover, track and characterize Apophis in order to test the planetary defense system's ability to observe, carry out hypothetical risk assessment and prediction and communication.
However, the fact that the asteroid in question was Apophis was kept a secret. The Minor Planet Center (MPC), which is recognized for its position measurements of smaller cosmic bodies, prevented new observations of Apophis that were part of the exercise from being linked with previous ones in its database. That way, there were no astronomical surveys that inked it to Apophis.
This "new" asteroid was fist spotted by the NASA-backed Catalina Sky Survey on December 4, 2020 which noted its position in the sky to the MPC. After that, other systems began picking it up, such as the NASA-backed Asteroid Terrestrial-impact Last Alert System (ATLAS) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS).
Later, it was spotted by NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission orbiting the Earth and its observations were linked to the others via the MPC.
By December 23, the "new" asteroid's discovery was announced by the MPC and scientists began gathering more data and measurements in order to calculate the orbit and determine if it would hit the planet.
Other observatories were involved as well, including the Northolt Branch Observatories in England, the Tien-Shan Astronomical Observatory in Kazakhstan and the Wise Observatory in Israel.
"The shared and coordinated efforts of astronomers around the world taught us what observational and computational efforts still need to be further developed, where are our bottlenecks in terms of data collection and how to improve our collaboration," explained Dr. David Polishook of Israel's Weizmann Institute of Science. "In future drills, we will use fainter and smaller targets to see how much we can stretch out our current astronomical technology."
And the new efforts at essentially rediscovering Apophis had other benefits, too.
In March 2021, as Apophis made flew past the planet, astronomers from NASA's Jet Propulsion Laboratory (JPL) used the Goldstone Solar System Radar to better image and measure its distance and velocity to fully refine our understanding of the orbit – ruling out a 2029 impact.
Further, by using a detailed NEOWISE examination with infrared that wouldn't be possible through ground observations, more data was gathered about Apophis's size, shape and possibly even composition – something that could help us understand just how powerful of an impact this asteroid would bring. This information was published in a separate study published in the same journal.
Asteroid defense
Asteroids make up one of the most numerous types of objects in the solar system. Currently, over 1,113,000 asteroids are known to exist in the solar system, according to NASA, but those are just the ones definitively identified, with experts always finding more.
Currently, there are a few proposed methods scientists are considering to try and prevent an asteroid impact.
Currently, the most notable mission is NASA's Double Asteroid Redirection Test (DART) mission, which will test the possibility of asteroid deflection.
"Come September, we will move forward with a physical experiment to deflect an asteroid by a kinetic impact," explained Polishook, who is part of the DART mission and will be monitoring the impact from Israel.
"That will be the first test for our planetary defense techniques."
Time will tell if this can succeed.