Sailing the Seas of Saturn’s Moon Titan

 

Humanity has landed a rover on Mars. Now, say scientists, it’s time to land a boat on Titan. This outlandish scenario could become reality, according to engineers presenting their proposals today (27 September 2012) at the European Planetary Science Congress. 

Paddle concept for TALISE probe. This rendering of the proposed TALISE probe shows one possible means of propulsion: paddle wheels on either side of the probe. Image Credit: SENER

Titan, Saturn’s largest moon, is one of the most Earth-like bodies in the Solar System. With a thick atmosphere, a diameter between that of Earth and the planet Mercury, and a network of seas, lakes and rivers, it is in many respects more like a planet than a moon like the Earth’s.

The Cassini-Huygens mission, which studied Titan extensively in the 2000s, confirmed that lakes, seas and rivers of liquid hydrocarbons (similar to household gas) exist, covering much of the satellite’s northern hemisphere. Although it eventually landed on solid ground, the Hugyens lander was designed to be able to float for a short period.

Screw concept for TALISE probe. This rendering of the proposed TALISE probe shows one possible means of propulsion: screws on either side of the probe. Image Credit: SENER

The new plans, called the Titan Lake In-situ Sampling Propelled Explorer, proposes a boat-probe, propelled by wheels, paddles or screws. The probe would land in the middle of Ligeia Mare (the biggest lake, near Titan’s north pole), then set sail for the coast, taking scientific measurements along the way. The mission would last around six months to a year.

“The main innovation in TALISE is the propulsion system,” says Igone Urdampilleta (SENER), a member of the TALISE team. “This allows the probe to move, under control, from the landing site in the lake, to the closest shore. The displacement capability would achieve the obtaining of liquid and solid samples from several scientific interesting locations on Titan’s surface such as the landing place, along the route towards the shore and finally at the shoreline.”

Wheeled concept for TALISE probe. This rendering of the proposed TALISE probe shows one possible means of propulsion: wheels on either side of the probe. Image Credit: SENER

Titan’s environment is too cold for life as we know it, but its environment, rich in the building blocks of life, is of great interest to astrobiologists. The satellite’s atmosphere is made up largely of nitrogen (like Earth’s), is rich in organic compounds and hydrogen cyanide, which may have played a role in the emergence of life on Earth.

The TALISE concept is being developed as a partnership between SENER and the Centro de Astrobiología in Madrid, Spain. This mission concept is the result of a ‘Phase 0’ study. In the following phases the feasibility study and a preliminary mission architecture would be realised to consolidate a possible technical proposal for future space science mission call.

Source: Europlanet

Water Once Flowed from the Southern Highlands of Mars

 

ESA’s Mars Express has observed the southern part of a partially buried approximately 440-km wide crater, informally named Ladon basin. The images, near to where Ladon Valles enters this large impact region reveal a variety of features, most notably the double interconnected impact craters Sigli and Shambe, the basins of which are criss-crossed by extensive fracturing.

The image shows the interconnected craters Sigli and Shambe, believed to have formed when a large meteorite fragmented in to two pieces just before impact. Extensive fracturing can be seen within the craters. Above the craters (west), creek-like flow channels can be seen leading in to the wider impact basin region to the right (north).
Credits: ESA/DLR/FU Berlin (G. Neukum)

This region, imaged on 27 April by the high-resolution stereo camera on Mars Express is of great interest to scientists since it shows significant signs of ancient lakes and rivers.

Sigli and Shambe dominate this image, which highlights the deep fracturing within the crater walls. The shape of the craters leads scientists to believe they were formed from the same impactor, which fragmented into two pieces just before hitting Mars.
Credits: ESA/DLR/FU Berlin (G. Neukum)

Large-scale overview maps show clear evidence that vast volumes of water once flowed from the southern highlands. This water carved Ladon Valles, eventually flowing into Ladon basin, an ancient large impact region.

Elliptical craters like this 16 km-wide example are formed when asteroids or comets strike the surface of the planet at a shallow angle.

Ladon basin is seen here in broader context. The smaller rectangle shows the region covered in this ESA Mars Express HRSC image release. Ladon Valles, which flows in to Ladon basin, is north of the well-known craters Holden and Eberswalde, which were potential landing-site candidates for NASA’s Mars Science Laboratory. 
Credits: NASA MGS MOLA Science Team

Scientists have suggested that a fluidised ejecta pattern indicates the presence of subsurface ice which melted during the impact. Subsequent impacts have created a number of smaller craters in the ejecta blanket.

