The spacecraft deliberately sank into Saturn’s upper atmosphere at a high speed and plunged itself into the planet just after 6:30 a.m. ET Friday. Given the amount of time it takes signals to reach Earth, the final signal and last bits of data will reach the Deep Space Network’s Canberra Station in Australia about an hour and a half later.
NASA will confirm the spacecraft’s demise, expected at 7:55 a.m. ET.
For about a minute, Cassini was able to transmit new data about the planet’s composition as long as its antenna remained pointed toward Earth, with the assist from small thrusters. Then, the spacecraft burned and disintegrated due to the heat and high pressure of the hostile atmosphere. It became part of planet it set out to explore.
No spacecraft has ever been so close to Saturn.
“You can think of Cassini as the first Saturn probe,” said Linda Spilker, Cassini project scientist.
On Thursday, Cassini took its last images and transmitted all the data on its recorder to prepare for the final plunge.
Why the dramatic ending?
Cassini had its closest approach with Saturn’s moon Titan on Monday, dubbed a “goodbye kiss” by the mission’s engineers because it provided the gravity assist that sent the spacecraft on its final encounter with Saturn.
Mission scientists and operators gave Cassini this fiery send-off on purpose. Although many other options were considered — such as “parking” the spacecraft in orbit — they didn’t want to risk Cassini colliding with any of Saturn’s moons.
Cassini data and observations revealed that while seemingly inhospitable to us, the moons Enceladus and Titan could be habitable for some form of life. And NASA didn’t want to risk contaminating the moons or any future studies of them with Earth particles. Although Cassini has been in space for 20 years, microbes from Earth could still exist on the spacecraft without air, water or protection from radiation.
Although the mission itself has ended, the data and observations provided by Cassini will provide new details about the planet, its unique rings and its moons for decades to come.
During the final plunge, the Ion and Neutral Mass Spectrometer acted as the “nose” of the spacecraft, directly sampling the composition and structure of the atmosphere — something that can’t be done from orbit, said Hunter Waite, team lead for the spectrometer.
This was in the hopes of investigating the “ring rain” phenomenon discovered by NASA’s Voyager mission in the early 1980s, in which it appeared that the rings were raining down material on the planet and causing changes in the atmosphere. The spectrometer could determine what material is from the rings and what material is part of the atmosphere.
What Cassini taught us and what’s next
Inspired to learn more after flybys of Saturn by NASA’s Voyager missions, the Cassini mission was designed to be an international effort that united NASA, the European Space Agency and the Italian Space Agency.
It is known as the Cassini-Huygens mission because it delivered the European agency’s Huygens probe to Titan, the “first descent and landing on a world in the outer solar system,” according to NASA.
The Cassini mission has been extended twice and finally used up the last of its rocket propellant this week.
In the end, Cassini witnessed about half of a Saturn year. When the craft arrived, Saturn’s northern hemisphere was emerging from winter. As seasons on Saturn last about seven Earth years each, Cassini was just able to witness summer in the northern hemisphere before the mission ended.
It has traveled nearly five billion miles, executed 2.5 million commands, conducted 162 targeted flybys of Saturn’s moons, completed 294 orbits and its collected data has led to the publication of nearly 4,000 research papers.
When Cassini arrived, it witnessed a giant storm circling the planet for nine months. We learned that there are 3-D structures in the rings. Serendipitous observations showed that icy jets erupt from Enceladus. And Titan not only has seas and lakes of liquid ethane and methane, it has an atmosphere of chemicals that rain down, forming a unique chemistry that could lead to life.
“Cassini has transformed our thinking in so many ways but especially with regard to surprising places in the solar system where life could potentially gain a foothold,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate, in a statement.
“Cassini has enabled those future missions to be possible,” said Jim Green, NASA’s director of planetary science.
Intrigued by Cassini’s discoveries, scientists have submitted concepts for future “spacecraft to drift on the methane seas of Titan and fly through the Enceladus plume to collect and analyze samples for signs of biology” that are under consideration, according to NASA.