Planetary Defense Exercise Finds Apophis… Again

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

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…