From Newsgroup: sci.space.news


https://saturn.jpl.nasa.gov/news/2894/

Cassini
Titan (T-119): A Unique "Double Midnight" Flyby

Artist's rendition of the position of Saturn and Titan during T-119

During Cassini's T-119 Titan flyby on May 6, the Radio Science
Subsystem, or RSS, will observe an atmospheric occultation, in which
Cassini appears to go behind Titan's atmosphere as seen from Earth. The
way the atmosphere modifies Cassini's radio signal will be used to
profile the thermal structure of the atmosphere and learn more about how
it varies with Titan's seasons. RSS continues with a short bistatic
scattering observation, with the radio signal's ground track possibly
crossing small lakes on Titan. Data from this observation may yield
information about Titan's surface (including reflectivity, roughness,
and dielectric constant) that will improve our understanding of the
moon's composition.

Key Points

The T-119 flyby is a unique "double midnight" flyby, in that it occurs
when Titan is on the night side of Saturn and the closest approach by
Cassini is on the nightside of Titan as well.

Scientists have found that Titan's upper atmosphere and ionosphere
change depending on a variety of factors, including Titan's location in
its orbit through Saturn's magnetosphere, timing with respect to the
11-year solar cycle, and the geometry with respect to Titan and
orientation with respect to the Sun of the closest approach. The only
way to understand the influence of each of these factors on Titan's
upper atmosphere and ionosphere is to make observations over a wide
range of varying geometries.

During the flyby, the Ion and Neutral Mass Spectrometer, or INMS, will
make measurements of Titan's atmosphere when the nightside receives the smallest possible infusion of energy from the sun. This helps scientists understand how the sun drives Titan's upper atmospheric chemistry, while density observations provide insight on how quickly Titan's atmosphere
responds to inputs, relative to the length of Titan's day.

The Magnetospheric Imaging Instrument, or MIMI, will measure the
energetic ion and electron environment during the flyby. MIMI data will
be used to estimate the energetic particle input from the magnetosphere
into Titan's atmosphere and ionosphere. This will help interpret the atmospheric characteristics (the ionization layers and scale heights)
observed by RSS. Cassini's observations have demonstrated that the magnetospheric environment near Titan is much more variable and complex
than scientists could ever have anticipated.



Titan Flyby at a Glance

Date
May 6, 2016

Altitude
603 mi (971 km)

Speed (relative to Titan)
13,198 mph (5.9 km/sec)

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