The D68 ringlet is the innermost feature in Saturn’s rings. Four clumps that appeared in D68 around 2014 remained evenly spaced about 30 apart and moved very slowly relative to each other from 2014 up until the last measurements were taken in 2017. D68's narrowness and the distribution of clumps could either indicate that we have a collection of source bodies in a co-orbital configuration or imply

Measurements of visible and near-infrared reflection (0.38–5 μm) and mid-to-far-infrared emission (5–200 μm) from telescope and satellite remote-sensing instruments make it possible to investigate the composition of planetary surfaces via electronic transitions and vibrational modes of chemical bonds. Red spectral slopes at visible and near-infrared wavelengths and absorption features at 3.3 and 3

Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N2/CO abundance ratio, typically larger than ∼0.05, and at least 2–3 times higher than the one measured in 67P/Churyumov–Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O (H2O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation

Using the Cosmology Large Angular Scale Surveyor, we measure the disk-averaged absolute Venus brightness temperature to be 432.3 2.8 K and 355.6 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz, respectively. At both frequency bands, these are the most precise measurements to date. Furthermore, we observe no phase dependence of the measured temperature in either band. Our measurements

Earth’s rotation rate and the evolution of the Earth–Moon system have been controlled by tidal dissipation in Earth’s ocean. Attempts to model the tidal history have shown incomplete compatibility with observations and unclear isolation of the most important controlling factors. Here it is shown that a relatively simple model with no explicit description of the continents (their effects are instead

The Juno orbiter has continued to collect data on Jupiter's gravity field with unprecedented precision since 2016, recently reporting a nonhydrostatic component in the tidal response of the planet. At the mid-mission perijove 17, Juno registered a Love number k 2 = 0.565 0.006 that is −4% 1% (1σ) from the theoretical hydrostatic . Here we assess whether the aforementioned departure of tides from hydrostatic

The surfaces of airless bodies such as lunar and S-type asteroids typically become spectrally redder in visible to near-infrared reflectance with longer exposures to space weathering. However, some carbonaceous asteroids instead become spectrally bluer. Space weathering experiments on carbonaceous meteorites have provided some clues as to the space weathering products that could produce spectral bluing

The Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission orbited the Moon from 2014 September to 2015 April and observed a dynamic, permanently present dust cloud produced by continual meteoroid bombardment. For the latitudes observed by LDEX, the sporadic background contribution to the impacting dust flux is dominated by helion (HE), apex (AP), and

The Ina irregular mare patch, an ∼2 3 km summit depression on an ancient ∼22 km diameter shield volcano, displays two very enigmatic units: (1) dozens of dark convex-upward mounds and (2) a very rough, optically immature floor unit with very sharp morphologic contacts between the two. Controversy surrounds the age interpretation of Ina; superposed impact crater size–frequency distributions (CSFDs)

Mars’ transition from an early “warm and wet” to a “cold and dry” environment left fingerprints on the geological record of fluvial activity on Mars. The morphological and mineralogical observations of aqueous activity provided varying constraints on the condition and duration of liquid water on the Martian surface. In this study, we surveyed the mineralogy of Martian alluvial fans and deltas and investigated

Interior models of Uranus and Neptune often assume discrete layers, but sharp interfaces are expected only if major constituents are immiscible. Diffuse interfaces could arise if accretion favored a central concentration of the least volatile constituents (also, incidentally, the most dense); compositional gradients arising in such a structure would likely inhibit convection. Currently, two lines of

Given a light source, a spherical reflector, and an observer, where on the surface of the sphere will the light be directly reflected to the observer, i.e., where is the specular point? This is known as the Alhazen–Ptolemy problem and finding this specular point for spherical reflectors is useful in applications ranging from computer rendering to atmospheric modeling to GPS communications. Existing

We present observations of main-belt comet (MBC) 259P/Garradd from 4 months prior to its 2017 perihelion passage to 5 months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of kg s−1 (assuming

