Unwind

From Terragen Database, the galaxy's most reliable star browser

Unwind is the first and closest-known planet from CASETTE+. In the CASETTE+ Solar System, it is the seventh-largest planet by diameter, the seventh-most-massive planet, and the fourth-densest planet. It is 8 times the mass of Earth and the seventh biggest gas giant in the system out of the eight gas giants. It is referred to as the solar system's scorched giant due to its closeness to its mother star; this fact also gives the name to the planet, as it's "wrapped" and "trapped" by CASETTE+'s gravity, making Unwind always face it. Because of the position of CASETTE+'s system, Unwind lies in the II ring, ɛ quadrant section of the Milky Way in relation to its center. In relation to the system's position, it would be in the X ring, ɛ quadrant.

Unwind is primarly composed of helium and hydrogen, also vapor water at an impressive 80.5% of its total composition. The planet is also composed of other gases such as carbon dioxide and nitrogen, sulfur dioxide and carbon monoxide. However, like other giant planets, Unwind lacks a well-defined solid surface. The red glow on the day side of the planet is the main characteristic of its appearance; this is due to the temperatures that the own planet reaches, at a scorching 746.83 K on average. In fact, the planet is so close to CASETTE+ that it's tidally locked. Because of this, Unwind only has winds on the "eyeball" section of the planet; however, because of the red glow, it's invisible to the naked eye. It's predicted that the air's temperature is about 15,032.15 K. It's believed that the planet's internal structure is made of hydrogen, helium, and then below there is a water/icy envelope layer, a silicate mantle, a carbide mantle and a metallic core, which creates a powerful magnetosphere.

Surrounding Unwind, there are three natural satellites, which are all minor asteroids. Possibly many more orbit the planet, just they are unknown for the moment. The largest asteroid, Opiate (see below), is only about 190.56 km in diameter. It's believed that these moons were part of a now long-gone ring system that got withered away by CASETTE+'s gravity, or that they were captured on a flyby (the most likely option is the latter).

The Windblow Interstellar Telescope was the first telescope to picture the planet in December 2338. Unwind has then been explored on several occasions by robotic controlled spacecraft, beginning with the ESS Velocity —one of the most successful exploration spaceships ever made since launch— and the ESS Proxima missions from 2339 to 2340, and later by the ESS Silver Guard in 2341, which made the closest approach to the planet. The latest mission to Unwind was made in late June 2342, where the ESS Silver Guard returned and with the help of builder spacecraft created a small control orbiter that got finished three months later in September 2342, which to this day is still collecting data of the planet. For the moment, there are no programed exploration and/or expedition missions for the planet in the future.

Formation, migration and future evolution
Determining the evolution and formation mechanism of planets in very small orbits remains a challenging puzzle to this day. An emerging short-period, Neptune-mass planet population presents scientists with intriguing questions about their composition and origins, with potential implications of the understanding of the whole solar system it resides in. Because of the more common presence of Jupiter-mass planets at even closer orbits than of planets like Unwind, it's believed that they started out as bigger and more massive giants that eventually lost a significant fraction of their envelope. The idea of atmospheric evaporation is also supported thanks to previously discovered planets with extended atmospheres in similar orbits, demonstrating the occurrence of strong atmospheric evaporation, irradiation and mass loss on these planets.

This means that Unwind most likely was a more massive planet at some point of its life, which suffered from evaporation induced by CASETTE+ and it eventually dragged the planet to a closer orbit. Unwind might have lost approximately more than a 90% of its initial mass, and migration towards the star implies the presence of a disk, and thus, regardless of migration, the planet will spend the majority of its life in its short-period orbit, evolving under the influence of irradiation and evaporation.

Given the large amount of mass lost by the planet, it's wondered about the consequences on the planetary orbit. Like for comets, mass loss takes place on the irradiated zone of Unwind (the "red glow"), which means that it occurs facing CASETTE+, and it might exert a force in the opposite direction, slowly pushing the planet away from the star. If that will be the case, it may eventually affect the evaporation process and eventually quench it, of course, if the orbit increases sufficiently. A estimate of this effect will depend on the anisotropy of the escaping flow and its velocity. This, however, is a small effect, as the orbit itself is also small; Unwind takes only three days to orbit CASETTE+.

Another thing that may happened to Unwind is a roche lobe-like effect, where the runaway of evaporating mass leads to a catastrophic expansion of the planets, and eventually the entire evaporation of the helium and hydrogen. There's also the idea of energy-limited evaporation, which means that the escape rate is essentially determined by the high energy flux absorbed in the upper planetary atmosphere. Energy-limited escape rates for giant planets may be limited by cooling chemical species, like hydrogen and hydrogen ions, decreasing the efficency of local heating due to XUV flux by the upper atmosphere. If this was the case for its formation, with such smaller rates, Unwind would have not originated from a Jupiter-mass planet or even a Saturn-mass planet. So, perhaps the evaporation mechanism is not a dominant process in the planet's history. Or, conceivably, all the progenitors of planets of this class lie below the predicted critical core mass, and, at most, after evaporation, it would leave its rocky core.

