Credits: NASA/Durham
University/Glasgow University/Jacob Kegerreis/Luís Teodoro
On a clear night, with a decent
amateur telescope, Saturn and its series of remarkable rings can be seen from
Earth’s surface. But how did those rings come to be? And what can they tell us
about Saturn and its moons, one of the potential locations NASA hopes to search
for life? A new series of supercomputer simulations has offered an answer to
the mystery of the rings’ origins – one that involves a massive collision, back
when dinosaurs still roamed the Earth.
According to new research by NASA and its partners,
Saturn’s rings could have evolved from the debris of two icy moons that
collided and shattered a few hundred million years ago. Debris that didn’t end
up in the rings could also have contributed to the formation of some of
Saturn’s present-day moons.
“There’s so much we still don’t
know about the Saturn system, including its moons that host environments that
might be suitable for life,” said Jacob Kegerreis, a research scientist at
NASA’s Ames Research Center in California’s Silicon Valley. “So, it’s exciting
to use big simulations like these to explore in detail how they could have
evolved.”
NASA’s Cassini mission helped scientists
understand just how young – astronomically speaking – Saturn’s rings and
probably some of its moons are. And that knowledge opened up new questions
about how they formed.
To learn more, the research team
turned to the Durham University location of the Distributed Research using
Advanced Computing (DiRAC) supercomputing facility in the United Kingdom.
They modeled what different collisions between precursor moons might have
looked like. These simulations were conducted at a resolution more than 100
times higher than previous such studies, using the open-source simulation code,
SWIFT, and giving scientists their best insights into the Saturn system’s
history.
Saturn’s rings today live close to
the planet, within what’s known as the Roche limit – the farthest orbit where a
planet’s gravitational force is powerful enough to disintegrate larger bodies
of rock or ice that get any closer. Material orbiting farther out could clump
together to form moons.
By simulating almost 200 different
versions of the impact, the team discovered that a wide range of collision
scenarios could scatter the right amount of ice into Saturn’s Roche limit,
where it could settle into rings.
And, while alternative explanations
haven’t been able to show why there would be almost no rock in Saturn’s rings –
they are made almost entirely of chunks of ice – this type of collision could
explain that.
“This scenario naturally leads to
ice-rich rings,” said Vincent Eke, Associate Professor in the Department of
Physics/Institute for Computational Cosmology, at Durham University and a
co-author on the paper. “When the icy progenitor moons smash into one another,
the rock in the cores of the colliding bodies is dispersed less widely than the
overlying ice.”
Ice and rocky debris would also
have hit other moons in the system, potentially causing a cascade of
collisions. Such a multiplying effect could have disrupted any other precursor
moons outside the rings, out of which today’s moons could have formed.
But what could have set these events
in motion, in the first place? Two of Saturn’s former moons could have been
pushed into a collision by the usually small effects of the Sun’s gravity
“adding up” to destabilize their orbits around the planet. In the right
configuration of orbits, the extra pull from the Sun can have a snowballing
effect – a “resonance” – that elongates and tilts the moons’ usually circular
and flat orbits until their paths cross, resulting in a high-speed impact.
Saturn’s moon Rhea today orbits
just beyond where a moon would encounter this resonance. Like the Earth’s Moon,
Saturn’s satellites migrate outward from the planet over time. So, if Rhea were
ancient, it would have crossed the resonance in the recent past. However,
Rhea’s orbit is very circular and flat. This suggests that it did not
experience the destabilizing effects of the resonance and, instead, formed more
recently.
The new research aligns with evidence that Saturn’s
rings formed recently,
but there are still big open questions. If at least some of the icy moons of
Saturn are also young, then what could that mean for the potential for life in
the oceans under the surface of worlds like Enceladus? Can we unravel the full story
from the planet’s original system, before the impact, through to the present
day? Future research building on this work will help us learn more about this
fascinating planet and the icy worlds that orbit it.
Still image from a computer
simulation of an impact between two icy moons in orbit around Saturn. The
collision ejects debris that could evolve into the planet's iconic and
remarkably young rings. The simulation used over 30 million particles, colored
by their ice or rock material, run using the open source SWIFT simulation code.
Credits: NASA/Durham
University/Glasgow University/Jacob Kegerreis/Luís Teodoro
For
researchers:
- This
research was published in The Astrophysical Journal, Sep. 26, 2023: A Recent Impact
Origin of Saturn's Rings and Mid-sized Moons
- More
information about the open source SWIFT simulation code used in this
research can be found here.
For news
media:
- Members
of the news media interested in covering this topic should reach out to
the NASA Ames newsroom.
Author: Frank Tavares, NASA's Ames Research Center
Source: New Simulations Shed Light on Origins of Saturn’s Rings and Icy Moons | NASA
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