Tag Archives: Cassini

Titan’s Southern Sea

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Titan_southern_seaOr what’s left of it. The red outline traces the ancient shoreline. The largest remaining lake in Titan’s southern hemisphere, Ontario Lacus appears as black within that basin. The black indicated that it is filled with liquid.

This picture is assembled from images was obtained by the Cassini spacecraft’s radar instrument during July, 2009, and January, 2010. Mission scientists estimate the ancient sea was possibly as large as 475 X 280 km across but probably only a few hundred meters deep. Ontario Lacus is about 80 X 235 km and probably on the order of 10 meters deep. Seas may have covered large parts of Titan’s southern hemisphere less than 50,000 years ago.

Titan, Saturn’s largest moon, is the only body in the Solar System other than the Earth that has large open bodies of liquid. The temperature on Titan runs around 94 K (about -290 °F), so that liquid is not water. It’s methane and ethane. While over one hundred lakes and three seas are seen around Titan’s north pole, the south pole only has a few small lakes. It’s been suggested that cycles similar to Milankovich cycles on Earth cause long-term transfers of liquid hydrocarbons between the poles and that it’s now the north poles turn to keep the bulk of the liquids. Less than 50,000 years ago, the cycle may have reversed, nearly emptying the southern seas.

Image Credit: NASA

Thunder and Lightning on Saturn

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head_to_tailThis collection of images from the Cassini spacecraft orbiting Saturn shows the evolution of a massive thunder storm that circled all the way around the planet and fizzled out when it ran into its own tail. The storm was first detected on 5 December, 2010. It developed a head of bright clouds which began rapidly moving west and also spawned a much slower moving clockwise-spinning vortex.

The bright clouds at the head of the storm are indicated with red triangles. Yellow triangles mark the vortex.

The top image was taken not long after the start of the storm on 22 January, 2011. It shows the bright head of the storm just ahead of the vortex by about 40,000 km. The next image from 5 May shows that the head of the storm had traveled around the planet and started approaching the vortex from the east. The storm’s body had stretched over 220,000 km, and the head was within about 80,000 km of the vortex. That image also shows that the  vortex was losing steam compared to the head of the storm. The third image was taken on 14 June. The head of the storm had made its way roughly 290,000 km—almost entirely around the planet, and it was about to catch up with the vortex. The head of the storm was just 14,000 km east of the vortex. The bottom image, from 12 July, 2011, shows that the storm fizzled once the head and vortex met. Only the vortex remains; the bright cloud has disappeared. By late August, the storm stopped generating lightning for good.

These are false color images with the colors denoting the altitudes of the clouds. Red data is from a wavelength of radiation that penetrates the atmosphere deep down to the top of the tropospheric cloud deck (750 nm). Green represents an intermediate wavelength above the troposphere (728 nm). Blue is for a wavelength that penetrates only to the top of tropospheric haze (890 nm). White is for thick clouds at high altitudes.

Image Credit: NASA

Beautiful Plumage

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If you google “beautiful plumage,” the first hit is the YouTube video of the Monthy Python Dead Parrot sketch. That’s what I first thought of when I saw the headline on the NASA site for this photo of Saturn’s moon Enceladus. I had to chuckle.beautiful_plumage

This copy is from NASA’s caption of the picture—

Like a proud peacock displaying its tail, Enceladus shows off its beautiful plume to the Cassini spacecraft’s cameras.
Enceladus (313 miles, or 504 kilometers across) is seen here illuminated by light reflected off Saturn.
This view looks toward the Saturn-facing side of Enceladus. North on Enceladus is up and rotated 45 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 18, 2013.
The view was acquired at a distance of approximately 483,000 miles (777,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 173 degrees. Image scale is 3 miles (5 kilometers) per pixel.

Image Credit: NASA

Saturn and Meteors

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Saturn_meteorsThe solar system is full of small, speeding objects. These objects frequently pummel planetary bodies. Saturn’s rings are the only location besides Earth, the Moon, and Jupiter where astronomers have been able to observe impacts as they occur. The meteoroids at Saturn are estimated to range from about a centimeter up to several meters in size. NASA’s Cassini spacecraft has found the first direct evidence of small meteoroids breaking into streams of rubble as they crashed into Saturn’s rings.

