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Proxima Centauri


Diche Bach
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Recently, there has been much interest in Sol's closest known stellar neighbor,  Proxima Centauri  (4.224 light years away), owing to the August 2016 discovery of a near-Earth-sized terrestrial planet orbiting it within its "habitable zone," an orbital range within which the temperature could allow liquid water.

However, some more recent analyses suggests that, the planets exposure to high-energy ultra-violet radiation probably means: No Earth-like atmosphere for Proxima b.

Even more fascinating, just yesterday it was reported that ALMA discovered dust belts and an 'unkown source' around the star.

In years past, I can recall the star being dismissed in terms of its prospects to host habitable candidate exoplanets, mainly because it is such small red dwarf star. In hindsight, clearly, we have not heard the last from Proxima Centauri!  So I thought a general purpose thread to discuss the star and any future discoveries or analyses pertaining to it would be apt.

For my purposes at this point, I'm curious about a couple questions:

(1) How far would the "radiation kill zone" described in the "No Earth-like atmosphere" article extend out from the star? My physics is too elementary for me to know if the bad rads the article focuses on (apparently " high-energy extreme ultraviolet radiation" is the main culprit?) would have diminishing effects at any of the distances involved (e.g., "30 AU to the outer 'Cold Belt' described in the more recent ALMA discovery).

(2) How large or potent of a magnetosphere would be required to "protect" Proxima b from the atmosphere-stripping effects described?

(3) Are there geologically and cosmologically feasible processes which could shield a celestial body from the harmful rads described? For example, (and going entirely hypothetical here, not referring specifically to any features known about the Proxima system) could a moon orbiting a large parent (say Neptune) with a large enough magnetosphere be protected?

Lastly,

(4) I was edified some years ago when one of the more knowledgeable KSP forum members clarified that Jupiter is highly radioactive. I wonder if, under certain special circumstances, a combination of a star and a more proximal parent body might allow for surface liquid water on some moons somewhere out there? Yes I'm aware that several of the outer planet moons are thought quite strongly to have liquid water under large bodies of ice, but I'm just curious if a parent planet of "just right" configuration might emit just the right wavelengths (while not being a 'star' though perhaps toward the 'brown dwarf stage?) to keep a moon sufficiently warm and protected from cosmic radiation?

-=-=-

Beyond that, hopefully the thread might turn into a good multi-purpose general thread about the Proxima system!

I appreciate anyone's comments or thoughts!

Edited by Diche Bach
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Hi,

i doubt any one of your questions can be answered with a clear figure. These are all model calculations based on a few real life observations and a lot of added and mixed assumptions, aka guessing.

We don't even know Proxima b's exact orbital parameters, nor its exact radius or mass or even if it has an atmosphere. We don't know the sun's magnetosphere, only its mass and surface temperature and that it has a high metallicity.

Moar data :-)

Let's wait for GMT, E-ELT and TMT and until then have a T and speculate.

 

Edit: to (3) and the reference to geology: on earth a partly molten iron core did help, together with temperature differences in the inner core and some sort of convection, transformed into sort of a helical movement by Coriolis forces from the rotation of the whole thing.

Would it suffice elsewhere ? What if it is tidally locked ? Would that block or lessen a magnetic field ? *shrug*

 

Edited by Green Baron
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Afaik for example Mercury's magnetic field isn't by far strong enough to stand against the solar wind. Also a magnetic field does shield against charged particles and but how much does it shield from radiation like x-ray or uv ? Would you for such a shielding to be effective need special atmospheric configurations (like in earth ;-)) ?

Skin cancer in Australia 'cause higher uv levels ;-/

Edited by Green Baron
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Well, the issue with Proxima b seems to be that the high rate of rads bathing the rock would have ionized the molecules that would have been its nascent atmosphere thus "stripping" it of its atmosphere over time.

ADDIT: and that is, I presume based on an assumed magnetosphere for Proxima b that falls within the "expected range" for a rock of its size and suspect composition.

So my question(s) is(are):

1. How big/powerful does a magnetosphere have to be to prevent that level or solar atmosphere killing

2. Is it even possible for a magnetosphere to do that?

3. Are there other ways that an atmosphere could have "survived" within a close enough range to Proxima that they are "warm enough" for liquid water (thus the interest in moons of frozen giants).

Edited by Diche Bach
elaboration of the main questions for getting the thread going
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4 hours ago, Green Baron said:

Afaik for example Mercury's magnetic field isn't by far strong enough to stand against the solar wind. Also a magnetic field does shield against charged particles and but how much does it shield from radiation like x-ray or uv ? Would you for such a shielding to be effective need special atmospheric configurations (like in earth ;-)) ?

Skin cancer in Australia 'cause higher uv levels ;-/

An magnetic field only protect against charged particles not standard radiation. However charged particles hurt the top of the atmosphere a lot. x-rays get absorbed deeper down.

Australia get lot of skin cancer. Obviously population has light skin, but so with lots of people in south America. But might well be more watered out and less good data, say Brazil probably don't differentiate on skin color in skin cancer statistic. 
 

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Okay, I'll answer this according to OP's questioning.

1) You know that Proxima Centauri is a red dwarf right ? They don't normally emit UV and X-ray - in fact, their emission is such of a low-energy one that many have questioned whether photochemical water breaking process found in chlorophyll back on Earth is possible on such bodies.

2) As with above, not much.

1, 2 & 3) Red dwarfs are known to have "tantrums" every now and then. Star Flares so to speak. The biggest problem a close-orbiting-planet faces is that they're more vulnerable to get a hit of these flares at maximum energy.

Is there anything one can do to avoid them ?

Well, not much. Even a magnetic field as strong as the Earth's isn't strong enough to hold some historical solar flares. Now, getting some 30 magnitude greater than that (almost 10^30) ? Really ?

