The observable Solar System can be divided into three distinct regions: the rocky terrestrial planets including the asteroids at 0.39 to 4.2 astronomical units (AU) from the Sun (where 1 AU is the mean distance between Earth and the Sun), the gas giant planets at 5 to 30 AU from the Sun, and the icy Kuiper belt objects at 30 to 50 AU from the Sun. The 1,000-kilometre-diameter dwarf planet Sedna was discovered ten years ago and was unique in that its closest approach to the Sun (perihelion) is 76 AU, far greater than that of any other Solar System body. Formation models indicate that Sedna could be a link between the Kuiper belt objects and the hypothesized outer Oort cloud at around 10,000 AU from the Sun. Here we report the presence of a second Sedna-like object, 2012 VP113, whose perihelion is 80 AU. The detection of 2012 VP113 confirms that Sedna is not an isolated object; instead, both bodies may be members of the inner Oort cloud, whose objects could outnumber all other dynamically stable populations in the Solar System.

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

We present observations of thermal emission from fifteen transneptunian objects (TNOs) made using the Spitzer Space Telescope. Thirteen of the targets are members of the Classical population: six dynamically hot Classicals, five dynamically cold Classicals, and two dynamically cold inner Classical Kuiper Belt Objects (KBOs). We fit our observations using thermal models to determine the sizes and albedos of our targets finding that the cold Classical TNOs have distinctly higher visual albedos than the hot Classicals and other TNO dynamical classes. The cold Classicals are known to be distinct from other TNOs in terms of their color distribution, size distribution, and binarity fraction. The Classical objects in our sample all have red colors yet they show a diversity of albedos which suggests that there is not a simple relationship between albedo and color. As a consequence of high albedos, the mass estimate of the cold Classical Kuiper Belt is reduced from approximately 0.01 M ⊕ to approximately 0.001 M . Our results also increase significantly the sample of small Classical KBOs with known albedos and sizes from 21 to 32 such objects. ⊕ Keywords: Infrared Observations, Kuiper Belt, Trans-Neptunian Objects, Trojan Asteroids We include in our analysis those objects which fall into the Classical regime (the main Kuiper Belt) in either of the two major TNO classification systems described by the Deep Ecliptic Survey (DES) team (Elliot et al. 2005) and described by Gladman et al. (2008). Both classification systems rely on numerical integrations over 10 Myr to determine orbital behavior.The main difference between the two classification systems lies in the definition of Scatter(ing/ed) Disk Objects (SDOs). According to Gladman et al. (2008), SDOs are only the objects "currently scattering actively off Neptune" as evidenced by a swiftly changing semimajor axis in the orbital integrations, specifically a change greater than or equal to 1.5 AU. In contrast, the DES system uses a time-averaged Tisserand parameter less than 3 relative to Neptune to separate the Scattered-Near KBOs from the Classical KBOs. The Detached TNOs of Gladman et al. (2008) have eccentricities greater than 0.24 while the DES Scattered-Extended KBOs have Tisserand parameters greater than 3 relative to Neptune and eccentricities greater than 0.2 (Elliot et al. 2005). As a result, some objects that are Scattered-Near and Scattered-Extended in the DES system are Classical KBOs according to Gladman et al. (2008).

The redshift distribution of the short-duration GRBs is a crucial, but currently fragmentary, clue to the nature of their progenitors. Here we present optical observations of nine short GRBs obtained with Gemini, Magellan, and the Hubble Space Telescope. We detect the afterglows and host galaxies of two short bursts, and host galaxies for two additional bursts with known optical afterglow positions, and five with X-ray positions ( ∼ < 6 ′′ radius). In eight of the nine cases we find that the most probable host galaxies are faint, R ≈ 23 − 26.5 mag, and are therefore starkly different from the first few short GRB hosts with R ≈ 17 − 22 mag and z ∼ < 0.5. Indeed, we measure spectroscopic redshifts of z ≈ 0.4 − 1.1 for the four brightest hosts. A comparison to large field galaxy samples, as well as the hosts of long GRBs and previous short GRBs, indicates that the fainter hosts likely reside at z ∼ > 1. Our most conservative limit is that at least half of the five hosts without a known redshift reside at z > 0.7 (97% confidence level), suggesting that about 1/3 − 2/3 of all short GRBs originate at higher redshifts than previously determined. This has two important implications: (i) We constrain the acceptable age distributions to a wide lognormal (σ ∼ > 1) with τ * ∼ 4 − 8 Gyr, or to a power law, P (τ ) ∝ τ n , with −1 ∼ < n ∼ < 0; and (ii) the inferred isotropic energies, E γ,iso ∼ 10 50 − 10 52 erg, are significantly larger than ∼ 10 48 − 10 49 erg for the low redshift short GRBs, indicating a large spread in energy release or jet opening angles. Finally, we re-iterate the importance of short GRBs as potential gravitational wave sources and find a conservative Advanced LIGO detection rate of ∼ 2 − 6 yr −1 .