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2024 LH1, the second closest close approach
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On Thursday, 6 June 2024, at 09:21 UTC a small asteroid, of 2 to 4 meters, was discovered by the Catalina Sky Survey on top of the Catalina Mountains in the desert of Arizona. A few minutes after the reports of their discovery to the Minor Planet Center, our imminent impact monitoring system (Meerkat) issued an alert. That alert was actually not for an impact, but for a very close approach. Indeed, a few hours later at 14:01 the new object (known under the name of C43AUL1 at the time) flew over the Catalina Sky Survey telescope itself at distance of 1750 km. Such a close fly-by is actually the second closest observed (non-impacting) fly-by from a known asteroid, the closest being 2020 VT4 that flew at a distance of only 373 km from the surface.

A few minutes before the closest approach, our team of observers at the NEOCC observed 2024 LH1 from the Haleakala Observatory located in Hawaii to improve its orbit, but also to obtain valuable physical properties information. The object was moving so fast on the sky that the only way to observe the object was to start a 20 seconds exposure tracking the stars and let the asteroid pass-by in the field of view.

On the image of the trail of the asteroid, one can notice that the asteroid look like blinking. This is not an artefact, and this blinking is due to the rotation of the object. Using a newly developed tool by our team, we were able to extract the lightcurve of 2024 LH1 and determine that it rotates around itself once every 3.68 seconds. This is the third fastest rotation rate for an asteroid ever observed. The fastest being 2024 BX1 whose rotation is 2.5888 seconds and has been obtained using the same technique.

Caption: Observation of 2024 LH1 by one of the Las Cumbres Observatory 0.4m Clamshell telescope located at the Haleakala Observatory on the island of Maui in Hawaii.