Titan News 2017
January 14, 2017 : Flash-Back On the Remarkable Achievement of the Huygens Probe Which Landed at a Low Latitude On Titan About Twelve Years Ago
Prior to the Cassini-Huygens mission, nobody knew what the landscape of Titan looked like because the hazy or smoggy atmosphere of Saturn's largest moon is completely opaque from outer space. Researchers were fascinated and intrigued by this exotic and unique world which appears to be the second largest moon in the Solar System. Ganymede, the giant moon of Jupiter, is slightly bigger than Titan but paradoxically it is devoid of any significant atmosphere. Crazy or optimistic hypotheses regarding the nature of Titan's surface had been advanced such as the presence of a global ocean of methane or ethane.
Researchers knew that the environmental conditions on Titan allowed the potential presence of liquid methane, liquid ethane or liquid propane on the surface of the Orange Moon. At the relatively significant distance of Titan and Saturn from the Sun, the energy received from our own star is particularly low so that the environmental temperature on the Opaque Moon is aroud -179 degrees Celsius, -292 degrees Fahrenheit or 94 Kelvin. The atmospheric pressure at the level of the soil is around 1,5 Bars which is higher than that at sea level on Earth. Scientists knew that the atmosphere of Titan was dominated by molecular nitrogen and that methane represented the second most abundant compound in the hazy atmosphere. That's why the hypothesis of a global ocean of hydrocarbons was put forward by many scientists.
The Cassini-Huygens spacecraft reached the Saturnian System in mid-2004. The Cassini probe was equipped with several instruments such as the Radar Mapper and the Visual and Infrared Mapping Spectrometer or VIMS. Researchers were going to be able to collect data regarding the meteorology and the surface of Titan thanks to the Radar Mapper and thanks to the infrared and near-infrared eyes of the Cassini probe in particular. As soon as 2004, the Cassini probe collected the first data regarding the surface of the Opaque Moon revealing a contrast between high-albedo areas and low-albedo areas mostly found at low latitudes. Some scientists believed that those dark areas contrasting with bright areas represented seas or oceans of liquid methane or ethane even if some specialists argued that the low-albedo regions were not dark or uniform enough to be composed of liquids.
The Cassini probe of NASA dropped the lander known as Huygens on December 24, 2004 for a 20-day journey towards the surface of the Orange Moon. The Huygens module and its atmospheric shield could be compared with a flying saucer. The Huygens probe would have to withstand the harsh conditions of Titan's atmosphere. The designers or developers of the Huygens probe proposed by the European Space Agency had anticipated several configurations regarding the touchdown including a splash into a sea or ocean of hydrocarbons. That's why the Huygens module was able to float on an hypothetical sea, lake or river. The lifespan of the Huygens probe was particularly short due to its limited level of energy. The Huygens probe couldn't count on the solar energy which is too weak at this distance for conventional solar panels. The module had to rely on nuclear energy which would fuel the living probe for a few hours once on the surface of the giant moon.
The Huygens module performed a spectacular plunge into the Titanian atmosphere acquiring key data regarding the atmosphere and the landscape. A multitude of panoramic views were obtained from the parachuted probe and transmitted to the Cassini orbiter which had to be in the right place to collect the data. The Cassini spacecraft would rapidly go down below the horizon of the Huygens probe preventing new data from coming. During the atmospheric descent, the probe managed to obtain key data regarding the environmental temperature, the density, the atmospheric pressure, wind speed, the nature of the complex organics or the nature of the haze or the dense atmosphere. From the altitude of about 45 miles or 70 kilometers, the sky became clearer and the landscape could be discerned. The probe took remarkable images of the landscape revealing a radical contrast between a dark or brownish plain resembling a sea and bright hills resembling a glacier or banquise. Researchers and the general public were fascinated by what they saw. Dark sinuous channels in the bright areas or in the hills were clearly discerned in the views. Those channels are likely drainage channels or dried-up rivers. The aerial views led some persons or scientific journalists to advance that the dark plain corresponded to a methane sea.
During the historical atmospheric descent, hundreds of images were taken with the Descent Imager/Spectral Radiometer or DISR allowing the creation of a video of the descent. The area where the Huygens probe landed probably undergoes seasonal rainfall. That's what the aerial images suggest. Methane or ethane rain can produce strong erosional processes sculpting the landscape in the same way as on Earth and can engender canyons or steep ravines. The dark channels may also correspond to fractures even if the hypothesis for drainage channels at low latitudes is favored. After the touchdown, the Huygens probe survived and collected captivating views of the soil and the horizon. Eroded stones or pebbles could be clearly discerned near the probe implying that the probe may have landed onto an ancient river.
