Letters of Intent received in 2016

LoI 2018-1891
Focus Meeting: [A post Dawn Look at the Pristine Solar System]

Topics

- Surface composition and implications
- Interior structures
- Evolution and collisional history
- Volatile production and delivery
- Solar System formation/evolution
- Meteoritic parent bodies
- Surface geology
- Ground observations
- Formation models
- Future exploration

Rationale

Ceres and Vesta are the two most massive bodies in the Main Asteroid Belt. The two asteroids survived the collisional history of the Solar System, contrary to most other bodies in the Main Belt and among the Trans-Neptunian objects. Hence Vesta and Ceres still record the physical and chemical conditions typical of the early Solar System, i.e. the epoch of planetary formation.
NASA’s Dawn mission made extraordinary advances in our knowledge of these two bodies. The results obtained by Dawn have contributed to change dramatically our views and understanding of Solar System evolution.
Dawn orbited more than a year around each asteroid, taking color and hyperspectral images by means of the Framing Camera and the Visible and InfraRed spectrometer and mapped the surface elemental composition by means of Gamma Ray and Neutron Detector. Dawn has mapped almost completely both asteroids, producing very precise shape models and enabling scientific investigation of the surface geology, surface mineralogy, subsurface elemental composition and gravity and interior properties.
Dawn confirmed the link between Vesta and HED meteorite clan and the dichotomy between the southern and the northern hemisphere, already observed by the Hubble Space Telescope, showing the fine structure of a huge impact basin surrounding the South Pole. Two unexpected, important, discoveries were made during the mapping phase: the presence of dark, hydrated material likely released by impacts with carbonaceous chondrites, the occurrence of olivine deposits in the Northern hemisphere, not expected from existing Vesta formation models.
The observations at Ceres revealed for the first time the presence of widespread ammoniated phyllosilicates and of carbonates. In particular, carbonates are supposed to be solid residue of crystallization of brines that reached the surface from below. This may also indicate the current occurrence of fluids at depth. The strong interest in Ceres has been corroborated by the outstanding discovery of a few, localized regions hosting water ice and other ones containing organics. In addition, Dawn revealed a transient atmosphere around Ceres, which may be consistent with the water vapour molecules detected by the Herschel telescope. It has been postulated that volatiles could be delivered by cryovolcanic activity and form a haze in regions of the surface.
Many questions about Ceres are however still unanswered, e.g. a) what is the best meteorite analogue for Ceres?; b) do fluids really occur on the Ceres subsurface?; c) what is the component contributing most to the dark albedo of Ceres? ; d) how are volatiles produced or delivered?
The present meeting aims to encourage debate about the key-questions on the Solar System raised by Vesta and Ceres exploration, by inviting and accepting contributions from all the scientists involved in the analysis of Dawn data and all the activities supporting such analysis, i.e. theoretical and numerical modelling, meteorite studies, telescopic observations from ground or space