Maps of the O 2 ( 1 Δ ) Emission During the Mars Pre - Aphelion Season

Introduction . Ozone and water are key species for understanding the stability and evolution of Mars’ atmosphere; they are closely linked (along with CO, H, OH, and O) through photochemistry [1-6]. Measurements of ozone on Mars have been made by both ground based telescopes [7-13] and spacecraft [14-17]. Some of these measured the total column density of ozone [8, 11, 14] while others measured ozone above 20 km [9,10, 13]. These latter measurements are performed by measuring the O2(Δ) emission rates. Together, these results give insights into the vertical column profile of ozone on Mars. Photolysis of ozone by UV light from the sun produces O(P) and O2(Δ) with 90% efficiency [18]. The O2(Δ) state has a relatively long radiative lifetime (~ 1 hour) [19]. The O2(Δ) state can also be quenched by collisions with CO2. At altitudes less than 20 km, quenching dominates so the O2(Δ) emission near 1.27 μm traces the presence of ozone in the middle atmosphere of Mars. Since 1997, we have been measuring the O2(Δ) emission using CSHELL at the NASAIRTF [10,20]. We have found large variations of the emission rate throughout the Mars year [21]. We report observations that were made between Ls = 333 and Ls = 50 since 2004 (Table I). At Ls = 333, no emissions were detected; for Ls = 357 and Ls = 20, emissions were strong in the polar regions. For Ls = 50, emissions were strong at all measured latitudes. These results will be compared to previously reported results for Ls = 67 [10].