1. Changes on the smooth region of Imhotep
Olivier Groussin et al.
7 July 2015

2. Auger et al. (2015)

3. Temporal evolution No changes yet since 5 Sept. 2014:
24 May 2015 (01:34)
Changes become visible:
3 June 2015 (06:59)
5 June 2015 (07:03)
13 June 2015 (13:41)
13 June 2015 (15:20)
18 June 2015 (07:17)
23 June 2015 (10:54)
1 July (03:56)
2 July (05:37)

4. At least three features are appearing and expanding rapidly
(50 cm/hour).

5. (Water?) ice is being exposed where the expanding feature reaches and “cleans” a consolidated terrain discontinuity.

6. Link with activity
13 June 2015

7. Link with activity
13 June 2015

8. Link with activity
23 June 2015

9. Link with activity
23 June 2015

10. Link with activity (summary)
As usual, it is not easy to trace jets down to the surface
Conclusion #1 – Some jets may potentially come from the smooth terrains
This is a possible solution, not unique (projection effects)
Conclusion #2 – No jets seem to be associated with the new, expanding feature

11. Not standard erosion by mean of sublimation
Argument #1 – No jets seem to be associated with this expanding feature
Argument #2 – The expanding rate of 50 cm/hr (1.4 x 10-4 m/s) is 2 orders of magnitude larger than the sublimation AU:
Erosion rate H2O = 4.9 x 10-7 m/s
Erosion rate CO2 = 3.3 x 10-6 m/s
Erosion rate CO = 5.1 x 10-6 m/s
Argument #3 – The “excavated material” would amount to 2.5 x 106 kg per day during 10 days (2.5 x 107 kg total), i.e. roughly one Deep Impact per day!
 Material moved but did not escape the nucleus for most of it

12. Possible scenarios Flows / displacement on the surface
Not really compelling since the gravitational slope is null
Cavity collapse: primordial void or more recent (pits formation)
The surface material sinks slowly into the interior as the upper “mantle” disintegrates
Material sinking: “siphon process”
The surface material sinks into the interior through one or several fractures recently opened
The surface material sinks into a degassing conduit recently opened
 Fluidization may speed up the process in both cases

13. A B C D

14. Terrestrial analogues (sinkholes)

15. What could be the end state?
Formation of a new pit
Formation of a new basin
Apparition of a roundish feature
Apparition of new terrain discontinuities
Other ???

16. Other known examples? 9P/Tempel 1 From Mike A’Hearn
From Antoine Pommerol

17. Conclusions
A very interesting topic! No scenarios are yet fully satisfying…
More observations over the summer will provide an answer to many questions, in particular on the processes involved, time scales and the end state.
Following a recommendation from Holger, I have started to write a A&A letter. First draft to be distributed on Friday?