Scientists have discovered in the data collected by the interplanetary station “Galileo” 20 years ago, new evidence of the existence of water geysers on the icy satellite of Jupiter – Europe.
Europe – the smallest of the four largest moons of Jupiter, called the Galileans. Its radius is 200 kilometers shorter than the radius of the moon, and the orbit lies about 670,000 kilometers from the gas giant. A special interest in this celestial body arose in the late 1990s, when the existence of the subglacial ocean was predicted on the basis of an analysis of the magnetic field of the satellite carried out by Galileo.
It is assumed that the ocean is under a 25-kilometer layer of ice, and its depth reaches hundreds of kilometers in depth. The ocean in Europe does not freeze because of the heating of the satellite’s interior, which is caused by the tidal forces of Jupiter. In addition, scientists suggest the existence of geothermal activity on the ocean floor, which may prove to be a sufficient condition for the emergence of life.
One of the proofs of the presence of the ocean in Europe is the geysers that emit water vapor, which was recorded by the Hubble Space Telescope in 2012, 2014 and 2016. Emissions were detected over the equatorial region and the southern pole of the satellite, stretching to 200 kilometers in height and had a non-permanent character – the greatest activity was observed when the satellite was as far from Jupiter. However, these discoveries were made at the limit of the capabilities of the telescope and astronomers would like to get evidence of the existence of geysers in situ.
Astronomers led by Xianzhe Jia claim to have found such evidence by analyzing the data collected by the magnetometer and the PWS (Plasma Wave Spectrometer) instrument on the Galileo apparatus during two close spans over the equatorial and southern regions of Europe in 1997 and 2000 years. During these spans, the minimum distance from the vehicle to the icy surface of the satellite was nearly 2000 kilometers, which is today a record low.
During the flight over the equatorial region of Europe in December 1997, approximately one minute before the passage of the most close point to the surface of the satellite, the magnetometer recorded a change in the magnetic field strength by hundreds of nanotubes in 16 seconds. At this time, the PWS instrument recorded local changes in the electric field and the electron density of the plasma surrounding the apparatus. In order to verify whether such phenomena can be associated with the passage of the apparatus through the water flare (or plume) of the geyser, astronomers have constructed a three-dimensional magnetohydrodynamic model that describes the effect of ejection on the properties of plasma and fields in the vicinity of the satellite.
The calculated location of the water ejection from the surface of Europe recorded during the close passage of the Galileo apparatus in December 1997. Xianzhe Jia et al. / Nature Astronomy (2018)
Modeling tracks the behavior of O + ions (a representative of the magnetospheric plasma), O2 + (representative of ions originating from the surface of Europe) and electron plasma, and takes into account the processes of ionization, recharge and recombination occurring in the atmosphere of Europe, as well as the water emission parameters obtained in the course of observations different telescopes. It was assumed that the shape and structure of emissions in Europe is similar to that of geysers on Saturn’s satellite Enceladus.
As a result, it turned out that the models described the observational data well and allowed to limit the location of the source of the plume through which Galileo flew in December 1997. In the case of a close span in 2000, the observations of changes in the magnetic field can not be interpreted as the effect of the emission of a geyser. These findings underscore the value of data collection at short distances from or on the satellite surface. This task is facing a new generation of missions to the system of Jupiter – Europa Clipper, Jupiter Icy Moon Explorer and Joint Europa Mission, which are expected to be launched in the early 2020s.
The presence of subsurface oceans in the solar system is assumed for several satellites of the giant planets (Europe, Ganymede, Callisto, Enceladus and Triton), as well as in dwarf planets, for example, in Pluto or Ceres. More information about extraterrestrial oceans can be found in our material “guidebook” “Sea inside”.