asteroid close approach, 2011 Nov 08

On Wed, 02 Nov 2011 06:11:13 -0500, "U-m757\\bud"
wrote:

The asteroid is supposed to be about magnitude 11.5, making it barely visible
in small teelscopes. There's a finder chart in the November, 2011, issue of
Sky and Telescope. Closest approach is about sunset in the mid-US.
I think the only interesting part is that the asteroid is moving fast
enough for motion to be visible if you can manage to find it.

Tricky visually, but trivial with the smallest of scopes and the most
basic of imaging equipment.

For the sake of general interest: Can we examine Brad's "lunar
glancing impacts" in greater depth? How does an airless body, like the
Moon, affect impacting bodies? I presume the final angle of impact (on
a theoretically smooth lunar surface) would be mass/velocity/approach
angle dependent? Despite a preponderance of round craters, of all
sizes, there do seem to be signs of lunar chain craters. Suggesting a
bouncing/glancing trajectory of a "smallish" object travelling at high
enough velocity (or having enough momentum) to cause a Dambuster's
"skipping" effect. Hardly a "glancing off" since they never escaped
the Moon's gravity again. How large and/or fast does a B.R.A.D (Big
Rogue Alien Destroyer) have to be, in reality, to achieve a true
"glancing impact" on the Moon? In best Hollywood, bone crunching
style! Perhaps it's not such a simple question?

Chris.B wrote:
For the sake of general interest: Can we examine Brad's "lunar
glancing impacts" in greater depth? How does an airless body, like the
Moon, affect impacting bodies? I presume the final angle of impact (on
a theoretically smooth lunar surface) would be mass/velocity/approach
angle dependent? Despite a preponderance of round craters, of all
sizes, there do seem to be signs of lunar chain craters. Suggesting a
bouncing/glancing trajectory of a "smallish" object travelling at high
enough velocity (or having enough momentum) to cause a Dambuster's
"skipping" effect. Hardly a "glancing off" since they never escaped
the Moon's gravity again. How large and/or fast does a B.R.A.D (Big
Rogue Alien Destroyer) have to be, in reality, to achieve a true
"glancing impact" on the Moon? In best Hollywood, bone crunching
style! Perhaps it's not such a simple question?

Think celestial mechanics. The impactor is coming in on a hyperbolic
trajectory. If the distance from the focus of the hyperbola to the
vertex -- from the center of the body to periapsis -- is less than the
body's radius, you've got impact. More and you've got a close flyby.
In order to have a grazing impact, the trajectory can't go very far
beneath the surface. It's a low probability event, but it does happen.

It's instructive to use the same "B plane" approach that JPL navigators
use for spacecraft. Set up a plane perpendicular to the incoming
asymptote of the hyperbola, and examine the point in this plane where
the asymptote -- not the trajectory itself -- intersects the plane.
Given the mass of the body and the incoming velocity ("V-infinity"), you
can determine what the miss distance must be in the B-plane in order to
have a grazing impact. Think of the B plane as a dartboard: you have to
hit a fairly narrow ring. It will turn out that *lower* velocities will
have a higher chance of a grazing impact, because the trajectory is bent
more.

The above is pretty much independent of the size of the impactor, at
least until it gets well beyond "dinosaur killer" size.

I also seem to recall that craters appear circular until the angle of
incidence gets to be quite large, on the order of 70(?) degrees from
vertical.

Chains of craters can be explained by binary objects. You're not going
to get a "skipping" effect like a stone on a lake -- you'll get a splash
with secondary craters.

-- Bill Owen

On Wed, 2 Nov 2011 13:11:08 -0700 (PDT), "Chris.B"
wrote:

For the sake of general interest: Can we examine Brad's "lunar
glancing impacts" in greater depth? How does an airless body, like the
Moon, affect impacting bodies? I presume the final angle of impact (on
a theoretically smooth lunar surface) would be mass/velocity/approach
angle dependent?

