Study of Active Mainbelt Object through Sample Acquisition Summer School Alpbach 2008 BLUE TEAM 1 Outline • Scientific Background • Payload • Mission Profile • Planetary Protection • Budgets • Critical Issues • Conclusions 2
Introduction • What is SAMOSA? – Sample return mission to a main belt comet (MBC) – Return a sample of ~50g – In-situ investigation and remote sensing • Why? – MBC are unusual objects and not well understood – They may give us information about: - Stellar evolution - Planet formation - Emergence of life • Why a sample return? – Equipment on earth is more precise – More answers could be found – More questions will emerge 3 What are Main-Belt Comets (1)? - - In 2006, a population of objects was discovered in the - Main Belt showing cometary activity - � Main-Belt Comets (MBC) - - Currently three such objects are known: - 133P/ Elst-Pizarro 176P/ LINEAR - P/2005 U1 Read - For EP the activity is definitely driven by sub- limation of volatiles on the surface: - Finson-Probstein modelling confirms continuous activity over at least 5 months along the orbit - Activity was observed at the same orbital position in 3 consecutive apparitions (1996, 2002, 2008), inactivity at other parts
What are Main-Belt Comets (2)? - Water is not stable at the surface in the Main Belt over long periods � It must have been stored below the surface for some 10 9 a � An impact must have exposed it to sunlight recently � The crater surface is young (<10 3 a?) � There is no regolith in the crater area 5 What are Main-Belt Comets (3)? The Themis Family The MBCs are members of the Themis Family of asteroids: - Dynamically it fits - They have the BVRI colours of C-type asteroids, but not of comet nuclei and TNOs - It is dynamically unlikely to insert a comet to an orbit in the Main Belt - There are indications that water ice is present on the surface of 24 Themis - Orbits in the Themis Family are long-term stable � The MBC are former members of a now disrupted protoplanet still containing volatiles � They are still close to their formation region in the pre-solar disk
What is the Themis Family? The Themis Family - Some asteroids are clustered in families with similar orbital elements and similar spectroscopic properties -These families were formed by the collisional disruption of a larger parent body (protoplanet) -The Themis Family is one largest families: - primitive C-type asteroids - largest object (24 Themis) ~200 km in diameter - parent body was ~380 km in diameter - parent body was disrupted ~ 2 Ga ago What to do? What to do at the MBC? - Aquire a sample of volatile and non-volatile material from one MBC � go in the crater - Get a sample that includes sub-surface material (>1cm) � drilling - Determine the morphological and mineralogic context on the MBC � global mapping - Return some tens of grams of the sample to Earth � re-entry - Determine the physical microstructure in situ � microscopic investigation What to do on the way to the laboratory? - Keep the sample below 0°C at all times � avoid aqueous alteration - Monitor the temperature continuously � trace the sample environment - Ensure high level of cleaness to minimize contermination with terrestrial material � avoid analysis of terrestrial organics - Ensure high density of the sample container � avoid loss of volatiles in space 8
What to do? What to do at the MBC? - Aquire a sample of volatile and non-volatile material from one MBC � go in the crater - Get a sample that includes sub-surface material (>1cm) � drilling - Determine the morphological and mineralogic context on the MBC � global mapping - Return some tens of grams of the sample to Earth � re-entry - Determine the physical microstructure in situ � microscopic investigation What to do on the way to the laboratory? - Keep the sample below 0°C at all times � avoid aqueous alteration - Monitor the temperature continuously � trace the sample environment - Ensure high level of cleaness to minimize contermination with terrestrial material � avoid analysis of terrestrial organics - Ensure high density of the sample container � avoid loss of volatiles in space ...AND WHY? 9 Link to pre-planetary disk Modelling Results for the pre-planetary disk: - Models of the pre-planetary disk provide the abundance of materials as a function of the distance from the proto-Sun Si in minerals as a function of distance from the proto-Sun - The comparison with observations allows us to constrain the conditions in the pre-planetary disk - The model results depend on a number of parameters (turbulence, initial mass, diffusion,...) A sample from a MBC (volatiles and non-volatiles, well constrained formation region) allows to constrain the conditions in the pre-planetary disk Concentration of hydrocarbons as a function 10 of distance to the proto-Sun