As the solar wind flows by the Moon, an antisunward-directed low-density wake forms as the plasma expands to fill in the trailing void in the plasma flow. Analytical modeling and modern plasma simulations suggest that plasma quasi-neutrality could possibly be broken close to the terminator obstruction as solar wind electrons expand into the wake ahead of the ions, leading to the formation of a standing

The analysis of solar wind material implanted within lunar soil has provided significant insight into the makeup and evolutionary history of the solar wind and, by extension, the Sun and protosolar nebula. These analyses often rely on the tacit assumption that the Moon has served as an unbiased recorder of solar wind composition over its 4.5 billion yr lifetime. Recent work, however, has shown that

The apparent clustering in longitude of perihelion ϖ and ascending node Ω of extreme trans-Neptunian objects (ETNOs) has been attributed to the gravitational effects of an unseen 5–10 Earth-mass planet in the outer solar system. To investigate how selection bias may contribute to this clustering, we consider 14 ETNOs discovered by the Dark Energy Survey, the Outer Solar System Origins Survey, and the

The Schrdinger basin on the south polar lunar far side has been highlighted as a promising target for future exploration. This report provides a high-resolution geologic map in the southwest peak-ring (SWPR) area of the Schrdinger basin, emphasizing structural features and detailed mapping of exposed outcrops within the peak ring. Outcrops are correlated with mineralogical data from the Moon Mineralogical

We analyze images of a rock on Ryugu acquired in situ by MASCam, the camera on the mascot lander, with the aim of identifying possible carbonaceous chondrite (CC) analogs. The rock’s reflectance ( at phase angle ) is consistent with Ryugu’s average reflectance, suggesting that the rock is typical for this asteroid. A spectrophotometric analysis of the rock’s inclusions provides clues to its CC group

Recent photometric surveys of Trans-Neptunian Objects (TNOs) have revealed that the cold classical TNOs have distinct z-band color characteristics and occupy their own distinct surface class. This suggested the presence of an absorption band in the reflectance spectra of cold classicals at λ > 0.8 μm. Here we present reflectance spectra spanning 0.55–1.0 μm for six TNOs occupying dynamically cold orbits

We present observations of the sudden outburst of the A Carinid meteor shower recorded with the Southern Argentina Agile MEteor Radar Orbital System (SAAMER-OS) near the south toroidal sporadic region. The outburst peaked between 21 UT and 22 UT on 2020 October 14 and lasted 7 days (199 ≤ λ ⊙ ≤ 205), with a mean Sun-centered geocentric ecliptic radiant of λ g − λ ⊙ = 271.04, β g = −76.4, and a geocentric

We report the detection of CH3OH emission in comet 46P/Wirtanen on UT 2018 December 8 and 9 using the Atacama Compact Array (ACA), part of the Atacama Large Millimeter/Submillimeter Array (ALMA). These interferometric measurements of CH3OH along with continuum emission from dust probed the inner coma (<2000 km from the nucleus) of 46P/Wirtanen approximately one week before its closest approach to Earth

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for several weeks surrounding its closest approach to Earth (Δmin ∼0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared

Motivated by recent visits from interstellar comets, along with continuing discoveries of minor bodies in orbit of the Sun, this paper studies the capture of objects on initially hyperbolic orbits by our solar system. Using an ensemble of ∼500 million numerical experiments, this work generalizes previous treatments by calculating the capture cross section as a function of asymptotic speed. The resulting

A 54 km diameter Noachian-aged crater in the southern highlands of Mars contains unusually well preserved inverted fluvial channel networks and lacustrine deposits, all of which formed completely inside the crater. This “closed-source drainage basin” (CSDB) crater is distinct from previously documented fluvially breached or groundwater-fed crater basin lakes on Mars. We compare our observations to

