Planetary Defense Exercise Finds Apophis… Again

In a test of asteroid detection capabilities, several observatories and spacecraft participate in the “discovery” of asteroid Apophis.

Beth Johnson

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IMAGE: Clockwise from top left are three of the observatories that participated in a 2021 planetary defense exercise: NASA’s Goldstone planetary radar, the Mount Lemmon telescope of the Catalina Sky Survey, and NASA’s NEOWISE mission. At bottom left is an illustration of the path of Apophis’ close approach in 2029. CREDIT: NASA/JPL-Caltech/University of Arizona

It’s been a moment since we brought you news of a hazardous asteroid because, well, there aren’t any hazardous asteroids at the moment. Don’t let sensational clickbait headlines convince you otherwise. What we do have, however, is a neat story of how the global planetary defense community discovered asteroid Apophis… again.

Back in December 2020, the near-Earth asteroid Apophis began a close-ish approach to Earth, and as a test of our asteroid detection capabilities, this approach was used as an exercise. First, the Minor Planet Center basically wiped out the data from their surveys of all preexisting Apophis observations. This meant that other surveys couldn’t connect any new observations with those existing ones. For all intents and purposes, Apophis hadn’t been discovered, yet.

Now it was up to the various ground-based telescopes and surveys to do their jobs. And they succeeded beautifully. On December 4, 2020, the Catalina Sky Survey got the first detection, which turned up in their survey to be something new, of course. Then ATLAS and Pan-STARRS detected the “new” object. Next up, NASA’s NEOWISE captured observations from space, which were linked to all the ground-based observations and allowed scientists to see the object’s motion through the sky.

On December 23, the Minor Planet Center logged the object into the system as the confirmed discovery of a “new” near-Earth asteroid. And that was when all the calculations began. Scientists have detailed those results in a new paper in The Planetary Science Journal with lead author Vishnu Reddy, who notes: 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.

The final piece of the puzzle for this test came when the Goldstone telescope took radar observations during March 2021 — the closest approach of Apophis — of the “new” object that allowed for precise measurements of the…

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Beth Johnson

Planetary scientist, podcast host. Communication specialist for SETI Institute and Planetary Science Institute. Buy me a coffee: https://ko-fi.com/planetarypan