Monday, July 18, 2016

I know what happened to Philae!

EIn a previous post, I explained the "sieve" effect of opening and closing cracks sifting boulders to generate the distribution of boulders on different gravitational slopes.

This effect, and nucleus surface cracks are ubiquitous on every area of 67P, including Abydos. On the approach to perihelion, cracks around Philae would be expanding and contracting. Philae, the size of a fridge and lying on its side, is destined to be worked and jiggled into a nearby crack. The first effect is to make barriers to communication in both reception and transmission, as both the main radio and secondary are dropped with Philae deeper into the crevice that it was already half way in. Only the extent of its legs stop Philae from sinking many meters down to the below layer of the surface. Only the strength of the sunlight and occasional fortunate alignment of Rosetta with a line of sight to its partly buried antennas enabled any transmission at all.

This would mean that finding Philae is going to be much harder! All that is likely to be visible on the surface is the legs...


 Credits: CNES/D. Ducros

The "sieve" effect on 67P

This effect explains the relationship between the cracks on the surface of 67P, and the distribution of Boulder sizes at different gravitational slopes.

During the higher temperatures and energy of perihelion, the expansion, contraction and transferred forces along the surface of the nucleus cause what can only be described as "duck quakes". Smaller rocks fall into the many deep cracks, while large monoliths stay stuck on the surface. On relatively (gravitationally) horizontal areas, the medium term effect is for all smaller and medium size boulders to be consumed into the surface as rubble, and for larger boulders (eg. Cheops, Tekhenu) to remain stranded on an otherwise pebbly looking "plain" (eg, Hapi, Imhotep, Anuket). 

The "sieve" effect also explains larger, more long term cracks such as those on Anuket and Hapi. Mid sized, "wedge shaped" boulders can get stuck in a crack and manage to hold it open, and stopping it from the dynamic process that tends to fill them in with smaller rubble. This appears to be the case in the longer term cracks in both Anuket and Hapi - see the OSIRIS images below. Cracks are punctuated by boulders that seem to be wedged stuck in the cracks.

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:

Tuesday, July 05, 2016

Tekhenu region overhang collapse into Anuket crack

Another significant and exciting find in the Anuket region near Tekhenu (we will defines Tekhenu region encompassing these screenshots when we work out suitable boundaries)
This appears as a collapse into the crevice which defines part of the Anuket crack. Because it is an overhang collapsing, it can give useful upper bounds for surface strength measurement.

Again, many thanks to A.Cooper for the annotations that help with understanding the nature of the changes and their relationship with nearby changes.

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
All dotted annotations by Marco Parigi and A. Cooper

Saturday, July 02, 2016

New Nav Cam image of Anuket and Anubis

The latest Rosetta Blog post features an image which the context of several areas of change can be located. Tekhenu, and the area of the main Anuket crack is in profile and foreshortened. The rockfall area (Sah) is just in shadow on the edge of a raised layer of rough cometary surface.

In the foreground is the "Dinosaur footprint" sublimative erosion which expanded the area relative to the boulders, which remain unchanged. This has been explained in A. Cooper's blog, and I will put a link in in time.

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
All annotations by Marco Parigi