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Titan

1. Structure & Major Surface Features

2. Hydrocarbon Lakes on Titan

3. The Atmosphere....Why is it There?

Overview

3Titan’s radius is ~50% larger than the Moon.

It is the only other body in our Solar System known to have liquids on the surface.

Comparative ‘Satelliteology’ 4

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TitanGanymede Callisto

Parent Jupiter Jupiter Saturn

Radius 2631 km 2410 km 2575 km

Density 1.93 g/cm3 1.83 g/cm3 1.88 g/cm3

Atmosphere No No Yes

Magnetic field Yes No No

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This model suggests the cool and sluggish interior of Titan failed to fully differentiate.

In addition to the hazy surface of Titan (yellow), the layers in the cutaway show an ice layer starting near the surface (light gray), an internal ocean hypothesized from other Cassini data (blue), another layer of ice (light gray) and the mix of rock and ice in the interior (dark gray).

This illustration shows the likely interior structure of Titan deduced from gravity field data collected by the Cassini spacecraft. Radio science data suggests that Titan's interior is a cool mix of ice studded with rock, though the outermost 500 kilometers appear to be ice, essentially devoid of any rock.

6A model of Titan’s interior structure.

Titan’s Surface 7

The atmosphere of Titan is thick and hazy, making it impossible to see the surface at visible wavelengths of light.

Therefore, radar imaging systems provide important information about surface features and their scattering properties.

Titan 8

The Surface of Titan 9

In this radar mosaic, it is clear that Titan is dominated by bright and dark regions. The bright regions contain ice and some rock, and some features may be related to cryovulcanism.

The dark regions are now known to contain large dune fields, likely composed of hydrocarbons.

The Surface of Titan 10

During the descent, the Huygens probe imaged the surface at various resolutions.

Some of these images revealed the spectacular morphology of Titan’s surface.

At first glance it is eerily similar to Earth: channels, mountainous regions, low regions.

But on Titan, it is not rock and water that create this morphology but is instead ice and hydrocarbons.

Landing on Titan 11

On January 4, 2005, the Huygens probe entered Titan’s atmosphere and landed on the surface.

This provided the first-ever view of the true surface of Titan.....but no ‘oceans’!

The Surface of Titan 12

Dunes at the equator, but ‘waveless’ lakes at the pole...

Titan’s Dunes.... Linked to Long-Term Climate Cycles? 13

1-2 km wide ~100 m tall 100+ km long ~13% of surface

Composed of sand-sized solid hydrocarbons, NOT silicates/rock.

Dunes thought to represent modern daily, tidal & seasonal winds... but climate models fail to reproduce the observed dune patterns.

Recent work suggests shifts in wind direction and sediment availability over time; re-orientation of dune crests might take 3,000 Saturn years!

The Surface of Titan: Ontario Lacus 14

A smooth, wave-sculpted shoreline, like that seen on the southeastern side of Lake Michigan, can be seen at the northeastern part of the lake. Smooth lines parallel to the current shoreline could be formed by low waves over time, which were likely driven by winds sweeping in from the west or southwest.The southeast shore features a round-headed bay intruding into the shore. The liquid-filled depressions appear to be relatively recent.

The middle part of the western shoreline shows the first well-developed delta observed on Titan. The shape of the delta shows that liquid flowing down from a higher plain has switched channels on its way into the lake, forming at least two lobes.

Titan is the only other world in our solar system known to have standing bodies of liquid on its surface. Because surface temperatures at the poles average a chilly 90 K, the liquid is a combination of methane, ethane, and propane, rather than water. Ontario Lacus has a surface area of about 15,000 square kilometers, slightly smaller than its terrestrial namesake, Lake Ontario.

The Surface of Titan: Lakes on Titan 15

Temperatures on Titan are so low that ice behaves like rock. Liquids erode the icy surface away and produce morphologies similar to how rock erodes by water on Earth.

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Disappearing Lakes? 17

The Surface of Titan: Lakes on Titan 18

What’s in the Lakes?

Titan’s Atmosphere 19

Pressure: 1.5 bars 1-2% CH4, remainder is mostly N2.

Orange haze is likely due to presence of more complex organics, possibly promoted by UV breakdown of methane.

Titan’s Atmospheric Puzzle: Why Does it Have One?? 20

• Titan’s environment was colder than that of Ganymede and Callisto. Jupiter is volatile poor relative to Saturn.

• Titan’s atmosphere is impact generated. Lower impact velocities at Titan could permit retention of volatiles from impacting icy bodies.

• Mabye all three bodies had atmospheres but escape driven by magnetospheric and solar UV removed the atmosphere of Ganymede and Callisto. Solar wind not as strong at Titan [still need a source in this scenario].

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• Is the atmosphere from degassing of original accretionary materials on Titan (clathrates/hydrates)?

• Was the atmosphere delivered after accretion through volatile-rich impactors?

• How do we tell the difference?

Titan’s Atmospheric Puzzle: Why Does it Have One??

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• N isotopes suggest the source may have been comets, not original accretionary material from Titan.

• N isotopes are distinct from Earth.

• Do the atmospheres of Earth and Titan have different origins/sources?

• Original form of N may have been ammonia or ammonia hydrates (NH3·H2O).

Titan’s Atmospheric Puzzle: Why Does it Have One??

23Titan’s Atmosphere

Orbit of Titan produces seasonal variations, and interaction of UV radiation with upper atmosphere leads to an atmospheric cycle in which complex organic compounds can be produced.

Titan’s Methane Cycle 24

Lunine and Lorenz 2009