Ross 154 is a red dwarf star located at 9.7 light years from us. Its spectral classification is M3.5V, which means it belongs to the brightest of the dim M-Type Stars, Main Sequence Stars. It is known to be a flare star. Most eruptive Flare Stars, like UV Ceti or Wolf 359, are too violent to allow settlers to colonize them.
The star[]
Ross 154 has a mass of 17% of our sun, Sol, a radius of 24% of Sol's, surface temperature of 3340 K and appears to be young and fast rotating.
Very interesting is its flare activity, which is rather stable. Flares seem to occur every two days and last longer then in case of other Flare Stars. Usually, during flares, Ross 154 increases in brightness by 3 to 4 magnitudes (15 to 40 times).
In case of most flare stars, like UV Ceti of the Luyten 726-8 system, flares occur without a warning, during which within minutes the flare outshines the star by a few magnitudes and then vanishes. There is no way to say when UV Ceti or Proxima Centauri will blow another cataclysmic flare, it could be next day or next year.
The flares of Ross 154 are far longer, lasting hours, are predictable and because of this allow settlers to get used to them. However, like in case of all flares, they come with massive releases of ultraviolet and X rays, as well as with significant amounts of blue light. Because of this, we can model flare activity into a computer simulation to see if there is a habitable zone around this star.
Habitability[]
To calculate the Habitable Zone around Ross 154, we need to run two simulations: one with the star without flares and one with flares.
Without flares, the star emits light according to the blackbody theory. This implies the following values (compared to our sun, Sol, for which all values are considered 1):
- Solar Constant (Ks): 0.0111
- Infrared light: 0.0254
- Red light: 0.00811
- Visible (yellow) light: 0.00476
- Blue light: 0.00274
- UV light: 0.00000446.
Based on the solar constant, the limits where terraforming is possible become:
- Inner limit for Anti-Greenhouse Technology, where Ks is 20x Earth's: 0.0236 AU
- The orbit of an Earth-Like Planet, where Ks equals Earth's: 0.105 AU
- Outer limit for Greenhouse Gases, where Ks is 1/1000 of Earth's: 3.34 AU.
- Additional outer constraint: where red light is too dim for plants (1/1000 Earth's): 2.85 AU
- Additional outer constraint: where blue light is too dim for plants (1/1000 Earth's): 1.44 AU
- Additional inner constraint: where UV radiation is too strong (100x Earth's): 0.000211 AU
The resulting habitable area where terraforming is feasible is 0.0236 - 1.44 AU.
To get a model for Ross 359 with flares, we need to increase stellar temperature until the star shines 30 times brighter. This is possible if we increase temperature from 3340 to 13380 K. Again, all values are given compared to Sol, where all values are normalized at 1:
- Solar Constant (Ks): 0.334
- Infrared light: 0.121
- Red light: 0.220
- Visible (yellow) light: 0.293
- Blue light: 0.463
- UV light: 18.1
Based on the solar constant, the limits where terraforming is possible become:
- Inner limit for Anti-Greenhouse Technology, where Ks is 20x Earth's: 0.129 AU
- The orbit of an Earth-Like Planet, where Ks equals Earth's: 0.578 AU
- Outer limit for Greenhouse Gases, where Ks is 1/1000 of Earth's: 18.3 AU.
- Additional outer constraint: where red light is too dim for plants (1/1000 Earth's): 14.8 AU
- Additional outer constraint: where blue light is too dim for plants (1/1000 Earth's): 21.2 AU
- Additional inner constraint: where UV radiation is too strong (100x Earth's): 0.426 AU
The resulting habitable area where terraforming is feasible is 0.426 - 14.8 AU.
This simulation shows us how Ross 154 looks like with and without flares. What we need to do next is compare the values:
- 0.0236 - 1.44 AU without flares
- 0.426 - 14.8 AU with flares.
A safe area can be seen between 0.426 and 1.44 AU. This is the best place for a planet to be terraformed. It has enough light for plants to grow, Earth-like temperature can be achieved and UV radiation is not too high, both during flares and without flare activity.
Since flares don't last continuously, it might be possible for a planet to be terraformed even closer to the star. Maybe between 0.3 and 0.426 AU, the atmosphere can mediate effects of flares, while plants and animals can learn to live with UV and X bursts.
Also, the added light (especially blue) and heat that occurs during flares might allow for planets located further away to be terraformed, probably between 1.44 and 2 AU.
Planetary System[]
No planets have been detected or proposed around Ross 154. If they exist, they must be smaller then Earth or very far, otherwise they would have been found. No dust or asteroid disks have been identified, too, which is rather unusual for a young star.
Being a flare star, Ross 154 has a strong Stellar Wind for its size, about 20% the strength of our sun's solar wind.
Whatever planets and asteroids orbit closer then 0.6 AU, are expected to lack water, as, during flare activity, temperature rises significantly and water sublimates. This is despite the fact that, otherwise, at 0.6 AU, one would expect temperatures similar to Jupiter's moons in the Solar System. In the same way, at 2 AU, where temperatures should be similar to Solar System's Kuiper Belt, carbon dioxide and ammonia are expected to sublimate during flare events. This would create severe problems, as settlers will have to carry nitrogen ice from far away in order to terraform any planet.
Also, because of flares and the stellar wind they create, it is highly likely that most planets below 1 AU lost their atmospheres.
Conclusion[]
Ross 154 is a very challenging star. Having a predictable flare activity, terraforming is possible, but not easy.