Martian Meteorology: Insights from the Phoenix Mission to the Martian Arctic

1. Martian Meteorology: Insights from the Phoenix Mission to the Martian Arctic • John E. Moores • April 15, 2009

2. Talk Roadmap • Mars Primer, Phoenix Mission Background • The Surface Stereo Imager (SSI) Data • Supra-Horizon Movies • Zenith Movies • Wind Telltale Mirror • Winds and Blowing Dust • Clouds and Water Ice • Trends and Conclusions

3. Why do we care? • Understanding the behaviour of wind, water and dust at the landing site • Why we see what we see locally • Compliment to LIDAR observations • Inputs to Modelling Efforts • Direct observation of atmospheric parameters helps to refine the big picture of past and present climate on Mars • Observations may be applicable to the terrestrial stratosphere • Pure interest • Animations of cloud help us to understand extraterrestrial weather from the human scale • Must not let terrestrial analogs overcome the data

4. Mars Primer • 4th planet from the sun • Smaller than Earth • Atmospheric pressure is 6 mBar (600hPa) • Main constituents are CO2 (95%) N2 (2.7%) and Ar (1.6%) • Up to 100 pµm of water vapor • Seasonal cycle is more extreme than the Earth due to • high orbital eccentricity (9%) • Similar axial tilt (25.4°) • The atmosphere condenses seasonably at the winter pole • Most water is contained in two polar caps, though much more may be buried in a deep cryosphere • The surface is blanketed by superfine dust (1.6 micron radius) which gives the planet and the sky its colour

5. The Phoenix Mission • First mission to the Martian Arctic! • Hundreds of Scientists, Engineers and students came together in Tucson, AZ over the summer of 2008 to run the mission • Some were present to study data, others to resolve hardware issues, but many had specific day to day operational roles • Lived on “Mars Time” for almost three months • Martian day is 24hours and 39minutes • Each and every sol produced debate about where to focus the next sol's resources • Investigations had to fit into tight constraints of power, data volume, temperature and workload • Not every desire could be accommodated

6. Launch to Landing • Launched in July of 2007 • 9 month interplanetary cruise • “7 minutes of terror” • Landed on May 25th, 2008 • late northern hemisphere spring (LS=76.74°) • Measurements were taken for 151 Sols (Martian days) • Single Lander at 68° N, 125° W • Equivalent to the Mackenzie River Delta on Earth

7. The Spacecraft MET mast (Temp/Wind) LIDAR CDR  50 Days ATLO  196 Days Ship  596 Days Launch  675 Days EDL  971 Days Surface Stereo Imager MECA: microscopy, electro- chemistry, conductivity TEGA: Thermal and Evolved Gas Analyzer RA Camera Robotic Arm Ice tool, scraper blades Barry Goldstein – Project Manager Glenn Knosp – Project Business Manager Thermal and Electrical conductivity probe

8. Major Mission Firsts • Physical Chemistry/Geology • Trenched the regolith down to sublimating ice and icy soil • Chemistry • Detection of a highly oxidizing compound, a perchlorate • Detection of carbonates without significant sulfates • Atmosphere • First Mars operation of an Atmospheric LIDAR • Detection of virga and falling snow

9. The Surface Stereo Imager and the Atmospheric Datasets • Making movies on Mars

10. Surface Stereo Imager • Co-I: Mark Lemmon, built at the University of Arizona • Based on the Imager for Mars Pathfinder • Camera head sits on 84cm extendable mast • Eyes set 15cm apart • FOV: 13.8 degrees • “Cross-eyed” • Two 1024x1024 MER flight spare CCDs • Excellent S/N at Martian Temperatures (<1DN/100ms) • 12 filters for each eye from violet to NIR

11. Atmospheric Datasets • Zenith Movies • SSI Camera pointed nearly vertically, 10 frame captures • Differential Frames to bring out contrast and movement in the atmosphere • Many bispectral datasets • Captures the direction of winds aloft • Captures spectral data to differentiate between ice and dust in the atmosphere • Supra-Horizon Movies • Identical to Zenith Movies, except pointed just above the horizon • Longest path length through the atmosphere • Good for determining morphologies • Can detect atmospheric layering and wind shear • Also captures spectral data for particle differentiation • Telltale Mirror Analysis • 7441 images taken over the course of the mission

12. LIDAR and Winds Aloft • Zenith movies can directly measure the direction of features moving aloft • LIDAR input is required to determine the height of features • Using the height of greatest backscatter • Agrees well with the pixels around the zenith • Still leaves a great deal of error • Precise heights may not be known (ranges only) • SSI is limited in the range of speeds that are calculable • Selection Biases for overlaps

13. Blue to Red Ratios • Martian Atmosphere is coloured red by the presence of dust • Well understood particle size (1.6µm radius) from Viking, MPF, MER • Larger particles, such as water ice, will scatter more isotropically • Flatter spectral profile • Higher signal in the blue compared to dust • By dividing what we see at two spectral points by what we expect can derive a blue to red ratio • However, there is a fair bit of spectral variation across the sky • Must be compensated for using a radiative transfer code

14. Results for Blowing Dust • Insights from Zenith Movies • and Telltale Mirror Analysis

15. Dust in the Background • Dust is distributed relatively evenly in the lower atmosphere • Features can be formed by density variations at different altitudes • Gives rise to “billowy” features • Dust is a constant feature of the martian atmosphere and gives the sky (and the surface) its red colour Optical depth trend over the course of the mission. Courtesy of Mark Lemmon

