# Planatary habitation, red dwarfs

Good morning. Just a fair warning, my posts are novel-like in length. (Appropriate, since I write novels.)

I am actually doing research for a current fiction book I am writing, and I am looking for any possible oversights or considerations that I may have overlooked. Just take into account that this is a fiction book, which I simply wish to have as much "reality" in, as possible. (I know it's an oxymoronic and ironic statement.)

Here is the situation. This planet was previously inhabited, and has been colonized by humans. The planet they adopt, is one of two, within a "orange/red star" goldilocks zone. One was shifting out of the habitable zone, thus being too difficult to "manage" or "sustain". The other, which was chosen, had just entered this zone, a few billion years ago. Thus, was more sustainable and would be sustainable longer.

The calculations I have, which are hardly relevant to the story, but to those who scrutinize the facts, they would be... (Gotten through trial and error on several planetary simulator programs, and facts from WiKi, which fit the original concept of the story.)

The star is a K/M class star, with a temperature of 4200K and a solar mass of about 0.21 (More red than orange, but a brighter red.) It has aged well, with low flare-bursts, and one perpetual "flare" at each solar axis. (Part of the reason it is slightly brighter.) The sun-spots avoid the equatorial plane of the sun, favoring the rotational poles, and thus, has less variance of darkness and suitable UV radiation.

The planet they colonize, has these attributes. The AU distance is 0.4->0.5, with a relative earth-mass value of 0.4->0.5. Thus, it is rather small, and about as close as mercury is, to our sun. The planet, unlike mercury but as planets of this region would be expected to do, has a rotation that makes it always face the sun on one side. It also has no moving surface/plates, and only one massive volcanic exposure, from the offset molten core, which faces the solar side. The dark side gets heat through the green-house effect, though it is thinner atmosphere, and underwater boiling jets from the fresh-water oceans. There is little rain, and moderately even and constant winds. There is, however, a lot of snow-fall before the solar-south. This would have left the air at the south completely dry, except the room-temp humidity from the cavernous depths, transfers steam and humidity from the sea-vents. (Think of it as home insulation. The spongy non-molten side of the planet acts as insulation and distribution for heat. It also makes that side of the planet face away from the pull of the sun, being the gravitational top.)

The part that I could not simulate was the following... But here I have taken the freedom of fictional creative writing, to justify what I can not apply physics to. (But I would rather have physics involved here, where possible.)

The planet has two moons. One half as large as our moon, so it is similar in scaled distance and orbit, except that it has a wobble to it. It travels around the planet from solar-north to solar-south, along the sun-facing axis. The wobble is caused by the odd rotation and also the secondary disruptive pull of an equatorial micro-moon. This second smaller moon rides just above the thin atmosphere, close to the planets surface. Though this is un-natural by "our physics on earth", for this planets unique composition, it is acceptable.

Now the specific thing I was having issues with, is the speed of the smaller moon. The size of the planet is about half the mass of earth 0.4->0.5, but this still leads me to believe that this smaller mass moon, about the size of Connecticut, would have to be traveling unusually fast. Too fast for the fiction in the book. (Part of the reason the fiction counters that unrealistic speed.)

I assume, that the moon with relative scale to ours, would be traveling 2x our speed, since the planet and the moon is 50% the mass. Thus both forces of pull would be halved, thus speed would be doubled, for orbit stability? (Like how closer planets to the sun, even larger in mass, are faster in orbit.) This leads me to estimate that the smaller moon, being smaller and closer to the planet, would have to be traveling nearly 1000x that speed. Or, since it is lighter, would it be traveling 1000x slower, or the same, at this closer distance to this lower mass body?

If it is any matter... the mini-moon also has nearly no rotational speed on its own axis. It is rotating, but literally at a walking speed. (Eg, if this were a merry-go-round, you could walk onto it, or off of it, without trouble. Or an escalator belt.)

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Staff Emeritus
Thread moved to science fiction writing.

Mentor
Orbital periods very close to the surface depend only on the average density of the object (and the gravitational constant). If your planet is a scaled-down version of earth, it should be the same, roughly 84 minutes (a bit more due to the distance to the surface).
This question did not need the long text around it...

It also has no moving surface/plates, and only one massive volcanic exposure, from the offset molten core, which faces the solar side. The dark side gets heat through the green-house effect, though it is thinner atmosphere, and underwater boiling jets from the fresh-water oceans. There is little rain, and moderately even and constant winds. There is, however, a lot of snow-fall before the solar-south. This would have left the air at the south completely dry, except the room-temp humidity from the cavernous depths, transfers steam and humidity from the sea-vents. (Think of it as home insulation. The spongy non-molten side of the planet acts as insulation and distribution for heat. It also makes that side of the planet face away from the pull of the sun, being the gravitational top.)
That looks very unrealistic I think.

