About small bodies

The COMET-ORB (expert community on space dynamics) is pleased to announce that a seminar on small bodies (structure, physical parameters, ephemerides, and more) will take place on April 11^th 2023.

This one-day seminar will give the opportunity to many specialists to present their work about the physical aspects of small bodies (comets, asteroids, natural satellites, etc.), and also on some space mission aspects (instruments, orbits, etc…).  The presentations will be related to challenging present and future missions such as Osiris Rex, MMX, DART, etc…

There are three options for attending the seminar:

• either on-premises in the amphitheatre,
• or remotely with the livestorm tool in real time,
• or in deferred time with the recording.

In all cases, registration is mandatory. You must specify whether or not you will be present.

Because we size the coffee breaks and meals based on the registration list, we kindly ask you to register on-premises if you intend to come. If you are unable to attend after an on-premises registration, please let us know by sending an e-mail to : comet-orb@cnes.fr

The conference venue is : ISAE-Supaero, 10 avenue Edouard Belin, TOULOUSE

Registering for remote participation will allow you to have a link to connect to the presentations, and will give you the possibility to ask questions.

In all cases of registration, you will be able to access the recording of the presentations afterwards, with the livestorm link. Please note that registration is required to access the replay.
 

This program is preliminary, schedules are not yet set, and titles may change.

Abstracts :

Asteroid Exploration: Recent results on the geophysical environments of primitive asteroids from the OSIRIS-REx and Hayabusa2 missions

Daniel Scheeres (University of Colorado)

The past few years have been marked by a number of significant advances in asteroid exploration. NASA’s OSIRIS-REx spacecraft and the Japanese Hayabusa2 spacecraft have both carried out highly successful missions. The main goal of both of those missions was to collect samples from primitive asteroids and return them to Earth for further analysis. In order to place these valuable samples into appropriate context both missions also explored the physical and geophysical environment of these bodies. In this talk some main results on the geophysics of these bodies based on in situ measurements will be reviewed and their implications for asteroids and their future exploration discussed. 

Probing the physical properties of the surface and sub-surface of asteroids

Naomi Murdoch (ISAE)

The quantification of the physical and mechanical properties of the surface and sub-surface of asteroids is critical for planetary defense, for reducing the risks of space missions involving surface interactions (sampling, landing, roving, …), and for understanding the geophysical evolution of these bodies.  The mechanical properties of asteroids can be estimated through interpretations of the small body’s geomorphology and surface features, and measured directly from in-situ measurements. In this talk we will discuss what can we infer about asteroid properties from remote observations and what their surfaces can tell us about their physical properties. We will also discuss some lessons learned from recent missions and the implications for future in-situ geophysical exploration of asteroids.

Evolutionary dynamics of rubble-pile asteroids as granular systems

Fabio Ferrari (Politecnico di Milano)

Evidence supports the idea that asteroids are rubble piles, that is, gravitational aggregates of loosely consolidated material. This makes their dynamics subject not only to the complex N-body gravitational interactions between its constituents, but also to the laws of granular mechanics. The evolutionary dynamics of rubble-pile asteroids can be therefore studied using the granular N-body problem, in which the dynamics of individual rubble-pile constituents are driven both by mutual gravity, contact and collision interactions. This approach is used here to identify dynamical transitions and predict the qualitative behavior of these objects, with application to evolutionary processes involving rubble piles’ interiors and surfaces. Results are presented in the context of the DART/Hera mission, involving the origin of the Didymos binary system.

Simulations on the Radio Science Experiment for the Hera mission

Riccardo Lasagni Manghi (University of Bologna)

Aiming to launch in October 2024, the Hera mission represents ESA’s contribution to the asteroid impact and deflection assessment (AIDA) collaboration.
The main goal of this mission is to characterize the physical properties of the binary asteroid system Didymos in the aftermath of NASA’s DART impact on Dimorphos.
In this context, the Radio Science Experiment (RSE) onboard Hera will provide a key contribution to the mission success by estimating the gravity fields of Didymos and Dimorphos by means of a precise orbit determination process.

