This is a question of great scientific and titillating public interest. We know that 66 million years ago an asteroid 10 kilometers in size slammed into the Earth just off the coast of what is now the Yucatan Peninsula in the Gulf of Mexico, carving out the 180-kilometer-wide Chicxulub crater and setting off a complicated chain of events that killed off something like 75% of all species on the planet including all the non-avian dinosaurs, so yeah, understanding it seems important.
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For a while it was thought it could be a comet, but samples of the impactor retrieved from various sites around the world dated to the time of the impact strongly suggest it was a kind of asteroid called a carbonaceous chondrite. A chondritic asteroid is one that is primitive, formed when the solar system was very young, and is composed of small grains of material that haven’t undergone any real change since. Chondrites make up the vast majority of meteorites that fall to Earth, more than 80%. On the other hand, carbonaceous ones, which are high in carbon content and therefore dark, are pretty rare, making up just 3-5% of meteorites that fall to Earth.
So the impactor comes from a rare population of asteroid. Here’s where things get a little strange: When you look at the biggest craters on Earth, presumably from the biggest asteroids, something like half look to be produced by carbonaceous chondrites. So while they’re rare overall, the big ones seem to like hitting Earth.
Also, it’s known that these kinds of big dark asteroids tend to orbit in the outer part of the asteroid belt, farther from the Sun. Yet theoretical studies have shown that we should expect very few impactors from that part of the belt.
So we have contradictory ideas here. Where are these big dark rocks coming from? And how often do they hit us?
What they wanted to find out was how main belt asteroids get knocked into orbits that get them near Earth (too near, if you know what I mean). In general this is due to the gravity of Jupiter, which has a strong effect, but is limited to certain regions of the belt — what are called resonances, where the asteroid’s orbital period is a simple ratio of Jupiter’s. In this case, the asteroid orbits the Sun, say, three times for every once Jupiter does, or 8 to 3, or 5 to 2. When that happens the rock gets a periodic kick in orbital energy from the giant planet, and that can, over time, send it plummeting down toward the Sun … and Earth.
Another force is called the YORP effect, and is due to sunlight subtly influencing the asteroid’s orbit. This has been modeled many times, but in general the models have concentrated on the parts of the belt where the resonance effects are strongest.
What’s new here is the team looked at the entire asteroid belt as a potential source of big, dark, threatening rocks. They also looked preferentially at big rocks, ones with a diameter 5 kilometers or larger, and that also orbit the Sun farther out than 375 million kilometers on average; using real data from the WISE observatory (an infrared satellite that observed asteroids) that means 42,721 objects.
What they found is surprising. About half of the main belt big rocks that get moved into near-Earth orbits come from the middle to outer parts of the asteroid belt! This is 10 times higher than previous estimates, which said asteroids from this part of the belt were rare. But this jibes with the result that something like half the big rocks that hit us are carbonaceous chondrites, since those come from the outer belt. If true, this resolves that tension. They find that the chances of the dinosaur killer coming from the middle to outer main belt are 60%.
They also found that one asteroid 5 kilometers wide or larger escapes from the main belt into a near-Earth trajectory roughly every 100,000 years. Those tend to break up or fall into the Sun after about a hundred million years or less, but some impact the inner planets. According to their simulations, we can expect roughly 25 impacts from asteroids bigger than 5 km in size every billion years, or about one every 40 million years. A dinosaur killer 10 km in size is more rare, once every 250 – 500 million years. Those numbers line up fairly well with what’s seen as far as big impacts on Earth.
So does this solve the mystery? Well, kinda. It does show that a lot more rocks from the outer belt can eventually hit us, which is a big step. There are hints that while big dark rocks come from the outer belt, smaller dark ones come from the inner belt, which suggests the forces acting on these rocks is different for different parts of the belt. Also, the inner belt seems to produce fewer big rocks that can impact us than older models predicted. It’s not clear why.
There are still lots of things left to figure out here, but that’s typical. It takes massive computers a long time to do the simulations, so as they get faster it becomes easier to run various models and change parameters. In general that means we learn more since new things are tried and found to work… or importantly not to work, since sometimes old ideas turn out not to be right. That’s science.
Every step we take here gets us a little bit closer to understanding what happened all those millions of years ago when the dinosaurs had a Very Bad Day™. If we want to make sure we have a future — at least concerning asteroid impacts — then learning more about the behavior of these rocks is a Very Good Idea.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
