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1

You write: One planet is pretty much a perfect copy of Earth and the other planet is 20% less massive with a radius 10% smaller. So the smaller planet has 0.90 of the radius of Earth and 0.80 of the mass of Earth. A planet with 0.9 the radius of Earth should have a volume of 0.729 the volume of Earth. If its average density was equal to that of Earth, it ...


0

Oversize "Metal"-heavy Brown Dwarf I suppose in theory you could somehow have a planet that was massive enough to be a red dwarf but which was predominantly elements heavier(*) than hydrogen and helium. So the core of the planet would be hot enough and have a high enough pressure to fuse hydrogen, but it's choked by carbon and heavier elements ...


2

That is not stable over geological time. Systems like Pluto and Charon require one to be much more massive than the other so that their orbits don't intersect. If the masses are the same, it may take some millions of years but the planets will collide. That's because any slight perturbation in their orbit will cause one planet to go to a very slightly lower ...


6

Huge gas giant rotating fast. Behold the glowing sky of Io! https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA01637 This eerie view of Jupiter's moon Io in eclipse (left) was acquired by NASA's Galileo spacecraft while the moon was in Jupiter's shadow. Gases above the satellite's surface produced a ghostly glow that could be seen at visible ...


0

This is not a realistic scenario, but may work for a sci-fi universe. Imagine a rogue planet with some orbiting moons out in the darkness of interstellar space. Also imagine some alien race that can construct low-mass (less than a star) wormhole-like portals. They construct a pair of such portals, one in orbit of a star far away, and one in orbit of the ...


1

Just yeet out a Gas Giant So in general, you could have such a System. If you look at the Jupiter System, it is pretty much its own "Solarsystem". You got a bunch of Moons around a Central Object with a shi┬┤tton of debris flying around. This could just from natrually in the middle of nowhere. One might argu that such a System is just like or one. ...


25

A single big planet and a single big star orbiting around? No. Wikipedia has a list of star extremes. This star is the smallest, 7% the mass of our sun. (So about $7*10^{28}$kg) This planet is the largest, 20 * times the mass of jupiter (So about $3.7*10^{28}$kg) These are very close in mass, they'll orbit around a point 2/3rd the distance from the sun to ...


32

What you are describing is a rogue planet with moons. This is a planet that does not orbit any star, either having been ejected from its original solar system, or never having belonged to a solar system in the first place. This would not be aptly described as a solar system, since there is no star, but you could have a rogue planet with moons orbiting it. A ...


0

Supposedly stars moving away from us look red and those moving towards us have a blue hint. The direction of the visible spectrum.


5

A pretty normal star you see, stars don't move that fast compared to other stars, and even travelling at light speed the closest star would take half a decade to reach earth, most stars however aren't the closest star and would take centuries moving at light speed, however your star isn't going to be moving at light speed so it would literally take thousands ...


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