There is still much to be learned about Uranus, 30 years after Voyager 2's flyby
Thirty years have passed since Voyager 2 made the only visit by a spacecraft to the solar system’s seventh planet, Uranus. But the data sent back by the little probe is still teaching us something about that distant gas giant.
Case in point: On Oct. 21 two scientists at the University of Idaho proposed that the tipped over planet has two more moons than previously thought.
The scientists, Robert Chancia (a graduate physics student) and Matthew Hedman (a UI assistant professor of physics), examined data of radio transmissions by Voyager 2 through Uranus’ ring system, which had been discovered in 1977. Decoding of the wave patterns evident in the data indicated that there was an accumulation of ring material near the edges of both the alpha and beta rings of the planet.
Chancia and Hedman then basically worked backward to figure out what might account for that pattern and concluded that the most likely explanation is that a small moon, no larger than 14 kilometers in diameter, sits just outside each ring.
The tiny satellites, if they are there, would be responsible for a phenomenon known as moonlet wakes, which can explain why the Uranian rings are particularly narrow.
The possibility that Uranus may have more moons than have yet been observed by human telescopes and space probes is not surprising. After all, many small satellites have been found orbiting the solar system’s king of rings, Saturn. It is reasonable to expect that where there are rings, there are moons.
What may be surprising to the reader is that these moonlets can have such an obvious impact on the rings to which they are adjacent.
As Professor Richard G. French, an astrophysicist at Wellesley College, told Science for the Future:
“In this case, both moons are slightly exterior to the rings, so they orbit slightly more slowly than the rings themselves. As the ring particles pass the moon, their orbits are slightly perturbed, resulting in a ripple pattern within the ring that is detectable as a periodic wavelike structure.”
The moons, if they do exist, could not be seen by Voyager 2 because their small size is beyond the imaging capacity of that probe’s on-board camera. Nor is it likely that we will be able to see them by aiming the Hubble Space Telescope in their direction. As French also told Science for the Future, the moonlets are really quite dark and “bloody far away,” too.
William Herschel discovered Uranus in 1781. Chancia and Hedman have not only suggested that the planet is a more interesting place than we had yet discovered in the 235 years since then. They have also reminded us again that, in science, we are never finished with our learning.
