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

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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


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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


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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


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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


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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



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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



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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


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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.]

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What Makes a 'Moon'? (The Answer Is More Complicated Than You'd Think)
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Not all moons look like the spherical glowing orb that hovers above Earth. In fact, to be a moon, a space rock technically only has to be the natural satellite of a star’s satellite.

That said, these rocks don’t all look, or act, alike. They come in a variety of shapes, sizes, and types, and they all have unique behaviors. For example, Jupiter has 53 known moons—including the solar system’s largest moon, Ganymede—and many of them have elliptical, backwards orbits. Meanwhile, Mars has two moons, and they're irregularly-shaped, dark satellites that orbit the planet’s equator in circles.

Since there are hundreds of moons—and even more conditional ones—in our solar system, this raises a question: Should we deem each and every one of these secondary satellites a “moon”? And if not, should the distinguishing criteria include factors like orbit, size, shape, or visibility from a planet’s surface?

MinuteEarth’s Kate Yoshida explores these questions in the video below.

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Should You Keep Your Pets Indoors During the Solar Eclipse?
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By now, you probably know what you’ll be doing on August 21, when a total solar eclipse makes its way across the continental United States. You’ve had your safety glasses ready since January (and have confirmed that they’ll actually protect your retinas), you’ve picked out the perfect vantage point in your area for the best view, and you’ve memorized Nikon’s tips for how to take pictures of this rare celestial phenomenon. Still, it feels like you’re forgetting something … and it’s probably the thing that's been right under your nose, and sitting on your lap, the whole time: your pets.

Even if you’ve never witnessed a solar eclipse, you undoubtedly know that you’re never supposed to look directly at the sun during one. But what about your four-legged family members? Shouldn’t Fido be fitted with a pair of eclipse glasses before he heads out for his daily walk? Could Princess Kitty be in danger of having her peepers singed if she’s lounging on her favorite windowsill? While, like humans, looking directly at the sun during a solar eclipse does pose the potential of doing harm to a pet’s eyes, it’s unlikely that the thought would even occur to the little ball of fluff.

“It’s no different than any other day,” Angela Speck, co-chair of the AAS National Solar Eclipse Task Force, explained during a NASA briefing in June. “On a normal day, your pets don’t try to look at the sun and therefore don’t damage their eyes, so on this day they’re not going to do it either. It is not a concern, letting them outside. All that’s happened is we’ve blocked out the sun, it’s not more dangerous. So I think that people who have pets want to think about that. I’m not going to worry about my cat.”

Dr. Jessica Vogelsang, a veterinarian, author, and founder of pawcurious, echoed Speck’s statement, but allowed that there’s no such thing as being too cautious. “It’s hard for me to criticize such a well-meaning warning, because there’s really no harm in following the advice to keep pets inside during the eclipse,” Vogelsang told Snopes. “It’s better to be too cautious than not cautious enough. But in the interest of offering a realistic risk assessment, the likelihood of a pet ruining their eyes the same way a human would during an eclipse is much lower—not because the damage would be any less were they to stare at the sun, but because, from a behavior standpoint, dogs and cats just don’t have any interest in doing so. We tend to extrapolate a lot of things from people to pets that just doesn’t bear out, and this is one of them.

“I’ve seen lots of warnings from the astronomy community and the human medical community about the theoretical dangers of pets and eclipses, but I’m not sure if any of them really know animal behavior all that well," Vogelsang continued. "It’s not like there’s a big outcry from the wildlife community to go chase down coyotes and hawks and bears and give them goggles either. While we in the veterinary community absolutely appreciate people being concerned about their pets’ wellbeing, this is a non-issue for us.”

The bigger issue, according to several experts, would be with pets who are already sensitive to Mother Nature. "If you have the sort of pet that's normally sensitive to shifts in the weather, they might be disturbed by just the whole vibe because the temperature will drop and the sky will get dark,” Melanie Monteiro, a pet safety expert and author of The Safe-Dog Handbook: A Complete Guide to Protecting Your Pooch, Indoors and Out, told TODAY.

“If [your pets] have learned some association with it getting darker, they will show that behavior or at a minimum they get confused because the timeframe does not correspond,” Dr. Carlo Siracusa of Penn Vet Hospital told CBS Philly. “You might put the blinds down, but not exactly when the dark is coming but when it is still light.” 

While Monteiro again reasserts that, "Dogs and cats don't normally look up into the sun, so you don't need to get any special eye protection for your pets,” she says that it’s never a bad idea to take some extra precautions. So if you’re headed out to an eclipse viewing party, why not do your pets a favor and leave them at home. They won’t even know what they’re missing.

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