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Old 2008-10-07, 07:24   #1
cheesehead
 
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Default First pre-impact discovery for NEO search!

Wow!

The search for near-earth objects (NEOs) (AKA NEAs - Near Earth Asteroids) yesterday morning found one that was predicted (98%+ probability) to hit Earth last night over Sudan.

http://neo.jpl.nasa.gov/news/news159.html

Quote:
Small Asteroid Predicted to Cause Brilliant Fireball over Northern Sudan

Don Yeomans
NASA/JPL Near-Earth Object Program Office
October 6, 2008

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.

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.
This is historic: the first pre-impact discovery (and orbit calculation) of a natural object before it Earth!

http://www.astro.hr/humor/Asteroid_Tracking.gif

Notice that this shows that the current search capability for NEOs/NEAs is capable of finding and tracking objects so small -- about 3 meters (10 feet) in this case -- that they pose no surface danger (as well as larger ones, that is). The real problem in searching is that it's hard to find these rocks in the parts of the sky that are too close to the direction to the Sun, and far enough away so that any potential collision of a really big one could be detected years in advance.

I await reports of any observations of the bolide or (!) fragments found.

Last fiddled with by cheesehead on 2008-10-07 at 07:29
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Old 2008-10-07, 14:47   #2
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When I saw a news report yesterday afternoon about this, I thought the statement that it had been found "last night" had to be a typo of some kind. Then I got an Info Alert from JPL/NASA about it. Absolutely amazing that they are now able to calculate the ephemeris of each new object that fast. I haven't seen any photos yet of it coming through the atmosphere- Please post links if you find any.

Norm
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Old 2008-10-07, 15:56   #3
ewmayer
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Yes, this was very interesting news. See my related post in the Soapbox "New U.S. President" thread. Why there? - you ask...

Last fiddled with by ewmayer on 2008-10-07 at 15:56
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Old 2008-10-07, 16:14   #4
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Quote:
Originally Posted by cheesehead View Post
Wow!

The search for near-earth objects (NEOs) (AKA NEAs - Near Earth Asteroids) yesterday morning found one that was predicted (98%+ probability) to hit Earth last night over Sudan.

http://neo.jpl.nasa.gov/news/news159.html



This is historic: the first pre-impact discovery (and orbit calculation) of a natural object before it Earth!

http://www.astro.hr/humor/Asteroid_Tracking.gif

Notice that this shows that the current search capability for NEOs/NEAs is capable of finding and tracking objects so small -- about 3 meters (10 feet) in this case -- that they pose no surface danger (as well as larger ones, that is). The real problem in searching is that it's hard to find these rocks in the parts of the sky that are too close to the direction to the Sun, and far enough away so that any potential collision of a really big one could be detected years in advance.

I await reports of any observations of the bolide or (!) fragments found.
Having spent my whole work day (and four
extra [unpaid!] hours) yesterday dealing with
incoming observations of 2008 TC3, I'm actually
glad the object hit the atmosphere and is no more!

We were lucky to find this object. It's only about
two meters in diameter and we can only see such
objects when they are very close to the earth.
Which means if they are going to hit us at the discovery
apparition, the event will occur within a few days.

Larger objects, likely to survive atmospheric
entry mostly intact, can be seen much further out
and we have much longer lead times to possible
impacts.

Gareth Williams, Minor Planet Center
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Old 2008-10-07, 16:38   #5
ewmayer
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Hi, Gareth - nice to hear about this from the horse's mouth as it were. Must've been quite exciting for you folks.

Hey, remember that no-longer-useful-to-me Alphaserver I mentioned in one of discussions earlier this year? I intend to donate it to some educational institution which could use it [most likely as fileserver] before end of the year - you said you didn't really have a need for another Alpha, but just thought I'd check once more. Going once, going twice...
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Old 2008-10-07, 16:53   #6
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Quote:
Originally Posted by ewmayer View Post
Hi, Gareth - nice to hear about this from the horse's mouth as it were. Must've been quite exciting for you folks.
It was a hectic day and I'm working from home today
to unwind.

