Thanks to NordVPN for sponsoring today’s video.
The Cassini mission to the Saturn system has captured the hearts of many people across
the world.
Not only was it a fantastic feat of engineering, it was ambitious with its mission objectives,
it was a completely successful mission, and it took some of the most spectacular images
of space that we have ever seen.
During its 13 years around Saturn, it sent back an incredible 635 GB of data, from which
more than 4,000 science papers have been published.
It discovered 6 new moons.
It confirmed that icy moons have subsurface oceans of salty, liquid water which may well
be habitable.
It landed a probe on Titan.
It observed Saturn’s peculiar storms.
And during all this time, it travelled in excess of 7 billion kilometres.
In my opinion, and probably in the opinion of many of you, it was one of the greatest
missions of all time.
Now, I’ve already covered a lot of the Cassini mission in other videos, but one thing a lot
of you have wanted to see were the images it captured near its mission’s end, before
it entered Saturn’s atmosphere and disintegrated.
Some of these final images are fantastic, although be aware that Cassini is not capable
of real-time video capture.
Still, they are definitely worth having a look at.
I’m Alex McColgan, and you’re watching Astrum, and together we will discuss the final
images Cassini ever took.
The final phase of Cassini’s mission was named the Grand Finale, where Cassini performed
some of the most dangerous manoeuvres of its whole mission.
Mission controllers sent Cassini into an eccentric, elliptical orbit over the planet’s poles,
and daringly, through gaps in the rings.
The last few orbits took it closer to the surface of Saturn than it had ever been before,
giving scientists a new view and perspective of Saturn.
The first time lapse we will look at is from the 8th September 2017, only one week before
the end of Cassini’s mission.
One of the main focuses of Cassini during its mission was the moon Enceladus, one of
the prime candidates in the solar system to contain life in a subsurface ocean.
Cassini discovered over 100 water plumes erupting through the moon’s crust from this ocean,
water which freezes in the space environment and has now formed the beautiful E ring around
Saturn.
This ring is very tenuous, only visible when backlit by the Sun, and is potentially the
bluest naturally occurring object in the solar system.
Here is a great view of Enceladus’ effect on the densest part of the E ring, you can
see the plumes disturbing and replenishing the ring.
Cassini’s final look at Enceladus’ plumes were captured in this remarkable time lapse
taken over a 14-hour period.
On the 11th September, Cassini was near the furthest point of its final orbit and captured
this beautiful mosaic in natural light.
Visible are the thickest of Saturn’s rings, D, C, B, A and F, with Saturn’s short shadow
being cast over them.
Saturn’s northern hemisphere was experiencing summer during this time, which means that
Saturn’s famous hexagon storm is visible in all its glory.
You can also just about notice Saturn’s subtle bands in natural light.
What’s really interesting about this image, however, is that the nightside of Saturn is
dimly illuminated.
This is due to light reflecting off the rings, meaning Saturn’s nights in the hemisphere
facing the Sun don’t get that dark.
Below the glow of the rings, Saturn is pitch black.
As Cassini began to approach Saturn again on the 12th of September, it took images of
Saturn’s atmosphere near the planet’s terminator line.
Incredibly, because the Sun is low in the sky here, huge cloud structures can be seen
casting shadows that stretch for many kilometres.
You may think this is a close-up of Saturn, but actually we are looking at a scene about
5,500km across.
Saturn’s moon Titan could easily fit in this shot.
Cassini was getting closer and closer to Saturn.
On the 13th September, it peered one last time at Daphnis, a shepherd moon keeping the
A ring in check.
The gravity of Daphnis causes ripples in the ring, and some of you keen observers will
notice ripples in front of the moon, as well as behind.
This is due to the orbital speeds of the rings and the moon.
The inner ring orbits faster than Daphnis, meaning the ripples overtake the moon, exposing
more ring material to the moon’s gravity.
