Page 50 - Astronomy - October 2017 USA

The twin spacecraft took long, looping journeys
to explore the outer solar system. by Richard Talcott;
illustrations by Roen Kelly

he Voyager 1 and 2 probes delivered the first detailed views of the solar
system’s four giant planets and their large, shockingly diverse moons.
Voyager 2 lifted off from Cape Canaveral, Florida, on August 20, 1977,
with Voyager 1 following 16 days later. (The latter earned top billing by
Ttaking a shorter, faster trajectory that got it to Jupiter first.) CA = Closest approach
= Dots every four hours
Scientists designed both to investigate Jupiter, Saturn, and
their surroundings in exquisite detail. Voyager 1’s trajec-
tory past Saturn ultimately flung it out of the ecliptic
plane where all the planets reside.
Mission planners targeted Voyager 2 to have VOYAGER 1
the option to continue on to Uranus and Closest approach
March 5, 1979
Neptune, provided Voyager 1 achieved its to Jupiter: 0 hour
goals. Once it did, NASA gave the go-
ahead for Voyager 2’s “Grand Tour.” The
trajectory exploited a rare planetary To Sun
alignment that allowed a spacecraft to
fly past all four outer worlds in a rela- AMALTHEA
CA: –5 hours
tively short period of time using a min- IO
imal amount of fuel. The alignment of CA: +3 hours Jupiter
the late 1970s and 1980s occurs only 300,000
miles
every 175 years or so.
500,000
Now, 40 years after launch, Voyager 1 kilometers
lies 140 astronomical units (AU; the aver- EUROPA
CA: +6 hours
age Earth-Sun distance) from the Sun, and
Voyager 2 resides 116 AU away. Both probes GANYMEDE
CA: +14 hours
continue to explore the solar system’s outer
reaches from their unique vantage points. CALLISTO JUPITER’S O RBIT
CA: +29 hours
CALLISTO
Richard Talcott is a senior editor of Astronomy, CA: –34 hours
EUROPA
and vividly remembers all six Voyager encounters. CA: –5 hours GANYMEDE
CA: –15 hours
Where are they now? To Sun
AMALTHEA
CA: –2 hours
VOYAGER 2
July 9, 1979
Closest approach
HELIOSHEATH
to Jupiter: 0 hour
VOYAGER 2
Jupiter IO
August 30, 2007
Crosses the CA: +1 hour
TERMINATION SHOCK
NEPTUNE termination shock
URANUS
SATURN JUPITER’S O RBIT
VOYAGER 1
February 17, 1998
Becomes the most distant 300,000 miles
human-made object
500,000km
VOYAGER 1
VOYAGER 1
December 16, 2004
Crosses the August 25, 2012
termination shock Passes the reach
of the solar wind