Thread by @jesserogerson

T-6 days until @CassiniSaturn burns up in the upper atmosphere of #Saturn. It's has flown for 13 years, and will take pics to #GrandFinale

I'll be highlighting my fav images from @CassiniSaturn over the next week in anticipation of the #GrandFinale on Sept 15. Starting with...

1/ @CassiniSaturn launched aboard a Titan IVB/Centaur in a spectacular night-time launch. Oct 15, 1997. 7 year trip to #Saturn #Grandfinale

2/ En-route to #Saturn, Cassini flew-by Jupiter and took some of the best images to date including this animation of the clouds #Grandfinale

3/ @CassiniSaturn took this image on May 7, 2004, just a few months before orbital insertion at #Saturn on July 1, 2004. #Grandfinale

4/ A month before insertion into #Saturn's orbit, @Cassini discovered two new moons: Methone and Pallene, June 1, 2004

5/ Back in 2004, only 18 moons were known, now there are 60... a combination of @CassiniSaturn imaging and ground based work has found them

6/ Again, before arriving at #Saturn, @CassiniSaturn caught two storms merging. both 1000 km wide, moving 5ish m/s. March 2004 #GrandFinale

7/ A close flyby of the moon #Phoebe on June 10, 2004 reveals a very irregular topology. Looks like an asteroid! @CassiniSaturn #Grandfinale

8/ Btwn June 30-July 1, 2004, @CassiniSaturn performed an engine burn that made it the first human-made object to orbit #Saturn #Grandfinale

9/ In Oct 2004, @CassiniSaturn flew by #Titan within 1200km. This shot from the flyby suggests a stratified atmo. 1of127 flybys #Grandfinale

10/ on Dec 23, 2004, @CassiniSaturn released the #Huygens probe, which will eventually land on the surface of #Titan. #Grandfinale

11/ Jan 14, 2005 #Huygens entered upper atmosphere of #Titan taking 2.5 hrs to reach ground. Measuring atmos all the way down #grandfinale

12/ Here's a great video of the landing using real imagery #GrandFinale

13/ At 12:43UTC on Jan 14, 2005 the #Huygens probe landed on #Titan, becoming the furthest soft-landing ever achieved by humans #grandfinale

14/ #Huygens operated for abt 90min before it lost contact w @CassiniSaturn. Here's an infamous image from a surreal world #grandfinale

15/ @CassiniSaturn went on to make 127 more flybys of #Titan, which is the only Moon in the solar system with an atmosphere #grandfinale

16/ @CassiniSaturn confirmed there are lakes of Methane/Ethane on #Titan. The only other body in Solar System that has liquids #grandfinale

17/ RIGHTNOW @CassiniSaturn is receiving a "Goodbye Kiss" frm #Titan a final distnt flyby of #Saturn's largst moon at 119,049km #GrandFinale

18/ Iapetus, a 1500km-wide moon of #Saturn, famous for its dramatic two-tone colouration and 1300km-wide equatorial ridge #GrandFinale

19/ it's funny, this equatorial ridge business was weird when they discovered it back in 2005. That's just the tip of the iceberg, though

20/ Much later on, @CassiniSaturn started finding moons embedded in the rings that sported a similar feature to Iapetus. We'll get to that..

21/ @CassiniSaturn detects geysers on #Enceladus in early 2006, confirming a massive liquid water ocean below the ice surface #GrandFinale

22/ #Enceladus became a major focus of the @CassiniSaturn mission after that. Liquid water is an important ingredient for life here on Earth

23/ In 2008, @CassiniSaturn gets close to the plumes, even flying through them. Analysis of the water flying into space begins #GrandFinale

24/ #Enceladus is only 500km-wide but contains MORE water than the entire Earth! Here it is next to Great Britain for scale #GrandFinale

25/ the "tiger stripes:" the locations on #Enceladus where the Geysers shoot into space. Composed of: salts, organic compounds #GrandFinale

26/ This iconic image is perhaps my favourite one of #Enceladus. Its plumes are so large and frequent they are CREATING #Saturn's E ring

27/ Not only is #Enceladus perhaps the best place to go looking for life in our Solar System, it also influences the entire Saturnian system

28/ #Enceladus is contributing to the ring structures of #Saturn. An impressive feat for a moon the size of England #GrandFinale

29/ I'm almost 30 tweets into this #GrandFinale recap and I haven't even talked about the rings or the #Saturn itself!