On the other hand, the outer ring travels slower than Daphnis, meaning the ripples lag
behind the moon.
By the time the ring material reaches Daphnis on either side again, the ripples have already
smoothed out.
On the same day, Cassini had one last look around the Saturn system.
It captured a view of Titan, a moon it focused on heavily during its mission, a remarkable
world with a thick nitrogen atmosphere.
It also peered at Saturn’s rings, with the uneven F ring just about visible at the bottom
of the image.
And as Saturn got bigger, it took one last look at Enceladus over a 40-minute period
before it disappeared from view behind the limb of Saturn.
The final image Cassini ever took was looking over the region where it would plunge into
the atmosphere.
It was night-time here, and so Saturn is lit up by light reflected off the rings.
On the final day, photos were not on the science agenda.
As beautiful as they are, they use up a lot of valuable bandwidth, and scientists wanted
to get every bit of data real time before the spacecraft was destroyed.
This was a unique opportunity; we had never probed Saturn before this.
When Cassini first hit the tenuous parts of Saturn’s atmosphere, it was traveling 123,000km/h.
The remnants of Cassini’s fuel were deployed by its thrusters to keep Cassini’s antenna
aimed at Earth.
At this point, Cassini was 1,900km above Saturn’s clouds.
A minute later, these thrusters were firing at maximum capacity to keep Cassini from spinning
out of control.
Cassini was directly sampling Saturn’s atmosphere, but this atmosphere was also heating Cassini
up.
Just 10 seconds later, the thrusters were overcome, and Cassini began to tumble, cutting
off communication with Earth.
Cassini’s onboard computers at this point would have been trying to figure out what
was going wrong.
Gyroscopes and star trackers would tell the computer that it is spinning, and it likely
would have gone into a safe mode to divert power in an attempt to right itself.
A minute or so later, the spacecraft would have disintegrated altogether and burned up
in Saturn’s atmosphere.
As data started arriving 1 and a half hours later on Earth, this final part of the mission
was deemed to be a great success.
Cassini recorded data from direct analysis of Saturn’s atmosphere, its ionosphere,
dust particles in the atmosphere, from magnetic field measurements and perhaps more that has
yet to be uncovered from the data.
And that’s the amazing thing about the Cassini mission, it just keeps on giving.
Science papers and discoveries are still being made as the data it collected is being analysed
and re-examined.
And great news, missions to the Saturn system do not end here.
Titan will be getting a lander, named Dragonfly, which will actually be a drone powered by
a radioisotope thermoelectric generator, and its mission is to fly around Titan, directly
sampling Titan’s surface in various locations.
So, there we have it, a look at the legacy of Cassini, and of its spectacular final images.
Did you know that spacecraft use something known as the Deep Space Network to communicate
with mission controllers on Earth?
These are giant communication facilities around the world so that no matter the orientation
of Earth, spacecraft like Cassini can send back data.
You too send and receive data all the time over the internet, some of which you may not
want unscrupulous people to see, like credit card info and personal information.
This is why NordVPN may be of interest to you.
NordVPN will provide double encryption for your data, so that you can make a purchase
online while at an airport or a coffee shop and still be secure.
NordVPN is also available throughout the world, even China, and it allows up to 6 simultaneous
connections, meaning that you and your family can still access your Netflix or Amazon Prime
library while abroad with their unlimited bandwidth, plus you can be safe in the knowledge
that you are protected.
Use the link https://nordvpn.org/astrum and the coupon code ‘astrum’ at checkout,
and you can get 70% off their 3-year plan, plus an additional month for free.
If you want anymore info about NordVPN, check out the link for their YT channel in the description.
Thanks for watching!
And a big thank you to those of you that support this channel, in whatever way that may be.
For those of you that are interested, Astrum merch is now live!
Find the link in the description and use the discount code “EARLYBIRD” to get a 15%
discount until the 30th June.
I hope you like it!
All the best, and see you next time.