The gigantic blue planet made up largely of water and which may have a sea of liquid diamond inside it, our beloved Neptune, has a new satellite accompanying it. And there are now seven moons – as far as regular satellites are concerned -: Naiad, Talase, Despina, Galatea, Larisa, Proteus and now … Hippocampus.
A team of astronomers from the SETI Institute in Mountain View, California (USA) used more than a decade of observations with the Hubble Space Telescope to find this moon, of which there is evidence for the first time in 2013 when a strange was observed white dot near Neptune in Hubble Space Telescope observations.
The smallest moon on the most remote planet in the solar system could be a portion of a neighboring moon that was shot down by a comet. And it is that the largest moons tend to swallow the small ones as satellites are formed. Some experts, like Mark Showalter, believe that Hippocampus is a piece of Proteus that was detached from a massive collision with a comet. Recall that Proteus has a massive crater, called Pharos , which is so large that the impact nearly broke the moon. The collision could have raised a cloud of debris that could eventually coalesce into a smaller moon. Maybe Hippocampus. Proteus is therefore Hippocampus’s closest neighbor, orbiting some 12,000 kilometers away.
The moon Hippocampus is approximately 21 miles in diameter , the researchers report in their study published in the journal Nature.
Why this name?
The name Hippocampus refers to the half-horse, half-fish creature from Greek mythology, who pulled a chariot for the god Poseidon (the Roman Neptune). In order not to break tradition, all the moons of Neptune have names related to the sea in Greek and Roman mythology.
Showalter jokes that “The real story is that I’m very fond of seahorses.”
The disparate and numerous moons
Planets may stand out in the solar system, but they are outnumbered by moons. There are hundreds, and there are all kinds, like a cosmic tray of assorted chocolates. Our own moon is an arid, rocky world covered in craters. Enceladus, from Saturn, and Europa, from Jupiter, are frozen, wrapped in a thick layer of ice with a liquid oceanic center. Io, another moon of Jupiter, is molten, its surface constantly being redesigned by flowing lava …
Astronomers have observed these and other moons for centuries, first with homemade telescopes and now with spacecraft worth millions of euros. Many moons are well studied and their characteristics are documented in astonishing detail, but it is clear that we have yet to discover and Hippocampus is a case in point.
To identify it, astronomers dove into a drawer of five-year-old photographs, examining each one to unravel the mystery of that white dot discovered in 2013. The dot appeared again and again. It was a moon. It was Hippocampus.
This new moon is about 100 million times fainter than the faintest star visible to the naked eye . Even to Hubble, an extremely powerful instrument, the moon appears as a blur in photographs. The collection of moons in our solar system is rich and wonderful, but it is only a sample of what is out there. Welcome to the group, Hipocampo.
Neptune has seven inner moons (illustrated here with the planet’s rings), and the smallest one already has a name: Hippocampus.
Reference: MR Showalter et al . The seventh inner moon of Neptune. Nature . Vol. 566, February 21, 2019, p. 328. doi: 10.1028 / s41586-019-0909-9.
Images credit: NASA, ESA, and J. Olmsted / STSc / AJ Verbiscer / Nature 2019, MR Showalter et al / Nature 2019
