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    New theory behind Chicxulub impactor that killed the dinosaurs – Harvard Gazette

    New theory explains origin of comet that killed the dinosaurs.

    By Juan Siliezar Harvard Staff Writer

    Date

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    It was tens of miles wide and forever changed history when it crashed into Earth about 66 million years ago.

    The Chicxulub impactor, as it’s known, was a plummeting asteroid or comet that left behind a crater off the coast of Mexico that spans 93 miles and goes 12 miles deep. Its devastating impact brought the reign of the dinosaurs to an abrupt and calamitous end, scientists say, by triggering their sudden mass extinction, along with the end of almost three-quarters of the plant and animal species then living on Earth.

    The enduring puzzle has always been where the asteroid or comet originated, and how it came to strike the Earth. And now a pair of Harvard researchers believe they have the answer.

    In a study published in Scientific Reports, Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard, and Amir Siraj ’21, an astrophysics concentrator, put forth a new theory that could explain the origin and journey of this catastrophic object and others like it.

    Using statistical analysis and gravitational simulations, Loeb and Siraj say that a significant fraction of a type of comet originating from the Oort cloud, a sphere of debris at the edge of the solar system, was bumped off-course by Jupiter’s gravitational field during its orbit and sent close to the sun, whose tidal force broke apart pieces of the rock. That increases the rate of comets like Chicxulub (pronounced Chicks-uh-lub) because these fragments cross the Earth’s orbit and hit the planet once every 250 to 730 million years or so.

    “Basically, Jupiter acts as a kind of pinball machine,” said Siraj, who is also co-president of Harvard Students for the Exploration and Development of Space and is pursuing a master’s degree at the New England Conservatory of Music. “Jupiter kicks these incoming long-period comets into orbits that bring them very close to the sun.”

    It’s because of this that long-period comets, which take more than 200 years to orbit the sun, are called sun grazers, he said.

    “When you have these sun grazers, it’s not so much the melting that goes on, which is a pretty small fraction relative to the total mass, but the comet is so close to the sun that the part that’s closer to the sun feels a stronger gravitational pull than the part that is farther from the sun, causing a tidal force” he said. “You get what’s called a tidal disruption event and so these large comets that come really close to the sun break up into smaller comets. And basically, on their way out, there’s a statistical chance that these smaller comets hit the Earth.”

    The calculations from Loeb and Siraj’s theory increase the chances of long-period comets impacting Earth by a factor of about 10, and show that about 20 percent of long-period comets become sun grazers. That finding falls in line with research from other astronomers.

    The pair claim that their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

    Avi Loeb.

    “Our paper provides a basis for explaining the occurrence of this event,” Loeb said. “We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs.”

    Loeb and Siraj’s hypothesis might also explain the makeup of many of these impactors.

    “Our hypothesis predicts that other Chicxulub-size craters on Earth are more likely to correspond to an impactor with a primitive (carbonaceous chondrite) composition than expected from the conventional main-belt asteroids,” the researchers wrote in the paper.

    This is important because a popular theory on the origin of Chicxulub claims the impactor is a fragment of a much larger asteroid that came from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. Only about a tenth of all main-belt asteroids have a composition of carbonaceous chondrite, while it’s assumed most long-period comets have it. Evidence found at the Chicxulub crater and other similar craters that suggests they had carbonaceous chondrite.

    This includes an object that hit about 2 billion years ago and left the Vredefort crater in South Africa, which is the largest confirmed crater in Earth’s history, and the impactor that left the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years.

    The researchers say that composition evidence supports their model and that the years the objects hit support both their calculations on impact rates of Chicxulub-sized tidally disrupted comets and for smaller ones like the impactor that made the Zhamanshin crater. If produced the same way, they say those would strike Earth once every 250,000 to 730,000 years.

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    Aside from composition of comets, the new Vera Rubin Observatory in Chile may be able to see the tidal disruption of long-period comets after it becomes operational next year.

    “We should see smaller fragments coming to Earth more frequently from the Oort cloud,” Loeb said. “I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments.”

    Loeb said understanding this is not just crucial to solving a mystery of Earth’s history but could prove pivotal if such an event were to threaten the planet again.

    “It must have been an amazing sight, but we don’t want to see that side,” he said.

    This work was partially supported by the Harvard Origins of Life Initiative and the Breakthrough Prize Foundation.

    New theory behind Chicxulub impactor that killed the dinosaurs – Harvard Gazette

    Source : news.harvard.edu

    What was the approximate mass of the asteroid that killed the dinosaurs?

    Answer (1 of 29): You must be talking about the Chicxulub crater. It is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. It was formed by a large asteroid or comet about 11 to 81 kilometres (6.8 ...

