Ancient hydrothermal seafloor deposits on Mars

Ancient hydrothermal seafloor deposits in Eridania basin on Mars
Joseph R. Michalksi, Eldar Z. Noe Deobrea, Paul B. Niles, and Javier Cuadros
Summarized by Mike Hils

What data was used? High resolution imaging and spectroscopy data about mineralogy and geology

Methods: Used data from instruments on the Mars Reconnaissance Orbiter, a satellite currently orbiting Mars:

    HiRISE (High Resolution Imaging Science Experiment) was used to define the ancient basin boundaries and to inspect the types of features and rocks located in the Eridania basin. HiRISE is a camera onboard the Mars Reconnaissance Orbiter than can resolve objects to about a foot long on the surface of Mars.

    CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) to study the minerals and rocks found in the Eridania Basin. Materials bounce light off of them in a consistent pattern and energy, and spectrometers can analyze that light and identify the material on Mars’ surface.

Results: The Eridania Basin was probably up to 1.5 km (0.9 mi) deep, and flowed into a canyon named Ma’adim Vallis. Images from HiRISE show that the western half of the basin consists of massive stone that lacks bedding planes and has eroded into buttes and mesas. The basin would have held about as much water the Caspian Sea on Earth currently does. This basin is shaped different than many of the other Martian basins, and it is thought that a covering of ice kept sediment from settling on the bottom. A comparison of the craters in this part of the basin suggest that these rocks are about 3.77 Ga (G = giga, SI prefix for billion, a = annum, Latin for year) old.

Analysis from CRISM found evidence of minerals and rocks associated with deep ocean water on Earth, including iron and magnesium rich clays, serpentinite, carbonates, and chlorides. For example, serpentinite, a metamorphic rock that looks like green marble, forms when basalt reacts with warm, deep sea water. Carbonate minerals are common on Earth in the form of limestone, marble, seashells, and corals. The authors suspect that the carbonate formed due to hydrothermal interactions. Chlorides, such as salt (sodium chloride), form on Earth when water evaporates.

Map of the Martian terrane with colors indicating highs (orange) and lows (blue) of an ancient sea. The data points in the legend are minerals that were identified at each location.

Why is this study important? This study is important in two ways. First, one idea for the origin of life on Earth is that it developed around hydrothermal vents in the ocean. Although ancient rocks have been found suggesting such environments in the past, they have been significantly altered by weathering and metamorphism, and vital information has been lost. Martian sites, which haven’t been altered nearly as much as Terrestrial ones, might be a good proxy for understanding early environments on Earth. Secondly, the identification of such sites on Mars could provide key places to look for signs of life on Mars.

The big picture: Understanding how life began is a huge problem that scientists in many fields are exploring. Life may have evolved on Earth, or it may have arrived here from some other body. The identification of hydrothermal environments on Mars would allow scientists to gain a better understanding of hydrothermal environments on Earth as life was evolving and try to see if life could have started here. This would also allow astrobiologists to look for evidence of extraterrestrial life on Mars.
Two other bodies in our solar system may harbor life around hydrothermal vents. Jupiter’s moon Europa and Saturn’s moon Enceladus are both covered in salty water capped with ice, and both experience tectonic activity due to the gravitational pull from their host planets. In addition, organic molecules (chemicals made mostly of carbon that are often associated with organisms) have been detected in water escaping from Enceladus. If life could have evolved in hydrothermal environments on Earth and Mars, it is likely Europa and Enceladus both host extraterrestrial life now.

Citation: Michalski, J., Dobrea, E., Niles, P., Cuadros, J. 2017. Ancient hydrothermal seafloor deposits in Eridania basin on Mars. Nature Communications, 8:15978. doi: 10.1038/ncomms15978

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