Small asteroid misses Earth by only four thousand miles

In article ,
Rodney Kelp wrote:
We're in the middle of an asteroid super highway. It's only a matter of time
before an accident happens and we get rear ended. Not all of them come from
the asteroid belt between mars and jupiter. Some could have sailed from
another galaxy or exploding supernova.

Possibly... but last I heard, no meteor -- let alone asteroid -- of
definitely extra-solar origin (velocity at Earth exceeding solar-system
escape velocity there) has ever been detected. Extrasolar dust grains
have been detected by spacecraft, but that's all.

The dominant hazard *is* objects perturbed from the main asteroid belt,
with an important secondary threat from comets (perturbed from the Kuiper
Belt or the Oort Cloud, farther out).
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote in message ...
In article ,
Rodney Kelp wrote:
We're in the middle of an asteroid super highway. It's only a matter of time
before an accident happens and we get rear ended. Not all of them come from
the asteroid belt between mars and jupiter. Some could have sailed from
another galaxy or exploding supernova.

Possibly... but last I heard, no meteor -- let alone asteroid -- of
definitely extra-solar origin (velocity at Earth exceeding solar-system
escape velocity there) has ever been detected. Extrasolar dust grains
have been detected by spacecraft, but that's all.

The dominant hazard *is* objects perturbed from the main asteroid belt,
with an important secondary threat from comets (perturbed from the Kuiper
Belt or the Oort Cloud, farther out).

How about the remnants of the K-T event on Yucatan ?

I read that 12 % of the ejecta escaped. Is there not a remarkable
amount of 1.00xx year objects compared with the others on neo ?

And if the Moon gets rearended, a good part of the ejecta must have
lunar escape speed, but not enough speed to escape Earth thereafter.
That must be how the meteorites identyifyed as moon rock got here.

Regards

Carsten Nielsen
Denmark

In article ,
Carsten Nielsen wrote:
The dominant hazard *is* objects perturbed from the main asteroid belt,
with an important secondary threat from comets (perturbed from the Kuiper
Belt or the Oort Cloud, farther out).

How about the remnants of the K-T event on Yucatan ?
I read that 12 % of the ejecta escaped...

Long gone. The survival time for small objects in an orbit very similar
to Earth's is short, because they'll make frequent (by geological time
standards) close encounters with Earth, which will alter their orbits
rapidly. (Close encounters are much more likely than actual hits.) The
timescale for them to be driven into the Sun or out to Jupiter (and thus
out of the solar system), or, less likely, to hit an inner planet, is
millions of years, not even tens of millions.

Is there not a remarkable
amount of 1.00xx year objects compared with the others on neo ?

Not that I'm aware of, once you allow for observational selection effects.
(The smaller objects are seen only when quite close, and tracked well
enough for orbit determination mostly when making a relatively slow
encounter, which strongly biases the selection toward near-Earth orbits.)

And if the Moon gets rearended, a good part of the ejecta must have
lunar escape speed, but not enough speed to escape Earth thereafter.
That must be how the meteorites identyifyed as moon rock got here.

It doesn't even have to be a rear-end impact, since ejecta go out in a
wide range of directions.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Carsten Nielsen wrote:

How about the remnants of the K-T event on Yucatan ?

I read that 12 % of the ejecta escaped.

Cite? This would be interesting info for the panspermia arguments I
sometimes participate in.

Is there not a remarkable
amount of 1.00xx year objects compared with the others on neo ?

I don't see that. The folks at jpl list four .99 year, seven 1.00 and
eight 1.01 year NEOs. For comparison there are three 1.99, five 2.00 and
six 2.01 year NEOs and four 2.99, six 3.00 and two 3.01 NEOs.


--
Hop David
http://clowder.net/hop/index.html

Henry Spencer ) wrote:
: In article ,
: Rodney Kelp wrote:
: We're in the middle of an asteroid super highway. It's only a matter of time
: before an accident happens and we get rear ended. Not all of them come from
: the asteroid belt between mars and jupiter. Some could have sailed from
: another galaxy or exploding supernova.

: Possibly... but last I heard, no meteor -- let alone asteroid -- of
: definitely extra-solar origin (velocity at Earth exceeding solar-system
: escape velocity there) has ever been detected. Extrasolar dust grains
: have been detected by spacecraft, but that's all.

: The dominant hazard *is* objects perturbed from the main asteroid belt,
: with an important secondary threat from comets (perturbed from the Kuiper
: Belt or the Oort Cloud, farther out).

What about metorite impact material achieving escape velocity from
something like the moon, Mercury or Mars? Are these considered to be too
small to have devastating effects to the earth?

Eric

: --
: "Think outside the box -- the box isn't our friend." | Henry Spencer
: -- George Herbert |

Rodney Kelp ) wrote:
: We're in the middle of an asteroid super highway. It's only a matter of time
: before an accident happens and we get rear ended. Not all of them come from
: the asteroid belt between mars and jupiter. Some could have sailed from
: another galaxy or exploding supernova.

Why another galaxy when there is enough debris in the solar neighborhood
that would suffice? Oort Cloud remnant maybe. Asteriod from the belt that
has or has had perturbations?

Reflecting back on your "another galaxy" comment, how could we know that
a flying chunk of debris, whatever it is, came from outside our own
galaxy? Once it got here, what would be present to indicate that that
object had originated outside of our Milky Way? I don't think anyone could
definitively state that object X, containing characteristic set Y,
is extra-Milky Way. We simply don't know our galaxy well enough to even
consider that.

Besides galaxies, like people, might all have a unique ID, but be made
up of similar "DNA".

You've have been watching AMC's "Andromeda Strain" recently haven't you?

Eric

: "Jim Oberg" wrote in message
: ...
:
: Small asteroid misses Earth by only four thousand miles
:
:
: http://www.newscientist.com/news/news.jsp?id=ns99996307
:
:
: Jim Oberg asks -- were there any other possibile sensors
: thatr might have detected (but not identified) this bogie?
: Visual? Radar? IR?
:
:
: Asteroid shaves past Earth's atmosphere
:
: 13:59 23 August 04
:
: NewScientist.com news service
:
: The closest observed asteroid yet to skim past the Earth without hitting
: the
: atmosphere, was reported by astronomers on Sunday.
:
: The previously unknown object, spanning five to 10 metres across, has been
: named 2004 FU162. It streaked across the sky just 6500 kilometres -
: roughly
: the radius of the Earth - above the ground on 31 March, although details
: have only now emerged.
:
:
:


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