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Sioux Falls Scientists endorse Cosmic Collisions for showing us how Earth
has been radically changed by many cosmic collisions for a long, long time.

Cosmic Collisions
Our Explosive Universe

Cosmic Collisions (2010) - 225 minutes
Cosmic Collisions at Amazon.com

Right now, massive meteors and asteroids are orbiting dangerously close to Earth. Some may even be poised to hit us in the foreseeable future! Where are they? What type of damage will they cause? What can we do to stop a caroming asteroid that's headed toward us, or prevent future Near Earth Objects from lining us up in their sights.


  • EARTH:
    • They have left deep scars all over the face of our planet and are responsible for one of the biggest extinctions in history. Scientists believe that its not a question of if they'll strike again, but when. Cosmic Collisions: Earth covers everything there is to know about meteor clashes with our planet and how scientists are preparing for the next deadly assault on Earth.
    • Our solar system is a cosmic pinball machine. Rock piles as big as cities plow into planets and leave destruction in their wake. Cosmic Collisions: Solar System travels through our cosmic neighborhood as we examine how collisions created our moon, left gashes on Jupiter, and how pieces of Mars ended up in our own backyard.
    • Galaxies smash into each other, stars collide with the force of several nuclear bombs and black holes fuse in a deadly fireworks display. Even our own galaxy marches toward a clash with its closest neighbor, Andromeda. Cosmic Galaxies journeys through space as we examine the cosmic battles being waged between celestial bodies.
    • Since the Earth's creation 4.5 billion years ago, the planet has been struck by a series of catastrophes, each one pushing life to the edge of extinction. But from disaster comes new life - and while the dominant species on the planet were wiped out, hardier creatures survived and thrived, moving into the vacuum left by the extinction. These creatures in turn took over the planet until they themselves fell victim to yet another mass extinction. The Earth's history is rife with prehistoric disasters that have molded the planet and changed the course of evolution. But with each disaster came another leap forward on the evolutionary trail from single celled bacteria to humankind itself. Without this series of events, neither mankind nor any of the life we see around us would be here today.
    • Episodes: Birth of the Planet, Snowball Earth, Planet of Fire, Asteroid Strike.

4-10-19 The very strong case for an asteroid defense system
No, really — this is serious. limate change is a serious threat to human society. But even the most extreme worst-case future scenario wouldn't wipe out humanity instantly. There's only one thing that might do that — a major asteroid or comet impact. Big asteroid strikes are very rare, of course, but if one were to come along, we would all be dead in a matter of months — and while a small one wouldn't be so bad, it could still cause devastating losses. It sounds a bit silly, but there is a very strong case for the American government to set up a planetary asteroid defense system. It wouldn't cost much — just a few satellites and telescopes to keep track of all potential threats, and developing some collision or gravity-based techniques to deflect them if necessary. The New Yorker recently published a fascinating profile of a paleontologist named Robert DePalma who has discovered what appears to be fossils of animals who died in the Cretaceous-Paleogene extinction event. It has been widely accepted that a big asteroid impact in Mexico probably caused the extinction, but until DePalma's discoveries in the Hell Creek Formation in North Dakota, nobody had found dinosaur fossils very close to the Cretaceous-Paleogene geological boundary layer (suggesting that perhaps they died out earlier than the impact). If DePalma is right, it will be a landmark finding for the field. Pretty cool science! But the article also has a harrowing description of what happened when the Chicxulub impactor (a comet or asteroid, perhaps 11-81 kilometers wide) smashed into the Yucatan Peninsula 66 million years ago, creating a crater 93 miles in diameter. First came fire, as the kinetic energy released by the impact scorched everything in a 1,500-mile radius, and red-hot ejecta landed all around the world. Continent-wide firestorms burned up about 70 percent of all the world's forests, and huge tsunamis tore up the Gulf of Mexico. Then it got a lot worse: The dust and soot from the impact and the conflagrations prevented all sunlight from reaching the planet’s surface for months. Photosynthesis all but stopped, killing most of the plant life, extinguishing the phytoplankton in the oceans, and causing the amount of oxygen in the atmosphere to plummet. After the fires died down, Earth plunged into a period of cold, perhaps even a deep freeze. Earth’s two essential food chains, in the sea and on land, collapsed. About 75 percent of all species went extinct. More than 99.9999 per cent of all living organisms on Earth died, and the carbon cycle came to a halt. Big land animals fared particularly poorly — virtually everything weighing more than 5 kilograms was wiped out. Mammals at that time were mostly small, so the ones that survived were able to evolve into larger species after the ecosystem began to recover. In the history of our planet, that's almost as bad as it gets (only the Permian-Triassic extinction was worse). But it's worth noting that even a small asteroid can cause enormous damage. In 2013, one only about 66-feet wide exploded in the sky near Chelyabinsk Oblast in Russia, shattering windows across the city and causing about 1,500 injuries. The explosion was as powerful as a large nuclear weapon — a direct hit on a major city would have killed millions. So what do we do? The first thing is to track and record all the near-Earth objects, which is already underway with many projects across the globe and in space. Years ago, Congress required NASA to track 90 percent of objects one kilometer and over, which was accomplished as of 2011 — but smaller ones are still being racked up by the thousands. All told, nearly 20,000 near-Earth objects have been found at time of writing. Meanwhile, NASA's Jet Propulsion Laboratory has an automated system to detect which objects are a threat.

