Image: NASA/ESA/M. Showalter/SETI Institute

That’s right, with help from observations gathered by Hubble, astronomers have discovered a new moon in orbit around Neptune. This brings the total Neptunian lunar count to fourteen. Creatively called S/2004 N1, this is the first Neptunian moon discovered in more than a decade. The moon was first observed by Hubble between 2004 and 2009, but it wasn’t spotted until earlier this month while Mark Showalter from the SETI Institute was conducting research on Neptune’s ring system. Astronomers currently estimate S/2004 N1 to be between 16 and 20 kilometers in diameter (or, about 12 miles), and it has a nearly circular orbit, which it completes every 23 hours.


The discovery of S/2001 N1 does raise a ton of new questions about the history of our solar system’s outermost planet, specifically in regards to Neptune’s largest moon, Triton.


Triton has a diameter of 2705 kilometers and orbits Neptune in retrograde; meaning in the opposite direction to Neptune’s spin. This has led scientists to hypothesis that Triton was captured by Neptune’s gravitational pull some 4-bilion years ago. This capture event would have thrown the entire Neptunian system into chaos, likely causing the destruction or ejection of any moons Neptune originally possessed. Then the debris cloud from the old moons would have gathered together to form the moons that we see today.


Image: NASA/ESA/M. Showalter/SETI Institute

S/2004 N1 has found a very comfortable home between the orbits of Proteus, the second outermost moon (Triton is the farthest out), and Larissa. S/2004 N1’s small stature is a conundrum; such a moon should have been absorbed into the surrounding Neptunian moons or completely destroyed. On the subject, Showalter said, “(S/2004 N1) is far enough away that its orbit is stable. Once you put it there, it will stay there. The question is, how did it get there?”


Obviously, a new moon warrants a new name. Showalter and his team was also responsible for the discovery of Kerberos and Styx – Pluto’s two newest and most recently named moons. Whereas Showalter held a public naming contest for those moons, the International Astronomical Union had the final say. It’s very possible Showalter will probably do something similar for S/2004 N1. Neptune’s moons are currently named after minor water deities found in Greek and Roman mythology; it’s very likely S/2004 N1 will receive a similar name in an effort to preserve the nomenclature.

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