Where did the dinosaur-killer asteroid come from?
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.
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?
To investigate, a team of astronomers modeled how asteroids in the main belt behave. This has been done before, but they did something a little different.
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.
They used computer simulations to model the physics of how the asteroids move over the course of a billion years, including effects from all the planets (except wee Mercury, which is too small to affect them) and the YORP effect. In general, YORP changes an asteroid’s orbit very slowly over time until it gets into a resonance, and then the rock gets moved rapidly into a new and potentially threatening orbit.
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.
Bird reports rose during lockdowns | Cornell Chronicle – Cornell Chronicle
Around 80% of bird species examined in a new study were reported in greater numbers in human-altered habitats during pandemic lockdowns, according to new research based on data from the eBird program at the Cornell Lab of Ornithology.
In the paper, “Reduced Human Activity During COVID-19 Alters Avian Land Use Across North America,” published Sept. 22 in Science Advances, researchers compared online eBird observations from the United States and Canada from before and during the pandemic. They focused on areas within about 100 km of urban areas, major roads, and airports.
Vast amounts of data from a likewise vast geographic area were vital for this study. The researchers used more than 4 million eBird observations of 82 bird species from across Canada and the U.S.
“A lot of species we really care about became more abundant in human landscapes during the pandemic,” said study senior author Nicola Koper of the University of Manitoba, which led the research. “I was blown away by how many species were affected by decreased traffic and activity during lockdowns.”
Reports of bald eagles increased in cities with the strongest lockdowns. Ruby-throated hummingbirds were three times more likely to be reported within a kilometer of airports than before the pandemic. Barn swallows, a threatened species in Canada, were reported more often within a kilometer of roads than before the pandemic.
A few species decreased their use of human-altered habitat during the pandemic. Red-tailed hawk reports decreased near roads, perhaps because there was less roadkill when traffic declined. But far more species had increased counts in these human-dominated landscapes.
The authors filtered pandemic and pre-pandemic eBird reports so that the final data sets had the same characteristics, such as location, number of lists, and level of birdwatcher effort.
“We also needed to be aware of the detectability issue,” said co-author Alison Johnston, assistant director of the Center for Avian Population Studies and Ecological Data in the Lab of Ornithology. “Were species being reported in higher numbers because people could finally hear the birds without all the traffic noise, or was there a real ecological change in the numbers of birds present?”
The study tested whether better detectability might be a factor in the larger bird numbers reported. If it was, the scientists expected that to be more noticeable for smaller birds, which are harder to detect beneath traffic noise. However, effects were noticed across many species, from hawks to hummingbirds, suggesting that the increased numbers were not only caused by increased detectability in the quieter environments.
“Having so many people in North America and around the world paying attention to nature has been crucial to understanding how wildlife react to our presence,” says lead author Michael Schrimpf, a postdoctoral fellow at the University of Manitoba. “Studies such as this one rely on volunteer birdwatchers, so if you enjoy watching wildlife, there are many projects out there, like eBird and iNaturalist, that can use your help.”
The study was funded by Natural Sciences and Engineering Research Council of Canada with in-kind support provided by Environment and Climate Change Canada and the Cornell Lab of Ornithology.
SpaceX Crew Dragon cupola provides awe-inspiring view of the Earth from space – Californianewstimes.com
Give a few seconds (or a minute or two if needed) to startle and gaze at the Earth’s scenery from the recently launched SpaceX Crew Dragon above.
on Wednesday,Tied to the SpaceX Crew Dragon with one of the upgrades: Cupola. The transparent dome at the top of the Dragon Capsule provides the Inspiration 4 crew with the best views of the Earth that up-and-coming astronauts can dream of. This is the first time a cupola has been installed on a dragon. Dragons typically carry astronauts and cargo to the ISS, with docking ports at the top instead of windows.
A short video posted to the SpaceX Twitter account hours after the launch shows the cupola’s transparent dome against the Earth, which is a pale blue marble.
As the Crew Dragon orbits from a height of 585 kilometers (more than 360 miles), our planet is exposed to the sun and slowly roams around the orbs.
Inspiration 4’s crew (commander Jared Isaacman, doctor’s assistant, childhood cancer survivor Haley Arseno, aerospace engineer Chris Sembroski, African-American geology professor Sian Proctor) are in orbit for three days. Ride and stare at the cupola and the earth.
And did you say that the cupola is right next to the dragon’s toilet? Yeah, the view of the earth should be visible from the crew dragon’s bathroom. Isaacman told insiders Toilets are one of the few places where you can separate yourself from others with privacy curtains and have the best toilet windows of mankind. “When people inevitably have to use the bathroom, they will see one view of hell,” he said.
Astronauts who have been to space often talk about a phenomenon called the “overview effect.” Looking at the planet from above, the idea is that the way we think about the planet and the mass of humankind that depends on it will change. There may be a lot of revelation at the end of the Inspiration 4 journey, as I don’t know if they thought of it while sitting in the can.
The mission is the first mission to take off from the Florida coast on Wednesday night and be launched with four civilians. It is expected to return to Earth on Saturday and land in the Atlantic Ocean.
SpaceX Crew Dragon cupola provides awe-inspiring view of the Earth from space Source link SpaceX Crew Dragon cupola provides awe-inspiring view of the Earth from space
Oldest human footprints in North America found in New Mexico – Al Jazeera English
Fossilised footprints dating 23,000 years push back the known date the continent was colonised by thousands of years.
Footprints dating back 23,000 years have been discovered in the United States, suggesting humans settled North America long before the end of the last Ice Age, according to researchers.
The findings announced on Thursday push back the date at which the continent was colonised by its first inhabitants by thousands of years.
The footprints were left in mud on the banks of a long-since dried up lake, which is now part of a New Mexico desert.
Sediment filled the indentations and hardened into rock, protecting evidence of our ancient relatives, and giving scientists a detailed insight into their lives.
The first footprints were found in a dry lake bed in White Sands National Park in 2009. Scientists at the United States Geological Survey recently analysed seeds stuck in the footprints to determine their approximate age, ranging from 22,800 to 21,130 years ago.
“Many tracks appear to be those of teenagers and children; large adult footprints are less frequent,” write the authors of the study published in the American journal Science.
“One hypothesis for this is the division of labour, in which adults are involved in skilled tasks whereas ‘fetching and carrying’ are delegated to teenagers.
“Children accompany the teenagers, and collectively they leave a higher number of footprints.”
Researchers also found tracks left by mammoths, prehistoric wolves, and even giant sloths, which appear to have been approximately at the same time as the humans visited the lake.
The Americas were the last continent to be reached by humanity.
For decades, the most commonly accepted theory has been that settlers came to North America from eastern Siberia across a land bridge – the present-day Bering Strait.
From Alaska, they headed south to kinder climes.
Archaeological evidence, including spearheads used to kill mammoths, has long suggested a 13,500-year-old settlement associated with so-called Clovis culture – named after a town in New Mexico.
This was considered the continent’s first civilisation, and the forerunner of groups that became known as Native Americans.
However, the notion of Clovis culture has been challenged over the past 20 years, with new discoveries that have pushed back the age of the first settlements.
Generally, even this pushed-back estimate of the age of the first settlements had not been more than 16,000 years, after the end of the so-called “last glacial maximum” – the period when ice sheets were at their most widespread.
This episode, which lasted until about 20,000 years ago, is crucial because it is believed that with ice covering much of the northern parts of the continent, human migration from Asia into North America and beyond would have been very difficult.
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