A familiar substance is hiding in plain sight over the moon of Europe of Jupiter. Using a spectacular analysis, planetary scientists at Caltech and the Jet Propulsion Laboratory, Caltech governing NASA, discovered that the yellow color seen on parts of Europe's surface was actually sodium chloride, a compound known to Earth as table salt, which is the main part of saltwater.
The discovery indicates that the salty subsurface ocean of Europe can chemically resemble the ocean of the Earth more than previously thought, difficult decades of speculation about the composition of the water and making it potentially a lot more interesting for the study. The search was published in Science Advances on June 12.
Flybys from the Voyager and Galileo spacecrafts led scientists to conclude that Europe was covered with a layer of salty liquid water covered with an icy shell. Galileo brought an infrared spectrometer, used by scientists to examine the composition of the surface they are examining. Galileo's spectrometer found ice water and a substance that appears to be magnesium sulfate salts ̵
All have changed the new, higher spectral resolution data from the W. M. Keck Observatory in Maunakea suggesting that scientists do not see magnesium sulfates in Europe. Most of the sulpate words that were previously used actually contained different absorptions that should be seen in higher quality Keck data. However, the spectra of the regions expected to reflect the internal composition is lacking in any properties of sulfur absorptions.
"We thought we could see sodium chlorides, but they are really bad in an infrared spectrum," says Mike Brown, Richard and Barbara Rosenberg Professor of Planetary Astronomy at Caltech and co-author of Science Advances paper.
However, Kevin Hand at JPL irradiated ocean accounts in a laboratory under Europe-such as conditions and found that some new and unique features emerge after lighting, but in the visible portion of the spectrum. He saw that the salts changed the colors to the point that they could recognize the analysis of the visible spectrum. For example, sodium chloride has become a shade similar to that seen in a geologically young area of Europe known as Tara Regio.
"Sodium chloride is a bit like unseen ink on the surface of Europe Before you irradiation, say it there, but after lighting, the color appears to you," said Hand, scientist at JPL and co- author of Science Advances paper.
"No one has seen the wavelength of the European spectra before this spatial and spectral resolution has occurred. The Galileo spacecraft has no visible spectrometer, it has a near-infrared spectrometer," says Caltech, a graduate student Samantha Trumbo, the author of the paper.  "Traditionally, all the spectacular spectroscopy is in infrared on the surface of the planet, because where most of the molecules sought by scientists have their main features," says Brown.
Hubble Space Telescope, Brown and Trumbo identified a unique absorption spectrum at 450 nanometers, which correspond to irradiated salt precisely, proving that the yellow color of Tara Regio is reflected in the presence of irradiated sodium chloride in surface.
"We have been able to do this assessment on the Hubble Space Telescope over the past 20 years," Brown says. "It's a nobody who thought to look."
While the search does not guarantee that sodium chloride is derived from the subsurface ocean (this may, in fact, be just proof of the various types of materials that are tailored to the cold ice of the month ), the authors of the study indicate that it permits a reevaluation of the geochemistry of Europe.
"Magnesium sulfate has only been leached to the ocean from rocks on the ocean floor, but sodium chloride may indicate that the oceanic ocean is hydrothermally active," says Trumbo. "That means Europe is a much geologically interesting planetary body than ever believed."
This research is supported by the NASA Earth and Space Science Fellowship Program, the Space Telescope Science Institute, and JPL.