Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions (2006) 7069.pdf

OVERVIEW OF THE MISSION. P. H. Smith1, 1Lunar and Planetary Lab, University of Arizona, Tucson, AZ 85721, [email protected].

Introduction: The Phoenix lander is ples of this biological paydirt and test for the next mission to study the surface of signatures related to biology. Mars in situ. By studying the active water Baseline Mission: After the initial as- cycles in the region, it complements sessment of the landing site by the science the Mars Exploration Rovers that look at team, the primary science phase of the the ancient history of Mars contained in mission begins with the collection of sur- the solid rocks. Lacking mobility, Phoenix face samples. Two major science instru- explores the subsurface to the north of the ments receive and analyze the samples. lander, studying the mineralogy and The first is the thermal evolved gas ana- chemistry of the soils and ice. lyzer (TEGA). A sample is delivered to a Scientific Objectives, Phoenix Follows hopper that feeds a small amount of soil the Water: The Phoenix mission targets into a tiny oven, which is sealed and the northern plains between 65 and 72 N. heated slowly to temperatures approaching High-resolution images from the Mars Or- 1000 C. The heater power profile neces- biter Camera on the Mars Global Surveyor sary to maintain a constant temperature spacecraft show a “basketball-like” texture gradient contains peaks and valleys that on the surface with low hummocks spaced indicate phase transitions. For instance, 10’s of meters apart; polygonal terrain, or ice will show a feature at its melting point patterned ground, is also common. These of 0 C and jarosite has strong endoenthal- geologic features may indicate the expan- pic transitions at 670 and 950K [4]. sion and contraction of the permafrost [1]. Gases driven from the sample are com- Science goal #1: Study the history of bined with a carrier gas and piped to a water in all its phases. The circumpolar mass spectrometer. The spectra of the plains are active and hold clues to the cycle gases change as a function of release tem- of water transport on Mars. Orbiter meas- perature. Isotope ratios for H, O, C, and N urements show large seasonal variations in as well as heavier gases like Ar and Xe the atmospheric humidity and CO2 frost provide scientific clues to the origin of the blanketing the winter surface. volatiles. Quantifying the volatile inventory The second instrument provides a mi- locked into the arctic soils and the water croscopic, electro-chemical, and conduc- chemistry of wet soils, even at one loca- tivity assessment (MECA) of the soils. tion, is a giant step toward modeling the Microscopic examination of tiny grains weather processes and climate history of (less than 200 microns diameter) gives Mars [2]. clues to the emplacement process: aeolian, Liquid water changes the soil chemistry lacustrine, or fluvial. A probe on the RA in characteristic ways. Obliquity wander scoop measures the electrical and thermal and precession are known to strongly in- conductivity of the soil. fluence the climate on time scales of The MECA wet chemistry 50,000 or more. Does the water ice accepts small samples into a warm beaker, melt and wet the overlying soil on cycles and water is added to the soil while stir- commensurate with orbital dynamics? ring. Special chemical sensors return data Science goal #2: Search for evidence of concerning the water chemistry including: a habitable zone. Microbial colonies can the salt content and its composition, the survive in a dormant state for extremely acidity, and the trace mineral concentra- long periods of time. Recent work [3] tion. shows that as water ice melts onto soil References: [1] Boynton, W.V. et al. crystals at temperatures as cold as –20 C (2002) Science 297, 81. [2] Smith, M. D. microbes are activated and are able to (2002) JGR 107, 5115. [3] Jakosky, B. M. search for food. As temperatures increase, (2003) Astrobiology 3, 343-350. [4] Ming, growth and reproduction begin. Instru- D.W., et al. (1996) LPSC XXVII, 883. ments on the Phoenix lander receive sam-