Context. Exomoons are expected to orbit gas giant exoplanets just as moons orbit Solar System planets. Tidal heating is present in Solar System satellites, and it can heat up their interior, depending on their orbital and interior properties. Aims. We aim to identify a tidally heated exomoon's (THEM) orbital parameter space that would make it observable in infrared wavelengths with MIRI/JWST around Ïμ Eridani b. We study the possible constraints on orbital eccentricity and interior properties that a successful THEM detection in infrared wavelengths can bring. We also investigate what exomoon properties need to be independently known in order to place these constraints. Methods. We used a coupled thermal-tidal model to find stable equilibrium points between the tidally produced heat and the heat transported within a moon. For the latter, we considered a spherical and radially symmetric satellite with heat being transported via magma advection in a sublayer of melt (asthenosphere) and convection in the lower mantle. We incorporated uncertainties in the interior and tidal model parameters to assess the fraction of simulated moons that would be observable with MIRI. Results. We find that a 2RIo THEM orbiting Ïμ Eridani b with an eccentricity of 0.02 would need to have a semi-major axis of 4 planetary Roche radii for 100% of the simulations to produce an observable moon. These values are comparable with the orbital properties of the satellites of the Solar System gas giants. We placed similar constraints for eccentricities up to 0.1. We conclude that if the semi-major axis and radius of the moon are known (e.g., with exomoon transits), tidal dissipation can constrain the orbital eccentricity and interior properties of the satellite, such as the presence of melt and the thickness of the melt-containing sublayer.

Interplanetary missions have typically relied on Radio Science (RS) to recover gravity fields by detecting their signatures on the spacecraft trajectory. The weak gravitational fields of small bodies, coupled with the prominent influence of confounding accelerations, hinder the efficacy of this method. Meanwhile, quantum sensors based on Cold Atom Interferometry (CAI) have demonstrated absolute measurements with inherent stability and repeatability, reaching the utmost accuracy in microgravity. This work addresses the potential of CAI-based Gradiometry (CG) as a means to strengthen the RS gravity experiment for small-body missions. Phobos represents an ideal science case as astronomic observations and recent flybys have conferred enough information to define a robust orbiting strategy, whilst promoting studies linking its geodetic observables to its origin. A covariance analysis was adopted to evaluate the contribution of RS and CG in the gravity field solution, for a coupled Phobos-spacecraft state estimation incorporating one week of data. The favourable observational geometry and the small characteristic period of the gravity signal add to the competitiveness of Doppler observables. Provided that empirical accelerations can be modelled below the nm/s ² level, RS is able to infer the 6 × 6 spherical harmonic spectrum to an accuracy of 0.1–1% with respect to the homogeneous interior values. If this correlates to a density anomaly beneath the Stickney crater, RS would suffice to constrain Phobos’ origin. Yet, in event of a rubble pile or icy moon interior (or a combination thereof) CG remains imperative, enabling an accuracy below 0.1% for most of the 10 × 10 spectrum. Nevertheless, technological advancements will be needed to alleviate the current logistical challenges associated with CG operation. This work also reflects on the sensitivity of the candidate orbits with regard to dynamical model uncertainties, which are common in small-body environments. This brings confidence in the applicability of the identified geodetic estimation strategy for missions targeting other moons, particularly those of the giant planets, which are targets for robotic exploration in the coming decades.

