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.
Rare ‘big fuzzy green ball’ comet visible in B.C. skies, a 50000-year sight
In the night sky, a comet is flying by Earth for the first time in 50,000 years.
Steve Coleopy, of the South Cariboo Astronomy Club, is offering some tips on how to see it before it disappears.
The green-coloured comet, named C/2022 E3 (ZTF), is not readily visible to the naked eye, although someone with good eyesight in really dark skies might be able to see it, he said. The only problem is it’s getting less visible by the day.
“Right now the comet is the closest to earth and is travelling rapidly away,” Coleopy said, noting it is easily seen through binoculars and small telescopes. “I have not been very successful in taking a picture of it yet, because it’s so faint, but will keep trying, weather permitting.”
At the moment, the comet is located between the bowl of the Big Dipper and the North Star but will be moving toward the Planet Mars – a steady orange-coloured point of light- in the night sky over the next couple of weeks, according to Coleopy.
“I have found it best to view the comet after 3:30 in the morning, after the moon sets,” he said. “It is still visible in binoculars even with the moon still up, but the view is more washed out because of the moonlight.”
He noted the comet looks like a “big fuzzy green ball,” as opposed to the bright pinpoint light of the stars.
“There’s not much of a tail, but if you can look through the binoculars for a short period of time, enough for your eyes to acclimatize to the image, it’s quite spectacular.”
To know its more precise location on a particular evening, an internet search will produce drawings and pictures of the comet with dates of where and when the comet will be in each daily location.
Coleopy notes the comet will only be visible for a few more weeks, and then it won’t return for about 50,000 years.
Extreme species deficit of nitrogen-converting microbes in European lakes
Sampling of Lake Constance water from 85 m depth, in which ammonia-oxidizing archaea make up as much as 40% of all microorganisms
An international team of researchers led by microbiologists from the Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH in Braunschweig, Germany, shows that in the depths of European lakes, the detoxification of ammonium is ensured by an extremely low biodiversity of archaea. The researchers recently published their findings in the prestigious international journal Science Advances. The team led by environmental microbiologists from the Leibniz Institute DSMZ has now shown that the species diversity of these archaea in lakes around the world ranges from 1 to 15 species. This is of particularly concern in the context of global biodiversity loss and the UN Biodiversity Conference held in Montreal, Canada, in December 2022. Lakes play an important role in providing freshwater for drinking, inland fisheries, and recreation. These ecosystem services would be at danger from ammonium enrichment. Ammonium is an essential component of agricultural fertilizers and contributes to its remarkable increase in environmental concentrations and the overall im-balance of the global nitrogen cycle. Nutrient-poor lakes with large water masses (such as Lake Constance and many other pre-alpine lakes) harbor enormously large populations of archaea, a unique class of microorganisms. In sediments and other low-oxygen environments, these archaea convert ammonium to nitrate, which is then converted to inert dinitrogen gas, an essential component of the air. In this way, they contribute to the detoxification of ammonium in the aquatic environment. In fact, the species predominant in European lakes is even clonal and shows low genetic microdiversity between different lakes. This low species diversity contrasts with marine ecosystems where this group of microorganisms predominates with much greater species richness, making the stability of ecosystem function provided by these nitrogen-converting archaea potentially vulnerable to environmental change.
Maintenance of drinking water quality
Although there is a lot of water on our planet, only 2.5% of it is fresh water. Since much of this fresh water is stored in glaciers and polar ice caps, only about 80% of it is even accessible to us humans. About 36% of drinking water in the European Union is obtained from surface waters. It is therefore crucial to understand how environmental processes such as microbial nitrification maintain this ecosystem service. The rate-determining phase of nitrification is the oxidation of ammonia, which prevents the accumulation of ammonium and converts it to nitrate via nitrite. In this way, ammonium is prevented from contaminating water sources and is necessary for its final conversion to the harmless dinitrogen gas. In this study, deep lakes on five different continents were investigated to assess the richness and evolutionary history of ammonia-oxidizing archaea. Organisms from marine habitats have traditionally colonized freshwater ecosystems. However, these archaea have had to make significant changes in their cell composition, possible only a few times during evolution, when they moved from marine habitats to freshwaters with much lower salt concentrations. The researchers identified this selection pressure as the major barrier to greater diversity of ammonia-oxidizing archaea colonizing freshwaters. The researchers were also able to determine when the few freshwater archaea first appeared. Ac-cording to the study, the dominant archaeal species in European lakes emerged only about 13 million years ago, which is quite consistent with the evolutionary history of the European lakes studied.
