How Can Planetary Movements Affect Time and Illumination on an Inhabited Planet?

[delie]

I was able to numerically simulate an Earth sized planet that was temporarily stable in a habitable zone in a octonary system. The Earth sized planet was orbited by a moon, & the moon was orbited by a 4km diameter asteroid 33434 Scottmanley ( https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=33434 ), and asteroid Scottmanley was in turn orbited by the great pyramid. The Earth sized planet orbited a Sun sized star, outside the habitable zone of the Sun sized star, but the Sun sized star orbited within the habitable zone of 21 solar mass star Rigel, and Rigel was a distant binary of another Rigel. Each of the Rigels were orbited closely by a 1/10th solar mass Proxima Centauri & 2 Suns, for a total of 8 stars, an earth sized planet, a moon of the planet, an asteroid orbiting the moon, and the great pyramid orbiting the asteroid.

The system remained stable enough for liquid water to remain on the Earth sized planet for quite some time, roughly 10k Earth years. Unfortunately, after that period of relative tranquility an orbital perturbation made the planet's parent star drift too close to the overall barycenter of the entire system, which further perturbed & degraded the Sun's orbit around its Rigel sized parent star. First the planet froze with an average surface temp of -5F close to the overall system barycenter, then the Sun & its planet took a death plunge directly towards the very close vicinity of the Rigel sized star where the surface of the planet exceeded 1600 degrees Fahrenheit, & next the planet was stripped of the sun it was orbiting by a close pass with another star and then the planet was thrown clear of the entire system through a gravitational slingshot effect, though it retained its moon. Together the planet & its moon froze as they drifted away into the emptiness of space.

During the time that the orbits had remained relatively stable, the Pyramid had 6 different orbital parents:

Pyramid -orbited-> Asteroid -orbited-> Moon -orbited-> Earth -orbited-> Sun (1 solar mass) -orbited-> Rigel (~21 solar mass) -orbited-> Barycenter (~46 solar mass total system)

I've watched the whole thing. Universe Sandbox apparently doesn't account for variables such as radiation pressure, curvature of space, dark matter (which apparently is itself currently under assault)...

However, I really do appreciate the insight it can give us into some simulations.

Out of curiosity and theoretically speaking, if Earth were to be slingshot into space like in your simulation, would it be possible for another planet to "catch it" back into a relatively stable orbit, say by another Rigel? What about the slingshot speed? Would it remain constant throughout the voyage?

 

[delie]

A professional source, but classic and hopefully not too hard for the results:
https://articles.adsabs.harvard.edu//full/1916ApJ...43..103R/0000114.000.html
Includes phase curve of Moon to 150 degrees.
Note how powerful is the opposition surge of full Moon and how dramatically crescent Moon fades.
Moon 30 degrees from full shows 14/15 of the disc, yet only 1/2 of the light. At 150 degrees, the crescent is 1/15 the area of the disc, yet about 1/250 the brightness.
Jupiter does NOT fade that way. True, Earth comes closer to Jupiter at opposition - if Jupiter is 5 AU from Sun on average, then it is 4 AU at opposition and 6 AU at conjunction, making Jupiter 2,25 times dimmer.
But Jupiter at opposition is about 16 000 times dimmer than Moon. Which means that if Jupiter near conjunction fades to twice dimmer than at opposition, and Moon is 250 times dimmer as narrow crescent, ten Jupiter is still over 100 times dimmer than the crescent Moon.
Jupiter outshines all fixed stars, but does not illuminate night sky like Moon does.
Now note that for an observer on rotating Earth, Sun is above horizon half the time. So is Moon.
Moon is plainly visible in blue daytime sky. It stays in place when clouds drift by.
Over a month, the Moon varies to being visible no part of night (new Moon) through increasing part of evening (waxing crescent and gibbous), whole night (full Moon) to decreasing part of morning (waning moon). As the monthly average, one half of time at night is moonlight... on average, at least a small part of every night is moonlit (since moon is not exactly in conjunction) and at least a small part is not (moon is not exactly full - indeed, exact full moon is eclipsed). 3/4 of all time, Sun, Moon or both are above horizon and 1/4 time both are below.
Since Moon is dim to start with and fades when not full, a night lit by a narrow crescent moon is not very bright.

Now consider a planet of binary star. Like α Cen Ab.
At its periapse, B comes to 11,2 AU of A. Since Ab is in habitable zone, the A-Ab distance is about 1,2 AU.
Because of the stability requirement, we can find compelling reason why the A-Ab orbit should be at a low inclination to A-B orbit - like Moon is within 5 degrees of ecliptic, and Jupiter too.
Therefore, α centauri B must come to opposition and to conjunction with A for Ab regularly.
But unlike the case with Moon, and like the case with Jupiter, the period of oppositions and conjunctions of α centauri B must be close (not exactly equal) to α centauri A orbital period - the local year. (Which is close to 1,3 Earth years).

