Scarred Janus

Spots on Janus

Facing Janus

Profile of Janus

Janus and Rings

Rugged Janus

Shadows of Janus

North on Janus

Janus: God of Beginnings

Mimas Occults Janus

Janus: Down South

The Two Faces of Janus

Two-Faced Janus

Janus Pole Crater

Janus Rides the Rings

Janus Ring Shadow Premiere

Two Lights on Two-faced Janus

Saturn rings appear curved in this view from NASA Cassini spacecraft, which also shows the moon Janus in the distance. Janus is at the bottom of the image and is farther from the spacecraft than the rings are.

Janus (111 miles or 179 kilometers across) seems to almost stare off into the distance, contemplating deep, moonish thoughts as the F ring stands by at the bottom of this image. From this image, it is easy to distinguish Janus' shape from that of a sphere. Many of Saturn's smaller moons have similarly irregular shapes that scientists believe may give clues to their origins and internal structure. Models combining the dynamics of this moon with its shape imply the existence of mass inhomogeneities within Janus. This would be a surprising result for a body the size of Janus. By studying more images of Janus, scientists may be able confirm this finding and determine just how complicated the internal structure of this small body is. This image is roughly centered on the side of Janus which faces away from Saturn. North on Janus is up and rotated 3 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 28, 2012. The view was obtained at a distance of approximately 54,000 miles (87,000 kilometers) from Janus. Image scale is 1,700 feet (520 meters) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18299

The irregularly shaped moon Janus keeps up its lonely orbit as seen by NASA Cassini spacecraft. Even though Janus shares its orbit with the moon Epimetheus, they never get very close to one another.

The Cassini spacecraft catches a glimpse of Janus, an irregularly shaped moon. Lacking sufficient gravity to pull itself into a round shape, Janus has had its lumpy primordial shape only slightly modified by impacts since its formation.

Janus, passing between the rings and NASA Cassini orbiter, poses for a snapshot taken by the spacecraft narrow-angle camera.

Janus floats above the meandering clouds of Saturn. A few of the large craters on the moon are just visible

The Cassini spacecraft provides this dramatic portrait of Janus against the cloud-streaked backdrop of Saturn

From hundreds of thousands of kilometers away, the Cassini spacecraft spies craters on the surface of the moon Janus.

In reality, Janus and the rings both orbit Saturn and are only weakly connected to each other through their mutual gravitational tugs. At specific locations in the rings, these gravitational tugs result in orbital resonances, which lead to some beautiful waves being created in the rings. See PIA10452 for an example. Janus is 111 miles, or 179 kilometers, across. This view looks toward the sunlit side of the rings from about 19 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 5, 2014. The view was acquired at a distance of approximately 1.2 million miles (2.0 million kilometers) from Janus and at a Sun-Janus-spacecraft, or phase, angle of 35 degrees. Image scale is 7 miles (12 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/pia18304

Shadows darken parts of some of Janus large craters as NASA Cassini takes a close look during its flyby of this Saturnian moon on March 27, 2012.

NASA Cassini spacecraft captures Saturn tiny irregular moon Janus surrounded by the vast, dark expanse of the outer solar system.

Janus, Saturn small moon named after the two-faced god, here displays two illuminated hemispheres taken by NASA Cassini spacecraft.

Saturn moon Janus, its rugged surface shown in shadow and light, passes before the planet rings in this image taken by NASA Cassini spacecraft.

A wide shadow is cast onto the thin F ring and the A ring by the moon Janus in this image taken as Saturn approached its August 2009 equinox.

NASA Cassini spacecraft looks toward the south pole and cratered surface of Saturn moon Janus in this image taken by the narrow-angle camera.

