spacecraft was acting as a data relay set on the horizon.
That low transmission path led to some interesting radio
multipath effects (see the May 2006 issue of SERVO).
Not all deserts have sand dunes, but, off in the
distance in its descent images, a couple of long, narrow
dark sand dunes can be seen. These dunes and tens of
thousands more were mapped over subsequent years by
Cassini’s radar instrument (since the project began, I’d
morphed from aerospace engineer into planetary scientist
and geologist — I led planning of the radar observations
and reported the discovery of Titan’s dunes in 2006) and
remarkably cover about 15% of Titan’s surface area — a
much bigger fraction than on Earth or Mars (with a
diameter of 5,150 km, Titan itself is larger than the planet
Mercury, and is only just the second largest moon in the
solar system).
Titan’s dunes are the size and shape of the largest
dunes on Earth — in the Arabian and Namib deserts, tens to
hundreds of km long, regularly spaced 2-3 km apart, and
often over 100 m high!
So, Titan is a desert world, right? Well, no. It turns out
that Titan — which has an equatorial tilt ( 26. 7 degrees)
much like the Earth’s — has seasons, and gets much more
rainfall at higher latitudes than low ones. Its seasons are
long, since Saturn and Titan take 29. 5 Earth years to go
around the sun. When Cassini arrived, it was just past the
peak of southern midsummer (2002), and Cassini’s cameras
and big telescopes on Earth (like the Keck) snapped
methane clouds puffing up around the south pole where
46 SERVO 05.2015
Figure 8. Sun glinting off the dead flat surface of the hydrocarbon
lake, Jingpo Lacus on Titan in 2009, as seen in the near-infrared (five
microns wavelength) by Cassini's visual and infrared mapping
spectrometer.
Figure 7. Cassini camera color-composite of Titan in 2014. This
portrayal is slightly false-color — the red channel in the picture
here is actually of light in the near-infrared (940 nm — the same
wavelength as a typical TV remote control) which pierces the
orange smog better than visible light. The North pole is towards
the upper left, and the irregular dark spots there are Titan's seas.
The fainter, larger dark areas at the right of the image are the
equatorial sand seas.
Resources
Author
www.lpl.arizona.edu/~rlorenz
Author talk (SETI Institute) about exploring Titan
www.youtube.com/watch?v=cgyWaoaIW3Q
NASA Cassini website, with latest pictures of Titan
http://saturn.jpl.nasa.gov
NASA Institute for Advanced Concepts (NIAC)
www.nasa.gov/directorates/spacetech/niac/
Huygens descent videos
Dashboard version showing radio data and
image/sensor acquisition sequence
www.youtube.com/watch?v=QbmcoL3OqPk
Narrated version for 10th Anniversary
www.youtube.com/watch?v=9L471ct7YDo
Related N&V /SERVO articles
R D Lorenz, “Demonstrations of Multipath Interferences,”
SERVO Magazine, Vol. 4 No. 5, pp 35-38, May 2006
(illustrating an effect seen in Huygens Radio signal)
R D Lorenz, “Frisbee Black Box,”
Nuts & Volts, Vol. 25 No. 2, pp 52-55, February 2004
(Measuring dynamics of spinning, flying objects
in anticipation of Huygens descent)