Proxima Centauri b

[PortalHunter]

So this is a recent find, apparently. Quite exciting for exoplanetary research. A habitable zone exoplanet super close to Sol. Sounds nice so far.

Wikipedia article:
https://en.wikipedia.org/wiki/Proxima_Centauri_b

Here's the journal, published today:
http://www.nature.com/nature/journal/v53...19106.html

Space.com:
http://www.space.com/33834-discovery-of-...spc_514630

It has a minimum mass of 1.27 M⊕. The radius is at least about 1.1 R⊕, assuming a rocky composition and a density equal to that of the Earth.

Looks like we might have a chance to make a colonized Gaian terrestrial planet there.

[Drashner1]

It's a fun discovery - but until and unless definitive evidence (or at least more solid evidence) of a biosphere is discovered, I would argue against describing it as a Gaian in OA. That would be getting ahead of ourselves.

My 2c worth,

Todd

[radtech497]

Running a few numbers on this planet, I find the ranges of uncertainty are probably not conducive to making Proxima b a "Gaian" world, even stretching the definition to its limits. For one thing, Proxima Centauri was much more active in its youth than it is now, and even now emits X-rays at levels comparable to Sol. It has an activity period of about fourteen months (compared to about 11 years for Sol) and randomly emits flares that brighten the star by perhaps an order of magnitude. The main effect of this activity, with regard to Proxima b, is that after its primary atmosphere (mostly hydrogen and helium) had been stripped away, the intense stellar bombardment might have impeded the development of a secondary atmosphere. Beyond that, the uncertainties connected with the planet's orbital eccentricity (up to 0.35) mean that it may only transit the "habitable zone" rather than reside there, and have both a periastron and an apoastron that lay outside that zone. Third, the planet became tidally locked to its star within five millennia of its formation. Finally, the values assumed for the planet's bulk density (5515 kg/m^3, the same as Earth) and its albedo (0.30, about the same as Earth), may be entirely without merit. Even the planet's mass, ranging from a minimum of 1.27 Earth masses to a 90% probability it is not more than three Earth masses, gives quite a range,

Could such a world evolve life? Possibly, though it would probably be very different from life found on Earth (or even elsewhere in the Solar System). If it were to emerge, I would expect it to reside either in the deeper parts of whatever oceans/seas/lakes as may exist and/or deep underground, as a defense against radiation. This would have the effect of leaving the surface largely unpopulated and barren in aspect. Those few lifeforms that did evolve for life on the surface would need to be very hardy, seeing as they would need radiation protection and possibly thermal protection as well. I suppose they could remain dormant until temperatures were conducive to having their biosolvent in a liquid state, though this might limit them to only a few days out of every "year" (11.186 days); they might lead a sort of punctuated existence, spending their time between periods of frenzied activity and inert dormancy. Any plant life on the surface would most likely be black, in order to maximize the longer wavelengths of light emitted by Proxima Centauri. A more robust genome would be necessary, or at least one that is highly fault-tolerant. Variable atmospheric pressures might also be a factor, depending on whether the atmosphere (if any) has a sufficient quantity of carbon dioxide; if not, the atmosphere might collapse on the "dark side" only to thaw again when and if the planet librated. Surface bodies of liquid water may then be problematic, though subsurface deposits might not be affected as much. It is possible, even likely, that orbital surveys of Proxima b might show a dry, lifeless world not unlike the first images of Mars. But images can be deceiving.

Radtech497

[Dark]

Can we have an EG article on it?

[four]

Running a few numbers on this planet, I find the ranges of uncertainty are probably not conducive to making Proxima b a "Gaian" world, even stretching the definition to its limits. For one thing, Proxima Centauri was much more active in its youth than it is now, and even now emits X-rays at levels comparable to Sol. It has an activity period of about fourteen months (compared to about 11 years for Sol) and randomly emits flares that brighten the star by perhaps an order of magnitude. The main effect of this activity, with regard to Proxima b, is that after its primary atmosphere (mostly hydrogen and helium) had been stripped away, the intense stellar bombardment might have impeded the development of a secondary atmosphere. Beyond that, the uncertainties connected with the planet's orbital eccentricity (up to 0.35) mean that it may only transit the "habitable zone" rather than reside there, and have both a periastron and an apoastron that lay outside that zone. Third, the planet became tidally locked to its star within five millennia of its formation. Finally, the values assumed for the planet's bulk density (5515 kg/m^3, the same as Earth) and its albedo (0.30, about the same as Earth), may be entirely without merit. Even the planet's mass, ranging from a minimum of 1.27 Earth masses to a 90% probability it is not more than three Earth masses, gives quite a range,

Well, couldn't a magnetic field counteract this? Proxima b is more massive than Earth, and despite being tidally locked it still rotates once every 11 days, so I would have thought that it would develop a magnetic field. Would a magnetic field as strong as, or stronger than, Earth's blunt the effects of solar flares?

Even if solar flares are still damaging, they wouldn't affect life on the dark side of the planet (although life on the dark side would have the problem of not having a source of sunlight for photosynthesis).

Being a tidally-locked planet, Proximab would likely have a thin band of habitable land on the horizon, between the light side and the dark side.

The eccentricity problem is probably overstated: the orbital period is only 11 days! Would the planet really cool down a large amount during such a short winter? After all, the atmosphere and oceans trap heat.

We have an article on Vesperian type worlds (i.e. tidally-locked). While information about this planet is uncertain, it could well be either life-bearing or terraformable.

