Astronomy

Meteor traveling through atmosphere without hitting Earth

Meteor traveling through atmosphere without hitting Earth

Is it possible (however unlikely) to have a meteorite miss Earth so narrowly and at such flat angle that it would enter atmosphere, travel few (dozens, hundreds, thousands?) kilometers getting as close as few kilometers to the ground without hitting anything and then leave atmosphere without any significant, leaving millions of humans staring agape at the sky?

Or does gravity and air friction prevent this by either making such flat trajectory impossible or by slowing down meteorite enough to make it fall to the ground?


yes it is possible,they are called Earth grazers or Earth-grazing fireball. they are not rare but only few incidents are recorded.

for more details read this Wikipedia page https://en.wikipedia.org/wiki/Earth-grazing_fireball


Meteors & Meteorites

They&rsquore all related to the flashes of light called &ldquoshooting stars&rdquo sometimes seen streaking across the sky. But we call the same object by different names, depending on where it is.

Meteoroids are objects in space that range in size from dust grains to small asteroids. Think of them as &ldquospace rocks."

When meteoroids enter Earth&rsquos atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or &ldquoshooting stars&rdquo are called meteors.

When a meteoroid survives a trip through the atmosphere and hits the ground, it&rsquos called a meteorite.


Ultra-rare meteor footage shows HUGE fireball streaking across sky and breaking up

INCREDIBLE footage of a fiery meteor streaking across the night sky last week has gone viral online.

Captured from a research boat off the coast of Tasmania, the video shows space debris flashing a brilliant green before harmlessly breaking apart.

The vessel, called the RV Investigator, is operated by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO).

The national research group broadcasts a 24/7 livestream from a camera on top of the ship.

"The meteor crosses the sky directly in front of the ship and then breaks up," CSIRO Voyage Manager John Hooper said last week.

"It was amazing to watch the footage and we were very fortunate that we captured it all on the ship livestream."

He added: "The size and brightness of the meteor was incredible."

According to a CSIRO blog post, the meteor, which was bright green, appeared on November 18.

It was spotted by the bridge crew and reported to the science staff on board.

At the time of the recording, Investigator was in the Tasman Sea about 60 miles (100km) off the southern Tasmanian coast.

Investigator is currently carrying out seafloor mapping for Parks Australia and running sea trials for marine equipment.

CSIRO astronomy expert Glen Nagle said the footage acts as a reminder that space is far from empty.

"Over 100 tonnes of natural space debris enters Earth's atmosphere every day," Mr Nagle said.

"Most of it goes unseen as it occurs over an unpopulated area like the southern ocean."

What's the difference between an asteroid, meteor and comet?

  • Asteroid: An asteroid is a small rocky body that orbits the Sun. Most are found in the asteroid belt (between Mars and Jupiter) but they can be found anywhere (including in a path that can impact Earth)
  • Meteoroid: When two asteroids hit each other, the small chunks that break off are called meteoroids
  • Meteor: If a meteoroid enters the Earth's atmosphere, it begins to vapourise and then becomes a meteor. On Earth, it'll look like a streak of light in the sky, because the rock is burning up
  • Meteorite: If a meteoroid doesn't vapourise completely and survives the trip through Earth's atmosphere, it can land on the Earth. At that point, it becomes a meteorite
  • Comet: Like asteroids, a comet orbits the Sun. However rather than being made mostly of rock, a comet contains lots of ice and gas, which can result in amazing tails forming behind them (thanks to the ice and dust vapourising)

He added: "Many meteors were once asteroids, travelling through space on their own trajectory.

"As they enter our atmosphere, they become meteors – and their entry can be visually spectacular."

Thousands of bits of space debris – many of them meteors – are tracked by Nasa throughout the year to keep an eye on their trajectories.

Fortunately, most are too small to pose any threat to Earth, and those that are dangerously large aren't projected to hit our planet any time soon.


There could be meteors traveling at close to the speed of light when they hit the atmosphere

Artist’s concept of the meteorite entering Earth’s atmosphere. Credit: University of Oxford

It's no secret that planet Earth is occasionally greeted by rocks from space that either explode in the atmosphere or impact on the surface. In addition, Earth regularly experiences meteor showers whenever it passes through clouds of debris in the solar system. However, it has also been determined that Earth is regularly bombarded by objects that are small enough to go unnoticed—about 1 mm or so in size.

