Saturn’s Moon Saturn’s Moon Titan Titan

ASL – NASA AMESASL – NASA AMES

Renee Condori Apaza, Renee Condori Apaza, Bishun N. Khare, Bishun N. Khare, Christopher P. McKayChristopher P. McKay

The Advanced Studies LaboratoriesThe Advanced Studies Laboratories

The Giant MoonThe Giant Moon Titan was the sixth moon ever to be discovered, in 1655 by Dutch astronomer Christian Huygens. Named due to its massive size, Titan was originally thought to be the solar system’s largest moon.

That title goes to Ganymede (Jupiter)

Through a large telescope, Titan appears as a pale orange ball. Even Voyager 1 saw little detail.

Value of space missionsValue of space missions Voyager 1Voyager 1

Extremely little known Extremely little known about Titan prior to about Titan prior to Voyager 1Voyager 1

Provided enormous Provided enormous amount of information amount of information about Titan’s about Titan’s atmospheric atmospheric compositioncomposition

Also provided estimates Also provided estimates of atmospheric of atmospheric structure and structure and temperaturetemperature

Cassini-Huygens (NASA-ESA)Cassini-Huygens (NASA-ESA) Utilized the information Utilized the information

learnt from Voyager to learnt from Voyager to includeinclude Imaging spectrometer to Imaging spectrometer to

see through the haze see through the haze (VIMS)(VIMS)

GCMS on Huygens to look GCMS on Huygens to look at atmosphere composition at atmosphere composition during descentduring descent

SSP surface science SSP surface science packagespackages

http://saturn.jpl.nasa.gov/home/index.cfm

Useful facts about Useful facts about TitanTitan

Titan’s diameter of 5150 km is larger than Titan’s diameter of 5150 km is larger than Mercury but smaller than MarsMercury but smaller than Mars

Titan rotates very slowly – one Titan Day Titan rotates very slowly – one Titan Day corresponds to about 16 Earth dayscorresponds to about 16 Earth days

Titan is tidally locked around Saturn just like our Titan is tidally locked around Saturn just like our own Moon own Moon Same face always points toward SaturnSame face always points toward Saturn Orbital period must also be 16 Earth daysOrbital period must also be 16 Earth days

With Saturn’s orbital period being 29.5 Earth With Saturn’s orbital period being 29.5 Earth years, a year on Titan contains about 673 Titan years, a year on Titan contains about 673 Titan DaysDays

Inclined at 26.7° to the Sun (cf Earth’s ~23°) => Inclined at 26.7° to the Sun (cf Earth’s ~23°) => Titan experiences seasonsTitan experiences seasons

Without being able to take soundings we know Without being able to take soundings we know very little about its internal structurevery little about its internal structure

Titan’s surface is Titan’s surface is obscured by cloudsobscured by clouds

Titan’s size was originally Titan’s size was originally over-estimated: we are over-estimated: we are looking at dense, thick layers looking at dense, thick layers of of opaque hazeopaque haze, not the , not the surface.surface. Voyager 1 snapshots of the Voyager 1 snapshots of the planet’s edge (1980) showed planet’s edge (1980) showed that the haze was that the haze was multi-multi-layeredlayered.. Voyager 1 was crucial in determining the size of Voyager 1 was crucial in determining the size of Titan - used radio waves to penetrate the haze Titan - used radio waves to penetrate the haze

The atmosphere shows very distinct haze layers. The origin ofthese layers is not yet understood (possibly related to a wave-type phenomenon in the atmosphere).

Tholin and Titan haze

Atmospheric Atmospheric CompositionComposition

In addition, the atmosphere contains several percent of methane, and many compounds of H, C, Ar : but no free O2.

We now know that the atmosphere is largely composed of nitrogen. Sound familiar?

