Planetary surfaces

Abstract:

NASA’s New Horizons spacecraft continues to explore the Kuiper belt after its historic close flybys of the Pluto system in 2015 at ~33 astronomical units (AU) [1] and the cold classical Kuiper belt object (KBO) Arrokoth in 2019 at ~43 AU [2].  New Horizons is located at ~61.7 AU as of this writing in May 2025, and travels about 3 AU per year.  New Horizons has sufficient power, propellant, and communications capability to continue operations until the mid-to-late 2040s and, thus, should be able to collect data out to distances of ~120 AU or greater. In its extended mission, New Horizons’ main planetary science focus is studying Kuiper belt dwarf planets and small KBOs, and their environment.  We will provide an overview of results for the dwarf planets and smaller KBOs observed by New Horizons from a distance ([3-6]; also see Porter et al., 2025 abstract at this conference).  New Horizons can observe KBOs from much higher phase angles than possible from Earth, and some of the observed KBOs come as close as 0.1 AU to the spacecraft.  This allows for the study of shapes, poles, surface properties, and  searches for close satellites in some cases.  New Horizons also made high-phase, color observations of the ice giants Uranus and Neptune [7] in coordination with the Hubble Space Telescope and as an exoplanet observation analogue.  Further, the New Horizons Student Dust Counter continues to observe elevated dust fluxes at larger distances than expected, and the team is exploring possible explanations for why the dust flux has not yet started to decrease as predicted by previous models [8, 9].  We will also highlight some new products and findings related to Arrokoth, including a new shape model [10], images draped onto the shape model, and a study placing Arrokoth’s crater size-frequency distribution into the context of those on other small bodies [11].  Looking towards the future of New Horizons: We will provide a status update on the ground-based, Subaru Telescope search [12-14] for a future close flyby target and other KBOs that New Horizons could observe as point sources.  We will also discuss how future work would enhance the chances of finding a future flyby target for New Horizons, including the additional use of machine learning/artificial intelligence, supercomputing, and potential observations from the Vera Rubin Observatory (also see Kavelaars et al. 2025 abstract in this conference) or the Roman Space Telescope.References:[1]  Stern S. A. et al., 2015, The Pluto system: Initial results from its exploration by New Horizons, Science 350, id.aad1815. doi:10.1126/science.aad1815[2]  Stern S. A. et al., 2019, Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object, Science 364. doi:10.1126/science.aaw9771[3]  Verbiscer A. J. et al., 2024, The New Horizons Photometric Phase Angle Survey of Deep Outer Solar System Objects: From the Kuiper Belt to the Scattered Disk, 55th Lunar and Planetary Science Conference. 3040, 2531.[4]  Verbiscer A. J. et al., 2022, The Diverse Shapes of Dwarf Planet and Large KBO Phase Curves Observed from New Horizons, The Planetary Science Journal 3, 95. doi:10.3847/PSJ/ac63a6[5]  Verbiscer A. J. et al., 2019, Phase Curves from the Kuiper Belt: Photometric Properties of Distant Kuiper Belt Objects Observed by New Horizons, Astron. J. 158. doi:10.3847/1538-3881/ab3211[6]  Porter S. B. et al., 2016, The First High-phase Observations of a KBO: New Horizons Imaging of (15810) 1994 JR1 from the Kuiper Belt, ApJ Letters 828. doi:10.3847/2041-8205/828/2/L15[7]  Hasler S. N. et al., 2024, Observations of Uranus at High Phase Angle as Seen by New Horizons, The Planetary Science Journal 5, 267. doi:10.3847/PSJ/ad8cdb[8]  Corbett T. et al., 2025, Production, Transport, and Destruction of Dust in the Kuiper Belt: The Effects of Refractory and Volatile Grain Compositions, Astrophys J. 979, L50. doi:10.3847/2041-8213/adab75[9]  Doner A. et al., 2024, New Horizons Venetia Burney Student Dust Counter Observes Higher than Expected Fluxes Approaching 60 AU, pp. arXiv:2401.01230.[10]  Porter S. B. et al., 2024, The Shape and Formation of Arrokoth, 55th Lunar and Planetary Science Conference. 3040, 2332.[11]  Knudsen I. E. et al., 2024, An Analysis of Impact Craters on Small Bodies Throughout the Solar System, The Trans-neptunian Solar System.[12]  Yoshida F. et al., 2024, A deep analysis for New Horizons' KBO search images, Publications of the Astronomical Society of Japan 76, 720-732. doi:10.1093/pasj/psae043[13]  Fraser W. C. et al., 2024, Candidate Distant Trans-Neptunian Objects Detected by the New Horizons Subaru TNO Survey, The Planetary Science Journal 5, 227. doi:10.3847/PSJ/ad6f9e[14]  Buie M. W. et al., 2024, The New Horizons Extended Mission Target: Arrokoth Search and Discovery, The Planetary Science Journal 5, 196. doi:10.3847/PSJ/ad676d