Staff Emeritus
There are lots of things wrong here.

- You aren't going to get very much greenhouse warming on the dark side of the planet with a "thin" atmosphere. You need a thick atmosphere, much closer to Venus' atmosphere than Mars'.

- Your inner moon is impossible. Read up about the Roche limit. Also, the atmosphere doesn't just stop abruptly. The Earth's atmosphere reaches out (tenuously) for well over a thousand of miles. Atmospheric drag will eventually bring that moon down. Regarding orbital velocity, read up on Kepler's laws.

- Your outer moon is impossible if your planetary system has gas giants. Read up on the Kozai mechanism.

Mentor
A Connecticut-sized moon has a diameter of ~100km, if it has the same density as the planet it needs a minimal height of 1/4 planet radius above the surface. With twice the density, it can orbit everywhere (unless the atmosphere becomes an issue), and with a bit less than that, it might still have some internal strength or rotation to help.

The orbit of the moon would degrade due to tides and maybe the atmosphere - if your story allows a crash in the future (many millions of years), that's fine, otherwise it might need more careful tuning.

Thanks to the replies... except those noted.

Ouch to the move to science fiction... especially since the question was about the "reality" of the astrological aspects. But whatever to that judgment call... It isn't like I was asking how big of a bullet is needed to kill a Klingon. That would be science fiction physics.

To the comment about "too long, didn't read"... Next time I'll write it in a txt for your intellectual understanding.

Yes, the lower moon was my only "unreal" component I was battling with. Like I said, the rest has already been confirmed as possible. The details were mentioned, only because I thought they might be relevant, as those were the details I had to use in the other calculations for the simulations. Though they are as rare to find as earth-like conditions themselves, but possible for sustaining life similar to us. Possible as far as the latest "believable" credited sciences are concerned, directly from NASA.

To the comment about an earth moon not being possible because a solar system has gas giants... What?!?! We have gas giants, with moons, and last time I checked, we had an earth moon! The rest makes sense though. Unless you were implying that a super gas giant would not have an earth moon in a red-dwarf solar system. Which I can understand, because the gas/atmosphere would extend into that orbiting moons reach. I expect this outer moon to be well out of reach of the atmosphere, and the inner one to be at the edge of it. Proportionally, this planets atmosphere would be thin (not as deep)... not thin, as in, sparse.

To the comment about the reality of greenhouse gasses being "enough". That has already been confirmed as plausible by every simulation. Again, it may be my poor choice of words. Thin as in (shallow), not thin as in sparse. Only with static-surfaces, which do not digest CO2 like earths crust does, and ones with little rain, is this possible. The volcanic activity is the primary source of gas. The subterranean vents are the primary heat delivery. The CO2 is just the insulating blanket, which remains due to constant humidity without rain. (Only snow, which constantly melts back to the fresh water, not the lands.)

To the comment on the atmosphere reach and also the impact comment... Yes, this moon is intended to crash. The friction of the thin atmosphere (low height), is expected to play a role in that.

I just don't know how to calculate the expected speed for that moon, at the point where it decides to break orbit and has crossed the threshold to decide it is going to impact dive. (Which is why I didn't post this in a "fiction" area, where I would get no realistic answer to my astrological physics question.)

So, by the last post I saw... at 1/4 the planets radius, is where it would last have been stable. Until something added mass, slowing it down and increasing the gravitational pull, which would bring it crashing down... (I am assuming it would be fine until it reached satellite-level above the atmosphere. As long as it wasn't traveling Mach-400.)

But what speed would it have to be traveling at that point, to maintain that orbit? Would that be a faster orbit, or a slower orbit than our moon? (I am inclined to believe faster.)

Looking at the listed references now... (If it makes the moon slower, being lower mass by volume, that is fine. Otherwise, if being higher mass helps it get realistically closer, then I can adjust for that too. But moon-orbit simulators are not as common as planet simulators, or life-simulators. The only ones I find, are limited to one moon, or multiple moons but have no range close to satellite range.)

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Found part of my answer... minus specifics... Attempting to manually calculate now. Would be going super fast.