Slowed evolution of freshwater archaea
The major freshwater species in Europe changed relatively little over the 13 million years and spread almost clonally across Europe and Asia, which puzzled the researchers. Currently, there are not many examples of such an evolutionary break over such long time periods and over large intercontinental ranges. The authors suggest that the main factor slowing the rapid growth rates and associated evolutionary changes is the low temperatures (4 °C) at the bottom of the lakes studied. As a result, these archaea are restricted to a state of low genetic diversity. It is unclear how the extremely species-poor and evolutionarily static freshwater archaea will respond to changes induced by global climate warming and eutrophication of nearby agricultur-al lands, as the effects of climate change are more pronounced in freshwater than in marine habitats, which is associated with a loss of biodiversity.
Publication: Ngugi DK, Salcher MM, Andre A-S, Ghai R., Klotz F, Chiriac M-C, Ionescu D, Büsing P, Grossart H-S, Xing P, Priscu JC, Alymkulov S, Pester M. 2022. Postglacial adaptations enabled coloniza-tion and quasi-clonal dispersal of ammonia oxidizing archaea in modern European large lakes. Science Advances: https://www.science.org/doi/10.1126/sciadv.adc9392
PhDr. Sven-David Müller, Head of Public Relations, Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH
Phone: ++49 (0)531/2616-300
About the Leibniz Institute DSMZ
The Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures is the world’s most diverse collection of biological resources (bacteria, archaea, protists, yeasts, fungi, bacteriophages, plant viruses, genomic bacterial DNA as well as human and animal cell lines). Microorganisms and cell cultures are collected, investigated and archived at the DSMZ. As an institution of the Leibniz Association, the DSMZ with its extensive scientific services and biological resources has been a global partner for research, science and industry since 1969. The DSMZ was the first registered collection in Europe (Regulation (EU) No. 511/2014) and is certified according to the quality standard ISO 9001:2015. As a patent depository, it offers the only possibility in Germany to deposit biological material in accordance with the requirements of the Budapest Treaty. In addition to scientific services, research is the second pillar of the DSMZ. The institute, located on the Science Campus Braunschweig-Süd, accommodates more than 82,000 cultures and biomaterials and has around 200 employees. www.dsmz.de
Scientists are closing in on why the universe exists
Particle astrophysicist Benjamin Tam hopes his work will help us understand a question. A very big one.
“The big question that we are trying to answer with this research is how the universe was formed,” said Tam, who is finishing his PhD at Queen’s University.
“What is the origin of the universe?”
And to answer that question, he and dozens of fellow scientists and engineers are conducting a multi-million dollar experiment two kilometres below the surface of the Canadian Shield in a repurposed mine near Sudbury, Ontario.
The Sudbury Neutrino Observatory (SNOLAB) is already famous for an earlier experiment that revealed how neutrinos ‘oscillate’ between different versions of themselves as they travel here from the sun.
This finding proved a vital point: the mass of a neutrino cannot be zero. The experiment’s lead scientist, Arthur McDonald, shared the Nobel Prize in 2015 for this discovery.
The neutrino is commonly known as the ‘ghost particle.’ Trillions upon trillions of them emanate from the sun every second. To humans, they are imperceptible except through highly specialized detection technology that alerts us to their presence.
Neutrinos were first hypothesized in the early 20th century to explain why certain important physics equations consistently produced what looked like the wrong answers. In 1956, they were proven to exist.
Tam and his fellow researchers are now homing in on the biggest remaining mystery about these tiny particles.
Nobody knows what happens when two neutrinos collide. If it can be shown that they sometimes zap each other out of existence, scientists could conclude that a neutrino acts as its own ‘antiparticle’.
Such a conclusion would explain how an imbalance arose between matter and anti-matter, thus clarifying the current existence of all the matter in the universe.
It would also offer some relief to those hoping to describe the physical world using a model that does not imply none of us should be here.
Guests in this episode (in order of appearance):
Benjamin Tam is a PhD student in Particle Astrophysics at Queen’s University.
Eve Vavagiakis is a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellow in the Physics Department at Cornell University. She’s the author of a children’s book, I’m A Neutrino: Tiny Particles in a Big Universe.
Erica Caden is a research scientist at SNOLAB. Among her duties she is the detector manager for SNO+, responsible for keeping things running day to day.
*This episode was produced by Nicola Luksic and Tom Howell. It is part of an on-going series, IDEAS from the Trenches, some stories are below.
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