Janus and Tethys demonstrate the main difference between small moons and large ones. It's all about the moon's shape. Moons like Tethys (660 miles or 1,062 kilometers across) are large enough that their own gravity is sufficient to overcome the material strength of the substances they are made of (mostly ice in the case of Tethys) and mold them into spherical shapes. But small moons like Janus (111 miles or 179 kilometers across) are not massive enough for their gravity to form them into a sphere. Janus and its like are left as irregularly shaped bodies. Saturn's narrow F ring and the outer edge of its A ring slice across the scene. This view looks toward the unilluminated side of the rings from about 0.23 degrees below the ring plane. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Oct. 27, 2015. The view was obtained at a distance of approximately 593,000 miles (955,000 kilometers) from Janus. Image scale at Janus is 3.7 miles (6 kilometers) per pixel. Tethys was at a distance of 810,000 miles (1.3 million kilometers) for an image scale of 5 miles (8 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18353

Although Janus should be the least lonely of all moons -- sharing its orbit with Epimetheus -- it still spends most of its orbit far from other moons, alone in the vastness of space. Janus (111 miles or 179 kilometers across) and Epimetheus have the same average distance from Saturn, but they take turns being a little closer or a little farther from Saturn, swapping positions approximately every 4 years. See PIA08348 for more. This view looks toward the sunlit side of the rings from about 19 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 4, 2015. The view was acquired at a distance of approximately 1.6 million miles (2.5 million kilometers) from Janus and at a Sun-Janus-spacecraft, or phase, angle of 91 degrees. Image scale is 9 miles (15 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/pia18315

Pan and Janus

Janus in View

Saturn moon Epimetheus passes in front of Janus in this mutual

Sunlight passing through the Cassini Division between Saturn A and B rings sweeps across and illuminates the surface of the moon Janus in this image captured by NASA Cassini spacecraft. Go to the Photojournal to view the animation.

Janus peeks out from beneath the ringplane, partially lit here by reflected light from Saturn. A couple of craters can be seen on the moon surface. To the right, two faint clumps of material can be seen in the dynamic F ring

The Janus/Epimetheus Ring

Atlas, Pandora and Janus

The Cassini spacecraft eyes a prominent crater on the moon Janus.

The small moon Janus is almost hidden between the planet rings and the larger moon Rhea in this image captured by NASA Cassini spacecraft. The northern part of Janus can be seen peeking above the rings.

Saturn rings appear curved in this view from NASA Cassini spacecraft, which also shows the moon Janus in the distance. Janus is at the bottom of the image and is farther from the spacecraft than the rings are.

Cassini gazes down toward Saturn unilluminated ringplane to find Janus hugging the outer edge of rings

Seen from the unlit side of Saturn A ring, the shadow of the moon Janus is cast across the Encke Gap.

The shadow of the moon Janus crosses the Encke Gap as it strikes the plane of Saturn rings in this image taken as the planet approached its August 2009 equinox.

In their orbital ballet, Janus and Epimetheus swap positions every four years -- one moon moving closer to Saturn, the other moving farther away. The two recently changed positions

Saturn moon Janus orbits in front of the rings, which are partially darkened by the shadow of the planet in viwe from NASA Cassini spacecraft. Saturn shadow obscures about half the rings.

Saturn rings occupy the foreground of this image captured by NASA Cassini spacecraft. The small moon Janus appears to hover above, while the far larger moon Rhea is partially obscured by the rings.

Saturn moon Epimetheus moves in front of the larger moon Janus as seen by NASA Cassini spacecraft. The moons are lit by sunlight on the left and light reflected off Saturn on the right.

NASA Cassini spacecraft looks past the cratered south polar area of Saturn moon Rhea to spy the moon Dione and the planet rings in the distance. Dione wispy terrain can be seen on the trailing hemisphere of that moon.