Earth atmosphere ends at ~180 km (Low satellite orbit) {For NASA's majority of belief. Enough atmosphere is not there to interfere. Though it may extend further, it is not significant in volume, related to satellites.}

180-2,000 km (low)
2,000-35,780 km (med)
>35,780 km (high)

Orbit-levels... Above surface, not from center of planet.
Moon @ 384,000km (60x radii of earth) @ 1023 m/s (2287 mph) (Mach 3)
My moon @ 20 km (My atmosphere limit) @ ? m/s (? mph) (Mach 400 lol :P)

Planet diameter ~6,787km / My moon ~xxx 120km xxx 5km (Edited for reality. Ignore the 120)
Planet mass ~0.107447 of Earth (Mars size and density 0.38 to earth gravity)
Moon mass ~???
(Earth ~12,756km / moon ~3,476km)

Another reference... Closest moon in our solar system, to a planet...

Of all the moons in the Solar System, the one which orbits closest to its planet is the tiny Martian satellite, Phobos.
Phobos is 9,378 km 5,827 miles from the centre of Mars - which corresponds to 5,981 km 3,716 miles above the Martian surface.
Phobos is a small potato-shaped irregular moon, measuring 27 x 22 x 18 km (17 x 14 x 11 miles). It is dark and covered with dusty craters and is almost certainly an asteroid which was captured by Mars' gravity many millions of years ago.

lol, I need it to be closer than that!

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Just a brief reply about the polar flares and high latitude sunspots (starspots). The driving force in the sun for spots is the coriolis force acting on deep convection cells. The mag fields caused by convection get wound up into helices and eventually burst out of the surface as prominences between pairs of spots. The coriolis force doesn't exist at the poles or equator. So solar spots are concentrated at mid-latitudes. Red dwarves have strong convection from the core to the surface and so are expected to have lots of spots and CME. The goldilocks zone is close in, so the radiation hitting the planet would be horrible. Also, I wonder what is the mechanism for the polar flares you mention? I'm not really a pro in this field - just some ideas that popped up as I read your post. Very interesting stuff, since most stars out there are red dwarves.

Mentor
You cannot choose the "height" of your atmosphere like that. The density is (roughly) expontentially decreasing, with a scale height just set by the chemical composition, temperature and surface gravity. Surface gravity is lower for your planet, so the scale height is probably larger. Your atmosphere extends further outwards compared to earth, if you have the same pressure at ground level.

Earth atmosphere ends at ~180 km (Low satellite orbit) {For NASA's majority of belief. Enough atmosphere is not there to interfere. Though it may extend further, it is not significant in volume, related to satellites.}
The ISS orbits at ~400km and needs frequent re-boosts to counter air resistance.

But what speed would it have to be traveling at that point, to maintain that orbit? Would that be a faster orbit, or a slower orbit than our moon? (I am inclined to believe faster.)
See post 4.
The speed of the moon is nearly independent of its mass.

Planet diameter ~6,787km
That would give ~1/8 of earth's mass, not 1/2.

To the comment about an earth moon not being possible because a solar system has gas giants... What?!?! We have gas giants, with moons, and last time I checked, we had an earth moon! The rest makes sense though. Unless you were implying that a super gas giant would not have an earth moon in a red-dwarf solar system. Which I can understand, because the gas/atmosphere would extend into that orbiting moons reach. I expect this outer moon to be well out of reach of the atmosphere, and the inner one to be at the edge of it. Proportionally, this planets atmosphere would be thin (not as deep)... not thin, as in, sparse.
The issue could be the inclination. I interpreted your poles in such a way that the large moon has no inclination, apparently D H interpreted it in another way.
What is "solar-south" and "solar-north", what is defined as equator, and what is the inclination of your moons?

Staff Emeritus
Yes, the lower moon was my only "unreal" component I was battling with.
There are *lots* of unreal components. Your planet's atmosphere and its greenhouse effect, gravitation, and the large moon.

To the comment about an earth moon not being possible because a solar system has gas giants... What?!?! We have gas giants, with moons, and last time I checked, we had an earth moon!
Yes, the Earth has a moon, but it is in a nearly equatorial orbit. It is not in a polar orbit. That's how I read your "It travels around the planet from solar-north to solar-south, along the sun-facing axis." A polar orbiting moon is not possible if the planetary system has gas giants. The Kozai mechanism (google that term) would cause the moon's eccentricity to grow and grow. After a short time, the moon would either crash into the planet at perifocus or would be perturbed out of orbit at apofocus. It would take about a decade for the Moon to crash into the Earth if our Moon's orbit was polar rather than nearly equatorial.

