Eyeball Earths

[Timerover51]

I found this interesting report online on "water-trapped" worlds, also called "eyeball Earths". being tidally locked Earth-sized planets orbiting a red dwarf star.

http://www.astrobio.net/exclusive/5564/water-trapped-worlds-

What I thought was so interesting is that these type of planets are very close to the way Mercury is treated in GDW's Space: 1889 game. All you need to do is get a copy of Conklin's Atlas of the Worlds, along with a copy of the basic rules, and you are in business.

 

[starship_captain62]

Tide locked planets

Just considering a few variations of this theme:

What about a planet on the outer edge of the habitable zone with only the part of the planet directly facing it's sun just warm enough to support life? Imagine the sun staying permanently overhead!

The exact opposite, where the planet is on the inner edge? Only a patch on the night side could then be habitable with it's residents enjoying a permanent night.

In the article referenced there is a painting of a theoretical planet with amoon orbiting a red dwarf. What if this planet was a gas giant and the moon was habitable? In this case the habitable moon would be tide locked to the gas giant. The moon now gets a 'day' every time it orbits the parent gas giant, but of course you could only see the gas giant from one heisphere of the moon.

Just some ideas for variationts on the night side Glacier/twiligbt temperate zone/ sunward facing desert theme.

 

[aramis]

In the article referenced there is a painting of a theoretical planet with amoon orbiting a red dwarf. What if this planet was a gas giant and the moon was habitable? In this case the habitable moon would be tide locked to the gas giant. The moon now gets a 'day' every time it orbits the parent gas giant, but of course you could only see the gas giant from one heisphere of the moon.

Just some ideas for variationts on the night side Glacier/twiligbt temperate zone/ sunward facing desert theme.

The inbound face would likely not experience a whole lot of "Dark" - the relative size of the GG in the sky (30° or more), even if dim, would provide a considerable amount of light; twilight most of the time. The true "Dark" period would be when the star is eclipsed by the parent GG.

Also fun: A pair of close orbiting reds could produce up to about 1.4x the normal red star ecosphere radius (√2), and without the tidelocking. The resulting "dusky mid-day" would be relatively stable, brightest and warmest when neither star is in eclipse of the other, and coldest when the pair are in eclipse. Given the high likelihood of a resonant orbit, this could result in a pretty unified local calendar even without moons.

Actually, the overall ecosphere would probably be the average of eclipsed and non-eclipsed - so about 1.2x distances.

 

[Timerover51]

Just considering a few variations of this theme:

What about a planet on the outer edge of the habitable zone with only the part of the planet directly facing it's sun just warm enough to support life? Imagine the sun staying permanently overhead!

The exact opposite, where the planet is on the inner edge? Only a patch on the night side could then be habitable with it's residents enjoying a permanent night.

In the article referenced there is a painting of a theoretical planet with amoon orbiting a red dwarf. What if this planet was a gas giant and the moon was habitable? In this case the habitable moon would be tide locked to the gas giant. The moon now gets a 'day' every time it orbits the parent gas giant, but of course you could only see the gas giant from one heisphere of the moon.

Just some ideas for variationts on the night side Glacier/twiligbt temperate zone/ sunward facing desert theme.

I have already thought of the Gas Giant/Planet-sized satellite combination, as I thought that is what Regina is.

 

[Carlobrand]

Y'know, I've had Book 6 in hand for, well, close to three decades I guess, and it never occurred to me that Regina wouldn't have much of a night.

 

[Timerover51]

Y'know, I've had Book 6 in hand for, well, close to three decades I guess, and it never occurred to me that Regina wouldn't have much of a night.

I cannot remember if Regina is tidally locked or not, but either way, some portions of it would have a night. Either it would be the side that faced away from the Gas Giant if tidally locked, or the side not facing the Gas Giant if rotating.

 

[Carlobrand]

Lessee:

If I'm reading the table right, Regina orbits 55 radii from Assiniboia, a "large GG", therefore a gas giant of roughly Saturn-Jupiter size or larger. Without a mass, I don't think we can estimate an orbital period for Regina, but it's about twice as far out as Callisto from Jupiter, and Callisto's tidally locked, so maybe, especially if Assiniboia's significantly larger than Jupiter. Callisto runs a 16.7 day orbit.