According to a new study by Harvard astronomers Amir Siraj and Prof. Abraham Loeb, it is possible that Earth's atmosphere is bombarded by larger meteors—1 mm to 10 cm (0.04 to 4 inches) – that are extremely fast. These meteors, they argue, could be the result of nearby supernovae that accelerate particles to sub-relativistic or even relativistic speeds—from several thousand times the speed of sound to a fraction of the speed of light.

Their study, titled "Observational Signatures of Sub-Relativistic Meteors", recently appeared on the arXiv pre-print server and has been submitted to the Astrophysical Journal. Their work addresses an ongoing mystery in astrophysics, which is whether or not the ejecta created by a supernova can be accelerated to relativistic speeds and travel through the interstellar medium to reach Earth's atmosphere.

The existence of these kinds of meteors, which would measure about 1 mm in diameter (0.04 inches), has been proposed by several astronomers in the past, including Lyman Spitzer and Satio Hayakawa. The question of whether or not they could survive the trip through interstellar space has also been studied at length. As Siraj explained to Universe Today via email:

"Empirical evidence indicates that at least one supernova has rained heavy elements on Earth in the past. Supernovae are known to release significant quantities of dust at sub-relativistic speeds. We also see evidence of clumpiness or 'bullets' in supernova ejecta. The fraction of mass contained in small clumps is unknown, but if just 0.01% of the dust ejecta is contained in objects of millimeter size or larger, we would expect one to appear in the Earth's atmosphere as a sub-relativistic meteor every month (based on the rate of supernovae in the Milky Way galaxy)."

Meteors are pieces of comet and asteroid debris that strike the atmosphere and burn up in a flash. A brilliant Perseid meteor streaks along the summer Milky Way as seen from Cinder Hills Overlook at Sunset Crater National Monument—12 August 2016 2:40 A.M. (0940 UT). It left a glowing ion trail that lasted about 30 seconds. The camera caught a twisting smoke trail that drifted southward over the course of several minutes. Credit: Jimmy Westlake

Despite having a sound theoretical basis, the question remains as to whether or not meteors larger than a grain of dust enter Earth's atmosphere at sub-relativistic or relativistic speeds. These would be meteors that measure 1 mm (0.04 in), 1 cm (0.4 in), or 10 cm (4 in) in diameter. Much of the problem has to do with our current search methodology, which is simply not set up to look for these kinds of objects.

"Meteors typically travel near 0.01% of the speed of light," said Siraj. "Therefore, current searches are tuned to find signals from objects moving at that speed. Meteors from supernovae would travel a hundred times faster (around 1% of the speed light), and so their signals would be significantly different from typical meteors, making them easily missed by current surveys."

For the sake of their study, Siraj and Loeb developed a hydrodynamic and radiative model to track the evolution of hot plasma cylinders that result from sub-relativistic meteors passing through the atmosphere. From this, they were able to calculate what kind of signals would be produced, thereby providing an indication of what astronomers should be on the lookout for. As Siraj explained:

Map displaying location and energy of meteor explosions detected by CNEOS. Credit: NASA/CNEOS

"We find that a sub-relativistic meteor would give rise to a shock wave that could be picked up by a microphone, and also a bright flash of radiation visible in optical wavelengths—both lasting for about a tenth of a millisecond. For meteors as small as 1 mm, a small optical detector (1 square centimeter) could easily detect the flash of light out to the horizon."

With this in mind, Siraj and Loeb outlined the kind of infrastructure that would allow astronomers to confirm the existence of these objects and study them. For instance, new surveys could incorporate infrasound microphones and optical-infrared instruments that would be able to detect the acoustic signature and optical flashes created by these objects entering our atmosphere and the resulting explosions.

Based on their calculations, they recommend that a global network of about 600 detectors with all-sky coverage, which could detect a few of these types of meteors per year. There is also the option of searching through existing data for signs of sub-relativistic and relativistic meteors. Last but not least, there is the possibility of using existing infrastructure to look for signs of these objects.

A good example of this, Siraj explained, is to be found in NASA's Center for Near-Earth Object Studies (CNEOS) network and database: "In addition, we note that the U.S. government's global classified network of sensors (including microphones and optical detectors) that provides the CNEOS Fireball and Bolide Database likely comprises a capable existing infrastructure. We urge the U.S. government to declassify broader swaths of the CNEOS data so scientists can search for sub-relativistic meteors without spending more taxpayer money to develop a new global network—with one already in operation!"

