# Future asteroid impact?

4 views

### Richard Akerman

Oct 16, 1990, 11:59:00 AM10/16/90
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My former supervisor mentioned to me that he had heard vaguely that someone (in
New South Wales?) had found an asteroid whose orbit would intersect with that
of earth sometime in the future. Can anyone give me more details on this? I'm
not talking about an earth approacher or 1989 FC.

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= Richard J. Akerman | BitNet: Akerman@QUCdnAst * | =
= Incompetent Physics | INet: Ake...@Bill.Phy.QueensU.Ca * | "I will go =
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### Gregory Carter

Nov 1, 1990, 5:53:57 PM11/1/90
to
Hello!

Neato net news group. Can anyone TELL ME, some few simple equations for
figuring out:

The size of the CRATER of an impact event, given:

Density of impact body (Asteroid)
Speed(Asteroid)
Mass

Density of the target body being impacted
Mass

And anything MORE would be helpful...just how much can you tell say,
from what kind and amounts of material would be ejected, if say

CERES hit the Earth? What would happen?

--Gregory

### Mike Van Pelt

Nov 1, 1990, 9:32:07 PM11/1/90
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In article <1990Nov1.2...@daffy.cs.wisc.edu> gca...@globey.cs.wisc.edu (Gregory Carter) writes:
>Neato net news group. Can anyone TELL ME, some few simple equations for
>figuring out: The size of the CRATER of an impact event, given:

There's a pretty good treatment of this in the article "Giant Meteor
Impact", which was a "science fact" article in Analog in the late
sixties/early seventies. It was reprinted in one of the Analog
Annuals, back when they called them "Analog n" where n was from 1 to 6.
I forget the author.
--
Mike Van Pelt | What happens if a big asteroid hits Earth?
Headland Technology | Judging from realistic simulations involving a
(was: Video Seven) | sledge hammer and a common laboratory frog, we
...ames!vsi1!v7fs1!mvp | can assume it will be pretty bad. -- Dave Barry

### Richard Akerman

Nov 5, 1990, 11:10:44 AM11/5/90
to
While the field of asteroid studies is a rich and diverse one, it seems that
all everyone wants to know about is asteroid impacts. My field of study is
asteroid orbital evolution but I do have lots of asteroid references. I
apologise if my information is somewhat dated.

Like everything, calculating the results of an asteroid impact is complicated.
Here is the exact formula:

"...the diameter, D , of a terrestrial impact crater can be estimated from
t

D = c * K (W * rho /rho )^(1/3.4)
t f n a t

where c is the crater collapse factor (nominally 1 for craters <~ 3 km
f
diameter and 1.3 for craters >~ 4 km in diameter), K =0.074 km
n
kilotons^(-1/3.4) is an empirical constant derived from the diameter and
explosive yield for the Jangle U nuclear crater, rho = 1.8 g cm^-3 is the
a
estimated density of the alluvium at the Jangle U site in Yucca Flat, Nevada
rho is the mean density of the target rocks, and
t
W= pi * d^3 * delta * v^2/ (12 * 4.19 * 10^10) kilotons TNT equivalent is the
kinetic energy of a projectile of diameter d, density delta, and velocity v,
all measured in cgs units." (Shoemaker, 1983)

More generally, one can use:

Diameter Number of objects Impact probability Impact energy
(km) (impacts/year) (* 5*10^20 ergs)

10 10 10^-8 10^9
1 1 000 10^-6 10^6
0.1 100 000 10^-4 10^3

(after Gehrels, 1985)

assuming simple scaling laws. Note that 5*10^20 ergs = 13 000 tons TNT
equivalent, or the energy released by the Hiroshima A-bomb.

I have a lot more information along these lines if anyone is interested.

_References_

Gehrels, T. 1985 Asteroids and comets. _Physics Today_ 38, 32-41.
[an excellent general overview of the subject for the layman]

Shoemaker, E.M. 1983 Asteroid and comet bombardment of the earth.
_Ann. Rev. Earth Planet. Sci._ 11, 461-494.
[very long and fairly technical but a comprehensive examination of the
subject]

### Richard Akerman

Nov 6, 1990, 12:59:33 PM11/6/90
to
I thought that it might be useful to provide a list of some of the better
references on the subject of asteroids and impacts in particular.

_References_

Alvarez, L. W., Alvarez, W., Asaro, F. & Michel, H. V. 1980 Extraterrestrial
cause for the Cretaceous-Tertiary Extinction. _Science_ 208, 1095-11108.

[the seminal paper demonstrating that an iridium anomaly of presumably e
asteroidal origin is synchronous with the K-T boundary. Professional-level]
[In the October 1990 _Scientific American_ there is an article by Alvarez
decribing the current status of the impact hypothesis and a counter-articlle
on the volcanic hypothesis]

Cunningham, C.J. 1988 _Introduction to Asteroids: The Next Frontier_.
(Richmond: Willmann-Bell, Inc.)

[An excellent book which examines all aspects of asteroids and asteroid studies
very well-written, fascinating reading. General-level. Recommended for
anyone interested in asteroids. Provides an extensive list of references.]

Gehrels, T. 1985 Asteroids and comets. _Physics Today_ 38, 32-41.

[A very good general-interest article on asteroids and comets. T. Gehrels is
on of the major asteroid researchers. General-level.]

