CLOSE
Original image

Collision Course: A Brief Guide to Earth's Most Interesting Impact Craters

Original image

A Norwegian family arrived at their cabin to open it up for the spring and found a surprise: a large rock had smashed through the roof. It was identified as a 1.3 pound breccia meteorite. It didn't hurt anybody, and its sale price should easily cover the damage to the roof; meteorites are valuable to collectors. But although most meteorites are very small, and to date nobody has been more than bruised by one, some of them are big and make a violent impression where they hit. Here are a few of the more interesting impact craters around:

Barringer Crater, Arizona, USA


View Larger Map

Also known as "Meteor Crater," this was the first crater identified, due to its relatively pristine appearance. It's young, as craters go -- just 50,000 years old -- and it was created by a nickel-iron meteorite about 50 meters across, excavating a crater about 1.2 km across.

Obolon' Crater, Poltava Oblast, Ukraine


View Larger Map

Not all craters are so obvious; sometimes their structure is only apparent in aerial views. Obolon' Crater was detected from the presence of shocked minerals in the surrounding, a tell-tale sign of an impact event. It's 20 km across and is estimated to be about 169 million years old, though there is some evidence it may be quite a bit older. (More on that next.)

Manicouagan Crater, Quebec, Canada


View Larger Map

Visible from space as a ring-shaped lake, this 100 km multi-ringed crater (with a 70 km central ring that is now Manicouagan Reservoir) was created by the impact of a 5km asteroid about 216 million years ago. What's interesting about this crater is that, if you account for plate tectonics and then roll the clock back about 216 million years, this crater has an eerily precise alignment with several other craters: Rochechouart in France, St. Martin in Manitoba, Obolon' in the Ukraine, and Red Wing crater in North Dakota. All of these craters may have been produced by a meteor train, the result of an object breaking up due to tidal forces or collisions.

Gosses Bluff Crater, Northern Territory, Australia


View Larger Map

What's left of this one is only 5 km across, but that's really only the central uplift that is found in some larger craters; the outer rim has mostly eroded away. This crater dates back about 142 million years. The local Aborigines regard it as sacred and, interestingly, give it an origin story hinting at its true origins: their story is that the child of the morning and evening stars fell out of the sky and hit the Earth in this spot; the shape of the bluff is evocative of its origin.

Karakul Crater, Pamir Mountains, Tajikistan


View Larger Map

This relatively young crater (between 5 and 25 million years old) is in Tajikistan and features a large lake at its center. The overall depression is 52 km across.

Sudbury Basin, Ontario, Canada


View Larger Map

This highly elliptical and also frighteningly large impact crater is difficult to see; it is shallow (the blow was a glancing one) and is heavily eroded and largely covered in vegetation. There is a large lake at one end, and the shape of it is crudely visible as human settlement has been mostly in the valley. The impactor would have been about 10-15 km in size, and struck the Earth about 1.849 billion years ago.

Vredefort Crater, Free State Province, South Africa


View Larger Map

Sudbury is big, but it's not the biggest. At 300 km across, Vredefort is the biggest confirmed impact crater on Earth. It's also the second oldest, at a little over 2 billion years of age. This impactor was probably 5-10 km, but traveling on a more direct course than the one that created Sudbury.

Chicxulub Crater, Yucatan, Mexico

This is not the largest crater on Earth, and you cannot see it at all from the surface. But it's one of the most famous, because this is the one widely suspected to have done in the dinosaurs. It's 180 km across, and the impactor is believed to have been at least 10 km across, striking Earth with a force of roughly 96 teratons of TNT. Geologic evidence indicates that the region was completely underwater at the time, and it would have produced a phenomenal tsunami.

[Gravity map created from public data by Milan Studio and released through Wikimedia Commons.]

Original image
Land Cover CCI, ESA
arrow
Afternoon Map
European Space Agency Releases First High-Res Land Cover Map of Africa
Original image
Land Cover CCI, ESA

This isn’t just any image of Africa. It represents the first of its kind: a high-resolution map of the different types of land cover that are found on the continent, released by The European Space Agency, as Travel + Leisure reports.

Land cover maps depict the different physical materials that cover the Earth, whether that material is vegetation, wetlands, concrete, or sand. They can be used to track the growth of cities, assess flooding, keep tabs on environmental issues like deforestation or desertification, and more.

