A&A 583, A35 (2015)
DOI:
10.1051
/0004-6361/201525947
c ESO 2015
Astronomy
&
Astrophysics
Rosetta mission results pre-perihelion
Special feature
Geomorphology of the Imhotep region on comet
67P/Churyumov-Gerasimenko from OSIRIS observations
A.-T. Auger
1,2
, O. Groussin
1
, L. Jorda
1
, S. Bouley
2,3
, R. Gaskell
4
, P. L. Lamy
1
, C. Capanna
1
, N. Thomas
5
,
A. Pommerol
5
, H. Sierks
6
, C. Barbieri
7
, R. Rodrigo
8,9
, D. Koschny
10
, H. Rickman
11,12
, H. U. Keller
13
, J. Agarwal
6
,
M. F. A’Hearn
14
, M. A. Barucci
15
, J.-L. Bertaux
16
, I. Bertini
17
, G. Cremonese
18
, V. Da Deppo
19
, B. Davidsson
11
,
S. Debei
18
, M. De Cecco
20
, M. R. El-Maarry
5
, S. Fornasier
15
, M. Fulle
21
, P. J. Gutiérrez
22
, C. Güttler
6
, S. Hviid
23
,
W.-H. Ip
24
, J. Knollenberg
23
, J.-R. Kramm
6
, E. Kührt
23
, M. Küppers
25
, F. La Forgia
7
, L. M. Lara
22
, M. Lazzarin
7
,
J. J. Lopez Moreno
22
, S. Marchi
26
, F. Marzari
7
, M. Massironi
27,28
, H. Michalik
29
, G. Naletto
30,17,19
, N. Oklay
6
,
M. Pajola
28
, L. Sabau
31
, C. Tubiana
6
, J.-B. Vincent
6
, and K.-P. Wenzel
10
(A
ffiliations can be found after the references)
Received 23 February 2015
/ Accepted 12 May 2015
ABSTRACT
Context.
Since August 2014, the OSIRIS Narrow Angle Camera (NAC) onboard the Rosetta spacecraft has acquired high spatial resolution images
of the nucleus of comet 67P
/Churyumov-Gerasimenko, down to the decimeter scale. This paper focuses on the Imhotep region, located on the
largest lobe of the nucleus, near the equator.
Aims.
We map, inventory, and describe the geomorphology of the Imhotep region. We propose and discuss some processes to explain the formation
and ongoing evolution of this region.
Methods.
We used OSIRIS NAC images, gravitational heights and slopes, and digital terrain models to map and measure the morphologies of
Imhotep.
Results.
The Imhotep region presents a wide variety of terrains and morphologies: smooth and rocky terrains, bright areas, linear features, roundish
features, and boulders. Gravity processes such as mass wasting and collapse play a significant role in the geomorphological evolution of this region.
Cometary processes initiate erosion and are responsible for the formation of degassing conduits that are revealed by elevated roundish features on
the surface. We also propose a scenario for the formation and evolution of the Imhotep region; this implies the presence of large primordial voids
inside the nucleus, resulting from its formation process.
Key words.
comets: individual: 67P
/Churyumov-Gerasimenko – methods: data analysis
1. Introduction
Cometary nuclei, formed in a cold environment far from the Sun,
are excellent tracers of the formation and evolution processes of
the solar system, making their study particularly relevant (e.g.,
Weidenschilling 2004
). Their physical nature, composition, dis-
tribution, formation, and evolution are fundamental for under-
standing how planets formed and evolved, and ultimately how
water was brought to Earth (e.g.,
Dones et al. 2004
;
Duncan
et al. 2004
;
Hartogh et al. 2011
). Since the formation of the solar
system, comets have been a
ffected by collisions, dynamical per-
turbations, irradiation processes, and thermal alteration, which
have modified their physico-chemical properties and their orbits
(e.g.,
Weissman et al. 2004
;
Bockelée-Morvan et al. 2004
;
Delbó
et al. 2014
). As a result of the sublimation of ices as the comet
approaches the Sun, cometary activity is expected to be the main
process altering the external layers of the nucleus. However, this
process is still poorly understood, and we do not know to which
extent it a
ffects the surface and whether primordial unaltered re-
gions still exist on the nucleus. The geomorphology of the nu-
cleus provides key elements to address these questions.
Past studies on the geomorphology of cometary nuclei (1P
/
Halley, 19P
/Borrelly, 81P/Wild 2, 9P/Tempel 1, 103P/Hartley 2,
and 67P
/Churyumov-Gerasimenko) have revealed several types
of terrains and geological features (
Britt et al. 2004
;
Brownlee
et al. 2004
;
Thomas et al. 2007
,
2013a
,
b
,
2015b
;
Basilevsky
& Keller 2007
;
Sierks et al. 2015
). The variety of terrains in-
cludes smooth, mottled, pitted, and brittle terrains as well as
terrains with exposed consolidated materials. Features include
dark and bright spots, mesas, ridges, mounds, pits, and circu-
lar features, some of which are tentatively interpreted as impact
craters. Layering has also been observed or at least suggested
on 9P
/Tempel 1 and 81P/Wild 2. Finally, flows have been pro-
posed to explain the large smooth areas observed on Tempel 1
(
Belton & Melosh 2009
). The origin and chronological evolu-
tion of most, if not all, of the terrains and geological features are
still very uncertain, if not completely unknown.
The Rosetta mission from the European Space Agency is
orbiting comet 67P
/Churyumov-Gerasimenko (hereafter 67P)
since August 2014. The Optical Spectroscopic and Infrared
Remote Imaging System (OSIRIS;
Keller et al. 2007
), composed
of two cameras, has acquired thousands of images of the nucleus
surface with several filters in the visible, near-UV, and near-
infrared wavelength range (250–990 nm). This instrument o
ffers
a unique opportunity to study the geomorphology of a comet nu-
cleus in detail and with unprecedented spatial resolution (up to
the decimeter scale).
Article published by EDP Sciences
A35, page 1 of
13