Helin, E. F. 1987 Near-earth asteroid searches: Status and prospects.
pp. 147-156 in _The Evolution of the Small Bodies of the Solar System_
M. Fulchignoni & L. Kresak, eds. (North Holland: Amsterdam).

[Helin is a key researcher in this area. Professional-level.]

Lemonick, M.D. 1989 Whew! That was close. _Time_ 133(#4?), 54.

[The popular media take(s) a look at asteroid 1989 FC]

Morrison, D. & Chapman, C.R. Target earth: It _will_ happen. _Sky &_
_Telescope_ 79 (March 1990), 261-265.

[Very broad general overview. They have also published a book on the topic
called something like _Cosmic Catastrophes_. Check last year's S&T for more
info.; there should be an ad for it somewhere.]

_Physics Today_ 1982 Dinosaur extinction due to asteroid? _Physics Todday_
35, 19-21 (Abstract).

Pierce, D.A. 1990 A "hollow" asteroid. _Sky & Telescope_ 79, 272-273.

[near-earth asteroid observations described by someone who has actually done
them]

Shoemaker, E.M. Asteroid and comet bombardment of the earth. _Ann. Rev.._
_Earth Planet. Sci._ 11, 461-494.

[Comprehensive. Shoemaker is another major asteroid researcher.
Professional-level.]

_Sky & Telescope_ 1987 Pinpointing near-earth asteroids. _Sky &_
_Telescope_ 74, 576 (Abstract).

[The difficulties of detecting near-earth asteroids.]

Spratt, C.E. The Aten-Apollo-Amor close-approach minor planets.
_J. Roy. Astron. Soc. Can._ 81, 8-18.

[General interest article with lots of information about the AAA asteroidds.]

Wetherill, G. W. 1979 Apollo objects. _Scientific American_ 240, 54-655.

[An excellent general-interest examination of the Apollo earth-crossing
asteroids by one of the chief researchers in the field.]

Of course, the asteroid "bibles" are:

_Asteroids_ 1979 T. Gehrels, ed. (Tucson: Univ. of Arizona Press)
_Asteroids II_ 1989 R. Binzel, T. Gehrels & M.S. Matthews, eds. (Tucson: Univ.
of Arizona Press)

I hope this is somewhat useful. There are zillions more references but I tried
to select the most useful.

Richard Akerman

### Richard Akerman

Nov 6, 1990, 5:49:20 PM11/6/90
to
Sorry to bombard everyone with asteroid information but I thought that I would
add that the Planetary Society provides Helin and Shoemaker with support for
their Planet-Crossing Asteroid Search (PCAS). In the latest _Planetary Report_
(Vol. X, No. 5; Sept./Oct. 1990) there is a short article by Helin describing
the current status of PCAS. There is also a short discussion of what we could
do to stop an incoming asteroid in the Q&A section. As well, Morrison and
Chapman's book _Cosmic Catastrophes_ (which I gather describes in detail the
impact hypothesis for dinosaur extinction at the K-T boundary and everything
you ever wanted to know about the earth being smashed, destroyed, diced, sliced
and generally fried) is available from the Society for \$23.00 (\$20.50 if you're
a member).

Richard Akerman

### Richard Akerman

Nov 6, 1990, 6:04:06 PM11/6/90
to
In article <9...@qusuna.queensu.CA> ake...@qucis.queensu.CA (Richard Akerman) writes:
>"...the diameter, D , of a terrestrial impact crater can be estimated from
> t
>
>D = c * K (W * rho /rho )^(1/3.4)
> t f n a t
>
>where c is the crater collapse factor (nominally 1 for craters <~ 3 km
> f
>diameter and 1.3 for craters >~ 4 km in diameter), K =0.074 km
> n
>kilotons^(-1/3.4) is an empirical constant derived from the diameter and
>explosive yield for the Jangle U nuclear crater, rho = 1.8 g cm^-3 is the
> a
>estimated density of the alluvium at the Jangle U site in Yucca Flat, Nevada
>rho is the mean density of the target rocks, and
> t
>W= pi * d^3 * delta * v^2/ (12 * 4.19 * 10^10) kilotons TNT equivalent is the
^^^^^^^^^^^^

I think from some quick calculations given that 1 Mt TNT = 4.19*10^22 ergs
the above number should be 4.19*10^19 for correct results. I guess that's
what I get for copying directly from the article without checking their
results. My thanks to Michael Woodhams for pointing this out.

>kinetic energy of a projectile of diameter d, density delta, and velocity v,
>all measured in cgs units." (Shoemaker, 1983)

Richard Akerman
Incompetent Physics Grad. Student with malfunctioning .signature

Richard J. Akerman | BitNet: Akerman@QUCdnAst * |

Incompetent Physics | INet: Ake...@Bill.Phy.QueensU.Ca * | "I will go

Queen's University | INet: Ake...@Iris1.Phy.QueensU.Ca |

Kingston, Ontario | INet: Ake...@QUCIS.QueensU.Ca | - Arthur Dent

Disclaimer: Take heart; my opinions are probably wrong.

Quote #2: The mind is an epiphenomenon arising from the activity of the brain.

### Richard Akerman

Nov 7, 1990, 8:15:46 AM11/7/90
to
Just a note for those of you actually interested in calculating cratering
things: typical asteroid densities range around 3 g cm^-3 and earth-impact
velocities range around 20 km/s. Also note that, as is evident from the units,
the D formula previously given produces results in kilometers. One could of
t
course use a K of 74 m kiloton^(-1/3.4) to obtain results in meters.
n