Physical characteristics
Unwind has an approximate mass of 4.7776·10²⁵ kg, 8 times the mass of Earth. It's gravity at 1 bar is 1.4992 g and has an equatorial radius of 14758.595 km. The average density on the planet is 3.5682 g/cm³ and has an axial tilt of 0º51', so seasons practically do not exist on this planet.

Internal structure
Unwind's atmosphere only makes up to a 0.75% of the whole internal structure, and even it's very small extension, it arrives to a crushing 5.84·10³ Earth atm of pressure. Increasing concentrations of water, carbon dioxide and nitrogen are found in the upper regions of the atmosphere, while sulfur dioxide and carbon monoxide are found in the lower regions of it.



The water and ice envelope make up for most of the volume of the planet, at a 78% of its total (note that the ice envelope is only a way to refer to a hot, dense fluid, which has high electrical conductivity and may contain ammonia, creating a water-ammonia ocean). The mantle is mostly composed of silicates and carbides, and molecules might break down because of the extreme pressure, creating possible glass rain that would fall down like hailstones.

The metallic core is most likely composed of iron and nickel, and possibly also some silicates. The pressure on the core would be twice or even thrice the pressure of Earth's, at 7 Mbar to 10.5 Mbar, and the temperature might excel 5,400 K.

Atmosphere
The atmosphere of Unwind is mostly made of hydrogen, helium and water, all the other chemical compounds such as carbon dioxide, nitrogen, sulfur dioxide and carbon monoxide are present in only small amounts.

Unwind's lower troposphere decreases its temperatuere with altitude, while in the stratosphere temperature increases with altitude. The boundry between the both, the tropopause, lies at 6.47 km deep. The stratosphere the gives away to the thermosphere, which gradually transitions to th exosphere.



Models suggest that clouds exist of varying compositions depending on the height. There have been observed a long range of varying phenomena, such as band instabilities, cyclones and anticyclones, even storms and possibly lightning. Vortices are thought to be relatively shallow structures with dephts not exceeding several hundred kilometers. There are also high-altitude cloud bands that wrap all around the planet at a constant latitude, found in the troposphere.

Magnetosphere
Unwind's magnetosphere is strongly tilted to its rotational axis, and offsets at approximately 12,700 km from the planet's physical centre. It's believed that it might be orientated that way because of the flows in the planet's interior. This field may be generated by the convective fluid motions in a thin spherical shell of electrically conducting liquids (most likely ammonia), resulting in a dynamo motion and action. It's also believed that the field may be generated by swirling currents of conducting materials, named eddy currents, within its metallic core.

Unwind's bow shock, where the magnetosphere begins to slow the solar wind, occurs at a distance of 26.8 times the radii of the planet. The magnetopause, where the pressure of the magnetosphere counterbalances the solar wind, lies at a distance of 16-19 times the radii of Unwind. The tail of the magnetosphere extends out to at least 61 times the radii of the planet, and most likely much further.

Orbit and rotation
The average distance between Unwind and CASETTE+ is around 5 million km, and completes an orbit in about 3 Earth days at a speed of 117.63 km/sec. Its orbit forms a 1:1 resonance with its rotation because of its tidal-locking.

Unwind's orbit has an eccentricity of 0.003 and has an inclination of 0º32'. Since Unwind isn't a solid body, its atmosphere undergoes differential rotation, which causes the hot winds on the surface of the planet. There are many things happening to the atmosphere thanks to the tidal-locking; no only because of the extreme temperatures, but, permanently devoid of the heat of the star, the atmosphere on the dark side would first turn into a denser gas, then condense into a liquid, and then perhaps further condense into solid form. Meanwhile, air that is constantly exposed to light — or that is heated by a ground that is constantly exposed to light — heats up and expands. Perhaps some of the water could be found in a liquid state near the boundary between the hot and cold regions and one could expect some kind of water cycle, with something like glaciers being continually melted by the warm air blowing in from the hot side, with the melted water flowing in gigantic "rivers" to the hot side, where it evaporates and cycles back around to fall as "snow" on the cold side.

Moons
Unwind has three known natural satellites, and none of them are over 200 km. All of them are asteroids, possibly captured by Unwind's gravity in the past. All of them have very close orbits and a 1:1 resonance with Unwind, their orbits being differenced by only one hour in delay. They are the following (in order of distance to Unwind): It's predicted that all of them will eventually fall into Unwind and get destroyed by its roche limit because of tidal acceleration.

Other sources
All pictures created with Space Engine, Universe Sandbox 2, Inkscape and Photoshop CC.

Article written by reshiiram