• NASA Missions Provide New Insights into 'Ocean Worlds' in Our Solar Sys

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    NASA Missions Provide New Insights into 'Ocean Worlds' in Our Solar System
    Jet Propulsion Laboratory
    April 13, 2017

    Two veteran NASA missions are providing new details about icy, ocean-bearing moons of Jupiter and Saturn, further heightening the scientific interest
    of these and other "ocean worlds" in our solar system and beyond. The
    findings are presented in papers published Thursday by researchers with
    NASA's Cassini mission to Saturn and Hubble Space Telescope.

    In the papers, Cassini scientists announce that a form of chemical energy
    that life can feed on appears to exist on Saturn's moon Enceladus, and
    Hubble researchers report additional evidence of plumes erupting from Jupiter's moon Europa.

    "This is the closest we've come, so far, to identifying a place with some
    of the ingredients needed for a habitable environment," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at Headquarters in Washington. "These results demonstrate the interconnected nature of
    NASA's science missions that are getting us closer to answering whether
    we are indeed alone or not."

    rC| DOWNLOAD VIDEO Ingredients for Life at Enceladus

    The paper from researchers with the Cassini mission, published in the
    journal Science, indicates hydrogen gas, which could potentially provide
    a chemical energy source for life, is pouring into the subsurface ocean
    of Enceladus from hydrothermal activity on the seafloor.

    The presence of ample hydrogen in the moon's ocean means that microbes
    - if any exist there - could use it to obtain energy by combining the
    hydrogen with carbon dioxide dissolved in the water. This chemical reaction, known as "methanogenesis" because it produces methane as a byproduct,
    is at the root of the tree of life on Earth, and could even have been
    critical to the origin of life on our planet.

    Life as we know it requires three primary ingredients: liquid water; a
    source of energy for metabolism; and the right chemical ingredients, primarily carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. With this finding, Cassini has shown that Enceladus - a small, icy moon a billion miles farther from the sun than Earth - has nearly all of these ingredients for habitability.

    Cassini has not yet shown phosphorus and sulfur are present in the ocean,
    but scientists suspect them to be, since the rocky core of Enceladus is thought to be chemically similar to meteorites that contain the two elements.

    "Confirmation that the chemical energy for life exists within the ocean
    of a small moon of Saturn is an important milestone in our search for habitable worlds beyond Earth," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

    Graphic illustrating how scientists think water interacts with rock at
    the bottom of the ocean This graphic illustrates how Cassini scientists
    think water interacts with rock at the bottom of the ocean of Saturn's
    icy moon Enceladus, producing hydrogen gas. Credit: NASA/JPL-Caltech/Southwest Research Institute
    rC| Larger image

    The Cassini spacecraft detected the hydrogen in the plume of gas and icy material spraying from Enceladus during its last, and deepest, dive through the plume on Oct. 28, 2015. Cassini also sampled the plume's composition during flybys earlier in the mission. From these observations scientists
    have determined that nearly 98 percent of the gas in the plume is water,
    about 1 percent is hydrogen and the rest is a mixture of other molecules including carbon dioxide, methane and ammonia.

    The measurement was made using Cassini's Ion and Neutral Mass Spectrometer (INMS) instrument, which sniffs gases to determine their composition.
    INMS was designed to sample the upper atmosphere of Saturn's moon Titan.
    After Cassini's surprising discovery of a towering plume of icy spray
    in 2005, emanating from hot cracks near the south pole, scientists turned
    its detectors toward the small moon.

    Cassini wasn't designed to detect signs of life in the Enceladus plume
    - indeed, scientists didn't know the plume existed until after the spacecraft arrived at Saturn.

    "Although we can't detect life, we've found that there's a food source
    there for it. It would be like a candy store for microbes," said Hunter
    Waite, lead author of the Cassini study.

    The new findings are an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean. Previous results, published in March 2015, suggested hot water is interacting with rock beneath the
    sea; the new findings support that conclusion and add that the rock appears
    to be reacting chemically to produce the hydrogen.

    The paper detailing new Hubble Space Telescope findings, published in
    The Astrophysical Journal Letters, reports on observations of Europa from
    2016 in which a probable plume of material was seen erupting from the
    moon's surface at the same location where Hubble saw evidence of a plume
    in 2014. These images bolster evidence that the Europa plumes could be
    a real phenomenon, flaring up intermittently in the same region on the
    moon's surface.

    The newly imaged plume rises about 62 miles (100 kilometers) above Europa's surface, while the one observed in 2014 was estimated to be about 30 miles
    (50 kilometers) high. Both correspond to the location of an unusually
    warm region that contains features that appear to be cracks in the moon's
    icy crust, seen in the late 1990s by NASA's Galileo spacecraft. Researchers speculate that, like Enceladus, this could be evidence of water erupting
    from the moon's interior.

    "The plumes on Enceladus are associated with hotter regions, so after
    Hubble imaged this new plume-like feature on Europa, we looked at that location on the Galileo thermal map. We discovered that Europa's plume candidate is sitting right on the thermal anomaly," said William Sparks
    of the Space Telescope Science Institute in Baltimore. Sparks led the
    Hubble plume studies in both 2014 and 2016.

    The researchers say if the plumes and the warm spot are linked, it could
    mean water being vented from beneath the moon's icy crust is warming the surrounding surface. Another idea is that water ejected by the plume falls onto the surface as a fine mist, changing the structure of the surface
    grains and allowing them to retain heat longer than the surrounding landscape.

    For both the 2014 and 2016 observations, the team used Hubble's Space Telescope Imaging Spectrograph (STIS) to spot the plumes in ultraviolet
    light. As Europa passes in front of Jupiter, any atmospheric features
    around the edge of the moon block some of Jupiter's light, allowing STIS
    to see the features in silhouette. Sparks and his team are continuing
    to use Hubble to monitor Europa for additional examples of plume candidates and hope to determine the frequency with which they appear.

    NASA's future exploration of ocean worlds is enabled by Hubble's monitoring
    of Europa's putative plume activity and Cassini's long-term investigation
    of the Enceladus plume. In particular, both investigations are laying
    the groundwork for NASA's Europa Clipper mission, which is planned for
    launch in the 2020s.

    "If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them," said Jim Green, Director of Planetary Science, at NASA Headquarters.

    Hubble's identification of a site which appears to have persistent, intermittent
    plume activity provides a tempting target for the Europa mission to investigate

    with its powerful suite of science instruments. In addition, some of Sparks' co-authors on the Hubble Europa studies are preparing a powerful ultraviolet camera to fly on Europa Clipper that will make similar measurements to Hubble's, but from thousands of times closer. And several members of the Cassini INMS team are developing an exquisitely sensitive, next-generation version of their instrument for flight on Europa Clipper.

    For more information on ocean worlds in our solar system and beyond, visit:

    https://www.nasa.gov/specials/ocean-worlds

    News Media Contact
    Felicia Chou
    NASA Headquarters, Washington
    202-358-0257
    felicia.chou@nasa.gov

    Preston Dyches
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-7013
    preston.dyches@jpl.nasa.gov

    Donna Weaver / Ray Villard
    Space Telescope Science Institute, Baltimore
    410-338-4493 / 410-338-4514
    dweaver@stsci.edu / villard@stsci.edu

    2017-106

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