30/ I mean, the rings are easily the most iconic thing abt #Saturn. They're huge, impressively thin, bright, with insanely complex structure

31/ Funny story: Galileo "discovered" the rings in 1610 but he didn't know what they were. In fact, he called them #Saturn's "Ears"

32/ Anther funny story: every time I google "Rings of Saturn" I get links to an american deathcore metal band. They have some cool album art

33/ This image was taken when the Sun was on the other side of #Saturn, illuminating the rings from @CassiniSaturn's POV #GrandFinale

34/ taken July 19, 2013 it's AKA "The Day the #Earth Smiled" because we're all visible in the picture! Also #Mars and #Venus are there too!

35/ "That's here. That's home. That's us ... on a mote of dust, suspended in a sunbeam." This image makes me think of Sagan #GrandFinale

36/ It was only the 3rd time #Earth had been imaged frm the outer solar system, and the first time we new in advance it was going to happen!

37/ Hence, "The Day the Earth Smiled." It's worth posting again. I think this is my favourite image @CassiniSaturn took #GrandFinale

38/ Beautiful #GrandFinale

39/ As one can imagine, this picture ALSO had a bunch of #Saturn's moons in it, as well as impressive details on the rings. #GrandFinale

40/ The @CassiniSaturn imaging team has a detailed rundown of the image. Definitely worth a read #GrandFinale ciclops.org/view/7699/The-…

41/ Believe it or not, we still don't know exactly how long a day is on #Saturn. You would think it's an easy planetary property to measure

42/ @NASAVoyager measured 10h39m24s in 1980/81, but upon arrival @CassiniSaturn measured 10h45m45s. They can't both be right? #GrandFinale

43/ this begs the question: how do we measure a planet's day? Can't you just count how long it takes for a surface feature to go around?

44/ historically this has been tough with #Saturn, because its surface is so damn uniform there's nothing to track! (image viaBjörn Jónsson)

45/ planetary scientists have found a way around this, however, by simply measuring the rotation of a planet's magnetic field. #grandfinale

46/ On Earth, our mag field is not aligned with our geo axis, thus, every time the Earth spins once, the mag field "wobbles" #grandfinale

47/ Apply this same theory to #Saturn and we should be able to measure the day, right? WRONG. Saturn isn't going to make it that easy

48/ #Saturn's Magnetic field is almost perfectly aligned with its rotation axis. That means no mag field wobble while it spins #GrandFinale

49/ Nevertheless, attempts were made with @CassiniSaturn and the length of day turned out to be 6 min longer than measured by @NASAVoyager

50/ Another unexpected result! After @CassiniSaturn took data for two more years, a more refined measurement: 10h47m6s #GrandFinale

51/ I honestly don't know how long #Saturn's day is, but I've heard times ranging from 10h 30 m up to 10 h 50 m. #GrandFinale

52/ Check out this super close-up of #Saturn's moon Iapetus (36 m/pix). The tones are overlapping, dark soil covered by lighter #GrandFinale

53/ By mid 2008, @CassiniSaturn had completed its mission! 4 years orbiting the ringed world. This image was taken Jan 2008 #GrandFinale

54/ Of course story doesn't end there. @CassiniSaturn's mission was extended to 2010, which would take us through #Saturn's equinox

55/ It was officially renamed to the Cassini Equinox Mission, and would include 60 more orbits of #Saturn, flybys of many moons #GrandFinale

56/ #Saturn's axis is tilted like Earth, so it has solstices/equinoxes. At Equinox, the rings are parallel to the plane of Saturn's orbit

57/ @CassiniSaturn was there in Aug2009 at the moment of Equinox and snapped this image. Can you find the shadow of the Rings? #GrandFinale

58/ With #Saturn at Equinox, the rings were seen as edge-on. And the rings are insanely flat. It's incredible how flat they actually are

59/ The rings are 160,000 km wide and less than 1km thick, even as little as 10m thick at some points. 10 metres! #grandfinale

60/ That's a 1:160000 ratio. regular paper has a ratio of 1:2794. Making the #rings of #saturn technically flatter than a piece of paper

61/ Look at that! The rings are SO flat. During Equinox, Earth can see this but @CassiniSaturn was able to do many ring crossing orbits

62/ Since #Saturn's rings are so flat, even small irregularities are easily visible at #Equinox, because they cast long shadows #GrandFinale

63/ in the previous image, the shadows cast on the rings are being created by structures within the rings that are 2.5 km high #GrandFinale

64/ Look at THIS one! Holy. The shadow is 36 km long cast by an object about 300 metres in diameter embedded within the rings #GrandFinale