Quote:
Hey, remember that no-longer-useful-to-me Alphaserver I mentioned in one of discussions earlier this year? I intend to donate it to some educational institution which could use it [most likely as fileserver] before end of the year - you said you didn't really have a need for another Alpha, but just thought I'd check once more. Going once, going twice...
I think the problem with the Alphaserver was that
it wasn't very fast. So thanks for thinking of us, but
it wouldn't be useful to us.

Btw, I need to contact you for a current Mlucas code
snapshot.

Gareth
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Old 2008-10-07, 18:16   #7
Uncwilly
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I read that KLM was informed (ahead of time) that one of their flight crews might actually see the entry. They reported back that they had seen within 15 seconds of the project time. They were 750 miles from it, yet still saw it.
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Old 2008-10-07, 20:53   #8
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Quote:
Originally Posted by Graff View Post
Having spent my whole work day (and four
extra [unpaid!] hours) yesterday dealing with
incoming observations of 2008 TC3, I'm actually
glad the object hit the atmosphere and is no more!

We were lucky to find this object. It's only about
two meters in diameter and we can only see such
objects when they are very close to the earth.
Which means if they are going to hit us at the discovery
apparition, the event will occur within a few days.

Larger objects, likely to survive atmospheric
entry mostly intact, can be seen much further out
and we have much longer lead times to possible
impacts.

Gareth Williams, Minor Planet Center

Wow- THE Gareth Williams??!! As an avid comet seeker, for many years
I was a subscriber to the IAU circulars and the MPECs, so the name is very
familiar. Those little white cards, arriving by snail-mail, and then in the later
years by e-mail, were a huge factor in my everyday life. Always bringing
news of a new distant supernova, new asteroid, or a comet to chase.
Many wonderful nights spent racing out to the desert with the latest
circulars in hand to see something new.

The current state-of-the art is incredible: discovery one night,
disintegration in the atmosphere the next.

Norm
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Old 2008-10-07, 21:43   #9
cheesehead
 
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Quote:
Originally Posted by Spherical Cow View Post
Absolutely amazing that they are now able to calculate the ephemeris of each new object that fast.
Edit: For other, future readers of this thread besides Spherical Cow and Graff:

Of course, the calculations themselves take only a moment on a modern PC. The real time constraint is getting enough measured positions of an object in the night sky, over a long enough arc so that the individual position uncertainties are small in comparison. Only then can a meaningful orbit with small-enough uncertainty to allow future predictions be computed.

Mathematically, three exact observations (each of them a two-dimensional position vector from the observer plus its associated time of measurement) are sufficient (except in weird cases) to give enough data for calculation of an orbit. In practice, no measurement is exact, so the larger the number of observations and the longer an arc in the sky they cover, the better-determined the orbit can be, with smaller uncertainties. With a new object, the highest priority is to get enough observations to produce a orbit precise enough to re-find the object the next time it's in a favorable position to be seen from Earth. Once the same object can be observed in four different years (well, four oppositions, which is generally about the same), its orbit can be computed precisely enough to allow its position ephemeris to be calculated for many years into the future, and make it elegible to be named by the discoverer.

An object as close to Earth as this one was when discovered is plenty close enough for its motion to take it over a substantial arc during a short time. Then the problem becomes one of keeping up with it -- if the initial observer gets only one position, no orbit can be projected; if only a couple of positions an hour or so apart, then the preliminary path projection may not be good enough for other observers to find it (which, after all, is just a small point of light among millions of other points of light). If the object is passing very, very close, its motion across the sky will be fast, making it more difficult to find based on just an imprecise preliminary path.

Quote:
Originally Posted by Spherical Cow View Post
As an avid comet seeker, for many years I was a subscriber to the IAU circulars and the MPECs,
Oh ... you already knew all that stuff.

Last fiddled with by cheesehead on 2008-10-07 at 21:51
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Old 2008-10-07, 21:57   #10
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Quote:
Wow- THE Gareth Williams??!!
I was just reading the Forum with the laptop
sitting with my wife on the loveseat. I just showed
her the above remark and she was most chuffed.

Gareth

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Old 2008-10-07, 22:04   #11
cheesehead
 
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Chuffed? Hmmm ...

http://english2american.com/dictionary/c.html (entry has important caveats!)

Hope that's okay. Some other online dictionaries might mislead, not having the above important caveats.

Last fiddled with by cheesehead on 2008-10-07 at 22:21
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