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Guide to Things That Could Hit the Earth

Updated on August 19, 2013

Comets, meteoroids and asteroids

This lens is very schizoid. The first half is literally about a disaster that could end the world and the second half is as romantic as gazing at the moon with your loved one or ones. These two very different moods -- pain and pleasure, curse and blessing -- are very much linked. When we look into the night sky and see a nova or shooting star, we don't stop to think that that nova may be another civilization's sun and billions of people are dying nor do we consider that the shooting star that we wish upon may land or its impact may kill a lot of people elsewhere on Earth. We are only thinking of romance or the ooh and ahh excitement of fireworks.

It is okay to feel excitement or romance. I am not trying to spoil the magic for you. Au contraire mon frere. I am adding to the mystery and wonder and deepening the mix of emotions to add sympathy for people we know not. And if we knew them, then we would try to help them -- just as we wish they would help us if our star went nova or if a planet killer too large to deflect or detour was headed to destroy the Earth.

Only a few short years ago, such ideas would have been laughed at as fantasy. Now after Jupiter was struck by a comet and the Earth has had a few close calls, even my own family and even otherwise short-sighted members of Congress are demanding to know what measures are being taken to insure our survival. So we can relax a little and let the romance and excitement return. But now we are a little bit wiser.

It also turns out that ordinary people have an important role to play as spotters. Professional astronomers very much depend upon the accurate observations of amateur astronomers like you in order to know what to train the big telescopes upon, so you at home -- do not let them down!!!


The first part of this lens is coverage of the historic event of the 15th of February 2013 when the Russians were treated to sights in real life that everyone wishes were only in the movies. Fortunately the Russians saw nothing like the K-T extinction that the dinosaurs saw (there is a video of that here, just look) or you would not be reading these words. And nothing like the movie Deep Impact. I was working on this lens before 2012 DA14, when that asteroid was upstaged by a once in a century rock that, according to Nova, Earth hit rather it hitting Earth. This rock was orbiting the sun when Earth came along and struck it.

The second part of this lens begins with the section called comets and is for anyone who is clueless and wants a clue. It pretty much assumes that you have near zero knowledge of astronomical objects that move faster than stars, planets and moons.


This artist's conception shows the impact of a hypothetical planet that was destroyed when it collided with Earth to form the Moon. You will never again look at the moon quite the same way.

Credit: NASA/GSFC.

Meteor Strike | NOVA (premieres Wed. March 27th at 9/8c on PBS)

A blinding flash of light streaked across the Siberian sky, followed by a shuddering blast strong enough to damage buildings and send more than 1,000 people to the hospital. Within days, armed with this unprecedented crowd-sourced material, NOVA crews hit the ground in Russia along with impact scientists as they hunted for fragments from the explosion and clues to the meteor's origin and composition. Their conclusions add up to a chilling picture of how close we came to a far worse disaster.

Nova: Meteor Strike

2012 DA14 - Historic Event: It was not discovered by professional scientists but by amateur astronomers.

2012 DA14 - Historic Event: This is the asteroid's closest shave ever.

2012 DA14 - Historic Event: This is the closest fly-by of any rock this large since records of asteroids began.

2012 DA14 - Historic Event: Russian meteor probably coincidence (maybe not).

Did 2012 DA14 hit Russia?


What hit Russia on Friday morning?

A rock.

Was it one meteor or a shower?


Is it connected with the asteroid 2012 DA14 close pass on Friday night?

No. Both the Royal Astronomical Society and the European Space Agency agree on this.

Editor's Note -- I am not sure which is more disturbing. That it was unrelated and we didn't see it coming is bad. If it had been connected with 2012 DA14, then we would have to worry about its kin folk dropping by and setting a spell. Also bad.

Explanation: Comets are basically dirty snowballs. After comets evaporate and boil off all their water (and other volatiles) from going around the Sun for millions of years, what is left is rocks. These rocks continue to follow the orbit of the comet but we call them meteor showers. Asteroids are rocks with a similar origin. This is why when you see one rock, it is probably part of a family. Meteor showers can be identified by the last part of the name "-ids" such as The Leonids. The most notable asteroid families are those with 4 Vesta (The Vestians), 15 Eunomia (The Eunomians), and 8 Flora (The Florians). Trojans are not a specific population of asteroids but a description of a type of asteroid that orbits near a planet or moon near its L4 and L5 Lagrangian points. Meteor showers of dust-sized particles are fun to watch in the night sky. Asteroid showers of Russia-sized planet killers are no fun to watch in the day sky -- if you can even see the one that has your name on it.

2012 DA14 - Historic Event: Russian meteor called the biggest bolide since Tunguska.

Chelyabinsk as seen by Landsat 7.


