Top 10 Meteorites

It's a little bit terrifying to think that there are giant rocks, flying straight at our planet, on a regular basis, but it's true.

Good thing we've got our atmosphere to help fry the occasional wayward piece of asteroid or comet as it heads our way … but once in a while, and handful (or more) make it through and we get everything from pretty shooting stars to terrifying meteor fireballs, not to mention the occasional nice-looking extraterrestrial rock.

1: Tunguska Event

The meteor that flew through the earth's atmosphere in 1908 over Siberia exploded just a few miles from the Siberian surface.

The explosion had the force of an atomic bomb and flattened some 800 square miles of trees. It took years for scientists to begin investigating in the remote, unpopulated area; one hundred years later, they're still looking for conclusive evidence of a strike, in the form of a crater or meteor fragments.

Some now believe a nearby lake may conceal a crater. And recently, some decidedly stranger theories on Tunguska have popped up, with one claiming an alien spaceship destroyed the earth-bound comet just before it hit in an attempt to spare our planet destruction. Huh.

Special Honorable Mention: KT Extinction meteorite

You know, it's the asteroid that may have killed the dinosaurs … and over half off all the species on the planet. Scientists aren't 100 percent sure that an asteroid caused the so-called "K-T Extinction", but they have some good reasons to believe that the culprit came from outer space.

Most of the soil deposited during the time of the extinction (known as the K-T layer) has an awful lot of Iridium in it, something that isn't so common on earth, but it sure is on asteroids.

Scientists figure sometime around 65 million years ago, the earth was hit by one or more Iridium-filled meteors or comets, triggering atmospheric dust and widespread climate change. And where did this massive meteorite hit?

No one's sure, but some researchers believe a crater on the Yucatan peninsula in Mexico may mark the spot.

2: Hoba Meteorite

Weighing in at, oh, sixty tons, the Hoba meteorite, which still resides where it touched down in Namibia, is the largest known meteorite on the planet. The flat slab of iron fell to earth sometime around 80,000 years ago, so we don't really know what kind of pyrotechnic show accompanied its arrival, but it took until 1920 for humans to come across it, when a farmer plowing his field came across its metallic top just below the surface. Since then, the Hoba site has become a national monument, drawing thousands of visitors each year.

3: Willamette Meteorite

Weighing in at somewhere around 15 tons and ten feet tall, this massive, pitted iron meteorite is believed to be the remains of the iron core of a planet that was involved in a collision billions of years ago.

It landed on our planet a mere thousands of years ago, and while it wasn't "discovered" by Westerners until 1902, the meteorite had long been revered by the Native American Clackamas tribe as a healing source called Tomanowos.

These days, Tomanowos rests at the American Museum of Natural History in New York City (as it has since 1906), but the tribe recently struck a deal with the museum, allowing the meteorite to remain on display so long as the Clackamas can visit for ceremonial purposes.

4: Sikhote-Alin

When this massive iron meteor roared out of the sky in February of 1947, witnesses said it was brighter than the sun. And when an explosion ripped it apart as it fell to earth, it rained down fragments across a half-mile square in the Sikhote-Alin mountains in Siberia.

The entry and explosion were visible as far as two hundred miles away. Over the years, meteorite hunters have descended on the area in search of the distinctive, slightly metallic, pock-marked, twisted and curved iron speciments.

Smaller Sikhote-Alin fragments are still selling today. Get yours while they last.

5: Sylacauga/Hodges Meteorite

Sometime in the fall of 1954, while a 31-year-old Alabama housewife named Ann Hodges napped on her sofa, an eight-and-a-half pound meteorite was roaring through the sky.

Moments later, it smashed through her roof and smacked her on the hip. That'll teach you to sleep on the job (kidding).

Luckily, Hodges was left bruised but otherwise unharmed by the grapefruit-sized rock, which her neighbors described as a fireball shooting through the sky. Hodges became a minor celebrity and later donated the meteorite to the Alabama Natural History Museum.

More recently, a German boy claimed he too was hit by a meteorite while walking to school in June of this year. The 14-year-old German student said he saw a flash of light just before he was hit by the pea-sized meteor. Who knew a pebble could be so dangerous?

6: ALH 84001

It's such a catchy-sounding name, right? Well, the actual meteorite is far more impressive than its generic-sounding name.

ALH 84001 (let's call it "Al" for short) was discovered in Antarctica in 1984, some 13,000 years after it arrived from Mars.

Yes, Mars.