Abstract:

We present work to update current maps of the thermal properties of Enceladus using thermal observations from the Cassini Composite InfraRed Spectrometer (CIRS).  In 2010, the first maps of Enceladus’ thermal inertia were published that used what CIRS data was available at the time (Howett et al., 2010). These maps were resolved into some latitude zones, and overall conveyed lower thermal inertia and albedo at higher latitudes, and confirmed that like other cold, icy moons of Saturn its surface had low (< 50 MKS) thermal inertia.  Improvements to these maps using the totality of the CIRS Focal Plane 1 data (10-600 cm-1 / 16.7-1000 μm) from the mission with updated error estimates will yield better spatial resolution in addition to higher precision estimates of thermal inertia and albedo.   This will be particularly useful for improving models of surface temperature or estimating endogenic heat fluxes, like those at Enceladus’ south pole, associated with dissipation of heat from beneath.Acknowledgements: Thanks are given to the NASA Cassini Data Analysis program that funded this work (80NSSC20K0477 and 80NSSC24K0373). Reference:Howett, C.J.A., Spencer, J.R., Pearl, J. and Segura, M., 2010. Thermal inertia and bolometric Bond albedo values for Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus as derived from Cassini/CIRS measurements. Icarus, 206(2), pp.573-593.

Abstract:

Mars has an axial tilt of 25.2°, comparable to that on Earth of 23.4°. This gives rise to very similar seasons, and even leads to our definition of Martian time, aligning the solar longitudes (Ls) such that Ls 0° and 180° occur at the equinoxes. In the northern hemisphere, between the equinoxes, the north polar region experiences polar days without darkness in spring and summer, and days of total darkness in the fall and winter. The dark polar winters give rise to a polar vortex that encircles the polar region and encircles an atmosphere of very cold and dry air bound within (1-3).The Atmospheric Chemistry Suite (ACS) mid-infrared channel (MIR) on the ExoMars Trace Gas Orbiter (TGO; 4) operates in solar occultation mode in which the Sun is used as a light source when the atmosphere lies between the Sun and TGO. The tangent point locations of ACS MIR observation necessarily lie on the solar terminator on Mars. At the poles when either polar night or polar day are experienced, there is no terminator, and solar occultations are restricted to outside such a region. The latitudinal distribution of ACS MIR solar occultations during the north polar fall and winter over four Mars years (MYs) is shown in Fig. 1. The furthest northern extent of observations occurs at the equinoxes, and falling northern boundary is seen between, as the north pole points further away from the Sun (similarly in the south, where it is polar day).While direct observations of the north polar vortex are forbidden with solar occultations, the polar vortex is not perfectly circular (1-3) and occasionally, descends into the illuminated region where we are making observations. The characteristic signs that we are sampling the polar vortex are a sudden drop in temperature below 20 km, the almost complete reduction in water vapour volume mixing ratio (VMR) and an enhancement in ozone VMR, the latter of which is extremely rare (5).To measure the extent of the polar vortex, we use temperature measurements from the Mars Climate Sounder (MCS; 6, 7) on Mars Reconnaissance Orbiter (MRO). We define the polar vortex as the average temperature over 10-20 km being within a boundary of 170 K (30). We introduce a novel technique to determine this boundary during a 1° Ls period using an alpha hull. We show that we can accurately measure the area of the polar vortex and achieve similar results to (3). The impact of the southern summer and dust activity is clearly visible in the time series of the northern polar vortex extent, leading to maxima occurring at the equinoxes, and shrinking toward perihelion. The impact of global dust storms and the late season dust storms are also pronounced.We will show the vertical structure of water vapour and ozone VMRs inside and outside the north polar vortex, the results of a search for polar vortex temperatures from the near-infrared channel (NIR) of ACS (along the dark blue dots in Fig. 1), and show whether these results agree with the polar vortex extent measurements using MCS.       Figure 1: The latitudes of ACS MIR solar occultation as a function of time (solar longitude Ls) during northern fall (Ls 180-270°) and winter (Ls 270-360°). Data from Mars years (MYs) 34-37 are indicated with colours. The region of interest in searching for polar vortex excursions is highlighted in blue.References:(1) Streeter, P. M. et al. J. Geophys. Res. 126, e2020JE006774 (2021).(2) Streeter, P. M., Lewis, S. R., Patel, M. R., Holmes, J. A., & Rajendran, K. Icarus 409, 115864 (2024).(3) Alsaeed, N.R., Hayne, P. O. & Concepcion, V. J. Geophys. Res. 129, e2024JE008397 (2024).(4) Korablev, O. et al. Space Sci. Rev. 214, 7 (2018).(5) Olsen, K. S., et al. J. Geophys. Res. 127, e2022JE007213 (2022).(6) Kleinböhl, A., et al. J. Geophys. Res., 114, E10006 (2009).(7) Kleinböhl, A., Friedson, A. J., & Schofield, J. T. J. Quant. Spectrosc. Radiat. Transfer. 187, 511-522 (2017).

