We studied small, uniquely-shaped craters found on the surface of lineated terrain in the Ismenius Lacus region of Mars. By utilizing MOC and THEMIS satellite images, we located terrain including lineations (viscous flow features), smoothing of topography, and morphologic features such as polygons and gullies, which appear to be strong evidence of preexisting ice deposits

Gillespie, A.

McConnell, B. S.

Newsom, H. E.

Wilt, G. L.

NASA Technical Reports Server

INVERTED MARTIAN CRATERS IN LINEATED GLACIAL VALLEYS, ISMENIUS LACUS REGION, 
MARS.  B. S. McConnell1, G. L. Wilt2, A. Gillespie3 , H. E. Newsom4, 1Highland High School, Albuquerque, NM 
87108 bmcconne@unm.edu 2Shikellamy Senior High School, Sunbury, PA 17801 grierwilt@gmail.com 3UT 
aimeeg@unm.edu 4Univ. of New Mexico, Institute of Meteoritics, Dept. of Earth & Planetary Sciences, Albuquer-
que, NM 87131 newsom@unm.edu  
 
 
Objective We studied small, uniquely-shaped cra-
ters found on the surface of lineated terrain in the Is-
menius Lacus region of Mars [1].  By utilizing MOC 
and THEMIS satellite images, we located terrain in-
cluding lineations (viscous flow features), smoothing 
of topography, and morphologic features such as poly-
gons and gullies, which appear to be strong evidence 
of preexisting ice deposits.   
Figure 1. Index map of MOC and THEMIS images 
examined in this study. 
 
Background Because of Mars’s dynamic obliq-
uity, a consistent tilt pattern is evident in which it cy-
cles through every several million years. According to 
Mustard et al. [1], if the obliquity exceeds 30o, the ice 
at the north and south poles become very unstable and 
relocates by sublimation to the mid to high latitudes. 
This is known as a Martian Ice Age. The most recent 
Ice Age occurred about 10 Myrs ago when the obliq-
uity was at a steep 35o and the primary water ice was 
located in the 30-60o latitude bands.  
Hypothesis A specific region, Ismenius Lacus with 
the latitude range of 30-65o, was selected because it 
has a vast array of heavily cratered canyons and gullies 
and evidence of unusual features suggesting the pres-
ence of preexisting ice in the region [2].  The compari-
son of craters in both lineated and non-lineated terrain 
led us to the discovery of very unusually structured 
craters located in the lineated terrain. The craters lo-
cated in these areas often consisted of multiple rim 
rings and plateau-like centers [2].  
We developed and tested models for the origin of 
these unusual circular features.  Based on our observa-
tions, we suggest that meteors impacted the Martian 
surface sometime in the last ice age and the meteors 
penetrated several meters of dust and ice.  After their 
formation, they gradually filled back in with new lay-
ers of sediment and debris. As the tilt changed back to 
a less dramatic and current obliquity of roughly 22-
26o, the ice sublimated. As the icy layers sublimated, 
the surface collapsed and left the uniquely structured 
inverted morphology [e.g. 3,4]. 
 
Methods Images were utilized to observe crater 
morphology in the Ismenius Lacus region. High reso-
lution Images were examined from the Mars Global 
Surveyor (MGS) Mars Orbiter Camera (MOC) on the 
Malin Space Science Systems (MSSS) website, and 
from ASU’s Thermal Emissions Imaging System 
(THEMIS) website. 
 
Figure 2 Example 
comparing a fresh 
bowl-shaped crater 
(above) and an 
older inverted cra-
ter (below). 
 
 
 
 
 
We viewed every MOC image in the southern re-
gion of Ismenius Lacus by this process. After the high-
resolution MOC images were inspected, the photo-
graph was copied and pasted into Adobe Photoshop. In 
Photoshop, we searched the pictures for craters and 
then cropped each crater, with respect to the image 
size. The image size was vital for scaling the craters. 
Each high-resolution photo had different meter/pixel 
resolution, so an MS Excel record had to be kept for 
each image, and a template of 100x100 pixels was 
used per image. This process was done for and ap-
proximate total of 100 craters. After the craters were 
cropped and recorded, they were printed out to be 
thoroughly examined and analyzed. 
Based on our sample, the inverted craters range in size 
from 150-400 meters in diameter.  Resolution of the 
images limited the recognition of the smallest inverted 
craters.  
Observations After careful and complete examina-
tion of the high-resolution images, we observed that 
Role of Volatiles and Atmospheres on Martian Impact Craters 2005 3021.pdf
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there were relatively few craters in the lineated terrain 
and even fewer fresh bowl-shaped craters when com-
pared to the surrounding area.  The fact that there are 
so few craters suggests that the surface is young and 
reflects a fairly recent chain of events, such as an Ice 
Age, which caused this phenomenon. 
Experiments In testing our hypothesis, we used 
multiple methods. 
 
