We present the science case, reference design, and project plan for the Stage-4 ground-based cosmic microwave background experiment CMB-S4.

CMB-S4 Science Case, Reference Design, and Project Plan

The Near-Earth Asteroid Thermal Model (NEATM, Harris, 1998) has proven to be a reliable simple thermal model for radiometric diameter determination. However NEATM assumes zero thermal emission on the night side of an asteroid. We investigate how this assumption affects the best-fit beaming parameter, overestimates the effective diameter and underestimates the albedo at large phase angles, by testing NEATM on thermal IR fluxes generated from simulated asteroid surfaces with different thermal inertia. We compare NEATM to radar diameters and find that NEATM overestimates the diameter when the beaming parameter is fitted to multi-wavelength observations and underestimates the diameter when the default beaming parameter is used. The Night Emission Simulated Thermal Model (NESTM) is introduced. NESTM models the night side temperature as an iso-latitudinal fraction (f) of the maximum day side temperature (Maximum temperature calculated for NEATM with beaming parameter = 1). A range of f is found for different thermal parameters, which depend on the thermal inertia. NESTM diameters are compared with NEATM and radar diameters, and it is shown that NESTM may reduce the systematic bias in overestimating diameters. It is suggested that a version of the NESTM which assumes the thermal inertia = 200 S.I. units is adopted as a default model when the solar phase angle is greater than 45 degrees.

Investigation of Systematic Bias in Radiometric Diameter Determination of Near-Earth Asteroids: the Night Emission Simulated Thermal Model (NESTM)

The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft has been conducting a two-band thermal infrared survey to detect and characterize asteroids and comets since its reactivation in 2013 December. Using the observations collected during the fourth and fifth years of the survey, our automated pipeline detected candidate moving objects that were verified and reported to the Minor Planet Center. Using these detections, we perform thermal modeling of each object from the near-Earth object (NEO) and Main Belt asteroid (MBA) populations to constrain their sizes. We present thermal model fits of asteroid diameters for 189 NEOs and 5831 MBAs detected during the fourth year of the survey, and 185 NEOs and 5776 MBAs from the fifth year. To date, the NEOWISE Reactivation survey has provided thermal model characterization for 957 unique NEOs. Including all phases of the original Wide-field Infrared Survey Explorer survey brings the total to 1473 unique NEOs that have been characterized between 2010 and the present.

https://iopscience.iop.org/article/10.3847/PSJ/ab7820/pdf

Asteroid Diameters and Albedos from NEOWISE Reactivation Mission Years 4 and 5

Thermophysical models allow for improved constraints on the physical and thermal surface properties of asteroids beyond what can be inferred from more simple thermal modeling, provided a sufficient number of observations is available We present thermophysical modeling results of observations from the NEOWISE mission for two near-Earth asteroids which are the targets of the DESTINY+ flyby mission: (3200) Phaethon and (155140) 2005 UD Our model assumes a rotating, cratered, spherical surface, and employs a Monte Carlo Markov Chain to explore the multi-dimensional parameter space of the fit We find an effective spherical diameter for Phaethon of $46^{+02}_{-03}~$km, a geometric albedo of $p_V=016\pm002$, and a thermal inertia $\Gamma=880$ $^{+580}_{-330}$, using five epochs of NEOWISE observations The best model fit for (155140) 2005 UD was less well constrained due to only having two NEOWISE observation epochs, giving a diameter of $12\pm04~$km and a geometric albedo of $p_V=014\pm009$

Thermophysical modeling of NEOWISE observations of DESTINY+ targets Phaethon and 2005 UD

We report 491 new near-infrared spectroscopic measurements of 420 near-Earth objects (NEOs) collected on the NASA InfraRed Telescope Facility as part of the MIT-Hawaii NEO Spectroscopic Survey. These measurements were combined with previously published data from Binzel et al. and bias-corrected to derive the intrinsic compositional distribution of the overall NEO population, as well as of subpopulations coming from various escape routes (ERs) in the asteroid belt and beyond. The resulting distributions reflect well the overall compositional gradient of the asteroid belt, with decreasing fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER distance from the Sun. The close compositional match between NEOs and their predicted source populations validates dynamical models used to identify ERs and argues against any strong composition change with size in the asteroid belt between ∼5 km and ∼100 m. A notable exception comes from the overabundance of D-type NEOs from the 5:2J and, to a lesser extend, the 3:1J and ν 6 ERs, hinting at the presence of a large population of small D-type asteroids in the main belt. Alternatively, this excess may indicate preferential spectral evolution from D-type surfaces to C and P types as a consequence of space weathering, or point to the fact that D-type objects fragment more often than other spectral types in the NEO space. No further evidence for the existence of collisional families in the main belt, below the detection limit of current main-belt surveys, was found in this work.