Al was born from the lava of a Martian volcano about four and a half billion years ago. It then sat on the Martian surface until about 15 million years ago, when another asteroid or meteorite knocked it free, sending it hurtling towards earth, where it landed in the Allan Hills of Antarctica.

Buried inside Al was evidence of possible early Martian life, in the form of fossilized remains of what may have once been some very, very small bacteria. It turns out Al was kind of an interesting guy, for a rock.

7: Orgueil Meteorite

The Orgueil meteorite burned through the atmosphere in May of 1864, disintegrating into 20 pieces on its way to Orgueil, France.

The fragments were soft enough to be cut with a knife and soon the Orgueil samples had made their way to museums around the world.

Since then, the Orgueil meteorite's caused nothing but controversy, with scientists speculating that its organic material might be proof of extraterrestrial life and puzzling over what looked to be fossilized remains in the meteor. Exciting stuff right?

Not really. While the meteorite itself was real, its signs of life were a fraud.

The culprit? Some pollen seeds glued onto the space stone with a little coal dust. Not so out of this world at all.

8: Peekskill Meteorite

In 1992, the Peekskill meteorite streaked across the sky in a greenish blaze from Kentucky to Pittsburgh, all the way to Peekskill, NY , where it attacked a perfectly innocent parked car.

The 1980 Chevy Malibu, which survived with only a massive dent and later went on to tour the world as the car who survived a meteorite attack. While the meteorite had impeccable aim, it was otherwise quite ordinary: about the size and weight of a bowling ball, although not so round, and made up of the most common type of meteorite stone.

What was unusual was the degree to which the Peekskill meteor was studied. Because its trail took it across much of the east coast, its path and trajectory were caught on video and analyzed by scientists, making its orbit, entry and impact one of the most analyzed ordinary meteor strikes ever.

9: Murchison Meteorite

The Murchison meteorite broke into hundreds of pieces as it fell over Australia in September of 1969.

The largest of the pieces was over one hundred pounds, while the smallest were less than one pound.

It streaked to the ground in a massive fireball, trailed by a hazy tail, before it broke into fragments… and those fragments have been extensively studied ever since.

It turns out that the Murchison meteorite contains a wide array of amino acids, the building blocks of life, making them of particular interest to curious astrobiologists.

10: Allende Meteorite

The Allende meteorite that crashed to earth in 1969 over Mexico broke up into hundreds of fragments that, all put together, would weigh several tons. Since then, those fragments have become collector's pieces.

Many of the black stone pieces are covered by a glassy exterior formed by the high temperatures during entry into our atmosphere, and scattered throughout Allende's ancient fragments (the meteor contains particles that may be older than the solar system) are olivine and even microscopic diamonds.

After all, why should stars be the only ones who get to sparkle?

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Top 10 Strangest Things in the Universe

The more we look among the stars and galaxies, the weirder things seem to get.

Even space itself is puzzling, for example. Recent studies suggest that the fabric of the universe stretches more than 150 billion light-years across -- in spite of the fact that the cosmos is 13.7 billion years old.

From super-fast stars to the nature of matter, here we cover other strange and mysterious elements of the universe.

10. Hypervelocity Stars

If you've ever gazed at the night sky, you've probably wished upon a shooting star (which are really meteors).

But shooting stars do exist, and they're as rare as one in 100 million.

In 2005, astronomers discovered the first "hypervelocity" star careening out of a galaxy at nearly 530 miles per second (10 times faster than ordinary star movement).

We have ideas about what flings these rare stars into deep space, but aren't certain; anything from off-kilter supernova explosions to supermassive black holes might be responsible.

9. Black Holes

Speaking of black holes, what could be stranger?

Beyond a black hole's gravitational border -- or event horizon -- neither matter nor light can escape. Astrophysicists think dying stars about three to 20 times the mass of the sun can form these strange objects. At the center of galaxies, black holes about 10,000 to 18 billion times heavier than the sun are thought to exist, enlarged by gobbling up gas, dust, stars and small black holes.

What about mid-sized types? Perhaps surprisingly, evidence is both scarce and questionable for their existence.

8. Magnetars

The sun spins about once every 25 days, gradually deforming its magnetic field.

Well, imagine a dying star heavier than the sun collapsing into a wad of matter just a dozen miles in diameter.

Like a spinning ballerina pulling his or her arms inward, this change in size spins the neutron star -- and its magnetic field -- out of control.

Calculations show these objects possess temporary magnetic fields about one million billion times stronger than the Earth's. That's powerful enough to destroy your credit card from hundreds of thousands of miles away, and deform atoms into ultra-thin cylinders.