On the other hand, if Regina's tidally locked with Assiniboia, then it's "day" with respect to its sun could be weeks to a month long. I can't find any mention of it being tidally locked or having a weeks-long day, and that would have distinct climate impacts on this "rich" world. I'd tend to make Regina have a more normal day to avoid potential canon conflicts. On the other, other hand, 3 of the four worlds orbiting Assiniboia inward from Regina boast habitable conditions, two of which are farm worlds, so either this tidal lock thing is irrelevant to climate - at least with respect to farming - or for some reason Assiniboia's moons aren't getting tidally locked.

55 radii from a 60 to 120 thousand kilometer radius sphere makes Assiniboia as seen from Regina a bit over twice the apparent diameter - there's a word for that, I know - of Earth's moon as seen from Earth. Lusor's brighter, but Regina/Assiniboia's farther out and in a habitable zone, so light level's roughly similar. Assiniboia's 8 times farther out than the moon but many times larger, twice the apparent diameter from Regina as I mentioned. So, bigger but not as bright? Which means Regina gets a dimmer "moonlit" night lit by a bigger but dimmer orb, but still a night - in fact, more night than we get here.

Best guess is you've got to be inside roughly 14 radii before your nights get brighter than Earth's moonlit nights. Redes, 3 radii from the GG, must have some interesting nights.

Okay, I don't feel so bad about not looking at the gas giant angle before now.

 

[aramis]

I cannot remember if Regina is tidally locked or not, but either way, some portions of it would have a night. Either it would be the side that faced away from the Gas Giant if tidally locked, or the side not facing the Gas Giant if rotating.

Let's consider this a minute. Sunward is for this purpose 0° "true". When Regina is at 0°, regina's 275°-85° are in pretty close to full daylight, and it's getting about 16x (see below) the reflected light that we get from luna. Easily a dusk level. But the generated IR from the planet itself will make it warmer, too.

Luna is about 30° at ~385,000.km and is 3474 km diameter. 110.8:1
Assiniboia is a LGG, and regina is 55 radii away. Which means it's between 60,000 km and 120,000km radius, and so Regina is between 3.3Mkm and 6.6Mkm distant, and assinoboia is roughly 55:2 ratio, or 27.5:1 ... 4x the diameter, 16x the surface area.

The generated IR means that dark isn't going to be so cool, except when it's at 180° from the star. Plus, much of the time, there's an almost equally bright source - the companion star.

 

[starship_captain62]

Writup of a eyeball world

A number of years ago there were a series of posts called RICE papers where a detailed writeup of a world done. I have attempted one for an Eyeball planet over the last couple of days which was largely inspired by this discussion. As a newbie to COTI, how do I post this wruiteup? It is about 950 words and has a couple of maps. Should it be a word doccument or PDF? I think it might be a bit long just to copy/paste into the message board.

Cheers

 

[Carlobrand]

...Luna is about 30° at ~385,000.km and is 3474 km diameter. 110.8:1
Assiniboia is a LGG, and regina is 55 radii away. Which means it's between 60,000 km and 120,000km radius, and so Regina is between 3.3Mkm and 6.6Mkm distant, and assinoboia is roughly 55:2 ratio, or 27.5:1 ... 4x the diameter, 16x the surface area. ...

Dammitdammitdammit!!! I compared the lunar diameter to the GG's radius! Jeez, but I feel stupid now! :nonono:

 

[Carlobrand]

Let's consider this a minute. Sunward is for this purpose 0° "true". When Regina is at 0°, regina's 275°-85° are in pretty close to full daylight, and it's getting about 16x (see below) the reflected light that we get from luna. Easily a dusk level. But the generated IR from the planet itself will make it warmer, too.

Luna is about 30° at ~385,000.km and is 3474 km diameter. 110.8:1
Assiniboia is a LGG, and regina is 55 radii away. Which means it's between 60,000 km and 120,000km radius, and so Regina is between 3.3Mkm and 6.6Mkm distant, and assinoboia is roughly 55:2 ratio, or 27.5:1 ... 4x the diameter, 16x the surface area.

