Models illustrating the formation of our Solar System indicate that the deuterium to hydrogen ratio (DH) should be considerably higher in the frigid outer Solar System than it is in the warmer and well-lit inner region where Earth dwells closer to our Sun–along with the other inner planets: Mercury, Venus, and Mars. Deuterium is more abundant in the giant cold dark molecular clouds that serve as the birthplace of stars. Our Sun was born in the swirling folds of just such a dark and lovely cloud. Some models predict that DH should be approximately 10 times higher in the Saturn system than on our own planet. However, the new measurements reveal that Phoebe is traveling to the beat of a different drum.
“The discovery of an odd deuterium to hydrogen isotopic ratio for Phoebe means that it was formed in and comes from a far part of the Solar System,” Dr. Clark explained in the December 3, 2018 PSI Press Release. “Phoebe’s D/H ratio is the highest value yet measured in the Solar System, implying an origin in the cold outer Solar System beyond Saturn,” he added.
The team of astronomers also measured the carbon-13 to carbon-12 ratio on another major moon of Saturn, Iapetus, along with that of Phoebe. Iapetus, which also has a D/H ratio similar to that of our own planet, also has a carbon-13 to carbon-12 ratio close to Earth’s values. In contrast, Phoebe’s value is almost five times higher in the carbon isotope. The carbon dioxide presence put limits on how much of Phoebe could have evaporated to space following its formation, leaving only the possibility that Phoebe was born in the frigid outer regions of our Solar system.–much farther from our Sun than its adopted parent-planet Saturn. This means that Phoebe was likely evicted from its birthplace into an orbit where it was ultimately gravitationally snared by Saturn. Precisely how far from our Sun Phoebe was born is unknown. This is because there are currently no measuremtns of D/H or Carbon-13-carbon-12 for the frozen icy surfaces found on Pluto or KBOs circling our Star beyond Pluto. But this methodolgy will aid astronomers in their quest to attain such measurements of the surface ices.
The measurements were made from NASA’s Cassini spacecraft by astronomers using its Visual and Infrared Mapping Spectrometer (VIMS) over the course of the mission. A later, improved callibration of the instrument, that was finished early in 2018, provided the precision necessary for these measurements of reflected light from Saturn’s moons and sparkling icy rings. The new method of measuring isotopic ratios on solids like water ice and carbon dioxide ice using reflectance spectroscopy remotely will allow important measurements of isotopic ratios for other bodies throughout our Solar System, thus putting additional necessary constraints on models of its formation more than 4 billion years ago.
Because the D/H values observed in the Saturn system are close to that of our own planet’s values, a similar source of water must have existed for both the inner and outer regions of our Solar System. New models now need to be developed to show where the alteration from inner to outer Solar System exists.
NASA’s Europa Clipper mission could also be used to measure isotopic ratios on the icy Galilean moons of Jupiter, noted Dr. Clark in the December 3. 2018 PSI Press Release. Europa is one of Jupiter’s Galilean moons, and it is thought to contain a sloshing subsurface ocean of liquid water hidden beneath its cracked icy crust. The other three Galilean moons–all discovered by Galileo Galilei in 1610–are Io, Ganymede, and Callisto. Dr. Clark is a co-investigator on the mission, and he hopes to make those important measurements. mkv movies download 2019