Cassini’s fiery final plunge
BY the time you read this, the Cassini spacecraft will be no more.
Last night, Cassini was scheduled to fly into the planet Saturn, burning up in its atmosphere and ending a spectacular 13-year study of the famous ringed planet.
This was no accident: Cassini’s demise was quite deliberate. The spacecraft had been dancing around the system of Saturn and its moons, but was running out of manoeuvring fuel. It was time to end the mission, even though its instruments were still operating.
But why? I have been asked this question many times. Couldn’t it remain in orbit around Saturn for a very long time?
Actually, it could, and likely would. However, with no fuel, mission controllers would no longer have any control over its movements, and there would have been a possibility, however small, that Cassini would collide with one of Saturn’s moons.
In particular, there was concern that moon would be Titan or Enceladus, and this was largely because of the discoveries made by NASA’s Cassini and its piggybacked European Space Agency craft Huygens.
Titan is the largest of Saturn’s moons. With a diameter of 5150km, it is the second largest moon in the solar system. It can be seen through even a small telescope as a starlike point of light orbiting Saturn about every 16 days.
Titan has a nitrogen atmosphere which, amazingly, gives rise to an atmospheric pressure at Titan’s surface that is greater than that at the surface of the Earth.
We have learned that Titan has rivers and oceans of liquid methane, and a subsurface water ocean. The Huygens craft landed on Titan in 2005 and sent back wonderful images of the moon as it descended, and from the surface. Huygens’ information, together with Cassini’s images and measurements made during its flybys of Titan, have made it even more clear to us that this moon is worthy of much further study.
One of the most important aspects of Titan is that its atmosphere is thought to be similar to that of the Earth a very long time ago, before life developed. This could offer important clues about the formation of life, not only on Earth, but elsewhere.
The moon Enceladus has also delighted space scientists. It is covered with ice, and Cassini has revealed to us that not only does it have a subsurface salty ocean, but also that it has jets of water being emitted through its surface. There has even been speculation about the possibility of hydrothermal vents on the ocean’s floor.
Enceladus, too, may offer clues to the formation of life, and some think that there is even a possibility of life in some form existing there.
An especially exciting thought is that given that we have now discovered thousands of planets orbiting stars other than our sun, these planets in many cases may have moons as fascinating as Titan and Enceladus.
Indeed, we have no reason to think that our solar system is unique in any way.
The importance of these moons in our study of life in the universe is the reason for scientists destroying Cassini before it can contaminate one of these moons.
It is a space version of disposing of one’s waste thoughtfully!
Of course, a great deal of care must be taken with craft that are deliberately designed to land on an object, such as Huygens on Titan, missions to the moon, and landers on the surface of Mars.
However, given that Cassini’s mission was over, destruction by plunging into Saturn was the most obvious way of doing the right thing.
The anticipated loss of signal occurred last night because early in the dive into Saturn, Cassini’s antenna would no longer have been able to point toward Earth.
It is hoped that Cassini’s last transmission to us will include the results of sampling Saturn’s atmosphere, but we will probably have to wait a while before this can be confirmed.
Although Cassini is now gone, there will be plenty more outer-planet information coming from Juno in orbit around Jupiter, which is continuing its exciting orbital mission.