The building blocks of Titan and Enceladus are believed to have formed in a late-stage circumplanetary disk (CPD) around Saturn. Evaluating the evolution of the abundances of volatile species in this disk as a function of the migration, growth, and evaporation of icy grains is then of primary importance to assess the origin of the material that eventually formed these two moons. Here we use a simple

Weathering of silicate rocks at a planetary surface can draw down CO2 from the atmosphere for eventual burial and long-term storage in the planetary interior. This process is thought to provide essential negative feedback to the carbonate-silicate cycle (carbon cycle) to maintain clement climates on Earth and potentially similar temperate exoplanets. We implement thermodynamics to determine weathering

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

Using the Hubble Space Telescope, Saturn was observed in 2018, 2019, and 2020, just after the northern hemisphere summer solstice. Analysis of multispectral imaging data reveals three years of cloud changes associated with a 70 N storm that began in 2018. Additionally, there is an increase in equatorial brightness and perhaps haze optical depth at 0 to 7 N. There are small midsummer changes at the

Any rotorcraft on Mars will fly in a low-pressure and dusty environment. It is well known that helicopters on Earth become highly charged due, in part, to triboelectric effects when flying in sandy conditions. We consider the possibility that the Mars Helicopter Scout (MHS), called Ingenuity, flying at Mars as part of the Mars 2020 Perseverance mission, will also become charged due to grain-rotor triboelectric

A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature

A new era of exploration of the low radio frequency universe from the Moon will soon be underway with landed payload missions facilitated by NASA's Commercial Lunar Payload Services (CLPS) program. CLPS landers are scheduled to deliver two radio science experiments, Radio wave Observations at the Lunar Surface of the photoElectron Sheath (ROLSES) to the nearside and Lunar Surface Electromagnetics Experiment

Light emitted from Venus’s surface can be viewed through spectral “windows” in its atmosphere, in the near-infrared (NIR) around 1000 nanometer (nm) wavelengths. The NIR emissivity of Venus’s surface can constrain rock types and their weathering state; emissivities can be measured directly or calculated from reflectances. We measured the reflectances of igneous and sedimentary rocks at Venus’s surface

The porosity of an asteroid is important when studying the evolution of our solar system through small bodies and for planning mitigation strategies to avoid disasters due to asteroid impacts. Our knowledge of asteroid porosity largely relies on meteorites sampled on Earth. However, chondrites sampled on Earth are suggested to be sorted by strength. In this study, we obtained an estimate of the most

We introduce a new method for analyzing sparse photometric data of asteroids and apply it to Zwicky Transient Facility observations of the Jupiter Trojan asteroids. This method relies on the creation of a likelihood model that includes the probability distribution of rotational brightness variations at an unknown rotation phase. The likelihood model is analyzed via a Markov Chain Monte Carlo to quantify

The present study combines Radio and Plasma Wave Science/Langmuir Probe and Ion and Neutral Mass Spectrometer data from Cassini’s last four orbits into Saturn’s lower ionosphere to constrain the effective recombination coefficient α 300 from measured number densities and electron temperatures at a reference electron temperature of 300 K. Previous studies have shown an influx of ring material causes

Fundamental scientific objectives concerning the surface and subsurface material and dynamics of the Moon are the drivers for the use and advancement of penetrators, which emplace a suite of scientific instruments by impact into a planetary surface, typically at velocities of dozens to hundreds of meters per second. Small lunar penetrators are poised to become a valuable new tool for lunar science

Ice clouds containing benzene (C6H6) have recently been detected in the stratosphere at the south pole of Titan. Their subsequent aging process induced by long-UV solar photons could lead to a photoreactivity that may release some volatile organic compounds in the gas phase. The characterization of this volatile organic fraction coming from the photoprocessing (λ > 230 nm) of such icy C6H6 has been

Seismometers deployed on the Moon by the Apollo astronauts from 1969 to 1972 detected moonquakes and impacts, and added to our understanding of the lunar interior. Several lunar missions are currently being planned, including the Commercial Lunar Payload Services (CLPS), the Lunar Geophysical Network, and the astronaut program Artemis. We propose a microseismometer for the Moon: the Silicon Seismic

