Terra's Big Neighbor

[stevebowers]

Don't forget the possibility of using Storrs Hall's Weather machines to increase or decrease albedo and redistribute heat. Several fairly earthlike planets in OA would be very uncomfortable without this sort of thermal redistribution.

However using a technological fix like this leaves the population open to weather tyranny. Whoever controls the climate in a location has a lot of power over the people who live there. This is also true of any artificial habitat, of course.

[xilman]

Putting high pressure at sea level is begging for a severe greenhouse problem. Why not make the whole planet more habitable with lower pressure?

A high N_2 and/or Ar concentration will give high pressure and low greenhouse effect.

[iancampbell]

Question: Does the planet have to have an Earthlike climate throughout?

Well, it's obviously going to be warmer regardless. But the more Earthlike the merrier.

Or just in parts of it?If the latter, how about a planet with two polar continents (covering the poles, extending to 50-70 degrees north and south), with an unbroken equatorial ocean.

Equatorial oceans put low albedo terrain at the highest insolation area of the planet. The references I provided indicate you probably want desert terrain around the equator. You can put the cloud-generating oceans at middle latitudes. The poles, if the low tilt is cooperating, will be large ice caps.

Planet about 2-3 earth mass, and at Venus' distance from the Sun. Planet has Earthlike atmosphere composition, thinner atmosphere creating more temp. variation, about 0.75 atm, avg. temp. 80-90 celsius at equator, 5-40 celsius on coasts of polar continents depending on latitude, interior of polar continents variable but often below freezing.

Why not push for as Earthlike as possible before modeling data pushes back?

Four - Another way of getting a planet some of which is habitable and some not is a planet with extensive high-altitude upland regions. Something about the size and height of the Tibetan plateau, on a planet otherwise generally like Earth except that sea level is about 2-3 bar of pressure and 60C or so, would probably be quite comfortable. (I'm not professional in this area, so the details might be wrong and probably are.)

Putting high pressure at sea level is begging for a severe greenhouse problem. Why not make the whole planet more habitable with lower pressure?

This is for use in a fictional work, right? Personally, I think that a planet a large proportion of which is uninhabitable makes for some interesting story possibilities.

Yes, of course there would be a strong greenhouse effect at sea level. As a more severe version of this, it is thought that the conditions at an altitude of about 40km in Venus's atmosphere are relatively benign. (As far as temperature and pressure are concerned, anyway.)

Incidentally, an atmosphere with a high proportion of N2 and a partial pressure of oxygen similar to Earth's would probably be useless to humans. NItrogen narcosis sets in at a relatively low pressure.

[stevebowers]

Note that nitrogen-rich atmospheres are likely to be very common among terrestrials. Nitrogen is an atmophile element, more likely to be found in an atmosphere or as ammonia than as part of a planet's crust. Human colonists after the middle First Federation period were regularly given minor tweaks to avoid irritations like nitrogen narcosis and carbon dioxide poisoning, significantly increasing the number of planets that could be settled.

[Cray]

Yes, of course there would be a strong greenhouse effect at sea level. As a more severe version of this, it is thought that the conditions at an altitude of about 40km in Venus's atmosphere are relatively benign. (As far as temperature and pressure are concerned, anyway.)

That is an excellent point. Venus does have Earthlike conditions (pressure, temperature) at higher altitude. I wonder how you'd move them to ground level. You'd end up with the problems of the big solar-thermal mass of the ground and ocean right under your feet but...

If you can get those Earth-like conditions someplace on Venus, then you can probably get it elsewhere.

[Cray]

Would a clone of Luna be naked-eye visible from Earth if it was orbiting this alternate Venus?

[stevebowers]

Some people have apparently seen the satellites of Jupiter, which is much further away.
http://denisdutton.com/jupiter_moons.htm
All of the Galilean moons would be visible to the naked eye if Jupiter were not so close; Ganymede is mag 4.5 for example. The Venusian Luna would be much brighter, because it is closer to the Sun and closer to us. The separation between Jupiter and Ganymede is 5 arc minutes, while the maximum separation between Venus and Venus-Luna when the planet is brightest (at a distance of around 80 million km) would be 16 arc minutes, so it should be visible quite easily, although not all the time.

[stevebowers]

If I've calculated it correctly, Venus-Luna would have a magnitude of -0.2, about as bright as Alpha Centauri. Mercury is a lot brighter, despite being of comparable size, simply because it is much closer to the Sun.

[iancampbell]

Yes, of course there would be a strong greenhouse effect at sea level. As a more severe version of this, it is thought that the conditions at an altitude of about 40km in Venus's atmosphere are relatively benign. (As far as temperature and pressure are concerned, anyway.)

That is an excellent point. Venus does have Earthlike conditions (pressure, temperature) at higher altitude. I wonder how you'd move them to ground level. You'd end up with the problems of the big solar-thermal mass of the ground and ocean right under your feet but...

If you can get those Earth-like conditions someplace on Venus, then you can probably get it elsewhere.

Yup. I was postulating a rather less severe Venus-type hothouse (maybe 450K and 10 bar at sea level, and much more water) with a suitably high upland area or several, leaving livable conditions at ground level but in a limited number of places of relatively small area.

Actually, I stole the idea from Niven; his world of Plateau with Mount Lookitthat is pretty much like this. Except for the height of the plateau; he sets it at 40km high, which is probably impossible. (The crush strength of rocks isn't high enough.)

[stevebowers]

An artificial Mount Lookitthat made of diamondoid foam is probably possible; maybe some planets could be colonised in this way, rather than using Landis balloons.