An Amazing Image of Saturn's Rings for the Holidays

Carolyn Porco, the dynamic leader of the Imaging Team for the Cassini Mission (exploring Saturn and its neighborhood), has sent a remarkable holiday greeting card from Saturn and I wanted to share it with you.

What we are looking at is a view of the inner part of Saturn's complicated ring system (mainly the so-called B ring.) We are seeing about 750 miles of the white rim of the B ring, beyond which is the dark emptier space called the Cassini Division. You can see a number of thin "ringlets" in that division toward the upper part of our picture.

But what is really stunning is what the long shadows cast by the Sun reveal at the edge of the bright main ring. You can see peaks or thin mountains of ice particles, sticking up more than a mile and a half (2 km) above the plane of the rings. Compare those heights with the typical height of the ring system, which is about 10 meters (or about 30 feet) in most places.

Here is what Carolyn says about the image, "Cassini scientists believe that this is one prominent region at the outer edge of the B ring where large bodies, or moonlets, up to a kilometer or more in size, are found. It is possible that these bodies significantly affect the ring material streaming past them, and force the particles upward, in a "splashing" manner."

She continues, "This image [taken in 2009] and others like it are only possible around the time of Saturn's equinox, which occurs every half-Saturn-year, or about every 15 Earth years. The illumination geometry that accompanies equinox lowers the sun's angle to the ring plane and causes structures jutting out of the plane to cast long shadows across the rings."

The rings of Saturn are made of billions and billions (as Carl Sagan used to say) of individual chunks of ice -- mostly water ice. The particles range in size from smaller than a sand grain to larger than a modern SUV. We have known for some time that the interaction of moons and rings in the Saturn system can create a wide range of artistic patterns using the ring particles as their raw materials. But these tall icicles or icy towers are among the most spectacular we have ever seen.

Happy Holidays. May 2015 bring all of us more amazing views of our cosmic environment and increase our understanding that the differences that separate us on Earth are so trivial compared to the truly alien nature of what's out there.

[Click on the image to make it bigger and see even more detail!]

You Could Name a Crater on the Planet Mercury

The team of scientists and educators behind the Messenger spacecraft orbiting the planet Mercury is giving the public the chance to nominate artists, writers, or composers whose names deserve to be on one of five craters on the hot little planet closest to the Sun.

There have been a number of publicity campaigns recently that deal with naming things, but this one is the real thing. By international agreement, the naming of worlds and features in space is done by a special committee of the International Astronomical Union (the U.N. of astronomers.) But the committee is happy (when there is no duplication or veering from tradition) to honor the wishes of the discoverers. And the Messenger team, having discovered many new craters on the wonderful close-up images they have obtained, is happy to give the public a chance to participate.

Also by agreement, Mercury's huge population of impact craters is going to be named only for well-known composers of music, serious artists, and writers of renown. The most famous people in these categories (Beethoven, Van Gogh, Tolstoy) already have craters named for them. So now, it's time to find less well-known people from a wide range of cultures to be honored. The Messenger team will submit their 15 favorite entries to the committee to select the names of five newly discovered craters. You can see photos of the craters and get all the details on the contest website: http://namecraters.carnegiescience.edu/home

You are encouraged to check first to see if your favorite candidates don't already have a crater. I was pleased to see that Jean Sibelius, one of my favorite composers, was already on the list. On the other hand, Alexander Scriabin, who took romantic music in amazing new directions, and wanted to combine sound and light long before there were laser shows, still hasn't got a crater to his name anywhere in the solar system. Maybe some of us have to nominate him.

The rules say anyone you nominate has to have been publicly known for at least 50 years and dead for at least three. But beyond that, you are encouraged to get -- pardon the expression -- creative. The contest starts today and is open for only one month. There is no prize, only the satisfaction of knowing that you have helped put someone whose work you really enjoy on another world.

To see all the people who have given their names to features in the solar system, you can search at: http://planetarynames.wr.usgs.gov/AdvancedSearch  (putting the last name into the field called "Feature Name.")

The Lake that Built a Mountain on Mars

NASA’s instrument-laden Curiosity Rover is now at the foot of Mt. Sharp, its ultimate target on Mars. New results from the rover have confirmed and filled in our ideas about what the 3-mile high mountain is doing in the middle of 96-mile wide Gale Crater. And, most important, the new observations give us even more confidence in the notion that ancient Mars was very different from Mars today – it may well have had a much thicker atmosphere, flowing rivers, and occasionally full lakes of water.

Mt. Sharp is an interesting mountain, in that it seems to be built up out of layer after layer of sediment. This material might have been carried to the center of the crater by either water or winds, scientists thought. The new results indicate that both water and wind may have had a role in building Mt. Sharp over the millennia.

We already knew that one or more dry river channels end at Gale Crater, making it likely that long ago, water probably flowed into the crater. Over long periods of time, the crater lake may have formed and evaporated again and again. Rivers flowing over the red sands of Mars would have carried quite a bit of sediment into the crater and would have deposited this material in its center. As the central mountain began to accumulate, the next river flood would lap up against it. The resulting waves could carry material higher than the river’s original level, thus building up the mountain further.

When the lake was dry, the big wind storms, that other instruments have shown us are a regular feature of Mars weather, could have added wind blown sand to the top of the mountain. So Mt. Sharp could have grown during both wet and dry periods.

Curiosity is only at the bottom of the mountain right now, but it has the ability to climb up to higher layers over the coming months. Scientists are very interested in what the layers higher up might reveal to us about how Mt. Sharp grew and how the climate on ancient Mars changed as time passed.

Our top picture, taken on Mars on Nov. 2, shows some of the layers building up at the bottom of Mt. Sharp in a formation scientists have nicknamed "Whale Rock." For a version of this picture that shows scale, see: http://photojournal.jpl.nasa.gov/figures/PIA19081_fig1.jpg 

The picture below is an earlier "selfie" that the Curiosity rover took showing its instruments and cameras at work. Click on either photo and you'll see a larger version, full of amazing detail -- straight from the surface of Mars!