We analyze Kepler photometry of transiting planet candidate KOI-972.01, accounting for both stellar variability and gravity darkening. KOI-972.01 stands out because of its small radius, less than that of Neptune, and because of its intermediate orbit period at 13.12 days, long enough to avoid significant tidal evolution, and thus it represents an underexplored exoplanet class. The parent star of KOI-972

We present measurements of comet 46P/Wirtanen obtained by the NEOWISE spacecraft in 2017 through 2019. We detected signal in excess of the dust in the 4.6 μm channel attributable to the presence of CO, or more likely, CO2 emission. The excess, when the comet was outbound at a heliocentric distance of 1.9 au, was consistent with a CO2 production rate of 1.3(0.07) 1026 molecules per second, which is

Manx objects approach the inner solar system on long-period comet (LPC) orbits with the consequent high inbound velocities, but unlike comets, Manxes display very little to no activity even near perihelion. This suggests that they may have formed in circumstances different from typical LPCs; moreover, this lack of significant activity also renders them difficult to detect at large distances. Thus,

We present an analysis of the accuracy of geometric albedos determined for asteroids through the modeling of observed thermal infrared radiation. We show that albedo uncertainty is dominated by the uncertainty on the measured H V absolute magnitude, and that any analysis using albedos in a statistical application will also be dominated by this source of uncertainty. For all but the small fraction of

The parent of the Quadrantid meteor shower is the inactive solar system small body (196256) 2003 EH1. EH1 has likely only gone dormant in the past few hundred years, and may be related to the bright comet C/1490 Y1. Compared with the other best-studied inactive meteor shower parent (3200) Phaethon, EH1 has received comparatively minimal characterization of its surface properties. We present the first

The polarization state of radar echoes from planetary bodies contains information about the scattering mechanisms present on the surface and thus the near-surface physical properties. Polarimetric radar scatter from complex surfaces, such as those observed for spacecraft-visited near-Earth asteroids (NEAs), is not well understood in terms of relating observed polarimetry to surface properties. Here

We have calculated the amount of radioactive heat production (RHP) that could possibly prevent the postulated underground ocean of Enceladus from freezing. An internal heat source is necessary to justify the observed heat output from Enceladus and to allow the tidal dissipation heating models to work. Also based on the terrestrial evidence, we have assumed that the most common radiogenic element that

The Mars Reconnaissance Orbiter's Shallow Radar (SHARAD) emits radar signals and records their reflections from layer boundaries within the Martian north polar ice cap. Previous studies have suggested that the ice cap is composed of thin dust-rich layers between thicker layers of nearly pure water ice. The prevailing hypotheses suggest that each dust-rich layer represents either a period of ice sublimation

Planetesimals are compact astrophysical objects roughly 1–1000 km in size, massive enough to be held together by gravity. They can grow by accreting material to become full-size planets. Planetesimals themselves are thought to form by complex physical processes from small grains in protoplanetary disks. The streaming instability (SI) model states that millimeter/centimeter-sized particles (pebbles)

Titan’s ionosphere contains a plethora of hydrocarbons and nitrile cations and anions as measured by the Ion Neutral Mass Spectrometer and Cassini Plasma Spectrometer (CAPS) on board the Cassini spacecraft. Data from the CAPS Ion Beam Spectrometer (IBS) sensor have been examined for five close encounters of Titan during 2009. The high relative velocity of Cassini with respect to the cold ions in Titan’s

The factors contributing to the initial selection of a dune site near the Selk impact structure on Titan as the first landing site for the Dragonfly mission are described. These include arrival geometry and aerodynamic/aerothermodynamic considerations, illumination, and Earth visibility, as well as the likely presence of exposed deposits of water-rich material, potentially including materials where