7. Neutrinos

Pull out a dime from your pocket and hold it up for a second… guess what? About 150 billion tiny, nearly massless particles called neutrinos just passed through it as though it didn't even exist.

Scientists have found that they originate in stars (living or exploding), nuclear material and from the Big Bang. The elementary particles come in three "flavors" and, stranger still, seem to disappear on a whim.

Because neutrinos occasionally do interact with "normal" matter such as water and mineral oil, scientists hope they can use them as a revolutionary telescope to see beyond parts of the universe obscured by dust and gas.

6. Dark Matter

If you put all of the energy and matter of the cosmos into a pie and divvy it up, the result is shocking.

All of the galaxies, stars, planets, comets, asteroids, dust, gas and particles account for just 4 percent of the known universe. Most of what we call "matter" -- about 23 percent of the universe -- is invisible to human eyes and instruments.

For now.

Scientists can see dark matter's gravitational tug on stars and galaxies, but are searching feverishly for ways to detect it first-hand. They think particles similar to neutrinos yet far more massive could be the mysterious, unseen stuff.

5. Dark Energy

What really has everyone on the planet confused -- including scientists -- is dark energy.

To continue with the pie analogy, dark energy is a Garfield-sized portion at 73 percent of the known universe. It seems to pervade all of space and push galaxies farther and farther away from one another at increasingly faster speeds.

Some cosmologists think this expansion will leave the Milky Way galaxy as an "island universe" in a few trillion years with no other galaxies visible.

Others think the rate of expansion will become so great that it will result in a "Big Rip." In this scenario, the force of dark energy overcomes gravity to disassemble stars and planets, the forces keeping particles sticking together, the molecules in those particles, and eventually the atoms and subatomic particles. Thankfully, humankind probably won't be around to witness to cataclysm.

4. Planets

It might sound strange because we live on one, but planets are some of the more mysterious members of the universe.

So far, no theory can fully explain how disks of gas and dust around stars form planets -- particularly rocky ones.

Not making matters easier is the fact that most of a planet is concealed beneath its surface. Advanced gadgetry can offer clues of what lies beneath, but we have heavily explored only a few planets in the solar system.

Only in 1999 was the first planet outside of our celestial neighborhood detected, and in November 2008 the first bona fide exoplanet images taken.

3. Gravity

The force that helps stars ignite, planets stay together and objects orbit is one of the most pervasive yet weakest in the cosmos

Scientists have fine-tuned just about every equation and model to describe and predict gravity, yet its source within matter remains a complete and utter mystery.

Some think infinitesimal particles called gravitons exude the force in all matter, but whether or not they could ever be detected is questionable.

Still, a massive hunt is on for major shake-ups in the universe called gravitational waves. If detected (perhaps from a merger of black holes), Albert Einstein's concept that the universe has a "fabric" of spacetime would be on solid ground.

2. Life

Matter and energy abound in the universe, but only in a few places is the roll of the cosmic dice perfect enough to result in life.

The basic ingredients and conditions necessary for this strange phenomenon are better understood than ever before, thanks to abundant access to life here on Earth.

But the exact recipe -- or recipes -- to go from the basic elements of carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur to an organism is a prevailing mystery.

Scientists seek out new areas in the solar system where life could have thrived (or still may, such as below the surface of watery moons, in hopes of arriving at a compelling theory for life's origins.

1. The Universe

The source of energy, matter and the universe itself is the ultimate mystery of, well, the universe.

Based on a widespread afterglow called the cosmic microwave background (and other evidence), scientists think that the cosmos formed from a "Big Bang" -- an incomprehensible expansion of energy from an ultra-hot, ultra-dense state.

Describing time before the event, however, may be impossible.

Still, atom smasher searches for particles that formed shortly after the Big Bang could shed new light on the universe's mysterious existence -- and make it a bit less strange than it is today.

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Life of the Sun

The Sun is a perfectly normal example of a star, formed from the solar nebula 4.6 billion years ago.

The Birth of the Sun

The Sun (and all the planets) started their lives in a giant cloud of cold molecular gas and dust. And then about 4.6 billion years ago, something bumped into the cloud, like the gravity from a passing star, or shockwaves from a supernova, causing the cloud to collapse. With the collapse, the mutual gravity from the particles in the cloud pulled together, and formed pockets of denser material in the cloud. These were star forming regions, and one of them was to become the Solar System.
As the cloud collapsed, conservation of momentum for all the particles in the cloud made it start spinning. Most of the material ended up in a ball at the center, but this was surrounded by a flattened disk of material. The ball at the center would eventually form the Sun, while the disk of material would form the planets. The Sun spent about 100,000 years as a collapsing protostar before temperature and pressures at the core ignited fusion at its core. The Sun started as a T Tauri star – a wildly active star that blasted out an intense solar wind. And then, just a few million years later, it settled down into its current form. The life of the Sun had begun.

