A team of scientists recently published a study suggesting that Saturn’s famous rings may be the result of an ancient moon colliding with the planet about 160 million years ago.
The study says a moon called Chrysalis orbited the gas giant for several billion years before colliding with it and disintegrating.
Scientists at the Massachusetts Institute of Technology (MIT) performed calculations that determined how Saturn’s axis of rotation changed over time.
The results show that another object once revolved around it, but when it got too close to the gas giant, it broke apart and formed the characteristic rings around Saturn.
The loss of this moon also explains why Saturn tilts at 26.7 degrees in its rotation, as indicated by its fast rings.
The planet’s tiny rings, only 150 million years old and tilted about 26.7 degrees with respect to their orbit around the Sun, appear too large to have formed during the formation of Saturn itself.
“Like a butterfly cocoon, this moon was dormant for a long time, and then suddenly became active, and rings appeared,” said study lead author Professor Jack Wisdom.
Since the early 2000s, astronomers have believed that Saturn’s tilt is due to the planet’s “orbital resonance” with its neighbor Neptune.
Two planets have “orbital resonance” if their rotation periods match and they exert a uniform gravitational force on each other.
The “resonance” theory came about because Saturn was “advancing” or oscillating, spinning at about the same speed as Neptune’s orbit.
But observations by NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, showed that Titan, Saturn’s largest moon, could actually be responsible for the wobble.
This is because Titan is migrating away from Saturn faster than expected, at a rate of about 11 centimeters per year, so it was thought that the moon’s gravity could tilt the planet.
However, this theory is based on Saturn’s moment of inertia, or how mass is distributed within the planet, which is still unknown.
Its slope can behave differently depending on whether the material is more concentrated and dense at its core or closer to the surface.
Scientists used some of Cassini’s recent observations to map Saturn’s gravitational field. They then used this data to model the distribution of mass within the planet and to calculate the moment of inertia (a physical term for a stationary body’s resistance to motion).
They were surprised to find that the newly determined moment of inertia placed Saturn close to Neptune but out of resonance with Neptune.
This indicates that the two planets may have once rotated in sync, but no more. And then scientists said: “We were looking for ways to remove Saturn from the echo of Neptune.”
Scientists have revised the mathematical equations that describe how Saturn’s axis of rotation changes over time.
They suggested that Saturn’s axial tilt could have been affected by the loss of the Moon, as it would have removed it from Neptune’s echo.
For these phenomena to occur, the 84th hypothetical moon Chrysalis would have to be the size of Iapetus, the planet’s third largest moon.
The team concluded that Chrysalis, while in orbit, was pulling on Saturn in such a way that its tilt matched that of Neptune.
However, it is likely that the Moon entered the chaotic orbital region sometime between 200 and 100 million years ago.
This means that the moon experienced a series of close encounters with Iapetus and Titan, and eventually approached Saturn around 160 million years ago.
The collision tore Chrysalis apart, allowing Saturn and Neptune to lose their echoes as the Moon’s gravitational influence faded.
Titan’s constant outward migration and its effect on the Saturn-Neptune echo means that Saturn’s tilt subsequently decreased, but remained at its current value of 26.7 degrees.
A small portion of Chrysalis’s mass was left hanging in orbit, and it broke into icicles and formed rings from these fragments.
Professor Wisdom added: “This is a very good story, but like any other result, it should be studied by other scientists.”
Source: Daily Mail
You must log in to post a comment.