The payoff for this would be nothing less than the ability to study an entirely new set of objects that regularly interact with Earth's atmosphere. It would also provide a new perspective to the study of supernovae by allowing astronomers to place important constraints on the ejecta they produce. With this in mind, a low-cost, global network of all-sky cameras seems well worth the investment.


The Mystery of the Dark Asteroid That Scorched Russia

O n a June morning in 1908, above a sleepy forest in the Siberian Taiga plush with larches, spruces, and black bears, something flashed so bright and hot in the sky that a hunter 10 miles away, near the Middle Tunguska River, tore his shirt off thinking it was on fire. Locals described some variation of a “fiery ball flying north.” A loud explosion, releasing the equivalent of three to five megatons of TNT, followed. The resulting shock wave, the largest in recorded history (185 times more powerful than the Hiroshima bomb), spread out over 1,000 square miles. Some 30 people were in the vicinity. Many of them were knocked unconscious, and at least three were killed. Houses and millions of trees toppled over and charred. Somehow, hours later, astronomers in Europe and Asia witnessed a night sky so bright that, “at midnight,” according to one testimony, “it was possible to read the newspaper without artificial lights.”

For a time, it seemed that a similarly mysterious event may have happened in 2013—again over Russia. Near the snow-covered factory town of Chelyabinsk, a 66-foot meteor exploded over the hills, 16 miles above ground. It, too, for a moment, burned brighter than the sun, and emanated intense heat, according to eyewitness reports. The Chelyabinsk meteor blasted down doors and shattered windows in a nearby town, injuring over 1,000 people. Then a hole was discovered in a frozen lake, and a half-ton chunk of space rock was found in the lakebed.

The so-called “Tunguska event’’ is different. It remains a mystery. After decades of scientific expeditions, no one has found a crater or any debris from a meteorite or comet—nothing to conclusively indicate a violent collision with the Earth. In their 2008 book, The Tunguska Meteorite: 100 Years of the Great Puzzle, authors A.I. Voitsekhovskii and V.A. Romeiko catalog 66 theories about the event. Lots of them are implausible (for example, a gaseous explosion emanating from the bowels of the earth). But some are less far-fetched. Recently a new theory has joined the fray, positing that a “dark asteroid,” composed of light-absorbing iron, caused the destruction and the peculiar light show.

DEADLY WAKE: This photograph was taken in 1927 during the first Soviet research expedition, led by Russian meteorologist Leonid Kulik, to uncover the cause of the Tunguska event. He was able to interview local witnesses but left without any evidence of an impact. Wikimedia Commons

Over the years, the Tunguska enigma has seeped into the imagination of popular culture and science fiction. In Indiana Jones and the Kingdom of the Crystal Skull, the Tunguska event is suspected to be a result of cosmic tourism, as cadavers found at the blast site are discovered to be interdimensional travelers. In Star Trek, the Tunguska event is seen as the result of Vulcan good will: A devastating meteor was headed toward Western Europe and a Vulcan survey ship deflected it into the relatively uninhabited forest. The X-Files ran an episode called “Tunguska,” where a military expedition mining meteoric remains discovers a black oil harboring alien microbes capable of possessing human bodies. Isaac Asimov took a shot at explaining it in his story, “The Mad Scientist.” Even Ghostbusters references it.

Early theories ranged across the space-rock spectrum. One is that a comet caused the Tunguska event. A flying fireball, after all, is a common description of a comet, even though comets are made of ice. Their mostly icy composition somewhat accounts for the absence of any meteoric material near the event site, since burning ice would vaporize. The forest-felling blast from a comet is also conceivable, since it could, in theory, explode after colliding with the dense air close to Earth. (The Chelyabinsk meteor, speeding at over 40,000 miles per hour, shattered upon contact with the troposphere, the thin bubble of breathable air that we inhabit, as if it were a brick wall.)

“But a comet is not just made of ice,” Vladimir Pariev, an astrophysicist at the Lebedev Physical Institute of the Russian Academy of Sciences, in Moscow, is quick to point out. “It also includes some stone and, if a comet of that size would have exploded over Siberia, there would have almost certainly been some debris discovered.” He doesn’t outright reject the possibility of a comet but acknowledged the difficulties surrounding that hypothesis, such as its inability to explain the bright night sky witnessed over Europe several hours later. But if it wasn’t a comet, what could cause such destruction?

It’s possible that the remainder of the Tunguska-event grazer is among those rocks caught in an elliptical orbit around our star.