Link to Planet Formation Modelling Results for Planet Formation: - Orbits in the Themis Family are stable over long times (order Ga): � Formation distance from proto-Sun well constrained - Themis Family is well known � Size and nature of the protoplanet parent body is constrained - Crystallisation age determination is possible Correlation between distance from Sun, accretion � The time of formation can be determined time, protoplanet diameter, and temperature. - Minerals and volatiles allow us to constrain the temperature regime � Maximum temperature/pressure in history can be determined - The cooling rate can be determined � The burial depth during formation can be constrained No other object provides such a large number Temperature versus time in of well-constrained parameters! 11 a 20 km-size body. Link to Meteorites - Carbonaceous chondrites are the oldest meteorites available on Earth -They contain organic matter - They are partly affected by aqueous alteration - The alteration products (carbonates) are important for isotopic studies - C-type asteroids (Themis Family) are the assumed parent bodies of the carbonaceous chondrites A sample from a MBC provides the first link between the meteorite collections on Earth and astronomical objects It is possible to correlate isotopic and elemental composition of different minerals and volatiles (water) in the parent body 12
Link to Impact Science - Impact studies suffer from poor constraints on basic material properties (internal energy, equation of state,...) - Such properties can be constrained from the conditions during an impact - The Themis Family was disrupted in an catastropic collision and volatiles are present in fragments � The volatile compostion can constrain the maximum temperature in the body during impact The understanding of the conditions during impacts is important for the history of Earth: What material (water, organics) delivered to Early Earth survives the impact? � What is available for the formation of life? 13 Link to the Origin of Life - Most water on Earth does not come from comets: D/H in SMOW : 15.6 x 10 -5 D/H in water in the cometary coma is twice that value - Does the water come from the Main Belt? - What is D/H in other organic compunds? Isotopic analysis in the volatile sample can determine the origin of terrestrial water - Carbonaceous Chondrites contain organic material - Their parent bodies have impacted on the Early Earth � What organic material was present on the Early Earth? The laboratory analysis allows to make an inventory of organic matter that came to Earth in Impacts 14
Sample Analysis Why return a sample? Planet Formation � Dating � Isotopic composition Planet Formation � Cooling rate � Elemental composition on microscale Origins of Life � Organic composition � high precision & sensitivity Planet Formation, Protoplanetary disk � Microscopic mineral composition � high spatial resolution Origins of Life � Isotopic ratios in minor volatile species � high accuracy and sensitivity This implies: The required analysis needs: - Ground-bound instrumentation (TEM, SIMS, GC-MS,...) - Sample decisions - Complex sample preparation - Analysis adaptivity � The Sample has to be returned to ground 15 Overview: Analysis of the returned sample Volatiles and Imaging Organic Compounds Sample microstructure Optical Microscopy, Identification of soluble GC-MS, HPLC-MS, SEM and volatile compounds MALDI Sample topography AFM Identification of non Cluster Ion ToF-SIMS Elemental distribution SEM-EDX, TEM-EELS volatile and non soluble compounds Cooling rate SEM-EDX, TEM Structure investigations NMR techniques, MS-MS Bulk and Isotopic investigations Mineral Composition (e.g. Age Dating) Bulk elemental ICP-AAS, composition X-Ray Tomography Crystallization age High resolution MS Radiation age (ICP-MS, nanoSIMS, 3D elemental ToF-SIMS, nano-SIMS H/D ration (ice) solid state MS, Laser distribution ablation MS…) Mineral structure TEM, RAMAN, X-ray Diffraction 16
Recommend
More recommend
