We report on g, r and i band observations of the Interstellar Object 1I/'Oumuamua (1I) taken on 2017 October 29 from 04:28 to 08:40 UTC by the Apache Point Observatory (APO) 3.5m telescope's ARCTIC camera. We find that 1I's colors are g − r = 0.41 ± 0.24 and r − i = 0.23 ± 0.25, consistent with visible spectra (Masiero 2017; Ye et al. 2017;Fitzsimmons et al. 2017) and most comparable to the population of Solar System C/D asteroids, Trojans, or comets. We find no evidence of any cometary activity at a heliocentric distance of 1.46 au, approximately 1.5 months after 1I's closest approach distance to the Sun. Significant brightness variability was seen in the r observations, with the object becoming notably brighter towards the end of the run. By combining our APO photometric time series data with the Discovery Channel Telescope (DCT) data of Knight et al. (2017), taken 20 h later on 2017 October 30, we construct an almost complete lightcurve with a most probable single-peaked lightcurve period of P 4 h. Our results imply a double peaked rotation period of 8.1 ± 0.02 h, with a peak-to-trough amplitude of 1.5 -2.1 mags. Assuming that 1I's shape can be approximated by an ellipsoid, the amplitude constraint implies that 1I has an axial ratio of 3.5 to 10.3, which is strikingly elongated. Assuming that 1I is rotating above its critical break up limit, our results are compatible with 1I having modest cohesive strength and may have obtained its elongated shape during a tidal distortion event before being ejected from its home system.

The recently discovered object P/2019 LD2 (by the Asteroid Terrestrial-impact Last Alert System) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 yr. We find that 2019 LD2 is currently in the vicinity of a dynamical “Gateway” that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ∼3 yr to less than once every 70 yr, if 2019 LD2's nucleus is ∼1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition.

We present a new analysis of Spitzer observations of comet 29P/Schwassmann-Wachmann 1 taken on UT 2003 November 21, 23, and 24, similar to a previous investigation of the observations (Stansberry et al. 2004), but using the most recent Spitzer data pipeline products and intensive image processing techniques. Analysis of images from the IRAC 5.8 & 8.0 µm bands and the MIPS 24.0 & 70.0 µm bands resulted in photometry measurements of the nucleus after a suite of coma modeling and removal processes were implemented. SW1 was not identified in the 5.8 µm image from the previous work so its incorporation into this analysis is entirely new. Using the Near Earth Asteroid Thermal Model (Harris 1998) resulted in a nucleus radius measurement of R = 30.2 +3.7 −2.9 km and an infrared beaming parameter value of η = 0.99−0.19 . We also measured an infrared geometric albedo, p 5.8 = 0.5 ± 0.5. Extrapolating a 0.04 V-band albedo and using a normalized reflectivity gradient S = 14.94 ± 1.09 [% (1000Å)−1 ] (Duffard et al. 2014) we recover an infrared albedo of p 5.8 = 0.31 in the near infrared consistent with the value recovered from thermal modeling. The dust composition extracted from IRS spectra are very comet-like, containing mainly amorphous ferromagnesian silicates (but with a minority of crystalline silicates as well), water ice, and metal sulfides.

We report the beginning of activity for comet C/2015 ER61 (PANSTARRS), the first instance of watching a long-period comet turn on. Pre-discovery observations and observations from the NEOWISE space telescope suggest that the nucleus is large, with a radius of R N  ∼ 9 km, assuming an albedo of 0.025. Our photometric data follows the comet from r = 8.9 to 4.8 au as it moved into solar conjunction in 2016 July. Our sublimation model shows that activity began near r = 8.8 au (true anomaly, TA = −139°) in early 2015, driven by CO2 sublimation, which peaked in 2016 April at r = 5.1 au (TA = −127°). Appreciable water sublimation began around r = 5.0 au. Our sublimation model is consistent with an active water sublimation area of 1% of the surface (equivalent to 10.2 km2), and an active surface area for CO2 sublimation of 0.029% (0.3 km2). The CO2 production rate at r = 4.66 au as measured by NEOWISE is (8.4 ± 2) × 1025 s−1. If CO2-ice had been present on the surface, dust dragged from the surface by sublimation would have been observed much farther out—as far as 20 au. Our thermal models suggest that the CO2 ice was present at a depth of 0.4 m. The comet came out of solar conjunction in 2016 December and, unless it brightens significantly, is unlikely to have water production rates much higher than a few ×1028 s−1.

The Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) provides the first opportunity to observe the migration of a solar system small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now. The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multiwavelength observations of LD2 from 2020 July 2–4: Gemini North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO Submillimeter Telescope millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleus’s effective radius to ≤1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has g ′ − r ′ = 0.70 ± 0.07 , r ′ − i ′ = 0.26 ± 0.07 , a dust-production rate of ∼10–20 kg s−1, and an outflow velocity between v ∼ 0.6–3.3 m s−1. We did not detect CO toward LD2 on 2020 July 2–3, with a 3σ upper limit of Q(CO) < 4.4 × 1027 mol s−1 (⪅ 200 kg s−1). Near-infrared spectra show evidence for water ice at the 1%–10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus, it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long-baseline monitoring effort.