The interconnected craters Sigli and Shambe are thought to have formed later when an incoming projectile split into two pieces just before impact. The joined craters were then partly filled with sediments at some later epoch.

Above the interconnected craters of Sigli and Shambe (west), flow channels can be seen leading in to the large impact basin. The outflow of Ladon Valles itself can be seen towards the bottom of the image (east). Scientists have detected clay minerals within these deposits, suggesting the relatively long-lasting presence of liquid water in the past. 
Credits: ESA/DLR/FU Berlin (G. Neukum)

Deep fractures can be seen within the craters whilst in the central and right part of the image, smaller craters and more subtle curved fractures appear. These fractures on the basin floor extend beyond the image borders and form concentric patterns. The fractures are believed to have evolved by compaction of the huge sediment loads deposited within the impact basin.

The outflow of Ladon Valles in to Ladon basin is located towards the east of Sigli and Shambe Craters, towards the bottom of the image. Here, and in several other parts of the image, lighter-toned layered deposits can be seen. Researchers have detected clay minerals within these deposits, suggesting a relatively long-lasting presence of liquid water in the region’s past.

In addition, winding, valley-like dendritic structures running into the larger basin can be seen above Sigli and Shambe Craters, running in to the larger impact basin, again indicating flowing water at some distant epoch.

This colour-coded plan view is based on a digital terrain model of the region, from which the topography of the landscape can be derived. The colour coding brings in to stark relief the fracturing inside Sigli and Shambe and the winding flow channels above (west) of the craters leading in to the relatively flat impact basin. Centred at around 18°S and 329°E, the image has a ground resolution of about 20 m per pixel.
Credits: ESA/DLR/FU Berlin (G. Neukum)

This anaglyph 3D image can be viewed using stereoscopic glasses with red–green or red–blue filters. The image shows the concentric arc-shaped fractures in the wider impact basin, as well as the more extensive fracturing inside the interconnected craters Sigli and Shambe. Centred at around 18°S and 329°E, the image has a ground resolution of about 20 m per pixel.
Credits: ESA/DLR/FU Berlin (G. Neukum)

Source: The European Space Agency (ESA)

Titan’s River Networks Point to a Puzzling Geologic Past

 

For many years, Titan’s thick, methane- and nitrogen-rich atmosphere kept astronomers from seeing what lies beneath. Saturn’s largest moon appeared through telescopes as a hazy orange orb, in contrast to other heavily cratered moons in the solar system. Findings suggest the surface of Saturn’s largest moon may have undergone a recent transformation.

Images from the Cassini mission show river networks draining into lakes in Titan’s north polar region.
Image credit: NASA/JPL/USGS

In 2004, the Cassini-Huygens spacecraft — a probe that flies by Titan as it orbits Saturn — penetrated Titan’s haze, providing scientists with their first detailed images of the surface. Radar images revealed an icy terrain carved out over millions of years by rivers of liquid methane, similar to how rivers of water have etched into Earth’s rocky continents.

While images of Titan have revealed its present landscape, very little is known about its geologic past. Now researchers at the Massachusetts Institute of Technology (MIT) and the University of Tennessee at Knoxville have analyzed images of Titan’s river networks and determined that in some regions, rivers have created surprisingly little erosion. The researchers say there are two possible explanations: either erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms.

“It’s a surface that should have eroded much more than what we’re seeing, if the river networks have been active for a long time,” says Taylor Perron, the Cecil and Ida Green Assistant Professor of Geology at MIT. “It raises some very interesting questions about what has been happening on Titan in the last billion years.”

A paper detailing the group’s findings will appear in the Journal of Geophysical Research-Planets.

River networks on Titan.  Credit:  Taylor Perron/Ben Black; ESA/NASA/JPL/University of Arizona; NASA/JPL


What accounts for a low crater count?

Compared to most moons in our solar system, Titan is relatively smooth, with few craters pockmarking its facade. Titan is around four billion years old, about the same age as the rest of the solar system. But judging by the number of craters, one might estimate that its surface is much younger, between 100 million and one billion years old.

What might explain this moon’s low crater count? Perron says the answer may be similar to what happens on Earth.

“We don’t have many impact craters on Earth,” Perron says. “People flock to them because they’re so few, and one explanation is that Earth’s continents are always eroding or being covered with sediment. That may be the case on Titan, too.”

For example, plate tectonics, erupting volcanoes, advancing glaciers and river networks have all reshaped Earth’s surface over billions of years. On Titan, similar processes — tectonic upheaval, icy lava eruptions, erosion and sedimentation by rivers — may be at work.

