Comet from edge of solar system ‘killed the dinosaurs’

WASHINGTON: Sixty-six million years ago, a huge celestial object struck off the coast of what is now Mexico, triggering a catastrophic “impact winter” that eventually wiped out three-quarters of life on Earth, including the dinosaurs.

A pair of astronomers at Harvard say they have now resolved long standing mysteries surrounding the nature and origin of the “Chicxulub impact”.

Their analysis suggests it was a comet that originated in a region of icy debris on the edge of the solar system, that Jupiter was responsible for it crashing into our planet, and that we can expect similar impacts every 250 million to 750 million years.

The duo’s paper, published in the journal Scientific Reports this week, pushes back against an older theory that claims the object was a fragment of an asteroid that came from our solar system’s Main Belt.

“Jupiter is so important because it’s the most massive planet in our solar system,” lead author Amir Siraj said.

Jupiter ends up acting as a kind of “pinball machine” that “kicks these incoming long-period comets into orbits that bring them very close to the Sun”.

So-called “long-period comets” come from the Oort cloud, thought to be a spherical shell surrounding the solar system like a bubble made of icy debris the size of mountains.

The long-period comets take about 200 years to orbit the Sun, and are also called sungrazers because of how close they pass.

Because they come from the deep freeze of the outer solar system, comets are icier than asteroids, and are known for the stunning gas and dust trails they produce as they melt.

But, said Siraj, the evaporative impact of the Sun’s heat on sungrazers is nothing compared to the massive tidal forces they experience when one side faces our star.

“As a result, these comets experience such a large tidal force that the most massive of them would shatter into about a thousand fragments, each of those fragments large enough to produce a Chicxulub size impactor, or dinosaur-killing event on Earth.”

Siraj and his co-author Avi Loeb, a professor of science, developed a statistical model that showed the probability that long-period comets would hit Earth that is consistent with the age of Chicxulub and other known impactors.

The previous theory about the object being an asteroid produces an expected rate of such events that was off by a factor of about ten compared to what has been observed, Loeb said.