Composition of Composition of Titan’s Titan’s atmosphere atmosphere (Ralph Lorenz and Jacqueline (Ralph Lorenz and Jacqueline

Mitton. 2002) Mitton. 2002)

MoleculeMolecule Relative abundance Relative abundance on Titan on Titan

(Earth)(Earth)

NN22 97% 97% (78%) (78%)

CHCH44 3% (0.000175%)(0.000175%)

HH22 0.2%0.2%

(0.000055%)(0.000055%)

COCO22 Aprox. 10 ppm Aprox. 10 ppm (0.0384%)(0.0384%)

CC22HH66 0.002%0.002%

(0.000175%)(0.000175%)

CC22HH44 10 ppm 10 ppm (0.0004%)(0.0004%)

Earth vs Titan AtmospheresEarth vs Titan Atmospheres

Temperature of TitanTemperature of Titan

Naively applying the radiation balance model to Naively applying the radiation balance model to Titan we find the estimate for it’s temperature is:Titan we find the estimate for it’s temperature is:

This is actually very close to the found answerThis is actually very close to the found answer Haze created in Titan’s atmosphere serves to Haze created in Titan’s atmosphere serves to

increase albedo – compensating for any increase albedo – compensating for any greenhouse effect that might occur.greenhouse effect that might occur. Sometimes called an “anti-greenhouse effect” Sometimes called an “anti-greenhouse effect”

but is equivalent to the scenario involved in a but is equivalent to the scenario involved in a “nuclear winter”“nuclear winter”

K 90 K 5.9

278K

278

AUin

p

pd

T

Temperature in the Temperature in the atmosphereatmosphere

Phase diagram for methanePhase diagram for methane

One bar is about1 atm.

Pressure at surfaceof Titan isabout 1.5 bar

Expect to find bothliquid and gaseous forms of methane

Titan’s average surface temp

Atmospheric Atmospheric chemistry…chemistry…

Titan’s atmosphere is a giant chemistry lab: UV Titan’s atmosphere is a giant chemistry lab: UV light from the distant Sun splits up some of the light from the distant Sun splits up some of the native methane and nitrogen molecules, native methane and nitrogen molecules, e.g.e.g.

CHCH44 + photon → CH + photon → CH22 + H + H + H + H

CHCH44 + photon → CH + H + H + photon → CH + H + H22

The highly reactive radicals will then bond The highly reactive radicals will then bond together in new ways, forming heavier chemicals together in new ways, forming heavier chemicals which are expected to condense and rain out.which are expected to condense and rain out.

Comparatively straightforward to form very Comparatively straightforward to form very long chain hydrocarbons through reactions with long chain hydrocarbons through reactions with CH radicals (see G&S 180).CH radicals (see G&S 180).

Over billions of years, huge lakes of liquid Over billions of years, huge lakes of liquid hydrocarbons should have accumulated on the hydrocarbons should have accumulated on the surface…surface…

Tholin’s Chemistry Tholin’s Chemistry Reactions Reactions

Titan’s “Climate”Titan’s “Climate” At 94 K water At 94 K water

will not will not evaporate so evaporate so there is virtually there is virtually essentially no essentially no water vapor in water vapor in the atmospherethe atmosphere

Clouds are Clouds are composed of composed of methane/ethane methane/ethane and other simple and other simple organic organic moleculesmolecules

Precipitation of Precipitation of the clouds should the clouds should also result in also result in liquid methane & liquid methane & ethane rain!ethane rain! Will help form Will help form

the proposed the proposed lakes and seas lakes and seas of of hydrocarbonshydrocarbons

Polar cloud formation

Lakes of hydrocarbons…. an artist’s impression

This view of Titan taken on Feb. 25, 2007, reveals a giant lake-like feature in Titan's North Polar Region. It is approximately 1,100 kilometers (680 miles) long and has a surface area slightly smaller than that of Earth's largest lake, the Caspian Sea.

Water on TitanWater on Titan

Titan is much too cold for surface liquid Titan is much too cold for surface liquid water, with a temperature of 94 K (-water, with a temperature of 94 K (-178°C)178°C) However, it has been proposed that However, it has been proposed that water could exist temporarily in melt pools water could exist temporarily in melt pools produced by impacts.produced by impacts.

There may also be liquid water under There may also be liquid water under the ice-like surfacethe ice-like surface

Large melt pools hundreds of meters Large melt pools hundreds of meters deep might take deep might take centuriescenturies or even or even milleniamillenia (if mixed with ammonia) to freeze (if mixed with ammonia) to freeze completely.completely.

