Cassini Beams Back First Images from New Orbit | Hacker News Reader

Cassini Beams Back First Images from New Orbit

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217 pointsdevinp39 comments

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

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

I like this work and the presentation by Tianlu Yuan (2013) about how our knowledge about the subject progressed -- the first photos were made by Voyager (1981-82):

http://www-hep.colorado.edu/~tianlu/public/saturnHex_paper.p...

http://www-hep.colorado.edu/~tianlu/public/saturnHex_present...

"In the 1980s images of Saturn taken by Voyager led to Godfrey's surprising discovery of a hexagonal structure on the planet's north pole [9]. Now, over three decades later, Saturn's north polar hexagon remains, superficially unchanged and not entirely understood. Voyager's iconic images proved a challenge to explain theoretically, but with additional data from ground based observations and the HST in the early 90s, and images from the Cassini mission more recently, our knowledge of many physical parameters forming the hexagon has increased. Along with observation, laboratory experiments and numerical simulations have helped foster greater understanding of the possible causes of the jet's six-sided shape."

The more recent pictures (2016) are also interesting, as the color has changed(!):

http://www.forbes.com/sites/startswithabang/2016/10/31/satur...

And for completeness, the comics from 2010:

http://www.smbc-comics.com/comic/2010-07-06

I read the article and thought I must research into the hexagonal madness. Turned to comments, HN's transcendent consciousness wins again! Cheers gewoonkris.

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!

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

> Saturn's south pole does not have a hexagon, according to Hubble observations; however, it does have a vortex, and there is also a vortex inside the northern hexagon. (o)

could the fact that there is only one hexagon imply a consequence of the 'hairy ball theorem'?(i)

(o) https://en.wikipedia.org/wiki/Saturn's_hexagon

(i) https://en.wikipedia.org/wiki/Hairy_ball_theorem

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/

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

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

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

If you think Saturn's big:

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.

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.

I like how, when showing the increasing star size, they show a little piece of the next, bigger, star just to let you know "hey, we're not done yet!". There are big things out there, people.

For me personally this is the definitive video of "practical scale". It doesn't go out of its way to dazzle me with larger and larger pieces of an incomprehensibly large puzzle. Instead it is a simple cause + potential effect, nothing more ;)

https://youtu.be/HFT7ATLQQx8?t=55

Personally I find that pictures and the idea of those giant super smooth planets make me feel uneasy and downright scary.

Something along the line; "Way too big, way too smooth to be natural. Almost hostile, evil"

Have you played SpaceChem? You should, if not.

I'll give a try.

It always reminds me about Total Perspective Vortex.

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...

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

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/

> 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.

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.

Saturn also has way cooler moons. Enceladus with jets of water. Titan with lakes and a thick atmosphere. Mimas, which looks like the death star.

It's hard not to find Saturn intriguing, the rings, the colors, the moons. It's the first time I saw something through a telescope that was awe inspiring. It almost seemed cartoonish with it's vibrancy and sharp edges. It's enough to make anyone want to take up astronomy.

yeah. I also found seeing the moons of jupiter around jupiter pretty amazing. can kind of see how galileo came to the conclusions he did.

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

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...

without having travelled to other planets its pretty premature to have any opinion.

The source: https://www.nasa.gov/feature/jpl/cassini-beams-back-first-im...

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

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?

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...

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

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

It looks like… nipple.

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

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

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

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.

Sorry it wasn't up to your interplanetary satellite standards.

"So far" seems like a really weird way to describe a mission that's been active for the last 12 years.

How can you not be amazed by those photos?

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