This view from NASA's Cassini spacecraft shows a wave structure in Saturn's rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn's rings are much more tightly wound. In this case, every second wave crest is actually the same spiral arm which has encircled the entire planet multiple times. This is the only major density wave visible in Saturn's B ring. Most of the B ring is characterized by structures that dominate the areas where density waves might otherwise occur, but this innermost portion of the B ring is different. The radius from Saturn at which the wave originates (toward lower-right in this image) is 59,796 miles (96,233 kilometers) from the planet. At this location, ring particles orbit Saturn twice for every time the moon Janus orbits once, creating an orbital resonance. The wave propagates outward from the resonance (and away from Saturn), toward upper-left in this view. For reasons researchers do not entirely understand, damping of waves by larger ring structures is very weak at this location, so this wave is seen ringing for hundreds of bright wave crests, unlike density waves in Saturn's A ring. The image gives the illusion that the ring plane is tilted away from the camera toward upper-left, but this is not the case. Because of the mechanics of how this kind of wave propagates, the wavelength decreases with distance from the resonance. Thus, the upper-left of the image is just as close to the camera as the lower-right, while the wavelength of the density wave is simply shorter. This wave is remarkable because Janus, the moon that generates it, is in a strange orbital configuration. Janus and Epimetheus share practically the same orbit and trade places every four years. Every time one of those orbit swaps takes place, the ring at this location responds, spawning a new crest in the wave. The distance between any pair of crests corresponds to four years' worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades' worth of the orbital history of Janus and Epimetheus. According to this interpretation, the part of the wave at the very upper-left of this image corresponds to the positions of Janus and Epimetheus around the time of the Voyager flybys in 1980 and 1981, which is the time at which Janus and Epimetheus were first proven to be two distinct objects (they were first observed in 1966). Epimetheus also generates waves at this location, but they are swamped by the waves from Janus, since Janus is the larger of the two moons. This image was taken on June 4, 2017, with the Cassini spacecraft narrow-angle camera. The image was acquired on the sunlit side of the rings from a distance of 47,000 miles (76,000 kilometers) away from the area pictured. The image scale is 1,730 feet (530 meters) per pixel. The phase angle, or sun-ring-spacecraft angle, is 90 degrees. https://photojournal.jpl.nasa.gov/catalog/PIA21627

On March 13, 2006 Cassini's narrow-angle camera captured this look at Saturn and its rings, seen here nearly edge on. The frame also features Mimas and tiny Janus (above the rings), and Tethys (below the rings). "Above" and "below" the rings is mostly a matter of perspective here. All three moons and the rings orbit Saturn in roughly the same plane. The night side of Mimas is gently illuminated by "Saturnshine," sunlight reflected from the planet's cloud tops. Images taken using red, green and blue spectral filters were combined to create this natural color view, taken at a distance of approximately 1.7 million miles (2.7 million kilometers) from Saturn. The Cassini spacecraft ended its mission on Sept. 15, 2017. https://photojournal.jpl.nasa.gov/catalog/PIA18323

The moons Mimas and Janus seem insignificant in front of the immensity of Saturn in this NASA Cassini spacecraft image. Mimas is visible above the rings near the center; Janus is barely detectable as a tiny speck of light below the rings on the left.

Janus and Epimetheus continue to separate, following their orbital swap in January 2006. Until 2010, Janus will remain the innermost of the pair, whose orbits around Saturn are separated by only about 50 kilometers 31 miles on average

Janus is spotted over Saturn north pole in this image while Mimas shadow glides across Saturn in this image from NASA Cassini spacecraft. Janus is the faint dot that appears just above Saturn north pole.

The Cassini spacecraft looks toward the Saturnian horizon as Dione and Janus glide past

Saturn and its rings are prominently shown in this color image, along with three of Saturn's smaller moons. From left to right, they are Prometheus, Pandora and Janus. Prometheus and Pandora are often called the "F ring shepherds" as they control and interact with Saturn's interesting F ring, seen between them. This image was taken on June 18, 2004, with the Cassini spacecraft narrow angle camera 8.2 million kilometers (5.1 million miles) from Saturn. It was created using the red, green, and blue filters. Contrast has been enhanced to aid visibility. http://photojournal.jpl.nasa.gov/catalog/PIA06422

Saturn moons Janus and Prometheus look close enough to touch in this stunningly detailed view

The shadow of the moon Janus dwarfs the shadow of Daphnis on Saturn A ring in this image taken as the planet approached its August 2009 equinox.

The shadow of the moon Janus dwarfs the shadow of Daphnis on Saturn A ring in this image taken as the planet approached its August 2009 equinox.

