Is a theoretical 2/3rds - 7/10ths Earth big enough to have the magnetic field, atmosphere and plate tectonics to do this, or will I wind up geologically killing the planet?
I have been toying with the idea of some kind of 31st & 1/2 Century space adventure story. Basically, at this point, humanity has managed to come together enough to develop fusion technology, and explore space in earnest for the last few hundred years. There's no magic, no replicators (but there are nanobots and asteroid mining), no warp drives (but there are relativistic speeds attainable, topping out at about .95c; and suspended animation for people and robot ship crews). It is also assumed:
Lightspeed is a "hard" barrier for the foreseeable future, and affects travel and comms. Colonies are intended to be permanent. The Motherships can continue to sustain life to get the settlement established; if things go catastrophically wrong, there is a factor of safety timewise to abort the mission and return to Earth, or stay for a few generations; but it's an either-or.
There very likely are intelligent beings in the Universe, but they exist too far away from us to visit or communicate. If there are hyperintelligent beings that have surmounted these problems, we are too primitive to be of interest to them.
Humanity has, by this point, established permanent settlements beyond the Solar System. This one would be the 5th extrasolar colony, and still within 60Ly of Earth.
The hypothetical Planet X would have the following characteristics: Edited based on contributions.
Star: FxV type; Planet X is in both the Conservative Habitable Zone and UV Habitable Zone (with a thicker ozone layer than Earth's)
Age: 1.3 - 3Gy. Not enough time to develop intelligent life, but that's not a problem, because humans are arriving from off-world.
Mass: 0.65 - 0.7 Earth-masses
Radius: 0.965 - 1.02 Earth-radii (less dense silicates, nearly pure iron core)
Gravity: 0.68-0.7 G.
Satellites: 1; with a large iron core, about 0.011 +/- 0.003 planetary masses. Appears smaller than Earth's moon due to much greater density. Slightly higher albedo than Earth's Moon. In stable orbit 105 +/- 5% of the distance the Moon is relative to Earth.
Atmosphere: ~1 earth-atmosphere at sea level; 25% oxygen, remainder inert and trace gases, more ozone, more xenon compared to Earth.
Average Surface Temperature: 278.5K, +5.35 C.
Rotation Speed: Somewhat faster than Earth's, resulting in a 17-19 hour day-night cycle, and likely strong winds and very apparent aurorae.
Axial Tilt: About the same as Earth's, resulting in distinct seasons.
Oceans of liquid water exist, as do large polar icecaps. ~30% of the surface is land, although extensive glaciation at the poles make it difficult to tell whether the poles are land or ice.
The planet is home to plant life, mostly algae and kelp-like plants in its oceans; early zooplankton may be starting to develop. On land, lichens, mosses; tall, spindly trees, but no multicellular animal life.
My biggest concern for a sub-Earth sized planet around a brighter and hotter star would be having a big enough active iron core to keep a strong enough magnetic field to resist the stronger solar wind, (despite the greater distance), and yet still have enough silicates left for plate tectonics. I figure a big, ferrous moon will help, through the tidal forces it will exert, along with the rapid rate of rotation.
Does this planet have all the necessary ingredients to maintain an active core, tectonics, magnetosphere and atmosphere, or would it be a geological time bomb?