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(meteorobs) Re Fwd: "CLOSEST FLYBY EVER"

Wow, we're at the stage where our "planetary defense" search
telescopes are finding 20 meter objects? That's getting close
to the size (within a few orders of magnitude of the mass) of
a "normal" fireball, folks! The term "Asteroid" might be some-
what grandiose for such an object - even if it were to happen
to be of asteroidal origin (rocky or iron-bearing), as opposed
to being cometary (icy volatiles and weakly cohesive dust).

For comparison's sake, the meteoroid that caused the Peekskill
fireball was estimated to be from 0.5 to 1 meter across - but
that "only" reached a peak magnitude of about -13... Depending
on imponderable factors of velocity, density, composition, and
aerodynamics - an object 20 m wide (say 4000m3) MAY not cause
a fireball much brighter than peak magnitude -20 or so.

(In fact, if it were cometary - with a density potentially as
low as 0.3 g/ml, and possibly a much higher albedo than rocky
material, so that detection likelihood were correspondingly
greater - the resulting fireball could be still fainter... Of
course much more depends on velocity of entry Vinf: Peekskill
was only traveling at 15km/s. Maybe this would've been faster?
But probably not by much, if it's in a prograde Aten orbit...)


Now -20 sounds mind-bogglingly bright. But it's possible that
such a fireball, entering over more sparsely populated areas,
during cloudy weather, at a late hour - might not even be re-
ported by any civilian witnesses! Now this ISN'T to disparage
in any way the professional astronomical community's ever-in-
creasing prowess at finding solar-system objects... But there
does seem to be a slight tendency to hyperbole (even by other-
wise staid scientists) when the subject turns to "saving the
planet"... So I just wanted to inject a bit of perspective. :)


BTW, does anyone have plans to try to observe this tonight?

Clear skies,
Lew Gramer




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