The newly released land cover map of Africa shows the continent at an extremely detailed resolution. Each pixel represents just 65.6 feet (20 meters) on the ground. It’s designed to help researchers model the extent of climate change across Africa, study biodiversity and natural resources, and see how land use is changing, among other applications.

Developed as part of the Climate Change Initiative (CCI) Land Cover project, the space agency gathered a full year’s worth of data from its Sentinel-2A satellite to create the map. In total, the image is made from 90 terabytes of data—180,000 images—taken between December 2015 and December 2016.

The map is so large and detailed that the space agency created its own online viewer for it. You can dive further into the image here.

And keep watch: A better map might be close at hand. In March, the ESA launched the Sentinal-2B satellite, which it says will make a global map at a 32.8 feet-per-pixel (10 meters) resolution possible.

[h/t Travel + Leisure]

Original image
NSF/LIGO/Sonoma State University/A. Simonnet
arrow
Space
Astronomers Observe a New Kind of Massive Cosmic Collision for the First Time
Original image
NSF/LIGO/Sonoma State University/A. Simonnet

For the first time, astronomers have detected the colossal blast produced by the merger of two neutron stars—and they've recorded it both via the gravitational waves the event produced, as well as the flash of light it emitted.

Physicists believe that the pair of neutron stars—ultra-dense stars formed when a massive star collapses, following a supernova explosion—had been locked in a death spiral just before their final collision and merger. As they spiraled inward, a burst of gravitational waves was released; when they finally smashed together, high-energy electromagnetic radiation known as gamma rays were emitted. In the days that followed, electromagnetic radiation at many other wavelengths—X-rays, ultraviolet, optical, infrared, and radio waves—were released. (Imagine all the instruments in an orchestra, from the lowest bassoons to the highest piccolos, playing a short, loud note all at once.)

This is the first time such a collision has been observed, as well as the first time that both kinds of observations—gravitational waves and electromagnetic radiation—have been recorded from the same event, a feat that required co-operation among some 70 different observatories around the world, including ground-based observatories, orbiting telescopes, the U.S. LIGO (Laser Interferometer Gravitational-Wave Observatory), and European Virgo gravitational wave detectors.

"For me, it feels like the dawning of a next era in astrophysics," Julie McEnery, project scientist for NASA's Fermi Gamma-ray Space Telescope, one of the first instruments to record the burst of energy from the cosmic collision, tells Mental Floss. "With this observation, we've connected these new gravitational wave observations to the rest of the observations that we've been doing in astrophysics for a very long time."

A BREAKTHROUGH ON SEVERAL FRONTS

The observations represent a breakthrough on several fronts. Until now, the only events detected via gravitational waves have been mergers of black holes; with these new results, it seems likely that gravitational wave technology—which is still in its infancy—will open many new phenomena to scientific scrutiny. At the same time, very little was known about the physics of neutron stars—especially their violent, final moments—until now. The observations are also shedding new light on the origin of gamma-ray bursts (GRBs)—extremely energetic explosions seen in distant galaxies. As well, the research may offer clues as to how the heavier elements, such as gold, platinum, and uranium, formed.

Astronomers around the world are thrilled by the latest findings, as today's flurry of excitement attests. The LIGO-Virgo results are being published today in the journal Physical Review Letters; further articles are due to be published in other journals, including Nature and Science, in the weeks ahead. Scientists also described the findings today at press briefings hosted by the National Science Foundation (the agency that funds LIGO) in Washington, and at the headquarters of the European Southern Observatory in Garching, Germany.

(Rumors of the breakthrough had been swirling for weeks; in August, astronomer J. Craig Wheeler of the University of Texas at Austin tweeted, "New LIGO. Source with optical counterpart. Blow your sox off!" He and another scientist who tweeted have since apologized for doing so prematurely, but this morning, minutes after the news officially broke, Wheeler tweeted, "Socks off!") 

The neutron star merger happened in a galaxy known as NGC 4993, located some 130 million light years from our own Milky Way, in the direction of the southern constellation Hydra.

Gravitational wave astronomy is barely a year and a half old. The first detection of gravitational waves—physicists describe them as ripples in space-time—came in fall 2015, when the signal from a pair of merging black holes was recorded by the LIGO detectors. The discovery was announced in February 2016 to great fanfare, and was honored with this year's Nobel Prize in Physics. Virgo, a European gravitational wave detector, went online in 2007 and was upgraded last year; together, they allow astronomers to accurately pin down the location of gravitational wave sources for the first time. The addition of Virgo also allows for a greater sensitivity than LIGO could achieve on its own.