The Saturnian equinox in summer 2009 was an excellent time to see the debris kicked up by meteoroid impacts. The very low sun angle on the rings caused the clouds of debris to stand out brightly against the darkened rings. The tiny particles forming these clouds have a range of orbital speeds around Saturn, and the clouds they form are pulled into diagonal, extended bright streaks as can be seen in the five pictures above.

The objects hitting the rings in these photos were probably roughly the same size as the Russian meteor of last February.

Image Credits: NASA

Jupiter from Saturn

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Jupiter_from_SaturnThis is Jupiter as seen from Saturn’s orbit by the Cassini spacecraft. Cassini‘s cameras were specially designed to photograph the nearby bodies in the Saturn system, but as this image demonstrates, the cameras are pretty good telescopes. At the time this picture was taken, the distance to Jupiter was more than 11 times the distance between Earth and the Sun, a range of around 1.8 billion kilometers from Jupiter, or slightly farther than the average Earth-Saturn distance. Scale in the original image was about 10,000 kilometers per pixel—the Earth would show up as a single pixel at that scale.

Images taken using red, green and blue spectral filters were combined to create this natural color picture. The picture was contrast enhanced and magnified by a factor of two and a half to enhance the visibility of cloud features on the planet.

Image Credit: NASA

Clouds on Titan

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IDL TIFF fileUsing a filter sensitive to near infrared light (938 nm), the Cassini spacecraft peered through the haze in Titan’s equatorial region down to its surface. It also caught a vortex of clouds hovering over the moon’s south pole (just to the right of the terminator on the moon’s dark side). The lit terrain seen here is on the Saturn-facing hemisphere of Titan. North on Titan and rotated 11 degrees to the left of up in this picture.

Image Credit: NASA

Moons

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moons_SaturnRhea, Enceladus, and Dione are three of Saturn’s moons.  This is what they looked like as seen from the Cassini spacecraft on 25 April, 2011. Saturn is also present in the picture on the left but is too dark to see. Rhea is closest to Cassini. It is the largest moon in center of the image. Enceladus is to the right of Rhea. Dione is to the left of Rhea and is partially covered by Saturn.

Image Credit:  NASA

Morning Star

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Venus was one of the morning stars last month. It has moved back into the glow of the Sun and will become an evening star in April. Here’s an unusual view of Venus as a morning star.Venus from Saturn 2

In this picture from NASA’s Cassini spacecraft dawn on Saturn is greeted by Venus. The inner planet appears just off the edge of Saturn in the upper right, directly above the white streak of Saturn’s G ring. Saturn’s E ring is also visible, looking blue because of the scattering properties of the dust that comprises the ring. The bright spot near the E ring is a distant star.

Another image of Venus and Saturn was taken when Cassini flew through the shadow of Saturn. This allowed the spacecraft to look back in the direction of the Sun and Venus and to take a backlit image of Saturn and its rings in a particular geometry which reveals details about the rings and Saturn’s atmosphere that cannot be seen at lower viewing angles. Venus can be seen through the rings.Venus from SaturnImage Credit: NASA

A Reflection from Titan

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titan_lake_flashThis image shows a flash of sunlight reflected off a lake on Titan, Saturn’s largest moon. Its northern hemisphere is shrouded in darkness for nearly 15 years, but the sun begins to illuminate the area again as it approaches its spring equinox. The Cassini spacecraft was able to detect the glint at the beginning of Titan’s spring in 2009. The moon’s hazy atmosphere scatters and absorbs many wavelengths of light, including most of the visible spectrum. But an onboard instrument was able to detect the glint in infrared wavelengths that can penetrate through Titan’s atmosphere. This image was created using wavelengths of light in the 5 µm range.

Image Credit: NASA

Moons at Work

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moons_at_workSaturns rings are divided into distinct bands. The Saturnian moons Prometheus and Pan are both caught “shepherding” their respective rings in this image (click the image to embiggen it). Through their gravitational effect on nearby ring particles, one moon maintains a gap in the outer A ring, and the other helps keep another ring narrowly confined.

Prometheus (86 km across) and its partner Pandora (not seen here), maintains the narrow F ring seen at the bottom left in this image. Pan (28 km across) clears the Encke gap in as it moves along the gap’s center. The other bright dot near the inner edge of the Encke gap is a star in the background.

