A NASA planetary defense exercise simulated a new global threat. Here's what happened

How prepared would the world be if astronomers detected a "potentially hazardous" asteroid as it made its way towards Earth?

More than 100 astronomers around the world participated in an exercise last year designed to simulate such a scenario and test the operational readiness of the world's planetary defense systems.

In this particular case, they used data from a real asteroid's close approach to Earth as a mock encounter with a "new" potentially hazardous asteroid, a press statement reveals.

Stress-testing the Earth's planetary defense

The asteroid used for the exercise, Apophis, was essentially removed from the planetary defense-monitoring database for the purposes of this exercise. Though Apophis came close to Earth on a recent near flyby in December 2020, it ultimately flew safely past our planet without causing any damage.

The participants of the recent exercise pretended they were discovering Apophis for the first time as it approached Earth so they could simulate how they would react in a similar real-world situation. 

The participants showed that they were able to detect Apophis — which is the target of a real-life NASA asteroid sample collection mission called OSIRIS-APEX — using current technologies and then track it until they could determine it would safely fly past Earth.

The exercise was organized by the International Asteroid Warning Network and NASA's Planetary Defense Coordination Office. They published the results of the exercise in a paper in the Planetary Science Journal on Tuesday, May 31.

For a short time after its real, non-simulated discovery in 2004, astronomers thought Apophis had a significant chance of impacting Earth in 2029 or later. However, more precise measurements of its trajectory since that time show that it doesn't pose a significant risk to Earth over the next 100 years.

The organizers of the exercise used data from Apophis' most recent close approach, which occurred between December 2020 and March 2021. "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 and even determining if, and where, it might hit Earth," said Vishnu Reddy, associate professor at the University of Arizona’s Lunar and Planetary Laboratory in Tucson, who led exercise.

'The exercise was a resounding success'

Participants on the project highlighted the role that NASA's space observatory NEOWISE could play in a real-life detection of a potentially hazardous asteroid. NEOWISE orbits far above Earth's atmosphere, letting it make infrared observations that would not be possible on Earth due to moisture in the atmosphere blocking light at these wavelengths.

"The independent infrared data collected from space greatly benefited the results from this exercise," said Akash Satpathy, a UArizona graduate student who also took part in the 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."

Scientists also predicted potential impact locations during the exercise and were able to simulate the impact energy of Apophis were it to hit Earth. Such data could be used to help disaster response operations in a real-world scenario.

All in all, the participants "were able to detect, track and learn more about a potential hazard with great efficiency. The exercise was a resounding success," said Michael Kelley, a program scientist with the Planetary Defense Coordination Office in NASA's Planetary Science Division.

Last year, NASA and ESA astronomers teamed up for a similar exercise that simulated an asteroid impact scenario with Earth. They found that with current technologies, we would be defenseless in the face of a certain impact scenario with Earth detected six months in advance.

Still, planetary defense technology is evolving at a fast pace, and missions such as NASA's DART aims to show that we can alter the trajectory of an asteroid on a collision course with our planet. NEOWISE's successor, the NEO Surveyor, is also scheduled to launch around the year 2026, significantly improving the capacity of astronomers to detect potentially hazardous near-Earth asteroids.