1. Searching for New Surface Features on Mars
Sean Marshall
Adviser: Dr. Phil Christensen
School of Earth and Space Exploration

2. Background
Nighttime infrared (IR) images from the Thermal Emission Imaging System instrument (THEMIS) on the 2001 Mars Odyssey orbiter
Nighttime images have more contrast (after processing), and they tell you more about the area’s physical properties
Nighttime IR, from THEMIS image I
Daytime IR, from THEMIS image I

3. Background About 50,000 nighttime IR THEMIS images
Need images that were taken at the same location (but at different times)
Spatial sampling of 100 m per pixel
My expectation: just a few new features
I expected 3 pixels to be the threshold of visibility

4. Procedure Get a list of nighttime IR images:
Both of decent quality
With at least 50% overlap
Within 5° LS of each other, to avoid seasonal differences
LS is solar longitude, a way of keeping track of the time of year (and the season) on Mars
0° is the beginning of northern spring, 90° is the beginning of northern summer, and so on.
There are about 180 pairs, with more coming.
Look up images in the online THEMIS database
Open them in GIMP
Align the top of the overlapping section

5. Procedure Flicker back and forth between images
Inspired by Clyde Tombaugh
Image from The Planetary Society
Record any important differences
Scroll down to the next section
Repeat with the next section, then with the next images

6. Complications Noisy images Different brightness between images
Unprojected images
Could project, but that is slow
In general, sophisticated corrections to these problems are possible but slow
THEMIS nighttime IR images I (left) and I ; image credit NASA/JPL/ASU

7. Complications Upside-down images
The “footprints” (100 meters per pixel) in different THEMIS images don’t generally align
Possible false negatives?
From MRO HiRISE image PSP_006917_1595; image credit NASA/JPL/UofA; scaled to 2.8 m/pixel

8. Results
I carefully analyzed 66 image pairs, which represent 0.56% of the Martian surface
On average, images in a pair were taken 43 months apart
No features that were clearly new
Dozens of “noise effects”, where something looked like a new feature, but on closer analysis turned out to be a result of noise
It can be hard to tell the difference…

9. Results 67.113 E, 13.197 N: Noise effect? Or new crater?
In Syrtis Major
About 3 pixels across (which is about 300 m)
I (April 2002)
I (January 2006)
5-image animation

10. Conclusions
A feature would have to be at least 5 pixels wide/long to clearly not be a noise effect
Image sampling rate averages to 0.16% of the Martian surface per (Earth) year
So, suppose there was one new crater in the surveyed area that I missed, and assume that impacts occur randomly at a fairly constant average rate…
That would work out to about 600 new craters (500 m diameter or more) on the entire surface of Mars per (Earth) year
But that is an upper limit
Actual rate lower; quite possibly much lower

11. Acknowledgments Phil Christensen Chris Edwards, Sylvain Piqueux
Advising
Chris Edwards, Sylvain Piqueux
Consulting
Jonathon Hill
Instructing
Dale Noss
Script generating
Everyone at Space Grant!

12. Image sources
Arizona Space Grant Consortium logos from
ASU logo from
Slides 1, 2, 3: ASU THEMIS,
Slide 4: The Planetary Society,
Slides 5, 7, 8: ASU THEMIS, image credit NASA/JPL/ASU,
Slide 6: University of Arizona HiRISE,