A body which strikes the Moon is typically in an elliptical orbit
around the Sun. In the case of the Moon, which is essentially a binary
planet with the Earth, a body passing within the system undergoes some
perturbation, which tweaks (possibly substantially) the original
orbit. Depending on the velocity of the object with respect to the
Moon (which is largely determined by the eccentricity of its orbit),
it may actually be captured by the Moon, in which case it will enter
an approximately hyperbolic orbit with respect to the Moon, or it may
simply crash at something above the lunar escape velocity. In any
case, the effect of the Moon's gravity is to somewhat focus bodies
into collisions- in other words, the Moon appears to have a larger
collisional cross section than its actual size. But not by a lot.

Despite a preponderance of round craters, of all
sizes, there do seem to be signs of lunar chain craters. Suggesting a
bouncing/glancing trajectory of a "smallish" object travelling at high
enough velocity (or having enough momentum) to cause a Dambuster's
"skipping" effect.

A few percent of impacts are at low angles- under 15° or so, which can
create oval craters or crater chains. Crater chains are not caused by
skipping, however. They are caused by secondary debris, or by multiple
impacts as the parent breaks up before the impact (like Hale-Bopp).

Hardly a "glancing off" since they never escaped
the Moon's gravity again. How large and/or fast does a B.R.A.D (Big
Rogue Alien Destroyer) have to be, in reality, to achieve a true
"glancing impact" on the Moon? In best Hollywood, bone crunching
style! Perhaps it's not such a simple question?

Any body which enters at greater than the lunar escape velocity could
theoretically touch the surface and then continue out into space
again- it doesn't matter whether it's a marble or an asteroid. But in
reality, I think a non-glancing impact is likely to eject more
material from the lunar surface. That's probably the mechanism that
explains lunar meteorites on Earth. However, there's nothing to
suggest that anything from the Moon has ever hit the surface of the
Earth with hypersonic velocity. Stuff knocked off the surface of the
Moon is likely to be too small to survive to the ground as anything
other than ordinary meteorites- that is, harmless, non-cratering
events of interest mainly to people who like owning expensive rocks.

On Nov 2, 8:15*am, Chris L Peterson wrote:
On Wed, 2 Nov 2011 06:25:29 -0700 (PDT), Brad Guth

wrote:
No, it wouldn't. No debris would be large enough to reach the Earth's
surface. At most, we'd see a meteor shower, and it wouldn't be dense
enough to be much of a *threat to our satellites.
You have such a simulator?

Yes. Such impacts are modeled with a variety of simulation tools. In
this case, however, you can get a pretty good estimate of the likely
issues simply by looking at energy- which is not very large.
But your simulator can't be public accessed or much less tweaked?

If this 400 meter sphere of potential doom is made of fluff (less than
2 g/cm3), you could be right. If the asteroid is mostly metallic and
pushing 8+ g/cm3 would put a whole other interpretation to this one.
Do you know what it's made of?


Are you saying that glancing blows do not happen?

No, although they are very rare.

Any contact of similar or greater mass at 13+ km/sec would yield
enough impact secondary shard exit velocity to escape the moon, and
thousand tonne shards of paramagnetic basalt are going to be
problematic.

No, they are not (and what does "paramagnetic" have to do with
anything?) If you're so interested in simulation, where's yours? How
do you think that a lunar collision with a mere 400 meter asteroid is
going to produce a flurry of Earth-directed, non-frangible debris with
individual diameters greater than 10-20 meters, which would be the
minimum requirement for reaching the ground with high velocity?

You really don't have any idea at all what you are talking about.

And again, you haven't addressed the FACT that there is zero
possibility of this body striking the Moon at all.

3.5+ g/cm3 = paramagnetic basalt. (1 m3 = 3.5 tonnes)

Again and again, you keep taking credit for the miss. This means you
also get the blame and responsibility for future hits. How's your
personal liability insurance coverage for having caused global trauma?
(got 100 trillion worth of insurance coverage?)

Your interpretation of zero-risk from any impact of 264e6 tonnes at 13
km/sec is noted.

Perhaps the worse case for Earth is a 1000 m3 solid of fused
paramagnetic basalt that'll eventually find its way to Earth, not to
mention a glancing blow whereas the asteroid lives on to return
another day.

