
Cassini Beams Back First Images from New Orbit - devinp
http://sciencebulletin.org/archives/7953.html
======
gewoonkris
For those who are also wondering about the briefly mentioned hexagon-shaped
jet stream:

 _One hypothesis, developed at Oxford University, is that the hexagon forms
where there is a steep latitudinal gradient in the speed of the atmospheric
winds in Saturn 's atmosphere. Similar regular shapes were created in the
laboratory when a circular tank of liquid was rotated at different speeds at
its centre and periphery. The most common shape was six sided, but shapes from
three to eight sided were also produced. The shapes form in an area of
turbulent flow between the two different rotating fluid bodies with dissimilar
speeds_

Source:
[https://en.wikipedia.org/wiki/Saturn's_hexagon](https://en.wikipedia.org/wiki/Saturn's_hexagon)

Paper (paywalled):
[http://www.sciencedirect.com/science/article/pii/S0019103509...](http://www.sciencedirect.com/science/article/pii/S0019103509004382)

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grzm
Thanks for providing these references. The hexagonal cloud formation was the
first thing I noticed and was hoping someone would have already provided
references in the comments. One of the great aspects of the HN community!

~~~
intransigent
I think it's a sphere packing thing. [0] Equally sized circles touching on
edges "like" to pack into a six-up orientation, not unlike a revolver pistol.

My hunch is that it's an artifact of pi, somehow. Six being easily factored to
three, which has close proximity to pi.

[0]
[https://en.m.wikipedia.org/wiki/Sphere_packing](https://en.m.wikipedia.org/wiki/Sphere_packing)

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mxvzr
What amazes me the most about the Cassini mission is the drastic inclination
changes they managed to achieve around Saturn (see the GIF in the hero section
[1]). At first I thought the spacecraft must have had some serious delta-v
budget, but in fact the bulk of it was provided by Titan [2] (noteworthy: this
page also mentions the Cassini-Huygens communication issue that was uncovered
during flight, for which the workaround was already mentioned on HN [3]).
Truly amazing work from the navigation team.

[1] [https://saturn.jpl.nasa.gov/news/2966/ring-grazing-
orbits/](https://saturn.jpl.nasa.gov/news/2966/ring-grazing-orbits/)

[2]
[https://saturn.jpl.nasa.gov/mission/spacecraft/navigation/](https://saturn.jpl.nasa.gov/mission/spacecraft/navigation/)

[3]
[https://news.ycombinator.com/item?id=12483579](https://news.ycombinator.com/item?id=12483579)

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ajmurmann
Every time I see photos of the big gas planets like this, I imagine earth
orbiting the gas giant and feel very, very small and get what feels like mild
vertigo from the overwhelming scale. This is truly wonderful

~~~
pmoriarty
If you think Saturn's big:

[https://www.youtube.com/watch?v=GoW8Tf7hTGA](https://www.youtube.com/watch?v=GoW8Tf7hTGA)

(though this sort of thing is far more impressive when seen in VR)

But even better than that, for me, is going somewhere with very little light
pollution at night and simply looking up at the Milky Way. Nothing makes me
feel smaller and more in awe.

~~~
danielpatrick
My favorite segment of that is the universe's "web" of galaxies. There's
something pleasing about the way they've all arranged themselves. Much more
pleasing than the clustering of stars in a galaxy.

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mturmon
For more on the series of close orbits that will eventually take Cassini in
between Saturn and its innermost ring, see the project site at
[https://saturn.jpl.nasa.gov/news/2974/cassini-makes-first-
ri...](https://saturn.jpl.nasa.gov/news/2974/cassini-makes-first-ring-grazing-
plunge/)

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wrongc0ntinent
The sides the hexagon are slightly greater than the diameter of Earth.

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KineticLensman
For people who are interested , check out Nasa's JunoCam project [0], which
invites amateurs to conduct some of the target selection and image processing
required on the imagery returned from Jupiter Space. It's also worth noting
that JunoCam isn't one of the core scientific instruments on Juno. JunoCam is
more like a public outreach initiative bolted on to the real mission, which is
about studying the Jupiter's gravitational field, magnetosphere and
atmospheric characteristics using a range of sensors. That doesn't of course
detract from these wonderful images, but the primary science will not be based
on JunoCam outputs

[0]
[https://www.missionjuno.swri.edu/junocam/processing/](https://www.missionjuno.swri.edu/junocam/processing/)

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isomorphic
> _remind you that we’ve lived a bold and daring adventure around the solar
> system’s most magnificent planet_

Other than the one we're standing on, you mean.

