APOD: Water Vapor Discovered on Distant... (2019 Sep 17)

[APOD Robot]

Water Vapor Discovered on Distant Exoplanet

Explanation: Where else might life exist? One of humanity's great outstanding questions, locating planets where extrasolar life might survive took a step forward recently with the discovery of a significant amount of water vapor in the atmosphere of distant exoplanet K2-18b. The planet and it parent star, K2-18, lie about 124 light years away toward the constellation of the Lion (Leo). The exoplanet is significantly larger and more massive than our Earth, but orbits in the habitable zone of its home star. K2-18, although more red than our Sun, shines in K2-18b's sky with a brightness similar to the Sun in Earth's sky. The discovery was made in data from three space telescopes: Hubble, Spitzer, and Kepler, by noting the absorption of water-vapor colors when the planet moved in front of the star. The featured illustration imagines exoplanet K2-18b on the right, its parent red dwarf star K2-18 on the left, and an unconfirmed sister planet between them.

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[Antony Rawlinson]

"... 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]

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...

:---[===] *

[Geo]

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.
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”!

https://earthsky.org/space/k2-18b-habit ... ni-neptune

[orin stepanek]

Don't visit unless your spaceship has super boosters or you might have to staY!

[starsurfer]

"... 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?

[Chris Peterson]

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...

:---[===] *

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.

[neufer]

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.

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

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:

<<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.>>

[neufer]

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]

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.

You'd need cat 8 connections, that's for sure.

[BDanielMayfield]

"... 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?

The artist wasn't trying to make it look like a moon, but an interior planet in this system. The "unconfirmed" nature of this planet K2-18c depends on which source you read. The very short linked to Wikipedia article mentions this planet as fact. The reference it gives from the Open Exoplanet Catalog states this:

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

So they can tell from RV measurements of the star's light that the second planet is there, even though it doesn't transit the star like the outer planet does. Maybe some are questioning this though?

Bruce

[Astronymus]

Great, now it will be run over by tourists.

[TheOtherBruce]

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?

I'm also curious about what the orbit would do to surface conditions. Like many red dwarf systems, this one is tiny; the planet's orbit would fit well inside Mercury in our system. I agree with the wiki article, it's probably tidally locked, although the high eccentricity (about the same as Mercury) could mean it settled into a spin-orbit resonance like Mercury instead of a true tidal lock. Probably a bit on the chilly side — most of the orbit is slightly inside the Goldilocks Zone — so it might only be prime real estate for polar bears or penguins.

[BDanielMayfield]

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?

K2-18 b may be closer to a mini-Neptune than a super-Earth. Considering that our Neptune's density is 1.638gm/cm³ while Earth's is 5.514gm/cm³, and K2-18 b's is estimated at 2.38gm/cm³, this planet lays somewhat between Earth and Neptune in characteristics. And consider that it very likely has a very different atmosphere than Earth's:

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.

[Cousin Ricky]

The terminators on the planets are angled wrong with respect to the star.

[TheOtherBruce]

Ah, OK, I missed that bit about the planet having an at least partly hydrogen-helium atmosphere. Now I'm leaning more towards a mini-Neptune, where there might not be a solid surface at all apart from a possible rocky core.

[bystander]

Water Vapor Detected on K2-18b
viewtopic.php?t=39785

Two Super-Earths around K2-18
viewtopic.php?t=37820

[Cousin Ricky]

K2-18b’s reaction to being discovered (satire).