    SEE: The Impact That Wiped Out the Dinosaurs

    Chicxulub crater - Wikipedia

    “The Chicxulub crater (/ˈtʃiːkʃʊluːb/;

    Mayan:

    [tʃʼikʃuluɓ]) is an impact crater buried underneath the Yucatán Peninsula in Mexico.[3]

    Its center is located near the town of Chicxulub, after which the crater is named. [4]

    It was formed by a large asteroid or comet about 10 to 15 kilometres (6.2 to 9.3 miles) in diameter, [5][6]

    the Chicxulub impactor, striking the Earth. The date of the impact coincides precisely with the Cretaceous–Paleogene boundary (K–Pg boundary), slightly less than 66 million years ago,[2]

    and a widely accepted theory is that worldwide climate disruption from the event was the cause of the Cretaceous–Paleogene extinction event, a mass extinction in which 75% of plant and animal species on Earth became extinct, including all non-avian dinosaurs.

    The crater is estimated to be 150 kilometers (93 miles) in diameter [3] and 20 km (12 mi) in depth, well into the continental crust of the region of about 10–30 km (6.2–18.6 mi) depth. It is the second largest confirmed impact structure on Earth and the only one whose peak ring is intact and directly accessible for scientific research

    What was the approximate mass of the asteroid that killed the dinosaurs?

    Source : www.quora.com

    Asteroid Dust Found in Crater Closes Case of Dinosaur Extinction

    News, stories, and opinions on science, technology, health, education, business, policy, campus life, and more from The University of Texas at Austin.

    AUSTIN, Texas — Researchers believe they have closed the case of what killed the dinosaurs, definitively linking their extinction with an asteroid that slammed into Earth 66 million years ago by finding a key piece of evidence: asteroid dust inside the impact crater.

    Death by asteroid rather than by a series of volcanic eruptions or some other global calamity has been the leading hypothesis since the 1980s, when scientists found asteroid dust in the geologic layer that marks the extinction of the dinosaurs. This discovery painted an apocalyptic picture of dust from the vaporized asteroid and rocks from impact circling the planet, blocking out the sun and bringing about mass death through a dark, sustained global winter – all before drifting back to Earth to form the layer enriched in asteroid material that’s visible today.

    In the 1990s, the connection was strengthened with the discovery of a 125-mile-wide Chicxulub impact crater beneath the Gulf of Mexico that is the same age as the rock layer. The new study seals the deal, researchers said, by finding asteroid dust with a matching chemical fingerprint within that crater at the precise geological location that marks the time of the extinction.

    “The circle is now finally complete,” said Steven Goderis, a geochemistry professor at the Vrije Universiteit Brussel, who led the study published in Science Advances on Feb. 24.

    The study is the latest to come from a 2016 International Ocean Discovery Program mission co-led by The University of Texas at Austin that collected nearly 3,000 feet of rock core from the crater buried under the seafloor. Research from this mission has helped fill in gaps about the impact, the aftermath and the recovery of life.

    The telltale sign of asteroid dust is the element iridium – which is rare in the Earth’s crust, but present at elevated levels in certain types of asteroids. An iridium spike in the geologic layer found all over the world is how the asteroid hypothesis was born. In the new study, researchers found a similar spike in a section of rock pulled from the crater. In the crater, the sediment layer deposited in the days to years after the strike is so thick that scientists were able to precisely date the dust to a mere two decades after impact.

    “We are now at the level of coincidence that geologically doesn’t happen without causation,” said co-author Sean Gulick, a research professor at the UT Jackson School of Geosciences who co-led the 2016 expedition with Joanna Morgan of Imperial College London. “It puts to bed any doubts that the iridium anomaly [in the geologic layer] is not related to the Chicxulub crater.”

    The dust is all that remains of the 7-mile-wide asteroid that slammed into the planet millions of years ago, triggering the extinction of 75% of life on Earth, including all nonavian dinosaurs.

    Researchers estimate that the dust kicked up by the impact circulated in the atmosphere for no more than a couple of decades – which, Gulick points out, helps time how long extinction took.

    “If you’re actually going to put a clock on extinction 66 million years ago, you could easily make an argument that it all happened within a couple of decades, which is basically how long it takes for everything to starve to death,” he said.

    The highest concentrations of iridium were found within a 5-centimeter section of the rock core retrieved from the top of the crater’s peak ring – a high-elevation point in the crater that formed when rocks rebounded then collapsed from the force of impact.

    The iridium analysis was carried out by labs in Austria, Belgium, Japan and the United States.

    “We combined the results from four independent laboratories around the world to make sure we got this right,” said Goderis.

    In addition to iridium, the crater section showed elevated levels of other elements associated with asteroid material. The concentration and composition of these “asteroid elements” resembled measurements taken from the geologic layer at 52 sites around the world.

    The core section and geologic layer also have earthbound elements in common, including sulfurous compounds. A 2019 study found that sulfur-bearing rocks are missing from much of the rest of the core despite being present in large volumes in the surrounding limestone. This indicates that the impact blew the original sulfur into the atmosphere, where it may have made a bad situation worse by exacerbating global cooling and seeding acid rain.

    Gulick and colleagues at the University of Texas Institute for Geophysics and Bureau of Economic Geology – both units of the UT Jackson School – plan to return to the crater this summer to begin surveying sites at its center, where they hope to plan a future drilling effort to recover more asteroid material.

    Asteroid Dust Found in Crater Closes Case of Dinosaur Extinction

    Source : news.utexas.edu

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