~~~
dyukqu
Well said. But, you know, with all its moons and rings, Saturn is way _cool-
looking_ than any other planet in our Solar System. That's why they called it
that way, I guess.

~~~
prawn
Perhaps from a huge distance, but I think we win the title on any other scale.
Earth is pretty stunning.

~~~
isfield
It's like the school playground arguments over which computer is better, the
Amiga or Atari ST again. Only this time with planets. Imho Earth is better; it
has a blitter... I mean liquid water oceans...

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andreapaiola
The source: [https://www.nasa.gov/feature/jpl/cassini-beams-back-first-
im...](https://www.nasa.gov/feature/jpl/cassini-beams-back-first-images-from-
new-orbit)

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sakri
That large image (the first one) are the little "twirly things" smaller
"hurricanes" within the big one?

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caycep
the one concern i have - isn't the spacecraft fueled by a small plutonium
reactor? there's no risk of it going Big-B Boom?

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ekimekim
In short, no, there is no risk.

When we say a spacecraft is nuclear-powered, we're not actually referring to a
reactor (with rare exceptions[1]), but instead to something called a
Radioisotope Thermal Generator[2], or RTG for short.

Basically, an RTG contains radioactive material (material that undergoes
constant, passive radioactive decay). This constant decay produces heat, which
is then used to generate electricity via thermocouples. There's no feedback
loop or active control needed, at its simplest an RTG is a solid hunk of metal
with no moving parts.

There isn't physically enough of the radioactive material, let alone the
precise materials, pressures, and other things needed for a proper criticality
/ runaway fission effect like an atomic bomb. It's actually much harder to
make one than you think ;)

[1]
[https://en.wikipedia.org/wiki/Nuclear_power_in_space#Fission...](https://en.wikipedia.org/wiki/Nuclear_power_in_space#Fission_systems)

[2]
[https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)

~~~
dekhn
The risk comes at launch; if there is an explosion, the plutonium core can be
scattered over a wide area.

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wtk
It looks like… nipple.

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smegel
I have to say I've been pretty disappointed with Cassini so far.

Edit: reply was correct, I did in fact mean Juno.

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prewett
Are you thinking of Juno perhaps? That's not a photo-mission.

Cassini has:

\- found "sand" dunes, river channels, mountains, and lakes on Titan

\- landed a probe on Titan

\- photographed most of Saturn's moons

\- discovered gas jets on Enceladus and adjusted the mission to investigate
and discovered that they are caused by tidal compression which squeezes out
some of the subsurface ocean and forms one of Saturn's faint rings

\- discovered and researched how spokes and propellers form in the rings

\- documented the shepherding action of the shepherd moons on the rings

\- discovered the long-lasting polar hexagon feature

\- photographed the rings at equinox, which dramatically shows the vertical
displacement of the rings

\- plus way more

[http://saturn.jpl.nasa.gov](http://saturn.jpl.nasa.gov) is a better site.
There is a record of some of the top findings at
[https://saturn.jpl.nasa.gov/galleries/hall-of-
fame/](https://saturn.jpl.nasa.gov/galleries/hall-of-fame/)

~~~
IndianAstronaut
Cassini is my favorite space mission. It has really changed our view of the
solar system and beyond. Some of the most fascinating places are going to be
moons of these gas giants.

