Big Rocks & The Mayhem That Follows

If an Earth-like planet was struck by a 1000km-diameter planetoid (a
mini-version of the Mars-sized rock that might have hit Earth and
formed the moon), would it:

1) Pump enough heat into the environment to boil off the oceans?
2) Shatter the crust around the planet, or just a local continent?
3) What time scale do the effects take place over? Would it take weeks
or hours for the crust to sustain its damage? Weeks or hours for the
impact heat to suffuse the environment? Something in between?

Mike Miller, Materials Engineer

That depends on the relative speed it was travelling. More than likely a
1000km sized object travelling at any speed has enough energy to wipe
everything off this planet... in hours i'd assume...

"Mike Miller" wrote in message
om...
If an Earth-like planet was struck by a 1000km-diameter planetoid (a
mini-version of the Mars-sized rock that might have hit Earth and
formed the moon), would it:

1) Pump enough heat into the environment to boil off the oceans?
2) Shatter the crust around the planet, or just a local continent?
3) What time scale do the effects take place over? Would it take weeks
or hours for the crust to sustain its damage? Weeks or hours for the
impact heat to suffuse the environment? Something in between?

Mike Miller, Materials Engineer

(Mike Miller) writes:

If an Earth-like planet was struck by a 1000km-diameter planetoid (a
mini-version of the Mars-sized rock that might have hit Earth and
formed the moon), would it:

1) Pump enough heat into the environment to boil off the oceans?

It would not only boil the oceans, it would not only melt but volatize
significant amounts of both itself and the Earth.


2) Shatter the crust around the planet, or just a local continent?

There would not be _any_ crust left --- just a global layer of magma.


3) What time scale do the effects take place over?

For a straight-on impact, on the order of 1.5 minutes --- the time it takes
for the planetoid to move through its own diameter at escape velocity.

For a glancing impact, on the order of 90 minutes --- the time it takes for
the debris to orbit the Earth once.


Would it take weeks or hours for the crust to sustain its damage?

The crust would be demolished in on the order of hours --- the time it
takes for a seismic shock wave to propagate through the Earth.


Weeks or hours for the impact heat to suffuse the environment?

The heat will "suffuse" the atmosphere and biosphere in the time
that it takes the debris from the impact to re-impact the earth ---
on the order of 90 minutes or so. However, it will take on the order
of geological timescales for things to settle down and thermally
re-equilibrate.


-- Gordon D. Pusch

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(Gordon D. Pusch) wrote in message ...

For a glancing impact, on the order of 90 minutes --- the time it takes for
the debris to orbit the Earth once.

Just to be clear: are you saying that the oceans would boil off in 90
minutes, or is that also a matter of hours as the seismic waves
propogate around the globe?

Mike Miller, Materials Engineer

(Mike Miller) writes:

(Gordon D. Pusch) wrote in message ...

For a glancing impact, on the order of 90 minutes --- the time it takes
for the debris to orbit the Earth once.

Just to be clear: are you saying that the oceans would boil off in 90
minutes,

No, I am saying that for a glancing impact, most of the energy of the
incoming body is still stored in the spray of debris, which could in
principle make nearly a complete orbit around the Earth before re-impacting
the Earth. To an _ORDER OF MAGNITUDE APPROXIMATION_ (i.e., power of ten)
the timescale to orbit the Earth is on the order of 90 minutes, so I would
expect that most of the debris would re-impact on a time scale that is long
compared to 9 minutes, but short compared to 900 minutes; the later would
require the chunk of debris to be on a fairly eccentric elliptical fractional
orbit.

The energy involved is so enormous that the oceans would be boiled off
essentially as fast as the debris re-impacted the Earth. (The debris makes
its fractional orbit around the Earth at many times the speed of sound,
even in rock.)


or is that also a matter of hours as the seismic waves
propogate around the globe?

