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tracer
2012-Oct-23, 06:15 AM
Let's say we have an Earthlike planet, but it's JUST BARELY too close to its parent star to be inside the Goldilocks Zone. (Like, oh, say, Earth, in a billion years when the sun warms up. :eek: )

Is it possible, given that probably has some kind of an atmosphere, for the tropics to be too hot for liquid water, but NOT the upper latitudes? I.e. could we have a baked desert belt around the equator but oceans farther north and south?

Or would being too close for liquid water ANYWHERE on the surface also mean that the water vapor would be heated to the point where it reached escape velocity, thereby eventually draining the planet of ALL water, liquid or otherwise?

Colin Robinson
2012-Oct-27, 07:02 AM
Let's say we have an Earthlike planet, but it's JUST BARELY too close to its parent star to be inside the Goldilocks Zone. (Like, oh, say, Earth, in a billion years when the sun warms up. :eek: )

Is it possible, given that probably has some kind of an atmosphere, for the tropics to be too hot for liquid water, but NOT the upper latitudes? I.e. could we have a baked desert belt around the equator but oceans farther north and south?

I don't see why not. After all, as Earth is right now, water in Antarctica is usually found in the form of solid (ice) rather than liquid. On the sort of hotter Earth you are describing, maybe ice wouldn't exists anywhere on the surface, but Antarctica would have Amazon-like rainforests...


Or would being too close for liquid water ANYWHERE on the surface also mean that the water vapor would be heated to the point where it reached escape velocity, thereby eventually draining the planet of ALL water, liquid or otherwise?

Even if that happened eventually, there might be a period of flourishing life on the surface until the draining away of water was complete.

Paul Wally
2012-Oct-27, 03:44 PM
I think it also depends on how much water there is on the planet and the topography. There's no guarantee that the topography will consist of equatorial land flanked by two oceans to the North and South. For instance, if it is an ocean world we would have boiling water at the equator saturating the whole atmosphere with water vapour. This in turn could lead to a greenhouse effect turning the whole planet into a kind of sauna. Actually I believe there is such an exoplanet discovered with a water-vapour atmostphere, or it was speculated to have a water-vapour atmosphere, but I don't remember the name of the planet.

eburacum45
2012-Oct-28, 02:27 AM
Curiously enough, I've just finished a description of an Earth-like planet with a hot, dry equator and wet poles.
http://www.orionsarm.com/eg-article/508b48d94e043
If any rain falls in the equatorial regions it evaporates immediately and is carried back to the polar seas and lakes. I see this as a possible fate for the Earth in about a billion years time, with dry salty ocean beds and relics of the former biosphere at the former poles; but I suppose that this would only happen if the planet manages to lose most of its water somehow, probably through dissociation.

Rhadamant5186
2013-Jan-30, 08:39 PM
In all honesty there are so many factors to what makes a planet habitable that distance from its primary star is just one of many considerations.

Eccentric Orbit:
For instance imagine a planet with a highly eccentric orbit that passes through the 'goldilocks' zone. For half of the planet's orbit around its primary star water could be frozen or steam and the other half it could be liquid or solid.

Tidally Locked:
Imagine a planet where one side always faces the star and the other never does. One side would get blasted by radiation and the other side would be icy and cold. Just because a planet lands in the goldilocks zone doesn't mean would be nice to live on.

Surface Pressure:
This one is very important. Mars is in the goldilocks zone, but it doesn't have enough surface pressure to have an atmosphere. A planet like Venus as way too much atmospheric pressure and it would be hard to imagine inhabiting a planet like Venus even if it wasn't so close to the Sun.

Magnetosphere:
You won't hear much about this, but Mars probably became a dried up husk of a planet because it didn't have enough core density to have an active magnetosphere. The iron/nickel core of Earth creates a magnetized planet around our planet protecting us from radiation that would irradiate life on our planet and strip away our atmosphere. Mars' core went cold and the solar wind of the sun robbed Mars of its atmosphere. A planet without a magnetosphere probably isn't a very stable planet to inhabit, although it still might be habitable. The only way to keep an atmosphere if you don't have a magnetosphere would be to replace the gasses through processes like vulcanism or bio-organisms producing the gas.

There are so many other reasons why a planet sitting inside the 'Goldilocks' zone might not actually be all that habitable, but I presented a few obvious ones.

Rhadamant5186
2013-Jan-30, 08:40 PM
In all honesty there are so many factors to what makes a planet habitable that distance from its primary star is just one of many considerations.

Eccentric Orbit:
For instance imagine a planet with a highly eccentric orbit that passes through the 'goldilocks' zone. For half of the planet's orbit around its primary star water could be frozen or steam and the other half it could be liquid or solid.

Tidally Locked:
Imagine a planet where one side always faces the star and the other never does. One side would get blasted by radiation and the other side would be icy and cold. Just because a planet lands in the goldilocks zone doesn't mean would be nice to live on.

Surface Pressure:
This one is very important. Mars is in the goldilocks zone, but it doesn't have enough surface pressure to have an atmosphere. A planet like Venus as way too much atmospheric pressure and it would be hard to imagine inhabiting a planet like Venus even if it wasn't so close to the Sun.

Magnetosphere:
You won't hear much about this, but Mars probably became a dried up husk of a planet because it didn't have enough core density to have an active magnetosphere. The iron/nickel core of Earth creates a magnetized planet around our planet protecting us from radiation that would irradiate life on our planet and strip away our atmosphere. Mars' core went cold and the solar wind of the sun robbed Mars of its atmosphere. A planet without a magnetosphere probably isn't a very stable planet to inhabit, although it still might be habitable. The only way to keep an atmosphere if you don't have a magnetosphere would be to replace the gasses through processes like vulcanism or bio-organisms producing the gas.

There are so many other reasons why a planet sitting inside the 'Goldilocks' zone might not actually be all that habitable, but I presented a few obvious ones.

Rhaedas
2013-Jan-30, 11:01 PM
Plus, just to add, a habitable zone's edge would not be an edge, but a gradual area that makes conditions harsher for life's existence at the planet progresses out of the area. But it wouldn't mean a sudden change of the possibility. Life might migrate to better areas if it's a seasonal thing (that's what Earth's species often do), or adapt as things change for the worse. The Goldilock zone is more of a probability area of favorable conditions based on the star's radiation than a definite yes/no thing.

TooMany
2013-Jan-31, 12:25 AM
There was a sci-fi novel about a planet with it's axis of rotation in the plane of it's orbit. The people who had colonized the planet would migrate from one pole to other every 1/2 year in order to be in a warmed and lit part throughout the year in spite of extreme seasonal changes. Reminds me of the long seasonal migrations of some birds on earth.

R.A.F.
2013-Jan-31, 12:40 AM
Hey, Tracer...long time, no see...what's it been, a couple of years at least since you last posted? (and what, half a dozen or more years since that BA talk?)

Good to see ya participating again. :D

neilzero
2013-Jan-31, 04:50 AM
I suspect the danger has been exagerated. 140C at the Equator would barely boil sea water as the extra water vapor would increase sea level air pressure to about two bar. As the steam rose to higher altitude, it would cool due to the expanson = possibly cool enough to form ice even over the Equator at an altitude of 30 kilometers = sky cities. If we keep our 23 degree axial tilt, it will be pleasent temperatures, but dark near the poles about 5 months out of the year plus twilight for at least the 3 weeks of early March, but perhaps dangerously hot (without airconditioning) with the sun shining 24 hours per day during the other half of each year. The Elevation of the South Pole is high enough to make it cool. By then perhaps Mount Everest (or equivelent) will be at the South or North Pole. Neil