This week’s guess the planet image comes from Titan. Credit
for this image goes to the cassini team. Their image description states that there
1 km is 2.85 pixels across, north is towards the top of the image. This is a
Radar image, which allows us to peer through the thick haze of atmosphere that
surrounds the moon of Saturn. This means that it isn’t as crisp an image as
those which are available for many other solar system bodies. However we can
still learn a lot about the surface of this small world.
Using Radar gives us the opportunity to look at this image
in a different way, which makes the nature of the features much clearer. In
this 3d model of the area we can see that the round feature near the bottom of
the image above consists of a deep hollow directly adjacent to a large peak.
The
depressed region is Sotra Patera, and the mountain is Doom Mons. “Patera” means
bowl in Latin, so is used as the name for basins and depressions in planetary
nomenclature. Choosing names for features on other planets can be quite a complex
process. On Earth we have been naming the landscape for millennia. If you live
near a mountain you likely have a name for it.
When we look at another world for the first time we have to
come up with names for features pretty quickly, otherwise it makes it difficult
to talk about what we are seeing or to study the geomorphology. For almost a
hundred years the task of deciding what things can be called has fallen to the International
Astronomical Union, they have defined a series of latin words such as patera,
mons and Planitia, which define various easily identified geographical
features. These terms are thus used consistently across every planet except
earth, where traditional names of features predominate for cultural reasons. The
IAU then approve themes to be used to assign consistent names to specific
features. Doom Mons has quite an ominous name for a reason, mountains on titan
are named after fictional mountains in Middle Earth. Since this is the largest
mountain range on Titan it was assigned the name of the most significant
mountain in the Lord of the Rings. A large number of fictional and mythological
place names have been used for features across the solar system. More information
on planetary nomenclature can be found at this link.
Sotra Patera is the deepest of several craters in the
mountain range, which are believed to have formed as volcanic calderas. Unlike
its fictional counterpart Doom Mons doesn’t spill molten lava onto the
surrounding plains. Rather it is believed to be an icy Cryovolcano. The material
erupted form this volcano would not be molten rock, but rather a mixture of
water and ammonia, or perhaps similar in composition to the liquid hydrocarbons
which are found in Titan’s seas. Despite the radically different material, the morphology
of this area is a good match for volcanic terrains on Earth, where peaks and
craters form distinctive volcanic landscapes. The same processes are shaping
the environment, but the different temperature conditions mean that different
materials are involved.
This site is the best example of volcanic morphology on
Titan, but other features have also been observed which could be evidence of volcanic
events. The Cassini team are particularly interested in flow features,
and areas where the landscape seems to change between images,
possibly suggesting that volcanism is occurring in the present day. If Titans
cryovolcanoes are still active then this could explain why the moon has such a
thick atmosphere, as volcanic processes might replenish the gases which are
lost to space.
Image Credits
- Doom Mons and Sotra Patera NASA/JPL- Caltech Via Wikipedia
- Map of titan’s mountains NASA/JPL-Caltech/University ofArizona/USGS
- 3D model of area NASA/JPL-Caltech/ASI/USGS/University of Arizona
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