Could Miranda have plumes like Enceladus?
In 2006, the Cassini spacecraft first observed the now famous water plume eruptions were discovered on Enceladus. It is now known that water ice particles from the plumes on Enceladus feed into one of Saturn’s rings. When Enceladus was originally observed by the Voyager probes in the 1980s however, no plumes were detected. Uranus’s moon Miranda has a similar story.
Miranda’s enigmatic surface was first observed by the Voyager II spacecraft during its visit of the Uranus system in 1986, revealing that Miranda had bizarre regions of concentric ridges, now called coronae. Ariel was also revealed to have an unusual surface with ridges, smooth plains, and even possible cryovolcanism, volcanoes where the lava is water instead of molten rock.
Recent studies using spectroscopy, looking at what wavelengths or colors of light are absorbed or reflected by a material to determine its composition, have also revealed that Miranda may have short-lived ammonia compounds on its surface which would have to come from a subsurface liquid water ocean. This leads to a question. Could Miranda have plumes as well? So far plumes have not been detected at Miranda, but they were also not initially detected at Enceladus either.
Short of sending another spacecraft to explore the Uranus system, there is a way to try to answer this question. Large telescopes such as the ALMA, the Keck Observatory and the Hubble Space Telescope have been used to observe or search for plumes on icy moons, particularly Jupiter’s moon Europa.
One problem with Miranda having plume eruptions is that there is not an associated debris ring. If water ice particles are being spewed out of Miranda, they would be expected to collect in a ring around Uranus near Miranda’s orbit like with Enceladus and Saturn’s E-ring. This has not been observed at Miranda’s orbit at Uranus, which might indicate that there is not plume activity on Miranda.
On the other hand, there is also reason to suspect plume eruptions could be happening on Jupiter’s moon Europa, yet no debris rings are forming in Europa’s orbit. In Europa’s case, this might be because the plume eruptions are not energetic enough for the ice particles to escape Europa’s gravity. Europa is a relatively large icy moon (diameter = 3100 km or 1900 miles).
In the case of Miranda, which is considerably smaller (diameter ~ 470 km or 290 miles), it could be due to the eruptions on Miranda being primarily gas and having relatively few water ice particles. This could be due to a greater abundance of gases dissolved in Miranda’s subsurface ocean, though this is pure speculation at this point.
There is currently no evidence that plume eruptions are happening at Miranda, but we will not know unless we take look and the discovery would be very significant. This could be done using a spectrograph on one of the major telescopes, such as the Keck NIRSPEC instrument or the one on the James Webb Space Telescope to search for the spectroscopic signature which would indicate the presence of water vapor coming out of Miranda.
If observations of Miranda confirm the presence of plumes, it would mean that Miranda is still warm enough to have a subsurface ocean. This would mean that whatever heated up Miranda happened very recently in geologic time, confirming that Miranda has had a very interesting history.
In fact, computer models of the orbits of the Uranian moons predict they went through a phase of rapid orbital evolution. The shapes of their orbits changed, resulting in gravitational interactions between the other moons and Uranus which caused Miranda to become physically stretched back and forth, producing heat, like heat generated by the bending of a rubber band, to melt part Miranda’s ice layer about 500 million years ago. This would have been just yesterday in geologic terms.
Also, samples of Enceladus’s plumes taken by the Cassini spacecraft support the existence of possible hydrothermal vents on its ocean floor, potential habitats for early life in Earth’s oceans. Miranda may not have hydrothermal vents on its ocean floor, but the presence of plumes would be one more indicator that Miranda could be another Enceladus in that regard.
The discovery that there are not plumes on Miranda would also be interesting since this would reveal that not every geologically active icy moon has plumes. This would add to the known variety of ocean worlds and to our understanding of which are likely to support life, since a subsurface ocean by itself does not mean life.
Furthermore, discovering two similarly sized moons with active plume eruptions and subsurface oceans in the solar system would suggest that such environments could be common in other stars systems as well. This would give us a better idea of what icy bodies look like across the galaxy.
Thank you for reading my Substack! If you like what you read, feel free to share or subscribe and thank you again if you already have.
If you would like to support planetary science research, you can become a paid subscriber and double thanks if you already have.