Stuff already at Lagrangia?

Let me respond to a couple comments. (I'm currently reading this as a
digest, so I have a built-in time delay - as though I was living on an
asteroid, I suppose.)

Andrew,
I like your ideas about preserving raw data from pixel readouts, and doing
lots of post-processing (sort of like SETI-at-Home) to integrate on
potential moving objects. I'm not sure how long you get before the various
motions take you out of the field of view.

Currently, I think the robot telescopes first require the identification of
a point source in snapshots, and then identify three of these points
aligned in time to register as a candidate detection. I wonder if your
method could pick up objects below the threshold for being a clear point
source. But I also wonder if your method would provide a convincing enough
result to claim a detection without the visible point sources. One problem
is that there are so many mechanisms for CCD noise. And since they are in
fixed relative locations, you could get many artifacts when you try to
extract patterns from certain directions. But I think it is worth talking
to people who run projects like LINEAR. I think the people who work with
the processing software would be receptive to things like this, maybe more
so than the traditional astronomers (although they would eventually need to
be satisfied).

Here are some links for the larger search programs
http://neo.jpl.nasa.gov/programs.html

Lincoln Near-Earth Asteroid Research (LINEAR)
http://www.ll.mit.edu/LINEAR/

> > Eric: Are the Sun-Earth L4/L5 points observable in visible light from the
> > surface of the Earth?
>
>Yes ( if I understand your question ).
>It depends on your defintion of "observable".
>
>They are always 60 degrees away from the sun in the sky, sitting on the
>Ecliptic. So they can be above the horizon when the sky is dark, if that
>is your concern.

The specific Sun-Earth L4,L5 points are 60 degrees from the sun, but models
of halo orbits around them would range from close to the Earth to the far
side of the Sun. And the halo orbits can extend across a large region.

3753 Cruithne (1986 TO) is an example of an object in a Sun-Earth L3-L4-L5
halo orbit. (I list all three, since it wanders across the full range of
L3-L4-L5.) It is thought to be 5 km across.

The diagram in the SpaceDaily article is simplified. Take a look at the
York Univ. site with the real orbit models by the authors of the study. You
have to keep going through the diagrams, it just keeps getting more and
more complicated.

The Solar Trojans of Earth, SpaceDaily, Oct. 1999
http://www.spacedaily.com/news/asteroid-99k.html

Near-Earth asteroid 3753 Cruithne --Earth's curious companion--
http://aries.phys.yorku.ca/~wiegert/3753.html

For this object, the peculiar motions about the halo are so large, I am not
sure how much benefit there is from it being dynamically bound to the
Earth. It would be interesting to model some trajectories to visit it, to
see how much energy is required, and how frequent the opportunities are.

> Date: Thu, 30 Aug 2001 15:55:08 EDT
>
> > "A Search for Objects near the Earth-Moon Lagrangian Points"
> > Francisco VALDES, Robert A. FREITAS, Jr., ICARUS, 53, pp 453-457 (1983).
> >
> > They observed about 1000 square degrees around the Earth-Moon L3, L4, L5
> > (to 17-19th mag); near the Moon for halos around Earth-Moon L1 & L2
> > (10-18th mag); and the Sun-Earth L2 (14-16th). They used the 61cm
>
>==============
>
>I think we are interested in a different type of search. They were
>searching for dust. Since dust is highly subject to radiaiton pressure,
>and could potentially be repopulated by passing comets, then they were
>looking for a cloud which extended considerably beyond the lagrange points
>themselves, even looking at the unstable points.
>
>We are interested in stable objects orbiting the Earth/Moon L-4 and L-5
>points, that would considerably reduce the scope of the search versus what
>Valdez and Freitas did. The region of space we want to scan is a lot smaller.

I hope the example of 3753 Cruithne (in the Sun-Earth system) illustrates
why any search for objects in the Earth-Moon system should cover a large
area, including off the lunar orbit plane. That other paper specifically
mentioned they were not looking for dust (since their star trails did not
allow them to measure diffuse sources).

> > slowly against the background star trails. They also had some limitations
> > based on needing to search in regions of the sky with many background
> > stars.
>
>We need to schedule observing periods where this is not an issue. I
>think this means times when the L-4/5 points are well clear of the Milky Way.
>
>We also need to schedule times when the L-4/5 points will be in
>opposition, that would be 4 to 5 days prior to ( and after ) Full Moon.
>
>There might only be a few days per year which meet both of these criteria.
>
> > A big question is if the current NEO searches would have picked up
> > anything. The robot telescopes have been cranking along, sometimes going to
> >
> > 18th magnitude. But you have to play their search areas against the
> > location of the Moon.
>
>Or more specifically, against the two criteria I listed above.
>
>Somebody would need to run the ephemerides back over the period over which
>the images have been collected, then try to see if any images corresponded
>to the locations and times of interests.
>
>It is entirley possible that nonoe of the asteroid search images taken
>meet the criteria. On the other hand, we might just get lucky. It
>would be wonderful if somebody could mine the data and determine it for sure.

Those are good points. We have to work hard to get the opportunity of NEOs
to be considered, along with the threat.

Recently, I brought up the suggestion that we try to work with the people
who maintain prioritized observing lists of potential NEO threats, to
create another list of objects to observe as potential resource targets.
After an object is no longer considered a threat, it could still be a
potential resource, and light curves and colors/spectra become important to
characterize the objects size, rotation, and material classification. Often
the window for these observations is only a matter of days, and there are
already many amateur astronomers that check sites like NEODys each night.
Anyway, I will try raising this issue with them.

The NEO Confirmation Page
http://cfa-www.harvard.edu/iau/NEO/ToConfirm.html

NEODys - Near Earth Object Dynamic Site
http://newton.dm.unipi.it/cgi-bin/neodys/neoibo

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