[meteorite-list] Orbital debris watching radar REDUX
From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun Feb 12 04:47:11 2006
Whoops! The ultimate in late-night dopiness, replying
to my own post.
Some amplifications and clarifications occur to me right away.
First, the object that crosses the zero potential sheet with very little
residual velocity heads straight into the Earth and burns up in a
near vertical descent: no meteorites will be left from that encounter.
Simulations show that only a small fraction of one percent of lunar
debris make it to the Earth, about half the number of Martian
meteorites. Since the number of Lunaites is greater than half the
number of Martians, I think that shows we have underestimated
the number of impacts that occur in near Earth space. For all
practical purposes, the Earth and the Moon are co-targets,
proportional to their gravitational and geometric "target size,"
so the Earth is being impacted more than we think also...
Which in turn brings me back to my "greater fall rate"
The lunar object that has entered an Earth co-orbit has orbital
velocities very similar to the Earth's, the differences being mostly
in the geometry of the orbit. When there is a close encounter
between the Earth and the lunar object, the small rock is merely
deflected into an orbit that grazes the upper atmosphere enough to
An example would be a co-orbit with a period of 362 days instead
of the Earth's 365.25 days. The Earth and that object would pass by
each other every 104.35 years and maybe, just maybe, after 100
passes (10,000 years) of assorted closeness, they would get tangled
up and we'd get a new Lunaite. The object's velocity, relative to the
Earth's velocity, would be very small, a little faster or a little slower,
so it wouldn't be "falling from a great distance" as in the example of
direct transfer from the Moon to the Earth, but merely having its orbital
vectors adjusted into an atmospheric encounter... From there on in, it
takes the same chances as any meteoroid.
In such encounters, the object wouldn't be close to the Earth for more
than a few hours on each pass-by, so you'd be radar searching for
104 years in the hope of spotting something during a 100 hour passage,
not really practical, if you could do it at all, that is. Of course, the
is probably being passed by junk of all kinds all the time, slowly, in
co-orbits, without optical detection either, since the only way co-orbiters
could be detected would be viewing close to the horizon at dawn
and dusk -- the most impossible viewing angle imaginable from
the Earth's surface and the lousiest viewing conditions. And, when
co-orbiters are far enough away to be in a dark place in the sky,
they're too faint to be seen. Perfect.
The Earth has a blind spot...
Sterling K. Webb
----- Original Message -----
From: "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>
To: <cynapse_at_charter.net>; "Meteorite List"
Sent: Sunday, February 12, 2006 3:00 AM
Subject: Re: [meteorite-list] Orbital debris watching radar
> Hi, Darren,
> I gather from the phrase about having their orbits decay,
> that by "Earth orbit," you mean "in orbit about the Earth."
> Orbits around the Earth only "decay" because the orbit
> touches the uppermost atmosphere enough to cause drag
> which, however minute, reduces orbital velocity. It may seem
> logical that materials kicked off the Moon would easily and
> immediately end up in an orbit around the Earth, or at least
> some of them would.
> But the truth is that it is nearly impossible to get from the
> Moon to the Earth, and that lunar meteorites almost certainly
> do not arrive at the Earth that way, however illogical that sounds.
> The many simulations of transfer of materials around the
> solar system show the same result: impact materials from the
> Moon mostly go into eccentric solar orbits. a small percentage
> go into "co-orbits," that is, they enter solar orbits very similar
> to the Earth's orbit, sort of wandering along with us, and it is
> from that population that some get tangled up with the Earth's
> gravity and get pulled in. "Short" transit times are 10,000 years.
> When a lunar shows no cosmic ray exposure, that only means
> that it was less than 25,000 years.
> The reason why it's so hard to get from the Moon to the Earth
> is this: any object that falls to the Earth from a "great distance"
> achieves escape velocity by the time it gets very near to the
> Earth. And escape velocity is just that: you escape. No orbiting
> for you...
> There is a point, between the Earth and the Moon where the
> gravitational pull of the Earth and the Moon balance each other.
> Since the Earth is heavier than the Moon that point is closer
> to the Moon than the Earth. The point that lies in a straight line
> between the Moon and the Earth is the first LaGrange Point,
> But there are a multitude of points in every direction where
> equal force vectors from the Moon and the Earth meet: a sheet
> of zero gravitational potential.
> If an object is ejected from the Moon's surface toward the
> Earth without enough velocity to reach the zero sheet, it falls
> back toward the Moon.
> If it arrives at the zero sheet with just a smidge of velocity
> more than zero, it will fall toward the Earth, ramping up to
> escape velocity or near escape velocity at its closest approach
> then roar on out into the solar system.
> If it arrives at the zero sheet with a good deal of velocity
> more, it will fall on an Earth-influenced path and probably
> ramp up to a lot more than escape velocity...
> So, you see, stranger, thar ain't no way to get thar from here...
> Sterling K. Webb
> ----- Original Message -----
> From: "Darren Garrison" <cynapse_at_charter.net>
> To: "Meteorite List" <meteorite-list_at_meteoritecentral.com>
> Sent: Sunday, February 12, 2006 1:27 AM
> Subject: [meteorite-list] Orbital debris watching radar
> On a less argumentative subject, there is an idea I've been wondering
> about for
> a while. Thinking back to my wondering about what lunar meteorites do
> leaving the surface of the moon and reaching the surface of the Earth,
> there is
> the idea that some of them enter Earth orbit and then have their orbits
> until they fall. Given the really fresh lunars found lately, that would
> seem to
> imply that there could be more of them in orbit now.
> So, not really a coherent question but more of a musing-- just how small
> object at what distance can the radars that constantly track orbital space
> program junk around the Earth reliably track? And would there be any way
> determine if a piece of orbiting debris was junk or an incoming lunar?
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Received on Sun 12 Feb 2006 04:47:05 AM PST