Robin George Andrews
08/17/2021 10:50
Clarín.com
The New York Times International Weekly
Updated 08/17/2021 10:51 AM
Saturn's
icy rings
are not just aesthetic marvels.
One of them also records a beautiful planetary soundtrack.
The interior of the planet, hidden under a blanket of mostly hydrogen gas, is shaking.
An image provided by NASA shows Saturn's C and D rings.
The C rings occupy the lower half of this image and are brighter than the D rings. Photo NASA / JPL-Caltech / Space Science Institute via The New York Times.
This causes changes in the
local
gravitational field
, which pulls the particles from
Saturn's
extensive
C-ring
and makes them dance.
These idiosyncratic dances can take the form of spiral waves, and different sets of waves reveal the characteristics of particular features in Saturn's bowels.
In other words, Saturn
is an orchestra.
Different notes appear in the C ring, like those of a sheet music.
Scientists can read these notes, listen to the music, and identify the individual instruments and musicians performing, all without actually seeing the orchestra itself.
Using data from the
Cassini
mission
that ended in 2017, scientists have listened to and
deconstructed
a variety of symphonies in Saturn's C ring over the years.
Now, two researchers at
the California Institute of Technology -
Christopher Mankovich, a planetary scientist, and Jim Fuller, a theoretical astrophysicist - have decoded enough of this music to hear the sounds of one of Saturn's most puzzling features:
its core.
According to their article, published Monday in the journal
Nature Astronomy,
the nucleus is colossal:
It makes up
60% of
the planet's
radius
and is
55 times the mass of Earth.
And unlike solid ordered groups and metal, rock or ice material found in other worlds, the core is a pandemic Saturn amalgam of rocks and various ices are mixed with a
fluid metallic hydrogen.
The findings help researchers understand how Saturn and other gas giants like Jupiter were born.
"It's a very nice story," said Linda Spilker, a Cassini mission project scientist at NASA's Jet Propulsion Laboratory, who was not involved in the work.
The geological viscera of the Earth, the Moon and (more recently) Mars were mapped with seismometers, instruments that record the travel of seismic waves that travel around the planet and behave differently when passing through mechanically different layers.
Saturn, lacking a
solid surface,
makes this kind of detective work impossible.
Orbiting spacecraft can roughly map the structure of the inner layer cake of a gaseous planet by detecting
subtle changes in gravity.
But Saturn's core has such a weak effect on the planet's gravitational field that this trick cannot be used to accurately visualize it.
Fortunately, the
wiggling
of Saturn's C ring has revealed what traditional techniques cannot.
For the past three decades, scientists have observed the ring's strange spiral waves through images from the Voyager and Cassini missions.
And they finally reasoned that those spirals are being caused by
gigantic oscillations
inside Saturn.
"They are constant tremors that exist all over the planet," Mankovich said.
It is a technique known as "
kronoseismology
":
"kronos" is the Greek word for Saturn, and "seismo" belongs to tremors.
In 2019, it was used to solve another riddle:
How long is a day on Saturn?
About 10 and a half hours on Earth.
Now the core of Saturn has lit up.
Older models depicted the planet as a different layered cosmic candy.
Chronosismology has revealed the messy truth.
The core is not only made up of rock and ice, but also fluid metallic hydrogen, which was previously assumed to be a separate shell.
There's more rock and ice in the center and more fluid metallic hydrogen at the outer edges, but it's all mixed into a
chaotic cocktail.
Along with the transient change from fluid to gaseous hydrogen at the top, this work paints Saturn as a
large fuzzy ball.
Despite the continued success of the technique, scientists still don't know what causes the nucleus to oscillate and create those spiral waves in the C ring.
The Earth rings out like a bell when it is shaken by powerful tectonic tremors.
"But Saturn is fluid, so where are the tremors?" Asked Mark Marley, a planetary scientist at the University of Arizona and one of the early pioneers of chronosismology, who was not involved in the work.
The orchestra's musicians may finally meet, but the hunt for its elusive conductor continues.
c.2021 The New York Times Company
Look also
Two unexpected red objects appear in the asteroid belt
Missions to Mars, the Moon and beyond by 2021