After Cassini: Pondering the Saturn Mission’s Legacy

As the Cassini spacecraft nears the end of a long journey rich
with scientific and technical accomplishments, it is already
having a powerful influence on future exploration. In revealing
that Saturn’s moon Enceladus has many of the ingredients needed
for life, the mission has inspired a pivot to the exploration
of “ocean worlds” that has been sweeping planetary science over
the past decade.

“Cassini has transformed our thinking in so many ways, but
especially with regard to surprising places in the solar system
where life could potentially gain a foothold,” said Thomas
Zurbuchen, associate administrator for NASA’s Science Mission
Directorate at Headquarters in Washington. “Congratulations to
the entire Cassini team!”

Onward to Europa

Jupiter’s moon Europa has been a prime target for future
exploration since NASA’s Galileo mission, in the late 1990s,
found strong evidence for a salty global ocean of liquid water
beneath its icy crust. But the more recent revelation that a
much smaller moon like Enceladus could also have not only
liquid water, but also chemical energy that could potentially
power biology, was staggering.

Many lessons learned during Cassini’s mission are being applied
to planning NASA’s Europa
Clipper
mission, planned for launch in the 2020s. Europa
Clipper will fly by the icy ocean moon dozens of times to
investigate its potential habitability, using an orbital tour
design derived from the way Cassini has explored Saturn. The
Europa Clipper mission will orbit the giant planet — Jupiter
in this case — using gravitational assists from its large
moons to maneuver the spacecraft into repeated close encounters
with Europa. This is similar to the way Cassini’s tour
designers used the gravity of Saturn’s moon Titan to
continually shape their spacecraft’s course.

In addition, many engineers and scientists from Cassini are
serving on Europa Clipper and helping to develop its science
investigations. For example, several members of the Cassini

Ion and Neutral Mass Spectrometer
and Cosmic Dust Analyzer
teams are developing extremely sensitive, next-generation
versions of their instruments for flight on Europa Clipper.
What Cassini has learned about flying through the
plume of material
spraying from Enceladus will help inform
planning for Europa Clipper, should plume activity be confirmed
on Europa.

Returning to Saturn

Cassini also performed 127 close flybys of Saturn’s
haze-enshrouded moon Titan, showing it to be a remarkably
complex factory for organic chemicals — a natural laboratory
for prebiotic chemistry. The mission investigated the cycling
of liquid methane between clouds in its skies and great seas on
its surface. By pulling back the veil on Titan, Cassini has
ushered in a new era of extraterrestrial oceanography ­–
plumbing the depths of alien seas — and delivered a
fascinating example of earthlike processes occurring with
chemistry and at temperatures markedly different from our home
planet.

In the decades following Cassini, scientists hope to return to
the Saturn system to follow up on the mission’s many
discoveries. Mission concepts under consideration include
spacecraft to drift on the methane seas of Titan and fly
through the Enceladus plume to collect and analyze samples for
signs of biology.

Giant Planet Atmospheres

Atmospheric probes to all four of the outer planets have long
been a priority for the science community, and the most recent
Planetary
Science Decadal Survey
continues to support interest in
sending such a mission to Saturn. By directly sampling Saturn’s
upper atmosphere during its last orbits and final plunge,
Cassini is laying the groundwork for an eventual Saturn
atmosphere probe.

Farther out in the solar system, scientists have long had their
eyes set on exploring Uranus and Neptune. So far, each of these
worlds has been visited by only one brief spacecraft flyby
(Voyager 2, in 1986 and 1989, respectively). Collectively,
Uranus and Neptune are referred to as “ice giant” planets,
because they contain large amounts of materials (like water,
ammonia and methane) that form ices in the cold depths of the
outer solar system. This makes them fundamentally different
from the gas giant planets, Jupiter and Saturn, which are
almost all hydrogen and helium, and the inner, rocky planets
like Earth or Mars. It’s not clear exactly how and where the
ice giants formed, why their magnetic fields are strangely
oriented, and what drives geologic activity on some of their
moons. These mysteries make them scientifically important, and
this importance is enhanced by the discovery that many planets
around other stars appear to be similar to our own ice giants.

A variety of potential mission concepts are discussed in a
recently completed study,
delivered to NASA in preparation for the next Decadal Survey —
including orbiters, flybys and probes that would dive into
Uranus’ atmosphere to study its composition. Future missions to
the ice giants might explore those worlds using an approach
similar to Cassini’s mission.

The Cassini-Huygens mission is a cooperative project of NASA,
ESA (European Space Agency) and the Italian Space Agency.
NASA’s Jet Propulsion Laboratory, a division of Caltech in
Pasadena, manages the mission for NASA’s Science Mission
Directorate, Washington. JPL designed, developed and assembled
the Cassini orbiter.

More information about Cassini:

https://www.nasa.gov/cassini

https://saturn.jpl.nasa.gov

News Media Contact

Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches@jpl.nasa.gov

2017-238