Science

A fireball accelerating to 51,500 km / h spotted in the American sky

The object was spotted over North Carolina last Friday night (around 7:40 pm local time). At least 5 of those meteors were reported that night, according to NASA. It passed along the coast, becoming visible about 77 kilometers above the ocean, in front of the Camp Lejeune military base. It traveled nearly 26 miles before disintegrating over Morehead City.

This burning meteor followed a trajectory towards the northeast, at a speed of approximately 51,500 km / h. More than 80 people reported observing this impressive fireball on September 24. Fireballs are in fact meteors that appear brighter than the planet Venus, according to the American Meteor Society (AMS), so they generally don’t go unnoticed! In theory, they are even visible in broad daylight.

These events are not particularly rare. At the end of April, it is a bolide-type meteor that was probably observed in southeastern France. From Nice to Marseille and even Lyon, several people reported seeing an orange-red fireball, accompanied by a blue-green trail. More recently, on the night of September 5 or 6, it was in Brittany that we saw a dazzling light, followed by a detonation, due to the speed of the meteor as it entered the atmosphere.

Several thousand fireballs every day

A fireball designates a very bright meteor, of magnitude at least equal to or less than -4 (which corresponds to the magnitude of the planet Venus in the morning or evening sky). We speak of “fireball” when this fireball explodes in a final flash of light and fragments. Several thousand fireball magnitude meteors enter Earth’s atmosphere every day, according to AMS. However, most of them are obscured by daylight and occur over oceans or uninhabited areas.

These burning space rocks owe their brilliance to their large sizes and ultra-fast speeds (from 40,000 km / h to almost 260,000 km / h), which create a significant amount of friction when they enter Earth’s atmosphere. Their speed, which far exceeds the sound barrier, means that they are sometimes accompanied by a huge supersonic “bang.” Its apparent color can vary according to the elements that make up the rock – and which show different colors when they vaporize – but also according to speed; a higher kinetic energy level will intensify some colors compared to others.

With a speed of 51,500 km / h, the meteor seen last week off the east coast of the United States is not among the fastest. For comparison, the Draconid meteor swarm, which will light up the northern sky between October 7 and 11, is shooting at nearly 70,000 km / h. As for the Leonids in November, they can exceed 250,000 km / h!

The event is no less spectacular for lovers of celestial objects; The following video, which was captured by a home surveillance camera in Rowland Pond, North Carolina, shows the alien rock leaving a dazzling trail in the night sky before disappearing behind a distant tree blanket:

Sometimes devastating explosions

When they do not go completely unnoticed, most of these events offer nothing less than a magnificent spectacle. But it can happen that the energy released by larger cars causes serious damage. The Chelyabinsk meteor, which appeared in the Russian sky on February 15, 2013, south of the Urals, is one of the most explosive events on record recently.

The blast, roughly equivalent to 400 to 500 kilotons of TNT, or 26 to 33 times the energy released by the Hiroshima bomb, caused tremendous damage. This superbolic of almost twelve thousand tons fragmented in the atmosphere, between 20 and 40 km of altitude. The associated shock wave, along with the multiple fragments produced, struck Chelyabinsk and its surroundings, damaging buildings, smashing windows and injuring more than 1,000 people.

Also, in June 1908, a fireball exploded over the Toungouska Pierreuse River, in a sparsely populated region of the central Siberian plateau. The shock wave completely destroyed the forest within a radius of more than 20 km and caused damage over a hundred kilometers. As no impact has been observed at the site, the most plausible hypothesis is the disintegration of a meteoroid at an altitude of between 5 and 10 kilometers. A 2019 article suggests that the explosive power of the event could be between 20 and 30 megatons.

But these meteoric events are not a priori the most apocalyptic Earth has ever known: recent archaeological evidence suggests that a giant space rock exploded over the ancient city of Tall el-Hammam, some 3,600 years ago. This explosion with a power 1000 times greater than the Hiroshima bomb would have raised the air temperature to more than 2000 ° C, causing the instantaneous combustion of the entire city and all life.

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