January 2018
John Blakeslee
Gemini North and South Join in
Welcoming the Solar System’s First
Interstellar Emissary
Two months after the first electromagnetic counterpart to a
gravitational wave detection caused Gemini to “pull out all the stops”
in its effort to follow the event as long as possible, the Observatory
reprised its performance, but this time for a few nights only, when
the first known interstellar object streaked through our Solar System.
Observations were carried out with both the Gemini North and South
telescopes during late October 2017 and enabled astronomers to
characterize the peculiar properties of this exotic visitor.
Note: Parts of the following article are adapted from the Gemini Observatory press
release issued on November 20, 2017. The original release is available online.
Planet formation is a messy, sometimes violent, affair. The evidence is imprinted in the
countless impact craters that pockmark the face of our Moon and the other airless, rocky
bodies that retain the scars of the distant past. It is believed that numerous asteroids and
comets were ejected entirely during the early stages of our Solar System as a consequence
of interactions with the giant planets Jupiter and Saturn. The same should be true of all
other planetary systems with giant planets, which may comprise the majority of the sys-
tems around stars in the Milky Way. Doing the numbers, one finds that trillions of objects
must be wandering the vast expanses between the stars. However, the likelihood that any
one of these wanderers would make a close approach to another planetary system is tiny.
On October 19, 2017, a small near-Earth object discovered by the Pan-STARRS1 survey tele-
scope on Haleakala was found to be moving away from the Earth at a speed so high that
the Sun’s gravity was insufficient to prevent the object from escaping. Thus, the object was
January 2018 / 2017 Year in Review
GeminiFocus
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