Lalande 21185 is one of the nearest star to the Solar System. Its dim red light includes it among the M-Type Stars, where it is classified as an M2V star. While most M - type stars are Flare Stars, Lalande is much calmer. It is known to have occasional small flares (microflares), while big flares, common to stars like UV Ceti or Proxima Cen of the Alpha Centauri system), have never been detected around Lalande.
Since the 1950's, scientists suspected that Lalande 21185 has planets. While most claims have been refuted over time, currently, we know that some planets do exist around the star.
Star Properties[]
Lalande 21185 is a bright M - type star. Its mass is 39% of our sun's, Sol, its radius is 39% of Sol's and its surface temperature is 3600 K. The star produces X rays, which means its corona is active, but by far not in a too large quantity. It is known to have occasional flares, but again, they are too dim, never shining brighter then the star itself. For comparison, UV Ceti was recorded to emit a flare that overshined the star 75 times. Most of the light emitted by the star is in infrared, with more red then blue among the visible spectra. Ultraviolet light is dim.
By analysing the light emitted and using a computer simulation, we can calculate the following:
- Solar Constant: 0.0372 (Sol = 1)
- Near infrared light: 0.0766 (Sol = 1)
- Red light: 0.0301 (Sol = 1)
- Visible (yellow) light: 0.0194 (Sol = 1)
- Blue light: 0.00978 (Sol = 1)
- Near UV light: 0.0000604 (Sol = 1)
These numbers are rounded for an easy comparation with Sol, our sun. As one can see, Lalande 21185 produces more infrared then visible light, more red then blue light and almost no ultraviolet light. This will have profound implications for life.
Habitable Zone[]
By using Greenhouse Gases, one can terraform a planet that experiences temperatures of -200 C or at the orbit of Neptune in the Solar System. Greenhouse gasses offer a great thermal insulation and can retain heat even for a planet which receives a solar constant of 1/1000 to Earth's.
The use of Anti-Greenhouse Technology allows us to terraform planets located too close to their stars. The limit of this technology seems to be where the solar constant is 20 times higher then Earth's.
In case of Lalande 21185, the area where temperature on a planet can be controlled to make it habitable is between 0.0431 and 6.099 AU, with the orbit of a Habitable Zone Planet is at 0.193 AU.
On the other hand, Earth-like plants need light and they need both red and blue light. The limit for light is 1/1000 of what plants have on Earth. If either red or blue light falls below this limit, superior plants cannot survive. For Lalande 21185, the outer limit for red light is 5.49 AU and for blue light is 3.13 AU. Because of this, the area where a planet can be terraformed is reduced to 3.13 AU.
There are also a few other limits, like the fact that Lalande 21185 has occasional flares and a close inner planet would experience strong tidal stresses. However, these factors are difficult to include into a computer simulations. Based only on the parameters listed above, the area where a planet would be terraformable extends from 0.0431 to 3.13 AU, with the orbit of a habitable zone planet at 0.193 AU.
Planets[]
There have been repeated claims of planets around Lalande 21185. Peter van de Kamp suggested one, two or even three unseen companions to orbit around this star. His objects, by their mass, could be either planets or brown dwarfs. He did similar claims of planets around Barnard's Star, which were also proven to be fake. As for now (2022), we know of three planets. All planets proposed by Peter van de Kamp were supposed to orbit far away from the star, at over 7 AU. These planets would be easy to detect with today's technology.
- Planet b: 2.64 Earth masses, orbits at 0.0788 AU in 12.94 days.
- Planet d (unconfirmed): 4.1 Earth masses, orbits at 0.514 AU in 216 days.
- Planet c: 14.2 Earth masses, orbits at 2.845 AU in 2806 days.
Are these planets suitable for terraforming?
Planet b[]
Planet B orbits the star very close and experiences a similar solar constant with Mercury. Therefore, methods proposed to terraform Mercury should, in theory, work here too.
