Pits of 67P/Churyumov-Gerasimenko What do they tell us on comets?

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Bertram McKenzie
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1 Pits of 67P/Churyumov-Gerasimenko What do they tell us on comets? S. Besse, A. Guilbert-Lepoutre, C. Leyrat European Space Astronomy Centre (ESAC), Observatoire de Besancon, Observatoire de Paris And the ESAC OSIRIS team And all the OSIRIS team And all the ROSETTA instrument-teams for the science inputs S. Besse SSW meeting Spain 14/11/2017 Slide 1 Prepared for SSW 2017

2 67P/Churyumov-Gerasimenko 1000m S. Besse SSW meeting Spain 14/11/2017 Slide 2

3 67P/Churyumov-Gerasimenko 200m 1000m S. Besse SSW meeting Spain 14/11/2017 Slide 3

4 How can your schedule go totally wrong S. Besse SSW meeting Spain 14/11/2017 Slide 4

5 How can your schedule go totally wrong S. Besse SSW meeting Spain 14/11/2017 Slide 5

6 67P/Churyumov-Gerasimenko 1000m S. Besse SSW meeting Spain 14/11/2017 Slide 6

7 Applicable to other comets as well? Comet Borrelly 3000m Comet Hartley m Comet Wild 2 400m S. Besse SSW meeting Spain 14/11/2017 Slide 7

8 Difficult to compare comets to comets Wing-Huen et al, 2015 S. Besse SSW meeting Spain 14/11/2017 Slide 8

9 Difficult to compare comets to comets Wing-Huen et al, 2015 What can we learn from comets morphology, knowing that we cannot predict very well their history. S. Besse SSW meeting Spain 14/11/2017 Slide 9

10 What can we learn from those pits? Mercury s pyroclastic deposits We study comets because they have preserved (to a certain point) the original building blocks of the Solar System? By staying far away from the Sun (>2.5 AU), do they preserve their original chemistry, morphology and history of formation? This is the point to be questioned here! Are the pits providing a view inside the primitive composition and morphology of comets? What are they, how do they form, what do they tell us? 1. Good characterization of the features Geologist background 2. Good understanding of the evolution processed Modeler background S. Besse SSW meeting Spain 14/11/2017 Slide 10

11 67P/Churyumov-Gerasimenko Mercury s pyroclastic deposits Vincent, Bodewits, Besse et al., 2015 S. Besse SSW meeting Spain 14/11/2017 Slide 11

12 Seth region Mercury s pyroclastic deposits 200 m S. Besse SSW meeting Spain 14/11/2017 Slide 12

13 Seth region Pits grow Pits form Alcoves 200 m S. Besse SSW meeting Spain 14/11/2017 Slide 13 Inactive

14 Mapping Mercury s pyroclastic deposits Northern Hemisphere Colors for regions S. Besse SSW meeting Spain 14/11/2017 Slide 14

15 Mapping with Faculty funding Mercury s pyroclastic deposits Small Body Mapping Tool APL (USA) Northern Hemisphere Colors for regions S. Besse SSW meeting Spain 14/11/2017 Slide 15 Besse et al 2014

16 Mapping Mercury s pyroclastic deposits Southern Hemisphere Colors for regions S. Besse SSW meeting Spain 14/11/2017 Slide 16

17 Multiple views Mercury s pyroclastic deposits +X +Z -Z S. Besse SSW meeting Spain 14/11/2017 Slide 17 +Y

18 Hapi-Seth (N) Vs. Sobek-Anhur (S) El-Maarry et al (N), 2016 (S) S. Besse SSW meeting Spain 14/11/2017 Slide 18

19 Hapi-Seth (N) Vs. Sobek-Anhur (S) Massironi et al Neck Terraces Pits/Alcoves Terraces Neck Pits Alcoves S. Besse SSW meeting Spain 14/11/2017 Slide 19

20 How did we get there Mercury s pyroclastic deposits Are the Terraces and Pits relic of an ancient world? Very likely but to which extend? Are the Pits primordial? Most likely not primordial voids, but they tell us about the primordial heterogeneity What do we really need to answer Which mechanisms and material form the pits (e.g., sinkhole, ices, etc..)? What is the time scale of formation/preservation? Is 2 years of Rosetta data consistent with the formation of pits in a reasonable timescale? S. Besse SSW meeting Spain 14/11/2017 Slide 20

21 ESTEC Fellowship 2012 team Smart Modeler Geologist Aurelie Guilbert-Lepoutre S. Besse SSW meeting Spain 14/11/2017 Slide 21

22 ESTEC Fellowship 2012 team Smart Modeler Geologist Aurelie Guilbert-Lepoutre S. Besse SSW meeting Spain 14/11/2017 Slide 22

23 One comet revolution Mercury s pyroclastic deposits Aphelion Perihelion S. Besse SSW meeting Spain 14/11/2017 Slide 23

24 Ten comet revolutions Mercury s pyroclastic deposits Co2 ice Co ice ~1959 ~today S. Besse SSW meeting Spain 14/11/2017 Slide 24

25 Ten comet revolutions Co2 ice Co ice ~1959 ~today S. Besse SSW meeting Spain 14/11/2017 Slide 25

Some ideas on what s going on (1) Mercury s pyroclastic deposits Forming the pits from crystallization,

Very unlikely within one orbit of 67P Difficult to reach 100m in 60 years Should be the main driver for

Intimately linked to the layers, thus primordial origin But different erosion states Change in thermal

26 Some ideas on what s going on (1) Mercury s pyroclastic deposits Forming the pits from crystallization, sublimation, clathrate destabilization? Very unlikely within one orbit of 67P Difficult to reach 100m in 60 years Should be the main driver for morphology Are the Pits primordial? Intimately linked to the layers, thus primordial origin But different erosion states Change in thermal balance (e.g. close encounter) could be a trigger for the creations of pits What do the pits tell us? Erosion pattern points to compositional heterogeneities Within the heterogeneities, it is homogeneous (N/S, Lobes) S. Besse SSW meeting Spain 14/11/2017 Slide 26

27 Maybe some conclusions (2) Mercury s pyroclastic deposits Which mechanism is likely forming the pits? Creation by an impact very unlikely Ancient impact can create defects that act has point of focus for the depression evolution (by sublimation) How can the pits be active if they are that old! Is the activity linked to the frost deposition? What do the pits tell us on comets That we do not understand thermal evolution of small bodies That we do not understand the formation of comets Improvements and hopefully a paper! Refine thermal models, smaller granularity S. Besse SSW meeting Spain 14/11/2017 Slide 27 Explore the link pits/layer

be active if they are that old! Is the activity linked to the frost deposition?

28 Maybe some conclusions (2) Mercury s pyroclastic deposits Which mechanism is likely forming the pits? Creation by an impact very unlikely Ancient impact can create defects that act has point of focus for the depression evolution (by sublimation) How can the pits be active if they are that old! Is the activity linked to the frost deposition? What do the pits tell us on comets That we do not understand thermal evolution of small bodies That we do not understand the formation of comets Improvements and hopefully a paper! Refine thermal models, smaller granularity S. Besse SSW meeting Spain 14/11/2017 Slide 28 Explore the link pits/layer

ESAC Small Solar System bodies and Rosetta Group

ESAC Small Solar System bodies and Rosetta Group The current focus of the group is the analysis of images from the OSIRIS scientific cameras of the Rosetta mission. Research topics are: Surface features