Recently, Pariev and Sergei Karpov, of the Kirensky Institute of Physics in Siberia, along with other colleagues, revisited the Tunguska event. In two back-to-back articles published in the Monthly Notices of the Royal Astronomical Society, the authors argue that past expeditions to the Tunguska site were misguided. The investigators, they write, were looking in the wrong place, inspecting the ground for meteoric material. What they were looking for was actually unrecoverably scattered by stratospheric winds across Europe by nightfall on June 30, 1908. Karpov and Pariev suggest the compelling and elegant hypothesis that the cause of the Tunguska event was a rare type of meteor—known as a “grazer.”

Grazers are rare but not unknown to astronomers. These meteors, as the name suggests, graze the atmosphere without making contact with Earth’s surface. In 1972, the so-called “Great Daylight Fireball” passed over the United States and Canada after it bounced off the atmosphere, ascending back into space. Its entry angle allowed it to skip like a stone off the stratosphere and back into the light, rarefied air of the upper atmosphere without causing any damage to the surface of the Earth—unlike the grazer that Pariev, Karpov, and their colleagues suspect caused the Tunguska event. The researchers ran mathematical models of asteroid bodies, ranging in diameter from 50 to 200 meters, that could pierce the Earth’s atmosphere from an acute angle (9 to 12 degrees), skid as close to 10 to 15 kilometers from the surface, and continue with enough speed (about 30,000 miles per hour) to escape the atmosphere.

Their models revealed that stone and ice would completely disintegrate in the upper atmosphere. Only asteroids made of iron (which has much higher tensile strength, or resistance to breaking under stress, than stone or ice) and larger than 100 meters in diameter could sustain that grazing trajectory without shattering into pieces. This kind of object could pass through the atmosphere at Mach 60 (nearly 45,000 miles per hour), and return to its orbit around the sun.

If Aliens Exist, Here’s How We’ll Find Them

By Martin Rees & Mario Livio

Suppose aliens existed, and imagine that some of them had been watching our planet for its entire four and a half billion years. What would they have seen? Over most of that vast timespan, Earth’s appearance altered slowly and gradually. READ MORE

This would explain the bright night sky reported over Europe. If an iron asteroid of that size and trajectory passed through the atmosphere, for a few seconds it would shed its material at an incredible rate of 500,000 tons per second. It would shed this material at such a high temperature (over 10,000 degrees) that the outer layers of the rock would peel into plasma that would plume like smoke from the rock, combining with atmospheric elements and ultimately cooling into iron oxide particles that would collect water condensation and freeze into powdery snow. Any iron oxide vestiges of such a space rock would be indistinguishable from iron oxides of terrestrial origin. The iron oxide smoke would then travel through the stratosphere and place itself, by nightfall, over Europe. Normally, a cloud of iron oxide particles would obfuscate the sun and darken the sky but, at night, when the sun is at its moon-reflecting angle, it would hit the frozen iron oxide particles so as to make them glitter in the sky like so many miniscule moons, allowing someone to read, at midnight, a Dostoevsky novel outside.

Most asteroids loop around the asteroid belt between Mars and Jupiter, but there are thousands of asteroids orbiting the sun. It’s possible that the remainder of the Tunguska-event grazer is among those rocks caught in an elliptical orbit around our star. Astronomers would have to look for an emaciated but still spherical iron rock, about half the mass of its original, according to Karpov and Pariev’s calculations.

This remains a faraway task, for several reasons. Iron absorbs light, which makes the Tunguska asteroid a so-called “dark asteroid.” Optical telescopes struggle to detect such asteroids, as they can’t detect rocks within 45 degrees of the blinding sun (imagine the washed out screen from pointing a phone camera toward the sun), so the Tunguska meteor would only be visible along a shortcut of its horseshoe orbit. But infrared telescopes, in development now, would be able to detect the Tunguska rock and many more asteroids, potentially alerting us to devastating future impact events. The Chelyabinsk meteor, which would have leveled the city had it hit at just a slightly altered angle, wasn’t detected precisely because the sun shining behind it rendered it invisible to optical telescopes.

Paul Chodas, director of the Center for Near Earth Object Studies at the Jet Propulsion Laboratory at NASA, said, “We find about a dozen new asteroids every day.” NASA has identified about 95 percent of asteroids larger than 1 kilometer in the asteroid belt, but dark asteroids, including those orbiting the sun, present a more difficult challenge. Fortunately, infrared telescopes that would have detected the Chelyabinsk meteor are currently in production and should be deployed within three years, giving us a much better picture of the millions of rocks that swarm in space around Earth. Perhaps the iron sphere that toured Earth and slingshot back toward the sun over a century ago will be among the rocks in that picture. “It would be the ultimate test for our hypothesis,” Pariev said, “to find the Tunguska asteroid orbiting the sun in space.”

