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Small Asteroid On Collision Course With Earth
musatov writes "There's talk on The Minor Planet Mailing List about a small asteroid approaching Earth with a 99.8% probability of colliding. The entrance to the Earth's atmosphere will take place October 7 at 0246 UTC (2:35 after this story goes live) over northern Sudan, releasing the energy of about a kiloton of TNT. The asteroid is assumed to be 3-4 meters in size; it is expected to burn up completely in the atmosphere, causing no harm. As a powerful bolide, it may put on quite a show in the sky. For those advanced enough in astronomy to observe, check the MPEC 2008-T50 and MPEC 2008-T64 circulars. NASA's JPL Small Body Database has a 3D orbit view. The story has been already picked up by CNN and NASA."
They become meteors *once* they start to interact with the Earth's atmosphere. Until that time, they are classified as space objects, and the names seem to change dependent upon size and approximate mass.
If telephones are outlawed, then only outlaws will have telephones.
You're right. The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 Âm and 10 m across.
Small Asteroid Predicted to Cause Brilliant Fireball over Northern Sudan
A very small, few-meter sized asteroid, designated 2008 TC3, was found Monday morning by the Catalina Sky Survey from their observatory near Tucson Arizona. Preliminary orbital computations by the Minor Planet Center suggested an atmospheric entry of this object within a day of discovery. JPL confirmed that an atmospheric impact will very likely occur during early morning twilight over northern Sudan, north-eastern Africa, at 2:46 UT Tuesday morning. The fireball, which could be brilliant, will travel west to east (from azimuth = 281 degrees) at a relative atmospheric impact velocity of 12.8 km/s and arrive at a very low angle (19 degrees) to the local horizon. It is very unlikely that any sizable fragments will survive passage through the Earth's atmosphere.
Objects of this size would be expected to enter the Earth's atmosphere every few months on average but this is the first time such an event has been predicted ahead of time.
Wrong, it's a meteoroid in space, a meteor in the atmosphere, and if any of it makes it to the ground, it's a meteorite.
It's never an asteroid because it's not big enough.
"A very small, few-meter sized asteroid, designated 2008 TC3..." "It is very unlikely that any sizable fragments will survive passage through the Earth's atmosphere..." Let's pretend that "few-meter-sized" means 3m in diameter, that the space rock is perfectly spherical and will hit the Earth's surface in one piece. Mass of asteroid = density*volume = (3000kg/m^3)*(4*pi*(1.5m)^2/3) = 28274.334 kg (Density data from an eyeball-average of table in http://aa.usno.navy.mil/faq/docs/asteroid_masses) If it hits the surface at 12800m/s, then: Kinetic energy = .5*mv^2 = 2316233431638.683 J ~ 2316 gigajoules
1 ton TNT = 4.184GJ (from http://en.wikipedia.org/wiki/Joule), so the meteorite impact is roughly 553.6 tons of TNT.
Caveat emptor: many, many approximations.
Yes they "burned down". Yes, there are trajectories that let things land without burning up. But they make for lousy shows, since it requires the rock to skim the outer atmosphere just deep enough to slow below escape velocity, and then slowly (over a period of months or years) lose enough more energy that they reenter permanently. If that happens, and if they're metallic, and if they're really extremely spherical (no hot spots other than the obvious one - out front), then maybe they can make it to the ground substantially intact. Odds - well, literally astronomical.
"I do not agree with what you say, but I will defend to the death your right to say it"
It doesn't matter whether it hits the ground in one piece, splits into fragments, or burns up entirely before impact. The energy release is the same; only the location and form of the released energy will vary. I was assuming that the OP meant 1 kton of energy dissipated as heat into the atmosphere. It's a weird unit of measure to use for anything that isn't a point explosion, though. Still, I wonder how much it takes to noticeably affect anything beyond a temporary light show—the weather, perhaps. Probably more than this meteor has, even with your higher figure, unless it hits the ground.
A kiloton scale impact is a once a month thing. The only interesting thing about this collision is that we detected the object in advance. All the other ones have hit without warning. A 20 kiloton impact is a once a year event. It's only when you get to 10 megaton events that you have to worry about any effects on the ground, (apart from people looking at the bolide being temporarily or permanently blinded).
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