[meteorite-list] Earth Trojan asteroids

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Fri Jun 24 20:38:31 2005
Message-ID: <BE076B8CCE4CFE4D9598230D888B2ADF07C7D1_at_0005-its-exs01.mail.saic.com>

Hi Sterling, Doug, and any other lurking List members still following the
earth Trojan thread. A few comments related to the Earth Trojan magnitude
calculation. Sterling wrote:

> Yes, phase would be about 2/3rds if it was spherical, but small bodies
> rarely are, so that value could be highly variable.

The solar phase angle (the angle, as measured from the asteroid, between the
sun and earth) is 60 degrees, which results in a noticeable drop in visual
magnitude compared to how that same asteroid would appear at 1 a.u. and
at opposition (despite the fact that in the latter case the asteroid is
twice as far from the sun and thus receives 1/4 the sunlight!). For
instance,
if an asteroid at opposition and 1 a.u. from earth (2 a.u. from the sun)
has an apparent magnitude of +18.0, that same asteroid moved to the
earth-sun
L4 or L5 point would dim to magnitude +18.64 for a typical slope parameter
of
G=0.15 -- a drop of a factor of 1.8 in brightness. What this means is that
asteroids that wouldn't be missed at opposition could easily evade detection
at L4/5.

Sterling -- was this a typo? :

> Of course, we all know that Jupiter has Trojans (149 are known -- Jupiter
> has more of everything!) and even Nepture has one (known).

There are at least 1783 Jupiter Trojans (7 of which were found by me within
the last year :-).

Cheers,
Rob
Received on Fri 24 Jun 2005 08:38:14 PM PDT