In case of moonlight, full Moon is around 1000 times brighter than combined light of stars. Full moon used to have drastic effects on activity of people. Social events set at full moon or maybe waxing gibbous moon (You can stay out late if when it the time to get home the night is moonlit rather than just starlight+airglow!). Street lighting not lit when moonlight made it superfluous. Lunacy.
Now consider α Cen Ab. At opposition B is at 11,2-1,2=10 AU. B is 2,2 times dimmer than Sun in visible light. So it is 220 times dimmer at the distance of Ab - but since full Moon is 400 000 times dimmer than Sun, it still makes 1800 times brighter than full Moon. Comparable to twilight with Sun around horizon...

When B is near "full", then the whole night is going to be in "twilight" range of 50...500 lx. Which is not day - but neither is it "moonlit night", because that is in range of 0,25...0,05 lx.

Hey, I wanted to take a deeper dive into the article you posted a few weeks back but the page is not available anymore. Would you by any chance have the citation for the article?

 

[Devin-M]

Universe Sandbox apparently doesn't account for variables such as radiation pressure

Actually at 44:53 you can see a tail of debris sweeping past the Earth which is basically a comet’s tail from the moon becoming super heated which is caused by radiation pressure…

 

[DaveC426913]

would it be possible for another planet to "catch it" back into a relatively stable orbit, say by another Rigel?

Only if there were a third massive object in play. You need that "other planet" to arrange the capture.We had this discussion elsewhere a long time ago.

Take a hypothetical scenario where a planetoid plunges toward a star.
Imagine it somehow has just the right velocity to get captured and settle into a stable orbit.

Any such scenario can be reversed in time.

The scenario above, reversed in time would have a planetoid - in a stable orbit - suddenly and utterly spontaneously fly out of its orbit - moving at greater than escape velocity - and leave the system.

Makes no sense, no?

 

[snorkack]

Hey, I wanted to take a deeper dive into the article you posted a few weeks back but the page is not available anymore. Would you by any chance have the citation for the article?

Indeed, it failed for me, but apparently something made a couple of mistakes in the link.
Citation:
Title: The Stellar Magnitudes of the Sun, Moon and Planets
Authors: Russell, H. N.
Journal: Astrophysical Journal, vol. 43, p. 103-129 (1916).
Bibliographic Code: 1916ApJ....43..103R

in the heading, the name is written out:
by HENRY NORRIS RUSSELL
(the Russell of Hertzsprung-Russell?)

And trying the link again, too:
https://adsabs.harvard.edu/full/1916ApJ....43..103R

 

[delie]

Actually at 44:53 you can see a tail of debris sweeping past the Earth which is basically a comet’s tail from the moon becoming super heated which is caused by radiation pressure…

Oh. I misinterpreted the mechanical pressure as "pure momentum" if this makes any sense (e.g. acceleration of an object). Although, now that we're talking about it...

 

[snorkack]

Something which I just realized: if an α Centauri planet has Earth-like rotation, you could literally not have night for a hundred years!
Earth-like rotation is inherently not unlikely. Earth has rotation in 24 hours. So does Mars (well, 24 hours and 39 minutes but that´s still 24 hours). Earth has axial tilt 23 degrees 27 minutes. Mars has 25 degrees 11 minutes. Very close.
Look at the orbit of α Centauri:
https://en.wikipedia.org/wiki/Alpha_Centauri#/media/File:Orbit_Alpha_Centauri_AB_arcsec.png
Note that the half of orbit to the right takes a bit over 14 Earth years.
And now imagine α Centauri Bb at a low eccentricity orbit in habitable zone, low inclination of Bb orbit to the AB zodiac, Bb rotation period 24 hours, Bb axial tilt to Bb and Ab orbits at 25 degrees... and the axis at a suitable orientation to the AB apside line.

Since A will follow the zodiac in Bb sky, it will go through the full declination range, +25 to -25, over the 80 Earth year orbital period of AB. With the said suitable axis orientation, A is at positive declination for 65 Earth years of these 80, and at negative declination for 15 Earth years.
Which means that for an observer at latitude +90, A is circumpolar, never setting for 65 Earth years. Since B is smaller than Sun, I above established that the orbital period in B habitable zone may be about 0,63 Earth year, which means A may be circumpolar for over 100 Bb years in a row.

