First Images from the Mars Reconnaisance Orbiter (MRO)

Reached Mars on March 10Now: turning elliptical orbit intoa more circular orbit.

First test images.

Craters (fresh/old?)GulliesDunes

Begins collecting data inNovember.

$720 million mission.

ESA Venus Express Went into Orbit

$260 million mission.

25th Anniversary of the First Shuttle Launch

Reflection in the news media over the CrewExploration Vehicle.-lack of funds to accomplish-costs over 1/5 of NASA’s budget-requires significant transformation in NASA

Lecture 32. Titan and its Atmosphere.

reading: Chapter 8

Titan

Largest Moon of Saturn - 5150 km.Discovered by Christiaan Huygens in 1655.Voyager 1 flyby in 1980.In 2004, Cassini orbiter made close observations.Jan 2005, Huygens probe landed on the surface.Composition: ~50% water ice and ~50% rockSimilar composition as Ganymede & Callisto.

Density of water: 1.0 g/cm3

Titan/Callisto: 1.9 g/cm3

Earth: 5.5 g/cm3

May have a rocky core and a mantle of ice.

Rotates every 16 days, is in synchronous rotation.

Voyager found southern hemisphere to be brighter,are seasonal differences in brightness.

Earth: 12,700 kmMars: 6,800 kmGanymede:5262 kmMoon: 3476 km

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Titan’s Atmosphere

Unique that it has a dense atmosphere of 1.6 bars and is mostly N2.77-85% N2, 12-17% argon, 3-6% methane, 0.2% H2

Trace amounts of organic compounds:ethane, propane, hydrogen cyanide, CO2, CO, acetylene

Organic compounds when methane undergoes photochemicalreactions from the faint sunlight.

Produces a thick smog, hazy atmosphere.Haze layer is ~300 km above the surface. There are distinct layers in the haze.

Titan’s orbit is sometimes outside of Saturn’s magnetosphere.Solar wind particles may ionize the atmosphere and cause

some of the photochemical reactions in the atmosphere.

Thick atmosphere obscures the surface in visible light.

false-color Voyager 1 image of haze layers

Voyager Observations

Atmosphere structure and dynamics determined by 2 instruments:-radio occultation

How radio waves are scattered and bent as they pass throughthe atmosphere determine the T and density of the atmosphere

-infrared spectroscopyDifferent compounds absorb heat energy at differentwavelengths and vibrate. Measure how heat energyfrom sunlight is absorbed (produces peaks and valleys in the spectrum).Each compound has particularfingerprint.

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Voyager Observations, cont.

Voyager Observations, cont.

large number of hydrocarbons and N-containing compounds

Titan’s Surface

Surface temperature: -179˚CCold enough that methane (CH4) could be liquid.Cold enough that ethane (CH3CH3) could also be liquid.Thought there could be seas of liquid methane and ethane..

Freezing T Boiling TH2O 0˚C 100˚CNH3 -78˚C -33˚CCH4 -182˚C -164˚CCH3CH3 -183˚C -89˚C

at -179˚C, CH4 is solid/liquid/gas?at -179˚C, CH3CH3 is solid/liquid/gas?

Titan’s Surface

If there are regions where the surface is <-183˚C (cools 4˚C)you could have frozen mountains of methane and ethane ice!

Why is Titan so cold??at 9.6AU, sunlight is 100x weaker

So, if it is cold enough to liquify methane and ethane, why is therelots of methane in the atmosphere??

Could be places where it is slightly warmer than -164˚C where liquidmethane can turn into gas, once in the atmosphere cooling would produce

clouds and then methane rain.

Titan’s Surface

Hubble Space Telescope images:Peered through the clouds using infrared light.Observed dark and light regions on the surface.Couldn’t really figure out what they were due to.Methane/ethane Seas? Bright volcanic regions?

If Titan does have liquid seas,they should experience tides justlike the Earth as it revolves aroundSaturn!

Clouds

Scattered clouds.Composed of methane, ethane, or simple organic compounds.More complex organic compounds create the orange color.Clouds change hourly, presumably deposit methane rain onto the surface.

Tholins

Polymer formed from uv irradiation of CH4 or CH3CH3.Abundant on icy bodies in the solar system.

Coined by Carl Saganto describe unknown organic substancesobtained in Miller-Urey-type experiments usinggas mixtures found in Titan’s atmosphere.

Produce a thick orange goo.

When dissolved, they produce amino acidswith both handedness.

Polymers of C, H, and N.Over 75 different compounds in it.PAH family: benzene (1 ring), 2-4 ringscyclic compounds with C and N: includes bases found in nucleic acids

How are Tholins Produced?

UV light causesreactions to occurhigh in the atmosphere

(photochemicalreactions)

Solid particles -Tholins -likelyrain down to thesurface.

Speculation: could bekm-deep deposits oftholins on the surface.

Titan as a Model for Early Earth

Methane-rich, N2-rich atmosphere, lack of oxygen.An early methane greenhouse helps solve Earth’s Faint Young Sun

Problem.Photochemical reactions producing organic compounds.Some think there could have been similar hazes on early Earth.

Hydrogen cyanide in the atmosphere - is a prebiotic compound inthe abiotic synthesis of amino acids.

Titan is soooo cold - chemical reactions proceed very sloooowly.So fewer number of organic compounds are produced.At -179˚C a chemical reaction will be 1042 times slower than at

room temperature!

Life on Titan?

Do you have the 5 thing needed to have life?

Properties of Water that are Important for Life

It is the “universal solvent” because itcan dissolve the most substances than anyother liquid.

Electrical charge differential helps it dissolve ions, like sodium chloride.

Water molecules are attracted to each other -creates surface tension

Water forms drops, capillary action allows water to be sucked upplant roots and blood vessels

Water is a polar compound.Ions are needed for life!

Water can also dissolveuncharged organiccompounds, like sugars.

It is found in all three statessolid, liquid, gas on the Earth

Methane and Ethane Liquids

Are hydrocarbons - so have a greasy nature.

Are non-polar compounds so they:-don’t dissolve ions.-don’t have much surface tension.

Lecture 33. Cassini-Huygens Mission.

reading: Chapter 8