Australian Sky & Telescope - 04.2019

30 AUSTRALIAN SKY & TELESCOPE April 2019

units.Thatmeansthat,insteadofrecording

ionisedmoleculesconsistingofsixorsevenheavy

atomsinthisregionofTitan’satmosphere,CAPS

insteadfoundionsmadeof600or700heavy

atomsstucktogether,themassofsmallproteins

on Earth!

Unfortunately, CAPS was not designed to

identify such heavy ions. So although we know they’re

presenthighaboveTitan,we’llneedanothermissiontobe

able to identify them.

CHON: Life’s four building blocks

Thediscoveryoftheseverylargeionsisincrediblyimportant,

becauseithaschangedourunderstandingofthechemistry

occurringinTitan’satmosphereandofhow

itshydrocarbonhazesform.Indoingso,it

hasalsoalteredourideasabouthowplanetary

atmospheresworkingeneral.

We did not know that atmospheres were

capable of producing such large molecules,

especially so high in an atmosphere, where the

pressureisverylowandmolecularcollisions(whichbuild

largercompounds)arerare.Ifthesemoleculesaremadeof

thesameatomsrequiredforthesmallsetofmoleculesthat

life as we know it here on Earth uses — carbon, hydrogen,

oxygen,andnitrogen(collectivelydubbed‘CHON’)—then

theseionsmaybeimportantforunderstandingtheorigin

and evolution of life on Earth. If life exists on Titan, then

theycouldbeimportantforunderstandingitsrisethere,too.

Chemistryrequiresenergy.Theionosphereislargelycreated

byveryhigh-energyphotonsfromtheSun

impingingupontheatmosphere’smolecules

andknockingelectronsfree.Withsomany

photonsfloodingintoit,thisregionofTitan’s

atmospherehasmoreenergyavailableto

drivechemistrythanregionsdeeper

down, where few photons penetrate.

These photons are important for

breaking up N 2 ,whosepairedatomsshareatriple

bondthatisoneofthehardesttobreak;the

photonscapableofbreakingthisbondareonly

availableveryhighupintheatmosphere.

Theamountofenergyavailablematters

formanyofthequestionsweareasking,

becauseitmeansthedifferencebetween

nitrogen participating in the chemistry or

not.WeknewbeforeCassinithatTitan’s

atmospheric chemistry included substantial

amountsofcarbonandhydrogen,but

INMS measurements have shown us that

theionsinTitan’sionospherealsocontain

much more nitrogen than we expected to

findthere.Ifnitrogenisinvolvedinthe

chemistry, then three of the four elements

necessary for life are accounted for.

One additional discovery made by CAPS

shows that the final element, oxygen, might

be playing a role, too. Scientists didn’t know

aboutthesalty-waterplumesofEnceladusuntil

spotting them in data from Cassini. It turns out

WNORTHERN LAKESThis colourised mosaic of Titan’s

north pole was constructed using radar-mapping data from the

Cassinispacecraft;theedgesextenddownto50°Nlatitude.Using

Cassini’s observations, scientists discovered three seas (labelled) and

hundredsofsmalllakes.Nearlyallthelakesandseasareconfined

to a rectangle covering about 900 km by 1,800 km in the northern

hemisphere; only 3% of the liquid detected on Titan falls outside of

this area. The lakes might be seasonal features.

#6

Ethylene

#5

Propane

Ligeia

Mare

Punga

Mare

Kraken

Mare

LAKES: NASA / JPL-CALTECH / ASI / USGS; SURFACE FEATURES: SURFACE: NASA /JPL / ESA / UNIVERSITY OF ARIZONA; CRYOVOLCANO: NASA /

JPL

/ USGS / UNIV. OF ARIZONA; DUNES: NASA / JPL-CALTECH / ASI; MARE: NASA / JPL-CALTECH / ASI / CORNELL; HEMISPHERE: NASA / JPL-CA

LTECH /

SPACE SCIENCE INSTITUTE

ALIEN ‘EARTH’