12-18-18 Erosion has erased most of Earth’s impact craters. Here are the survivors
A recent discovery in Greenland may bring the known list to 191. When it comes to impact craters, Earth is the pauper of the solar system. Even with a recent, still-to-be-confirmed crater discovery under Greenland’s ice, there are fewer than 200 known impact craters on the planet. Mars, for comparison, has hundreds of thousands. Produced by falling space rocks, most impact craters on Earth have been wiped away over time by wind, rain, shifting ice and the crawl of tectonic plates. Here are the 190 confirmed survivors, as recorded in the Earth Impact Database, maintained by the University of New Brunswick in Canada — plus the newcomer in Greenland. Identifying and studying such features could give scientists clues about the history of Earth, including the evolution of life itself. Researchers have tried to link various craters to the five known mass extinctions, for example. But only the space rock that created Chicxulub, hidden under Mexico’s Yucatán Peninsula and the Gulf of Mexico, is widely accepted as causing a major die-off. That space rock left a crater 150 kilometers wide and may have done in the dinosaurs and many other creatures about 66 million years ago (SN: 2/4/17, p. 16). Popigai, in Siberia, which measures about 90 kilometers from rim to rim, might be connected to a smaller die-off of mostly marine creatures about 34 million years ago. But that’s far from settled. Chicxulub and Popigai are the largest craters dating to the last 100 million years. But the roughly 160-kilometer-wide Vredefort crater in South Africa edges out Chicxulub as the largest known ever. Estimates put Vredefort’s origin around 2 billion years ago, making it the oldest known impact crater too.

8-13-18 Asteroid strike may have forged the oldest rocks ever found on Earth
The oldest rocks ever found are over four billion years old and we don’t know how they formed – but a massive asteroid bombardment may be responsible. The oldest rocks ever found on Earth may have been born in an asteroid bombardment that happened over four billion years ago. Found at the Acasta River in Canada about three decades ago, these ancient granite, or felsic, rocks formed approximately 600 million years after the creation of the Earth, before any life arose. They contain a distinctive mix of elements compared to rocks that formed later, suggesting they may have been created by a different geological process. Tim Johnson at Curtin University, Australia and his colleagues simulated the potential conditions in which these rocks could have formed. They concluded that partial melting of the Earth’s surface at a temperature of 800 to 900°C under very low pressure may have contributed to their creation. It would have been impossible for the young Earth reach such high temperatures unaided, Johnson says. Instead, he says the late heavy bombardment, a period of intense asteroids impacts on Earth that also widely cratered the moon, may be responsible. “We know that the Earth was bombarded for 600–700 million years after its birth,” Johnson says. “The fact that they are the only felsic rocks older than four billion years that we know of instantly got me thinking about impacts as a possible cause.”

