1I/2017 U1 (‘Oumuamua) is Hot: Imaging, Spectroscopy, and Search of Meteor Activity

Abstract

Abstract1I/2017 U1 ('Oumuamua), a recently discovered asteroid in a hyperbolic orbit, is likely the first macroscopic object of extrasolar origin identified in the solar system. Here, we present imaging and spectroscopic observations of 'Oumuamua using the Palomar Hale Telescope as well as a search of meteor activity potentially linked to this object using the Canadian Meteor Orbit Radar. We find that 'Oumuamua exhibits a moderate spectral gradient of 10% 6% 100 nm 1  -( ) , a value significantly lower than that of outer solar system bodies, indicative of a formation and/or previous residence in a warmer environment. Imaging observation and spectral line analysis show no evidence that 'Oumuamua is presently active. Negative meteor observation is as expected, since ejection driven by sublimation of commonly known cometary species such as CO requires an extreme ejection speed of ∼40 m s −1 at ∼100au in order to reach the Earth. No obvious candidate stars are proposed as the point of origin for 'Oumuamua. Given a mean free path of ∼10 9 ly in the solar neighborhood, 'Oumuamua has likely spent a very long time in interstellar space before encountering the solar system.

On the Rotation Period and Shape of the Hyperbolic Asteroid 1I/‘Oumuamua (2017 U1) from Its Lightcurve

“…However, we are aware of three independent optical spectra (Fitzsimmons et al 2017;Masiero 2017;Ye et al 2017) that are all in general agreement. While the specific slope of reddening is somewhat different, the variation between them is at the tenth of a magnitude level.…”

“…The final uncertainty on the zero point is based on the scatter in the offsets, 0.01 mag. We note that 'Oumuamua's color has been reported to be slightly redder than solar (e.g., 10% per 0.1 μm −1 ; Ye et al 2017), but the difference from solar color has a small effect on our absolute calibrations, 0.01 mag. We thus obtained absolute calibrations by using the zero point derived above and applying an airmass correction to each image, described next.…”

“…Although it was reported that "a very deep, stacked image, obtained with the Very Large Telescope" showed it to be "completely stellar" (Meech 2017), no quantifiable assessment of these observations had been reported at the moment of submitting this Letter. Further, while astrometry and snapshot magnitudes in a variety of bandpasses have been regularly reported and we are aware of at least three optical spectra (Fitzsimmons et al 2017;Masiero 2017;Ye et al 2017), no lightcurve measurements, which yield insight into the physical characteristics of the object, had been reported at the time this Letter was submitted. While this Letter was under review, four papers presenting lightcurves were made public (Bannister et al 2017;Bolin et al 2017;Jewitt et al 2017;Meech 2017).…”

Pre-discovery Activity of New Interstellar Comet 2I/Borisov beyond 5 au

“…Early observations of 2I have revealed a sizeable coma (de León et al 2019;Guzik et al 2019;Jewitt & Luu 2019) and the detection of the emission from CN and atomic oxygen Opitom et al 2019;McKay et al 2019). This makes it distinctively different from the first discovered interstellar object 1I/'Oumuamua, which did not exhibit a detectable cometary feature such as a coma and/or a tail (Meech et al 2017;Ye et al 2017;'Oumuamua ISSI Team et al 2019). The detection of activity is important as it provides a way to probe the composition of the nucleus, which can be done through a direct analysis of gases in the coma, and by observing how the activity responds to different levels of insolation at different heliocentric distances.…”

Detecting Interstellar Objects through Stellar Occultations

“…'Oumuamua was the first interstellar object (ISO) reported in the Solar System (Meech et al 2017;Micheli et al 2018). Follow-up studies of 'Oumuamua were conducted to better understand its origin and composition (Bannister et al 2017;Gaidos et al 2017;Jewitt et al 2017;Mamajek 2017;Ye et al 2017;Bolin et al 2017;Fitzsimmons et al 2018;Trilling et al 2018;Bialy & Loeb 2018;Hoang et al 2018;Siraj & Loeb 2019a,b;Seligman et al 2019;Sekanina 2019). 'Oumuamua's size was estimated to be 200 m, based on Spitzer Space Telescope constraints on its infrared emission given its expected surface temperature based on its orbit (Trilling et al 2018).…”