Context. The apparent close encounters of two satellites in the plane of the sky, called mutual approximations, have been suggested as a different type of astrometric observation to refine the moons' ephemerides. The main observables are then the central instants of the close encounters, which have the advantage of being free of any scaling and orientation errors. However, no analytical formulation is available yet for the observation partials of these central instants, leaving numerical approaches or alternative observables (i.e. derivatives of the apparent distance instead of central instants) as options. Aims. Filling that gap, this paper develops an analytical method to include central instants as direct observables in the ephemerides estimation and assesses the quality of the resulting solution. Methods. To this end, the apparent relative position between the two satellites is approximated by a second-order polynomial near the close encounter. This eventually leads to an expression for mutual approximations' central instants as a function of the apparent relative position, velocity, and acceleration between the two satellites. Results. The resulting analytical expressions for the central instant partials were validated numerically. In addition, we ran a covariance analysis to compare the estimated solutions obtained with the two types of observables (central instants versus alternative observables), using the Galilean moons of Jupiter as a test case. Our analysis shows that alternative observables are almost equivalent to central instants in most cases. Accurate individual weighting of each alternative observable, accounting for the mutual approximation's characteristics (which are automatically included in the central instants' definition), is however crucial to obtain consistent solutions between the two observable types. Using central instants still yields a small improvement of 10-20% of the formal errors in the radial and normal directions (RSW frame), compared to the alternative observables' solution. This improvement increases when mutual approximations with low impact parameters and large impact velocities are included in the estimation. Conclusions. Choosing between the two observables thus requires careful assessment, taking into account the characteristics of the available observations. Using central instants over alternative observables ensures that the state estimation fully benefits from the information encoded in mutual approximations, which might be necessary depending on the application of the ephemeris solution.

This work evaluates the added benefit of using laser altimeter measurements for orbit reconstruction. As a spacecraft orbits a celestial body, its altimetry swaths progressively cross previous swaths. These locations, known as crossover points, yield valuable information about the orbited body and the spacecraft trajectory. The mathematical expressions for the inclusion of crossover measurements into orbit determination algorithms are presented and evaluated. It is shown that a first-order approximation of these expressions is insufficient and a more detailed expression is developed. To evaluate the impact of altimetry crossover measurements on orbit determination, the planetary mission Jupiter Icy moons Explorer (JUICE) by the European Space Agency (ESA) is used as a case study by means of a covariance analysis. In this initial analysis, the assumption is made that all altimetry measurements are obtained with nadir pointing which limits the direct applicability of our method until pointing is accounted for.

For planetary science, accurate clocks are mainly used as part of an onboard radioscience transponder. In the case of two-way radio data, the dominating data type for planetary radioscience, an accurate spacecraft clock is not necessary since the measurements can be calibrated using high-precision clocks on Earth. In the case of one-way radio data, however, an accurate clock can make the precision of one-way radio data be comparable to the two-way data, and possibly better since only one leg of radio path would be affected by the media. This article addresses several ways to improve observations for planetary science, either by improving the onboard clock or by using further variants of the classical radioscience methods, e.g., Same Beam Interferometry (SBI). For a clock to be useful for planetary science, we conclude that it must have at least a short-time stability (<1,000s) better than 10 ^{− 13} and its size be substantially miniaturized. A special case of using laser ranging to the Moon and the implication of having an accurate clock is shown as an example.

For planetary science, accurate clocks are mainly used as part of an onboard radioscience transponder. In the case of two-way radio data, the dominating data type for planetary radioscience, an accurate spacecraft clock is not necessary since the measurements can be calibrated using high-precision clocks on Earth. In the case of one-way radio data, however, an accurate clock can make the precision of one-way radio data be comparable to the two-way data, and possibly better since only one leg of radio path would be affected by the media. This article addresses several ways to improve observations for planetary science, either by improving the onboard clock or by using further variants of the classical radioscience methods, e.g., Same Beam Interferometry (SBI). For a clock to be useful for planetary science, we conclude that it must have at least a short-time stability (<1,000s) better than 10 ^{− 13} and its size be substantially miniaturized. A special case of using laser ranging to the Moon and the implication of having an accurate clock is shown as an example.

For planetary science, accurate clocks are mainly used as part of an onboard radioscience transponder. In the case of two-way radio data, the dominating data type for planetary radioscience, an accurate spacecraft clock is not necessary since the measurements can be calibrated using high-precision clocks on Earth. In the case of one-way radio data, however, an accurate clock can make the precision of one-way radio data be comparable to the two-way data, and possibly better since only one leg of radio path would be affected by the media. This article addresses several ways to improve observations for planetary science, either by improving the onboard clock or by using further variants of the classical radioscience methods, e.g., Same Beam Interferometry (SBI). For a clock to be useful for planetary science, we conclude that it must have at least a short-time stability (<1,000s) better than 10 ^{− 13} and its size be substantially miniaturized. A special case of using laser ranging to the Moon and the implication of having an accurate clock is shown as an example.