The planet is massive, 2.64 Earth masses. As so, it might hold an atmosphere, even if rarefied and similar to Mars. The planet should experience strong tidal friction from its slightly eccentric orbit and from the other planets. It must be a volcanic world. The atmosphere would be periodically eroded by flares and Stellar Wind, as the planet is too close to the star. It must also be tidal locked, which means its magnetic field cannot be too strong. The planet cannot defend itself against stellar wind and flares. Volcanism would gradually replenish the atmosphere lost through erosion. However, while volcanism brings carbon dioxide and sulphur, it does not replenish water and nitrogen.
The planet experiences a Solar Constant that is 5.99 stronger then Earth's and temperatures of 300 C. This is slightly cooler then Mercury. An atmosphere can create a greenhouse effect. However, it is unlikely that the planet has a thick atmosphere. Being tidal locked, the planet has a chance to accumulate water on the dark hemisphere.
For terraforming, the use of space mirrors is out of question, as the planet is very close to the star and has a small Hill sphere. There are no safe orbits around the planet and mirrors will tend to fall on the surface or be sent out of orbit. The use of Micro Helium Balloons seems to be the only option.
It is not known how volcanic the planet is. Colonization of the volcanic moon Io is impossible, as its huge volcanoes will render the atmosphere unbreathable and will disrupt the layer of greenhouse gasses needed. In the same way, if this planet is too volcanic, it might not be suitable for terraforming.
Planet d[]
This planet is as for now unconfirmed. It is located beyond the orbit of a Habitable Zone Planet and is out of the area where liquid water exists. However, terraforming might still be possible.
The planet has 4.1 Earth masses, so it is a Super-Earth. Mini Neptunes usually don't exist at this mass and so close to a star. Being further out, we can presume that its volcanism is far less active. The planet must have a stable and dense atmosphere. At its distance (0.514 AU), tidal forces are similar to Earth's, so we can presume that the planet is not tidal locked. Since it is more massive then the Earth, it can rotate for longer if exposed to the same tidal forces as Earth.
Surface temperature is expected to be -40 degrees C. There is a significant chance that this planet has an icy crust with a subsurface ocean, similar to the moons of Jupiter. However, as temperatures are higher, the crust should be less thick. Also, given its mass, the planet can support a dense atmosphere. If the atmosphere has plenty of carbon dioxide, which is a natural greenhouse gas, there is a chance that, at least in some areas, the ice crust can melt, exposing the ocean.
Terraforming of this planet could be relatively easy. It should have all the elements needed for life: water, carbon dioxide, light, a magnetic field and so on. However, there are two limitation factors. Firstly, because the planet is a super-Earth, its gravity is high. Humans will find it hard to adapt, to carry maybe twice their weight on their feet. Secondly, if the atmosphere is too dense, we would have to dispose some of the existing gas, which is not an easy task.
Planet c[]
At 14.2 Earth masses, this planet might be a Mega - Earth or could be one of the Mini Neptunes. Mega - Earths are something rare and usually they are cores of gas giants which have lost their gaseous envelopes. The planet orbits far, at 2.845 AU, a distance where temperature should be very low, of -170 degrees C. The solar constant is something like at the orbit of Uranus.
If the planet is a mini Neptune, is basically cannot be terraformed, as its surface (if it exists) lies very deep under the atmosphere, unable to be reached with any spaceship. However, there is a chance that this planet has one moon that can be suitable for terraforming. The techniques required for terraforming of such a moon should be similar to what was proposed for Triton.
The planet lies close to the end of the area where terraforming is possible (2.845 AU out of 3.13 AU). The main limiting factor is the lack of blue light. Because of this, plants will hardly grow and survive.
Given the mass and distance to the star, it is likely that this planet has a strong magnetic field which protects its innermost moons. Also, given the estimated temperature (-170 C), it is likely that water ice and carbon dioxide exist on its moons. If one moon has an atmosphere, it should have nitrogen and methane.
Conclusion[]
Lalande 21185 is a star that offers good conditions for terraforming. We know for now about the existence of two planets, maybe three, but there could be more out there.