Subject: Our First Interstellar Interloper
From: Daniel Adamo <[email-masked]>
To: ATIG <[email-masked]>
Date: Fri, 27 Oct 2017 10:39:31 -0700

ATIG Members-

The first object in human history observed to fly through the Solar System
on an interstellar trajectory was discovered on 19 October 2017.  Currently
designated A/2017 U1, the object was originally dubbed C/2017 U1 when
thought to be a comet immediately after discovery.  Its heliocentric orbit
eccentricity is 1.2, and its heliocentric asymptotic speed in nearby
interstellar space is 25.5 km/s.  You can read more about A/2017 U1 at
https://www.jpl.nasa.gov/news/news.php?feature=6983 and at
http://www.skyandtelescope.com/astronomy-news/astronomers-spot-first-known-i
nterstellar-comet/.

The attached PDF file plots heliocentric motion for A/2017 U1, Mercury, and
Earth from 4 August 2017 to 12 November 2017.  Perspective is that of an
observer at ecliptic longitude 270 deg; latitude 47 deg S.  This viewpoint
is very nearly normal to A/2017 U1's plane of hyperbolic heliocentric
motion.  From the plot, it's evident A/2017 U1 was difficult to observe from
Earth before closest approach because its direction was too close to the Sun
in our sky.  This important discovery, coming only 5 days afterward, is
indeed fortuitous.

-Dan