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Views of Moons

NASA’S CASSINI SPACECRAFT, in orbit around the planet Saturn, has been sending back some wonderful views of its moons. In particular, it has captured images where one moon seems to float in front of the other. Here we present a selection of recent images.

Cassini image of Titan and Tethys

Can you tell which of these moons in the foreground? It's Titan, the large one (diameter 5,150 kilometres; bigger than our Moon) with the orange atmosphere, with smaller, shiny, icy Tethys in the background. Titan was 2.3 million kilometres from Titan, and 3.4 million from Tethys when it took this image. Saturn's rings can be seen edge-on in the distance.

Cassini image of Rhea and Titan

This black-and-white image shows the moon Rhea (1,528 km diameter) in front of Titan. Cassini was 2 million kilometres from Titan and 1.3 million kilometres from Rhea when it took this image.

Cassini image of Titan and Dione

This view shows Titan again, this time with the much smaller moon Dione (1,123 km diameter) peering around from behind, with Saturn and its rings (edge-on) in the background. Cassini was 2.3 million kilometres from Titan and 3.2 million kilometres from Dione when it took the image. The haze that surrounds Titan can clearly be seen. Titan has a mostly nitrogen atmosphere that extends far from the surface. The surface pressure is about 1.5 times that on Earth.

Cassini image of Titan

In this view, Titan appears to float in front of Saturn and its rings. Titan is not only the second-largest moon in the Solar System; it's also about 300 kilometres wider than the planet Mercury!

More information: Cassini mission

Story by Jonathan Nally. Images courtesy NASA / JPL-Caltech / Space Science Institute.

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New images of an icy world

Cassini image of Rhea

NASA's Cassini spacecraft took this raw, unprocessed image of Saturn's moon Rhea on March 10, 2012. The camera was pointing toward Rhea from a distance of approximately 41,873 kilometres.

THESE RAW, UNPROCESSED IMAGES of Saturn’s second largest moon, Rhea, were taken on March 10, 2012, by NASA’s Cassini spacecraft. This was a relatively distant flyby with a close-approach distance of 42,000 kilometres, well suited for global geologic mapping.

At 1,530 kilometres diameter, Rhea is the ninth-largest moon in the Solar System.

During the flyby, Cassini captured these views of the moon’s cratered surface, creating a 30-frame mosaic of Rhea’s leading hemisphere and the side of the moon that faces away from Saturn.

The observations included the large Mamaldi (480 kilometres across) and Tirawa (360 kilometres across) impact basins and the 47-kilometre-wide “ray crater”Inktomi, one of the youngest surface features on Rhea.

Cassini image of Rhea

This second raw, unprocessed Cassini image of Rhea was taken from a distance of approximately 42,258 kilometres, and shows the moon's icy, cratered surface. The streaks on the right are an artefact of the imaging.

Cassini image of Rhea

Shadows help to give a 3D effect to Rhea's craters in this raw, unprocessed Cassini shot taken from a distance of approximately 42,096 kilometres.

Cassini image of Rhea

This raw, unprocessed shot was taken from much further away, approximately 115,060 kilometres, and shows Rhea's "terminator"—the dividing line between day and night.

Cassini has been investigating Saturn and its moons since 2004. This included dropping a probe called Huygens onto the surface of Saturn’s largest moon, Titan, in 2005. Launched in 1997, Cassini-Huygens mission is a co-operative project of NASA, the European Space Agency and the Italian Space Agency.

See all of Cassini’s raw images at NASA’s Saturn page.

Adapted from information issued by NASA / JPL-Caltech / SSI.

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Gallery – Quintet of Saturnian moons

Five of Saturn's moons

Five of Saturn's moons can be seen in this image taken by NASA's Cassini spacecraft.

A QUINTET OF SATURN’S MOONS can be seen in this view taken by the Cassini spacecraft.

Janus (179 kilometres wide) is on the far left. Pandora (81 kilometres) orbits between the A ring and the thin F ring near the middle of the image. Brightly reflective Enceladus (504 kilometres) appears above the centre of the image. Saturn’s second largest moon, Rhea (1,528 kilometres), is bisected by the right edge of the image. The smaller moon Mimas (396 kilometres) can be seen beyond Rhea also on the right side of the image.

This view looks toward the northern, sunlit side of the rings from just above the ringplane. Rhea is closest to the camera. Saturn’s rings are beyond Rhea and Mimas. Enceladus also is beyond the rings.