5-15-18 Falling mini-moons may have created Earth’s first continents
The early Earth was likely orbited by lots of small moons, which rained down onto the surface and could have built up ancient continents. Small moons might have rained down on the early Earth, splattering it with debris that helped shape our young world and potentially built the first continent. Scientists have long suspected that the moon was formed when a Mars-sized object named Theia collided with the proto-Earth roughly 100 million years after the formation of the solar system. The crash threw molten rock into orbit that coalesced to form our planetary companion. But Hagai Perets at the Technion Israel Institute of Technology in Haifa, Israel, and his colleagues argue that the crash wasn’t a singular event. He says we’ve missed a fundamental aspect in the formation and evolution of the Earth – that it was pummelled time and time again. So Perets, and his colleagues modelled those many collisions. The study adds a new twist to recent work, which speculates that the moon was formed by a large number of impacts as opposed to a single collision, says Jeffrey Andrews-Hanna at the University of Arizona, who was not involved in the study. “Not only was the Earth struck by multiple impactors, but it was then re-impacted by the debris and moonlets that were created by those impacts in the first place,” he says.

5-14-18 We’ve lost track of more than 900 near-Earth asteroids
More than 900 asteroids hurtling close to Earth were seen just once and then lost. Some may be kilometres across, and they could be just about anywhere. We have lost more than 900 near-Earth asteroids. We’d seen each of these potential near-Earth asteroids once, but we didn’t continue tracking them, so we don’t know where they are or if they’re on a crash course with Earth. Between 2013 and 2016, 17,030 potential near-Earth asteroid (NEA) candidates were added to a list maintained by the International Astronomical Union’s Minor Planet Center. Of those, about 11 per cent were categorised as “initially unconfirmed”. This means that the few observations we had were not enough to pin down an orbit, so we don’t know where on the sky to look to find these objects again. Peter Vereš at the Minor Planet Center and his colleagues sifted through the data to figure out why we lost track of so many of them. They found that the main factor is time. To nail down an asteroid’s trajectory, it has to be observed more than once across a period of a few hours. “We need to act fast,” says Vereš. “Tomorrow, that object could be on the other side of the sky, and nobody really knows where it will be.” Some telescopes take 20 hours or more to report potential NEAs, which makes them almost impossible to find again and confirm. Sometimes bad weather means that we can’t look again in the hours following the initial observation. And the objects can be moving up to tens of kilometres per second, hurtling across the solar system so fast that a few hours after we first saw them, they could be almost anywhere on the sky. Because we couldn’t calculate their orbits, we don’t know how close these asteroids could get to Earth, but Vereš says they could be anywhere from several times the moon’s distance to much closer than the moon.

5-25-17 Huge impact could have smashed early Earth into a doughnut shape
Huge impact could have smashed early Earth into a doughnut shape
Many rocky worlds may have spent time as a newly named planetary form called a synestia – a loosely connected blob of molten rock and dust with a dented middle. For a brief time during its infancy, Earth was not a planet. It was a hot, doughnut-shaped blob called a synestia. Rocky worlds can be pulverised by collisions with each other, mushrooming into synestias before cooling off and becoming more familiar-looking celestial spheres, a new study says. Worlds across the universe come in all shapes and sizes, from planetesimals to dwarf planets to giants with rings, but researchers don’t fully understand the ways they can change shape and size throughout their lifetimes, says Simon Lock, a graduate student at Harvard University. In the solar system’s early days, huge impacts would have frequently occurred as small bodies smashed into each other, broke apart, re-formed and smashed again. Previous studies have suggested such impacts could pulverise a section of a planet, leaving behind debris that would coalesce into a moon or a ring like the ones surrounding Saturn. But sometimes, the most violent collisions can vaporize entire worlds, heating them up and sending them spinning. Unlike a solid body in which all parts rotate at the same angular velocity, these gas blobs spin so fast that the outer edges spin at a higher rate than the inner material. Once they reach a certain point, called the co-rotation limit, the planet takes on a new structure with an inner region rotating at a steady rate, loosely connected to a bulbous disc that rotates around it. The disc is not disconnected from the central region like a planet and its rings, but it sits at the outer limit of the planet’s gravitational pull. “What happens is, eventually its radius goes far enough out that the edge of the body has the same velocity that it would if it was in orbit,” Lock says. “For Earth, the edge of where its satellites orbit would be the co-rotation limit.” It resembles a puffy red blood cell, or a doughnut with a dented middle.

Cosmic Collisions
Our Explosive Universe

Sioux Falls Scientists endorse Cosmic Collisions for showing us how Earth
has been radically changed by many cosmic collisions for a long, long time.