Category Archives: Cassini

Summer on Titan

It’s a cold summer,  temperature should be about – 179 C / -290 F.

NASA — NASA’s Cassini spacecraft sees bright methane clouds drifting in the summer skies of Saturn’s moon Titan, along with dark hydrocarbon lakes and seas clustered around the north pole.

Compared to earlier in Cassini’s mission, most of the surface in the moon’s northern high latitudes is now illuminated by the sun. (See PIA08363 for a view of the northern hemisphere from 2007.) Summer solstice in the Saturn system occurred on May 24, 2017.

The image was taken with the Cassini spacecraft narrow-angle camera on June 9, 2017, using a spectral filter that preferentially admits wavelengths of near-infrared light centered at 938 nanometers. Cassini obtained the view at a distance of about 315,000 miles (507,000 kilometers) from Titan.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Image: NASA/JPL-Caltech/Space Science Institute

Iapetus

That is not some sort of weird crescent on the Saturn moon Iapetus, The dark area is a deposit of dark material and is on the leading side as the moon orbits Saturn. The dark material is said to be a reddish brown color and has a low albedo, reflecting only about four percent of the light that hits it which I think is about the same as charcoal.

NASA – Iapetus is a world of contrast, with light and dark regions fitting together like cosmic puzzle pieces.

Cassini Regio on Iapetus (914 miles or 1,471 kilometers across) is covered in a layer of dark, dusty material creating a stark contrast to the much brighter region that surrounds it. This leads to the moon’s distinctive, two-toned appearance. To learn more about the cause of the contrast between regions, see PIA06166.

This view looks toward Saturn-facing hemisphere of Iapetus. North on Iapetus is up and rotated 20 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 11, 2017.

The view was obtained at a distance of approximately 1.6 million miles (2.6 million kilometers) from Iapetus. Image scale is 9 miles (15 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Tiny Mimas

Here’s a nice perspective on how huge Saturn really is compared to Mimas(upper right).

Image: NASA/JPL-Caltech/Space Science Institute

NASA — The low angle of sunlight along the slim crescent of Saturn’s moon Enceladus (313 miles or 504 kilometers across) highlights the many fractures and furrows on its icy surface.

This view looks toward the Saturn-facing hemisphere of Enceladus, which is dimly illuminated in the image above by sunlight reflected off Saturn. North on Enceladus is up and rotated 14 degrees to the left. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 26, 2016.

The view was obtained at a distance of approximately 104,000 miles (168,000 kilometers) from Enceladus. Image scale is 3,303 feet (1 kilometer) per pixel.

Did Enceladus Tip Over?

Here’s an annotated version.

mage credit: NASA/JPL-Caltech/Space Science Institute/Cornell University

NASA/JPL – Working with image data from NASA’s Cassini mission, researchers have found evidence that Saturn’s moon Enceladus may have tipped over, reorienting itself so that terrain closer to its original equator was relocated to the poles. This phenomenon is known as true polar wander.

Researchers discovered a chain of basins across the surface of Enceladus along with a pair of depressions that line up with an equator and poles, respectively, if the moon’s axis of rotation was reoriented by about 55 degrees of latitude.

These maps look toward the icy moon’s southern hemisphere, with colors representing highs and lows. Purple represents the lowest elevations, while red represents the highest.

The map at left shows the surface of Enceladus in its possible ancient orientation, millions of years ago. The chain of basins representing topographic lows can be seen in blue and purple, running along the equator, with an additional low region around the original south pole. The region that encloses the moon’s currently active south polar terrain, with its long, linear “tiger stripe” fractures, would have been at middle latitudes just south of the equator. The map at right shows the current orientation of Enceladus.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, California, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Icy Crescent

The plumes of Enceladus are not visible in this shot. The geometry between the Cassini spacecraft, Enceladus, and Saturn allows for the illimuation of the moon by “Saturn-shine” but it also puts the region of those southern plumes in what we could call “deep shadow”. The effect can be illustrated By increasing the exposure on the image – see here.

Here’s the original caption:
The low angle of sunlight along the slim crescent of Saturn’s moon Enceladus (313 miles or 504 kilometers across) highlights the many fractures and furrows on its icy surface.

This view looks toward the Saturn-facing hemisphere of Enceladus, which is dimly illuminated in the image above by sunlight reflected off Saturn. North on Enceladus is up and rotated 14 degrees to the left. The image was taken in visible light with NASA’s Cassini spacecraft narrow-angle camera on Dec. 26, 2016.

The view was obtained at a distance of approximately 104,000 miles (168,000 kilometers) from Enceladus. Image scale is 3,303 feet (1 kilometer) per pixel.

Saturn’s Summer Shadow

NASA –

The projection of Saturn’s shadow on the rings grows shorter as Saturn’s season advances toward northern summer, thanks to the planet’s permanent tilt as it orbits the sun. This will continue until Saturn’s solstice in May 2017. At that point in time, the shadow will extend only as far as the innermost A ring, leaving the middle and outer A ring completely free of the planet’s shadow.