The image was taken with the Cassini spacecraft narrow-angle camera on July 29, 2011. The view was acquired at a distance of approximately 1.1 million kilometres from Rhea and 1.8 million kilometres from Enceladus.

Adapted from information issued by NASA / JPL-Caltech / Space Science Institute.

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Trio of Saturnian moons

Three of Saturn's moons

Three of Saturn's moons captured by NASA's Cassini spacecraft. From left: Dione, Rhea and Enceladus.

NASA’S CASSINI SPACECRAFT snapped this image of three of Saturn’s moons and part of the planet’s rings.

Saturn is not illuminated in this image, but it can be detected as the dark patch on the left that lies behind the foreground rings but in front of the background rings. It also partially obscures the moon on the left.

That moon is Dione (1,123 kilometres wide), around 3.1 million kilometres from Cassini when this image was taken.

In the foreground is Rhea (1,528 km wide). It is closest to the camera, at a distance of about 2.2 million kilometres.

The third moon, on the right, is Enceladus (504 km wide), seen at a distance of about 3 million kilometres.

Enceladus is the source of much interest at the moment, as Cassini’s instruments have detected huge plumes of salty spray shooting up from cracks near it’s south pole, suggesting a liquid ocean lies beneath the frozen surface.

More information:

Cassini-Huygens mission

Cassini imaging team homepage

Story by Jonathan Nally, SpaceInfo.com.au. Images courtesy NASA / JPL / Space Science Institute.

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One image, five moons

Five of Saturn's moons in one image

Five of Saturn's moons appear in this single image taken by NASA's Cassini spacecraft.

NASA’s CASSINI SPACECRAFT snapped this image showing part of Saturn’s rings edge-on, and with five of the giant planet’s moons in the same frame.

The moon Rhea (1,528 kilometres in diameter) dominates the image, and is in the foreground of the tableau. Below it and appearing to sit on the rings, is Dione (1,123km wide). Dione is actually far in the background.

Just to the right of Dione is what looks like a small bump in the rings. This is actually Prometheus (86km wide), a “shepherd moon” that orbits Saturn along the inner edge of the F ring.

The tiny dot off to the right of the rings is Epimetheus (113km wide), and the larger moon right on the edge of the image is Tethys (1,062km wide). Epimetheus is very interesting, as it shares almost exactly the same orbit as another moon, Janus. In fact, their orbits are different by a factor of only 50 kilometres. And every now and then they come close together and swap positions!

Cassini was about 61,000 kilometres from Rhea when it took this image on January 11, 2011. Detail can be seen on Rhea down to about 2km per pixel.

Just so that you know what each of the moons looks like close up, here are images of them, also taken by Cassini.

Saturn's moon Rhea.

Saturn's moon Rhea.

Saturn's moon Dione.

Saturn's moon Dione.

Saturn's moon Prometheus.

Saturn's moon Prometheus.

Saturn's moon Epimetheus.

Saturn's moon Epimetheus.

Saturn's moon Tethys.

Saturn's moon Tethys.

Adapted from information issued by NASA/JPL/Space Science Institute.

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Saturn’s three-in-one

Image showing Rhea, Dione and Saturn's rings

This image shows two of Saturn's moons—Rhea (foreground, top) and Dione (background)—with the planet's famous rings in between.

THIS IMAGE ISN’T made up. It’s a real shot from NASA’s Cassini spacecraft, showing three components of the Saturnian system in the one frame.

In the foreground at top is the south polar area of Saturn’s moon Rhea. In the background is another moon, Dione, with Saturn’s almost edge-on rings in between.

Visible on Dione is its famous light-coloured ‘wispy’ terrain.

Rhea is 1,528 kilometres in diameter, and Dione is 1,123 kilometres wide.

At the moment the image was taken, on January 11, 2011, the Cassini spacecraft was about 61,000 kilometres from Rhea and 924,000 kilometres from Dione.

Detail down to a resolution of 358 is visible on Rhea, and to a resolution of six kilometres on Dione.

Story copyright 2011 Jonathan Nally, SpaceInfo.com.au. Image courtesy NASA / JPL / Space Science Institute.

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Moons with a view

NASA’s Cassini spacecraft has been orbiting Saturn since July 2004. The ringed planet has more than 60 moons, and Cassini has taken numerous images of them.

