My first Magazine Sky & Telescope - 02.2019 | Page 27
Spring Equinox
Voyager 1 Encounter
March 1980
August 2009
January 2039
November 12, 1980
u LONG VISIT
Cassini-Huygens
reached Saturn
just after the
planet’s perihe-
lion. After sending
Huygens to Titan’s
surface in 2005,
Cassini surveyed
the moon 127
times at various
distances.
N
Summer Solstice
December 1987
May 2017
October 2046
n
si
yge
u
i-H
is s i o
ns M
January 14, 2005
n
Perihelion
S
S
Aphelion
January 1974
July 2003
November 2032
Cassini-Huygens
Saturn Orbit Insertion
July 1, 2004
Cassini End of Mission
N
9 AU
September 15, 2017
10 AU
September 1988
April 2018
July 2047
Winter Solstice
S
May 1973
October 2002
April 2032
Saturn’s axial tilt
26.7°
N
S
Autumn Equinox
November 1995
April 2025
October 2054
Huygens Descent
N
1 Titan year = 29.5 Earth years
1 Titan day = 15.9 Earth days
heaviest molecule discovered before Cassini arrived in the
system and characterize the plasma environment. CAPS
Saturn system (C 6 H 6 , mass of 78). Scientists thought that
was capable of measuring a much larger range of ions than
would be good enough.
INMS, but it only had suffi cient mass resolution
It wasn’t. INMS found molecules all the way
to identify the composition of the light ions it was
up to its upper mass limit. That was frustrating:
designed to study.
It meant we wouldn’t be able to use INMS to tell
However, when CAPS starting making measure-
#4
what the heaviest species are in Titan’s atmosphere.
ments of Titan’s atmosphere during close fl ybys,
Acetylene
Luckily, the orbiter had a variety of instru-
it found something startling: negatively charged
ments. Another one, called the Cassini Plasma Spectrometer
ions with a mass-to-charge ratio of up to 10,000 atomic mass
(CAPS), was designed to analyze light ions in the Saturn
units. That means that, instead of recording ionized mol-
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