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An even closer unexpected approach
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Animation of the Earth close approach trajectory of asteroid 2020 JJ as seen from the Ecliptic North Pole. Each new animation frame represents a time variation of one hour in the real trajectory. Credit: ESA / NEOCC

Less than a week after the discovery of 2020 HS7 by University of Hawaii’s Pan-STARRS survey, on 4 May 2020 another telescope funded by NASA’s Planetary Defense Program, University of Arizona’s Catalina Sky Survey, discovered a new object that was already very close to Earth, and possibly in an impacting trajectory.

The events that unfolded over just a few hours showed how quickly the NEO community can react to a possible impactor, and gather the observations needed to accurately determine the trajectory of an incoming object.

The new asteroid, temporarily designated C2QQFV2 by the Catalina team, was detected in a set of four observations exposed by the Mt. Lemmon telescope between 05:53 and 06:16 UTC. Once the object was detected by their pipeline, and confirmed real by their observers, it was quickly reported to the MPC, which published the discovery observations at 06:38 UTC.

Within a few minutes, the various services monitoring the MPC's NEO Confirmation Page detected the new object, and run an analysis from which it became evident that the object was already very close, and had a ~5% chance of being on a collision course, for an impact happening less than 6 hours later.

These automatic alerts triggered various observers, including Catalina itself and the University of Hawaii’s ATLAS survey, to gather additional follow-up observations of the new object. At 07:12 UTC, less than an hour after the original discovery was achieved, the first follow-up observations started coming in, and within two hours, three other telescopes had collected additional observations from other locations.

With this new dataset, it immediately became evident that we had another near miss: the object would fly-by at about 12:03 UTC, at just 13 400 km from the Earth's centre.

The object, calculated to be between 3 and 6 metres in diameter, is now designated 2020 JJ, and it is already quickly receding from Earth. Had it been in a collision course, it would not have caused a significant threat, given its small size.

What is even more impressive is that the final dataset, collected over just two hours, is sufficient to determine the fly-by circumstances to a precision of about 10 seconds in time, and 5 kilometres in distance. Had the object been in a collision course, we would have been able to predict the point of entrance into the Earth's atmosphere with a comparable precision, showing how effective immediate optical follow-up can be at localising a possible imminent impact threat.