The generated IR means that dark isn't going to be so cool, except when it's at 180° from the star. Plus, much of the time, there's an almost equally bright source - the companion star.

Okay, guide me on this. Assiniboia presents 16 times the surface area as seen from Regina, but Assiniboia is from 8.5 to 17 times farther away, reflecing light that in that orbit is roughly similar to what we receive here on Earth. So, if Assiniboia's farther away, the light reflecting from it travelling farther to reach Regina, does that not mean it's not as bright? I'm still seeing the night as dimmer than on Earth, at least with respect to the reflected light from Assiniboia.

 

[aramis]

Okay, guide me on this. Assiniboia presents 16 times the surface area as seen from Regina, but Assiniboia is from 8.5 to 17 times farther away, reflecing light that in that orbit is roughly similar to what we receive here on Earth. So, if Assiniboia's farther away, the light reflecting from it travelling farther to reach Regina, does that not mean it's not as bright? I'm still seeing the night as dimmer than on Earth, at least with respect to the reflected light from Assiniboia.

Assinoboia presents well more than 16x the actual surface area. It presents 16x the angular area, being 4x the angular diameter. Or more. depending upon where it falls in the "how big is «bigger than 60,000 km radius»" ... but that doesn't matter for this because the apparent diameter remains the same whatever value we pick, because it's 55/2 times that distance.

We'll come at it the other direction...

luna is 3340km diameter - vs at least 120,000 - roughly 36x the diameter, and thus at least 1291x the area. Regina is 3,300,000 km out, while luna is 345,000 or so. 9.5x the distance, roughly. 1/91 as much of the reflected light arrives. 1291/91 is around 14.2x the light.

Also, a gas giant is likely to have a higher albedo (luna is .12 average) while gas giants in our system have albedos in the .25-.35 range. Thus double or triple the illumination factor. so 28-42x the brightness of a full moon on earth.

Plus, a companion star.
1/4 the year, the companion lights the dark night when between 135° and 225° orbital position (assiniboia→primary = 0°), because during that quarter, the companion is in the same 90° arc from assinoboia, and thus opposes regina. Probably about crescent moonlight level.

True darkness is only at opposition, during the nights when outside of assinoboia.

And don't forget - assinoboia, being at least jupiter sized, radiates compression-generated IR. Gonna be fun-warm.

 

[shaunhilburn]

And don't forget - assinoboia, being at least jupiter sized, radiates compression-generated IR. Gonna be fun-warm.

I hear this mentioned sometimes in world-building discussions. If true, how do gas giants have icy satellites? For this amount of warming, I think a gas giant would have to be hot enough to be luminous, enough to glow dull red at least.

 

[madmike]

Tidial flexing due to gas giant gravity will keep the inner moons warm and active geologically. Happens to Io and Titan.

 

[aramis]

I hear this mentioned sometimes in world-building discussions. If true, how do gas giants have icy satellites? For this amount of warming, I think a gas giant would have to be hot enough to be luminous, enough to glow dull red at least.

Icy moons need only be below about 210 K (the vapor point in vacuum).

But I forgot about the tidal heating.

Note that Jupiter puts out more IR than it receives. Not all of it is from the visible cloud layers; some radiates through (just as Earth's atmosphere lets some of the IR back out)...

It's a few degrees at most from the IR, but IR vision isn't unknown in nature, and it's going to be a source. Now, if it's a really big one, as they approach brown dwarf size, they become significant IR sources... As in Spectral Class Y, with emissions indicating 500K - 600K... and above 13 jupiter masses, that's likely from deuterium fusion; below, it's compression heating and residual IR. Note that some planemos are into the L/T range for temperatures of up to 1000K...

 

[shaunhilburn]

Icy moons need only be below about 210 K (the vapor point in vacuum)

I did a quick Excel simulation. A Jupiter-sized object with 270K cloud-tops warms up an earthlike satellite orbiting at 500,000 km by 66.8 K. It's not life-sustaining by itself, but it does augment the solar isolation and possibly make moons habitable somewhat beyond the conventional life zone.

Amazing. I never took this notion seriously, now I'll re-consider after running few more scenarios.