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."

Re:Asteroid? Why not meteor?

[tekrat]

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.

Re:Asteroid? Why not meteor?

[QuantumG]

It's an asteroid until it enters the atmosphere.

Re:Asteroid? Why not meteor?

[Martin Blank]

OK, fair point. I should have referenced meteoroids. But still, aside from a sensational headline, wouldn't this usually be classified as a meteoroid rather than an asteroid?

Re:Asteroid? Why not meteor?

[Bragador]

Meteoroid/meteor: Any of the small solid extraterrestrial bodies that hits the earth's atmosphere

Meteorite: A solid body that has arrived on the Earth or Moon from outer space. It can range in size from microscopic to many tons. Its composition ranges from that of silicate rocks to metallic iron-nickel.

Asteroids: Asteroids, also called minor planets or planetoids, are a class of astronomical objects. The term asteroid is generally used to indicate a diverse group of small celestial bodies.

Re:Asteroid? Why not meteor?

[sreid]

You're right. The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 Âm and 10 m across.

Here's the NASA article

[Bragador]

Small Asteroid Predicted to Cause Brilliant Fireball over Northern Sudan [nasa.gov]

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.

Re:Asteroid? Why not meteor?

[AJWM]

It's an asteroid until it enters the atmosphere.

No, if it's less than 10 meters diameter it's only a meteoroid.

The point of the article is the last line

[Gresyth]

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.

Re:Is this really news?

[Peter Cooper]

Supposedly it's the first time that an asteroid / meteor has been accurately (well, we'll see on that front!) predicted to enter the atmosphere at a specific time and location.

Re:Testing tractor beam theory.

[Fluffeh]

Firstly the mass of a satellite would not generate enough of a gravity well to nudge any object off a crash course with the earth. Secondly, as the object in question will be travelling at around 12.8km/s (That's just under 8 miles per second if you are American). The sort of gravity needed to change that trajectory considerably would likely cause much much more problems than this little lump of rock could ever cause.

Re:Asteroid? Why not meteor?

[xstonedogx]

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.

Re:Awesome!

[Anonymous Coward]

LinkyLinky
http://www.cfa.harvard.edu/icq/meteorites.html [harvard.edu]

Re:Asteroid? Why not meteor?

[freeabelian]

"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 [navy.mil]) 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 [wikipedia.org]), so the meteorite impact is roughly 553.6 tons of TNT. Caveat emptor: many, many approximations.

Re:Asteroid? Why not meteor?

[actionbastard]

By recent definition [wikipedia.org] this object should not be classified as an asteroid, but a meteoroid. Meteoroid is what the object is when travelling in space. Meteor is the visual phenomenon that you see as the object enters the Earth's upper atmosphere and frictional heating causes the surface of the object to melt and then form a plasma around the object. Meteorite is the remains of a meteoroid that entered the Earth's atmosphere and reached the ground.

It is entirely possible that this meteoroid -depending on its composition, stony, stony-iron, carbonaceous chondrite, or iron/nickel-iron and its velocity and angle of incidence to the Earth's atmosphere- could reach the ground and form a sizable crater. The accepted figure for crater size is roughly 25 times the diameter of the object at the time of impact with the surface. The Barringer Crater [wikipedia.org] was formed by an object estimated to be approximately 50 meters across at the time of impact. If this object reaches the ground at one-half of its present estimated size, it could form a crater 35 to 50 meters across. It would be quite the show if one were within a mile or two of the impact.

Re:Awesome!

[CrimsonAvenger]

One thing I've wondered, those small asteroids that hit the earth, say that land and are about the size of my fist, did those burn down to that size from a bigger size, or are there trajectories that it could land mostly without burning up. Like if it goes in at a really steep angle, could a rock the size of a basketball before it enters be about the size of a basketball when it lands, or is that pretty much impossible?

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.

Further Updates from jpl at T-60min

[robbak]

Update - 6:45 PM PDT (1 hour prior to atmospheric entry)

Since its discovery barely a day ago, 2008 TC3 has been observed extensively by astronomers around the world, and as a result, our orbit predictions have become very precise. We estimate that this object will enter the Earth's atmosphere at around 2:45:28 UTC and reach maximum deceleration at around 2:45:54 UTC. These times are uncertain by +/- 15 seconds or so. The time at which any fragments might reach the ground depends a great deal on the physical properties of the object, but should be around 2:46:20 UTC +/- 40 seconds.

T-750 and counting

Re:Asteroid? Why not meteor?

[sidb]

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.

This sort of impact happens once a month.

[SETIGuy]

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).

Re:Asteroid? Why not meteor?

[Anonymous Coward]

you are funny.

Re:Asteroid? Why not meteor?

[Sique]

No. To be an aster it must be able to sustain nuclear fusion. Because "astera" is latin and means "star".

And yes: Asteroids are literally "star-like thingies".

touchdown !

[freddy_dreddy]

http://dorigo.wordpress.com/2008/10/07/asteroid-2008-tc3-hits-sudan/ [wordpress.com]

Impact of Asteroid 2008 TC3 Confirmed

[Guppy]

http://neo.jpl.nasa.gov/news/news160.html [nasa.gov]

Confirmation has been received that the asteroid impact fireball occurred at the predicted time and place. The energy recorded was estimated to be 0.9 to 1.0 kT of TNT and the time of detection was 02:45:45 on October 7 (Greenwich Standard Time). More details on this detection will be forthcoming. An additional confirmation was apparently reported by a KLM airliner (see: (http://www.spaceweather.com [spaceweather.com]). As reported by Peter Brown (University of Western Ontario, Canada), a preliminary examination of infrasound stations nearest to the predicted impact point shows that at least one station recorded the event. These measurements are consistent with the predicted time and place of the atmospheric impact and indicate an estimated energy of 1.1 - 2.1 kT of TNT.

Just in case anyone's still checking all the way down here...