Stuff already at Lagrangia?

Thank you for the very informative note, Eric.

Ron Menich

Eric Dahlstrom
ssi_list@...
08/30/01 10:31 AM

Hubble would not be a good instrument to do this kind of survey task. Like
asking for the world's most expensive surgical knife when you want to mow
the lawn. But if you found some candidate objects, Hubble might be used to
characterize them..

I found an old copy of an article of an earlier survey that did not find
any objects.

I had looked into this as a possible Ph.D topic many moons ago. (I was
thinking about infrared searches of Sun-Earth L4&L5.) (It took me a little
while to find the 17 year old article - and my wife wonders why I keep
these things! :-)

"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
Burrell-Schmidt telescope at Warner&Swasey Obs, Kitt Peak. They basically
used the telescope on this project for three weeks over a year and took 137

plates.

They did not find anything. Here are their reported detection limits for
object diameters in meters (using lunar albedo). A 3 m object might be
around 50 tons, a 10 m object maybe 1000 tons, etc. And tasty carbonaceous
chondrites would have darker albedos, so could be large and still be
hidden. Within their limits you can still hide some stuff out there.

Earth-Moon
L1,L2: 3-30 m (or up to 60 m, with some assumptions)
L3: 1-3 m
L4,L5: 1-3 m

Sun-Earth
L2: 20-40 m

Their survey might be re-examined with current assumptions about potential
halo orbits, since the used photographic plates that tracked on assumed
average motions, and then tried to find objects stationary, or moving
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.

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.

- Eric Dahlstrom

PS. Back in 1983, F. Valdes was with KPNO, and R.A. Freitas was with
something called Xenology Research Institute, of Sacramento, CA. Looking
for nearby starships, I suppose.