--------------

I just had a look at the EG's article on Proxima Centauri. It looks like there's something wrong there: planet 2 is Lifthrasir, a cytherean-vesperian world. It has an orbital period of just over 2 earth days, which is much shorter than the real planet Proximab's orbital period of 11 earth days - however, Lifthrasir's semimajor axis of 0.09 AU is apparently longer than Proximab's semi-major axis of 0.05 AU?

There must be some problem there; the orbital data on that article probably needs rechecking.

[stevebowers]

http://www.orionsarm.com/eg-article/4ce52fdf5e9de
Planet no II, Lifthransir, is in approximately the same location as Proxima b, with similar ( but not identical) characteristics. I'll tweak the planet somewhat to make it a bit closer in character to the new planet, and maybe I'll move some of the outer planets a bit further away (there is no evidence yet that suggests there are other planets in this system, but there is no evidence they are not there, either.

Edit- I'll check all the orbits in that system and make them more realistic - and probably get rid of the innermost planet altogether.

[stevebowers]

This planet could potentially be quite a bit like Twilight, with an icy dark side and a habitable twilight zone. The subsolar point could be quite warm.

Alternately this could be a waterworld, with an eyeball configuration, like Yanqui.

A third possibility is a world in 3:2 resonance, like Mercury; this could be the most temperate version of all, and could probably be terraformed quite easily. Daytime would be a strange experience, however, as the Sun would move back and forth in the sky in a very odd pattern. Here's a Youtube video about Mercury's double sunrise
https://www.youtube.com/watch?v=nPprOO2u1gk

Does anybody have a preference between these three options?

[PortalHunter]

Does anybody have a preference between these three options?

Oh wow. That Mercury video was quite interesting. I don't think I've seen (m)any worlds like that in OA before. Perhaps that could be something to look into. I might make a video demonstrating that effect if we do so.

[stevebowers]

I second that.
I've updated the Proxima page; details below
(I suppose this article now requires a Terraformed Lifthransir image - shouldn't be too much of a problem. The local history could do with expansion as well, but I'll leave that up to anyone who fancies it. Any other comments?)


--------------------------------------------------
Star: Proxima Centauri
Type: M5.5 Ve
Luminosity: 0.0017 x Sol
Distance from Sol 4.2 ly (J2000 epoch); thus the closest star to Sol. Loosely bound to Alpha Centauri A+B.

Proxima Centauri was colonised during the Great Expulsion. Proxima has 4 planets; Lifthrasir, Skoll, Hati and Fenrir, and an extensive asteroid belt. The colonies among the asteroid belt were a centre for the Buddhist religion under Boddhichittamaittreya III and are now a sacred site of pilgrimage.

Visited by the spacecraft Ananas in 1040 AT at the start of Benedita Blue Sky Dacosta's epic trek across Terragen space.

Planets
I: Lifthrasir

Lifthrasir: Proxima Centauri b

Lifthrasir before terraforming
Type: resonant locked terrestrial, now terraformed to EuGaian
Radius: 7008 km
Gravity: 1.11 gees
Average Surface Temperature before terraforming 275 K (now 295 K)
Orbital Period: 0.03 standard years
Semi-major Axis: 0.05 AU
Eccentricity: 0.2
Inclination: 2.00
Surface Pressure: originally 3.9 atmospheres, now 1.4 atmospheres
Rotation Period: in 3:2 resonance with orbital period; it rotates three times for every two orbits around Proxima. This means the days are 22.4 standard days long. In some locations a double sunrise and sunset can be seen at various times, because of the complex relationship between the orbital speed and rotational speed.
Obliquity: 1.8
Albedo: 0.55
Lifthrasir was an early target for unmanned probes, but because of the possible threat from the nearby ahuman colony of Nessus, this world was not targeted by colony ships until the Great Expulsion. Settled by GAIA ark in 701 AT. The slow rotation of this world posed a challenge to early terraforming technology, but with the introduction of weather machines this was finally achieved in 1908 AT.

II: Skoll

Skoll

Image from John M. Dollan and Steve Bowers

Type: MicroJovian Type.
Radius: 23126 km
Mass: 14.322x Earth
Average Surface Temperature -181° C
Orbital Period: 6.3 standard years
Semi-major Axis 1.7 AU
Eccentricity: 0.005
Inclination: 1.00
Rotation Period: 65 standard hours
Obliquity: 18
Albedo: 0.51

III: Hati


Image from John M. Dollan and Steve Bowers

Type: MesoJovian Type.
Radius: 26796.5
Mass: 29.708 x Earth
Average Surface Temperature: -54° C
Orbital Period: 11.95 standard years
Semimajor Axis: 2.6 AU
Eccentricity: 0.006
Inclination: 1.00
Rotation Period: 42 standard hours
Obliquity: 28
Albedo: 0.50
Rings: 80000 km

IV: Fenris


Image from John M. Dollan and Steve Bowers

Type: Cryojovian.
Radius: 25477 km
Mass: 19.149 x Earth
Average Surface Temperature -226° C
Orbital Period: 49.4 standard years
Semi-major Axis: 6.7 AU
Eccentricity: 0.011
Inclination: 4.00
Rotation Period: 41 standard hours
Obliquity: 34
Albedo: 0.59

[stevebowers]

Note that anyone who writes about this system would need to address the fact that it is a flare star;

maybe over the history of this system, the flaring could be reduced or eliminated through the use of advanced technology, but this could mean that certain clades who are adapted to flare star behaviour would be unhappy.