The small, dark form of Janus cruises along in front of bright Saturn. The edge-on rings cast dramatic shadows onto the northern hemisphere

A pair of Saturn small, icy satellites accompany the planet rings in snapshot from NASA Cassini spacecraft. The rings are between Janus and Prometheus.

NASA Cassini spacecraft looks past Saturn rings and small moon Janus to spy the planet second largest moon, Rhea where lit terrain is seen.

Six of Saturn moons orbiting within and beyond the planet rings are collected in this Cassini spacecraft image; they include Enceladus, Epimetheus, Atlas, Daphnis, Pan, and Janus.

A quartet of Saturn moons are shown with a sliver of the rings in this view from NASA Cassini spacecraft. From left to right in this image are Epimetheus, Janus, Prometheus, and Atlas.

Saturn moon Janus casts a shadow on the F and A rings while the moon Prometheus, seen on the left of the image, creates a streamer-channel in the thin F ring.

A pair of Saturn small satellites, Janus and Pandora, accompany the planet rings in this image from NASA Cassini spacecraft presenting the view in dramatic diagonal fashion.

Two moons hover above the rings from this perspective, Enceladus 313 miles or 504 kilometers across, at left, and Janus 111 miles or 179 kilometers across, at right as seen by NASA Cassini spacecraft.

Saturn rings occupy the space between two of the planet moons in this image, taken by NASA Cassini spacecraft, which shows the highly reflective moon Enceladus in the background and the smaller moon Janus in the fore.

A pair of Saturn small moons orbit near the planet rings, which appear well illuminated in this view captured by NASA Cassini spacecraft. Janus is near the center of the image and Pandora is on the left.

Epimetheus 116 kilometers, or 72 miles across, at right and Janus 181 kilometers, or 113 miles across, at left are lit here by reflected greylight from Saturn. The Sun brightens only thin slivers of the moons surfaces.

A pair of Saturn moons, Pan and Janus, cast their shadows on the A ring in this NASA Cassini spacecraft image taken about a month and a half after Saturn August 2009 equinox.

A quintet of Saturn moons come together in this portrait from NASA Cassini spacecraft. Janus is seen on the far left, Pandora orbits near the middle, Enceladus appears above the center, and Rhea and Mimas are seen on the right side.

The small moon Janus overtakes the larger moon Rhea in a dance played out before Saturn and its rings in this image taken by NASA Cassini spacecraft. Go to the Photojournal to view the animation.

A gaggle of moons parade around Saturn rings in this image from NASA Cassini spacecraft in which the large moon Rhea passes in front of the small moon Janus. Go to the Photojournal to view the animation.

A pair of small moons join Saturn second largest moon in this NASA Cassini spacecraft image spotlighting Rhea in front of the rings. Janus is seen beyond the rings on the right and Prometheus is visible between the main rings and thin F ring on left.

From on high, the Cassini spacecraft spies a group of three ring moons in their travels around Saturn. Janus is seen at top, while Pandora hugs the outer edge of the narrow F ring. More difficult to spot is Pan, which is a mere speck in this view.

While studying Saturn atmosphere, NASA Cassini spacecraft happens to catch a view of two small, icy satellites. Mimas drifts past on the far right of the image. Janus appears as a black dot just below the rings near the center of the image.

The three very different moons seen here provide targets of great interest for planetary scientists studying the Saturn system. Captured here by Cassini, along with the rings, are Tethys at upper right, Enceladus below center and Janus at lower left

January Moon

A True Ring

Skipping a Ring

Dim Duo

Saturn Noir

Little Moons

Mountain of Ice

Ragged Crescent

Rings Return the Favor

Much as its name implies, tiny Epimetheus (Greek for hindsight) was discovered in hindsight. Astronomers originally thought that Janus and Epithemeus were the same object. Only later did astronomers realize that there are in fact two bodies sharing the same orbit. Janus (111 miles or 179 kilometers across) and Epimetheus (70 miles or 113 kilometers) have the same average distance from Saturn, but they take turns being a little closer or a little farther from Saturn, swapping positions approximately every 4 years. See PIA08348 for more. This view looks toward the sunlit side of the rings from about 29 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 1, 2015. The view was acquired at a distance of approximately 1.8 million miles (2.9 million kilometers) from Epimetheus and at a Sun-Epimetheus-spacecraft, or phase, angle of 89 degrees. Image scale is 11 miles (17 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/pia18305

