Cassini’s dive into Saturn capped off 20 years
of scientific discoveries and breakthroughs,
and even though the deep space probe is no more,
its sacrifice is yielding results.
During the orbital maneuvers that brought the probe
closer and closer to the gas giant,
Cassini passed inside the rings
and skimmed the planet’s upper atmosphere
several times.
On the first 11 orbits, the probe took measurements
using the Radio and Plasma Wave Science instrument,
and when scientists looked at the data,
they found that Saturn has a cold, dense ionosphere.
Cassini’s data provides the first up close
measurement
of the gas giant’s charged upper atmosphere.
Ionospheres are created when ultraviolet radiation from
the sun hits the atoms of a planet’s upper atmosphere,
splitting some of the atmospheric particles
into charged ions, and forming a plasma.
If you’ve ever picked up a radio broadcast
from thousands of miles away, you’ve interacted
with Earth’s ionosphere,
which reflects radio signals around the planet.
However, Saturn's ionosphere
is a little different than Earth’s.
The planet’s enormous rings affect the way
that the ionosphere is charged.
When Cassini passed into the shadow
the rings cast on the planet,
the amount of ionized plasma dropped immensely.
Saturn’s D-ring also appears
to be affecting the ionosphere.
Researchers theorize that an interaction known as
"ring rain" may explain some of the ionosphere’s quirks
While the shifting plasma in the ionosphere is a major finding,
it only came from the first 11 orbits of data,
so there is still much we can learn
from Cassini’s last hurrah.