Image Credit: NASA

Titanic Craters

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titan_cratersTitan is the only moon in the solar system with a thick atmosphere, and the only world besides Earth known to have lakes and seas on its surface. However, with a frigid surface temperature of around -290° F (94 K), the rain falling on Titan isn’t water. It’s liquid methane and ethane, compounds that are gases at room temperature on Earth.

Most of Saturn’s moons display their ancient faces pockmarked by thousands of craters. Titan, Saturn’s largest moon, looks younger than it really is because its craters are being eroded. Radar observations by the Cassini spacecraft show that dunes of hydrocarbon sand are filling in the craters.

This image taken with the Cassini radar shows two craters on Titan. On the left is crater Sinlap which is a relatively ‘fresh’ crater, with a depth-to-diameter ratio similar to is found on other large moons in the solar system such as Ganymede. One the right is Soi, an extremely eroded crater with a very small depth compared to similar craters on Ganymede. These craters are both about 80 km (almost 50 miles) in diameter.

Image Credit: NASA

 

Saturn in Infrared

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saturn_in_IRThis image was assembled from data collected in near-infrared wavelengths of light by the Cassini spacecraft. Blue indicates sunlight reflected at a wavelength of 2 µm, green to indicate sunlight reflected at 3 µm, and red to indicate thermal emission from the planet at 5 µm. Saturn’s rings reflect sunlight at 2 µm, but not at 3 or 5 µm, so they appear deep blue. Saturn’s high altitude haze reflects sunlight at both 2 and 3 µm, and so it appears green to blue-green. The heat emissions from the interior of Saturn are only seen at the 5 µm wavelength in the data; they appear red. The large dark band is the shadow of the rings, but the other dark spots and banded features in the image are clouds and small storms that outline the deeper weather systems and circulation patterns on Saturn. They are backlit by Saturn’s thermal emission, appearing in silhouette.

Image Credit: NASA

You’re On That Small Blue Dot

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newrings_cassiniBack in 2006, the Cassini spacecraft orbiting Saturn drifted in giant planet’s shadow and looked back toward the eclipsed Sun. Saturn’s rings lit up so much that new rings were discovered, although they are hard to see in this image. Saturn’s E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus and the outermost ring visible above, does show up in vivid detail. Far in the distance, at about 10 o’clock on the left, just above the bright main rings, is the almost ignorable pale blue dot of Earth. You may have to click on the image to embiggen it in order to see the Earth.

Image Credit: NASA

Tiny Tethys

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Tiny_TethysSaturn’s rings appear to dwarf Tethys (1,062 km or 660 mi across), which appears as a small dot at the upper left edge of the picture, although astronomers believe the moon is probably many times more massive than the entire ring system combined. This view looks toward the unilluminated side of the rings from about 18 degrees below the ringplane. The image was taken in green light with the Cassini spacecraft wide-angle camera in August, 2012. The view was acquired at a distance of approximately 2.4 million km (1.5 million mi) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 63 degrees. If you click on the image to embiggen it, the scale is 138 km (86 mi) per pixel.

Image Credit: NASA

Angled Saturn

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The Cassini spacecraft took this angled view toward Saturn in near infrared, showing the southern reaches of the planet with the rings on a dramatic diagonal. North on Saturn is up and rotated 16 degrees to the left. This view looks toward the southern, shadowed side of the rings which cast wide shadows on the planet’s southern hemisphere.

The moon Enceladus (about 500 km across) appears as a small, bright speck in the lower left of the image.

Image Credit: NASA

Tethys and the Rings

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We have no idea how old Saturn’s rings are. One possibility is that the rings were formed relatively recently in our Solar System’s history. It could be that only 100 million or so years ago a moon-sized object broke up near Saturn. One bit of evidence for young rings is the fact that the rings are so bright and relatively unaffected by numerous small dark spots caused by meteor strikes. However, a recent discovery raises the possibility that some of Saturn’s rings could be billions of years old—almost as old as Saturn itself. Inspection of images taken by the Saturn-orbiting Cassini spacecraft indicates that some of Saturn’s ring particles temporarily bunch and collide, effectively refinishing the surfaces of the ring particles by uncovering fresh bright ices. This picture taken by Cassini shows Saturn’s rings in their true colors. Tethys, one of Saturn moons, is visible in front of the darker rings.

