The Cassini spacecraft had been in operation much past its initial
four-year mission by the time it reached the end of its lifetime in orbit
around Saturn in 2017. Before entering Saturn's atmosphere as directed, it
had been extended for two years, then for
seven, and had spent 13 years observing Saturn, its moons, and its ring system.
As it did, it left 13 years' worth of data in our care, many of which still
contain numerous undiscovered riches.
While we can all agree that the complex ring system encircling the planet
is beautiful, one of the most basic problems regarding Saturn seems to be:
They have been there for how long?
They aren't more than 400 million years old and may even be less than 100
million years old, according to a recent Science research, which adds to a
growing body of data. If they are less than 100 million years old, this
would place the formation of Saturn's rings in the midst of the Cretaceous
epoch on Earth, while 400 million years would advance us to the time when
the progenitors of the
contemporary shark
and the first trees arrived on land.
Despite the rings' age, there are a few things we know for sure. The rings
are dispersed across a huge surface area and are only sometimes 20 meters
thick. They are likewise largely composed of pure water ice. The rings are made
up of around 98 to 99.9%
water ice
by volume and more than 95 percent distinct ice pieces by mass. Furthermore,
we are aware that there is a continuous shower of extremely small ice and
rock particles between the planets that we might just as readily refer to as
"dust."
The assumption is that since the rings are 95 percent water ice by mass
presently and have been repeatedly pelted by grit that is not ice, they must
have once been 100 percent pure water ice. Although it is improbable that
Saturn's rings have ever truly been made entirely of water ice, putting this
assumption places a time limit on their potential existence. The amount of
interplanetary dust that has been pelted upon the rings must be estimated at
this time; the more quickly the dust collects, the younger the rings must be
to still be so brilliant and frosty. Looking at the snow along the edge of a
road in this way is extremely technical; if it is new snow, it will appear
sparkling white. However, given enough time or traffic, dirt from the road
will mix with the snow, darkening it and turning it into a mound of
considerably less appealing frozen muck.
After the fact ring formation requires a catastrophic event.
This estimate was precisely what Cassini was able to offer.
The Cosmic Dust Analyzer, which was on board Cassini, was primarily made to determine the chemical
make-up of the particles it met, gauge their sizes, and determine their
direction and speed of motion before being caught. An estimation of the
journey that the particle of dust had travelled to get to Cassini is
possible using the direction and speed together. Most frequently, they
seemed to be drifting toward Saturn from the Kuiper Belt, a ring of ice
objects surrounding the sun just beyond the orbit of Neptune. Many of the
dust particles turned found to be falling inward from outside of Saturn's
gravitational field. The important micrometeorites, which are the dust
grains that have been found, are generally micron-sized particles that are
smaller than a
single red blood cell.
You may calculate the amount of time it would take to transition from a
pure, pristine ring of water ice to one that is "polluted" to its current
form by considering the pace at which Cassini encountered these
micrometeorites and the mass of those particles. One other supposition used
in this computation is that the micrometeorites also include a significant
amount of ice, meaning that only 10% of their mass is really increasing the
non-ice component of Saturn's rings. The rings may be much younger if that
proves out to be an underestimation and the dust is truly rockier than that.
Based on the observed speed of the incoming particles, there are also
certain estimates regarding how much of the ring mass melts away with each
collision.
The rings could only be 400 million years old before they would have to be
made entirely of water ice, based on all of these observations and
presumptions combined, and utilizing just the particles that Cassini
encountered and about which the study team felt quite positive that they
originated from outside Saturn. The age estimate reduces to 100 million
years if they include all the extra dust that they believe to be very likely
to have come from outside Saturn. The rings of Saturn are thus
younger
than blooming plants.
Saturn's rings are young, indicating that the planet itself did not
originate with the rings; Saturn formed with the other main planets in the
solar system about 4.5 billion years ago. After the fact ring formation
requires a catastrophic event. Maybe an ice-rich moon wandered
too near
to Saturn some 100 million years ago. Saturn's gravity would have been able
to stretch that unfortunate moon until it shattered, splitting into several
fragments, like a far more powerful version of Earth's tides. After all,
Mimas' mass is just 40% that of Saturn's rings, therefore a single moon that
broke apart would be sufficient. Alternatively, it might have been two moons
that collided,
killing both
of them.
When Saturn has rings, the solar system is at its most amazing. These rings
have shown us that they are feasible, that we should search for them on
other planets, and that we should appreciate their fleeting beauty.