16. Zenith movies of Dust • Some interesting zenith movies show the nature of the blowing dust Sol 008 Sol 009 Sol 054

17. Wind Directions • The direction of the winds aloft and at the surface appear to be correlated

18. Wind Speeds • Even with LIDAR difficult to get wind speed aloft • Tried correlating the wind speed with • Time of Day • Sol of Mission • Altitude • Altitude only relationship showing a reasonable correlation • Not unexpected • Saturated region highlighted • 2 populations, dust and cloud

19. Telltale Mirror • Diurnal Trend in Dust loading is also seen in the fractional coverage of the telltale mirror • Best explanation is the turning wind cleaning the mirror daily and re-depositing fines • Irradiation effects should be seen at 12:00 or 15:00 • Mirror accumulates dust in wind shadows

20. Closer look at the patterns • Sol 029 “hecto-telltale” 100 frames captured near the turn-around time show increased variability after 13:00 LTST • Mission-long trends with the diurnal effect removed show little variability • Thus the Diurnal trend Dominates • More consistent with wind scour then quiescent settling

21. Results for Water Ice Cloud • Insights from Zenith and Supra-Horizon Movies

22. Water Ice in the Martian Atmosphere • Phoenix was first to observe martian snowfall, but putative water ice clouds have been seen before • Diurnal cloud patterns on the larger volcanos • Formation of a polar hood • Cloud inferred from TIR and direct sensing with MOLA • The water ice clouds are largely absent for the first 79 sols of the mission • Supra-Horizon movies show some possible very thin clouds as early as the 60s Cirrus Clouds photographed by Opportunity rover at Endurance Crater

23. Supra Horizon Cloud Morphologies • Higher level regular clouds are common features in the supra-horizon movies Sol 78

24. Supra Horizon Cloud Morphologies • Starting on sol 94, optically thick, fluffier, more cumulus-like clouds are evident • These clouds have pronounced blue to red ratios Sol 94

25. Supra Horizon Cloud Morphologies • They have also been seen to form and sublimate from locally available water vapour Sol 112

26. Supra Horizon Cloud Morphologies • Morphologically distinct, streaky clouds are seen at night during the middle of the mission Sol 84

27. Supra Horizon Cloud Morphologies • The cloud-forms get increasingly complex, optically thick and appear to move faster across the sky as the mission progresses • But some days remain relatively dry Sol 132 Sol 148

28. Zenith movies of Water Ice • Zenith movies also show water ice cloud • Non-ideal viewing geometry • Can still get blue to red ratios out of the data Sol 141 Sol 101

29. Seasonal Trend • Quantitative: Blue to Red Ratios confirm more water ice later in the mission • Time-Varying Component has bigger increase then mean frame • Variability: Late in the mission there continue to be days when the BRR is low • Also the dust remains a significant atmospheric component • BRRs from Supra-Horizon Movies plot lower then for Zenith Movies

30. Diurnal Trend • A strong diurnal trend is also visible • A peak in cloudiness is observed around mid-day • Variable cloudiness in the early morning? (Selection bias effect) • The formation of cloud is inhibited in the early afternoon and evening • Sublimation? • Out of Water Vapor? • Boundary Layer decoupling? (formation of an intermediate stable layer) • The trend is also seen in the last 20 sols of the mission • Some days have strong cloud at midday • On some days cloud is absent

31. Extension to the first 50 sols • The Signal to Background ratio corresponds to the BRR of the Time Variable Component • Can use the Signal to Background ratio to get an idea of cloudiness early in the mission • A possible minimum is observed near sol 50 with water ice ramping up starting near sol 80

32. Virga • LIDAR has seen evidence of fall streaks at night, characteristic of Virga • The SSI has also observed this behaviour on several occasions during the day in Supra-Horizon movies Sol 126 Sol 80

33. Observed Wind Shear • Recall: Winds aloft match well with winds at the surface • Correspondence is good early in the mission when dusty conditions dominate • Later in the mission many features pass by too rapidly to observe • However, several supra-horizon movies show two layers moving at different rates and in different directions • Could locally-driven winds be interacting with larger-scale flows? Sol 096

34. Trends and Conclusions

35. Summary of Observations • Observed a diurnally rotating wind aloft matching with the wind telltale • Low-fidelity data for wind speed aloft shows no evidence for higher wind speeds aloft • Dustiness of the wind telltale mirror shows a diurnal pattern consistent with wind deposition and scour instead of settling • Variation in morphologies of cloud indicate an active hydrological cycle • Clouds have high BRRs, likely made of relatively large particles • BRRs have a diurnal trend peaking around 10:00 to 12:00 LTST • BRRs and Time-Varying Signal Strength are correlated and have a minimum near sol 50 • BRRs increase from sol 50 to sol 150 but show significant day to day variability • Virga and differential motion of cloud layers have been observed

36. Significance of Trends • Strongly expressed diurnal cycle in wind, dust movement and atmospheric water ice • Suggests the water and temperature cycles are dominated by local effects instead of transport • Consistent with water and much of the dust being confined to the PBL (LIDAR) and consistent surface air temperatures • Strongly expressed seasonal increase in atmospheric water ice • Progressively colder atmospheric temperatures later in the summer allow for more expression of cloud even with declining water vapor

37. Exceptions to the Rule • Some significant variability exists in the seasonal dataset • Very “dry” days can be seen late in the summer when cloud is increasing • Wind shear and multiple movements at different heights appear to be present occasionally • Argues for not insignificant regional transport of water ice/vapor

38. Thank-you!