Miass River in Chelyabinsk


Kirova Street, Chelyabinsk


Dash cams are common at least in this part of Russia which is why there are so many videos of it.



Meteorite Russian Urals Chelyabinsk cameras register the moment of explosion

first scene shows reaction of people

second scene shows door blown in


What was the death toll in Russia?

Zero. Some reports said thousands injured, but here are more reliable reports. Mikhail Valerevich Yurevich is the current governor of Chelyabinsk Oblast, the region affected. Governor Yurevich said that about 950 people sought medical attention in the city of Chelyabinsk alone. Of this number, at least 110 have been hospitalized. Two are in "heavy condition". According to the Emergency Ministry, 159 of the injured are children.


What is the relation between the Russian meteor and the point on Earth closest to 2012 DA14 at its closest?

The time difference between point B on the map Chelyabinsk, Chelyabinsk Oblast, Russia and point A on the map Pematangsiantar, Sumatra, Indonesia is: +1:0 hours. Both points are above the equator. In videos of the Russian meteor, it is seen to pass from left to right in front of the rising sun, which means it was traveling from north to south. Asteroid 2012 DA14's trajectory is in the opposite direction, from south to north.



What do we do if we spot something big heading for Earth?

Depends on who you are. If you are an amateur astronomer, then you report it to Spaceguard. Why? One, when the authorities act, this will save your life, the lives of your loved ones, the world's population and most importantly my life. Two, you have the privilege of naming the object. Three, like in that movie Deep Impact, you could be one of the few who gets evacuated. Four, if you are protective of your privacy, the authorities will respect that. Or you can report your sighting anonymously and let someone else take the credit.

If you are a bad person, then you can start a doomsday cult. However, this action will embarrass your family and you will probably cross some legal line and end up shot by a SWAT team sniper and the object rock never hits the Earth.

If you have panic attacks or anxiety attacks, then Google the words: "How to stop a panic attack".

If you think that the authorities will let most of the population get killed, then build something to escape the Earth. I have thoughtfully included links to help you with rational courses of action. Ultimate Screaming Lessons by Uri Nieto while funny is not useful unless the Earth survives and there is a need for metal rock singers who can scream on key.

3 Ways to Save Earth from an Asteroid

Science Show Hank gives us the skinny on three plans NASA scientists have come up with to save Earth from an asteroid impact. Hopefully we'll never have to use any of them.

Editor's Note -- I always get him confused with SIdeshow Mel.

2012 DA14 - Historic Event: Skyfall but a civil defense drill is planned

The bad news is that the drill will not be until 2022. The good news is that NASA will not be in charge. Not only have they lost shuttles in movies but in real life too.


2012 DA14 - Historic Event: A meteor causes injuries.

I know that big organizations are watching for big asteroids. Is anyone watching for small meteors like the Russian meteor?


Has a meteor ever killed anyone?

No. But it has been claimed a couple of times without conclusive proof.


Photographer: Jiang

Kehong/Xinhua/Zuma Press

Russian Meteor and Near-Earth Asteroid DA14's Paul Cox and Bob Berman discuss Near-Earth Asteroid 2012 DA14 and the Russian Meteor that caused widespread damage and injured around 500 people earlier today.

Later there are live images of Near-Earth Asteroid 2012 DA14 direct from the robotic telescopes in the Canary Islands.

the Russian meteor

Never mind Spaceguard. Never mind the big rocks. B612 and other organizations are moving to take care of the planet killers. I am worried about the little rocks that might hit my town. While they are worried about New York and Tokyo and London and big cities like that, no one really cares about the small rural towns. That Russian meteor managed to get through all those eyes on the sky, human and machine, and surprised everyone.

So my question is: Who is watching for the small rocks?

Answer: You are. Volunteers and civilians. I have a link to the organizations that they belong to.

historic event wrap-up - Russian meteor

two satellite images of the meteor and something not quite a crater but caused by debris fall from the meteor


Comets are mostly water ice and other volatiles and usually (not always) leave a tail always blowing away from the Sun when they are near it. "Near" means generally once inside the orbit of Mars because it is warmer in the Inner Solar System and colder in the outer Solar System -- too cold for the ice to melt and leave a tail. The way to remember the difference is to recall Halley's Comet or any famous comet and think to yourself: "Yeah, famous because they have a long tail and sometimes can be seen during the daytime. And back in history comets even caused panics because people didn't know what they were."

Comets come from the Oort Cloud which is the the outermost part of the Solar System with physical objects -- aside from the heliopause which is where interstellar space begins.





Comets have often been called dirty snowballs. There is a lot truth to this.


The way to tell the others apart is to look at the suffix or ending (or lack of it).

Asteroids are generally found in the Main Asteroid Belt. Everything you are asking about other than a comet is mostly rock. Asteroids tend to be very big rocks. Some are the size of big boulders, some the size of mountains and the biggest Ceres qualifies as a dwarf planet and is spherical (round like any globe). There are asteroids outside the Main Asteroid Belt. The biggest collection of asteroid-like objects is in the Kuiper Belt but I warn you that professional astronomers have a whole collection of strange names for these objects. It can be confusing unless you are into celestial mechanics, orbital dynamics and classification. Jupiter attracts a lot of incoming asteroids (so does Saturn) and they go into orbit around the outer planets. If asteroids bump into each other enough, they may accrete (clump together from weak gravity) and between friction, melting of rock, and churning of material end up round. But instead of becoming a dwarf planet like Ceres, they become moons. Despite being smaller than Jupiter, Saturn has been able to catch asteroids before they get to Jupiter (and they accrete into moons) and thereby keep up with Jupiter as far as having the most moons. Mars has two misshapen moons (not round) that are obviously captured asteroids and, like Jupiter, there are asteroids that are in Lagrangian type orbits with respect to Mars. This is true of Earth also. Many people are unaware that technically Earth has more than one moon. However, THE Moon (more properly called Luna) has a regular round orbit around Earth and regular round orbits around a planet are a qualification for a large object to be called a moon. There are exceptions and a few round moons in the Solar System have irregular orbits and a few irregular (misshapen) moons in the Solar System have round (regular) orbits. I am over-simplifying for clarity. A professional astronomer would dock me points for precision.

Asteroid Eros

Asteroid Gaspra

KT Asteroid Impact

Visualization of asteroid impact that killed dinosaurs sixty-five million years ago, based on accurate research and scientific fact. Created by Radek Michalik ( at the Science Institute of Columbia College in Chicago.


One last comment before moving on to the other objects: People like you and me are interested in these objects because if a large one smacks into where you are standing, then you could be pretty dead. On the other hand, if you are invested in a space mining company that hollows out one of these threats, then you could be pretty rich.

The K-T Event - What Really Happened To The Dinosaurs?


artist's depiction of the rock that killed the dinosaurs and left a crater off the Yucatan peninsula

KT Mass Extincton


The "-oid" suffix or ending tells you that they are found only in space. Asteroids and meteoroids and micro-meteoroids are all only in the void of space. If your spaceship runs into micro-meteoroids the size of a grain of sand, it could shatter your windshield or go through you like a bullet or cause explosive decompression. You have probably seen movies where some nut opens an airlock in space or a door on an airliner during flight and the other passengers are upset -- they can't breathe and passengers get sucked out of the cabin. For this reason, airlines frown on nuts bringing their assault weapons on planes and a similar ban will probably exist for spacelines.

[Late breaking news: Only in America does common sense get overruled by insanity. TSA Will Lift Ban Of Small Knives. This has nothing to do with space rocks but everything to do with rocks in our airheads and politicians.]


If you want to see a meteor shower, just ask your local reference librarian for help finding the nearest amateur astronomers club. They will be happy to tell you dates and times. Planetariums and astronomy teachers also know this information. If you watch the weather on TV, then you often hear local and national weather forecasts giving this information.

Meteors leave streaks that generally last less than a second in the night sky. Blink and you miss it. If a meteor is large and slow-moving and hits the atmosphere at a shallow angle, then it makes the local news and can be seen during the day. People are better informed these days and no longer call them UFOs. Remember, meteor has no special suffix or ending and that is how you know it is the rock in the sky -- not space and not on the ground.

Meteoroid, Meteor and Meteorite

Meteoroid, Meteor, and Meteorite

Speaking of which, meteorites are found on the ground. The easy way to remember, is to look at the suffix "-ite". The moment any rock from out there touches the ground, it becomes a meteorite. Another way to remember is to think of pyrite (Fool's gold), painite (one of the rarest and most valuable gems), taaffeite (another rare and valuable gem), malachite (another rare and valuable gem), graphite (pencils), granite (memorials and other uses), quartzite (contains quartz), and calcite (calcium carbonate, CaCO3). All these are just rocks to a geologist and all have the same suffix. You can even buy a meteorite on eBay and at a geology shop. If you want to buy a rock that came from outer space, then buy them from a reputable dealer who won't pass off a rock that has never traveled as a space rock.

To recap, "-oid" means it is in space (asteroids and meteoroids). A micro-meteoroid is simply a small meteoroid. The suffix "-ite" means that it has hit the ground. And the ground does not have to be on Earth. It can be the lunar surface, the Martian surface or the surface of any planet or large moon. [Small moons might be called big rocks like asteroid and so that is why I worded it that way.] A word like meteor has no suffix and that tells you that it is neither space nor ground but sky. Comet does not have the root word "-meteor-" and so you know it is not primarily a rock. Most things in the Solar System are either rock or ice. That ice is not always water ice. It can be dry ice, methane ice, ammonia ice and other kinds of volatile liquids and gases. This is important for you to know because now you understand that the Sun melts the ice and the comet starts leaving a tail blown by the supersonic solar wind. This wind blows so fast that the tail always points away from the sun even after a comet has rounded the sun and is headed back to the Oort Cloud to rejoin its fellow comets. The way to remember comet apart from asteroid, meteoroid, meteor and meteorite is that it is spelled very different and the word ends in the letter T. T stands for tail. The others don't have tails.

Here is where you say: "But meteors leave a streak." Yes, but that is not a tail. A comet tail lasts for weeks and even months. And then you say: "What about that meteor during the daytime that left a trail across the sky from horizon to horizon?" Trail not tail. Remember how airliners and high-altitude Air Force bombers leave condensation trails or contrails? That is not a tail. Why? I don't know. It is a reasonable comparison except by definition, comet tails are always in space and meteor streaks or trails are always in the atmosphere. The chemical composition may be different also. That is important because meteor burst communications uses ionized meteor trails to propagate signals between radio stations normally too distant to contact. While spectacular meteor showers are rare, lesser known meteor showers are continually pelting the Earth. Comet and their tails are so infrequent and usually so distant when they come through that using them to bounce signals is unreliable.

See? You are smarter than you give yourself credit. You questioned the answer and were thinking like a scientist who observes and notices similarities and differences. Give yourself an A plus.

As a reward for your courage in asking a question, here are the general times of meteor showers. Real simple: every month except February and March in the Northern Hemisphere. And even those months you might get lucky. Experienced meteor shower observers talk about peak times. Like with rain, it starts off slight, gets heavier and then slacks off again. November has several groups of meteors coming through: The Taurids, Andromedids, Alpha Monocerotids and Leonids. There are not only peak nights but peak hours during a given night so ask your local astronomy club what that time slot is (9 pm to 10pm versus 2am to 3am for example). If you live in a cloudy or rainy area, then don't bother. Either travel to a cloudless place or let it go.

No video does it justice. Don't expect anything resembling fireworks or like in the movies. It is not like that. It is simply a streak that lasts less than a second. But as someone who has seen meteors, I can testify that it is a cool experience and it is worth your effort to see under good observing conditions. Good observing conditions are way out in the boondocks away from city lights and picking a night when the weather forecast is for not a cloud in the sky. Dress warm in cold weather and dress cool in hot weather and bring what you need (food, necessities and bug spray) and take your trash with you when you leave to properly dispose of it. I suggest you do this activity with people you care about because some people like to wish upon a star.

P.S. Meteors are not falling stars. A real star would destroy the Earth.

What are Meteors, Meteoroids, and Meteorites?


Is this how the Pacific Ocean was formed?

Is this how Earth came to have one moon instead of two?

Meteors, Meteoroids and Meteorites.

Editor's Note -- The audio is about meteoroids and small asteroids but the video depicts an asteroid large enough to cause a global fire storm and leave behind the Pacific Ocean and what volcanologists call The Ring of Fire.



Image Credit: Wally Pacholka/

The Most Important Thing

We cannot see the far side of Earth's orbit around the Sun because the Sun and its blinding light is in the way. If a killer comet approached from that direction, it would not be visible until too late and even then, in the last few moments after our radar and other instruments had finally picked it up, it would be in the daytime sky still hidden in the glare of the High Noon sunlight and then----

The Sun

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    • Toni-Roman profile imageAUTHOR


      4 years ago

      @Namsak: Despite my sometimes dwelling on dismal topics, I always try to offer a solution to the worst of the worst case scenarios. On the day of writing this reply, another large asteroid nearly side-swiped the Earth.

      However, there is cause to breathe a little easier about the rocks that come in during the day from the direction of the Sun. Scientists are working on that particular problem right now and there is at least one foundation (maybe two) ready to supply funding for a sentinel or deep space monitor to be launched and put in a parking orbit or some other type of solar orbit so that it can keep an eye out for "unwelcome guests".

      Now roll over and go back to sleep. They gotcha covered . . .

    • profile image


      4 years ago

      Awesome lens. It's possible that a few thousand years ago that a meteor that hit Estonia killed people, although it's not known with certainty. Today there are multiple craters, the largest is called Kali.

    • profile image


      5 years ago

      Very detailed, very interesting and very scary lens! As you say it is likely that the one that gets us will go unnoticed until it hits. It is just as well we don't dwell on such things or we would be in a state of constant fear because it isn't a case of 'if' it is a case of 'when' it will happen.

    • greenmind profile image

      GreenMind Guides 

      5 years ago from USA

      Cool topic, lots of great images. But I'm going to try not to think about it too much....


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