Wolf 359 is one of the nearest stars to the Solar System. It is very dim and only visible with a good telescope. It is also known as CN Leonis. Wolf 359 is a main sequence, dim M - type star (a red dwarf) and a flare star, hence her spectral classification is M6Ve. For more details, see Main Sequence Stars, M-Type Stars and Flare Stars.
Wolf 359 appears in many works of fiction, often with its other name, CN Leonis.
Characteristics[]
Located in the constelation Leo, at only 7.86 light years from us, this dim star is so dim that it appears to have a magnitude of only 13.5, too dim to be visible through amateur telescopes. It has a mass of only 11% of our sun, Sol, a radius of 14.4% of Sol's and a surface temperature of 2750 K. Most of its energy output is in the infrared spectra and most of its visible light is red.
The star is small, slightly above the minimum mass required to fuse hydrogen. Because of this, fusion reactions are very slow. Wolf 359 has convective currents which mix matter between its core and its surface, allowing for virtually all hydrogen to be fused. These currents disturb the magnetic field and create spectacular flares. Also, because of slow hydrogen fusion, Wolf 359 will still be around here 7 to 8 trillion years from now. The star is considered very young.
Another aspect, specific to cool stars like Wolf 359, is the presence of chemical compounds in its photosphere, like titanium oxide or carbon monoxide.
Wolf 359 is known to be an eruptive flare star. Flare Stars are known to periodically emit flares (coronal mass ejections) that overshine the star's luminosity by many orders of magnitude. Its flares occur often and unpredictable, eroding atmospheres of possible planets and compromising terraformed worlds. Flares that radiate 100 times more light then the star itself are commonly detected, while microflares are supposed to occur almost continuously. Because of its flare activity, terraforming of any planets is basically impossible without far-future technology. Flares feed a dense Stellar Wind, which also erodes atmospheres of close orbiting planets. Like most M - type stars, Wolf 359 is expected to have a highly irregular heliosphere, with massive plumes advancing into interstellar space and large gaps allowing for cosmic rays to move close to the star. Flares start without a warning, within seconds they outshine the star, glow for minutes and then fade away.
Because of coronal activity, the star emits ultraviolet and X rays. As microflares occur almost continuously, there is an almost continuous emission of such radiation, which, during larger flares, reaches deadly doses.
Habitability[]
Wolf 359 is a dim star, which emits most of its light in infrared, most of its visible light in red and only little blue light.
- Solar Constant (total energy output): 0.00223 (Sol = 1)
- Red light: 0.00111 (Sol = 1)
- Visible (yellow) light: 0.000488 (Sol = 1)
- Blue light: 0.000138 (Sol = 1).
As one can see, Wolf 359 emits over 10 times more red then blue light.
An Earth - like planet would orbit at 0.0473 AU from the star, where the solar constant would be 1 (equal with Earth's).
Using Anti-Greenhouse Technology, one might argue that terraforming is possible even when the solar constant reaches a value of 20, which is achieved at a distance of 0.0106 AU. However, any Inner Planet will hardly survive the flares and will have its artificial atmosphere eroded fast. So, the inner limit should be considered much further, perhaps at 0.035 AU.
The further out, where Greenhouse Gases can keep a planet warm enough to have liquid water, where solar constant is 1/1000, is at 1.494 AU. However, plants need both red and blue light in an amount of at least 1/1000 of what is found on Earth. The outer limit for blue light is at 0.371 AU. Beyond that, plants will need artificial light to survive.
So, a safe estimation is that habitability around this star is between 0.035 and 0.37 AU. On the other hand, there is no way life can easily survive when powerful flares frequently increase ground temperature to over 500 degrees C and UV and X radiation sterilize all life it encounters. Conventional terraforming is out of question without planetary shields possibly developed in the far future.
On any celestial body orbiting Wolf 359, we talk about Paraterraforming, with domes and structures that can be covered in the event of a flare. Human settlements should be built underground. Warning systems should work continuously and advice people to take shelter immediately when a flare is imminent. Spaceships will be particularly affected and need to plan their journeys between the flares or use a protective shield. Each flare triggers an electromagnetic storm, which can render all electronics unfunctional.
Planets[]
Over time, not many planets have been proposed for Wolf 359. Still, recent data suggests that there might be two: a super-Earth and a Neptune-mass planet:
- Planet c: 3.8 Earth masses, orbits at 0.018 AU in 2.69 days.
- Planet b: 44 Earth masses, orbits at 1.845 AU in 2938 days.
Planet c[]
At 3.8 Earth masses, this planet is a Super-Earth. It is located very close to the star, at 0.018 AU. At that distance, Temperature must be high, around 300 C. Given the tidal forces at such a close orbit, it must be a Tidal Locked Planet, with one hemisphere experiencing endless daylight and the opposite one witnessing eternal darkness.
Having enough mass and being exposed to tidal stress, it is highly likely that planet c has its own magnetic field. However, there is no way a planet, so close to an eruptive flare star, to prevent stellar wind from erupting flares from touching the atmosphere. Volcanism might partially replenish the atmosphere. UV and X radiation would hydrolyse water molecules, releasing hydrogen and oxygen into space.
Even the dark hemisphere will not be quite safe. Sometimes, flares might just pass and shine from behind. Even if they will not release the same amount of heat, they will still release ionizing radiation. So, it is questionable if we might find water ice on the dark side.
The planet orbits very close to the star and has a narrow Hill sphere. It is unlikely that it has a satellite.
Planet b[]
This planet, having a mass of 44 Earths, is something comparable to Neptune. Estimated temperature is -208 degrees C, which is similar to Neptune in the Solar System. At 1.845 AU, it is too far to have enough light for plants to survive.
This planet should be far enough to survive flares. At its orbit, the effect of a flare outshining the star 100 times will be of -80 C. While this value is negligible for human life, it can still make some volatiles, like carbon dioxide, found in ices on the moons of Uranus and Neptune, to sublimate and be lost in space.
The stellar wind, which is about 20% of Sol's, should be felt like 6% of the solar wind felt at Earth's orbit in the Solar System. Of course, the stellar wind is far stronger when coming directly from a superflare, but still manageable. The planet most likely has a magnetic field.
Planet b should be in many aspects similar to Neptune in the Solar System and might have satellites, covered with water ice.
Others[]
Despite being a young star, Wolf 359 does not have any detectable dust disks, Kuiper belts or asteroid belts.
One cannot rule out the existence of smaller planets, in the size of Mars or like the moons of Jupiter or Saturn. Such objects have not been detected yet.
In Sci - Fi[]
Wolf 359 (or CN Leonis) appears in various sci-fi novels and movies. The most known apparition is probably in Star Trek. Around this star, a battle takes place between the humans and the Borg. Elite Dangerous lists CN Leonis as an industrial and mining system. In a Soviet sci-fi novel, the system appears as owned by a large capitalist corporation, Leo Baroni, exploiting the entire population through hard labour in mines and factories. Another novel points that an advanced civilization inhabits a planet in this system and its settlers influenced the Aztecs on Earth.
The truth is, whatever planets exist in Wolf 359 system, they are unsuitable for terraforming (see Where terraforming is impossible). The only future this system has is Industrial Colonization, especially if important resources are found there.