#weekendusers Could icy moons host habitable environments?


Large icy worlds have a deep hydrosphere composed of high pressure ices and a liquid ocean that could host extraterrestrial life. Scientists from the NASA Astrobiology Institute (US), the University of Bayreuth and DESY (both in Germany) are at the ESRF this weekend to find out more about them.

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Galileo Galilei already discovered the first icy moons four centuries ago, but they are still full of enigmas, and, to many of us, they could be more related to a Jules Verne novel than to real life.

There are many forms of ices in the universe depending on pressure and temperature conditions. The high-pressure forms of ice VI and VII are believed to be present in icy moons like Europa, Ganymede, or Titan and newly discovered ocean exoplanets. Contrarily to every day life water ice, these high-pressure ices can contain amounts of salt in their structure. This could be one of the keys to solve a question that puzzles scientists: whether there could be habitable environment in the deep oceans of our solar system and beyond. 


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Baptiste Journaux (left) in the lab and with Ines Collings on the new ID15B. Credits: C. Argoud.

The potential habitability of oceans in icy moons and exoplanets requires nutrients and chemical energy from exchanges with the silicate interior. As high-pressure ices are believed to be present between the ocean and the silicate core, this might only be achieved if salt-bearing ices can transport solutes upwards. Several observations of icy moons from space probes and ground or space telescopes, support the current presence of salts in their ocean, which suggests that the chemical exchange with the silicate core is indeed happening.

in-situ single crystal diffraction experiments at high pressure is the only way to obtain the structure of salty ice VI and VII at pressures and temperatures relevant for icy moons”, explains Baptiste Journaux, main researcher in the experiment working for the NASA Astrobiology Institute at the Earth and Space Sciences department of the University of Washington, in Seattle (US). 


All Earth water budget (oceans, rivers, lake, ice caps, groundwater) compared to Europa and titan estimated water budget. Credits: B. Journaux, modified from Kevin Hand (JPL/Caltech).

Journaux will spend this weekend at the ESRF´s ID15B, the new high-pressure diffraction beamline, with colleagues from the University of Bayreuth and DESY. They will try to track down where the salt ions go when the ice is submitted to 1-5 GPa, the pressure typical in icy moons. On ID15B they benefit from a small beam which allows different areas of the crystal that could have various amounts of salt to be probed. “The new set-up at ID15B is extremely stable with a very clean X-ray beam.  The fast acquisition times, combined with the user support for both technical and analytical aspects, makes ID15B one of the best place in the world to conduct high-pressure single-crystal diffraction experiments” says Sylvain Petitgirard, working at the Bayrisches Geoinstitut.

This experiment is a proof that in parallel to upcoming space missions from NASA (Europa clipper) and the European Space Agency (JUICE) to explore the diversity of our solar system ice-rich bodies, scientists also need to study the tiniest samples with nanometric precision, to fully unveil the secrets of our universe and its potential habitability.

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The team on the beamline. Credits: C. Argoud. 



Top image: The Ganymede moon, which contains 32.4% of water. Credits: NASA.