Image Credit: NASA

Saturn, Titan, and Changing Seasons

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This picture is a mosaic of six images—two each via red, green and blue spectral filters—combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on 6 May, 2012. The view looks toward the northern, sunlit side of the rings from just above the ring plane.

The giant moon Titan is silhouetted in front of Saturn as the planet is changing seasons. Titan, Saturn’s largest moon, measures 35,150 km across and is larger than the planet Mercury. It could have been a planet if it were on its own.

Saturn’s southern hemisphere, in its approach to winter, is taking on a bluish hue. This change seems to be caused by a reduced intensity of ultraviolet light. UV produces haze in Saturn’s atmosphere, and the increasing intensity of ultraviolet light in the hemisphere approaching summer causes the increase in haze. The presence of the ring shadow in the winter hemisphere enhances this effect. The reduction of smog and the consequent clearing of the atmosphere makes for a bluish hue. The presence of methane, which generally absorbs in the red part of the spectrum, in a now clearer atmosphere also enhances the blue. A different mechanism, the increased opportunity for direct scattering of sunlight by the molecules in the air, makes the sky blue, as on Earth.

Image Credit: NASA

The Jet Streams of Saturn

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A particularly strong jet stream can be seen churning through Saturn’s northern hemisphere in this false-color view from NASA’s Cassini spacecraft. The jet stream’s clouds can be seen in the upper right about a third of the way down from the top of the picture. They show up as a thin, bright orange line. Moving west (closer to the center of the image), the stream drops south. Farther to the west of the jog, blurrier jet stream clouds move along.

The winds of Saturn’s jet streams are zonal, that is, they move eastward or westward depending on latitude. This jet stream is located at about 42 degrees north latitude, and was first detected by the Voyager spacecraft. In the Voyager days, this jet stream had an undulating appearance, leading scientists to dub it the “ribbon wave.” Because the planet’s atmosphere is always changing, this jet stream now looks nothing like a ribbon.

Saturn’s atmosphere and its rings are shown here in a false color composite made from three images taken in near infrared light through filters that are sensitive to varying degrees of methane absorption. Red and orange colors in this view indicate clouds that are deep in the atmosphere. Yellow and green colors, most noticeable near the top of the view, indicate intermediate clouds. White and blue indicate high clouds and haze. The white clouds of the equatorial region appear oversaturated because the picture was processed to bring out the wave. The rings appear bright blue because they are outside of the atmosphere; they are not affected by methane absorption.

Image Credit: NASA

Titan and Tethys

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The Cassini spacecraft snapped this picture of a pair of Saturn’s moons, giant Titan beyond smaller Tethys. This view looks toward the Saturn-facing sides of the moons. Titan is about 5,150 km in diameter,  and Tethys is roughly 1,060 km across.

This picture was taken in visible green light with the spacecraft’s narrow-angle camera on in October, 2010. Titan is about 2.5 million km (2.5 Gm) from Titan. Tethys is only about1.5 million km away. If you click on the picture to embiggen the image, the scale is 15 km per pixel on Titan and 9 km per pixel on Tethys.

Image Credit: NASA

The Vortex of Titan

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Something’s going on over the south pole of Titan. A vortex of haze appears to be forming, but no one can explain why. This natural-color image shows the light-colored vortex which was found on images taken last month when the Cassini spacecraft flew by the largest of Saturn’s moons. Cassini is now able to see the southern vortex because its orbit around Saturn was recently boosted out of the plane of the orbits of the rings and moons. Clues about the odd feature are being gathered, but it will soon be winter in the southern hemisphere of Titan. The vortex, if it lasts, will be in darkness for the next few years.

Image Credit: NASA

Saturn in IR

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In this Visual and Infrared Mapping Spectrometer (VIMS) mosaic image captured by the Cassini spacecraft, Saturn’s famous rings are nearly invisible as seen edge-on across picture’s center. To the right (day side) of the terminator, the blue-green hues are visible sunlight reflected from Saturn’s cloud tops. On the left (night side), the lantern-like glow of infrared radiation from the planet’s warm interior backlights features at Saturn’s deeper cloud levels. The infrared glow also shines from beneath the broad shadows of Saturn’s rings sweeping across the planet’s upper hemisphere.

Image Credit: NASA