I was saying that it takes on the order of several hours for the seismic
waves produces by the impact to propagate from one side of the Earth to the
other --- where again, by "order of magnitude," I meant "more than several
tenths of an hour, and less than several tens of hours." However, unfortunately
I mis-remembered how long it takes for seismic waves to propagate through
the Earth: Characteristic seismic wave velocities are actually in the range
of 4--8 kps, so it will actually take less than an hour for P-waves (which
are the fastest seismic waves) to propagate completely through the planet.

Again, the amount of energy involved in such a large impact is so enormous
that the seismic shock waves it produces will completely shatter the crust
as they propagate through it. In the wake of the shock wave from the main
impact, plus the shock waves produced by the re-impacting debris, nothing
will be left but an ocean of magma, perhaps dotted with rapidly disintegrating
rafts of melting crust.


-- Gordon D. Pusch

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(Gordon D. Pusch) wrote in message ...

In the wake of the shock wave from the main impact, plus the shock waves
produced by the re-impacting debris, nothing will be left but an ocean
of magma, perhaps dotted with rapidly disintegrating rafts of melting crust.

Excellent, graphic description. Thank you, that was informative input.

Mike Miller, Materials Engineer

"Mike Miller" wrote in message
om...
If an Earth-like planet was struck by a 1000km-diameter planetoid (a
mini-version of the Mars-sized rock that might have hit Earth and
formed the moon), would it:

1) Pump enough heat into the environment to boil off the oceans?
2) Shatter the crust around the planet, or just a local continent?
3) What time scale do the effects take place over? Would it take weeks
or hours for the crust to sustain its damage? Weeks or hours for the
impact heat to suffuse the environment? Something in between?

Mike Miller, Materials Engineer

Try using the catastrophe calculator at the link provided:

http://www.lpl.arizona.edu/impacteffects/

In article ,
Gordon D. Pusch wrote:
I mis-remembered how long it takes for seismic waves to propagate through
the Earth: Characteristic seismic wave velocities are actually in the range
of 4--8 kps, so it will actually take less than an hour for P-waves (which
are the fastest seismic waves) to propagate completely through the planet.

Bear in mind that normal seismic waves are *not* shock waves. There is a
difference, and it matters in this case.

Again, the amount of energy involved in such a large impact is so enormous
that the seismic shock waves it produces will completely shatter the crust
as they propagate through it...

Quite so. And because shock waves alter the properties of the material as
they pass through it, they are *not* limited to the speed of sound in the
original material. The speed of a shock wave depends on how energetic it
is. Really energetic ones move much faster than the speed of sound. The
speed of sound is the speed at which *weak* disturbances propagate.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Christopher M. Jones) writes:

(Gordon D. Pusch) wrote in message ...
(Mike Miller) writes:

If an Earth-like planet was struck by a 1000km-diameter planetoid (a
mini-version of the Mars-sized rock that might have hit Earth and
formed the moon), would it:
[...]
3) What time scale do the effects take place over?

For a straight-on impact, on the order of 1.5 minutes --- the time it takes
for the planetoid to move through its own diameter at escape velocity.

For a glancing impact, on the order of 90 minutes --- the time it takes for
the debris to orbit the Earth once.

Close. Any "lithobraking" glancing impact will send the bulk of
the impactor on a decidedly sub-orbital path, a mere atmospheric
impact would probably not stop the impactor from simply passing
through and heading back out to interstellar space. Even on the
sub-orbital impact the apogee could be quite high, and it may
take hours for the impactor to come around again. More likely
is that substantial amounts of material from the impact (both
from the impactor and the crust) will head out on low sub-orbital
trajectories which will reimpact the far side of Earth on time
scales closer to 45 minutes (half an orbit).

As I noted in another post, "on the order of 90 minutes " means
"within a power of ten of 90 minutes," i.e., probably more than
9 minutes, and probably less than 900 minutes (15 hrs). Between
45 minutes and "several hours" is certainly bracketed within that range.


-- Gordon D. Pusch

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