Planet Pailly

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:

RING ARCS

Something’s wrong with Neptune’s rings.

Neptune has five rings, all named after astronomers or scientists associated with significant Neptune-related discoveries. They are (in order of increasing distance from Neptune):

• Galle: named after the guy who discovered Neptune, sort of. He had help from…
• Le Verrier: named after the guy who calculated Neptune’s exact position, allowing Galle to “discover” it.
• Lassell: named after the discoverer of Triton, Neptune’s largest moon.
• Arago: named after the teacher who encouraged Le Verrier in his calculations and helped defend Le Verrier in a dispute with…
• Adams: named after another person who calculated Neptune’s position before its discovery and started a fuss with Le Verrier over who deserved credit.

There was plenty of drama surrounding the discovery of Neptune, and that has been preserved in the names of the rings that also surround the planet.

Neptune has an unnamed sixth “ring,” if we can be generous enough to call it a ring, located between Arago and Adams. A small moon named Galatea also orbits within that gap. This unnamed ring doesn’t circle all the way around the planet, so it is better described as an “arc.”

Furthermore, a short segment of the outermost ring (Adams) is also broken up into several small arcs. These arcs were originally named Liberty, Equality, and Fraternity (bonus points to anyone who can tell me what the planet Neptune has to do with the French Revolution).

Later, two more arcs were found in the Adams ring, so the list became (in order):

• Courage: the faintest arc.
• Liberty: often described as the “leading arc,” even though Courage orbits ahead of it.
• Equality 1 and Equality 2: the Equalities are so close together that they’re almost a single arc.
• Fraternity: brings up the rear and is the largest and brightest of Neptune’s arcs.

The existence of these arcs doesn’t make a whole lot of sense. Ring particles should spread out the fill the gaps within a matter of months, yet the arcs have remained stable since their discovery in the 1980’s.

An orbital resonance with Galatea is almost certainly involved, but mathematical models of Galatea and the Adams arcs don’t always match with observations. Neptune may have an additional as-yet-undiscovered moon near its rings, or perhaps some other unknown factor is at work.

Probably aliens.

P.S.: Neptune isn’t the only planet with arcs in its rings. Saturn has them too. So Neptune: you don’t have anything to feel embarrassed about.

Links

Neptune’s Rings and “Ring Arcs” from JPL’s Voyager Mission webpage.

Rings of Neptune from Universe Today.

Stability of Neptune’s Ring Arcs in Question from Letters to Nature.

* * *

Today’s post is part of Neptune month for the 2015 Mission to the Solar System. Click here to learn more about this series.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:

CENTAUR

When it comes to large, rocky objects drifting through space, naming conventions can get tricky. Many are called asteroids. Others go by stranger names. Some of these objects are called centaurs.

Eh… no. It has nothing to do with horses, although these objects are sort of half one thing and half another. Most if not all centaurs could be classified as both asteroids and comets.

One definition of centaur is an object orbiting the Sun between the orbits of Jupiter and Neptune. More technical definitions involve an object’s semi-major axis, relative to the semi-major axes of Jupiter and Neptune, and non-resonant (i.e.: unstable) orbital periods. But I think a better way to describe centaurs is this: they are objects in a state of transition.

It is believed that most centaurs used to be Kuiper belt objects or objects from the scattered disk: basically, they were those large, icy things hanging out beyond Neptune. Due to gravitational interactions with Neptune and other gas giants, these objects have been pulled into increasingly eccentric (non-circular) orbits.

Eventually, most of these objects will transform into comets, with orbital paths that cut through the inner Solar System and bring them within melting distance of the Sun (allowing them to form cometary tails).

The Interanational Astronomy Union (I.A.U.) originally wanted to name all centaurs after actual centaurs from Greek mythology. However, some have been named after other hybrid or shape-shifting creatures, which I think is perfectly appropriate. Examples include Typhon (a snake or dragon hybrid), Ceto (a sea monster goddess), and Narcissus (a man who transformed into a flower).

In the future, centaurs could conceivably be named after the minotaur, the sphinx, or perhaps even Dracula. If the I.A.U. wants to have some fun, they could also use names like Ariel from The Little Mermaid, Constable Odo from Star Trek: Deep Space IX, or any of the Animagus characters from Harry Potter.

In fact, throughout fiction and mythology, there are plenty of hybrids and shape-shifters to chose from. So what names do you think the I.A.U. should give the next centaur asteroids?

Links

Centaurs: Cross-Dressing Comets That Go as Asteroids from Discovery News.

Centaur (minor planet) from Wikipedia.

JPL Small-Body Database Search Engine: List of Centaurs from JPL Solar System Dynamics.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:

CANTALOUPE TERRAIN

This is a cantaloupe.

And this is Triton, Neptune’s largest moon.

Wait, I think I got those mixed up…

In 1989, Voyager 2 became the first (and so far the only) spacecraft to visit Triton, and it sent back some weird pictures of Triton’s surface. Pictures like this one:

This heavily dimpled surface topography, which bears an uncanny resemblance to the skin of a cantaloupe, is unique to Triton. It may have formed due to a geologic process called diapirism, whereby blobs of warm material (called diapirs) force their way upward through layers of solid rock.

We know this process occurs on Earth and possibly a few other places in the Solar System. However, diapirism does not generally produce a cantaloupe-like appearance. That only happens on Triton, and no one’s entirely sure why.

So research continues on what scientists have officially named “cantaloupe terrain.”

Today’s post is part of Neptune month for the 2015 Mission to the Solar System. Click here to learn more about this series.

And click here to find out more about Europa’s chaos terrain.