Asteroid that turned into a meteor found in archival footage for the first time

Asteroid that turned into a meteor found in archival footage for the first time

Two years ago, US government sensors detected an exceptionally bright light over the western Pacific. Fortunately, it came from the passage of a large meteorite through the atmosphere, rather than a potential military threat, but it was so powerful that astronomers thought it deserved further investigation. By trawling through archival images, a team from the University of Western Ontario found what appears to be the asteroid’s trajectory 10 minutes before it hit Earth’s atmosphere.

Meteorites are exceptionally important sources of information about the formation of the Solar System. Those belonging to rarer categories are particularly valuable to astronomers. Recently, the increasing availability of video cameras has made it possible, on occasion, to track the path of the incoming object through the atmosphere. From this, it is sometimes possible to calculate the orbit of the object before it fell, establishing the sources of different types of meteorites.

After the detection known as CNEOS 20200918, astronomers searched for something better, thinking that anything that made such a bright flash should have been detectable in astrophotos. In an article submitted to the Planetary Science Journal, they report that their suspicion was correct, aided by additional detections from the ATLAS Haleakalā telescope in Hawaii and the Geostationary Lightning Mapper, a satellite-borne infrared detector.

Prior to its encounter with Earth’s atmosphere, asteroid CNEOS 20200918 was around 3 meters (10 feet) wide and weighed an estimated 23 tons by the authors, although they acknowledge this is based on some assumptions about its density. Ten minutes before it hit the atmosphere, when the image was taken, it was 11,900 kilometers (7,500 miles) from Earth, which, believe it or not, is pretty slow for a space rock. Its orbit was slightly larger than Earth’s but more elongated, so it crossed our path twice a year. The variation in its brightness indicates that it was spinning with unusual, but not exceptional, speed.

It is not the first time that an object has been photographed both in space and burning in the atmosphere. However, all five of the previous cases involved calculating an asteroid’s orbit before impact, for which we were on the lookout, most recently in the case of the object that hit the coast of Iceland in March. That particular event achieved internet fame when it was described in the highly memorable “half-giraffe” measure.

The authors, led by Dr. David Clark, have made similar efforts to find the asteroids responsible for the fireballs (very bright meteorites) in archival photographs, but so far without success.

Because the meteorite sank in the western Pacific, the chances of recovering any pieces are slim. The precision with which the orbit has been calculated increases the scientific value of comparing it with the composition of any fragment. However, it is unlikely to be considered so valuable that there will be moves to retrieve it from the ocean floor, as is happening with a 2014 meteorite thought to have come from outside the Solar System. It takes a really special space rock to justify that kind of effort.

On the other hand, the authors hope that if we can repeat this success with future bright meteors, we will one day do so with one that lands in a more accessible location.

A preprint of the document is available at ArXiv.org.

[H/T: New Scientist]

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