Australian Sky & Telescope - 04.2019

http://www.skyandtelescope.com.au 29

whenitwasdesigned(C 2 N 2 ,withanatomicmassof52)and
theheaviestmoleculediscoveredbeforeCassiniarrivedin
theSaturnsystem(C 6 H 6 ,massof78).Scientists
thought that would be good enough.
Itwasn’t.INMSfoundmoleculesalltheway
uptoitsuppermasslimit.Thatwasfrustrating:
Itmeantwewouldn’tbeabletouseINMStotell
whattheheaviestspeciesareinTitan’satmosphere.
Luckily,theorbiterhadavarietyofinstruments.Another
one, called the Cassini Plasma Spectrometer (CAPS), was

designed to analyse light ions in the Saturn system and

characterise the plasma environment. CAPS was capable

of measuring a much larger range of ions than

INMS, but it only had sufficient mass resolution

to identify the composition of the light ions it was

designed to study.

However, when CAPS starting making

measurements of Titan’s atmosphere during close

flybys, it found something startling: negatively charged ions

with a mass-to-charge ratio of up to 10,000 atomic mass

XLONG VISIT
Cassini-Huygens
reached Saturn
just after
the planet’s
perihelion. After
sending Huygens
to Titan’s surface
in 2005, Cassini
surveyed the
moon 127 times
from various
distances.

#4

Acetylene

C

as

sin

i-H

uyg

ensM

ission

S

9AU

10 AU

N

S

N

S

N

Saturn’s axial tilt

26.7°

S

N

Voyager 1 Encounter

November 12, 1980 Huygens Descent

January 14, 2005

Cassini End of Mission

September 15, 2017

Cassini-Huygens

Saturn Orbit Insertion

July 1, 2004

Summer Solstice

December 1987

May 2017

October 2046

Autumn Equinox

November 1995

April 2025

October 2054

Winter Solstice

May 1973

October 2002

April 2032

1 Titan year = 29.5 Earth years

1 Titan day = 15.9 Earth days

Perihelion

January 1974

July 2003

November 2032

Aphelion

September 1988

April 2018

July 2047

Spring Equinox

March 1980

August 2009

January 2039