Jupiter's moon Europa is an intriguing world. It is the smallest body in the solar system and the sixth-largest moon in the solar system, although it is the smallest of the four Galilean moons. The most intriguing is the subsurface ocean of Europe and the possibility of living.
The scientific consensus is that Europe has a subsurface ocean under its exceptionally smooth ice surface. The crust is estimated to be 10-30 km thick, and the ocean under it can be about 100 km deep. If this is true, then the volume of the ocean of Europe is about two or three times the size of Earth's oceans.
The interior of Europe is kept warm by tidal heating and probably by the radioactive decay of the elements in its rocky cloak. However, research shows that radioactive decay alone is not enough to generate heat in Europe. Regardless of the exact source of heat, it is enough to create a subsurface ocean.
It is probably an ocean of salt water that is important for life. Initially, the researchers thought that saltiness comes from magnesium chloride, which is basically Epsom salts. But a new study by scientists at Caltech / JPL shows that it may not be magnesium chloride, but rather sodium chloride, the same type of salt that makes the Earth's oceans salty.
The new study is called "Sodium chloride on the surface of Europe" and was published in the Science Advances of June 12. The authors are Samantha Trumbo, Michael Brown and Kevin Hand. Trumbo is the main author of the article.
The discovery stems from Hubble's observation on the surface of Europe. On the surface of the moon are yellowish areas that have remained somewhat mysterious until now.
The surface of Europe is a geologically young ice crust. So everything on the surface probably comes from the ocean below. This, as well as cracks and cracks in the icy shell, led the scientists to the conclusion that there is an ocean there. Ocean rich in sulphate salts.
However, new spectral data from the Keck Observatory suggest that the surface salts are not magnesium sulphates. There were no absorption lines in Keck's data indicating the presence of magnesium sulphates. These types of salt have very distinct absorption lines and they simply were not there. Scientists thought they could see sodium chloride on the surface, but the problem is that sodium chloride is not known in the infrared.
"We thought we could see sodium chlorides, but they're essentially devoid of infrared spectrum features," says Mike Brown, Richard and Barbara Rosenberg, professor of planetary astronomy at Caltech and co-author Scientific progress paper.
But Brown's colleague and possible co-author of the new article had an insight into this problem.
His name is Kevin Hand from JPL. He irradiated ocean salts in a laboratory in conditions similar to Europe. He discovered that after irradiation, sodium chloride was revealed in visible light, changing color. What color has changed? You guessed it: yellow. As in the yellow region on the surface of Europe, called Tara Regio.
"Sodium chloride is a bit like invisible ink on the surface of Europe. You can not say this before irradiation, but after irradiation the color skips over you – says Hand, a scientist at JPL and co-author Scientific progress paper.
"No one has ever seen spectral wavelengths of Europe that would have such spatial and spectral resolution. The Galileo the spacecraft did not have a visible spectrometer. He just had a near-infrared spectrometer, "says Samantha Trumbo, a Caltech graduate, the lead author of the article.
The three scientists then turned to the Hubble Space Telescope to develop this idea. They pointed to Hubble & # 39; and Europe and found the absorption line in the visible spectrum that perfectly matched the irradiated salt. This confirmed the presence of irradiated sodium chloride on Europe. The most likely source is the subsurface ocean.
"We had the opportunity to conduct this analysis using the Hubble Space Telescope for the last 20 years," says Brown. "Just nobody wanted to look."
This is a strong proof of the subsurface ocean's support with sodium chloride, such as the Earth's oceans. But this is not slam dunk. This may indicate different materials in the ice crust.
In any case, the survey presents more intrigues surrounding Europe.
According to the authors at the end of the article: "Regardless of whether the NaCl observed is directly related to the oceanic composition, its presence guarantees a reassessment of our understanding of the geochemistry of Europe."
If the salt in the ocean is magnesium sulphate, it could get into the ocean from rocks on the ocean floor. But if it's sodium chloride, it's a different story.
"Magnesium sulphate would simply get into the ocean from rocks on the ocean floor, but sodium chloride may indicate that the ocean floor is hydrothermal active," says Trumbo. "It would mean that Europe is a more geologically interesting planetary organism than previously thought."
Fire up the rocket. Let's go and find out!