Solar system

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: Enceladus Thermal Mapper (ETM) is an Oxford-built high-heritage instrument that is being developed for outer solar system operations. ETM is based upon the design of Lunar Thermal Mapper (LTM, launched on Lunar Trailblazer, Fig. 1). It has a strong heritage story, including MIRMIS (on Comet Interceptor), Compact Modular Sounder (on TechDemoSat-1) and filters shared with Lunar Diviner (on Lunar Reconnaissance Orbiter). ETM is a miniaturized thermal infrared multispectral imager, with space for 15 spectral channels (bandpasses) that can be tailored to the mission requirements. It consists of a five-mirror telescope and optical system and an uncooled microbolometer detector array. Real-time calibration is achieved using a motorized mirror to point to an onboard blackbody target and empty space. ETM has an IFOV of 35 mm, so assuming a 100 30 km orbit it will have a spatial resolution of 40 to 70 m/pixel and a swath width of 14 - 27 km. ETM Updates: Through UK Space Agency funding we have developed three areas of ETM: its filter profile, radiation tolerance and sensitivity to Enceladus-like surfaces. Filters: ETM is a push broom thermal mapper, which works by the detector being swept over a surface. Each of the detector’s 15 channels is made up 16 rows, which are coadded to increase the signal to noise. A recently completed preliminary study has updated ETM’s bandpasses to include filters between 6.25 mm and 200 mm to enable it to detect Enceladus’ polar winter (170 K). Depending on the mission goals not all channels need to be utilised to achieve this, making some available for additional studies (e.g. searching for salt). Radiation: The radiation environments of Enceladus are vastly different to those of the Moon. Recent radiation testing and analysis showed that the majority of ETM’s existing design is already highly radiation tolerant. With some additional shielding and one component change all parts can reach the radiation hardness required to operate in the Saturn-system. The additional shielding may be provided by the spacecraft structure, depending on the adopted design. Sensitivity: ETM’s sensitivity to cryogenic surfaces is currently predicted through a well-characterised model. However, as part of the LTM calibration campaign we plan to directly measure its sensitivity to

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 Cassini mission revealed endogenic activity at the south pole of Saturn’s moon Enceladus. The activity is concentrated along four fractures in Enceladus’ ice shell, which are much warmer than their surroundings and the source of Enceladus’ plumes. This work provides a review of the current state of knowledge of the energy and mass lost by Enceladus through this activity. Specifically, we discuss the composition of the plumes, along with their spatial and temporal variation. The mass flux loss predicted for the three plume constituents (gas, dust and charged particles) is reviewed and a total mass flux of ejected material that subsequently escapes Enceladus is estimated to be 2.1×1011 kg over a Saturn year. Given that Enceladus’ ocean is predicted to be 1019 kg this loss is sustainable in the very long term (∼1.5 billion Earth years). However, unless a resupply mechanism (such as serpentinization) exists molecular hydrogen is expected to be depleted within ∼1 million Earth years. The difficulty in determining Enceladus’ current heat flow is outlined, along with the advantages and disadvantages of the various techniques used to derive it. We find a robust lower limit for Enceladus’ exogenic production is 7.3 GW. Tidal heating models show endogenic emission of this level is sustainable, and Enceladus may have long-term near-surface heating (a result supported by studies of Enceladus’ geology). Finally, we offer suggestions for future observations, instrumentation, and missions. Enceladus remains a high-priority target for NASA, and as such it is highly likely that we will return to study this enigmatic world. Hopefully these missions will answer some of the questions that remain.

Abstract:

This study presents a comprehensive analysis of the Martian ionosphere using Mutual Radio Occultation (RO) observations between Mars Express and Trace Gas Orbiter, featuring 71 full vertical profiles out of a total of 124 measurements. Among these, 35 measurements were taken from regions with Solar Zenith Angles lower than 40°. The profiles also represent the largest data set for the lower M1 ionospheric layer during the midday ever measured. This paper has also been submitted with a comprehensive data set, which marks the first time MEX-TGO RO data has been made available to the community. Additionally, neutral temperature profiles have been extracted from the measurements. We find unexpected features in the lower thermosphere temperature behavior which we conclude is likely due to the effects of local circulation and associated dynamical heating rather than solar-controlled.