Surface properties of large TNOs: Expanding the study to longer wavelengths with the James Webb Space Telescope

Abstract

The largest trans-Neptunian objects (TNOs) represent an extremely diverse collection of primitive bodies in the outer solar system. The community typically refers to these objects as "dwarf planets," though the IAU acknowledges only four TNOs officially as such: Pluto, Eris, Makemake, and Haumea. We present a list of 36 potential candidates for reclassification as dwarf planets, namely candidate dwarf planets (CDPs), which cover a wide range of sizes, geometric albedos, surface colors and probably, composition. Understanding the properties across this population, and how those properties change with size, will yield useful constraints on the environment in which these TNOs formed, as well as their dynamical evolution, and bulk interior composition. TNO surface characteristics are ideal for study with the James Webb Space Telescope (JWST), which provides imaging and spectroscopic capabilities from ~0.6-28 μm. The four available science instruments, MIRI, NIRCam, NIRISS, and NIRSpec, and their capabilities for the study of TNOs, are presented. JWST will expand on the wavelength range observable from the ground in the near-infrared (0.6-5 μm) for compositional studies and will open a new window on TNOs in the mid-infrared (5-28 μm) for thermal characterization. DP CDP (36 TNOs)IAU accepted D > 900 km 450 < D < 900 km Pluto, Eris,

Analysis in the visible range of NASA Lucy mission targets: Eurybates, Polymele, Orus and Donaldjohanson.

“…Finally, Donaldjohanson, the only main belt object in the group of targets, shows, according to our visible spectrum, hints of the presence of hydrated materials. This fact, could be explored with additional data in the 3-microns region from ground-based facilities or using the James Webb Space telescope instrumentation, in particular NIRSpec will be ideal to search not only for the -OH absorption band but also for the complex absorption due to organic components expected to dominate the surface of primitive objects in the Solar System (Rivkin et al, 2016;Pinilla-Alonso et al, 2019).…”

Transneptunian Space

“…The inherent faintness of most TNOs means that much of our knowledge of TNO surface properties is based on broadband colors (TNO colors are measured as the magnitude difference between two filters; see, e.g., Schwamb et al 2018 for a recent color survey). Spectra of moving objects with m r > 21 are challenging to obtain, but there have been spectral studies of the largest and brightest dwarf-planet-sized TNOs (see, e.g., Pinilla-Alonso et al 2020 for discussion of dwarf planets). These spectral studies reveal the presence of a variety of ices (via absorption bands) on the surfaces of many objects, whereas other objects' spectra are relatively featureless.…”

“…Notice that essentially it is the product pD 2 that is observationally determined. Some TNO albedos have been measured by combining thermal and optical observations (reviewed by Stansberry et al 2008 andPinilla-Alonso et al 2020), allowing improved diameter estimates for those TNOs and providing a basis for using albedo assumptions to estimate diameters of others. Direct measurements of the diameters of a small number of TNOs have been made by observing stellar occultations (Section 6.3).…”

The DECam Ecliptic Exploration Project (DEEP). II. Observational Strategy and Design

“…Survey completion rates for the brightest objects are higher than for other TNO populations, with perhaps 75% of the dwarf planet-sized objects known in the Northern Hemisphere (Schwamb et al 2014) and a similar efficiency in the Southern Hemisphere (Sheppard et al 2011;Rabinowitz et al 2012) out to heliocentric distances of ∼100 au. These large bodies have diameters D  450 km (Tancredi & Favre 2008;Pinilla-Alonso et al 2020) and are typically brighter than red magnitude m R  20 interior to heliocentric distances of R  40 au. However, since there are far more small TNOs (D  100 km, m R  23) than large TNOs, the known sample of D ∼ 100 km TNOs is a small fraction of the inferred population.…”