Tiny, dust-sized particles in Saturn rings become much easier to see at high phase angle -- the angle formed by the Sun, the rings and the spacecraft. The brightest ring is the F ring; the next feature to the left is the outer edge of the A ring

These two moons are locked in a gravitational tango that causes them to swap positions about every four years, with one becoming the innermost of the pair and the other becoming the outermost

jsc2024e005963 (12/10/2023) --- A preflight image for the Compartment Cartilage Tissue Construct investigation shows that the Janus base nano-matrix (JBNm) aids in the anchorage and function of cartilage cells (indicated by red staining), facilitating the formation of the cartilage tissue matrix (indicated by green staining). Image courtesy of the University of Connecticut.

jsc2024e005964 (11/6/2023) --- A preflight image of the Janus base nano-matrix (JBNm) enabled cartilage tissue chip. The Compartment Cartilage Tissue Construct investigation uses biological materials that mimic DNA to develop a scaffold for regenerating cartilage tissues and tests the effect of a specific RNA on cartilage growth in space. Image courtesy of the University of Connecticut.

Jsc2025e036192 (4/4/2025) --- Stem cells grown along Janus Base Nanomaterial (JBNm) made on Earth. After four hours, the cells adhered to the scaffold. Biomimetic Fabrication of Multi-Functional DNA-Inspired Nanomaterials via Controlled Self-assembly in Space (DNA Nano Therapeutics-Mission 2) continues prior research on in-space manufacturing of nanomaterials that mimic DNA and have applications for vaccines and regenerative medicine. Image courtesy of University of Connecticut.

jsc2025e036195 (4/4/2025) --- A confocal microscope image shows a human cartilage cell, with its nucleus stained in blue, following delivery of Janus Base Nanoparticles (JBNp) and the subsequent release of bioactive mRNA (pink) that was translated into function protein (green). Biomimetic Fabrication of Multi-Functional DNA-Inspired Nanomaterials via Controlled Self-assembly in Space (DNA Nano Therapeutics-Mission 2) continues prior research on in-space manufacturing of nanomaterials that mimic DNA and have applications for vaccines and regenerative medicine. Image courtesy of University of Connecticut.

jsc2024e005962 (12/10/2023) --- A preflight image for the Compartment Cartilage Tissue Construct investigation shows that the Janus base Nanopieces (JBNps) delivered green fluorescence labeled therapeutic RNA into cartilage cells. Compartment Cartilage Tissue Construct uses biological materials that mimic DNA to develop a scaffold for regenerating cartilage tissues and tests the effect of a specific RNA on cartilage growth in space. Image courtesy of the University of Connecticut.

jsc2025e036194 (4/4/2025) --- Image of nanoparticles synthesized under 1g vs microgravity. Left: This transmission electron microscope image depicts the nano-scale structure of Janus Base Nanoparticles encapsulated with mRNA on ground. Right: This is a transmission electron microscope image of mRNA-encapsulated JBNp that was produced on ISS during the SpaceX CRS-31 mission. Here, you can see that the space-made JBNp is smaller and more uniform in size and shape with less background material, demonstrating the stark advantage that in-space manufacturing can provide JBNp: improved uniformity and drug loading. Image courtesy of University of Connecticut.

iss073e0025618 (May 8, 2025) -- Working in the space station’s Microgravity Science Glovebox, NASA astronaut Jonny Kim mixes proteins with Janus base nanomaterials, small molecules that mimic DNA base pairs, for DNA Nano Therapeutics-Mission 2. This investigation builds on previous work and aims to develop in-space manufacturing of nanomaterials that are less toxic, more stable, and more biocompatible than current drug delivery technologies. Better, more advanced drugs and easier methods for delivering them could improve quality of life for patients in space on Earth.