In addition to ground-based Doppler and range measurements, the RSE will make use of the optical images collected by the onboard navigation cameras and of the radiometric measurements from the inter-satellite link (ISL) between Hera and its two companion CubeSats, Juventas and Milani. Furthermore, Hera is equipped with a time-of-flight planetary altimeter (PALT), which will further constrain the spacecraft relative trajectory by measuring its distance from the surface of the target asteroids.

This talk will provide an overview of the RSE architecture and expected performance. In particular, we will characterize the accuracy of the gravity reconstruction as a function of the mission phase and of the availability of different measurement types by means of a covariance analysis.

LICIACube: Mission analysis and operations recaps

Giovanni Zanotti (Politecnico di Milano)

The challenges behind the LCIACube mission analysis are presented, highlighting the different constraints and objectives involved in the design of the trajectory, from DART-release to the fly-by of Didymos binary system. After that, the mission operations are described, with particular emphasis on the orbit determination and manoeuvring tasks that, involving the different teams, led to a successful fly-by and mission outcome.

LICIACube: Scientific analyses 

Elisabetta Dotto (Italian National Institute for Astrophysics)

On September 26, the NASA DART mission made its impact on Dimorphos, the small satellite of the binary asteroid Didymos.
It was the first planetary defense space mission to demonstrate the applicability of the kinetic impactor technique for the deflection of an asteroid.
An exceptional witness was LICIACube (Light Italian Cubesat for Imaging of Asteroids) , the nanosatellite managed by the Italian Space Agency (ASI), the first one operating in deep space.
LICIACube was launched together with DART in November 2021, after a 9.5 months cruise was released 15 days before the DART impact, and witnessed the event acquiring more than 400 scientific images of the produced effects.
The project will be presented and discussed together with the in situ observation strategy and the first obtained results.

Internal structure of small bodies from inversion of geodetic data

Sébastien Le Maistre / Alfonso Caldiero (Royal observatory of Belgium)

We propose an approach to constrain the interior structure of a small body from its gravitational potential via the level-set method. Gravity is among the primary outputs of any spacecraft mission to a small body, as it can be obtained simply by precisely reconstructing the orbit of the visiting spacecraft, or, as demonstrated by recent efforts, by tracking the motion of orbiting ejecta.

The inverse-source problem of determining a mass distribution from measurements of its exterior gravitational potential is, albeit well-studied, notoriously ill-posed. We mitigate the inherent non-uniqueness of the inversion by limiting our scope to piecewise-continuous mass distributions, which are composed of a few number of anomalies where the density is constant. The boundary of each anomaly is defined implicitly as the 0 level-set of a scalar field. Therefore, by modifying this field (called the level-set function) the shape and location of the anomaly are varied. 

The gravitational potential of a given density distribution is here computed via a mascons approximation: the body is modelled as a collection of point masses, and the sum of the contribution of each element provides the coefficients of the spherical harmonic expansion of the global potential. These predicted Stokes coefficients are then fitted to the measured values via an iterative least-squares approach. At each iteration, we estimate corrections to the level set function of each anomaly at the mascons location, as well as the corresponding density jump and the background density. The partials of the spherical harmonics coefficients with respect to the level-set functions are obtained via the chain rule.

We present preliminary results showing accurate retrieval of the ground-truth mass distribution in simulations, even when the synthetic Stokes coefficients are contaminated with moderate noise. We also discuss the application of the method to real data, such as the gravity coefficients measured by OSIRIS-REx for Bennu, or the outputs expected from future small bodies missions.

Gravity mutual potential applied to Phobos/Mars system for the MMX mission

Julien Laurent-Varin, Georges Balmino (CNES)

The gravitational interaction between two bodies is the sum of the contributions of the masses of the first body acting on the masses of the second. This exact calculation is complex to achieve and often approximated by taking into account one of the two bodies as a point mass. This approximation is quite valid when the bodies are relatively far apart, but if the bodies are gravitationally "close" and the masses are not uniformly distributed, then the approximation becomes important.
In the literature, the first terms could be taken into account, but in this presentation, we will focus on setting up the formal framework for an exact calculation in terms of harmonic development, and we will apply it to the Phobos/Mars and Dydymos/Dymorphos system.