Science

The sixth asteroid impact we saw coming

Space security

24/11/2022
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In brief

On Nov. 19, asteroid 2022 WJ1 became one of several small asteroids to impact Earth, but only the sixth we ever saw coming. For the second time this year, humanity predicted an asteroid impact. The approximately 3-foot-tall rock caused no damage and burned like a conspicuous ball of fire in the sky over Toronto. The detection, warning and previous sightings of this asteroid illustrate our rapidly increasing ability to warn of asteroid impacts, however small.

In depth

Sixth Sense

Time-lapse photo of WY1 2022 taken by astronomer Robert Weryk in Ontario, Canada

The first discovery of asteroid 2022 WJ1 came from the Catalina Sky Survey – one of the major projects dedicated to the discovery and follow-up of near-Earth objects (NEOs) – at 04:53 UTC (05:53 CET) on November 19 2022, just under four hours before impact.

The new asteroid was first imaged by Catalina’s 1.5 m Mt. Lemmon telescope and after four observations were made, it was reported to the Minor Planet Center (MPC) 38 minutes after the first detection at 05:31 UTC.

These four observations were enough to chart the asteroid’s path in the sky, and within minutes of this “astrometry” being published, ESA’s own internal monitoring software reported that the object had a ~20% chance of hitting the hit Earth and possibly hit somewhere. in North America in the next two to three hours. A few minutes later, other impact monitoring programs also sent out alerts with a similar scenario.

The first impact corridor calculated by ESA’s Meerkat tool at 05:36 UTC, based on early observations of asteroid 2022 WJ1

Following the possible impact reports, observers in Catalina and elsewhere in the US got follow-up sightings of the new asteroid. Less than 30 minutes after the first trigger, the impact was confirmed with excellent precision: the small asteroid, probably less than a meter in diameter, was supposed to hit somewhere between Lake Erie and Lake Ontario, near the US-Canada border, around 08.00. :27 UTC (09:27 CET).

Exactly at the predicted time, a ~1 m asteroid hit the atmosphere and became a brilliant fireball over the expected location. Read more about this event on ESA’s Near-Earth Object Coordination Center (NEOCC) web portal.

Asteroid impact: what’s the risk?

Due to the way the solar system was formed, small objects are in the majority in terms of their total population. It is estimated that there are 40-50 million small asteroids and ‘only’ 1,000 of the largest, giant ‘planet-killers’. The rest fall somewhere in between.

Infographic: Asteroid Hazard Explained

We currently know of more than 1.1 million asteroids, although there are many more. Of those discovered, about 30,600 travel in orbits that bring them close to Earth’s. These are the ‘near-earth asteroids’ (NEAs).

The reassuring news is that almost all giant asteroids have been found – over 95% – and none are of concern for the next hundred years. Astronomers tirelessly search for every last one.

Chelyabinsk asteroid track

Every few weeks, small, meter-sized asteroids hit Earth. They contribute to our understanding of asteroid populations, of fireballs and their composition, but they are not a major priority when it comes to planetary defense because they pose no real threat.

The objects we’re most concerned about are those “goldilocks asteroids” that are big enough to do damage if they hit, and there are plenty that we know will at some point. The infamous Chelyabinsk impact in February 2013 and the Tunguska impact in June 1908 fall into this category, and when it comes to discovering these asteroids, there is still a lot of work to be done.

Hera at Didymos

Therefore, ESA’s Planetary Defense Office is planning new ground-based telescopes and missions in space to improve our asteroid-detection capabilities, by sending the Hera mission to the Dimorphos asteroid hit by NASA’s DART mission to measure the deflection of asteroids. testing, and by working with the international community to prepare for the scenario where a larger asteroid is discovered on a collision course.

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