Marco Altamirano is a writer based in New Orleans and the author of Time, Technology, and Environment: An Essay on the Philosophy of Nature. Follow him on Twitter @marcosien.


How much force would a 4 kg meteor impact earth with?

This question is possibly going to reveal to PF how simplistic some of my understanding is but here goes.

F=MA refers to the energy needed to accelerate an object of given mass i.e. how much force does it take to accelerate a 4kg object at 1g = 40N per second.

However the OP isn't "what force does a 4kg asteroid undergo when falling to Earth", it's how much energy would the 4kg asteroid release. That would be worked out by figuring out the kinetic energy of the asteroid.

For another way to see why F=MA doesn't provide an answer to the OP consider this, using it the way you have done (where A is the acceleration in the gravity field of Earth) would give the same result for a 4kg asteroid travelling at 11kmps and one travelling at 111,000kmps.

This question is possibly going to reveal to PF how simplistic some of my understanding is but here goes.

F=MA refers to the energy needed to accelerate an object of given mass i.e. how much force does it take to accelerate a 4kg object at 1g = 40N per second.

However the OP isn't "what force does a 4kg asteroid undergo when falling to Earth", it's how much energy would the 4kg asteroid release. That would be worked out by figuring out the kinetic energy of the asteroid.

For another way to see why F=MA doesn't provide an answer to the OP consider this, using it the way you have done (where A is the acceleration in the gravity field of Earth) would give the same result for a 4kg asteroid travelling at 11kmps and one travelling at 111,000kmps.


Astronomers Tell You How and Where to Best View Meteor Showers

Throughout history, ancient peoples have witnessed meteor showers in awe and attributed special meaning to them. Sometimes they saw these blazing streaks of light as signs that doomsday was nigh others posit that the star mentioned in the birth of Jesus was actually a comet.

These days, we mostly see meteors for what they are in the eyes of science — space debris hitting Earth's atmosphere at suicidal speed. Sometimes, there are just a few strikes here and there. Full-on meteor showers, however, feature dozens or hundreds of glorious streaks per hour.

In many cases, you can't simply step out onto the sidewalk to see meteors, perhaps due to light pollution or physical obstructions like trees or buildings. But if you take the time to select a prime viewing spot, you may be in for the astronomical treat of a lifetime. Picking the best location might take a bit of homework on your part. Here are some tips to get you started, courtesy of two astronomers we talked with.

1. Be Prepared to Stay Up Very Late

"Meteors streaming into Earth's atmosphere are best seen after midnight when Earth itself is turned 'into the meteor stream,'" Paul A. Delaney, an astronomy professor at York University, in Toronto, says by email. "As Earth orbits the sun, at any given moment, half of the Earth is 'facing' in the direction of its orbital travel. As Earth spins on its axis, any spot on the surface at local midnight begins to rotate into this forward-facing half of Earth."

With that in mind, he says you'll get your best view of meteors from midnight to 6 a.m. local time. Before that, only the higher altitude meteors will be seen from the ground. If you remember just one thing about meteor viewing, this is it.

2. Get Away From City Lights

The next step in finding a primo meteor shower viewing location? Locating a pitch-black spot.

"It is here you can see many of the fainter meteors," says David Leake, director of the William M. Staerkel Planetarium at Parkland College in Illinois via email. "You don't want to be chased off private property, but if you can find a spot away from direct lighting and away from city light pollution, that's best."

Light pollution refers to excessive light that seeps into the sky from our civilized towns and cities (as seen in this light pollution map). It obscures many of the night sky's natural features, such as the Milky Way, to a degree that many lifelong city dwellers have never glimpsed it.

Meteor showers are no exception. If you live in a major metropolitan area, you may have to venture miles and miles away from the city's orange glow to see meteors in their full glory. You can use websites to find dark places near you.

If that's not option, you can always try closer to home.

"Maybe a nearby forest preserve or park is offering a meteor-watching event," says Leake. He also recommends checking with your local astronomy club for organized viewing activities.

Be sure to use red LED flashlights to preserve your night vision. It can take a half-hour or longer for your eyes to readjust to the dark night skies after you've been exposed to bright white light.

