Planetary surfaces

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:

Despite being often described as Earth’s sister planet due to a similar distance to the Sun and comparable size, Venus’s internal structure and geodynamic regime, together with its upper atmosphere dynamics and asteroid entry rates, are poorly constrained. Whereas Venus is a prime candidate for being a tectonically active planet and presents a very dynamic atmosphere, future missions will not constrain high frequency phenomena such as seismic waves, meteoroid impacts, and high frequency gravity waves. These short duration events can be used to infer Venus' seismicity, internal structure, upper atmosphere dynamics and the small Solar System bodies population [1].We present a mission concept that targets high rate observations of upper atmosphere airglow emissions on both the day and night side of Venus, as well as thermal imaging in the visible. These observations will allow us to image the propagation of acoustic waves generated by seismic waves, enabling us to investigate quake locations and magnitudes, as well as to determine the structure of the crust and upper mantle. Volcanic events will also be studied through the associated increase in surface and atmosphere temperature. In addition, variations in airglow emissions will constrain the transfer of mechanical energy from the lower atmosphere to the thermosphere, as well as atmosphere dynamics (winds) and composition, and its response to solar forcing. Finally, the observation of fireballs produced by asteroid entries will constrain the asteroid population that crosses Venus’s orbit.The instruments required to perform these high rate observations are presented. They are based on a strong heritage relying on previous implementations in planetary missions.The mission concept and spacecraft demand new capabilities in terms of on-board attitude determination and data processing capabilities. In particular, a dedicated on-board data processing unit capable of autonomously detecting different event types with advanced algorithms, including machine learning methods, has been identified as a key component of the mission. This unit will also be used to average out phenomena over different temporal and spatial scales. To maximise science return, the mission will adopt an operational concept involving the capability to download high rate event data from a first quicklook information, similar to the one implemented on InSight NASA mission.The feasibility of the mission, already partly demonstrated by VAMOS JPL/NASA mission concept study [2,3], is validated through a dedicated mission analysis study.References[1] Christou A.A., Gritsevich M. 2024. Feasibility of meteor surveying from a Venus orbiter, Icarus, 417, 15 July 2024, 116116, DOI 10.1016/j.icarus.2024.116116[2] Sutin, B.M. et al. In Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave, volume 10698. SPIE, 2018. doi:10.1117/12.2309439.[3] Didion, A. et al. In 2018 IEEE aerospace conference. IEEE, 2018.

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.