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The Last Time a (Really Big) Meteor Hit Russia

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In late 1908, the scientific community in St. Petersburg and Moscow was galvanized by vague reports filtering out of Siberia, telling of a gigantic, mysterious explosion that summer that had been witnessed only by a handful of native Evenki tribesmen and Russian settlers.

According to eyewitness reports gathered later by Leonid Kulik, at 7:17 am on June 30, 1908, a column of bright blue light became visible in the sky above central Siberia, followed by a huge explosion near Tunguska, a remote region located in the taiga (pine forest) northwest of Lake Baikal.

The explosion rocked the earth, leveled gigantic swaths of forest, and filled the sky with blinding light, according to one Evenki native, who later remembered: “Then I saw a wonder: trees were falling, the branches were on fire, it became mighty bright, how can I say this, as if there was a second sun, my eyes were hurting, I even closed them.” A Russian settler reported that the explosion blew out windows in buildings up to 40 miles away from the impact, accompanied by intense heat: “At that moment I became so hot that I couldn't bear it, as if my shirt was on fire… hot wind raced between the houses, like from cannons…” The explosion clearly occurred some distance above the ground, with one eyewitness recalling that “the sky split in two and fire appeared high and wide over the forest.”

The effects of the Tunguska Event were breathtaking: the explosion, measuring between 10 and 20 megatons (somewhere between 435 and 870 times the force of the Nagasaki bomb), leveled approximately 80 million trees over an area of 800 square miles, or around half a million acres. No surprise, the simple peasant folk who witnessed it assumed the worst, with one newspaper reporting that “women cried, thinking it was the end of the world.” Later, particulate matter in the atmosphere produced stunning sunsets around the world.

It’s still not clear what caused the Tunguska Event, but based on the eyewitness reports and butterfly-shaped blast pattern, most scientists agree it must have resulted from a meteor or comet exploding about six miles above the ground. The latest theory suggests the object measured around 100 feet across and weighed over 600,000 tons; that’s about three times the size of the world’s largest ocean liners, which weigh in at around 225,000 tons. Interestingly, many eyewitnesses described not just one but a series of explosions, raising the possibility that the event was caused by a string of meteors or parts of a disintegrating comet hitting the earth in succession.

However scientific expeditions led by Kulik beginning in 1921 were unable to recover any fragments of the meteor or comet, and subsequent investigations (including an Italian mission which may have found a crater caused by the explosion in 2007) have also come up empty-handed. Predictably, this has given rise to all sorts of bizarre conspiracy theories, including, yes, an extraterrestrial visitation. Why aliens would want to destroy a remote part of Siberia, and what they have against pine trees, remains unclear.

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Space
Here's Where You Can Watch a Livestream of Cassini's Final Moments
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It's been a road trip like no other. After seven years and 2.2 billion miles, the NASA orbiter Cassini finally arrived at the Saturn system on June 30, 2004. Ever since, it's been capturing and transmitting valuable data about the distant environment. From sending the Huygens probe to land on the moon Titan to witnessing hurricanes on both of the planet's poles, Cassini has informed more than 3000 scientific papers.

It's been as impressive a mission as any spacecraft has ever undertaken. And tomorrow, Cassini will perform one last feat: sacrificing itself to Saturn's intense atmosphere. Project scientists are deliberately plunging it into the planet in order to secure just a little more data—and to keep the spacecraft, which is running low on fuel, from one day colliding with a Saturnian moon that might harbor life.

Because it won't have time to store anything on its hard drive, Cassini will livestream its blaze of glory via NASA. The information will be composed mostly of measurements, since pictures would take too long to send. Instead, we'll get data about Saturn's magnetic field and the composition of its dust and gas.

"As we fly through the atmosphere, we are able to literally scoop up some molecules, and from those we can figure out the ground truth in Saturn’s atmosphere," Scott Edgington, a Cassini project scientist, told New Scientist. "Just like almost everything else in this mission, I expect to be completely surprised."

The action will kick off at 7 a.m. EDT on Friday, September 15. Scientists expect to say goodbye to Cassini less than an hour later. 

While you wait for Cassini's grand finale, you can check out some essential facts we've rounded up from Saturn experts. And keep your eyes peeled for a full recap of Cassini’s historic journey: Mental Floss will be in the control room at the Jet Propulsion Laboratory in Pasadena, California, to offer a firsthand account of the craft's final moments in space. 

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Big Questions
What Are the Northern Lights?
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Over the centuries, many have gazed up at one of the Earth’s most fascinatingly beautiful natural wonders: the Northern Lights. In the past couple of weeks, some lucky American stargazers have gotten the chance to see them from their very own backyards—and could again this week, according to Thrillist. But what are they?

Before science was able to get a read on what exactly was happening in the night sky, ancient tribes had their own theories for what caused the jaw-dropping light show. Many early beliefs had roots in religion, such as that the light was a pathway souls traveled to reach heaven (Eskimo tribes) or that the light was an eternal battle of dead warriors (Middle-Age Europe). Early researchers were a bit more reasonable in their approximations, and most surrounded the idea of the reflection of sunlight off the ice caps. In 1619, Galileo Galilei named the lights the aurora borealis after Aurora, the Roman goddess of morning, after concluding they were a product of sunlight reflecting from the atmosphere.

Today, scientists have come to the general agreement that the lights are caused by the collision of electrically charged solar particles and atoms from our atmosphere. The energy from the collisions is released as light, and the reason it happens around the poles is because that's where the Earth’s magnetic field is the strongest. In 2008, a team at UCLA concluded that “when two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.”

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Vassilis Angelopoulos, a UCLA professor of Earth and Space Sciences. "Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening."

The best time to see the Northern Lights is during the winter, due to the Earth’s position in relation to the sun (shorter days means darker night skies). And by the way, it’s not just the North Pole that puts on a show—there are Southern Lights, too. There are also aurora borealis on other planets—including Mars—so rest assured that future generations born “abroad” will not miss out on this spectacular feat of nature.

Haven’t seen them yet? Traditionally, the best places to catch a glimpse of the Northern Lights are in Iceland, Sweden, Norway, Finland, Greenland, northern Canada, and Alaska. Maybe you'll get lucky this week and sneak a peek from your very own window. Check out Aurorasaurus for regular updates on where they are showing.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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