65/ One of the coolest things @CassiniSaturn found in the rings were propeller features. Like the "Earhart Propeller" #GrandFinale

66/ There are so many of them! propellers everywhere #GrandFinale

67/ This one is called the "Santos-Dumont" after the Brazillian-French aviator

68/ Celui-ci porte le nom "Blériot;" l'aviateur français. Mais, quelle sont leur origine? #GrandFinale

69/ Here's a much larger and more dramatic example that @CassiniSaturn found, hinting at the origins of all the propellers #GrandFinale

70/ They're Moonlets! Tiny little moons that live in the rings of #Saturn. The previous image is that of the moon Daphnis #GrandFinale

71/ A closer image of Daphnis. Its gravitational influence has carved out the Keeler Gap and continues to influence the edges #GrandFinale

72/ A zoom-out of Daphins. It is next to the F ring, which ALSO sports gravitational perturbations by the moon Prometheus #GrandFinale

73/ Here's Prometheus making its mark on the wispy F ring. Look at that! It's beautiful! #GrandFinale

74/ also, is it just me, or when you hear 'Prometheus' do you think...

75/ ...back to the MOON Prometheus, here's an awesome gif of the little moon 'Shepherding' the F ring @CassiniSaturn #GrandFinale

76/ Here's another, Prometheus on the right, and the moon Pandora is on the left. The F ring in the middle #GrandFinale

77/ yup you read that right, Prometheus and Pandora both orbit Saturn. Bet you didn't know Aliens and Avatar were set in the same universe..

78/

79/ My movie sleuthing powers aside, here's a close up image of Prometheus. It's a tiny moon just 86x53km, F ring in background #GrandFinale

80/ Here's the entire ring structure... A mosaic with every ring, gap, and the distance scale along the bottom #GrandFinale

81/ The Encke Division is 300 km wide and has a tiny moon named Pan (20 km wide) within it. More gravitational perturbations #GrandFinale

82/ Perhaps my *favourite* image of the rings is this one: showing waves in the rings produced by the moon Janus' 2:1 orbital resonance

83/ Okay onto some other stuff. How about Mimas, the "Death star Moon." @CassiniSaturn snapped this shot in 2010 #GrandFinale

84/

85/ Mimas, roughly 400km wide, sports a *massive* impact crater, called Herschel, 140 km wide. It's 30% the width of the Moon! #GrandFinale

86/ The @CassiniSaturn Equinox Mission wrapped up in 2010, but have no fear, the mission was extend to Sept 2017 #GrandFinale

87/ This would take @CassiniSaturn through to summer solstice in the northern hemisphere, making the mission last a half a Saturnian year

88/ After hearing @CassiniSaturn was extended for another 7 years, planetary scientists were reached for comment:
#GrandFinale

89/ Just AFTER the mission extension in 2010, now officially called the Cassini Solstice Mission, THIS HAPPENED: #GrandFinale

90/ known as the Great White Spot, this storm is larger than Earth, and appears on #Saturn semi-periodically every 28.5 years #GrandFinale

91/ As #Saturn rotated, the storm stretched around the planet and, after a year, eventually engulfed itself in late 2011 #GrandFinale

92/ FYI, @CassiniSaturn is only 630000km frm #Saturn right now. 15 hrs away from burning up in the atmosphere #GoodbyeCassini #GrandFinale

93/A beautiful quintet of moons: Janus, Pandora, Enceladus, Rhea, and Mimas floating in the gravity of Saturn #GrandFinale #GoodbyeCassini

94/ This image was the result of the "Scientist for a Day" contest @NASA ran in Oct 2013. A high orbit over the north pole #GrandFinale

95/ because it was getting closer to summer solstice, the entire north pole is now visible. And LOOK at wind pattern #GrandFinale

96/ It's a hexagon! ... like... the wind seems to turn at sharp angles.... does wind do that? ... Power Rangers, what do you think?