 
 
 
 
 
Figure 3.  Numerical simulation of the three major 
sequences involved in inverted crater formation.  The 
first figure shows a fresh bowl-shaped crater.  The 
blue layers represent the sub-surface ice deposits.  This 
simulation represents a relatively low fraction of ice in 
the sub-surface.  The second image simulates the proc-
ess in which the crater is filled in with debris.  The 
third figure is the concluding phase, after the sub-
surface ice sublimates.  
 
Excel Model The Excel Model proved to be very 
useful in simulating layering and sublimation effects. 
With Excel, a series of rows and columns were used to 
simulate the surface and sub surface dust and ice layers 
of Mars (e.g. figure 3). Once the surface was estab-
lished, a symmetrical crater was formed by deleting 
several layers. Each individual column was summed 
up in a “Totals” row and the totals were then graphed. 
The graph, when finished, looked very similar to a 
typical bowl-shaped crater. To simulate dust storms 
and other weathering factors, new rows of dust and ice 
were formed inside the crater. To simulate the depart-
ing ice age, the ice layers were deleted and the graphs 
symbolized the shape and structure of the concluding 
craters. 
Physical Model The physical experiments were ex-
tremely useful in this project because our simulation 
was almost identical to the proposed inverted Martian 
crater process. In this experiment, the beginning phase 
consisted of three different materials; tin catering trays 
(to hold the surface that harbored the crater), dry ice 
(to simulate the sublimation of icy layers), and sand (to 
represent the Martian surface material). The tin was 
filled with layers of sand and ice to represent an ice 
age surface. After the surface was established, a crater 
was constructed by scooping out several layers in a 
confined area. Following the fabrication of the crater, 
several additional layers of sand and ice were applied.  
After this was complete, the tins were set in the sun so 
the ice would sublimate. Several hours later, the fin-
ished product looked identical the formations observed 
on the Martian surface in the high-resolution images. 
Conclusion We have come to the conclusion that 
the unique features of the selected craters are due to a 
recent Martian Ice Age. These craters originally 
formed on an ice-rich surface and were subsequently 
covered by sediments and additional ice.  Due to the 
alteration in Mars’ obliquity, the ice sublimated back 
to the poles and consequently, the surface collapsed 
causing strange features such as multiple rim rings and 
central plateaus. Through numerical and physical ex-
perimentation, we have shown that the proposed in-
verted Martian crater process is plausible. 
References 
[1] Mustard J.F. Head J.W. Kreslavsky M.A Mil-
liken R.E. Marchant D.R.(2003) Geological Observa-
tions, Climate Modeling, and Ice Stability: Evidence 
for a recent Martian Ice Age. Third Mars Polar Sci-
ence Conference. [2] Kargel J.S.* Molina B. Tanaka 
K.L. (2003) Martian Polar Ice Sheets and Mid-
Latitude Debris-rich Glaciers, and Terrestrial Analogs, 
Gullies, and Long-Term Glacial History; Head J.W. 
Shean D.E (2003) Tropical Mountain Glaciers on 
Mars: Evidence for Amazonian Climate Change. [3] 
François Costard Audouin Dollfus 
(1987)Thermokarstic Evolution of Impact Craters on 
Mars. Lunar and Planetary Science XVIII, 199. [4] 
Rene A. De Hon (1987)Ring Furrows: Inversion of 
Topography in Martian Highland Terrains 
Acknowledgments 
This project was supported by NASA SHARP pro-
gram (G.L. Wilt, A. Gillespie), and NASA PG&G and 
broker facilitator programs (B. McConnell, H. 
Newsom). 
 
Role of Volatiles and Atmospheres on Martian Impact Craters 2005 3021.pdf


Inverted Martian Craters in Lineated Glacial Valleys, Ismenius Lacus Region, Mars

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