To the comment about the reality of greenhouse gasses being "enough". That has already been confirmed as plausible by every simulation.
What kind of simulation? Have you adapted a Global Circulation Model (GCM) to your planet? That's the kind of simulation that is needed. BTW, you'll probably want a supercomputer on which to run that GCM.

Again, it may be my poor choice of words. Thin as in (shallow), not thin as in sparse.
That's book tossin' bad science fiction, at least for me. A dense atmosphere is necessarily thick. The two go hand in hand.

Look at it this way. Our Earth has a moderately thick atmosphere, but it only has a small amount of CO2. Even though the Earth rotates once per day, temperatures fall at nighttime. If the Earth was tidally locked, our atmosphere would not be near enough to keep nighttime temperatures from plummeting to the point that the atmosphere would freeze out.

You need a thick atmosphere with lots of CO2 and H2O. For more details, I suggest you read Joshi, Haberle, & Reynolds (1997), "Simulations of the Atmospheres of Synchronously Rotating Terrestrial Planets Orbiting M Dwarfs: Conditions for Atmospheric Collapse and the Implications for Habitability", Icarus 129, 450-465.

Earth atmosphere ends at ~180 km (Low satellite orbit) {For NASA's majority of belief. Enough atmosphere is not there to interfere. Though it may extend further, it is not significant in volume, related to satellites.}

Nonsense. Earth's atmosphere does not "end" at ~180 km. NASA knows this very well. Satellites in low Earth orbit (less than 1000 km) need to be re-boosted regularly lest the orbits decay due to atmospheric drag. The satellites would reenter (crash and burn) without these periodic reboosts. The time frame is on the order of months to decades, depending on satellite altitude and geometry.

That's more than enough for now.

Here's some math to answer the specific question you asked in the beginning:

(all calculations assuming mass of the satellite << mass of the planet)

You need to find the so-called "first cosmic velocity", that is the velocity required to put a body in circular orbit of radius r around a massive body.

From the force of gravity being equal to the centripetal force, it is found to be:
$V=\sqrt{\frac{GM}{r}}$
where M is the mass of the planet, r radius of the orbit, G gravitational constant.

Note, the mass of the satellite is nowhere in the equation. The velocity depends only on two variables - planet's mass and orbital radius.

It is going to be large, if close to the planet, as it is merely $\frac{1}{\sqrt{2}}$ lower than the escape velocity at a given height(radius).

Rather than plugging in actual numbers, you can use units where M is a fraction of Earth mass(so, $M=\frac{1}{2}M_E$ and similarly with r being a fraction of e.g., the Earth radius. This'll give you the velocity as a fraction of the first cosmic velocity at Earth's surface, which is 7,8 km/s.

So for 1/2 Earth mass and 4/5 Earth radius(roughly what the planet would have with the same density as Earth), you get $\frac{V}{V_E}=\sqrt{\frac{5}{8}}→V=\sqrt{\frac{5}{8}}V_E$

That gives you $V=6.2 km/s$

Note, this is the tangential speed of the satellite. The speed at which it'd descend towards the surface would be much lower. The satellite would fall at a very shallow angle, grazing the atmosphere over many revolutions until it hits the surface or disintegrates due to frictional heating.

And should you need the Roche limit:
$d=2.44R_M\sqrt[3]{\frac{\rho_M}{\rho_m}}$
RM is the radius of the planet, ρM is the density of the planet and ρm is the density of the satellite(works equally well with masses instead of densities).

If the satellite ever gets closer to the planet than d(measured between centres of the bodies), it will be torn apart by tidal forces. Simply make sure it's dense enough to survive.

Also, it's "astronomy" not "astrology".

@GeoffSimmons:
http://www.ncbi.nlm.nih.gov/pubmed/10472629
Full text: http://www.as.utexas.edu/astronomy/education/spring02/scalo/heath.pdf
The flares are not a problem, as the quiescent high-energy radiation levels of a red dwarf are very low, and flares merely raise them to the level we normally get from the Sun.

The goldilocks zone is close in, so the radiation hitting the planet would be horrible. Also, I wonder what is the mechanism for the polar flares you mention? I'm not really a pro in this field - just some ideas that popped up as I read your post. Very interesting stuff, since most stars out there are red dwarves.

Yes, many stars (pure red), which are all young, have those issues... on average. Hydrogen based, thus little "radiation" and more stability. However, there are exceptions to every creation. Stars are not just a "this is a star, here is the recipe"...

