Category Archives: Moons

Huygens: Lander of the Decade

If there is one probe in the last decade that was by far the most under-appreciated and most deserving of worldwide acclaim it was the Huygens probe that landed on Saturn’s largest moon Titan back in 2005.  Granted I was only sixteen year old at the time, but I don’t remember much being made about Huygens except by NASA.  Admittedly nowadays, the things that excite NASA rarely, if ever, excite the average U.S. citizen.  What a shame that is.  I know it’s rather daft to compare the 1969 Moon landing with the Huygens mission but the spirit of the first moon landing was surely present within NASA when Huygens touched down on Titan.  The mission was historic for several reasons.  It was the first time a man-made probe had landed on a moon.  It was, and still is, the most distant body a man-made probe has landed on.  Huygens also had great scientific value also from the brief glimpse it got of the surface of the alien moon.  It was the first time we had ever touched down on a world that was truly “alien”, in that we had little to no idea what to expect.

Huygens was part of a mission to Saturn that was 22 years in the making.  The Cassini spacecraft was the main probe that would visit Saturn for the first time since Voyager 1 passed by in 1980.  One moon in particular caught the attention of NASA during its Saturnian encounter, Titan.  Titan is Saturn’s largest moon and bears a striking similarity to Earth.  It has a dense atmosphere.  The first images of Titan showed the famous ‘thin blue line” that shows the presence of an atmosphere.  As the picture below shows, Titan’s atmosphere looks incredibly like our own atmosphere when seen from space.  From that point on NASA resolved that it would eventually send a probe there.

Titan’s atmosphere seen by Voyager 1 in 1980 Credit: NASA

The Cassini probe was launched on October 15, 1997 and arrived at Saturn on July 1, 2004.  The European Space Agency built Huygens probe was carried along with Cassini and during its first approach of Titan jettisoned the tiny probe on December 25, 2004.  It took another 20 days for Huygens to reach Titan but on January 14, 2005 NASA has finally achieved its goal of sending a probe to Titan.  It took two and a half hours for Huygens to descend through Titan’s atmosphere and took hundreds of images from its Descent Imager/Spectral Radiometer.  Once below the haze and clouds Titan revealed a surface that was very Earth-like in many ways.  Large mountains and hills covered with a lacework of what looked like streams and runoff flows of some kind of liquid, and even a shoreline of massive bodies of liquid.  It was later determined that the bodies of liquid were not water since the surface of Titan is a frigid -179°C.  The only element known to exist as a liquid at that extreme temperature is methane.  Methane also exists as a solid and a gas on Titan, the same way water exists as a solid, liquid, and gas on Earth.  The discovery revealed that the same way that Earth has a hydrological cycle, Titan has a methanological cycle.  There are vast lakes and oceans of liquid methane which evaporate and form methane clouds.  There is also even methane rain on Titan that falls in huge, slow moving rain drops due to the low gravity.  Life as we know it couldn’t exist on Titan, but if we were to find even single-cell organisms or bacteria growing there it would cause us to radically re-think our understanding of biology and the possibility of alien life.

Long story short, Huygens was a huge success and tons of extremely valuable scientific data was produced from the tiny little probe that was the caboose of Cassini for six years.  After the success of Huygens there should have been headline news stories about it on the 6 o’clock news across the world and front page news in all the newspapers.  There should have been parades celebrating the historic landing from New York to Hong Kong.  But alas, the world doesn’t get excited about space anymore.  Huygens will go down as one of mankind’s most successful missions as well as one of the most under-rated mission of all time.

For your viewing pleasure here are some of NASA/ESA’s images received from Huygens during its descent and once it touched down.  Enjoy.

Titan’s rocky surface from 10 km Credit: ESA/NASA/JPL/University of Arizona

Panorama of raw images from Huygens Credit: ESA/NASA/JPL/University of Arizona

Color image of smooth liquid-eroded pebbles at landing site Credit: ESA/NASA/JPL/University of Arizona

Enceladus Flyby

The Cassini spacecraft orbiting Saturn, everyone’s favorite planet (right??), will make it’s closest flyby of Saturn’s tiny, icy moon Enceladus since 2008 at 2:30 EDT today.  The probe will fly over Enceladus’ south polar region at an altitude of 46 miles (74 kilometers) near an area famous for its ice-spewing mega-geysers.  Cassini discovered active cyrovolcanism on Encledadus during its first flyby of the moon in 2005.  It astonished astronomers that a moon so cold and icy could have volcanic activity at all.  Further investigation lead to the discovery of a region in the southern hemisphere known as “the Tiger Stripes” where there are four large rifts in the icy surface.  Below the surface it is believed that there is a local or planetwide ocean of water that is heated far above what is expected of a small icy world so far from the Sun.  Enceladus must must have a hot core just like our own planet that is heated by the friction caused by the gravitational pull of Saturn and orbital resonances from other moons.  Since Enceladus orbits within Saturn’s rings very close to the planet it feels the strong gravitational pull of not only Saturn but of the ring system and the other moons that orbit Saturn.  The south polar region of Enceladus is particularly interesting to astronomers because it shows clear evidence of ongoing geological activity.  The southern terrain is largely free from impact craters which leads us to believe that the surface is being reshaped by the geological forces at work beneath the surface.  Enceladus is one of only three moons where we have seen eruptions; the other two being Jupiter’s moon Io and  Neptune’s moon Triton.

Massive ice geysers around the Tiger Stripes region of Enceladus' south pole suggest the presence of heated liquid H2O Credit: NASA/

The intrigue of the geysers has prompted Cassini’s mission control at the Jet Propulsion Laboratory to carry out a flyby of the south pole region to “taste” the icy vapor with a device called an ion and neutral mass spectrometer.  The data collected from the spectrometer will allow scientists to better understand the composition of the jets of ice and its subterranean source.  Cassini’s composite infrared spectrometer will also be taking pictures of the Tiger Stripes looking for hot spots under the surface similar to the ones recently found detailed in the picture below.

The geological activity and presence of water on Enceladus is extremely exciting for NASA because if there’s water and heat there could also be micro-bacterial life.  A discovery of life on Enceladus would be a massive breakthrough in understanding the picture of the universe and the early stages of life on our own planet as well.  So far it’s the moons, not the planets that are leading the race of potential for life, so I vote to study more moons!

Evidence of subterranean heat below the Tiger Stripes region on Enceladus Credit: NASA/J

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