Starship Asterisk*

TheOtherBruce wrote: ↑Tue Sep 17, 2019 7:22 pm

Boomer12k wrote: ↑Tue Sep 17, 2019 10:22 am 8 times the mass of Earth? We are going to have to be SUPER SAYANS to do anything there.... got anything smaller????

The figure for density (from the Wiki article) is awfully low, juggling the numbers gives a surface gravity only a little bit more than Earth's.

Which makes me wonder, what kind of planet could have such a low density (less than half Earth's) — could it be very low in heavier metals (unlike Earth's big nickel/iron core)? Could it have much more than Earth's thin surface smear of water?

Two separate analyses by researchers at Université de Montréal and University College London (UCL) of the Hubble data were published in 2019. Both examined spectra of starlight passing through the planet's atmosphere during transits, finding that K2-18b has a hydrogen–helium atmosphere with a high concentration of water vapor, which could range from between 0.01% to 12.5%, up to between 20% and 50%, depending on what other gaseous species are present in the atmosphere.

Boomer12k wrote: ↑Tue Sep 17, 2019 10:22 am 8 times the mass of Earth? We are going to have to be SUPER SAYANS to do anything there.... got anything smaller????

starsurfer wrote: ↑Tue Sep 17, 2019 12:20 pm

Antony Rawlinson wrote: ↑Tue Sep 17, 2019 6:39 am "... unconfirmed sister planet ..."? Does that mean suspected to exist from actual observations, or added purely speculatively for the purposes of the artist's image?

To me it looks like a moon orbiting the planet?

K2-18 c is a non-transiting planet identified in radial velocity measurements of the K2-18 system.

neufer wrote: ↑Tue Sep 17, 2019 1:18 pm

Chris Peterson wrote: ↑Tue Sep 17, 2019 12:50 pm
When we think about life on other planets, we should really be thinking about simple plant life, either in seas or on land. The sort of life that existed for most of the time life has been present on Earth. Even 8G would be no issue at all.

• I still cling to my 3G Star-trek flip phone.
  
  I don't think I could survive on an 8G planet.

Chris Peterson wrote: ↑Tue Sep 17, 2019 12:50 pm
When we think about life on other planets, we should really be thinking about simple plant life, either in seas or on land. The sort of life that existed for most of the time life has been present on Earth. Even 8G would be no issue at all.

• I still cling to my 3G Star-trek flip phone.
  
  I don't think I could survive on an 8G planet.

Geo wrote: ↑Tue Sep 17, 2019 11:15 am

Boomer12k wrote: ↑Tue Sep 17, 2019 10:22 am
8 times the mass of Earth? We are going to have to be SUPER SAYANS to do anything there.... got anything smaller????

I am thinking if any life...Aquatic, as it could use the buoyancy... but 8 times... I don't know... if anything could still float, let alone swim...

Actually I read that it’s 9 times Earth mass with a diameter of 2.7 Earths.

The nine masses are frightening but given the massive size of the planet the gravity (if I did my math right) comes out only to 1.23456 g which while a little uncomfortable it would no problem for a person of reasonable size and health, at least for short term visits.

https://en.wikipedia.org/wiki/K2-18b wrote:

Code: Select all

                     K2-18b      Neptune
-------------------------------------------------
Earth Masses:	    8.63±1.35    17.147
Earth RadiI: 	    2.71±0.07     3.883
Surface gravity	    1.18g         1.14g

Geo wrote: ↑Tue Sep 17, 2019 11:15 am
The main problem it seems that scientists think it’s much more likely to be a mini-Neptune rather than a super-Earth and it’s atmosphere is dominated by hydrogen.

I could envision a giant ocean planet, it would make a great movie. Maybe they could title it “Waterworld”!

• More a flooded Water Venus than a flooded Water Earth:

https://en.wikipedia.org/wiki/Neptune#Internal_structure wrote:
<<Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5% to 10% of its mass and extends perhaps 10% to 20% of the way towards the core, where it reaches pressures of about 10 GPa, or about 100,000 times that of Earth's atmosphere:

The mantle is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane. As is customary in planetary science, this mixture is referred to as icy even though it is a hot, dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean. The mantle may consist of a layer of ionic water in which the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises [oxygen bergs?] but the hydrogen ions float around freely within the oxygen lattice.

At a depth of 7,000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones. Scientists also believe that this kind of diamond rain occurs on Jupiter, Saturn, and Uranus. Very-high-pressure experiments at the Lawrence Livermore National Laboratory suggest that the top of the [core?] may be an ocean of liquid carbon with floating solid 'diamonds'. The core of Neptune is likely composed of iron, nickel and silicates, with an interior model giving a mass about 1.2 times that of Earth.>>

Boomer12k wrote: ↑Tue Sep 17, 2019 10:22 am 8 times the mass of Earth? We are going to have to be SUPER SAYANS to do anything there.... got anything smaller????

I am thinking if any life...Aquatic, as it could use the buoyancy... but 8 times... I don't know... if anything could still float, let alone swim...

:---[===] *

Antony Rawlinson wrote: ↑Tue Sep 17, 2019 6:39 am "... unconfirmed sister planet ..."? Does that mean suspected to exist from actual observations, or added purely speculatively for the purposes of the artist's image?

Boomer12k wrote: ↑Tue Sep 17, 2019 10:22 am 8 times the mass of Earth? We are going to have to be SUPER SAYANS to do anything there.... got anything smaller????

I am thinking if any life...Aquatic, as it could use the buoyancy... but 8 times... I don't know... if anything could still float, let alone swim...

:---[===] *