An asteroid is defined as any numerous, small, celestial body that revolves around the sun. Asteroids are typically several hundred kilometers in size and are usually found between the orbits of Mars and Jupiter. These asteroids are merely fragments of planets, or other celestial bodies that have broken off. The asteroids that come within a certian distance of Earth are of some significant importance to Earthlings, espically the ones with impressive sizes. Just the thought of the damage one could cause to a planet such as Earth is unnerving.
HOW DO WE NAME THEM?
With all of the asteroids that are in space there has to be a good way to keep track of them. The easiest way to keep track of asteroids is to name them. The process of naming the asteroid is fairly simple, for an astronomer. First, the asteroid actually has to be discovered to be named. Then, the newly discovered asteroid is given a provisional designation year of discovery and an alpanumeric code indicating the half-month of discovery and the sequence within that half-month. Once the asteroid's orbit has been confirmed, it is given a number, and later an official name. Usually the names coencide with the asteroid's discoverer and its discovery date.
HOW BIG ARE THEY?
Asteroids are unlike most celestial bodies when it comes to size and shape. The composition of asteroids depends on their origins, and in most cases are poorly understood. Some of the NEAs were at one time comets that have died out; few still still have their tails. Most NEAs were once driven out of the asteroid belt by gravitational interactions with Jupiter. A few of the largest are roughly spherical and are very much like miniature planets, such as Ceres, with a diameter of 975 kilometres. Most asteroids are much smaller, oddly shaped, and composed of piles of rubble held together loosely by gravity. Some have moons or are co-orbiting pairs of binary asteroids. All three conditions, as well as scattered asteroid families, may be the result of collisions which disrupted a parent asteroid. Sadly, or luckily, in some opinions, NEAs only survive in their orbits for a few million years. They are eventually eliminated by orbital decay and accretion by the sun, collisions with the inner planets, or by being ejected from the solar system by near misses with planets.
So what happens if one of these babies gets too close to Earth? When a NEA gets too close to the Earth? A NEA is classified as an asteroid that spends part of its orbit within 1+/- 0.2 AU (astronomical units) of the Earth[o.0]. 1 AU is equal to the distance from the Earth to the sun. So how close is too close? When an asteroid gets to be 0.5 AU or closer, it becomes what humans call a PHA (potentionally hazardous asteroid). The PHAs that are greater than 1km in diameter are the ones that could seroiusly harm life on Earth. Asteroids with diameters of 5-10m impact the Earth's atmosphere approximately once per year with as much energy as the atomic bomb dropped on Hiroshima (without the toxciccidy damages), approximately 15 kilotons (1,000 tons) of TNT. These ordinarily explode in the upper atmosphere, and most or all of the solids are vaporized. Objects with diameters of over 50 meters strike the Earth approximately once every thousand years, producing explosions comparable to the one observed at Tunguska in 1908. Asteroids with a diameter of one kilometer hit the Earth an average of twice every million year interval. Large collisions with five kilometer objects happen approximately once every ten million years. [X(] Scientists have said that from previous observations the asteroid, (29075) 1950 DA, has a 1 in 300 chance of hitting the Earth on March 16, 2880. This chance of impact for such a large object is roughly 50% greater than that for all other such objects combined between now and 2880. It has a diameter of about a kilometer. [beautiful, but dangerous]
THE BIRTHPLACE OF NEAs
most likely cause of doomsday (asteroid impact)
- Impacts may have contributed to many of the previous mass extinctions such as the one that killed the dinosaurs (in theory) and also onto future theories such as [ARMAGEDDON].
- The difference between now and then is that we (as humans) now have the technology to identify and predict hazardous objects and eventually prevent a catastrophy.
- To prevent these sorts of things from occurring, we must know the chemical and physical compostition of the NEAs.
- Asteroids are the chemical celestial bodies most likely to cause an extremely damaging impact because many fall into the size range necessary to both generate severe damage and be attracted by Earth's gravity.
- Libration Point- postions of equilibrium in a rotating body gravity field (there are 5 for Earth).
- Trojans are located in these Liberation Points.
OTHER INTERESTING INFO
- At 10 metres and below, these rocks are generally considered to be meteoroids.
- Neptune also has a few known trojans, and these are thought to be actually be much more numerous than the Jovian trojans. *However, they are often included in the trans-Neptunian population rather than counted with the asteroids.
- Ceres, originally considered a new planet, is the largest asteroid and is now classified as a dwarf planet. All other asteroids are now classified as small solar system bodies along with comets, centaurs, and the smaller TNOs.
- Two near-Earth asteroids have been visited by spacecraft: 433 Eros, by NASA's Near Earth Asteroid Rendezvous probe, and 25143 Itokawa, by the JAXA Hayabusa mission
- Over 5,490 near-Earth asteroids are known
- most NEAs were once driven out of the asteroid belt by gravitational interactions with Jupiter
- 3 major NEA families
- Atens have an average orbital radii closer than one astronomical unit (AU, the distance from the Earth to the Sun) and aphelia of greater than Earth's perihelion (0.983 AU), placing them usually inside the orbit of Earth.
- Apollos have an average orbital radii greater than that of the Earth and perihelia less than Earth's aphelion (1.017 AU).
- Amors have an average orbital radii in between the orbits of Earth and Mars and perihelia slightly outside Earth's orbit (1.017 - 1.3 AU). Amors often cross the orbit of Mars, but they do not cross the orbit of Earth.
- Many Atens and all Apollos have orbits which cross that of the Earth, so they are a threat to impact the Earth on their current orbits
- Amors do not cross the Earth's orbit and are not immediate impact threats, however their orbits may evolve into Earth-crossing orbits in the future
PHAs(the near asteroid threat)
Tro·jan 2 (trō'jən) Pronunciation Key adj. Of or relating to a celestial body, especially an asteroid, that is in one of the Lagrangian points of a two-body system. Used especially of any of a group of asteroids that orbit at Jupiter's distance from the sun, but 60° ahead of or behind the planet. dictionary.com
NEAs- near earth asteroids. For them to be classified as neas they have to be around the earths orbit. Some can be as big as ~32 kilometers. NEAs can only live up to 10-100 million years. They are later elimated by the sun or other planet collision. There are 3familes of NEAs: -Atens -Apollos -Amors Ther was a threat of a Earth impact when one hit Jupitar.It was a comet named [Shoemaker Levy 9]. Although there was a number of false alarms, there are a lot of asteriods to me classified as a threat.
Libration Point-any one of five points in the plane of a system of two large astronomical bodies orbiting each other, as the Earth-moon system, where the gravitational pull of the two bodies on an object are approximately equal, and in opposite directions. A solid object moving in the same velocity and direction as such a libration point will remain in gravitational equilibrium with the two bodies of the system and not fall toward either body.
Trojan: An object orbiting in the Lagrange points of another (larger) object. This name derives from a generalization of the names of some of the largest asteroids in Jupiter's Lagrange points: 588 Achilles, 624 Hektor, and 911 Agamemnon. Saturn's satellites Helene, Calypso and Telesto are also sometimes called Trojans.
These L-Points are located at 60 degrees ahead and behind the planet in its orbit. Most bodies have about 5 L-Points. In the image below, A contour plot of the effective potential due to gravity and the centrifugal force of a two-body system in a rotating frame of reference. The arrows indicate the gradients of the potential around the five Lagrange points — downhill toward them (red) or away from them (blue). Counterintuitively, the L4 and L5 points are the high points of the potential. At the points themselves these forces are balanced.
- The Planetary Report[(Visions of Exploration) Volume XXVIII Number 2 March/April 2008 p.5 ]
- wikipedia asteroids
- Davis, Kenneth C. Don't Know Much About The Universe?. New York, NY: HarperCollins Publisher Inc., 2001.
- Chartrand/Wimmer. Skyguide: A Field Guide For Amateur Astronomers. New York: Golden Press.
- [picture info.]
Long, long, ago...approximately 4 billion years to be exact, there was an asteroid with a British accent floating around in space... (in the mind of this particular asteroid) "Oh, hello! Almost didn't see you there, you gave me a fright ya did. WEll jolly good day to you! Or is it night? I really couldn't tell, you see, I'm floating around in space at the moment...or at least I thin I'm floating, if thats what you call it, floating, funny word, come to think of it, word's a funny word too isnt it? Well either way pleasure to meet you. I'd give you my name, but my mum didn't give me one...I really don't think you could call her a mum either, much less a her more of an it really, much like myself. "OOH look at that! More floating thingies like me! Well come on, lets join em'! (slowly floats towards mass of asteroids) "Ello everyone! My my, what is that big...blue? yes I think blue would be the word, I dunno why but I think wa I should call it,... what was I saying?.. Oh, yes, right, that big blue thing. What is it? It couldnt possibly be like any of us fellows, we're much smaller and rockier looking. Well, compared to that thing I'm smaller, but I find that I'm Quite large...well if you look at others like me I'm large... Oh my what was that strange sensation? It feels as if I'm being tugged toward taht big blue thing. Hmm I'm coming in pretty close to that thing now, WOW im getting REALLY close to that thing...geez why am i getting so close??? Oh look at that theres other stuff on this blue thing...HEY its kinda green too! and look at that! there are these things, what should i call them hmm oh i know [dinosarus!!!] yes there are losts of them and theyre all different shapes and sizes. Is it hot in here or is it just me? OMG! it IS me im on fire!!!! and im comeing in pretty fast, i really hope these things can move out the way, i dont have breaks on me, "Hello there! Um, if you dont mind im coming in for a landing now if you'd be so kind as to move i'd highly appreciate it!" [BOOM!!!] Cae'ly D. 22:57, 6 October 2008 (UTC)
I WAS HERE!!!!!!