3. Viewing Direction and Elevation Matter, Too

Think you've pinpointed a good, dark viewing location on a map? When you're perusing dark sky map, here's a pro tip: Keep the direction of any nearby cities in mind relative to the location of the celestial event you're hoping to see because even in places that are certified as dark sky areas, you may see the telltale orange glow of cities on the horizon.

If that glow happens to be in the same direction as your meteor shower, it could impact your viewing. And it will almost certainly impact any astro-photography you're hoping to do.

You might also want to get on higher ground.

"Elevation can help," says Leake. "The greater your altitude, the less dust and water vapor you are looking through and the more stars you will see. I would rate darkness over elevation, though, if you have to make a choice."

4. Relax and Enjoy the (Incredibly Violent) Show

You don't need fancy equipment to watch a meteor shower. It's more about being prepared to stay out in the wee hours of the morning, with appropriately warm clothes and any other creature comforts you prefer. A reclining lawn chair that folds all the way back will allow you to see as much of the sky as possible without wrecking your neck. You can lie on a blanket in a pinch.

"Too many times amateur astronomers are out using their telescopes, trying to figure out what to look at, changing eyepieces, aligning optics, focusing, etc.," says Leake. "Sometimes we forget to just look up! For a meteor shower, you need no equipment but maybe a lawn chair."

While you're watching pieces of space debris smash themselves into oblivion, appreciate the violence of the calamities you're witnessing.

"Meteors are pieces of the universe literally raining down onto the Earth," says Delaney. "They are a wonderful spectacle. They reveal how much material is actually in space and while most of the material is small stuff, occasionally we encounter a larger rock that could potentially be very dangerous to life on Earth (think dinosaur extinction)."

Thus, he says, meteor showers remind us of the shooting gallery in which Earth moves through continuously and how important it should be for astronomers and governments to be on the lookout in space for dangerous rocks.

Best Places to View Meteor Showers in the U.S.

Light-filled American cities like Los Angeles or New York City aren't great for astronomy events. But there are plenty of darker areas throughout America that are perfect. Here are a few choice spots, according to Accuweather.

  • Big Bend National Park in southern Texas has deep, black skies and plenty of camping. It's also incredibly remote.
  • Big Pine Key in Florida is far enough from city lights to make for excellent star gazing any time of the year. It hosts a stargazing party in the winter.
  • Denali National Park in Alaska has very dark skies and no mountains to obscure viewing.
  • The Finger Lakes region of New York is remote enough to escape big city light pollution, but still offers a lot of tourist attractions.
  • Plentiful public lands south of Tucson, Arizona, make for great camping. The clear, dark skies of this area and tall hills (which give you an elevated viewing platform) are reasons that the city boasts many space telescopes.
  • Brockway Mountain, Michigan, is great if you want to see lots of meteors. Its location makes it possible to see 50 or more meteors in an hour.

Did you know that meteors can be different colors? The velocity at which the meteor strikes the atmosphere can alter its color. The mineral composition matters, too. For instance, those with substantial magnesium may appear greenish or bluish. High iron content gives off a yellowish glow, and purple comes from debris carrying a lot of calcium.


How to Survive a Killer Asteroid

To revist this article, visit My Profile, then View saved stories.

To revist this article, visit My Profile, then View saved stories.

Let’s say for a moment you want to camp alongside the dinosaurs. But not just any dinosaurs. You want to camp alongside the most famous. The most fearsome. So let’s say you spin the dials on a time machine to 66.5 million years ago and you travel back to the late Cretaceous period.

There’s the tyrannosaurus hunting the triceratops. There’s the alamosaurus, one of the largest creatures to ever walk the earth. There’s the tank-like ankylosaurus crushing opponents with its wrecking-ball tail. And just as you settle down on one particular evening, there’s a brand-new star in the northern hemisphere sky.

The star won’t flash, flare up, or blaze across the horizon. It will appear as stationary and as twinkly as all the others. But look again a few hours later and you might think this new star seems a little brighter. Look again the next night and it will be the brightest star in the sky. Then it will outshine the planets. Then the moon. Then the sun. Then it will streak through the atmosphere, strike the earth, and unleash 100 million times more energy than the largest thermonuclear device ever detonated. You’ll want to pack up your tent before then. And maybe move to the other side of the planet.

The day the Chicxulub asteroid slammed into what is now a small town on Mexico’s Yucatán peninsula that bears its name is the most consequential moment in the history of life on our planet. In a prehistoric nanosecond, the reign of the dinosaurs ended and the rise of mammals began. Not only did the impact exterminate every dinosaur save for a few ground-nesting birds, it killed every land mammal larger than a raccoon. In a flash, Earth began one of the most apocalyptical periods in its history. Could you survive it? Maybe.

