Observations of the north polar water ice annulus on Mars using THEMIS and TES

Planetary and Space Science
By: , and 



The Martian seasonal CO2 ice caps advance and retreat each year. In the spring, as the CO2 cap gradually retreats, it leaves behind an extensive defrosting zone from the solid CO2 cap to the location where all CO2 frost has sublimated. We have been studying this phenomenon in the north polar region using data from the THermal EMission Imaging System (THEMIS), a visible and infra-red (IR) camera on the Mars Odyssey spacecraft, and the Thermal Emission Spectrometer (TES) on Mars Global Surveyor. Recently, we discovered that some THEMIS images of the CO2 defrosting zone contain evidence for a distinct defrosting phenomenon: some areas just south of the CO2 cap edge are too bright in visible wavelengths to be defrosted terrain, but too warm in the IR to be CO2 ice. We hypothesize that we are seeing evidence for a seasonal annulus of water ice (frost) that recedes with the seasonal CO2 cap, as predicted by previous workers. In this paper, we describe our observations with THEMIS and compare them to simultaneous observations by TES and OMEGA. All three instruments find that this phenomenon is distinct from the CO2 cap and most likely composed of water ice. We also find strong evidence that the annulus widens as it recedes. Finally, we show that this annulus can be detected in the raw THEMIS data as it is collected, enabling future long-term onboard monitoring.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Observations of the north polar water ice annulus on Mars using THEMIS and TES
Series title Planetary and Space Science
DOI 10.1016/j.pss.2007.08.008
Volume 56
Issue 2
Year Published 2008
Language English
Publisher Elsevier
Contributing office(s) Astrogeology Science Center
Description 10 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Planetary and Space Science
First page 256
Last page 265
Other Geospatial Mars
Google Analytic Metrics Metrics page
Additional metadata about this publication, not found in other parts of the page is in this table