If a 400 meter asteroid can get so close, then what's stopping a 4 km
version from doing the same or worse by actually making contact with
either our moon or Earth?

Do you have a plan?

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On Wed, 2 Nov 2011 16:48:05 -0700 (PDT), Brad Guth
wrote:

But your simulator can't be public accessed or much less tweaked?

Can yours?

If this 400 meter sphere of potential doom is made of fluff (less than
2 g/cm3), you could be right. If the asteroid is mostly metallic and
pushing 8+ g/cm3 would put a whole other interpretation to this one.
Do you know what it's made of?

It doesn't matter what it's made of. The collisional dynamics are
almost identical for stone or for iron. The KE released is determined
by mass, not density. The energy released is orders of magnitude
greater than the material strength of either stone or iron.

Again and again, you keep taking credit for the miss.

Credit? I'm simply pointing out that the trajectory is known, and it
WILL absolutely miss. There's no credit to take. It's simple
observation and simple physics. Bodies don't miraculously change
direction.

If a 400 meter asteroid can get so close, then what's stopping a 4 km
version from doing the same or worse by actually making contact with
either our moon or Earth?

Absolutely nothing. Fortunately, the size of asteroidal and cometary
bodies is described by a power law, and we therefore know that large
collisions are rare. But they happen. Perhaps by the time the next one
might occur, we'll have the technology to stop it. Or not.

Do you have a plan?

I've got more realistic worries to concern myself with. It's been
millions of years since the last asteroidal collision large enough to
have global effects, and is likely to be millions of years before the
next. There's a very good chance there will be no humans on Earth when
it happens.

That's about the Moon's orbit, so not very close.

On Nov 2, 4:57*pm, Chris L Peterson wrote:
On Wed, 2 Nov 2011 16:48:05 -0700 (PDT), Brad Guth

wrote:
But your simulator can't be public accessed or much less tweaked?

Can yours?

If this 400 meter sphere of potential doom is made of fluff (less than
2 g/cm3), you could be right. *If the asteroid is mostly metallic and
pushing 8+ g/cm3 would put a whole other interpretation to this one.
Do you know what it's made of?

It doesn't matter what it's made of. The collisional dynamics are
almost identical for stone or for iron. The KE released is determined
by mass, not density. The energy released is orders of magnitude
greater than the material strength of either stone or iron.

Again and again, you keep taking credit for the miss.

Credit? I'm simply pointing out that the trajectory is known, and it
WILL absolutely miss. There's no credit to take. It's simple
observation and simple physics. Bodies don't miraculously change
direction.

If a 400 meter asteroid can get so close, then what's stopping a 4 km
version from doing the same or worse by actually making contact with
either our moon or Earth?

Absolutely nothing. Fortunately, the size of asteroidal and cometary
bodies is described by a power law, and we therefore know that large
collisions are rare. But they happen. Perhaps by the time the next one
might occur, we'll have the technology to stop it. Or not.

Do you have a plan?

I've got more realistic worries to concern myself with. It's been
millions of years since the last asteroidal collision large enough to
have global effects, and is likely to be millions of years before the
next. There's a very good chance there will be no humans on Earth when
it happens.

Your denial of being in denial is noted. That's kind of the same
excuse GW Bush, Dick Cheney as well as our FBI/NSA/CIA/MI6/Pentagon
and DoD each had to say about OBL prior to 9/11, essentially informing
us by way of their obfuscation that we had nothing to worry about..

Your orbital simulator that can't be shown nor demonstrated in public
must be a really good one if it takes multiple 3-body variables into
account.

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On 11/1/11 11:15 PM, Brad Guth wrote:
On Nov 1, 9:02 pm, Sam wrote:


Brad, get a life! Look at the path of 2005_YU55 with respect to
the Earth and Moon
http://neo.jpl.nasa.gov/images/2005_...oach_movie.gif

Are you jacking off, again?


Hey Brad - Seen from a different perspective
http://neo.jpl.nasa.gov/images/2005_yu55b.jpg

Thank you, Bill and Chris, for sharing your time and expertise in
answering my lunar impact question so thoroughly.