An asteroid passed “close” to Earth and no one knew it would arrive

An asteroid passed “close” to the Earth and no one knew it would arrive

03 November 2021 10

Last week – on 24 October – a refrigerator-sized asteroid passed close to Earth , but astronomers discovered its existence only a few hours the event . The celestial body has reached its closest point, corresponding to Antarctica, at 3. 000 kilometers from Earth . It is a shorter distance than that of some satellites, and the third asteroid of which we know arrives so close to the planet without hitting it.

One of the most relevant aspects of the story is not so much the narrow escape – probably the celestial body, with a diameter of only 2 meters, would have disintegrated entering the earth’s atmosphere – as much as the fact that the object was not seen until after having traveled its trajectory closest to the Earth. The asteroid, named 2021 UA1 , went unnoticed because it approached the diurnal side of the Earth coming from the direction of the Sun; conditions which, together with the small size of the object, made sighting difficult, which took place only four hours after the passage.

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The asteroid 2021 UA1 is in effect a NEO (Near-Earth Objects) , i.e. a celestial body (category that includes comets and asteroids) that passes through a distance not exceeding 1.3 astronomical units (194, 5 millions of kilometers) from Earth. NASA uses ground and space telescopes to identify and monitor NEOs with the aim of defining their shape and composition, and identifying those potentially dangerous in case of impact with the planet. According to the parameters set by NASA, to be considered dangerous a NEO must have a diameter of not less than 140 meters. For this reason 2021 UA1 was anything but a threat, but its passage offers further food for thought on the techniques used for the identification and monitoring of these space objects.

To pass even closer to Earth (2. 950 kilometers) had been the asteroid 2020 HQ in August last year, but the record belongs to the asteroid VT4 which came close to ” suns ” 400 kilometers from the planet in November 2020, it is roughly the same altitude as the international space station. To improve detection and defense tools against NEOs, NASA has several projects in the pipeline including the NEO Surveyor infrared telescope, and the DART project which will go live on 23 next November.


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