Slashdot Mirror
Cassini Probe Will Dive Through Enceladus's Water Jets (nasa.gov)
An anonymous reader writes: NASA's Cassini probe has a daring mission tomorrow: dive through the water jets spraying from the south pole of Saturn's moon Enceladus. The probe will be a mere 30 miles above the surface, traveling at a relative speed of 19,000 mph. Researchers hope to gain insight into the chemical composition of the jets. "[T]he plumes are more than just gas and water: samples show that they also contain many of the building blocks essential to Earth-like life. This lends itself to the exciting possibility that organisms similar to those that thrive in our own deep oceans near volcanic vents exuding carbon dioxide and hydrogen sulfide might exist on Eceladus." The molecules suspended among the water may tell us whether Enceladus's oceans are capable of harboring life. "The spacecraft's sensors will pick up gases in the plume searching for the presence of molecular hydrogen (H2). The amount of H2 found could reveal how much hydrothermal activity is occurring in the ocean."
It sort of is, but Cassini only has a year or so left in its mission before it is out of propellant needed for adjusting its orbit around Saturn. From here on, missions will get riskier, finishing with the Grand Finale, where it orbits between Saturn and the innermost ring a couple dozen times, before it plunges into the planet to keep from possibly contaminating Enceladus
Consider the end scenarios:
1) Cassini crashes into Enceladus. Because it has no atmosphere to speak of and a solid surface, the spacecraft will impact on the ice and make a real mess. Fragments of the spacecraft may survive, more or less in the condition that they left Earth (although much older), including the plutonium RTGs. Eventually, these may work their way through the ice and into the subsurface ocean, contaminating a fairly interesting environment (the ocean-ice interface and the ocean-crust interface).
2) Cassini crashes into Titan. Because there is a significant atmosphere, Cassini will burn up to some extent, but some of it, surely, will survive re-entry, distributed over a large area, and thump into the surface. Due to the thick atmosphere and low gravity, the terminal velocity is quite modest (slower than Earth's), so any bits of Cassini that survive re-entry will have a pretty soft landing. This, too, is contamination of a fairly interesting environment (the surface-atmosphere interface, or in the hydrocarbon lakes).
3) Cassini is intentionally de-orbited into Saturn. Saturn is basically all atmosphere and has no surface to speak of: it'll burn up pretty much all the way down, eventually floating in the deepest parts of the planet that are especially dense enough so that even metals are buoyant. These deep reaches are also really hot, which will at least kill anything still alive or viable on the spacecraft, and probably just melt everything in some extreme chemistry. Compared to permanently scattering the spacecraft across a moon, the amount of time Cassini passes through the various layers of Saturn before reaching its hot death is quite brief. Finally, Saturn is the 2nd most massive planet in the solar system, 10^3 -to- 10^6 times the size of its moons, so any contamination from Cassini will be much more diluted.
So, considering that getting Cassini out of the Saturn system is not possible, tossing it into Saturn itself seems the best option.