The impact from a massive space rock may be a bigger threat to Earth than previously thought, according to astronomers keeping a close eye on giant comets.

An astronomy team from Armagh Observatory and Buckingham University, writing in the journal Astronomy and Geophysics, are closely monitoring hundreds of distant giant comets in the last 20 years, which they said pose a greater risk to life on Earth than asteroids.

The team of astronomers, comprised of Professors Bill Napier, Duncan Steel, and Mark Bailey and Dr. David Asher, explained that these centaurs act on unstable orbits that cross the paths of huge outer planets Jupiter, Saturn, Uranus, and Neptune. Through the gravitational fields of these massive planets, these bodies can occasionally be deflected toward Earth.

Napier said they have been tracking and analyzing any collision risk in the past three decades. Their work suggests the need to look past the immediate planetary neighborhood and beyond Jupiter’s orbit to detect centaurs or giant comets.

“If we are right, then these distant comets could be a serious hazard, and it’s time to understand them better,” he warned in an official release.

But what are centaurs really, and how do they behave?

These heavenly bodies are usually 50 to 100 kilometers (31 to 62 miles) wide or more, with masses larger than the full population of asteroids that have crossed Earth so far.

Based on calculations, a centaur will be deflected onto a path that crosses the living planet’s orbit approximately once every 40,000 to 100,000 years. Near Earth they are expected to turn into large fragment and dust, unleashing a storm of cometary debris and making impacts “inevitable,” as explained by the team.

A centaur is estimated to have arrived about 30,000 years earlier, based on current scientific knowledge and known related disruptions in ancient civilizations.

“This giant comet would have strewn the inner planetary system with debris ranging in size from dust all the way up to lumps several kilometers across,” wrote the researchers, who added that the dinosaurs’ extinction 65 million years ago and other significant mass extinctions are potentially linked to giant comet strikes.

While arguing that no risk was identified as imminent, the team reminded that comet strikes and collisions with Earth were mostly unpredictable.

"A centaur arrival carries the risk of injecting, into the atmosphere... a mass of dust and smoke comparable to that assumed in nuclear winter studies," wrote the researchers, ranking the magnitude of a centaur strike high among natural risks.

NASA is watching about 12,992 near-Earth objects discovered orbiting within the solar system, close to the planet’s own orbit. Around 1,607 of these are asteroids categorized as potentially hazardous.

The latest research has it that several hundreds more of these centaurs should make it to the official list of Earth-threatening space rocks. It remains unknown when exactly a comet will ricochet off the gravity path of one of the giant planets and hurtle toward Earth.

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