NASA scientists just received their last message from the Cassini spacecraft, which plunged into Saturn early Friday morning. Those final bits of data signal the end of one of the most successful planetary science missions in history.
“The signal from the spacecraft is gone and within the next 45 seconds so will be the spacecraft,” program manager Earl Maize reported from mission control at NASA’s Jet Propulsion Laboratory, just after 4:55 a.m. local time. “This has been an incredible mission, an incredible spacecraft, and you’re all an incredible team.”
One of the last pieces of data captured by Cassini was an infrared image of the place into which it took its final plunge. The image, taken 15 hours before the spacecraft’s demise, reveals a spot on Saturn’s dark side just north of the planet’s equator where the spacecraft disintegrated shortly after losing contact with Earth.
Cassini was the first probe to orbit Saturn. Built and operated at JPL, it was launched in 1997 and inserted into orbit in 2004. The spacecraft revealed the structure of Saturn’s rings and, by delivering the Huygens probe to the moon Titan, executed the first landing of a spacecraft in the outer solar system. It also exposed two moons – Titan, a land of methane lakes, and Enceladus, which has jets of water streaming from its southern pole – as prime targets in the search for life beyond Earth.
After 13 years in orbit, Cassini leaves researchers with still more mysteries to ponder: They don’t know the length of the Saturn day or understand the quirks of its magnetic field. And it will fall to a future mission to discover whether one of Saturn’s potentially habitable moons could truly be home to alien life.
It’s precisely because of its successes that Cassini had to die. Once the spacecraft ran out of fuel, NASA would not risk letting it remain aloft, where it might be knocked into Titan or Enceladus. In April, Cassini began 22 close-in orbits that took it between and behind Saturn’s rings. Earlier this week, NASA flew Cassini past Titan one last time, taking advantage of the moon’s gravitational pull to slingshot the spacecraft toward Saturn.
That “goodbye kiss” set Cassini on its final, fatal course. Just after 3:30 a.m. California time on Friday, Cassini entered Saturn’s atmosphere, plummeting at a pace of about 77,000 miles per hour. For a few minutes, the spacecraft’s thrusters fought to keep its high-gain antenna pointed toward Earth, so it could continue to send back real-time data from this uncharted territory.
During its last moments, the spacecraft’s instruments sampled the molecules in the planet’s atmosphere – information that scientists will use to understand the planet’s formation and composition. It also collected data that researchers hope will help them solve the mystery of the speed of Saturn’s rotation.
NASA was able to maintain a link with the spacecraft 30 seconds longer than the team anticipated.
“Those last few seconds were our first taste of the atmosphere of Saturn,” Watkins said. “Who knows how many PhD theses are in that data?”
Minutes later Cassini vaporized, just a small flash of light streaking across an alien sky. But because Saturn is so distant, Cassini’s final signals didn’t reach Earth until 83 minutes after the spacecraft was gone.
That last communication was displayed as a green spike of data on a screen above mission control. The spike shrank, then flickered, then flatlined.
“We call loss of signal,” said spacecraft operations manager Julie Webster at 4:55 a.m. local time.
There was utter silence at mission control. And then Maize spoke: “I’m going to call this the end of mission. Project manager, off the net.”
(c) 2017, The Washington Post · Sarah Kaplan