Comet C/2013 US10 (Catalina) was a dynamically new Oort cloud comet whose apparition presented a favorable geometry for observations near close-Earth approach (≃0.93 au)at heliocentric distances ≲2 au when insolation and sublimation of volatiles drive maximum activity. Here we present mid-infrared 6.0≲λ(μm)≲40 spectrophotometric observations at two temporal epochs from NASA’s Stratospheric Observatory

In 2019, the Research and Education Collaborative Occultation Network (RECON) obtained multiple-chord occultation measurements of two Centaur objects: 2014 YY49 on 2019 January 28 and 2013 NL24 on 2019 September 4. RECON is a citizen-science telescope network designed to observe high-uncertainty occultations by outer solar system objects. Adopting circular models for the object profiles, we derive

We present a deep imaging and spectroscopic search for emission from (3200) Phaethon, a large near-Earth asteroid that appears to be the parent of the strong Geminid meteoroid stream, using the 4.3m Lowell Discovery Telescope. Observations were conducted on 2017 December 14–18 when Phaethon passed only 0.07au from the Earth. We determine the 3σ upper level of dust and CN production rates to be 0.007–0

We present analysis of IR and optical spectroscopy of Jupiter-family comet (JFC) 46P/Wirtanen obtained in 2019 January, when the comet had sufficient geocentric velocity to enable studies of the hypervolatiles CO and CH4, as well as [O i] emission. These species could not be studied near closest approach in mid-December because there was insufficient Doppler shift to separate the cometary emission

Spectra of the comae of four comets were obtained with an integral field unit spectrograph on the Harlan J. Smith Telescope at McDonald Observatory. The passband of the spectrograph permitted the observation of C2, C3, CH, CN, and NH2 transitions for these comets. The classical Haser model was used to derive production rates for each observed species. The production rates obtained for the comets were

The exceptionally favorable close approach of Jupiter-family comet 46P/Wirtanen in 2018 December enabled characterization of its primary volatile composition with exceptionally high spatial resolution and sensitivities using the iSHELL spectrograph at the NASA Infrared Telescope Facility on Maunakea, HI. We sampled emissions from H2O, HCN, C2H2, NH3, C2H6, and CH3OH on UT 2018 December 21 using two

The great comet C/1995 O1 (Hale–Bopp) presented a remarkable opportunity to study its long-term brightness over four years. We used 2240 observations published in the International Comet Quarterly from 17 observers during 1995 July to 1999 September to create a secular lightcurve. In order to account for observer differences, we present a novel algorithm to reduce scatter and increase precision in

Some of the key components of any Planetary Spatial Data Infrastructure (PDSI) are the data products that end-users wish to discover, access, and interrogate. One precursor to the implementation of a PSDI is a knowledge inventory that catalogs what products are available, from which data producers, and at what initially understood data qualities. We present a knowledge inventory of foundational PSDI

The identity of the coloring agent(s) in Jupiter’s atmosphere and the exact structure of Jupiter’s uppermost cloud deck are yet to be conclusively understood. The Crme Brle model of Jupiter’s tropospheric clouds, originally proposed by Baines et al. and expanded upon by Sromovsky et al. and Baines et al., presumes that the chromophore measured by Carlson et al. is the singular coloring agent in Jupiter’s

We estimate the total population of near-Earth objects (NEOs) in the solar system using an extensive, “solar-system-to-pixels” fake-asteroid simulation to debias detections of real NEOs by the ATLAS survey. Down to absolute magnitudes H = 25 and 27.6 (diameters of ∼34 and 10 m, respectively, for 15% albedo), we find total populations of (3.72 0.49) 105 and (1.59 0.45) 107 NEOs, respectively. Most of

Extensive lava flows are found in the equatorial region of Mars, shaping the surface in a very distinct way. In radar images (at the decimeter scale), these flows are bright, with circular polarization ratios greater than one. This is a typical characteristic of extremely rough, blocky lava flows on Earth. Although the source of the extreme dm-scale roughness of Martian lava flows is unknown, their