A recent paper in Nature (“The seventh inner moon of Neptune”, Nature 21 Feb 2019) has reported the discovery of a new moon orbiting Neptune, which has been given the name Hippocamp. It is one of now six smallish moons (moon radius = 17 km, orbit radius = 105,000 km) found within the orbit of Proteus, which is a fairly large moon (moon radius = 204 km, orbit radius = 118,000 km). They are all dwarfed by the very large moon Triton (moon radius=1350 km, orbit radius = 355,000 km), which orbits yet farther out.
You can read more about Triton, which has several interesting features (e.g. retrograde motion), in the blog linked below.
The researchers used a number of observations of Neptune, taken by the Hubble Space Telescope to go moon hunting. One problem was that Neptune’s moons images get smeared during the long exposure times normally needed to bring them out, due to their proper motion. The team came up with some new algorithms that helped to “stack” images, even with the smearing effect, based on calculating where a given object would be on one image compared to another one taken at an earlier or later time, given various orbital parameters. Stacking the images basically means putting one on top of the other, in the computer, to increase the signal to noise ratio. By doing so, it is possible for objects to be seen that otherwise would be lost in the noise of the image (e.g. hot pixels, dim background stars, etc.). The researchers go into considerable detail regarding their methods, in the paper.
Little Hippocamp was missed by Voyage 2 in its 1989 flyby of Neptune, because it was just too small to register in that craft’s cameras very well. Recall that the Voyager flyby of Neptune was done at a high velocity, so there wasn’t much time for sightseeing, and aiming the cameras wasn’t easy. The researchers used data that they discovered about Hippocamp to retro-predict where it would have been during the flyby, to see if they could located the moon in those images. However they were all badly smeared and/or completely missed this small moon. Thus, this new imaging method had to be developed.
Hippocamp orbits very close to the much larger Proteus, as the schematic picture above shows, as does the still from the video, just above. In fact, it was probably even closer to Proteus in the past, as both moons are moving away from Neptune, due to tidal interactions, but the larger Proteus is migrating faster than little Hippocamp, due to its greater mass, and therefore greater tidal interaction with Neptune.
That leads to the hypothesis the Hippocampus might actually be a fragment of Proteus, broken off during a collision, perhaps with a comet from the far outer solar system that came into the region of Neptune, and collided with Proteus. That moon has a large crater, the Pharos Crater, that might be the evidence of that disruption. In its turn, Proteus may have been created from detritus of the capture of Triton by Neptune.
It is possible that Hippocamp might have been hit and broke apart a number of times during its history. That would account for some problematic features of the hypothesis, which are outlined in the paper.
Note, that though Hippocamp is small, it is still about 3 times larger than the asteroid that collided with the Earth 65 million years ago, likely leading to the extinction of the dinosaurs. So, if Earth collided with a Hippocamp sized object, it would be no small thing.
Given how far away Neptune is, we may not get a good picture of these moons for quite a while. However, the New Horizons mission does show that such missions are possible, if the money and political will are there. So, maybe we will get better information at that time.
By the way, Hippocamp was a sea-horse in Greco-Roman mythology, which is appropriate for Neptune, the god of the sea. Also, the hippocampus is an important part of the brain, and it looks something like a seahorse (the actual animal). It is thought to be involved with memory, special orientation and perhaps impulse control. And impulse control sounds like something a spaceship needs too, so it all fits together.
The seventh inner moon of Neptune”, Nature 21 Feb 2019
A new moon for Neptune”, Nature 21 Feb 2019
Wiki, Proteus (moon)
Now that you have read some real science (astronomy and astrophysics), you should read some science fiction. Either of the Kati of Terra series or the Witch’s Stones series would be excellent choices. Alternatively, you could try the short story “The Magnetic Anomaly”, which has lots of physics, and plenty about magnetic fields, perhaps affecting the brain’s hippocampus. J
Kati of Terra
How about trying Kati of Terra, the 3-novel story of a feisty young Earth woman, making her way in that big, bad, beautiful universe out there.
The Witches’ Stones
Or, you might prefer, the trilogy of the Witches’ Stones (they’re psychic aliens, not actual witches), which follows the interactions of a future Earth confederation, an opposing galactic power, and the Witches of Kordea. It features Sarah Mackenzie, another feisty young Earth woman (they’re the most interesting type – the novelist who wrote the books is pretty feisty, too).
The Magnetic Anomaly: A Science Fiction Story
“A geophysical crew went into the Canadian north. There were some regrettable accidents among a few ex-military who had become geophysical contractors after their service in the forces. A young man and young woman went temporarily mad from the stress of seeing that. They imagined things, terrible things. But both are known to have vivid imaginations; we have childhood records to verify that. It was all very sad. That’s the official story.”