If you make camp on the right continent, in the right environment, and you seek out the right kind of shelter, at the right altitudes, at the right times, you might stand a chance, says Charles Bardeen, a climate scientist at the National Center for Atmospheric Research who recently modeled the asteroid’s fallout for the Proceedings of National Academy of Sciences. Of course, even if you are on the opposite side of the world at the time of impact—which is the only way you can hope to make it out alive—he recommends you act quickly. As soon as you hear its sonic boom (don’t worry—you’ll be able to hear it from the other side of the world), get yourself to high ground and find underground shelter. Immediately.

You might think this sounds a bit alarmist. If you’re on the opposite side of the world—which you should be—why do you need to duck and cover from a city-sized rock landing 10,000 miles away? But you wouldn’t be the first to make the mistake of underestimating an asteroid. The cataclysmic risk posed by asteroids wasn’t well understood until World War I. Before then, most astronomers operated under the blissful naivete that massive impacts like Chicxulub were simply not possible.

When Galileo trained his telescope on the moon in 1609 and discovered perfectly circular craters dominating its topography, astronomers began to wonder how they formed. A few astronomers, like Franz von Gruithuisen, an early-19th-century German, proposed asteroid impacts as the cause. But most rejected this theory based upon one simple, supremely confounding fact: The moon’s craters are almost perfect circles. And, as anyone who has thrown a rock into dirt can tell you, that isn’t what an impact scar should look like. Instead, the mark will be oblong, oval, and messy. (Gruithuisen probably didn’t help his cause by also claiming to have seen cows grazing upon moon grass in these craters.) Further misleading any theorists, astronomers could make out little mountains in the center of each depression. Thus, for 300 years the majority of astronomers and physicists believed that (1) cows did not graze upon moon meadows, and (2) lunar volcanoes, rather than meteors, had pocked its face.

Then, in the early 1900s, astronomers like Russia’s Nikolai Morozov * began observing newly developed high explosives and made a rather startling discovery: Large explosions differ from thrown rocks in a number of ways, but most ominously—at least for our species’ continued existence—they leave circular craters regardless of their angle of impact. As Morozov wrote in 1909 after conducting a series of experiments, asteroid impacts would “discard the surrounding dust in all directions regardless of their translational motion in the same way as artillery grenades do when falling on the loose earth.”

*Morozov’s biography reads a little like The Count of Monte Cristo if you replace revenge with science. He spent 25 years as a political prisoner in a 14th-century castle turned prison on a small island outside Saint Petersburg, during which time he taught himself 11 languages and published works on everything from the structure of the atom to the geology of the Western Caucuses. Shortly after his release, he turned his attention to astronomy.

Before Morozov’s discovery, astronomers were aware that asteroids could be devastating. “The fall of a bolide of even ten miles in diameter … would have been sufficient to destroy organic life of the earth,” wrote Nathan Shaler, dean of Harvard’s Lawrence Scientific School and proponent of the volcano theory, in 1903. But most believed this was an entirely theoretical exercise, partly because, as Shaler noted in his defense of the lunar volcanism theory, the very existence of humanity proved this sort of impact could not have occurred.

Morozov’s calculations changed that. Once you know the true origins of the scars on the moon, you don’t have to be an astronomer—or even own a telescope—to arrive at the sobering conclusion that asteroids carry apocalyptic potential and that their impacts are inevitable.

Shaler was, in a way, presciently incorrect. An asteroid of nearly the size he described did impact Earth and did wipe out the planet’s dominant species. Only rather than wiping out humans it cleared the evolutionary path for a shrew-sized placental mammal to eventually crawl, walk, and consider a camping trip to the apocalypse.

You might think the survival of your shrewlike ancestor proves that a larger-brained mammal like yourself would stand a reasonable chance. Unfortunately, the shrew had a number of apocalypse-friendly adaptations humans have since lost. The shrew could survive on insects, burrow away from the heat, and had fur to warm itself during the freezing decade that followed. You could replicate some of the shrew’s survival strategies. You could burrow and expand your diet. But evolution has robbed you of others, and your opposable thumbs might not be enough to save you when that twinkling star enters Earth’s atmosphere at around 12.5 miles per second.