At apoapse and culmination, A is about 800 times dimmer than Sun, so at 25 degrees from horizon, it would provide about 45 lx ground illumination, year after year.
Note that as A travels along orbit, it would sink lower in sky... but simultaneously, it would be getting closer to B. So that would have a direction of compensating the sinking of A over decades... until A finally gets close to horizon and rapidly fades. At which point the alternation of polar day and night due to B means polar nights get dark, for the following period of 15 Earth years or maybe a bit over 20 local years.

 

[Vanadium 50]

you could literally not have night for a hundred years!

Depends on what you call "night". Alpha Cebtauri B would be between the brightness of the sun at Uranus and Neptune. Brighter than the moon, but nothing like daylight on earth,

Your complex analysis can be simplified: "sometimes the planet is more oe less between the two stars".

 

[snorkack]

Your complex analysis can be simplified: "sometimes the planet is more oe less between the two stars".

No.
At the beginning, I offered two possible causes why a place might be illuminated for a long time continually. First was that the planet is tidally locked to the star - that would be permanent for that side, while the dark side would be permanently dark. Second would be that the planet is freely rotating but is between the two stars. And my point is that this will be brief, every time it happens.
I did not notice a third reason.
The planet is rotating but a pole is turned towards the source of light.
On Earth, North Pole is exposed to sunlight on average from 19th of March (2 days before equinox - the 50 minutes of refraction plus Sun´s radius) to September 25th. Civil twilight is defined as period when Sun altitude is between -50 minutes and -6 degrees. Which means that civil twilight lasts 6th to 19th of March, and 25th of September to 9th of October.

Depends on what you call "night". Alpha Cebtauri B would be between the brightness of the sun at Uranus and Neptune. Brighter than the moon, but nothing like daylight on earth,

Comparable to twilight. Bright enough to make an Earth-like sky visibly (dark) blue, and make the dimmer stars of the constellation images invisible.
The orbital period of a planet in habitable zone of a star is limited by distance to the star, therefore brightness of the star.
Some stories feature planets of bright stars. Ford Prefect who saved Artur Dent in Hitchhiker´s Guide to Galaxy came from a planet orbiting Betelgeuse.
But many people do not like living on planets of bright stars, not only because of incidents like collapsing Hrung disaster but because astronomical evolution of a bright star is rapid and they worry about problems with geological evolution of planet keeping pace.
If your star has to be sun-like or dimmer, that will limit your year length - and therefore your polar day length.
Now, if you are orbiting two stars...
The secondary star generally needs to be at least 10 or so AU away, or else it will perturb the planet too uncomfortably.
The secondary star can be arbitrarily far away. But if it is far away, it is dim. Sun is only as bright as full Moon at 600 AU.
A sunlike star at 10...50 AU away, like α Centauri A from B, would dominate general lighting when B is below horizon, yet would not much perturb orbit or climate. And it would move much slower in sky than B has to be doing - therefore would allow much longer polar days than B itself does.
For an observer on one of Bb´s poles, B would be constantly visible for 180 degrees of orbit, and habitable zone means the orbit is about 240 days, so 120 days at a time of B up in sky. Plus twilight, but at 24 degrees inclination the civil twilights would be about 10 days in spring and autumn combined. Which means 100 days of polar night, 20 days of twilight, 120 days of polar day.
A would be visible.... depending on node line/apside angle. For 180 degrees of orbit, but AB orbit is eccentric. With a suitable node orientation, one Bb pole has A up 65 Earth years continuously, and down for 15 Earth years. The period with A set of course continues to have B rising and setting with the 240 day period.

 

[Vanadium 50]

I don't understand what you are saying. The only way to illuminate both sides of a planet is to have one star on one side and the other on the other. Anything else has dark.

 

[snorkack]

I don't understand what you are saying. The only way to illuminate both sides of a planet is to have one star on one side and the other on the other. Anything else has dark.

That is, you don´t catch the implied question answered? "Would it be day all the time"?
If the question is "How to illuminate whole planet at one time", the requirement will be that two stars must be pretty closely antipodal. Which will be a brief time, even if prone to recurring. And which simultaneously causes every place of the planet to be illuminated through rotation.
If the question is "How to illuminate one region of planet for an extended time compared to Earth rotation" then the first answer applies. But then it will not be the only answer. There will be two more answers:
2. The planet is tidally locked to one source of illumination. Then the near side will be permanently illuminated
3. One of the stars is illuminating a polar region. The pole turned towards the more distant, therefore slow moving star will be illuminated for a long time compared to polar days caused by nearby star.