I swear, everybody gets the cool news before me: an asteroid named 2009 BD was recently discovered, and it appears to have an orbit that is very similar to Earth’s. I could go on and on about resonances and horseshoe orbits and co-orbital debris, but you can read all about it at AstroProf’s page and Universe Today. And I still have nothing in my email inbox about it. Grrr.
The asteroid is not in danger of hitting us, and is only 10 meters across anyway. Something that big hitting us would explode high in the atmosphere (maybe dozens of kilometers high, depending on the composition of the asteroid; rock is fragile and it would detonate way up, but iron would get down lower before exploding) and rain down debris over some unsuspecting area — probably the ocean, given that’s 70% of the planet — but that’s about it. And again, this one won’t hit us, so don’t panic.
January 25th, 2009 at 6:21 pm
What we really need is a couple asteroids named Calvin and Hobbes! Although I suspect those would be civlization killers. :O
January 25th, 2009 at 6:36 pm
There is 1245 Calvinia, and 7012 Hobbes.
1245 Calvinia is 26 km wide and would cause a lot of damage if it hit, but luckily never gets within 1.8 AU of us.
I can’t find any physical dimensions on 7012 Hobbes, so I think it might be an imaginary asteroid.
January 25th, 2009 at 6:43 pm
DON’T PANIC!
Make sure you have your towel.
January 25th, 2009 at 6:47 pm
I come from the same tiny village as the guy who does the Doonesbury comic.
January 25th, 2009 at 7:25 pm
Dr. Phil Plait:
You’re right, Phil, and you could too if you subscribed to SpaceWeather.com as I do — I got an e-mail about asteroid 2009 BD in my in-box on 25 January, 2009, 19:49:20 GMT — and you can sign up for free Space Weather e-mail alerts here.
January 25th, 2009 at 7:30 pm
Hey Phil! This is kind of off topic but I wanted to let you know that this last week I was given a small $50 award by my boss at work for something I did she really liked. Its one of those company award things you redeem on the internet by choosing an online retailer to spend the award at. I saw a golden opportunity! I chose Barnes and Noble and bought both your books. I’m not trying to suck up here. I intended to read them some time but if you can get them for free, what the heck, right? You still get your copper and I get the pleasure of reading about the end of the world
Everybody wins!
January 25th, 2009 at 7:46 pm
“The asteroid is not in danger of hitting us …”
It’s nice to know the asteroid will come to no harm.
Now why would something a few tens of meters across ‘blow up’? I’d like to know the mechanics of that. It’s a pity Eugene Shoemaker isn’t around to set you straight.
Anxiously awaiting a description of how and why these things blow up …
January 25th, 2009 at 8:09 pm
Curious to see how pseudo-scientifica will harp on this phantom whale.
January 25th, 2009 at 9:03 pm
Anyone else kind of disappointed that it won’t hit? I imagine it would break up into a pretty spectacular shower of fireballs.
January 25th, 2009 at 9:57 pm
Well, say Hello to Cruithne!
January 25th, 2009 at 11:45 pm
MadScientist:
When meteoroids enter Earth’s atmosphere from outer space, they are usually travelling at a speed of more than 10 kilometres per second (6 miles/sec or 21,600 mph). Most are small and burn up quickly, but occasionally a larger one enters. As the meteoroid/asteroid travels through the atmosphere, the heat generated by compression of air in front of the object is caused by ram pressure — a shock wave generated by the extremely rapid compression of air in front of the meteoroid — and not due to friction as is often erroneously thought. This heat is immense and most meteoroids burn up or explode — due to thermal stresses and pressure differential between the front and rear of the object — before they reach the ground. A stony meteoroid of about 10 metres (30 ft) in diameter can produce an explosion of around 20 kilotons, similar to that of the Fat Man bomb dropped on Nagasaki, and data released by the U.S. Air Force’s Defense Support Program indicate that such explosions occur high in the upper atmosphere more than once a year.*
*Source — Wikipedia: Tunguska event; Ram pressure; Shock wave.
January 26th, 2009 at 12:18 am
@ Nick:
(7012) Hobbes has an H of 13.5, so a best estimate is a size near 7 km. With perihelion at 2.0 AU in the main belt it will never get close to Earth. It is actually named after British political philosopher Thomas Hobbes (1588-1679).
January 26th, 2009 at 12:18 am
It seems this asteroid doesn’t quite deserve all the attention its getting. Despite what’s been reported, It is not co-orbital with Earth. Co-orbitals can’t come this close to Earth. Using JPL’s numbers, here’s some diagrams of 2009 BD’s orbit.
This image shows its trajectory during its 4-year stint in Earth’s vicinity. This image was made in a rotating frame, which would keep the sun still if the image were zoomed out enough to show the sun.
http://orbitsimulator.com/gravity/images/2009BD_2.GIF
The next image shows the next 20 years of its orbit. This is also in a rotating frame. There’s nothing in this trajectory that suggests that this asteroid is co-orbital with Earth.
http://orbitsimulator.com/gravity/images/2009BD.GIF
January 26th, 2009 at 1:41 am
@IVAN3MAN:
Thanks for that; so it’s mainly mechanical stress that breaks up big rocks? I think I need some clarification on ‘explosion’ though; that implies a sudden generation and release of pressure. A lightning strike heats up the air at an incredible rate and this results in a very high pressure which in turn produces the thunder. Would a lightning strike be considered an ‘explosion’? Since all meteorites compress the air in front of them, don’t all meteorites ‘explode’ if we just take the compression wave as an explosive event? Shouldn’t we be saying “small meteorites explode” for consistency? Otherwise people may get the impression “bus-sized rocks explode, golf-ball-sized rocks don’t explode”.
When people say ‘a meteor explodes’ I imagine that means that pressure builds up in the meteor, the meteor fractures and the high-pressure gas scatters fragments everywhere. With meteors though I imagine the pressure is not internal (or is it), so I guess in a way it’s like putting explosives next to a wall and detonating the explosives – in such a case do we say “the wall exploded” or simply “the wall was demolished by an explosion”?
I’m still trying to understand what people mean when they say a meteor(ite) explodes; does it really explode or are people misusing the word?
January 26th, 2009 at 1:45 am
@ Phil
The Feb issue of the UK Sky at Night magazine gave Death from the Skies! a 5 star review.
January 26th, 2009 at 2:43 am
@Nick:
http://en.wikipedia.org/wiki/List_of_minor_planets:_7001%E2%80%938000
Wikipedia listing of asteroids, 7012 Hobbes is for real!
January 26th, 2009 at 4:25 am
MadScientist:
January 26th, 2009 at 4:35 am
ERRATUM:
MadScientist:
According to Wikipedia, an explosion is a sudden increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. So, a lightning strike would be an electrical explosion resulting from the rapid heating of the surrounding nearby air to about 10,000 °C (18,000 °F) nearly instantly, which is almost twice the temperature of the Sun’s surface. The heating causes rapid expansion of the air at supersonic speed, which creates a shock wave that is heard as thunder.
An asteroid/meteoroid, due to its motion, possesses kinetic energy (Ek = ½×m×v2), which is released as thermal energy upon rapid or sudden deceleration; it is this sudden release of thermal energy, when an asteroid/meteoroid breaks up in the atmosphere, which results in the rapid heating of the surrounding air as well as the object vaporizing, that causes the high-altitude explosion, such as the Tunguska Event — estimated energy: 10-15 megatons of TNT.
January 26th, 2009 at 4:41 am
Excuse me for the double post, but the formatting did not work out correctly the first time. Man, when the bloody hell are we going to get a preview/edit facility here?!
January 26th, 2009 at 5:55 am
@Marco:
Calvin’s pet tiger Hobbes is also named after the philosopher. Calvin of course is named after a different philosopher. Hobbes (the philosopher) is also featured in Monty Python’s “Philosopher Song” (… and Hobbes was fond of his dram …)
Calvin and Hobbes remains my all-time favorite cartoon. The pet tiger that was sometimes animated and sometimes a doll was brilliant. I’ve got to run now; Something Under the Bed is Drooling.
January 26th, 2009 at 6:30 am
What is a Doonesbury asteroid anyway? I’m missing a reference here, apparantly.
CJSF
January 26th, 2009 at 6:42 am
Adds: I know what Doonesbury is, just not getting the reference to the asteroid.
CJSF
January 26th, 2009 at 6:58 am
Looks like a cool rock. Too bad we discovered it as it flies by instead of before. Next time around will be in 90 years (2100 according to JPL’s orbit plotter). The fact that it takes so long to come around again means that one like it would be excellent for human (or even robotic sample return) exploration, because the relative velocity between it and Earth would be so low. I’ll post a link to an article I wrote about the effect in a follow-on in case links are still an issue.
January 26th, 2009 at 6:58 am
Here’s the article:
http://www.thespacereview.com/article/838/1
January 26th, 2009 at 7:08 am
BD is one of the characters in Doonesbury. The asteroid isn’t really named after the character; it’s just a coincidence of the naming scheme used for asteroids.
January 26th, 2009 at 7:43 am
CJSF asked: What is a Doonesbury asteroid anyway?
The asteroid is 2009 BD
BD is a character in Doonesbury.
January 26th, 2009 at 9:24 am
Oh, of course. *smacks forehead*. Thanks John.
I just didn’t scan it that way.
For my clarification, this size explosion can only happen high in the atmosphere, right? A 10m object can’t detonate just above the ground, can it?
CJSF
January 26th, 2009 at 11:10 am
I asked a question here about an AOL NEWS article that talked about astronomers watching the other side of the sun and it was deleted why???
January 26th, 2009 at 1:10 pm
Perhaps it was off topic? Or there was a server glitch?
Back ON topic:
I like the idea of visiting or at least rendezvousing with one of these “co-orbitals” (or whatever tony would call them). What *would* it take to do something like that with this or a similar object? How much lead time would we need? How complicated would the maneuvers be? How much might it cost?
Thanks.
CJSF
January 26th, 2009 at 1:21 pm
ICJSF,
think Sagan covers this scenario in “Pale Blue Dot” in the latter half of the book (sorry, been quite a while since I read it). Overall, it coud end up being about the same as a moon landing. Further to go, but no need to have a big launch off the body, so it’s a wash? I don’t really recall the fine details he went into, but it was a good intermediate step for going to Mars in how he wrote it (again, going by rusty memory).
January 26th, 2009 at 1:50 pm
Thanks, Larian. I wasn’t strictly talking about human rendeszvousing – though that would be interesting with a 10m object. What about a robotic mission?
CJSF
January 26th, 2009 at 2:56 pm
Given all the weird exoplanetary configurations out there, it would not be entirely surprising if at some point a system like this is discovered where the objects in question are jovian-type planets rather than pathetic lumps of space debris.
January 26th, 2009 at 4:42 pm
@MadScientist “Now why would something a few tens of meters across ‘blow up’? I’d like to know the mechanics of that.”
I don’t think the underlying physics is all that well understood. There seems to be great variability in what fragments of an impactor make it to the ground. Composition and impact angle probably are important factors. It’s been well known for quite some time that the Tunguska event of 1908 was an air burst happening at an altitude of 5 to 10 kilometers. As to what exactly causes the air burst there are a number of hypotheses. Perhaps the aerodynamic stress of entering the atmosphere opens up cracks that were already present in the object to begin with. The cracks widen causing the coefficient of drag to increase which produces more cracks so in a run-away feedback effect the object quickly fragments into smaller and smaller pieces and most of its kinetic energy is converted into heat – thus the explosion and fireball.
Composition seems to play a role since many iron-nickel impactors have a high enough tensile strength to withstand this aerodynamic disintegration process and make it all the way to the ground. Interestingly enough, if the object is big enough (say ~1 km in diameter or bigger) than it can make it all the way to the ground intact. I’m not sure where the cutoff size would be for when the object is big enough to make it all the way to the ground – probably ~125 m for a stony asteroid.
March 26th, 2009 at 1:59 am
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