#sub neptune

Family portrait of the Zwo-nmu planetary system (the system to which Gymnome--Eaurp Guz's homeworld and the setting of train puzzle dot exe (title pending)--belongs).

Labelled version and more below the cut.

LHS 3154 and it's Giant Planet

Until recently, the idea that a very low mass star could create a very large planet would have raised more than eye brows amongst those who study exoplanets and how they formed, even maybe a chuckle, but the more we search out from our Solar System and see the diversity just in our own local part of the galaxy, the more it challenges these and other assumptions about how our own Solar System came to be.

LHS 3154b is a Sub Neptune planet around 13.2 times the mass of our Earth (Neptune being just over 17 times the mass), and while Sub Neptune exoplanets are turning up pretty much everywhere, this one orbiting so close around it's barely M type star, is a bit of a confusion, how did a planet that's 35% the mass of it's parent star get to exist.

For comparison, Jupiter is .1% the mass of our Star.

The amount of matter required to make this small star, would seem to negate such a large planet forming, and when we look at many M type red dwarf stars, that's what we see, smaller rocky worlds.

The team spent much time trying to model what could possibly have created it, and in the end came to the conclusion there was either a lot more mass in the disk than was expected, or that the disk was surrounded by a very large pool of material that had been sucked in during the formation.

The team ruled out the idea of capture due to the orbital pattern of the planet, expecting a much more elliptical orbit had it been so (although, there are many processes that could have changed the orbit over billions of years that M type stars exist).

Hot Sub-Neptune Planets

When we look out to the stars and catalogue the planets orbiting them, we regularly bump into a type of planet that our Solar System for whatever reason, didn't create.

Planets close in to the star, a few times more massive than our Earth, but not quite as massive as the outer ice giant planets of Uranus and Neptune, these planets we call Sub Neptune, but not having any example of such a planet in our own system means, they are also the kind of planet we know least about.

Slowly, we are beginning to peel back the fog (quite literally) and find out more information about these planets, thanks to the JWST.

48 light years from Earth, orbiting a red dwarf star every 1.5 days is Gliese 1214 b, a sub Neptune planet that JWST has been watching closely recently, and has found some fascinating things.

Firstly the planet is tidally locked, this means the planet has a fixed side facing the sun, and the other side facing outwards. It would be like having the Atlantic ocean and countries around always in day, while the pacific being always at night.

Secondly, the planet is incredibly reflective, so much so, it had scuppered any previous attempts to derive any details from it, but JWST was up to the task. It looks like the entire planet is covered in a thick reflective cloud system, thought to be water or methane. If that was the case, then the planet almost certainly didn't start life so close to it's parent star, but has instead slowly migrated towards it.

Reflectivity is known as Albedo, above is a diagram of the % of reflectivity of different environments (top 100%, bottom 0%), what's interesting is, Water as a body is one of the lowest, while clouds (still made of water) reflect huge amounts. This is why the scientists assume the water or methane clouds are causing the huge reflectivity of the planet.

Thirdly, because of the way the planet has day/night sides, JWST was able to measure the temperature difference between the part day side, and the part night side as it transited the star.

This was a big surprise, as the temperatures were much lower than expected. 279'c on the day side, and 65'c on the night side.

I'm not sure I personally like the idea of being on a planet with 65'c water vapour flowing around me, never mind 279'c, but this was much lower than had previously been expected, and what led them to understand more about the nature of the materials that make up the atmosphere.

The question had always been, was there hydrogen or something more complex, and the answer is 100% more complex.

The Water Worlds

When you think of a water world, you probably imagine a world that is an entire ocean, with no land but yet, similar to being out at sea in the middle of the pacific ocean.

Until recently, they were just a theoretical possibility, but two planets that orbit a star Kepler 138, just 218 light years away in the constellation of Lyra, appear to be just that, except .. you may want to re-think what a water world is.

Both planets are slightly larger than our planet, yet their densities fall way below, not enough to be thought of as a gas planet (or a sub-Neptune) but not enough to be considered entirely rocky.

The conclusion is, both planets are in fact, water worlds.

But unlike oceans on Earth, these monsters have oceans 500 times the depth of our deepest one, and being closer to their star and slightly outside of the habitable zone, they are incredibly hot, and the water is under pressure far in excess of any ocean here on Earth.

As a result, the planet likely has a thick atmosphere of mostly steam, then moving down to a pressure where that steam liquifies and even further down, potentially solidifies at warmer temperatures than we normally see Ice.

Such environments would be totally unsuitable for us, but .. imagine if there was a moon orbiting such a planet, it would offer an intriguing base.

Sadly, our technology can only just about detect rocky planets, it will be a bit before we start finding moon systems, so for now, we only have the small amount of data by which to imagine what these worlds are really like.

Source :

Hycean Class Planets

In the search for life, went tend to look for the rather cringably termed "Earth 2.0", the small rocky planet in the habitable zone that could sustain liquid water, and we've found a fair number of these planets to date, but their size and proximity to their host star makes detailed readings very challenging.

A much more common find however are super-Earth's or sub-Neptune sized planets, generally overlooked for life on the basis the gravity would be far too extreme and the surface likely blanketed by a thick atmosphere similar to Venus that would both heat and crush any macro life at the very least.

However, Astronomers at the University of Cambridge UK think they may have come up with a more common and easier place to look, what they have termed the "Hycean World".

These classes of planets are 2.5 times the mass of the Earth and over, have atmosphere's of hydrogen and huge oceans of water on the surface. The atmospheric temperature and gravity would be too harsh for land based life as we know it, but under the water there certainly could be conditions for life to thrive.

The astronomers believe it may be easier to pick up on the traces of life in the atmosphere of these larger planets than trying to find biosignatures on smaller rocky planets, and have already identified a good number orbiting red dwarf stars within 150 light years of Earth.

One such exoplanet is the K2-18b, 111 light years away in the constellation of Leo and with a red dwarf star. The planet is 6 times the mass of Earth and sitting in the habitable zone of the star. Scientists think the planet is either mostly a rocky word with an atmosphere similar to Earth but FAR larger, or most likely, a water/ice world with a much thicker atmosphere.

Source : http://www.sci-news.com/astronomy/hycean-worlds-10004.html