Big Bang Baby!

19 11 2009

Fireballs.  They happen.  They happen far more often than you think.  Not usually over people, though.  But sometimes…

This picture was taken at seven minutes past midnight Tuesday night/Wednesday morning.  The fully illuminated landscape is a result of the ultra bright bolide that resembles the sun with a tail that you can see plummeting toward the ground.  Though it looks like it’s not far away, it’s many dozens of miles up and several hundred miles away from the camera.

Here’s the amazing part:  The corresponding sonic boom actually shook the ground hard enough that it set off seismic sensors in at least three states!  Now that’s a big kaboom!   Since sound travels a lot slower than light — only a mile every 4.8 seconds or so — it took the people in Salt Lake City (where this image was taken) 5 minutes after the sighting to hear it.

A lot of people saw this event, many more than normally would have, because they were outside watching the fantastic Leonid meteor shower.   But before you start putting two and two together, the Leonids did not produce this!  Though this happened during the Leonid peak, it does not appear that this meteor came from the direction of Leo (the whole reason we call this shower the Leonids in the first place).  That means it has another origin.  All we’re really sure of at this point was that it detonated very high up with a power of just under 1 kiloton.

If you go to spaceweather.com, you’ll possibly find some links to some news agencies.  Careful what you believe if you click on any of them.  One of the reports has a guy who has a friend who is studying astronomy and his friend told him that a green meteor means it contains iron and since this one was green that means it had a lot of iron in it so it must have survived all the way to the ground but its probably not very big maybe the size of a cheeseburger or something.  Wow.  All that just from being told the light was green, huh?  Hey, guess what.  They almost all have iron.  That green light is probably caused by the meteorite slamming into our atmosphere’s oxygen.  It glows green too, y’know.  And, of course, there’s a lot more to it than what I just handwaved as an explanation.  Just remember that you can’t really tell anything from a visual observation of the color — you need a spectral analysis to determine composition.  And be careful of the other things that the reporters were quick to leap on.  The probability of interviewing a common Joe with a solid astronomy background is rather slim.

Many annual showers can drop fairly bright fireballs, most notably the Leonids fireball outburst of 1998.  [I saw a dozen bolides brighter than magnitude -8 that night!]  But the Leonids is not a shower that can drop big things.  Most of the meteors you see in this shower are roughly the size of your fingernail.  A bolide this big requires a good sized rock.

The meteorite community is fairly certain that a meteorite was dropped from this event.  And it appears increasingly likely that it’s in western Utah at a place called the Dugway Proving Ground.  One thing *I’ve* gained from following this story is discovering the history of the DPG.  I would wager from the information available to me on the ‘tubes that it might be a while before anyone gets out there to search around for it, if in fact this turns out the be the impact point.  Also, after poking around I remembered that the Genesis probe touched down (and if you know the story you should be laughing) there back in 2004.  It’ll be interesting to see how long it takes for the military to let people look for debris.

There’s also a side story about some shimmering high-altitude clouds over Utah the next morning — six hours later.  It’s difficult to temporally link these two events together, but no one really has a better explanation.  Interesting, huh?

[What’s the difference between a fireball and a bolide?  Here’s a previous post where I address that.]

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New Earth

16 11 2009

It’s a stunning view.  And as the imagers and instruments on our spacecrafts keep improving, so will our understanding of the Heavens.  And the Earth.

crescent earth

The illuminated section is our South Pole, with the rest of the Earth so dark you can’t discern it from the emptiness that surrounds us.

If you’re wondering whether the crescent is waxing or waning, it’s waxing.  The motion of the spacecraft that took this picture — Rosetta — was bringing it closer to the Earth for a gravity assist to fling it outwards into our solar system for a rendezvous with comet 67P/Churyumov-Gerasimenko in 2014.  The successful swingby increased its speed from 13.3 km/sec to 16.9 km/sec.  In comparison, the space station maintains a speed of only 8 km/sec — or Mach 23.  So yeah, Rosetta is moving!  To get up to this amazing speed the spacecraft used the momentum of four planetary flybys, three of Earth and one of Mars.

Here’s the sequence of photos it took leading up to that beautiful one plastered on every science website in the blogosphere.  Each image in this animation was taken only one hour apart!

osiris_esb3_movie_g_H

Rosetta is on a mission to catch up with a comet and then set a lander on its surface! Since the comet is only 4km in diameter, it won’t have enough gravity to hold the lander to it; so the ESA plans to harpoon this white whale and ride on its back a while.  How long of a while?  That depends on how long it takes the comet to tear it apart.  Since this comet isn’t under thermal stress atm, it might survive for years — which is quite a different story than when Halley’s comet beat up an ESA probe named Giotto in a matter of minutes back in 1986.  That mission was uniquely different.  The comet Rosetta is headed for won’t be shedding material;  Giotto encountered Halley’s comet right after it passed the sun and had a tail a million miles long!  I remember when they launched it, way too late for a good look, kinda thrown together at the last minute sort of thing.  (I say that.  Of course, you know the whole operation was ran by some really smart engineers and was very well planned under the circumstances.)  It was outfitted with instruments and then flung toward the sun to pick up some terrific speed.  It then headed *toward* comet Halley in a nearly perpendicular direction that would have them passing each other at 68 km/sec!  As you can probably guess, this didn’t end well.  As it approached, the Giotto got pelted some 12,000 times by little ice chunks.  The antenna was hit, the aluminum and Kevlar shielding was demolished, and an impact with a “large” chuck with the mass of a paperclip (hey, it’s going really fast, ‘k?) sent it spinning out of control.  There is a happy ending to this tale, though.  A half-hour after it was knocked silly it re-stabilized itself and went on to produce good science for another 7 years — even making an unprecedented encounter with a *second* comet.

So now Rosetta is off to rendezvous with it’s own chunk of primordial ice.  The ESA will try to tell you of all the important science the probe should be able to do, but I think we all know why it’s really going… ’cause we all want to see what the surface of a comet really looks like!  I bet it’s cooler than we’ve ever imagined.

rosetta lander

Godspeed, Rosetta.