LIGO previously recorded four different instances of colliding black holes—objects with masses between seven times the mass of the Sun and a bit less than 40 times the mass of the Sun. This new signal was weaker than that produced by the black holes, but also lasted longer, persisting for about 100 seconds; the data suggested the objects were too small to be black holes, but instead were neutron stars, with masses of about 1.1 and 1.6 times the Sun's mass. (In spite of their heft, neutron stars are tiny, with diameters of only a dozen or so miles.) Another key difference is that while black hole collisions can be detected only via gravitational waves—black holes are black, after all—neutron star collisions can actually be seen.

"EXACTLY WHAT WE'D HOPE TO SEE"

When the gravitational wave signal was recorded, on the morning of August 17, observatories around the world were notified and began scanning the sky in search of an optical counterpart. Even before the LIGO bulletin went out, however, the orbiting Fermi telescope, which can receive high-energy gamma rays from all directions in the sky at once, had caught something, receiving a signal less than two seconds after the gravitational wave signal tripped the LIGO detectors. This was presumed to be a gamma-ray burst, an explosion of gamma rays seen in deep space. Astronomers had recorded such bursts sporadically since the 1960s; however, their physical cause was never certain. Merging neutron stars had been a suggested culprit for at least some of these explosions.

"This is exactly what we'd hoped to see," says McEnery. "A gamma ray burst requires a colossal release of energy, and one of the hypotheses for what powers at least some of them—the ones that have durations of less than two seconds—was the merger of two neutron stars … We had hoped that we would see a gamma ray burst and a gravitational wave signal together, so it's fantastic to finally actually do this."

With preliminary data from LIGO and Virgo, combined with the Fermi data, scientists could tell with reasonable precision what direction in the sky the signal had come from—and dozens of telescopes at observatories around the world, including the U.S. Gemini telescopes, the European Very Large Telescope, and the Hubble Space Telescope, were quickly re-aimed toward Hydra, in the direction of reported signal.

The telescopes at the Las Campanas Observatory in Chile were well-placed for getting a first look—because the bulletin arrived in the morning, however, they had to wait until the sun dropped below the horizon.

"We had about eight to 10 hours, until sunset in Chile, to prepare for this," Maria Drout, an astronomer at the Carnegie Observatories in in Pasadena, California, which runs the Las Campanas telescopes, tells Mental Floss. She was connected by Skype to the astronomers in the control rooms of three different telescopes at Las Campanas, as they prepared to train their telescopes at the target region. "Usually you prepare a month in advance for an observing run on these telescopes, but this was all happening in a few hours," Drout says. She and her colleagues prepared a target list of about 100 galaxies, but less than one-tenth of the way through the list, by luck, they found it: a tiny blip of light in NGC 4993 that wasn't visible on archival images of the same galaxy. (It was the 1-meter Swope telescope that snagged the first images.)

A NEW ERA OF ASTROPHYSICS

When a new star-like object in a distant galaxy is spotted, a typical first guess is that it's a supernova (an exploding star). But this new object was changing very rapidly, growing 100 times dimmer over just a few days while also quickly becoming redder—which supernovae don't do, explains Drout, who is cross-appointed at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto. "We ended up following it for three weeks or so, and by the end, it was very clear that this [neutron star merger] was what we were looking at," she says.

The researchers say they can't be sure if the resulting object was another, larger neutron star, or whether it would have been so massive that it would have collapsed into a black hole.

As exciting as the original detection of gravitational waves last year was, Drout is looking forward to a new era in which both gravitational waves and traditional telescopes can be used to study the same objects. "We can learn a lot more about these types of extreme systems that exist in the universe, by coupling the two together," she says.

The detection shows that "gravitational wave science is moving from being a physics experiment to being a tool for astronomers," Marcia Rieke, an astronomer at the University of Arizona who is not involved in the current research, tells Mental Floss. "So I think it's a pretty big deal."

Physicists are also learning something new about the origin of the heaviest elements in the periodic table. For many years, these were thought to arise from supernova explosions, but spectroscopic data from the newly observed neutron star merger (in which light is broken up into its component colors) suggests that such explosion produce enormous quantities of heavy elements—including enough gold to put Fort Knox to shame. (The blast is believed to have created some 200 Earth-masses of gold, the scientists say.) "It's telling us that most of the gold that we know about is produced in these mergers, and not in supernovae," McEnery says.

Editor's note: This post has been updated.

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios