Thursday, March 04, 2010

The Apophis Meteor, Is It A Threat?

Hello everybody. I’ve been meaning to write this blog for some time now. The topic changed since I agreed to write something. I was going to write about desertification and global warming but then I discovered Apophis. Although global warming and desertification are very serious problems and fascinating, Apophis has been fascinating me more than just about anything else except perhaps looking for a job. If you have a grant you want to spend for a possibly very interesting AIDs research problem please feel free to contact me via this blog, but for now I will write a bit about Apophis.

Apophis is not some strange new religion or devil worshiping cult I’ve gotten into. Apophis is a meteor or more accurately an asteroid due to get much too uncomfortably close to the Earth for the first time on April 13, 2029. And yes that does happen to be a Friday the thirteenth for all you triskaidekaphobics out there (If you are one you probably know what the word means. If not, look it up. This is a blog so I will assume you actually know how to look up obscure words in one of the dozen or so on-line
dictionaries.)

I found out about Apophis not because I used any extraordinary psychic abilities but I looked up asteroids on the internet. NASA has a web page,http://neo.jpl.nasa.gov/ca/, where they list near Earth objects. Near Earth objects are all the asteroids that are known to be in orbits anywhere around the sun that will come anywhere near the Earth. Ever since the theory that the dinosaurs were wiped out by a giant meteorite that hit the Earth, NASA has been funding a project employing astronomers to scan the skies looking for any nasty asteroids that threaten to hit the Earth or come anywhere close, photograph them, and plot their orbits. NASA lists not only the objects but coordinates understood by astronomers everywhere so that the astronomers can train their telescopes on the asteroids of interest.

Most asteroids orbit the sun further away than Mars and never approach Earth. Apophis is one of the asteroids with an orbit that regularly crosses the Earth’s orbit every 324 days and even crosses Venus’s orbit before heading back out to the territory beyond Mars. Some small asteroids often make an impact on Earth every day. There are groups of small meteors some of which hit the Earth every year in August and January. They may not ever impact your consciousness or you may be a regular meteorite watcher out twice a year watching the show of the meteorites burning up as they enter the atmosphere.

Usually, in an average year about 400 tons of rock impact the Earth’s atmosphere. Occasionally, a meteor is large enough to hit the surface of the Earth. Just a few months ago, a meteorite the size of a large marble hit a house and put a hole through the roof, luckily missing all the inhabitants.

As long as the asteroids remain outside of Earth’s atmosphere they are called asteroids. When they hit the atmosphere they are called meteors. If they actually survive the transit through the atmosphere and do not burn up, when they impact the ground they are called meteorites. Most meteors burn up before they ever touch the ground. If they come close to the Earth at any point or are expected to, they are called near Earth objects. If they are big enough they get names either after they hit or before.

There are thought to have been some impacts on the Earth of large meteorites some of which were thought to have changed history. Once, about some 65,000,000 years ago, a huge asteroid, somewhere about six to twelve miles in diameter, hit the Earth at Chicxulub in the Yucatan, Mexico. This ruined the day for most of the dinosaurs in its vicinity. It was also thought to have ruined the day for all of the land dwelling dinosaurs, and probably was very nearly the last day for most of the land dwelling dinosaur species except for the ancestors of modern birds. The blast when the meteorite hit caused an explosion equivalent to about as much as 100 million megatons of TNT, according to NASA’s astrobiology magazine[1]. The explosion and molten rock fragments raining back to the Earth after being thrown up by the impact were thought to have caused a huge, almost worldwide firestorm. Then the dust, soot and ashes from the impact and resulting fires precipitated an immediate and catastrophic ice age.

Apophis is a much smaller piece of rock thought to be about a quarter of a kilometer across, something like 250 meters or about 820 feet or a little less than a seventh of a mile. So although Apophis is nothing like the size of the asteroid that is thought to have wiped out the dinosaurs, you still wouldn’t want to be under Apophis if it hits the Earth.

Meteor crater in Arizona, a big hole 180 m or about 590 feet deep and 1.2 km or about 4,000 feet across is thought to have been caused by a meteorite that was somewhere between 10 to 50 m across or about 32 to 164 feet across which hit Arizona about 50,000 years ago[2]. If there was anybody in the neighborhood back then, I personally hold with some of the archaeologists who say that there are archaeological sites called preclovis which imply there were people in the Western Hemisphere prior to some 20,000 years ago, and good evidence of early migration into the U.S., so there might have been somebody in the neighborhood, but probably not. Anybody or any animals within about 24 kilometers or about 14 miles of the impact site in Arizona would have been injured and had their day ruined by the blast. Bits of molten rock thrown up by that meteorite impact have been found up to 8 miles away and caused injuries if they struck anybody or any animals and ignited brush and forest fires wherever they landed probably creating a large firestorm in the surrounding area.

There was thought to be a larger meteorite, probably some 4 km or about 2.5 miles across, much larger than the one that hit Arizona, which hit the Earth or exploded in the atmosphere some 12,900 years ago in Canada that was thought to have wiped out the Clovis culture in the U.S.[3] perhaps by wiping out all the people in the U.S. at that time. It was also thought to be large enough to have precipitated a worldwide ice age, called the Younger Dryas. This asteroid was discovered by finding a thin layer of soot and ashes overlying widely scattered prehistoric Clovis culture sites. The ashes were found to overlie a thin layer of dust which was enriched with iridium. Now iridium is found in higher concentrations in meteorites than in any Earthly soils. The layer of dust with high levels of iridium is thought to come from the asteroid itself. The layer of soot overlying the iridium layer is thought to come from widespread forest and brush fires. The fact that these layers overlie the last deposits of the Clovis culture implies that the Clovis culture ceased to exist after the meteorite strike 12,900 years ago.

So those catastrophes were caused by meteors hitting the Earth and Apophis is due to miss the Earth in 2019, why am I bothering to write about the asteroid Apophis?

The asteroid Apophis is due to come within about 20,000 miles of the Earth’s surface. It will miss hitting the Earth’s atmosphere but by astronomical distances it will barely miss the Earth’s atmosphere. Now relatively speaking, Apophis will come closer to Earth than you usually are to your tee shirt, if you are wearing your tee shirt next to your chest. Apophis will come a lot closer to the Earth than the Moon is. It will even come closer than the geosynchronous satellites.

Those geosynchronous satellites orbit around the Earth at a permanently fixed position that provide you with long distance telephone and TV service and weather reports. Now to demonstrate what keeps the geosynchronous satellites up in orbit, take a coke bottle, and fill it half full with water. Tie a string around the neck of that coke bottle and spin it around your head. If you do it right, none of the water will spill out. Now if you start twirling around while holding that string tied to the coke bottle out in front of you you will be able to spin around and twirl that coke bottle in front of you while spinning around. That coke bottle with the water in will stay in front of you all the time until you get dizzy and fall over. That coke bottle is like a geosynchronous satellite, and of course the Earth doesn’t ever get dizzy and fall over and stop spinning. You are spinning and the coke bottle is spinning around you but the coke bottle stays in front of you at all times. The water stays in the coke bottle even though if you stayed still and had someone hold that coke bottle out in front of you at the same angle all the water would pour out.

Now the orbits of the geosynchronous satellites are well known. None of them are expected to be anywhere near where Apophis is going to pass when Apophis gets here. If one of them were to be hit by Apophis, Apophis might have its trajectory altered so it hits Earth. Alternatively, it might have its trajectory altered so it will never come near Earth again. But given the speeds involved what would more likely happen is that Apophis would crumble or explode, and parts of it if not all would probably hit Earth. Just as if you were spinning that coke bottle with water in it and your brother came up and put his hand in front of the coke bottle. The water would spill all over the floor and you would get blamed for making a mess. (Hint: If you are going to try it, try it outside.)

When satellites wear out, sometimes their orbits decay. The satellites slow down and start dropping into lower and lower orbits and hitting more and more atmosphere which makes them slow down more and more and drop further into lower orbits. Now sometimes those satellites could not be steered into orbits which would make them land harmlessly in major oceans outside of shipping lanes or back on landing fields of any in their countries of origin. Sometimes those satellites were removed by blowing them up. This sometimes left a lot of little pieces of satellites in orbit. Also sometimes pieces fell off of satellites, and assumed stable orbits of their own. Also sometimes when satellites were launched they had pieces that fell off once they were in space. Those pieces of old satellites and things out in space which remain in orbit are called space junk. There are thousands of such pieces of space junk out there now, most of which do not have orbits mapped, many of which may well be in the trajectory of Apophis when it gets here. Unfortunately, a lot of those pieces of space junk are not as far from Earth as Apophis will be when it makes its closest approach so it could well hit some space junk.

So what happens when an asteroid hits a small piece of space junk? If we are lucky, and Apophis hits a small piece of space junk say the size of a wrench, nothing much. The asteroid would vaporize the piece of space junk and continue on its merry way. But possibly, due to the speeds involved and enormous energies, the asteroid Apophis might just explode into a dozen or more chunks some of which would make craters the size of meteor crater in Arizona or larger.

Look at it this way. If you take a small pebble, the size of a marble and drop it on a windshield of a car from about ten feet up (don’t try this at home, kids) you won’t be able to break the windshield of a car. But if you take that same pebble and drop if from the same ten feet up off of an overpass on a car doing 65 miles per hour plus on the interstate, you will almost certainly shatter the car’s windshield. (Don’t try that at home either, kids. And if anyone asks, I never did that either even as a young girl.)

So if Apophis hits a small piece of space junk even if it shatters into small pieces those pieces could possibly hit numerous buildings and ruin the day for a number of people. But even if those pieces just hit unoccupied areas they would start numerous fires. But even if Apophis breaks up in the atmosphere and none of the pieces hit the Earth that much dust in the atmosphere would have major climatological effects but probably not an ice age. Now if Apophis does not hit the Earth or break up, it is due back for a second near miss of the Earth in 2036. What the trajectory of the asteroid Apophis looks like after 2029 is not totally predictable. If I am vague on what happens if the asteroid hits space junk is because the factors that influence the result are not totally known. If the asteroid Apophis has its trajectory altered so it hits the Earth as one chunk either in 2029 it could cause a major local catastrophe, but probably not an ice age. There is also a small chance, estimated at about 1 in 5000, that Apophis will have its orbit altered by the near miss with Earth in 2029 even if it doesn’t hit any space junk so that it will come back and smack us dead on in 2036 thereby possibly ruining the day for some number of people.

How many? How much damage would Apophis do? Well Apophis is a lot smaller than the asteroid that wiped out the dinosaurs. But it still is a lot bigger than the one that left quite a large hole in Arizona. Apophis is only about 8.2 times as wide as the meteorite that left that big crater in Arizona, assuming the diameter of the Arizona meteor was about 100 feet. But the damage a meteorite does is increased according to the cube of the radius of the meteor. The damage a meteorite does depends on its composition, final velocity, where it hits, the angle of its impact and its mass. The mass of a roughly spherical meteorite is proportional to the cube of its radius. So Apophis might well do as much damage as about 550 meteorites the size of the one that hit Arizona. Or conversely, it could break up into as many as 550 meteorites that do as much damage as the one that hit Arizona 50,000 years ago.

According to simulations I ran on Arizona state University’s impact simulation system[4], if the entire asteroid is rocky and stays in one piece and hits on land, the blast from the impact might ruin your day and shatter windows and knock down buildings not sturdily constructed if you were within 200 to 300 miles of the impact site. (The exact composition of Apophis is not known either but I am guessing it is either entirely rocky or rocky-iron or maybe iron in composition and has no ice left on it because it has approached the sun numerous times and probably had all the ice on it melted off thousands of years ago.) Large pieces of molten rock thrown up by the impact would cause fire storms in that area, possibly even as far away as a thousand or two thousand miles, killing all the inhabitants not killed by the blast. Then the soot from the fires and dust kicked up into the atmosphere might cool the planet enough to cause an instant world wide winter and wipe out all the summers for a year or more maybe as many as ten years causing massive crop failures world wide. But if we are lucky, it probably will not be enough to cause an ice age. If the whole asteroid or large pieces of it hit in an ocean, it might throw up tidal waves 50 feet high lasting an hour. Then the extra water vapor in the atmosphere might cause a rapid increase in global warming lasting years.

If the asteroid Apophis fragments in 2029 or 2036 the damage might be more wide spread. The blast of each fragment would be smaller, but there would be more of them. Small fragments might be enough to ignite lots of local firestorms from the radiant heat of their passage and ejecta of chunks of molten rock tumbling back to Earth ignite fires everywhere around where the parts of Apophis land within a thousand miles or so.

So what can we do? There may be some 19 years left before the expected close encounter of the meteor kind in 2029, but we can’t use all that time to consider our options. Soon, if we hesitate too long, we start losing our options to do anything to prevent Apophis from hitting the Earth. I am not suggesting anybody start digging and stocking deep bunkers yet. If NASA wants to change the orbit of Apophis or destroy it permanently it may have to launch a mission in the next two to three of years which means with the usual NASA planning and preparation delays it probably should have started planning five years ago.

One friend suggested we start mapping and cleaning up space junk. This is probably a very good idea in and of itself. Should any satellite launch, unmanned or manned space craft run into a piece of space junk it could ruin their entire day. Even if all the space junk is cleaned up, there is no guarantee that some new space junk might end up being made after the cleanup is done with no time to remove it before the close approach of Apophis.

We could also alter the orbit of Apophis so it misses Earth by more than a few million miles instead of a few thousand. NASA has already landed one unmanned probe on an asteroid and could probably do it again. The asteroid could have a small rocket landed on it that could steer Apophis into an orbit that will miss Earth by millions of miles. Or a rocket could be put into a near approach to Apophis that will use the attraction of gravity between the rocket and Apophis to steer it into an orbit that will miss Earth by millions of miles.

And there is one other idea. Apophis will pass quite close to Venus, by astronomic distances, in 2016. If Apophis crashes on the surface of Venus, none of it will ever impact Earth, ever. Not in 2029, not in 2036 when it is scheduled to make its second near approach to Earth, or not any of the other near misses we might see in later years as Apophis crosses Earth’s orbit every 324 days. The explosions, and firestorms, or tidal waves, and climate alterations either way caused by Apophis or parts of it hitting Earth might be a calamity for Earth and most everybody on it then. However if Apophis could be redirected to hitting Venus, Apophis would never hit Earth ever. There will be a continuing threat from Apophis in the coming years forever until it hits Earth or Venus.

Now if Apophis hits Venus it could be the first step towards terraforming Venus and turning one very very hot planet into a planet cool enough to support terrestrial type life, such as you and me and your pet catfish. After all, Venus represents more real estate than ten Earths, since none of its surface is covered by oceans. But there are a few things wrong with the real estate on Venus at this point. First it is too hot. It is hot enough to melt lead, let alone you me and your pet catfish. Second there is no breathable atmosphere, but a seriously caustic atmosphere at intolerably high pressures. Third it is very far away. Fourth, there is no liquid water known to be on the surface.

If we start bombarding Venus with stray asteroids, Venus might be cooled enough in a few years, to support the primitive organisms of the types that produced the breathable atmosphere of Earth, some of which are known to tolerate very high temperatures, pressures, caustic environments and can still be found on Earth in some extreme environments. Once Venus is seeded with atmosphere producing organisms, the atmosphere might become breathable within a few years. I did actually run the numbers a few years ago and if you assume you can deliver a pound of live atmosphere producing organisms onto Venus that reproduce with a doubling time of two weeks or so, and they can survive there and reproduce, you can get a breathable atmosphere within a few years and an extreme temperature reduction.

If we could lower the temperatures, pressures, and give Venus a breathable atmosphere, that would make Venus very desirable piece of real estate indeed and prove a very interesting long term project for NASA. Probably by the time we get NASA to undertake a terraforming project, we will have an independent colony on the Moon willing and able to send colonists to Venus hopefully sometime in this century. But studying the impact of a meteor the size of Apophis on Venus would give us some data to start a realistic study of how to terraform planets even if the type of objects we might most like to use to impact Venus or Mars or even the Moon would contain cubic miles of ice. It might also give us some data we might need to use to alter the temperatures on Earth should global warming continue at the present rate or at an increasing rate. After all in the future we may well consider impacting the Earth with a medium or small sized comet or two to drastically lower Earth temperatures if the alternative is the Earth heating up to anything like the temperatures on Venus. But I would like to see the Earth have some experience with redirecting and aiming asteroids at planets before we as a people start tossing asteroids at our own planet. But I would hate to see us go extinct as a people or suffer catastrophic population crashes due to global warming or meteorite impacts because we never bothered to do anything to prevent possible drastic catastrophes. Janice Guidotti, M.D.

1. NASA’s Astrobiology Magazine, “Dinosaur Era Ended Instantly”, Matsos, Helen, Ed.
http://www.astrobio.net/pressrelease/994/dinosaur-era-ended-instantly

2. Guidebook to the Geology of Barringer Meteorite Crater, Arizona (a.k.a. Meteor Crater), David A Kring, 2007, Lunar and Planetary Institute,
http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/

3. NASA’s Astrobiology Magazine, “Comet Cools Clovis”, 8/23/07, Matsos, Helen, Ed. ,
http://saturn.astrobio.net/pressrelease/2437/comet-cools-clovis

4. http://www.lpl.arizona.edu/impacteffects/

For further reading, please see:
http://neo.jpl.nasa.gov/apophis/Apophis_PUBLISHED_PAPER.pdf