But identifying which of these geological phenomena may have modified Titan’s surface is a significant challenge. Images generated by the Cassini spacecraft, similar to aerial photos but with much coarser resolution, are flat, depicting terrain from a bird’s-eye perspective, with no information about a landform’s elevation or depth.

“It’s an interesting challenge,” Perron says. “It’s almost like we were thrown back a few centuries, before there were many topographic maps, and we only had maps showing where the rivers are.”

Titan, Saturn’s largest moon. Image credit: NOAA/NASA/ESA

Charting a river’s evolution

Perron and MIT graduate student Benjamin Black set out to determine the extent to which river networks may have renewed Titan’s surface. The team analyzed images taken from Cassini-Huygens, and mapped 52 prominent river networks from four regions on Titan. The researchers compared the images with a model of river network evolution developed by Perron. This model depicts the evolution of a river over time, given variables such as the strength of the underlying material and the rate of flow through the river channels. As a river erodes slowly through the ice, it transforms from a long, spindly thread into a dense, treelike network of tributaries.

Black compared his measurements of Titan’s river networks with the model, and found the moon’s rivers most resembled the early stages of a typical terrestrial river’s evolution. The observations indicate that rivers in some regions have caused very little erosion, and hence very little modification of Titan’s surface.

“They’re more on the long and spindly side,” Black says. “You do see some full and branching networks, and that’s tantalizing, because if we get more data, it will be interesting to know whether there really are regional differences.”

Going a step further, Black compared Titan’s images with recently renewed landscapes on Earth, including volcanic terrain on the island of Kauai and recently glaciated landscapes in North America. The river networks in those locations are similar in form to those on Titan, suggesting that geologic processes may have reshaped the moon’s icy surface in the recent past.

“It’s a weirdly Earth-like place, even with this exotic combination of materials and temperatures,” Perron says. “And so you can still say something definitive about the erosion. It’s the same physics.”

Source: Massachusetts Institute of Technology (MIT)

Surprise: Tropical Lakes on Titan!

 

NASA’s Cassini spacecraft has spied long-standing methane lakes, or puddles, in the “tropics” of Saturn’s moon Titan. One of the tropical lakes appears to be about half the size of Utah’s Great Salt Lake, with a depth of at least 3 feet (1 meter).

Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan

Saturn’s rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. Image Credit: NASA/JPL-Caltech/Space Science Institute 

The result, which is a new analysis of Cassini data, is unexpected because models had assumed the long-standing bodies of liquid would only exist at the poles. The findings appear in this week’s issue of the journal Nature.

Where could the liquid for these lakes come from? “A likely supplier is an underground aquifer,” said Caitlin Griffith, the paper’s lead author and a Cassini team associate at the University of Arizona, Tucson. “In essence, Titan may have oases.”

Understanding how lakes or wetlands form on Titan helps scientists learn about the moon’s weather. Like Earth’s hydrological cycle, Titan has a “methane” cycle, with methane rather than water circulating. In Titan’s atmosphere, ultraviolet light breaks apart methane, initiating a chain of complicated organic chemical reactions. But existing models haven’t been able to account for the abundant supply of methane.

“An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life.”

Global circulation models of Titan have theorized that liquid methane in the moon’s equatorial region evaporates and is carried by wind to the north and south poles, where cooler temperatures cause methane to condense. When it falls to the surface, it forms the polar lakes. On Earth, water is similarly transported by the circulation, yet the oceans also transport water, thereby countering the atmospheric effects.

The latest results come from Cassini’s visual and infrared mapping spectrometer, which detected the dark areas in the tropical region known as Shangri-La, near the spot where the European Space Agency’s Huygens probe landed in 2005. When Huygens landed, the heat of the probe’s lamp vaporized some methane from the ground, indicating it had landed in a damp area.

Areas appear dark to the visual and infrared mapping spectrometer when liquid ethane or methane are present. Some regions could be shallow, ankle-deep puddles. Cassini’s radar mapper has seen lakes in the polar region, but hasn’t detected any lakes at low latitudes.

The tropical lakes detected by the visual and infrared mapping spectrometer have remained since 2004. Only once has rain been detected falling and evaporating in the equatorial regions, and only during the recent expected rainy season. Scientists therefore deduce the lakes could not be substantively replenished by rain.

“We had thought that Titan simply had extensive dunes at the equator and lakes at the poles, but now we know that Titan is more complex than we previously thought,” said Linda Spilker, the Cassini project scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini still has multiple opportunities to fly by this moon going forward, so we can’t wait to see how the details of this story fill out.”

Source: Jet Propulsion Laboratory