The Main Sequence

The Sun, like most stars in the Universe, is on the main sequence stage of life. Every second, 600 million tons of hydrogen are converted into helium in the Sun’s core, generating 4 x 1027 Watts of energy. For the Sun, this process got going 4.6 billion years ago, and it has been generating energy this way every since. But there isn’t an unlimited amount of hydrogen in the core of the Sun. In fact, it’s only got another 7 billion years worth of fuel left.

As the Sun creates more helium at its core, the Sun burns a little more hydrogen. This causes the output of the Sun to go up. You won’t notice it now, but in about a billion years, the output from the Sun will have increased by 10%.

A more luminous Sun is bad news for Earth.

In 1.1 billion years from now, the Sun will be 10% brighter than it is today. This extra energy will cause a moist greenhouse effect in the beginning, similar to the runaway warming on Venus. But then the Earth’s atmosphere will dry out as the water vapor is lost to space, never to return.

In 3.5 billion years from now, the Sun will be 40% brighter than it is today. It will be so hot that the oceans will boil and that water vapor will be lost to space as well. The ice caps will permanently melt, and snow will be ancient history; life will be unable to survive anywhere on the surface of the Earth. The Earth will resemble dry hot Venus.

The Death of the Sun

All things must end. That’s true for us, that’s true for the Earth, and that’s true for the Sun. It’s not going to happen tomorrow, but one day in the far future, the Sun will run out of fuel and end its life as a main sequence star and die.

In about 6 billion years, the Sun’s core will run out of hydrogen. When this happens, the inert helium ash built up in the core will become unstable and collapse under its own weight. This will cause the core to heat up and get denser. The Sun will grow in size and enter the red giant phase of its evolution. The expanding Sun will consume the orbits of Mercury and Venus, and probably gobble up the Earth as well. Even if the Earth survives, the intense heat from the red sun will scorch our planet and make it completely impossible for life to survive.

When Will the Sun Burn Out?

Once it has become a red giant, the Sun’s death is just around the corner. It’ll still have enough heat and pressure at its core to begin a second stage of fusion, burning helium this time to form carbon. This phase will last for about 100 million years until this source of fuel is exhausted. Finally, the shell of helium becomes unstable causing the Sun to pulse violently. It will blow off a large fraction of its atmosphere into space over the course of several pulses.

When the Sun has blasted off its outer layers, all that will remain will be central core of carbon. In fact, it will be an Earth sized diamond with the mass of a star. This is a white dwarf, and it will still be hot enough to shine with thermal radiation. But it’s no longer generating solar fusion, and so it will slowly cool down until it becomes the same temperature as the rest of the Universe; just a few degrees above absolute zero. This will take about a trillion years to happen.

The Sun’s death will be complete.

Will the Sun Explode?

First, there’s no possible way that the Sun will ever explode. It might seem huge to us, but the Sun is a relatively low mass star compared to some of the enormous high mass stars out there in the Universe. When our Sun runs out of hydrogen fuel, it will expand up as a red giant, puff off its outer layers, and then settle down as a compact white dwarf star; slowly cooling down for trillions of years.

But let’s say that our Sun has about 10 times as much mass. Now we’re talking explosion. When this super massive Sun runs out of hydrogen fuel in its core, it switches over to converting atoms of helium, and then atoms of carbon. It keeps consuming heavier and heavier fuel in concentric layers, like an onion. Each layer takes a shorter period of time, all the way up to nickel, which might take a mere day to burn through.

Then iron starts to build up in the core of the star. And iron doesn’t give off any energy when it undergoes nuclear fusion. Because of this, the star has no more outward pressure in its core stopping it from collapsing inward. When about 1.38 times the mass of the Sun in iron collects at the core, it catastrophically implodes, releasing an enormous amount of energy.

Within 8 minutes, the amount of time it takes for light to travel from the Sun to Earth, an incomprehensible amount of energy would sweep past the Earth, and destroy everything in the Solar System. Supernovae can briefly shine more than an entire galaxy. A new nebula, like the Crab Nebula, would be visible to nearby star systems, expanding outward for thousands of years.

All that would remain of the Sun would be a rapidly spinning neutron star, or maybe even a stellar black hole.

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