97/ Here's a full top-down video of the pattern at the north pole. There are some good working hypotheses on why the wind does this, but

98/ ... Planetary scientists are still working it out. #GoodbyeCassini #GrandFinale

99/ On June 21, 2010 @CassiniSaturn made its closest flyby of #Titan to date, travelling to within 880km of the surface #GrandFinale

100/ I stacked a set of R,G,B images @CassiniSaturn took of that flyby to make this true colour image of #Titan #GrandFinale

101/ FYI, @CassiniSaturn has now taken its last images EVER of #Saturn and we're downloading the data via the DSN deepspace.jpl.nasa.gov

102/ From now until it burns up (abt 12 hrs from now) @CassiniSaturn will continuously broadcast back to Earth #GoodbyeCassini #GrandFinale

103/ people, It's starting to set in now... @CassiniSaturn is almost gone #GoodbyeCassini #GrandFinale

104/ So anyway, Summer solstice finally arrived for the Northern Hemisphere on #Saturn in May of this year! #GrandFinale #GoodbyeCassini

105/Now check this out, the north polar region COMPLETELY changed colour. Left: 2017, Right: 2013. More sunlight changes things!#GrandFinale

106/ okay #Saturn fans, want to see a really weird moon? (of course you do) #GrandFinale #GoodbyeCassini

107/ twitter, meet Hyperion. One of #Saturn's moons about 300 km in size . @CassiniSaturn did a couple flybys of it, most recent in 2015

108/ #Hyperion looks more like a chunk of coral than a moon. Seriously, here it is next to a piece of coral, can you tell which is which?

109/ Hyperion has a porosity of 40%. That means 40% of its total volume is ... empty. It's likely a conglomeration of smaller moonlets

110/ Over the summer, @CassiniSaturn flew over the North/South pole of #Saturn. Here's an RGB stack I did of the North Hexagon #GrandFinale

110/ Here's the same image stack, but closer to what the eye would see if you were there #GoodbyeCassini #GrandFinale

111/ This is another angle of the North Polar Hexagon. There's so much texture. So many clouds, storms.. #GoodbyeCassini #GrandFinale

112/ okay want to see another weird moon?

113/ For those following this thread since the beginning (clearly everyone), I said Iapetus' equatorial ridge feature will come back 'round

114/ Whelp.. BEHOLD the mother of all equatorial ridges. Atlas: the moon that is just one big equatorial ridge #GrandFinale #GoodbyeCassini

115/ Yes, that is what Atlas looks like. It's being affectionately called one of #Saturn's "Walnut Moons" (yes... plural)

116/ Meet the rest of the gang: Atlas (the big bro), Pan (the wild one), and Daphnis (the baby). They are the "Walnut Moons" of #Saturn

117/ yes... I gave the Walnut Moons Boy Band personalities.... What of it?

118/ Look at THIS image. It's insane. The differing colours of the hemispheres and paper-thin rings dissecting at the equator. #GrandFinale

119/ Okay now's the time to talk about why the #GrandFinale. Why destroy the @CassiniSaturn spacecraft?

120/ First off, @CassiniSaturn has run out of fuel. Very soon it would be impossible to change the trajectory of the craft.

121/Second, both #Enceladus and #Titan have VERY interesting chemistry happening on them. The former is a great place to go looking for LIFE

122/ Third, it's possible, however unlikely, that @CassiniSaturn could have Earth bacteria still aboard. Now let's add this up #GrandFinale

123/ You don't want your possibly contaminated spacecraft, that's dead in the water, to accidentally crash into Enceladus/Titan

124/ because it's possible, however unlikely, that you could contaminate/destroy any extraterrestrial life that exists there

125/ Thus, you have only one choice. The spacecraft must be destroyed. #ElrondWouldBeProud #GoodbyeCassini #GrandFinale

126/ The best way to destroy your spacecraft is by purposefully burning it up in the atmosphere of #Saturn. À la Galileo and #Jupiter

127/ And if you're going to destroy your spacecraft anyway, why not take some risks?

128/ Hence, the #GrandFinale: 22 orbits that dive between the Saturn and the rings. A gap that is only 8000 km wide, previously unexplored

129/ The @CassiniSaturn team didn't know what to expect, and on the first dive through the gap they found it to be completely empty!

130/ They measured the number particles that hit @CassiniSaturn as it passed through the gap. The result: very few! jpl.nasa.gov/spaceimages/de…

131/ And in the last few orbits, @Cassini has been so close to the clouds of #Saturn, it has actually been able to SAMPLE it #GrandFinale

132/ A few days ago, #Titan gave @CassiniSaturn a "Goodbye Kiss," a final distant flyby. Here's an image from that flyby. #GoodbyeTitan

133/ Not only was it a good bye, but @CassiniSaturn also took a gravitational nudge that sent it on its current trajectory... to burn up

134/ Here's a great graphic from one of the dives through the gap, showing @CassiniSaturn's POV as well as a cool video #GrandFinale

