GeminiFocus January 2018 - Page 7

a hyperbolic path passing through our region of space, rather than a closed elliptical (or borderline parabolic) orbit like the Earth and all other planets, as- teroids, and comets ever encountered within the Solar System. This meant that it must have originated from some other star system, the first definitively detected emissary from the stars. The object’s discovery was officially announced by the Minor Planet Cen- ter (MPC) on October 25th and given the provisional cometary designa- tion C/2017 U1. Gemini received a Director’s Discretionary Time (DDT) proposal from the discovery team for multi-band imaging with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South and obtained the requested observations on the evenings of October 25th and 26th. Although the target was ac- cessible from both Cerro Pachón and Mau- nakea, weather conditions in the North were poor on the first night, and therefore the two widely separately sites proved once again a major advantage. Two additional teams submitted DDT pro- posals for GMOS and Near-InfraRed Imager and spectrometer (NIRI) imaging at Gemini North and obtained data over three nights beginning on October 26th (UT October 27th). During the course of this campaign, the object’s provisional designation was changed to A/2017 U1 because no cometary tail was detectable in very long exposures. Thus, excluding sci-fi explanations, its sur- face must be rocky like an asteroid, rather than icy like a comet. The change with re- spect to the designation specified in the DDT programs initially caused the observing soft- ware not to find the target coordinates from the online NASA database, but the issue was quickly solved by alert Gemini staff. All three DDT programs were successfully completed in October and have produced publications. January 2018 Before the interstellar visitor sailed away from our shores forever, it was renamed once more. The naming convention for mi- nor planets (such as comets and asteroids) prescribed by the International Astronomical Union (IAU) did not allow a formal name to be assigned based on the too-brief arc of ob- servation. However, as explained in an MPC Circular issued on the 7th of November, “Due to the unique nature of this object, there is pressure to assign a name.” The will of the people was heard, and the IAU introduced a new designation scheme for interstellar ob- jects. The asteroid formerly known as A/2017 U1 received the permanent designation 1I (to indicate its status as the first interstel- lar object) and the name ‘Oumuamua. The name is of Hawaiian origin and connotes the idea of an advance scout, or a messenger “reaching out” to us. Figure 1. The trajectory of ‘Oumuamua, previously known as A/2017 U1, through our Solar System. Orbits of the eight major planets and a Halley-type comet are also shown. Credit: Brooks Bays, SOEST Publication Services, UH Institute for Astronomy Science Returns The scientific developments resulting from ‘Oumuamua’s passage through our Solar Sys- tem are even more remarkable than those related to nomenclature. The observations from Gemini and other observatories imply GeminiFocus 5