Sometimes, when the angles are just right, Cassini’s camera can fit more than one moon into its field of view—with one moon in the background and one in the foreground.

Many of the moons orbit near or within the planet’s famous rings, so the rings often appear in the images too.

Here’s a selection of recent shots showing some of Saturn’s natural satellites, large and small.

Rhea, Prometheus and Saturn's rings

In this view, the moon Rhea (1,530km wide) is on the far side of the rings. Much smaller Prometheus (86km wide) is on the nearside, orbiting between the main portion of the rings and the thin outer F ring. Camera distance to Rhea: approx. 1.6 million km. Camera distance to Prometheus: approx. 1 million km.

Dione and Titan

The cratered and cracked moon Dione (1,120km wide) seems to hang suspended in place in front of Titan (5,150km wide) in the background. Camera distance to Dione: approx 1.8 million km. Camera distance to Titan: approx. 2.7 million km.

Tethys and Dione

Dione, in the foreground of this image, appears darker than the moon Tethys (1,070km wide). Tethys appears brighter because it has a higher albedo than Dione, meaning Tethys reflects more sunlight. Camera distance to Dione: approx. 1.2 million km. Camera distance to Tethys: 1.8 million km.

Epimetheus and Janus

Saturn's moon Epimetheus (86km wide) moves in front of the larger moon Janus (179km wide) as seen by the Cassini spacecraft. Camera distance to Epimetheus: approx. 2.1 million km. Camera distance to Janus: 2.2 million km.

Janus and Prometheus

In this image, Janus is on the far side of Saturn's rings. Prometheus is on the nearside, orbiting in the gap between the main rings and the outer, thin F ring. Camera distance to Janus: approx. 1.1 million km. Camera distance to Prometheus: 1 million km.

Images courtesy of NASA / JPL / Space Science Institute.

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Saturnian moons line up

Image showing the moons Rhea and Epimetheus with Saturn and its rings in the background.

Image showing the moons Rhea and Epimetheus with Saturn and its rings in the background.

This amazing black and white image shows two of Saturn’s moons, Rhea and Epimetheus, against a backdrop of the planet and its rings.

Saturn has more than 60 known moons, each a different size and orbiting at different distances from the planet. They orbit at different speeds, and often overtake each other, leading to views like this when the Cassini spacecraft’s camera is pointed in the right direction.

Although they look close, the two moons are actually far apart. The view was obtained at a distance of approximately 1.2 million kilometres (746,000 miles) from Rhea, while Epimetheus is 400,000 kilometres further away at 1.6 million kilometres (994,000 miles).

The image gives a good indication of the scale of things in the Saturnian system. At 1,528 kilometres (949 miles) diameter, Rhea is by no means Saturn’s largest moon, yet it is more than one-tenth the width of Earth. Compare that with the huge bulk of Saturn in the background.

Epimetheus is tiny, only 113 kilometres (70 miles) wide.

At Cassini’s huge distance when it took this image, detail as small as 7 kilometres (4 miles) per pixel can be seen on Rhea, and 10 kilometres (6 miles) per pixel on Epimetheus.

Adapted from information issued by NASA / JPL / Space Science Institute.

Rings and moons

Cassini spacecraft image of Rhea, Prometheus and Saturn's rings.

Cassini spacecraft image of Rhea, Prometheus and Saturn's rings.

  • Rhea & Prometheus
  • Saturn’s rings seen edge-on
  • Images by the Cassini spacecraft

From just below the plane of Saturn’s thin rings, the Cassini spacecraft took this image of the rings edge-on with the planet’s second largest moon, Rhea, beyond.

Although Rhea may appear to be in the foreground of this image, it isn’t. The rings are closer. The small moon Prometheus, orbiting between the A ring and the thin F ring, is also visible within the rings near the upper middle of the image.

This view looks toward the Saturn-facing side of Rhea (1,528 kilometres wide) and the leading hemisphere of Prometheus (86 kilometres wide). This view looks toward the southern, unilluminated side of the rings from just below the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on January 31, 2010. The view was obtained at a distance of approximately 2.5 million kilometres from Rhea and approximately 2 million kilometres from Prometheus. Image scale is 15 kilometres per pixel on Rhea and 12 kilometres per pixel on Prometheus.

Adapted from information issued by NASA / JPL / Space Science Institute.