The Cassini probe which has been collecting key data regarding the atmosphere of Titan and its landscape is still operating today but its mission is expected to come to an end on September 15, 2017 with a big plunge into Saturn's atmosphere. The Cassini team members and NASA leaders have performed an extraordinary work over the years since the big start of the Cassini-Huygens mission in the Saturnian System in 2004. Here are some comments. Linda Spilker who is Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California advanced : « The Huygens descent and landing represented a major breakthrough in our exploration of Titan as well as the first soft landing on an outer-planet moon. It completely changed our understanding of this haze-covered ocean world.»
Carolyn Porco who is Cassini imaging team lead at Space Science Institute in Boulder, Colorado pointed out : « The Huygens images were everything our images from orbit were not. Instead of hazy, sinuous features that we could only guess were streams and drainage channels, here was incontrovertible evidence that at some point in Titan's history – and perhaps even now – there were flowing liquid hydrocarbons on the surface. Huygens' images became a Rosetta stone for helping us interpret our subsequent findings on Titan. » Since the beginning of the Cassini-Huygens mission, radar data obtained from the Cassini orbiter have clearly shown that the dark areas or low-albedo areas in the infrared or near-infrared spectrum found at low latitudes are dominated by Seif dunes or parallel and linear dunes extending over long distances and shaped by prevailing winds. As a result, one can advance the hypothesis that the low-albedo areas located at low latitudes may correspond to ancient seas.
Alex Hayes who is a Cassini scientist at Cornell University, Ithaca, New York argued : « Cassini and Huygens have shown us that Titan is an amazing world with a landscape that mimics Earth in many ways. During its descent, the Huygens probe captured views that demonstrated an entirely new dimension to that comparison and highlights that there is so much more we have yet to discover. For me, Huygens has emphasized why it is so important that we continue to explore Titan. » Researchers became aware in particular that there may be seasonal phenomena in the area such as seasonal rainfall or monsoon events. Eroded stones or pebbles identified on the surface near the probe were the proof that a stream of liquid hydrocarbons, methane, ethane or propane must have taken shape relatively recently where the probe landed.
Jim Green who is director of planetary science at NASA Headquarters in Washington advanced : « Twelve years ago, a small probe touched down on an orangish, alien world in the outer solar system, marking humankind's most distant landing to date. Studying Titan helps us tease out the potential of habitability of this tiny world and better understand the chemistry of the early Earth. » Thanks to the Radar Mapper, the infrared and near-infrared eye of the Cassini spacecraft, scientists have been in a position to obtain a relatively detailed map of Titan's surface and significant clues regarding the meteorology or the methane cycle on Titan. We know, now, that lakes, seas and rivers are found at high latitudes or in the polar regions of Titan. If we had known as soon as the start of the Saturnian journey that the pools of liquids were mostly concentrated in the high latitudes of the northern hemisphere, we would probably have sent the Huygens probe to seas or lakes like Kraken Mare, Ligeia Mare or Punga Mare. Are there huge waves as some researchers had predicted long ago ? Is there a complex organic chemistry within the pools of surface liquids dominated by hydrocarbons ? That's a major question we are eager to answer. Let's hope we'll have the answer very soon !
The image above corresponds to a panoramic view of the area where the Huygens probe landed on January 14, 2005. During its atmospheric descent, the Descent Imager/Spectral Radiometer acquired a multitude of images of its environment. This image represents a flattened (Mercator) projection of a view obtained at an altitude of 10 kilometers or 6 miles. One can notice the remarkable contrast between the dark, brownish plain and bright hills. Image Credit: ESA/NASA/JPL/University of Arizona.
The artist's impression above reveals the surface of Titan in a low-albedo area at a low latitude on Saturn's largest moon Titan. Radar images have clearly shown that the regions which appear dark and mark a clear contrast with bright areas at a low latitude are dominated by Seif dunes or linear and parallel dunes extending over long distances, influenced by prevailing winds. Winds and rainfall of methane or ethane can engender erosional processes like well-known meteorological processes occurring on Earth. Image Credit: Marc Lafferre, 2017.
- To get further information on that news, go to : https://saturn.jpl.nasa.gov/news/2987/huygens-ground-truth-from-an-alien-moon.