Over the course of NASA’s Cassini mission, the shadow of Saturn first lengthened steadily until equinox in August 2009. Since then, the shadow has been shrinking. These changes can be seen by comparing the shadow in the above view to its appearance as Cassini approached Saturn in 2004 (PIA06077), equinox in 2009 (PIA11667), and two years ago, in 2015 (PIA20498).

This view looks toward the sunlit side of the rings from about 10 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Feb. 3, 2017.

The view was acquired at a distance of approximately 760,000 miles (1.2 million kilometers) from Saturn. Image scale is 46 miles (73 kilometers) per pixel.

Image and caption : NASA/JPL-Caltech/Space Science Institute

Titan’s Clouds

Here is what is likely one of the last good looks at Titan’s atmosphere from Cassini.

From the Cassini caption: NASA’s Cassini spacecraft captured this view of bands of bright, feathery methane clouds drifting across Saturn’s moon Titan on May 7, 2017.

The view was obtained during a distant (non-targeted) flyby, during which Cassini passed 303,000 miles (488,000 kilometers) above the moon’s surface. Although Cassini will have no further close, targeted flybys of Titan, the spacecraft continues to observe the giant moon and its atmosphere from a distance.

The dark regions at top are Titan’s hydrocarbon lakes and seas.

The image was taken on May 7, 2017, at a distance of 316,000 miles (508,000 kilometers). The view is an orthographic projection centered on 57 degrees north latitude, 48 degrees west longitude. An orthographic view is most like the view seen by a distant observer. Image scale is about 2 miles (3 kilometers) per pixel.

What about the future of NASA exploration?  Following Cassini’s epic mission is going to be tough.

The proposals are being reviewed by NASA and while we don’t have specifics of course, we do have the six themes for the new proposals for a possible mission in the mid-2020’s:

  • Comet Surface Sample Return
  • Lunar South Pole-Aitken Basin Sample Return
  • Ocean Worlds (Titan and/or Enceladus)
  • Saturn Probe
  • Trojan Tour and Rendezvous
  • Venus In Situ Explorer

Keep in mind the first on the list is in progress, the OSIRIS-REx, which will rendezvous with and return a sample of asteroid Bennu.  Other than that, the only one I would change maybe, would be the Saturn Probe, my version would be the Neptune probe.  They all do look pretty good so the choice will not be easy.

Saturn’s North

Take a look at the northern reaches of Saturn as Cassini did a few months ago.  The structure in the atmosphere aside from the hexagonal formation is rather remarkable.  Click the image to get a larger version.

NASA – “Hail the Hexagon” – Saturn’s hexagonal polar jet stream is the shining feature of almost every view of the north polar region of Saturn. The region, in shadow for the first part of the Cassini mission, now enjoys full sunlight, which enables Cassini scientists to directly image it in reflected light.

Although the sunlight falling on the north pole of Saturn is enough to allow us to image and study the region, it does not provide much warmth. In addition to being low in the sky (just like summer at Earth’s poles), the sun is nearly ten times as distant from Saturn as from Earth. This results in the sunlight being only about 1 percent as intense as at our planet.

This view looks toward Saturn from about 31 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Jan. 22, 2017 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 939 nanometers.

The view was obtained at a distance of approximately 560,000 miles (900,000 kilometers) from Saturn. Image scale is 33 miles (54 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Crossing “The Big Empty”

The image above (as always thanks to NASA/JPL-Caltech/Space Science Institute) was taken on 29 April 2017 and has very minimal processing.

Later today (at 19:38 UTC) the Cassini spacecraft will make its second crossing in the gap between the rings of Saturn and the planet itself.

During the first crossing the spacecraft was oriented so the four-meter wide antenna was leading the way through the gap so it could act as a shield protecting instruments on the spacecraft. Not so long ago only few could imagine flying through that 2,000 km wide gap and nobody knew what they would find.  Will this dive be the same?  We will know tomorrow.

NASA — Cassini’s Radio and Plasma Wave Science (RPWS) instrument was one of two science instruments with sensors that poke out from the protective shield of the antenna (the other being Cassini’s magnetometer). RPWS detected the hits of hundreds of ring particles per second when it crossed the ring plane just outside of Saturn’s main rings, but only detected a few pings on April 26.

When RPWS data are converted to an audio format, dust particles hitting the instrument’s antennas sound like pops and cracks, covering up the usual whistles and squeaks of waves in the charged particle environment that the instrument is designed to detect. The RPWS team expected to hear a lot of pops and cracks on crossing the ring plane inside the gap, but instead, the whistles and squeaks came through surprisingly clearly on April 26.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”

“It was a bit disorienting — we weren’t hearing what we expected to hear,” said William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.”

The team’s analysis suggests Cassini only encountered a few particles as it crossed the gap — none larger than those in smoke (about 1 micron across).