Liquid assetsLiquid assets

If liquid water could survive for hundreds If liquid water could survive for hundreds of years, that is long enough for interesting of years, that is long enough for interesting chemistrychemistry Chemical reactions in surface melts Chemical reactions in surface melts could add oxygen from water to the N, C, could add oxygen from water to the N, C, H in the tholin to make carboxylic acids, H in the tholin to make carboxylic acids, purines and pyramidines (forms base found purines and pyramidines (forms base found in nucleic acids)in nucleic acids) As mentioned, Titan may well have a sub-As mentioned, Titan may well have a sub-surface ocean like Europesurface ocean like Europe

This is needed in many models to allow This is needed in many models to allow methane to escape from the interior, methane to escape from the interior, and replace the methane lost in the and replace the methane lost in the atmosphere by chemistry.atmosphere by chemistry.

Titan Cryovolcano ?Titan Cryovolcano ? Huygens team produced this picture of a possible Huygens team produced this picture of a possible volcano, with two outflowing ‘arms’.volcano, with two outflowing ‘arms’.Rather than spewing lava it is believed to spew a Rather than spewing lava it is believed to spew a slurry of methane, ammonia and water iceslurry of methane, ammonia and water ice

Titan GeographyTitan Geography Huygen’s gave us some incredible Huygen’s gave us some incredible

pictures of smaller scale features. pictures of smaller scale features. HillsHills Drainage featuresDrainage features Mud flats?Mud flats?

Note the camera stopped working before Note the camera stopped working before touchdown so there are no detailed touchdown so there are no detailed images from right above the landing site images from right above the landing site

The descent…The descent…

NASA movie

Panorama of Huygens Panorama of Huygens ImagesImages

Drainage features

Pictures taken while probe will still several km above surface

Full 360Full 360oo view view

The dark plain is pebbly, and cut by channels.

It is also wet with methane and ethane….

1 km

Ziels

View from the landing site

Oceanography on Titan?Oceanography on Titan? Finding another body with liquid content Finding another body with liquid content

presents the opportunity to hypothesize about presents the opportunity to hypothesize about the behaviour of those liquidsthe behaviour of those liquids

Scientists have modelled the expected wind-Scientists have modelled the expected wind-driven wave heights for hydrocarbon seas.driven wave heights for hydrocarbon seas.

Anyone for surfing on Titan?Anyone for surfing on Titan?

VariablesVariables TitanTitan EarthEarth

Significant wave Significant wave height / mheight / m

4.54.5 0.60.6

Wave speed / m sWave speed / m s-1-1 5.55.5 5.55.5

Wavelength / mWavelength / m 105105 1111

Period /s Period /s 11.511.5 3.53.5

Life on Titan?Life on Titan? As we might expect, the possibility seems As we might expect, the possibility seems

very remotevery remote If there is life it would probably be imbedded If there is life it would probably be imbedded

in a water layer embedded under icein a water layer embedded under ice Little oxygen though, and the low Little oxygen though, and the low

temperatures make this possibility even temperatures make this possibility even less probableless probable

Possibly earlier in its life Titan was Possibly earlier in its life Titan was sufficiently warm (following its formation) sufficiently warm (following its formation)

Alternatively, when the Sun becomes a Alternatively, when the Sun becomes a supergiant Titan’s temperature is expected to supergiant Titan’s temperature is expected to rise to (a balmy!) 170 Krise to (a balmy!) 170 K Still a long way from freezing point of Still a long way from freezing point of

water though…water though…

Summary Summary

Titan shows many incredible featuresTitan shows many incredible features Only liquid bodies observed in the solar other Only liquid bodies observed in the solar other

than Earththan Earth Huge seas of hydrocarbonsHuge seas of hydrocarbons

Only moon with a thick atmosphereOnly moon with a thick atmosphere Similar to Earth in that it is dominated by Similar to Earth in that it is dominated by

nitrogennitrogen Surface features consistent with erosionSurface features consistent with erosion

However, it seems highly doubtful it is a good However, it seems highly doubtful it is a good candidate for lifecandidate for life

THANKS SO MUCHTHANKS SO MUCH