Cassini ready for fatal rendezvous with Saturn
UNITED STATES: The course has been set. The end is in sight. There’s no turning back now. After 13 years of making dazzling discoveries in the Saturn system, Cassini’s time is just about up.
Tomorrow, the Nasa space probe will dive into Saturn at 112,000kmh. Within minutes, it will vaporise in the cloud tops of the ringed planet after valiantly fighting a battle it has no hope of winning.
Cassini’s small thrusters, designed to manoeuvre the twotonne spacecraft around the vacuum of space, will be no match for Saturn’s thicker-than-expected atmosphere. Within minutes of diving into the planet’s upper layers, the instruments that revealed the great hydrocarbon seas on Titan and the plumes of water ice shooting off Enceladus will be torn apart and melted.
After a small flash of light in the Saturnian sky, the spacecraft will be gone.
‘‘There’s no doubt about it, we’ll be sad at the loss of such an incredible machine,’’ said Earl Maize, programme manager for the Cassini mission at the Jet Propulsion Laboratory in La Canada Flintridge, California. ‘‘But we have a great sense of pride in what the mission accomplished.
‘‘We left the world informed, but still wondering. I couldn’t ask for more.’’
Cassini’s fate was sealed on Tuesday, when it made its final flyby past Titan, Saturn’s largest moon.
‘‘That slowed it down just enough so that what is going to happen on Friday is absolutely inevitable,’’ Maize said. ‘‘It got the velocity change it needed, and now it’s on its way into Saturn.’’
The spacecraft’s final moments have been scheduled down to the minute. It will begin a five-minute roll that will point its Ion Neutral Mass Spectrometer towards the direction of flight, allowing the instrument to gather as much data as possible about the chemical makeup of Saturn’s atmosphere in its final seconds.
At the same time, the spacecraft will reconfigure its systems to allow real-time data transmission back to Earth. One minute later, its high-gain antenna will point away Earth, and the signal from the spacecraft will be gone for good. It will take an additional 84 minutes for the radio silence to reach Earth.
‘‘We won’t watch it burn up,’’ Maize said. ‘‘We’ll watch it turn away from us.’’
Even in this final journey, Cassini has critical science duties to perform. The suicide dive has the advantage of taking the spacecraft’s instruments deeper into Saturn’s sky than they have ever been before. Hunter Waite, director of mass spectrometry at the Southwest Research Institute in San Antonio, Texas, and his team will also investigate the phenomenon of ‘‘ring rain’’, when water vapour and ice grains from the rings descend into the gas giant’s atmosphere.
Although most of Cassini’s instruments are still functioning flawlessly, its fuel tank is empty.
Mission planners decided that vaporising the spacecraft in Saturn’s atmosphere was the best way to keep it from accidentally contaminating the moons Enceladus and Titan, two of the solar system’s most promising candidates for hosting extraterrestrial life.
‘‘Because of the importance of Enceladus that Cassini has shown us, and of Titan, we had to make decisions on how to dispose of the spacecraft,’’ said Jim Green, Nasa’s director of planetary science. ‘‘We must protect those bodies for future exploration.’’
- LA Times