This is not red, not orange... By "averages". It is has that slight radioactive content, which could have been a dual-star system, one bigger red swallowing a smaller yellow star, or a yellow star that exploded, reformed as the red star with only a micro-fraction of the yellow stars contents remaining. (The heavier radiation having blasted away, while the lower mass gasses collapsed and reformed back into a red star. The "other stuff" from the star, forming the planets, or just ejecting from this system.)

My inspirations was one of the many stars that are red, with a small radioactive-stable tails. The tails themselves are not stable (in theory), for long. However, like black-holes, they consume along the equator and puke out the axis, which also consumes its own puke. (The perpetual flares)

Each stars "internal flow" is unique. Though the majority, of nearly singular composition, is "average". Those with more metallic core elements behave "abnormal". This is one of those unique stars.

The radiation from red dwarf suns, even in flashes, is mostly light and less "harmful radiation". The swirling field of the iron core of this planet, provides adequate protection. Since that core is not only near the surface at that side facing the sun, but it is also the majority of the mass of the planet, and the planet is out of the "goldilocks" zone of an "earth planet". It is in a "goldilocks" zone for "this planet". I believe the actual goldilocks zone, which also takes radiation into consideration, is 0.21->0.36 for this class star. This planet is in 0.4 to 0.5AU, outside of a normal earth-planet goldilocks zone, due to the freeze, which is combated by the CO2 and non-moving surface, and lack of rain. (Those were the major factors making the planet habitable.)

Old science, (science from 10 years ago), essentially said this was impossible. Today, through new science discoveries, they have found that planets like this are not only possible, but also the possible dominating habitable planets of the universe. (Being attached to stars that are the longest living stars in the galaxy. Which also proves the big bang is a crock of sugar-fantasy. Since none of these oldest stars ONLY contain those "big bang" gasses that would have been required. They all have metals. That history, from the stars themselves, disproves anything those big-bang expanding universe guys have ever said. As if that wasn't already unbelievable enough.)

Sad news... We don't have much longer in our microwave. Mars will just be a one-way ticket to the end of our solar system, if we ever get there. Unless we learn to live on the dark-side, and go underground... Our time on this planet is coming to an end. (Ok, in a few more million years, but still!) lol.

Staff Emeritus
The swirling field of the iron core of this planet, provides adequate protection.
Yet another problem! Mars doesn't have an appreciable magnetic field because it's too small. It's core has frozen out. Venus doesn't have an appreciable magnetic field because it's rotating too slowly. You have a Mars-sized planet that is rotating slowly (it's tidally locked). So what swirling field?

Also, it's "astronomy" not "astrology".

Before I stubbornly apologize for that stupid mistake... lol. Thank-you for all that information. Unfortunately, I am not a math professor, which is why I was using simulations. Knowing HOW did help though. Those showed me, and confirmed the HOW. Enough for what I was looking for.

My satellite will be able to travel close enough to be where I want it, before the "other forces", consume it to make it do what it does next. That got me within the 20 km mark with a 3km diameter object, at a speed I was able to accept as plausible.

So a big thank-you. Though, my planet is favoring the larger side, which is thinning my atmosphere potential. I can live with that, since I am, well, not going to live there myself. :P

Now for the apology to the quoted response...

Oops.. :P Actually, it is both.

"Astrology comprises several systems of divination based on the premise that there is a relationship between astronomical phenomena and events in the human world."

Every scientist refers to the stars as the heavens and finds them to be divine. Science is the understanding (relation/relativity), between astronomical stuff and human physics/world.

Thus, I was only partially wrong. (Ok, astrology was the wrong word... I just hate to admit I made that moronic mistake. Guess I should turn in my astrological club card. Surrender my telescope for a tarot-deck. :P)

Staff Emeritus
Also, it's "astronomy" not "astrology".
That was a very telling mistake.

Even more telling,
Before I stubbornly apologize for that stupid mistake... Thus, I was only partially wrong.

You were absolutely, 100% wrong.

It makes me wonder, is there any point in keeping this thread open? You've been told a number of problems with your scenario. You won't admit any of them as problems, and you apparently aren't willing modify your scenario so those readers with a lick of scientific knowledge won't toss your book because those glaring mistakes makes it impossible to suspend disbelief.

Can you use spreadsheets? Plug the equations in and it'll calculate everything for you.

Also, we'll have to ask you to not make usupported claims, and to not challenge the mainstream science unless you've got peer-reviewed papers to back you up. That comment about Big Bang is unacceptable as per the forum rules and can get you an infraction.

If you have some doubts about BB, ask away - although preferably in another thread in the astronomy/cosmology section of the forum.