Abstract:

Introduction: This presentation will describe the Modular Infrared Molecules and Ices Sensor currently in final assembly and test at the University of Oxford, UK and VTT Finland for ESA’s upcoming Comet interceptor mission.The Comet Interceptor mission: The Comet Interceptor mission [1] was selected by ESA as the first of its new “F” class of missions in June 2019 and adopted in June 2022.  Comet Interceptor (CI) aims to be the first mission to visit a long period comet, preferably, a Dynamically New Comet (DNC), a subset of long-period comets that originate in the Oort cloud and may preserve some of the most primitive material from early in our Solar System’s history. CI is scheduled to launch to the Earth-Sun L2 point with ESA’s ARIEL [2] mission in ~2029 where it will wait for a suitable DNC target.The CI mission is comprised of three spacecraft.  Spacecraft A will pass by the target nucleus at ~1000 km to mitigate against hazards caused by dust due to the wide range of possible encounter velocities (e.g. 10 – 70 km/s).  As well as acting as a science platform, Spacecraft A will deploy and provide a communications hub for two smaller spacecrafts, B1 (supplied by the Japanese space agency JAXA) and B2 that will perform closer approaches to the nucleus.  Spacecrafts B1 and B2 will make higher risk/higher return measurements but with the increased probability that they will not survive the whole encounter.The MIRMIS Instrument: The Modular InfraRed Molecules and Ices sensor (MIRMIS, Figure 1) instrument is part of the CI Spacecraft A scientific payload.  The MIRMIS consortium includes hardware contributions from Finland (VTT Finland) and the UK (University of Oxford) with members of the instrument team from the Universities of Helsinki, Lyon, NASA’s Goddard Space Flight Center, and Southwest Research Institute.MIRMIS will map the spatial distribution of temperatures, ices, minerals and gases in the nucleus and coma of the comet using covering a spectral range of 0.9 to 25 microns.  An imaging Fabry-Perot interferometer will provide maps of composition at a scale of ~180 m at closest approach from 0.9 to 1.7 microns.  A Fabry-Perot point spectrometer will make observations of the coma and nucleus at wavelengths from 2.5 to 5 microns and finally a thermal imager will map the temperature and composition of the nucleus at a spatial resolution of 260 m using a series of multi-spectral filters from 6 to 25 microns.  Figure 1: (Top) The MIRMIS instrument for ESA’s Comet Interceptor mission. (Bottom) The MIRMIS Structural Thermal model under test at University of Oxford.The MIRMIS instrument is compact (548.5 x 282.0 x 126.8 mm) and low mass (

Abstract:

NASA’s Lucy spacecraft flew by the main-belt asteroid (152830) Dinkinesh on 2023 November 1, providing a test of its instruments and systems prior to its encounters with the Jupiter Trojans and enabling an opportunity for scientific investigation of this asteroid. Analysis of disk-integrated radiance spectra of Dinkinesh collected by the Lucy Thermal Emission Spectrometer (L’TES) instrument during the close approach reveals a thermal inertia for Dinkinesh of 91 ± 24 J m−2 K−1 s−1/2 and a surface roughness of 35° ± 7° rms slope. These values for the thermal inertia and surface roughness are comparable to values derived for other small S-type asteroids such as (65803) Didymos. The Dinkinesh flyby also provided the opportunity to develop new techniques for extracting data when the target body does not fill the field of view of the L’TES instrument, which proved challenging for predecessors of this instrument such as OTES on OSIRIS-REx. The grain size of the regolith of Dinkinesh, estimated to be r=1.2−0.6+0.9 mm, is below expected trends with size but is comparable to that of similarly sized asteroids that are either binaries or may have undergone rotational fission in the past. These findings imply that fine-grained materials are being preferentially retained on the primaries of multiple systems, either by cohesive forces or by redeposition after impact events on the secondaries.