As the Voyager probes crossed the solar system, they collected a ton of discoveries. Among the recently discovered objects and phenomena was a large collection of small moons revolving around Jupiter, Saturn, Uranus and Neptune. Most of them were beyond the capabilities of ground-based equipment for shooting them, so we really needed to get closer to them.

Improvements in optical technology and the introduction of the Hubble Space Telescope into orbit made it possible to detect several small bodies that were missed by Voyagers, as well as small objects in other parts of the solar system, such as the Kuiper Belt. Thanks to advances in computing, it has become possible to see the tiny new moon in Neptune and to discover another moon for the first time.

In search of the moon of Neptune

Considering that Neptune has already been shot from the Voyager 2 spacecraft, there are still satellites that we have not yet discovered because of their small size. The easiest way to see them is to increase the exposure time, which increases the possibility of extracting weak signals from cosmic noise.
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The problem is that the previously discovered satellites of the planets rotate quite close to the planets themselves. And at some point, this movement creates a "circuit" that reliably holds the signal in noise.

A small team of researchers from SETI, NASA and Berkeley have come up with a way to compensate for this circuit. If you know the orbit of the body, you can predict how much it will move from one image to another. You can then configure several consecutive images to place objects on the same orbit in the same place, allowing you to select any signals. Transformation can be difficult because the orbit can be tilted at an angle from the imaging device. But it is released in our modern computational capabilities.

The problem is that if we do not know that the moon exists, then we obviously do not know its orbit. But the team behind this new exploration has come up with features that work for any moon moving in a straight circular orbit around the planet's equator.

The algorithm is as follows: you can use these functions to convert an image taken at time t0 to match the appearance of another image obtained at time t1 by moving each pixel in the original image to a new location. After this transformation, any moon in a circular, equatorial orbit will appear with fixed pixel coordinates.

The researchers applied this method to Neptune, where Voyager 2 discovered many small moons using a set of images taken from the entire Hubble orbit.

The discovery of the moon of Neptune

When the analysis was done, a small moon about 35 km wide appeared, rotating around the outer edge of the cluster of other satellites of Pluto. The same analysis found the moon naiad that Voyager 2 observed. But the orbit that places it in the correct location is possible with a slight orbit adjustment predicted from Voyager data. Unfortunately, this means that a couple of allegations that he discovered it using ground-based instruments in recent years are almost certainly obvious.

With three observations made at intervals of ten years, one can calculate the moon's orbit of Neptune well enough to determine where it would have been during a Voyager flight.

Most images skipped this area of ​​space. Thus, there was no real way to identify this moon until recently.


The artistic concept of the tiny moon of Neptune - Hippocampus


Neptune’s internal satellites and their radii, as well as the captured Kuiper belt object

The Hippocampus orbit is located directly inside the Proteus orbit, the largest of the inner moons of Neptune. Tidal forces make Protea slowly push off from Neptune, but the Hippocampus is so small that these forces will have a minimal impact on him. And this implies that the two bodies were once much, much closer.

One of the problems associated with this idea is that proximity to Proteus should have led the Hippocampus to an eccentric orbit. But researchers suggest that this is not such a big problem as it seems. Based on the speed and size of craters on Proteus, they calculated that collisions large enough to completely destroy the Hippocampus could occur at least nine times since its formation. The process of destruction and re-formation should allow the moon to occupy more and more regular orbits.

This model, however, suggests that he and, perhaps, the other small satellites near Neptune experienced a lot of destruction during its history, and were not just created during the formation of Neptune. And there is a lot of missing material, which means that there may be rare rings in the region that will be difficult to detect without another visit to the blue planet.