And I wouldn't so lightly dismiss the objections made by others. Your setup has got a lot of plausibility issues. Your post in response to GeoffSimmons rises a few more concerning what you understand about stellar evolution.
It's ok if you don't care about those though. It is science-fiction after all.

Yet another problem! Mars doesn't have an appreciable magnetic field because it's too small. It's core has frozen out. Venus doesn't have an appreciable magnetic field because it's rotating too slowly. You have a Mars-sized planet that is rotating slowly (it's tidally locked). So what swirling field?

Mars just doesn't have one... The size has nothing to do with that. Because Mercury is smaller, and has a molten core. Venus rotation had nothing to do with the cooling and death of the core. The core on this planet is active and swirling just like earths. Magnetic fields are not the source of heat, they are the source of protective fields.

The planet has days that lasts 4 years, and a year is over in about 30 days. (From the calculations I had simulated.)

The cores are radioactive in liquid core planets. Yes, they contain a massive (dense) formation of IRON (Only on this earth planet, but not on others), but they are still radioactive themselves, if they remain molten. They generate their own heat, not ONLY by compression of the density, but also by radiation that is absorbed by those protective metals.

When a star explodes, and throws molten minerals into space, they solidify into bubbles of molten composition. Those without radiation, eventually cool.. like mars did. Those who did have radiation, stay molten, like earth did. (Being in a warm location helps to regulate that heat, but the sun is not the source of our heat at the core, or the water would boil away. Like it did on mercury.)

Red dwarves are IR (Infra-red radiation) stars. The warmer orbits are closer to the star, which is why this planet is as close to the star as mercury is to our sun. From this star, that is not enough heat to sustain a molten core alone. The core has to be dense and radioactive, like earths, which it is.

The planet is as large as MARS with the same density... but that density is not even across the whole planet. The planet is mostly a sponge-like shell of volcanic chambers, as the molten core was pulled to one side, from the strong gravitational pull of the sun. (Like how a yolk is never centered in an egg.) That sponge-side has little mass itself, while the molten side has greater mass. (Atmosphere is higher on the darker side, snow falls slower, it has more "density" of CO2 there, thus, still remains warm enough, without the warmer under-temperature from the lava. Which also acts like insulation to the lava, stopping that cooler side from cooling it down further.

Now, eventually, in time, the whole planet will solidify, if that radiation dies-out, and it does not move closer towards the sun... but it is being pulled into the sun, as the earth is to our sun. Then the planet will become as cold and baron as mars is now. But even Pluto was molten at one time. This planet of mine is just moving into the goldilocks zone for this planets composition. It has plenty of time to live. The other planet was moving out, and will die soon.

Planets are hardy a regular formation. It is a lotto, like DNA... It all depends where you were born, and what your composition was, when you grew-up. The other planets live in the human slums. Which is the majority, compared to the Ritz home we call Earth.

Other food for thought... Our sun just swapped magnetic poles... Our poles swap too, and float... We are only magnetized with a polar average, because parts of the crust solidified with alignment, and that force is constantly challenged by the suns magnetism. (Just like when you place iron next to a magnet, without touching it, the far end can now pick-up more pieces of non-magnetized iron, because that magnetism transfers to the non-magnet. Everything is magnetic, to a point. You can boil water with magnetic fields, because it is magnetic. Drop a magnet on a block of aluminum or copper and it breaks the fall, because it is magnetic too. You can grab and throw aluminum with magnets, which is how trash and gold can be sorted from less magnetic materials like paper and plastic. Just because YOU can't feel the force, does not mean it isn't there, and active. Also note, you can turn rust back into iron, and when it turns into rust, it generates heat and strong magnetic fields. In both processes.)

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Staff Emeritus
Mars just doesn't have one... The size has nothing to do with that. Because Mercury is smaller, and has a molten core.
Size has a whole lot to do with it.

With regard to why Mercury has a molten core while Mars apparently doesn't, the answer is simple. Mercury is in an eccentric orbit and is much closer to the Sun. Mercury receives 15 times more solar radiation than does Mars. More importantly, tidal forces are over 60 times that for Mercury than Mars. Even more importantly, the non-circular nature of Mercury's orbit means those *huge* tidal forces are going to result in *huge* tidal heating. The tidal stresses would be much, much smaller if Mercury was in a circular orbit. Mercury, like Mars, would have a frozen core if it weren't for those tidal stresses.

