Page 32 - BBC Sky at Night - September 2017 UK

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Cassini’s final descent
will begin in a blue
Saturnian sky not entirely
alien from our own

Diving

into the
depths

This month, seasonal change are probably responsible for
the bluish colour in the ring-shadowed
the Cassini probe’s epic hemisphere,” she continues. “The haze particles
give Saturn its golden hue glow when sunlight
endeavour at Saturn shines on the atmosphere. When shadowed by the
comes to an end. rings, or in shadow in the winter, the haze seems
to dissipate, allowing scientists to see deeper into
ABOUT THE WRITER Ben Evans looks back the atmosphere. The blue colour is primarily
due to the absorption of light by methane.”
Ben Evans has
It offers a fittingly wistful reminder of home
written nine books on one of humanity’s for a mission conceived over three decades ago by
on space exploration
KEVIN GILL/FLICKR and is the senior greatest exploratory 17 nations, including NASA, ESA and the Italian
writer for
space agencies. Cassini launched in October 1997
missions into space
AmericaSpace.
and travelled 3.5 billion km to reach Saturn,
picking up gravitational boosts from Venus, Earth
peeding towards its doom at 33.5km/s, and Jupiter along the way. It arrived in July 2004,
the final moments of Cassini’s 20-year and released the tiny Huygens lander down to the
voyage may see the bus-sized spacecraft surface of the giant moon Titan in December of
Spass briefly through Saturn’s brilliant, the same year. Cassini went on to perform three
cobalt-blue skies, as it concludes one of the most extended phases of scientific study: in those past
spectacular scientific ventures in history. When 13 years it has orbited the planet over 290 times,
Cassini plunges into the ringed planet’s yellow- taking in Saturn’s equinox and part of its northern
brown atmosphere, the seasonal blue sky will summer solstice as it did so.
be uncannily reminiscent of Earth’s, a small
reminder of the world where it was created. A mission of discoveries
“Saturn’s atmosphere starts to turn blue in The mission found seven new moons and
the winter hemisphere,” explains Cassini project explored dozens of others, whose appearance
scientist Linda Spilker. “The ring shadow and ran the gamut from spherical to potato-shaped >

skyatnightmagazine.com 2017