At impacts of that speed, Earth’s atmosphere behaves like water. Smaller rocks—called meteors—hit the atmosphere like pebbles into a pond they decelerate rapidly at high altitudes, either burning away in their friction with the air or decelerating to their low-altitude terminal velocity. But the mountain-sized Chicxulub asteroid hits our atmosphere like a boulder into a puddle. It maintains its velocity until impact, plunging through the entire 60 miles of atmosphere in around three seconds. The asteroid screeches over Central America, emitting a sonic boom that reverberates across the continents.

It falls so quickly that the air itself cannot escape. Under intense compression, the air heats thousands of degrees almost instantly. Before the asteroid even arrives, compressed and superheated air vaporizes much of the shallow sea that covers the Yucatán in the late Cretaceous. Milliseconds later, the rock plunges through what’s left and slams into bedrock at more than 10 miles per second. In that instant, a few near-simultaneous processes occur.

First, the impacting meteor applies so much pressure to the soil and rock that they neither shatter nor crumble, but instead flow like fluids. This radical effect actually makes it easier to visualize the formation of the crater, because the undulations of the earth almost exactly replicate the double-splash of a cannonballer in a backyard pool. The initial splash in all directions is followed by a delayed, vertical sploosh when the cavity created by the impactor rebounds to the surface.


Second Record-Breaking Asteroid Zipped By Earth on Friday The 13th

A few months ago I wrote an article about the closest asteroid that ever passed by without hitting us. The record-breaking event involved an asteroid named ZTF0DxQ (or 2020 QG) and it flew by us at a close distance of 1,830 miles away. What’s even more eerie was that fact that nobody saw it coming until six hours after it flew by us. (The article can be read here.)

And now, three months later, a similar event just took place. On Friday, November 13 th (coincidence…?), another asteroid narrowly missed us and scientists didn’t see this one coming either. The asteroid, that’s been named 2020 VT4, zipped by us at an incredibly close distance of just 240 miles which made it the second space rock of the year to break the record of the closest non-impact approach. To put this into better perspective, the International Space Station orbits Earth from a distance of a little more than 200 miles above us.

And if that isn’t scary enough, it wasn’t noticed by the Asteroid Terrestrial-impact Last Alert System (or ATLAS) on Mauna Loa, Hawaii until the following day – 15 hours after it passed by. Since the space rock was somewhere between 16 and 33 feet in width, it would have just burnt up in our atmosphere over the South Pacific. But it still doesn’t give us much comfort as astronomers had no warning that it was even coming.

Experts have said that in order for there to be damage to the surface of our planet, an asteroid would need to be at least 82 feet in width and for there to be global damage it would have to be between 0.6 and 1.2 miles wide. And for the human population as well as plants and animals to all become extinct, the space rock would have to be around 60 miles in width.

For example, the asteroid that killed the dinosaurs around 66 million years ago was approximately 7.5 miles across. Another comparison was that the Chelyabinsk meteor that broke up over Russia in February of 2013 that caused a decent amount of damage with shattered windows and more than 110 people being hospitalized was about 30 times bigger than the 2020 VT4 asteroid that zipped by us last week.

And 2020 VT4 won’t be the only asteroid to fly past us on a Friday the 13 th as the much larger Apophis asteroid (around 984 feet wide) is suppose to do a close flyby on Friday, April 13, 2029. (A frame-by-frame image of 2020 VT4 traveling through space can be seen here.)


A small, car-sized asteroid just gave Earth a close shave

A newly spotted asteroid about the size of a car flew harmlessly past Earth this morning (April 12).

Astronomers calculated the asteroid, dubbed 2021 GW4, to be about 14 feet (4 meters) across — much too small to survive a journey through Earth's atmosphere if it were ever on course to collide with our planet, according to NASA.

But at its closest, at about 9 a.m. EDT (1300 GMT), the asteroid was about 16,300 miles (26,200 kilometers) away from Earth — less than one-tenth the distance between the Earth and the moon, and quite close as far as asteroid approaches go. The average distance between the Earth and moon is about 238,855 miles (384,400 km).

Today's visit is as close as the asteroid will come for the next century, according to early NASA calculations of the object's orbit, a nearly two-year loop around the sun.

2021 GW4 was first spotted on April 8 by astronomers at Mt. Lemmon Survey, which is part of a high-powered asteroid discovery project called the Catalina Sky Survey, which has already identified more than 500 asteroids this year, according to NASA's Center for Near Earth Object Studies.

To date, NASA has identified more than 25,500 near-Earth asteroids, most of which are too small to pose any threat to Earth. Their discoveries are simply bonuses as scientists carefully search for larger space rocks.