Venus rotation had nothing to do with the cooling and death of the core.
Venus does have a molten core. One of the key reasons it has a negligible magnetic field is its very slow rotation rate. The planet needs to be spinning somewhat rapidly to have an active magneto. Mercury's magnetic field is about 1% of Earth's, largely because Mercury rotates once every 58.6 days compared to Earth's once per sidereal day. Venus has an incredibly tiny field, in part because Venus rotates once every 243 days.

The core on this planet is active and swirling just like earths.
You already said your planet is orbiting a red dwarf and is tidally locked to it. So, no, the core on this planet is not swirling just like Earth's. It's more or less rotating with the planet as a whole, and if the planet isn't rotating fast enough, no magnetic field.

You specified a Mars-sized planet, so the core is most likely solid if the planet is in a circular orbit. You have a whole batch of other problems if the orbit is non-circular.

The planet has days that lasts 4 years, and a year is over in about 30 days. (From the calculations I had simulated.)
I thought you said the planet is tidally locked? So which is it?

Those without radiation, eventually cool.. like mars did.
That is completely wrong.

As per the above post, I consider this answered...

You have all given good points for consideration, which I apparently have to elaborate on, or reserve the right to just say, "Trust me" to the readers. (Or side-step the issue, like a politician. :P)

I think I like that this was moved to the SF section. I am enjoying these responses more than I think I would from those who would have normally answered.

Summary, for those who missed it...

Class K/M Orange/Red Dwarf star system.
This planet:
0.5 AU (~ same distance that Mercury is from our sun, faces sun same side)
0.4 earth-mass (~ Mars size and density, offset molten iron core)
Two moons, one 0.25 the mass/volume of the planet, traveling same scale as earth-moon distance away, with a wobble from pole to pole. One moon orbiting with a slow collision path just at the top of the atmosphere.
Low atmosphere with high viscosity and CO2 blanket, dark-side subterranean heat vents, no rain, no moving plates, one open-face massive volcano feeding the atmosphere. Fresh water seas, salt water lakes.

Average atmosphere ground temp: 87F
Surface deviation: 2500 feet above sea-level
Atmosphere average limit: 20 km (<1 km at solar-north exposed volcano, 60 km at solar-south crater)
Average humidity: 82%
Average rainfall: 5 ft per year (all at once, only at equator)
Average snowfall: 1000 ft per year (constant melting, glacial into sea at 2/3 on dark-side.)
Average light: 185% IR, 114% R, 92% G, 71% B, 32% UV (Life/Plant-supplemented)
Magnetic composition: Traveling polar regions on solar-north side only.
Ionic composition: 130% Solar-north, 280% solar-equator, 490% solar-south
Water: 75% surface fresh water, 4% surface salt water
Primary composition, by volume: Iron, Magnesium, Sulfur, Aluminum, Copper, Nitrogen, Hydrogen, Carbon, Chlorine, Calcium

Trails in the wind of the other earth-like planet, which is closer to the sun and loosing atmosphere, that is partially consumed by this orbiting planet. (It is hijacking the liquids and gasses blasted off the other planet.)

Native life, fresh-water bound carbon-based. Adopted life, land-bound magnesium-based. Human life, settled.

Reality level: 75% (Good enough for me!)

Staff Emeritus
Reality level: 75% (Good enough for me!)
Reality level: 0%. You have too many problems that would make me toss your book. Either make it fantasy or soft sci-fi where nobody cares about scientific explanations, or make it right. Those in-between books where an author who doesn't know the difference between astronomy and astrology but tries to be scientific (and is wrong): I toss the book and put that author on my "do not read" list.

Your outer moon cannot be in a polar orbit. It cannot be in a equatorial orbit at a distance comparable to the Earth-Moon distance. It needs to be considerably closer to the planet, well inside the Hill sphere (google that term), and it needs to be in in a near-equatorial orbit to avoid to the Kozai mechanism (google that term).

Your atmosphere is completely wrong. The atmosphere is necessarily thick if the planet Mars-sized planet and if the atmosphere is capable of sustaining life as we know it. 20 km is not thick.

Your inner moon is completely wrong. We've already pointed out the problems with atmospheric drag. You've added a new complexity in your recent posts, that of a (gravitationally) lumpy planet. Read this article, http://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit/, to see what happens to objects in a low orbit about something with a lumpy mass distribution.

Staff Emeritus
As per the above post, I consider this answered...

If you are referring to D H's post then I don't know how you can consider it answered. He has pointed out clearly where you are wrong. What exactly did you want to achieve posting here if you weren't going to take on board feedback?

Low atmosphere with high viscosity and CO2 blanket

You can't choose the height of an atmosphere, that's determined by the composition and gravity on the planet.

no rain

You have a planet mostly water with an average ground temperature of 30 degrees C. There will be rain unless the atmosphere has very high pressure.

