[meteorite-list] Japanese impact animation video

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat Jul 8 04:20:33 2006
Message-ID: <003301c6a267$4e40d240$3c394842_at_ATARIENGINE>

Hi, Francis, List,

    Hey, I nitpick, too. The key phrase in the nit
you picked is "if deflected." We could be hit by
Ceres IF it were deflected sufficiently, or we could
be hit by Mars IF it were deflected sufficiently...
and so forth. However, all of these bodies have
orbits that are stable for the long term, say, some
billions of years or more. Who's going to do the
deflecting? What deflects Kuiper Belt objects
anyway? What's THAT all about? There are
so many, they deflect each other? Hmm.

    If you want the improbable, let's just go for
the old XIXth century favorite: the interstellar
interloper! We giggle at the old astronomers
for so easily throwing out "interstellar interlopers"
as explanations; however, empirically we can only
say that none have been observed in the last
two centuries, the only only period of time for
which the technology of observation was sufficiently
developed for us to have detected one!

    The largest object that COULD hit us is the
minor planet 2060 Chiron, aka comet 95P:
Perihelion Distance: 8.4639422 AU; Orbital Period: 50.7 years
Eccentricity: 0.3831118; Inclination: 6.93540 degrees
Semi-Major Axis: ~13.70354 AU; Aphelion: ~18.94314 AU
Mass: 2 x 1018 to 1019 kg; Diameter: 148 to 208 km
Rotation Period: ~5.9 hours; Asteroid Classification: B-type
Discoverer: Charles Kowal; November 1, 1977

    Like all the other Centaur objects, its orbit is
only meta-stable, with a lifetime on the order of
no more than 100,000 or so. (Wiki says 10^6 to
10^7, but I think Wiki's whacky on this one.) Of course,
we don't know how long it's been in that Centaur orbit;
there's the rub. Is it new to the neighborhood? Just finished
unpacking 10,000 years ago? Or, is its lease up in only
another 4000 years? At any rate, a collision with a
Centaur object has a finite, non-vanishing probability.

    It has been calculated that in 1664 BC Chiron approached
Saturn to within approximately 16 million kilometres; only
3 million km further away than Saturn's largest outer moon
Phoebe, and within the orbital radii of many of Saturn's
newly discovered minor satellites. These approaches mean
trouble. The opportunity for an encounter with Saturn with
varying degrees of closeness recurs every 1493.115 years,
so there was one in 171 BC and another in 1322 AD, and
so forth... Not exactly highly infrequent events!

    Chiron, if deflected, stands an 80% chance of being
ejected to the outer system and a 20% chance of being
deflected to the inner system. If it became an inner
system object, well, would you want a rampaging
Centaur cavorting about in YOUR neighborhood?
especially one 100+ miles across?

    I don't know if Chiron would cause the sort of
damage in the video, but I think it's close. Here's
what the LPL Impact Calculator yields for a realistic
intercept with Chiron. (I placed the observer at the
antipodal spot, 20,000 km away from the impact.
That's where I'd want to be! Wouldn't you?)

Distance from Impact: 20000.00 km = 12420.00 miles
Projectile Diameter: 208000.00 m = 682240.00 ft = 129.17 miles
Projectile Density: 1200 kg/m^3 (if ICE, however, this figure
is based on Chiron having a bound rather than unbound coma,
without which density has been calculated to be 1875 kg.m^3.)
Impact Velocity: 47.00 km/s = 29.19 miles/s
Impact Angle: 45 degrees (average of random vectors)
Target Density and Type: All the same, doesn't matter.
Energy before atmospheric entry: 6.25 x 10^27 Joules =
1.49 x 10^12 MegaTons TNT, or if you like zeros,
1,490,000,000,000,000,000 tons of TNT.

The fireball has a diameter of 3160 miles.
Transient Crater Diameter: 784 km = 487 miles
Transient Crater Depth: 277 km = 172 miles
Final Crater Diameter: 1880 km = 1160 miles
Final Crater Depth: 2.86 km = 1.78 miles
The crater formed is a complex crater (ring basin).
The volume of the target melted or vaporized is
3.93e+07 km^3 = 9.43e+06 miles^3
Roughly half the melt remains in the crater,
where its average thickness is 81.4 km = 50.6 miles

At the observer's location (20,000 km away), the major
seismic shaking will arrive at approximately 4000 seconds:
Richter Scale Magnitude: 12.8
Mercalli Scale Intensity at a distance of 20000 km:
VI. Felt by all, many frightened, to VII. Damage negligible
in buildings of good design and construction; considerable
damage in poorly built or badly designed structures
Little rocky ejecta reaches this site; fallout is dominated
by condensed rock vapor from the projectile.

The air blast will arrive at approximately 60600 seconds.
Peak Overpressure: 211000 Pa = 2.11 bars = 29.9 psi
Max wind velocity: 296 m/s = 663 mph
Sound Intensity: 106 dB (May cause ear pain)
Damage Description: Multistory wall-bearing buildings
will collapse. Wood frame buildings will almost
completely collapse. Highway truss bridges will
collapse. Glass windows will shatter. Up to 90
percent of trees blown down; remainder stripped
of branches and leaves. Mind you, this is at the furthest
spot on the other side of the Earth! At 1/4th of the way
around the planet, or the very edge of the affected hemisphere,
the wind speed is 1660 mph, at 10,000 km. away.

    At "only" 8000 km. away, things get serious. The
thermal radiation is 20 times brighter than the Sun, and
all exposed persons will suffer serious 3rd degree burns
at about 80 seconds after impact. 2160 seconds later,
very small ejecta (dust) will land, 32 feet deep, hot and
suffocating. About 19000 seconds after that, a wind at
2540 mph will sweep over the spot. It is doubtful that
many, if any, humans in the affected hemisphere would

    Likely to extinct 90% to 96% of all life; hard to
calculate precisely, you know. Of course, we have not
suffered such an impact for the last 3,900,000,000 years,
so you could consider its probability to be low. But I look
at it this way: what if the MTI (Mean Time between Impacts)
for an object this size is 3,900,001,000 years...?

    Deflecting an object this large is a considerable problem.
Just look at the arguments we have today about how to deal
with a 500 METER rock on an intercept course! For a 100
KILOMETER body, I'd like to have lead time of a few centuries
at the very least and perhaps a millenium, a budget of 10^15
US dollars, a rational and united humanity, all possessing useful
skills, a solar-system-wide resource base...

    If you think a huge impact is improbable, what are the chances
of a rational and united humanity PLUS all those other things?
Talk about improbable!! [cackles hysterically and signs off.]

Sterling K. Webb
----- Original Message -----
From: "Francis Graham" <francisgraham_at_rocketmail.com>
To: <meteorite-list_at_meteoritecentral.com>
Sent: Friday, July 07, 2006 3:07 PM
Subject: Re: [meteorite-list] Japanese impact animation video
>> There is, of course, no object in the solar system
>> at the present time that could do that, but they
>> wanted all the drama they could get, I guess...
> I am not so sure one could categorically say that NO
> object exists in the solar system that could do that.
> A large Kuiper belt object, if deflected , might still
> hit the Earth just like that. We don't have a good
> enough map of the Kuiper belt to rule this out.
> But I nitpick. Sterling, your explanation was great,
> and I agree it is MOST IMPROBABLE that any solar
> system object today could do this.
> Seeing the nonflammable part of Big Ben enveloped by
> rock vapor was very sobering...
> Francis Graham
Received on Sat 08 Jul 2006 04:19:59 AM PDT

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