The April 26 Google Doodle celebrates the beginning of the end for NASA‘s Cassini Spacecraft. The satellite has been in Saturn’s orbit since 2004, taking pictures of the ringed gas giant and its 62 known moons to help scientists understand the second-largest planet in our Solar System. Later this year, Cassini will crash into Saturn, but not before taking some spectacular pictures along the way.
Today, Cassini will pass between Saturn and its rings to take a picture of the Earth from that unique perspective and begins making its first finale dive. According to Google, the spacecraft will take several swoops between the planet and its rings.
Here’s what you need to know about the Cassini Spacecraft and its mission.
1. NASA Is Preparing Cassini For Its ‘Grand Finale’ Dive & Should Crash Into Saturn in September
On April 4, NASA announced that Cassini would be taking its “Grand Finale” dive towards Saturn. It will cash into the planet on September 15, 13 years after it began orbiting Saturn in 2004 and 20 years after it was launched in October 1997 with the Huygens probe attached. On April 26, that dive begins when it drops in the middle of the largest gap in Saturn’s rings.
“No spacecraft has ever gone through the unique region that we’ll attempt to boldly cross 22 times,” Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, said in a statement. “What we learn from Cassini’s daring final orbits will further our understanding of how giant planets, and planetary systems everywhere, form and evolve. This is truly discovery in action to the very end.”
NASA engineers have calculated a flight plan that will allow Cassini to continue to send scientifically helpful information during the five-month dive. Cassini will travel through the unexplored regions between the planet and its rings before crashing.
“Cassini’s grand finale is so much more than a final plunge,” Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, said in a statement. “It’s a thrilling final chapter for our intrepid spacecraft, and so scientifically rich that it was the clear and obvious choice for how to end the mission.”
As for why NASA has decided that now is the time to end Cassini’s mission, the agency explains that they want to avoid having it crash into the moons Enceladus and Titan, contaminating them with Earth microbes.
2. The Total Cost for Cassini Was $3.27 Billion, With the U.S. Paying 80 Percent
The Cassini mission, like all NASA projects, did not come cheap. According to NASA, the total cost of the mission was $3.27 billion, of which $2.6 billion was paid by the U.S. The European Space Agency and the Agenzia Spaziale Italiana contributed a combined $660 million to the mission.
The cost also includes the Huygens probe. When Cassini was launched in 1997, the probe was attached to the satellite. It successfully landed on Titan, Saturn’s largest moon, in January 2005. It remains the only landing in the outer solar system.
The probe is named after Christaan Huygens, the Dutch mathematician and astronomer best known for discovering Titan and explaining Saturn’s rings. He also invented the pendulum clock and had an interest in creating more accurate clocks.
The Huygens probe was built by the European Space Agency and sent data from Titan’s surface for just 90 minutes, as its primary goal was to send data of Titan’s atmosphere.
Cassini has provided plenty of great images of Titan. On April 21, Cassini had its final close bush with the moon. According to NASA’s Jet Propulsion Laboratory, this took Cassini past a “point of no return,” committing NASA to the “Grand Finale” plan.
“With this flyby we’re committed to the Grand Finale,” Earl Maize, Cassini project manager at JPL, said in a statement. “The spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn’s atmosphere on Sept. 15 no matter what.”
3. Cassini Recently Discovered Secrets of the Moon Enceladus, Which Might Be Able to Support Life
Cassini has made countless fascinating discoveries during its orbit of Saturn, including close photos of the moon Pan that showed it looking like a ravioli. But the one that NASA was most excited about was one of Cassini’s latest discoveries.
Earlier this month, NASA announced that the moon Enceladus has a global ocean under its surface. The moon is just 314 miles (505 km) across, meaning that it’s small enough to fit inside the length of the U.K. The findings of the Cassini scientists were published in the journal Science on April 14.
As NASA explained:
Cassini revealed the dramatic truth: Enceladus is an active moon that hides a global ocean of liquid salty water beneath its crust. What’s more, jets of icy particles from that ocean, laced with a brew of water and simple organic chemicals, gush out into space continuously from this fascinating ocean world. The material shoots out at about 800 miles per hour (400 meters per second) and forms a plume that extends hundreds of miles into space. Some of the material falls back onto Enceladus, and some escapes to form Saturn’s vast E ring.
According to the New York Times, the scientists found that Enceladus has plumes of gas containing hydrogen. They believe that these are hydrothermal chemical reactions like the hot fissures in the Earth’s ocean. If these are like what we see at home, where the vents are filled with microbial life, it means that Enceladus and other “ocean worlds” might be welcoming to life.
“This is the closest we’ve come, so far, to identifying a place with some of the ingredients needed for a habitable environment,” Zurbuchen said in a statement. ”These results demonstrate the interconnected nature of NASA’s science missions that are getting us closer to answering whether we are indeed alone or not.”
Before Cassini discovered the plumes on Enceladus, NASA scientists dismissed the moon as too small to be interesting. But Cassini’s discovery made them rethink it. Unfortunately, Cassini won’t make any more close flybys of Enceladus during its lifespan and there are no future plans for more NASA missions to Saturn. So it could be a long time before NASA can finally further explore the tiny moon.
4. Cassini Has to Use Plutonium as a Power Source Because Saturn Is Too Far From the Sun
Cassini – and other satellites NASA has sent into deep space – cannot use solar power as a power source because it is traveling too far from the sun. Instead, it uses three radioisotope thermoelectric generators that are heated from the decay of about 73 lbs (33 kg) of plutonium, specifically plutonium-238. The substance is a byproduct of the process to make nuclear weapons.
Back in 1997, the Christian Science Monitor reported that there were protests at the time to stop NASA from hurtling Cassini into space. It was the largest single amount of plutonium ever used by a space device and some U.S. lawmakers called for the Cassini mission to be scrapped. The Florida Coalition for Peace and Justice even held a vigil at Cape Canaveral in the days before the launch.
Since Cassini ended up being a success, another problem has arisen. There’s not enough plutonium for NASA to power another deep space satellite. In 2013, Wired reported that the U.S. had only about 36 pounds of plutonium-238 left. In March 2015, the supply got so low that NASA only had enough to make three more batteries, Popular Science reported.
In December 2015, the Department of Energy stepped up to help NASA fix the plutonium-238 supply problem. The DOE agreed to make 50 grams of plutonium-238 at the Oak Ridge National Laboratory in Tennessee. It was the first time the substance was produced in the U.S. since the Savannah River Plant in South Carolina stopped making it in the late 1980s.
Full-scale production of plutonium-238 is still seven years away, Space.com reported in May 2016. Bob Wham, the Pu-238 project lead in the Nuclear Security and Isotope Technology division at Oak Ridge, said during a press conference in April 2016, said full-scale production might not start until 2023.
5. Cassini Is Named After Giovanni Domenico Cassini, an Italian Astronomer
The spacecraft is named after Giovanni Domenico Cassini, who lived from 1625 to 1712. Cassini didn’t discover Saturn and it was actually Galileo who first saw the planet’s rings. However, Cassini was the first to notice that there are divisions in Saturn’s rings. The Cassini Division, the most largest gap in Saturn’s rings, is named after Giovanni Domenico Cassini.
Giovanni Domenico Cassini also discovered four of Saturn’s satellites – Iapetus, Rhea, Tethys and Dione – between 1671 and 1684, according to Experimental Astronomy. As a mathematician, he also calculated Mars and Jupiter’s rotation periods.