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Space Topics: Saturn
Titan
Saturn's Largest Moon
When the Voyagers passed by Titan they found its surface to be hidden behind
an impenetrable barrier of orange haze. This global view shows a faint dichotomy
between the northern and southern hemispheres. Color: True color. Credit:
NASA / JPL / Calvin Hamilton |
Size: 5,150 kilometers - Saturn's largest
moon - 0.4037 Earths
Orbital radius: 1,221,830 kilometers - 20.3 Saturn radii -
outside Saturn's ring system
Orbital period: 15.945 days
Discovery: 1655 by Christiaan Huygens
Nearly as large as Mars and possessing an atmosphere thicker than Earth's,
Titan would unquestionably be considered a planet if it orbited the Sun
on its own. When scientists first began to understand what that atmosphere
was made of -- primarily nitrogen, with a large component of methane and
significant quantities of more complex organic molecules -- they quickly
realized that Titan would be a place where liquid methane or ethane could
be raining from the skies. Thanks to Cassini-Huygens it is now known
that Titan is a youthful planet whose surface is modified and its impact
craters erased by the action of flowing liquids and possibly even a methane
cycle of cloud formation, rain, runoff, and evaporation, akin to Earth's
water cycle. The world revealed to Huygens'
cameras as it descended to Titan's surface on January 14, 2005 contains
clear signs of river vallies and water-rounded rocks. And Cassini's
Titan RADAR mapper is obtaining detailed views of channels and valleys,
eroded impact craters, and windblown sand dunes that all speak of Titan's active
geology.
The surface of Titan has historically been difficult to explore because the
thick hazes of complex hydrocarbons that make its atmosphere so interesting
also prevent a clear view to its surface. Titan stands out for how deep
its atmosphere is, with layer upon layer of hazes making for a complicated
series of obstacles to the sight of orbiting instruments. Its highest hazes
may be 300 kilometers (190 miles) above the ground, nearly four times higher
than the highest clouds on any other planet. And these thick hazes are made
of piles of different compounds, a "witch's brew" of carbon, nitrogen,
and hydrogen compounds.
The Voyager cameras were unable to penetrate Titan's hazes, returning picture
after maddening picture of a nearly featureless upper atmosphere. Cassini-Huygens
was sent to Titan with cameras capable of piercing spectral "windows" in
the haze, a RADAR mapping instrument designed specifically to produce maps
of Titan's surface, and the Huygens probe, which was dedicated to the study
of Titan's atmosphere. Despite the quantity of data that has been returned
so far, Titan still presents many enigmas to scientists. The complex
interrelationships between its atmosphere, its surface, and its interior will
take lifetimes to untangle.
| |
Earth |
Titan |
| Average surface temperature |
290 K
15 C
60 F |
-90 K
-180 C
-290 F |
| Average surface pressure |
1 bar |
1.6 bars |
| Major gases |
77% Nitrogen
21% Oxygen
0.93% Argon
~ 1% water (varies) |
90-97% Nitrogen
0-6% Argon
2-5 % Methane
0.2% Hydrogen |
Minor gases
(ppm = parts per million) |
330 ppm carbon dioxide
18 ppm neon
5.2 ppm helium
1.5 ppm methane
1.1 ppm krypton
0.5 ppm hydrogen
0.4 ppm ozone
0.3 ppm nitrous oxide
0.12 ppm carbon monoxide
0.087 ppm xenon
0.01 ppm ammonia |
~45 ppm carbon monoxide
~10 ppm ethane
~2 ppm acetylene
~0.5 ppm propane
~0.2 ppm hydrogen cyanide
~0.1 ppm ethylene
~0.01 ppm carbon dioxide
~0.008 ppm water (at high altitude)
~0.005 ppm acetonitrile
~0.005 ppm cyanogen |
| Cloud layers: altitude and composition |
12-30 km
Concentrated Sulfuric Acid, everywhere but transparent 0-12 km
Sulfates, dust, sea salt, organic compounds, here and there, may be
transparent or opaque 0-12 km
Water clouds and fog, making on average 50% opaque cloud cover |
200-300 km, variable
detached haze layers 35-200 km, variable
photochemical haze layer made of carbon-nitrogen-hydrogen polymeric
compounds 10-15 km
methane liquid and ice clouds, about 10% cloud cover |
Only one feature on Titan was prominent on Earth-based telescopic observations
to be named prior to Cassini's arrival: Xanadu, a large bright-colored splotch
on Titan's leading hemisphere. Now that Cassini has arrived, Titan has
earned a complex naming scheme for its wide variety of features:
- Albedo features (large areas that are bright or dark) are named for
sacred or enchanted places, paradise, or celestial realms from all the
world's cultures.
- Craters and ringed features are named for wisdom deities.
- Facula (small, bright features) are named for islands on Earth that are
not politically independent. Faculae (chains of bright features) are
named for Earth archipelagos.
- Flumina (linear, channel-like features) are named for mythical or imaginary
rivers.
- Lacus (small, dark features) are named for lakes on Earth. An attempt
is made to find an Earth lake with similar shape to the Titanian lacus.
- Virgae (streaks or stripes of color) are named for rain deities.
- Other features are named for deities of happiness, peace, and harmony
from all the world's cultures.
