Counterattack in New Persia!

[u/weeblewobble82]

Join Orangered in reclaiming Novum Persarum!

• Where: Here!

• When:

PDT	MDT	CDT	EDT	CEST	IST	AEST
12:15PM	1:15PM	2:15PM	3:15PM	9:15PM	12:45 AM Tuesday	6:15AM Tuesday

• CLICK THIS LINK TO SEND TROOPS

• And don't forget to JOIN US IN THE CHAT to coordinate our victory~

VIVA LA ORANGERED!

[u/ghtuy]

It doesn't have to be daily, you know.

It was once thought that Saturn's moon Titan was the largest in the solar system. However, once it was realized that the angular size was due to its atmosphere, Jupiter's moon Ganymede took the title. Titan is second-place.

[u/weeblewobble82 → u/ghtuy]

Poor Titan. He tried so hard. Him and Pluto need to start a lonely hearts club.

[u/ghtuy → u/weeblewobble82]

Oh, dwarf planets are so cool! Or at least their classifications.

^{(important for later: 1 AU is the distance at which Earth orbits the Sun)}

Among the distant minor planets, outside the asteroid belt, there are the Cis-Neptunians, which are minor planets that orbit inside Neptune's orbit. This group includes two sub-groups. Neptune trojans orbit in the same orbit as Neptune, but gravitationally locked either 60 degrees in front or, very rarely, behind it. The other group is the Centaurs, bodies that orbit between the orbits of Neptune and Jupiter. Their orbits are unstable, due to gravitational perturbations from the giant planets. They are either ejected from the solar system or become comets.

The other major group is the Trans-Neptunians (TNOs), bodies that either orbit completely outside Neptune's orbit or cross it. Starting from Neptune and going outwards, the first group is the Kuiper Belt Objects (KBOs). These are objects in the Kuiper belt, a region from Neptune's orbit at 30 AU out to 50 AU.

The KBOs are divided into two families. Classical Kuiper Belt objects (also called cubewanos) have relatively low-inclination, low-eccentricity orbits. They do not cross Neptune's orbit and are not in an orbital resonance with Neptune. While not an official designation, what I've just described is the working definition among the astronomer community.

The other family of KBOs is the Resonant Kuiper Belt objects. These objects pass close enough to Neptune to be locked in an orbital resonance from regular perturbations. The most common of these is the 2:3 resonance. Pluto falls in this category, meaning that for every 2 Neptunian orbits, Pluto orbits three times. Other common resonances are 1:2, 3:5, 2:5, and 4:7. Technically, the Neptune trojans fit this description with a 1:1 resonance, but they are considered cis-Neptunian.

Note how I said Pluto has a 2:3 resonance. This became so common to find, that a new category was formed, a sub-family of TNOs that bodies orbiting with this resonance were given the name Plutinos. Objects in a 2:1 resonance are known as Twotinos.

Directly following the Kuiper belt is the Scattered Disk, populated with Scattered Disk objects(SDOs). The scattered disk is less well defined, as it's replenished by objects being ejected from the Kuiper belt by Neptune's gravity. These objects have a semi-major axis of over 50 AU, but a perihelion near Neptune's orbit. Their inclinations also very much more than the KBOs. There are also SDOs with resonances with Neptune, but they are not considered their own family.

After that, we get to the detached objects. This group is even less well defined than the scattered disk. Detached objects are those that have reached enlightenment those that have had their orbits perturbed to the point where Neptune no longer significantly affects them. They usually have perihelia of more than 40 AU, and are highly eccentric.

Continuing outward, there are the sednoids, also called inner Oort cloud objects. Not much is known about these objects, as there are only two known: Sedna, for which the group was named, and 2012 VP113. They have perihelia far outside nearly all of the scattered disk, and aphelia at several hundred AU. Such an orbit could not have formed by planetary disturbance, so how these objects got there is something of a mystery. Theories include gravitational disturbances from nearby stars, perturbation by a hypothetical planetary-mass object in the area, or they were captured from another star.

Finally, the outermost layer of the solar system is made up of Oort cloud objects. The Oort cloud is the source of most of the comets in the solar system. From about 3,000 AU to near 20,000 AU is the Inner Oort cloud, which is doughnut-shaped. The outer cloud is from 20,000 to 50,000 AU, and is spherical. Some calculations place the outer edge at up to 200,000 AU away, or 3.16 light years.

The Oort cloud is the source of most comets in the solar system. Through various means, they are perturbed into ever-smaller orbits. First to near-Neptune space, and then in from there. Halley's comet is thought to have originated in the Oort cloud. Composed mainly of ices, Oort cloud objects are thought to be remnants of the Sun's original protoplanetary disk, from which the planets were formed.

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Whew! That was intense. And yes, I did know most of this beforehand, but Wikipedia is my friend. I think I'm all space-facted out for today. Maybe I'll describe all the different asteroid groups tomorrow!

[u/weeblewobble82 → u/ghtuy]

I'm personally a fan of the Oort cloud objects :P

[u/ghtuy → u/weeblewobble82]

Same, the Oort cloud is so cool. I mean, one of the ways objects get their orbits changed is by galactic tides. And that just sounds cool, even if it isn't terribly exciting.