Fresh water seas, salt water lakes.

Lakes drain via rivers into oceans, it's highly contrived to get one case where this is reversed, a whole planet makes no sense.

Average atmosphere ground temp...

All of these figures are just a hodgepodge of numbers with no realistic backing.

Native life, fresh-water bound carbon-based. Adopted life, land-bound magnesium-based. Human life, settled.

Magnesium based life? The idea that two ecosystems based on radically different biochemistry could coexist on the same planet is as hard to believe as the rest of your ideas.

Reality level: 75% (Good enough for me!)

Not even close. For some readers it won't matter but for many these impossibilities will break their suspension of disbelief.

Spared the quotes...

The planet is tidally locked. Tidally locked planets still orbit and rotate. Lock is just a loose term to indicate its majority of face is static. Mercury is tidally locked, but it rotates on an axis, real slow. The inclination of the axis is what determines locking, or the super-super-slow rotation on a parallel axis. This axis is facing the sun. There is no sunrise or sunset for the planet as a whole. The equator will see the sun travel in a small "O" on the horizon, as it grazes the horizon and rises to noon, a fraction above the horizon. Our moon is tidally locked, but it still spins around. The face we see now is not the same face seen 3000 years ago.

Rotation is NOT the only pull that creates flow rotation of liquids. Hot to cold on a boiler-plate, and radiation itself, also creates "flow" required.

Venus does NOT have a significant IRON core or IRON crust, which is the ONLY reason, other than the low radiation of the core, why it has no strong magnetic field, besides the fact that it is too far from the biggest magnet in the system, the sun.

You are confusing magnetic alignment, (fields), with magnetism. Iron is highly magnetically structured. A measure of magnetism is NOT a measure of the cores molten value. That is like saying a car is safe, because it is painted white. Because my white car is safe. If Venus was Earth, with the same composition, you could get away with believing the things you read, which are all assumptions, not even real hypothesis. We don't know squat about venus, other than what we see. It is too hot to land, too impossible to see through the dense atmosphere, except with special cameras. Its rotation, nowhere in mention, being cited as "cause" of cooling or magnetic flow.

Also... you are completely ignoring the fact that RED DWARF stars are NOT RADIOACTIVE like our sun. All of your arguments, which I am not taking into consideration, are for planets in THIS SOLAR SYSTEM. The planet I am writing about is in a solar system with a red dwarf star. Magnetic shielding is like wearing sun-screen in a cave, in this system.

Flow only requires hot to cold, OR density-force. The spinning of a planet on its axis is NOT the only source of motion. The core pulls in, the sun pulls it to the bottom, the heat flows to the cool side, thus, flowing. Just not axial, so it does not have stable fixed-axle magnetic flows. It spirals, which is a more effective shielding than a fixed-pole field. (It is the AC of magnetism, to DC of power.) The point is, that it has a core, that is liquid and moving, with strong iron content. Even without a moving core, if the planet solidified with poles, that would be just as effective. Mars didn't solidify with poles. Obviously, it didn't have enough of a radioactive core, which is proof that iron content alone, which is what old scientists told us earth had, is not enough for sustaining a liquid core. I don't think any scientists, to this day, believes the core of earth is "just iron". They say it is a "iron rich core". Same way they say a planet is "tidally locked". There is no such thing as a planet that doesn't spin on some kind of axis. Everything is in motion, nothing is ever truly balanced. Nothing is ever truly average. Average is the least realistic of any composition. Average is the minority, in reality.

Ok, done with that...

Mars is also less dense than half earth. My planet, as I said, is 0.4 mars is 0.28, thus, mine has more volume packed into smaller space. Thus, a good fluid and solid mass core, around an insulated crust.

Venus it doesn't rain, there is no life, and there is nothing to balance the planet. It just pumps out more and more CO2 and is not in the goldilocks zone for its composition, which has got to be dumping onto our planet by billions of gallons each year. Forget human destruction, our own solar system is out to squash us. If Venus was behind earth, that is where its goldilocks zone would be located, for that planets composition. (There is not only "one" goldilocks zone. There is only "one goldilocks zone for earth-like composition", but not all planets are composed of earth-like composition, and still inhabitable.)

Staff Emeritus
OK then. You came here expecting acclaim. It didn't happen. You got scientific criticism instead. You aren't willing to accept that criticism. Your responses are essentially "Nyah, nyah, nyah, I can't hear you!"

Staff Emeritus