Flybys of Titan
Even if Titan were not such an interesting target Cassini would be compelled
to fly by Titan frequently. Titan's large mass provides Cassini with
gravity assists that change the shape of its orbit. Cassini only carried
enough fuel to Saturn to change its orbital velocity by a total of 400 meters
per second (900 miles per hour). The 46 Titan gravity assists provide
Cassini with a total velocity change of 33,000 meters per second (74,000 miles
per hour). How the orbit is changed by a flyby depends upon the latitude
and altitude of Cassini's path with respect to Titan, so the Titan flyby geometries
are dictated more by orbital dynamics than they are by the desires of scientists. Even
so, Cassini will build up a fairly complete data set of Titan's entire surface
and atmosphere over the course of the mission.
| Flyby |
Date |
Orbit |
Flyby
geometry |
Closest
approach
altitude |
RADAR
images? |
| T0 |
Jul 02, 2004 |
Rev 00 |
Outbound |
339,120 km |
|
| TA |
Oct 26, 2004 |
Rev 0A |
Inbound |
1,174 km |
yes |
| TB |
Dec 13, 2004 |
Rev 0B |
Inbound |
1,192 km |
|
| TC |
Jan 14, 2005 |
Rev 0C |
Inbound |
60,003 km |
|
| |
-- Huygens mission -- |
|
|
| T3 |
Feb 15, 2005 |
Rev 03 |
Inbound |
1,579 km |
yes |
| T4 |
Mar 31, 2005 |
Rev 05 |
Outbound |
2,404 km |
|
| T5 |
Apr 16, 2005 |
Rev 06 |
Outbound |
1,026 km |
|
| T6 |
Aug 22, 2005 |
Rev 13 |
Outbound |
3,669 km |
|
| T7 |
Sep 07, 2005 |
Rev 14 |
Outbound |
1,075 km |
yes |
| T8 |
Oct 28, 2005 |
Rev 17 |
Inbound |
1,353 km |
yes |
| T9 |
Dec 26, 2005 |
Rev 19 |
Outbound |
10,409 km |
|
| T10 |
Jan 15, 2006 |
Rev 20 |
Inbound |
2,043 km |
|
| T11 |
Feb 27, 2006 |
Rev 21 |
Outbound |
1,813 km |
|
| T12 |
Mar 19, 2006 |
Rev 22 |
Inbound |
1,951 km |
|
| T13 |
Apr 30, 2006 |
Rev 23 |
Outbound |
1,855 km |
yes |
| T14 |
May 20, 2006 |
Rev 24 |
Inbound |
1,879 km |
|
| T15 |
Jul 02, 2006 |
Rev 25 |
Outbound |
1,906 km |
|
| T16 |
Jul 22, 2006 |
Rev 26 |
Inbound |
950 km |
|
| T17 |
Sep 07, 2006 |
Rev 28 |
Inbound |
950 km |
|
| T18 |
Sep 23, 2006 |
Rev 29 |
Inbound |
950 km |
|
| T19 |
Oct 09, 2006 |
Rev 30 |
Inbound |
950 km |
|
| T20 |
Oct 25, 2006 |
Rev 31 |
Inbound |
950 km |
|
| T21 |
Dec 12, 2006 |
Rev 35 |
Inbound |
950 km |
|
| T22 |
Dec 28, 2006 |
Rev 36 |
Inbound |
1,500 km |
|
| T23 |
Jan 13, 2007 |
Rev 37 |
Inbound |
950 km |
|
| T24 |
Jan 29, 2007 |
Rev 38 |
Inbound |
2,726 km |
|
| T25 |
Feb 22, 2007 |
Rev 39 |
Outbound |
950 km |
|
| T26 |
Mar 10, 2007 |
Rev 40 |
Outbound |
950 km |
|
| T27 |
Mar 26, 2007 |
Rev 41 |
Outbound |
950 km |
|
| T28 |
Apr 10, 2007 |
Rev 42 |
Outbound |
950 km |
|
| T29 |
Apr 26, 2007 |
Rev 43 |
Outbound |
950 km |
|
| T30 |
May 12, 2007 |
Rev 44 |
Outbound |
950 km |
|
| T31 |
May 28, 2007 |
Rev 45 |
Outbound |
2,426 km |
|
| T32 |
Jun 13, 2007 |
Rev 46 |
Outbound |
950 km |
|
| T33 |
Jun 29, 2007 |
Rev 47 |
Outbound |
1,944 km |
|
| T34 |
Jul 19, 2007 |
Rev 48 |
Inbound |
1,300 km |
|
| T35 |
Aug 31, 2007 |
Rev 49 |
Outbound |
3,212 km |
|
| T36 |
Oct 02, 2007 |
Rev 50 |
Outbound |
950 km |
|
| T37 |
Nov 19, 2007 |
Rev 52 |
Outbound |
950 km |
|
| T38 |
Dec 05, 2007 |
Rev 53 |
Outbound |
1,300 km |
|
| T39 |
Dec 20, 2007 |
Rev 54 |
Outbound |
950 km |
|
| T40 |
Jan 05, 2008 |
Rev 55 |
Outbound |
950 km |
|
| T41 |
Feb 22, 2008 |
Rev 59 |
Outbound |
950 km |
|
| T42 |
Mar 25, 2008 |
Rev 62 |
Outbound |
950 km |
|
| T43 |
May 12, 2008 |
Rev 67 |
Outbound |
950 km |
|
| T44 |
May 28, 2008 |
Rev 69 |
Outbound |
1,348 km |
|
| T45 |
Jul 31, 2008 |
Rev 78 |
Outbound |
3,980 km |
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Map of Titan
Global map of Titan (simple cylindrical projection)
Global map centered at 180 degrees longitude (the anti-Saturnian point). The map is 2,048 pixels wide, and Titan's diameter is 5,150 kilometers, so the map resolution is 7.9 kilometers per pixel at the equator. Source
Credit: NASA / JPL / Space Science Institute / Fridger Schrempp
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Listen to the Sounds of Titan
Data from the Huygens landing site
Cassini RADAR images of Titan
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