page_title: Extraterrestrial liquid water
section_title: Spectroscopy
hierarchical_section_title: Extraterrestrial liquid water / Indicators, methods of detection and confirmation / Spectroscopy
caption_attribution_description: English: Color-Coded Clues to Composition Superimposed on Martian Seasonal-Flow Image http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA17934 Date added: 2014-02-10 Spacecraft: Mars Reconnaissance Orbiter (MRO) Instruments: High Resolution Imaging Science Experiment (HiRISE) This image combines a photograph of seasonal dark flows on a Martian slope with a grid of colors based on data collected by a mineral-mapping spectrometer observing the same area. The area is at Palikir Crater in the southern hemisphere of Mars. The photograph is from the High Resolution Imaging Science Experiment (HiRISE) camera. The composition information, as an image with pixels appearing as a grid of squares, is from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Both of these instruments are on NASA's Mar Reconnaissance Orbiter. The view is oriented with north toward the bottom. The scale bar at lower left indicates 90 meters (295 feet). These dark, warm-season flows are called "recurring slope lineae" or RSL. Researchers are using observations from Mars orbiters to study the possibility that RSL result from action of salty liquid water. This image was included in a paper by Lujendra Ojha of Georgia Institute of Technology, Atlanta, and co-authors in Geophysical Research Letters. The purple and pink colors of the CRISM image represent spectra with absorption of light at wavelengths of 920 nanometers and 530 nanometers. The strength of these absorption bands at this site varies seasonally -- weaker when the RSL are inactive and stronger when the RSL are active. Absorption at 530 nanometers can indicate a concentration of ferric iron, so this could be a clue that the fluctuations observed in the absorption bands of iron minerals may be related to the RSL activity. Other image products from the same Nov. 2, 2007, HiRISE observation are available at http://www.uahirise.org/PSP_005943_1380. The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., operates CRISM in coordination with an international team of researchers from universities, government and the private sector. The University of Arizona Lunar and Planetary Laboratory, Tucson, operates HiRISE, which was built by Ball Aerospace &amp; Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. For more about NASA's Mars exploration missions, see http://www.nasa.gov/mars and http://mars.jpl.nasa.gov.
context_page_description: Extraterrestrial liquid water is water in its liquid state that naturally occurs outside Earth. It is a subject of wide interest because it is recognized as one of the key prerequisites for life as we know it and thus surmised as essential for extraterrestrial life.
  With oceanic water covering 71% of its surface, Earth is the only planet known to have stable bodies of liquid water on its surface, and liquid water is essential to all known life forms on Earth. The presence of water on the surface of Earth is a product of its atmospheric pressure and a stable orbit in the Sun's circumstellar habitable zone, though the origin of Earth's water remains unknown.
  The main methods currently used for confirmation are absorption spectroscopy and geochemistry. These techniques have proven effective for atmospheric water vapour and ice. However, using current methods of astronomical spectroscopy it is substantially more difficult to detect liquid water on terrestrial planets, especially in the case of subsurface water.
context_section_description: Liquid water has a distinct absorption spectroscopy signature compared to other states of water due to the state of its hydrogen bonds. Despite the confirmation of extraterrestrial water vapor and ice, however, the spectral signature of liquid water is yet to be confirmed outside of Earth. The signatures of surface water on terrestrial planets may be undetectable through thick atmospheres across the vast distances of space using current technology.
  Seasonal flows on warm Martian slopes, though strongly suggestive of briny liquid water, have yet to indicate this in spectroscopic analysis.
  Water vapor has been confirmed in numerous objects via spectroscopy, though it does not by itself confirm the presence of liquid water. However, when combined with other observations, the possibility might be inferred. For example, the density of GJ 1214 b would suggest that a large fraction of its mass is water and follow-up detection by the Hubble telescope of the presence of water vapor strongly suggests that exotic materials like 'hot ice' or 'superfluid water' may be present.
caption: Liquid water has not been detected in spectroscopic analysis of suspected seasonal Martian flows.
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