Mapping the inside of the ice giants is difficult to say the least. Not only are they far away and therefore more difficult to observe, but their constant ice cover makes it extremely difficult to find what lies beneath. So scientists need to come up with more ingenious ways to see what’s inside them. A team from the University of Idaho, Cal Tech, Reed College and the University of Arizona believe they may have come up with a way to look at the structure of the rings of Neptune and Uranus.
However, this is not the first technique that scientists use. Previous efforts have tried to use the general technique of photometry to detect oscillations on the surface of the planet. These oscillations can then be related to the density of certain parts of the planet’s interior. Although the technique works well for Jupiter, the photometric data we have for the ice giants so far have proved insufficient to determine the same density profiles.
An alternative is the use of gravitational oscillations on the planet’s surface. In particular, there is a type of oscillation pattern known as “normal mode”. This oscillation pattern occurs when all parts of the system begin to oscillate with the same sinusoidal frequency. And the gravitational effects of normal oscillations inside the planet can be felt outside and reflected in the rings themselves.
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UT video discussing planetary rings in the solar system
This is also not the first time that models in the planet’s rings have been used to calculate its internal density. Saturn has a better-understood ring system than Uranus or Neptune, the two ice giants with known ring systems. Scientists have been performing seismological analyzes of Saturn’s ring system for years, using data from Voyager and Cassini. The result is a better understanding of some of the normal regimes of the planet’s interior and therefore an assessment of the composition of the planet’s core and the speed of rotation of most of its material.
Neptune and Uranus have a series of different rings, although they are not as well studied as those of Saturn. Some of these rings are attached by shepherd moons. But according to the new document, the same reflections of the density of resonant waves, obvious in Saturn’s rings, are probably present in the systems of the ice giant’s rings.
Moreover, the inner pastoral moons themselves may be affected by the same resonances. Some of the moons may even create their own resonances, such as the Lindblad resonance. More typically observed on a galaxy scale, Lindblad resonances are known to drive spiral-density waves that cause “hands” that can be seen in many spiral galaxies. But on a much smaller scale, the same effect occurs on planetary ring systems, including those of Saturn and most likely those of Neptune and Uranus.
UT video describing the Trident mission that will return to Neptune.
The problem with using these resonances reflected in the rings is often faced by science – there is not enough data. So far, no probe has been left long enough to draw the details needed to see the full range of the ring system. The authors of the article and many other researchers suggest that it is time to send a probe to the ice giants to effectively map ring systems, moons and countless other recently discovered objects that are so difficult to observe from Earth. But for now, this mission is still on the drawing board, so we will have to wait to fully understand the interior and ring system of these cold, barren worlds. At least when we finally send a probe this way, we will have the mathematical framework to help shed light on these dark places.
Learn more: A’Hearn et al – Seismology of the ring of the ice giants Uranus and NeptuneUT – The rings of NeptuneUT – Which planets have rings UT – How many rings does Uranus have?
Leading image: Impression of the artist from Uranus and his rings. Credit – NRAO / AUI / NSF / S. Dagnello
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