//
you're reading...

Geology

Oceanography in space! Using a satellite to profile an extraterrestrial lake

Mastrogiuseppe, Marco, Valerio Poggiali, Alexander Hayes, Ralph Lorenz, Jonathan Lunine, Giovanni Picardi, Roberto Seu et al. “The bathymetry of a Titan sea.” Geophysical Research Letters 41, no. 5 (2014): 1432-1437.

 Saturn’s largest moon, Titan, contains several hundreds of lakes.  Ligeia Mare is defined as a sea by the International Astronomical Union although, most would consider it more akin to a lake.  This group of researchers took advantage of an opportunity via the Cassini satellite orbiting Saturn to calculate the bathymetry of Ligeia Mare for the first ever bathymetry sounding of an extraterrestrial sea.

Figure 1.  An image generated by Cassini flybys to show portions of Titan’s surface (NASA).  As you can see, the image is not complete because we can only see the portions of the moon that Cassini flew over.  Four flybys were used to create this image. Figure 2. Diagram of satellite coverage with mapping coordinates used to create figure 1 (Lorenz 2008).

Figure 1. An image generated by Cassini flybys to show portions of Titan’s surface (NASA). As you can see, the image is not complete because we can only see the portions of the moon that Cassini flew over. Four flybys were used to create this image.

Figure 2. Diagram of satellite coverage with mapping coordinates used to create figure 1 (Lorenz 2008).

Figure 2. Diagram of satellite coverage with mapping coordinates used to create figure 1 (Lorenz 2008).

The Cassini-Huygens unmanned spacecraft was launched from Cape Canaveral on October 15, 1997.  Seven years later, the craft reached Saturn.  The craft was composed of two parts.  The Cassini is a Saturn orbiter while the Hyugens is a probe designed to land on Titan.  This study used data collected by the Cassini spacecraft during a flyby of Titan on May 23, 2013. 

This particular flyby was used because in order for Cassini RADAR to map the topography and the bathymetry of the lake, the wavelengths must propagate directly down from the craft.  For normal image mapping (Fig. 1; Fig. 2), the satellite collects images from an angle.  The echo soundings produce altimeter profiles (Fig. 3). These profiles indicate the echoes received by the satellite.  The first strong echo indicates contact with the surface of Ligeia Mare; the second, smaller peak indicates contact with the bottom of the sea (Fig. 4).

In order to tease out other variability in the sounding profiles, several processing methods were applied.  The end result is a profile of the surface and bottom of Ligeia Mare along the Cassini flyby transect (Fig. 5).  This sound profile can be converted to a depth profile (Fig. 5) based on the speed of the echo sounding waves and the time lapsed between when the pulse is emitted from the satellite and the echo is received.  This is a slight over-simplification; the National Geophysical Data Center provides a more detailed explanation.

Figure 3. Some of the Cassini altimeter data used to calculate lake depth.  The first large pulse denotes the surface of the lake; the second, smaller pulse denotes the bottom depth.

Figure 3. Some of the Cassini altimeter data used to calculate lake depth. The first large pulse denotes the surface of the lake; the second, smaller pulse denotes the bottom depth.

Figure 4. Satellite altimetry schematic (General Bathymetric Chart of the Oceans, GEBCO).

Figure 4. Satellite altimetry schematic (General Bathymetric Chart of the Oceans, GEBCO). 

Figure 5.  Upper: Satellite image of Ligeia Mare with superimposed satellite-sounding track; red circles indicate start and end of track.  Lower: Radargram obtained from processing echo soundings.  Note the straight, horizontal red line suggests the sea surface; the fainter red line below suggests the bathymetry.

Figure 5. Upper: Satellite image of Ligeia Mare with superimposed satellite-sounding track; red circles indicate start and end of track. Lower: Radargram obtained from processing echo soundings. Note the straight, horizontal red line suggests the sea surface; the fainter red line below suggests the bathymetry.

The greatest depth found in this profile was 160m.  As seen in figure 6, the northern shore has a gentler slope than the southern.  This matches previous conceptions of higher sedimentation in the north.

So is the bathymetry of this extraterrestrial sea different from what we might see on Earth?  Potentially.  Maximum depth in the Ligeia Mare probably does not exceed 160m significantly.  Under this assumption, the sea is fairly shallow relative to those on earth.  Another study by Lorenz et al. (2008) suggests that most large bodies of water the same width on Earth would reach about 350m.  Although, that estimation allows variability that would not exclude 160m depth.

Figure 6.  Bathymetric profile of Ligeia Mare (solid) with smooth polynomial (dashed) fitted to within an error of about 14m.

Figure 6. Bathymetric profile of Ligeia Mare (solid) with smooth polynomial (dashed) fitted to within an error of about 14m.

Recall that this is just one transect of the Ligeia Mare.  But, the researchers estimate that this profile is representative of the entire sea.  Using this assumption and satellite derived sea surface area (126,000km2), the mean depth is estimated to be around 70m and the volume is about 10,000km3.  This also yields an estimate of about 5000 gigatons (GT) of carbon (nearly 100 times the known terrestrial oil and gas reserves of Earth).  I don’t think we have to worry about mining energy from Titan anytime soon.  The 7-year trip each way seems hardly economical.

 

Cited

Lorenz, Ralph D., et al. “Titan’s inventory of organic surface materials.” Geophysical Research Letters 35.2 (2008).

 

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 9 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 10 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com