135/ in 8 hrs, @CassiniSaturn will burn up in the atmosphere over #Saturn. One of the most impressive and productive spacecrafts ever built

136/ I wish I was at @NASAJPL with @Astropartigirl and the other cool #NASASocial peeps following @CassiniSaturn's plunge #GoodbyeCassini

137/ oh I forgot about #Saturn's Aurora! These images were taken on June 21, 2005. New shots of the Southern Lights! #GrandFinale

138/ during a 2006 flyby of #TItan, @CassiniSaturn found a massive cloud at the North Pole of the Moon #GrandFinale #GoodbyeCassini

139/ The south polar vortex of #Saturn, imaged by @CassiniSaturn in 2008

140/ this one's known as 'The Rose,' a beautiful false colour image of the north polar vortex. It has insane detail... crazy #GoodbyeCassini

141/ almost there. 7hrs to go. About 350,000km away from burning up. That's the distance from the Earth to the Moon. #GoodbyeCassini

142/ I've run out of stories about @CassiniSaturn that I know... just posting images and counting down the minutes #GoodbyeCassini

143/ Holy crap check out #Saturn's clouds in this. Made frm Infrared images, and false coloured. Looks like a watercolour. cred: @kevinmgill

144/A VIDEO of Aurora on #Saturn. I didn't even know this existed! @CassiniSaturn took 472 images during an 81-hour period in 2008 for it

145/ Good morning all, I wake to a very sombre tone on the twitterverse. In T-1hr, @CassiniSaturn will burn up over the skies of #Saturn

146/ Of course we won't know for another 90min or so due to light travel time. #GoodbyeCassini #GrandFinale

147/@CassiniSaturn launched in1997. I turned 12 the day after it left Earth. For me, it has always been part ofthe solar system #GrandFinale

150/ Who stayed up all night at the #NASASocial down at JPL?? #GoodbyeCassini #GrandFinale

151/ Overnight, the DSN dishes in Canberra were given the @CassiniSaturn feed. Downloading constantly until the craft is gone #GrandFinale

152/Canberra is also listening to @NASAVoyager 2 at the moment, as you can see in the previous image. Two Titans of solar system exploration

153/ Getting close! only 100,000 km away from #Saturn. and @CassiniSaturn is continuously broadcasting data until it burns up #GrandFinale

154/ it's 6:30am EDT, the projected time for #Saturn atmospheric entry. This is @CassiniSaturn right now #GoodbyeCassini #GrandFinale

155/Right now in a sky 1.5 billion kilometres away, a small emissary from Earth is falling apart. Ending a 20 year long mission #GrandFinale

156/Due to the distance, the last transmission from Cassini won't be downloaded by the Deep Space Network until 7:55am EDT #GrandFinale

157/ A little more time, for those of us not ready to say #GoodbyeCassini. What? I'm not crying ... YOU'RE crying... #GrandFinale

158/ Cassini, a piece of humanity, has become a piece of #Saturn. We'll be forever grateful, and forever proud of what it's accomplished

159/ Just finished chatting with @HallieCBC at @CBCRadioCanada about Cassini's final moments and legacy #GrandFinale

160/one of the last images sent back frm Cassini last night. Searching for propeller features, can you see any? #GoodbyeCassini #GrandFinale

161/ Taken last night in its final image dump, a beautiful image of the F ring and Pandora or Prometheus, can't tell which. #GoodbyeCassini

162/ OH! There's one, a propeller feature! See it? Image taken Sept 14, 2017 6:17pm, Received Sep. 15, 2017 6:17am #GrandFinale

163/ "Cassini has changed the paradigm of where we might look for life, that will be one of her legacies" -Linda Spilkner #GrandFinale

164/ A final distant image of Daphnis, the moon that created the Keeler Gap. The moon disrupts the portions of the rings closest to it

165/ Cassini took this image in the direction it was travelling about 12 hrs before it burned up. It's looking at it's final resting place

166/ We're only a few minutes away until the Loss of Signal for @CassiniSaturn #NASASocial #GoodbyeCassini #GrandFinale

167/ "The entire spacecraft runs on 600W" "about half a hair dryer"'s worth of power. That's crazy! #GrandFinale

168/ "We have loss of signal" -@CassiniSaturn team. right on time 7:55 #GoodbyeCassini #GrandFinale

169/ "I hope you're all deeply proud of this amazing accomplisment" -Earl Maize, the Cassini Project Manager to his team #GrandFinale

170/Well I guess Ill leave it there. I've had the funnest week reliving the mission via this string of tweets #GrandFinale

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