The Debiased Compositional Distribution of MITHNEOS: Global Match between the Near-Earth and Main-belt Asteroid Populations, and Excess of D-type Near-Earth Objects

Automated asteroid detection routines set requirements on the number of detections, signal-to-noise ratio, and the linearity of the expected motion in order to balance completeness, reliability, and time delay after data acquisition when identifying moving object tracklets. However, when the full-frame data from a survey are archived, they can be searched later for asteroids that were below the initial detection thresholds. We have conducted such a search of the first three years of the reactivated NEOWISE data, looking for near-Earth objects discovered by ground-based surveys that have previously unreported thermal infrared data. Using these measurements, we can then perform thermal modeling to measure the diameters and albedos of these objects. We present new physical properties for 116 Near-Earth Objects found in this search.

Small and Nearby NEOs Observed by NEOWISE During the First Three Years of Survey: Physical Properties.

Automated asteroid detection routines set requirements on the number of detections, signal-to-noise ratio, and the linearity of the expected motion in order to balance completeness, reliability, and time delay after data acquisition when identifying moving object tracklets. However, when the full-frame data from a survey are archived, they can be searched later for asteroids that were below the initial detection thresholds. We have conducted such a search of the first three years of the reactivated Near-Earth Object Wide-field Infrared Survey Explorer data, looking for near-Earth objects discovered by ground-based surveys that have previously unreported thermal infrared data. Using these measurements, we can then perform thermal modeling to measure the diameters and albedos of these objects. We present new physical properties for 116 Near-Earth Objects found in this search.

Small and Nearby NEOs Observed by NEOWISE During the First Three Years of Survey: Physical Properties

Drift rates of major Neptunian features between 2018 and 2021

We present the first comprehensive study of NaCl and KCl gases in Io’s atmosphere in order to investigate their characteristics and infer properties of Io’s volcanoes and subsurface magma chambers. In this work, we compile all past spectral line observations of NaCl and KCl in Io's atmosphere from the Atacama Large Millimeter/submillimeter Array and use atmospheric models to constrain the physical properties of the gases on several dates between 2012 and 2018. NaCl and KCl appear to be largely spatially confined, and for observations with high spectral resolution, the temperatures are high (∼500–1000 K), implying a volcanic origin. The ratio of NaCl:KCl was found to be ∼5–6 in 2015 June and ∼3.5–10 in 2016 June, which is consistent with predictions based on observations of Io's extended atmosphere and less than half the Na/K ratio in chondrites. Assuming these gases are volcanic in origin, these ratios imply a magma temperature of ∼1300 K, such that the magma will preferentially outgas KCl over NaCl.

NaCl and KCl in Io’s Atmosphere

We present the ﬁrst comprehensive study of NaCl and KCl gases in Io’s atmosphere in order to inves-tigate their characteristics, and to infer properties of Io’s volcanoes and subsurface magma chambers. In this work, we compile all past spectral line observations of NaCl and KCl in Io’s atmosphere from the Atacama Large Millimeter/submillimeter Array (ALMA) and use atmospheric models to constrain the physical properties of the gases on several dates between 2012 and 2018. NaCl and KCl appear to be largely spatially conﬁned and for observations with high spectral resolution, the temperatures are high ( ∼ 500-1000 K), implying a volcanic origin. The ratio of NaCl:KCl was found to be ∼ 5-6 in June 2015 and ∼ 3.5-10 in June 2016, which is consistent with predictions based on observations of Io’s extended atmosphere, and less than half the Na/K ratio in chondrites. Assuming these gases are volcanic in origin, these ratios imply a magma temperature of ∼ 1300 K, such that the magma will preferentially outgas KCl over NaCl.

E. Redwing

Papers

Small and Nearby NEOs Observed by NEOWISE During the First Three Years of Survey: Physical Properties.

Small and Nearby NEOs Observed by NEOWISE During the First Three Years of Survey: Physical Properties

Drift rates of major Neptunian features between 2018 and 2021

NaCl and KCl in Io’s Atmosphere

NaCl&KCl in Io's Atmosphere