Neptune is the eighth planet in our solar system and orbits around the Sun at a distance of 2.8 billion miles. In comparison to Earth, that is approximately 30 times further from the Sun.
In August 1989, Voyager II passed by Neptune and detected a complex system of 13 moons, but six of them hadn’t been spotted before.
This year, thanks to the data from Hubble Space Telescope, astronomers discovered that there is one more moon. It was difficult to find because it wasn’t in the Voyager’s range. This moon’s name is Hippocamp.
An astronomer Mark Showalter from the SETI Institute stated that Voyager was very close to finding this moon, but it missed it numerous times. He added that Voyager II took photos of the entire Neptune, but due to Hippocamp’s small size, it is vague and undetectable in pictures.
Hippocamp is so distant that telescopes have difficulties locating it. It cannot be seen in the Hubble’s images of Neptune’s system, even with longer exposure. Showalter pointed out that they exposed Neptune with factor 50, but still, they weren’t able to detect it.
An image taken in 2016 helped astronomers spot Hippocamp. With the objective of locating it, scientists used a complex and lengthy process which enabled them to stack eight photos of it on top of each other, basically allowing them to have 40-minute exposure.
Their initial intent with this process was to discover vague arcs and incomplete rings around Neptune. Subsequently, they learned that they could find small and latent moons too. When they repeated the process with the entire image, the Hippocamp appeared.
Early Discoveries and Hypothesis
The team of scientists had announced that they could have discovered it in 2013, but they needed more time to establish its orbit and find out more about its size. Showalter says that when they find out something new, the process of establishing facts begins.
Until now, researchers discovered that Hippocamp reflects 9% of the light it receives. It’s likely that it is 20 miles (32 km) in diameter just like Neptune’s other moons. Another conclusion based on its orbit is that in the past, it was much closer to Neptune’s other moon Proteus.
An interesting fact is that Voyager revealed a large crater on Proteus, which indicates that it suffered a massive collision with another object 4 billion years ago. It is assumed that it had caused a big cloud of debris, which presumably led to the creation of Hippocamp. An astronomer at the University of Virginia, Anne Verbiscer, said that the origin of Hippocamp was yet to be established since this hypothesis was just a guess.
Throughout his career, Showalter discovered six moons in the solar system. One around Saturn, two around Uranus, two around Pluto and Hippocamp, respectively. He believes that there are no other hidden objects that can appear around Neptune. The technique used to find Hippocamp should have revealed other objects as well, but if we want to know more, we should send a spacecraft.