4) Actually, that have some probability of becoming "safer". The only problem is, sometimes, you end up being the "butterfly net" catching up these particles. See Io.

Edited by YNM
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1 hour ago, wumpus said:

There is also the issue that you can expect any planets to be tidally locked to its sun.  The only way to get a magnetosphere is if said tidal lock is somewhat faster than 1:1 (like Mercury's 3:2 resonance).

Ah didn't realize magnetosphere depended on spin . . . However, are you sure that spin is ESSENTIAL to the existence of a potent magnetosphere?

Quote

The structure and behavior of magnetospheres are dependent on several variables: the type of astronomical object, the nature of sources of plasma and momentum, the period of the object's spin, the nature of the axis about which the object spins, the axis of the magnetic dipole, and the magnitude and direction of the flow of solar wind.

The distance at which a planet can withstand the solar wind pressure is called the Chapman–Ferraro distance. This is modeled by a formula wherein {\displaystyle R_{P}}R_{P} represents the radius of the planet, {\displaystyle B_{surf}}B_{{surf}} represents the magnetic field on the surface of the planet at the equator, and {\displaystyle V_{SW}}V_{{SW}}represents the velocity of the solar wind:

{\displaystyle R_{CF}=R_{P}\left({\frac {B_{surf}^{2}}{\mu _{0}\rho V_{SW}^{2}}}\right)^{\frac {1}{6}}}R_{CF}=R_{P}\left({\frac {B_{surf}^{2}}{\mu _{0}\rho V_{SW}^{2}}}\right)^{\frac {1}{6}}

A magnetosphere is classified as "intrinsic" when {\displaystyle R_{CF}\gg R_{P}}R_{CF}\gg R_{P}, or when the primary opposition to the flow of solar wind is the magnetic field of the object. Mercury, Earth, Jupiter, Ganymede, Saturn, Uranus, and Neptune exhibit intrinsic magnetospheres. A magnetosphere is classified as "induced" when {\displaystyle R_{CF}\ll R_{P}}R_{CF}\ll R_{P}, or when the solar wind is not opposed by the object's magnetic field. In this case, the solar wind interacts with the atmosphere or ionosphere of the planet (or surface of the planet, if the planet has no atmosphere). Venus has an induced magnetic field, which means that because Venus appears to have no internal dynamo effect, the only magnetic field present is that formed by the solar wind's wrapping around the physical obstacle of Venus (see also Venus' induced magnetosphere). When {\displaystyle R_{CF}\approx R_{P}}R_{CF}\approx R_{P}, the planet itself and its magnetic field both contribute. It is possible that Mars is of this type.[5]

At another point in that wiki, there is mention of Dynamo Theory

As I said in OP, I'm happy for this thread to become a general purpose "all about Proxima Centauri" thread. But for my specific purposes right now, I want to know effectively "how much soft sci-fi arm-waving" would in fact be necessary to concoct an imaginary planet around Proxima Centauri that had at least SOME breathable atmosphere (maybe not 20% O^2, but perhaps 17 or 18%?).

Is it conceivable, that a planet has such a dynamic dynamo effect that it can produce a ridiculously powerful magnetosphere? 

Ah! It appears you are correct Wumpus. Spin IS required to generate an internal magnetosphere

Quote

There are three requisites for a dynamo to operate:

  • An electrically conductive fluid medium
  • Kinetic energy provided by planetary rotation
  • An internal energy source to drive convective motions within the fluid.[10]

In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core. A requirement for the induction of field is a rotating fluid. Rotation in the outer core is supplied by the Coriolis effect caused by the rotation of the Earth. The Coriolis force tends to organize fluid motions and electric currents into columns (also see Taylor columns) aligned with the rotation axis. Induction or creation of magnetic field is described by the induction equation:

I suppose however, that other processes MIGHT serve as a source of "rotation in the outer core." Tidal effects? Really rapid continental drift?

Edited by Diche Bach
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From a link Green Baron posted in the Mars thread  . . . Oh hey! I can use this! Vulcanology to the rescue!

Martian Paleoclimatology

Quote

Some scientists maintain that the great mass of the Tharsis volcanoes has had a major influence on Mars's climate. Erupting volcanoes give off great amounts of gas, mainly water vapor and CO2. Enough gas may have been released by volcanoes to have made the earlier Martian atmosphere thicker than Earth's. The volcanoes could also have emitted enough H2O to cover the whole Martian surface to a depth of 120 m (390 ft). CO2 is a greenhouse gas that raises the temperature of a planet: it traps heat by absorbing infrared radiation. So Tharsis volcanoes, by giving off CO2, could have made Mars more Earth-like in the past. Mars may have once had a much thicker and warmer atmosphere, and oceans and/or lakes may have been present.[10] It has, however, proven extremely difficult to construct convincing global climate models for Mars which produce temperatures above 0 °C at any point in its history,[11] although this may simply reflect problems in accurately calibrating such models.

That actually dovetails nicely with other design imperatives so I'll consider my questions in OP answered sufficient to reach the "tin" or "tinny" stage of on the soft-to-hard Science Fiction continuum . . .

 

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I see speculation whether the light from a red dwarf is sufficient to support photosynthesis (in chlorophyll, which is the only significant photosynthetic molecule in the Earth's biophere).  I had occasion not long ago to look up the surface temperature of another red dwarf, Gliese 581: 3,480 K.  Proxima's surface temperature is lower, at a mere 3,042 K.  However: a halogen lamp's filament (which outputs enough UV to give you a sunburn, with prolonged exposure to an unshielded lamp) runs at about 3200 K -- meaning Gliese 581 should be whiter than a halogen, and Proxima is still hotter than a common incandescent filament (which at 2700 K won't give you a sunburn, but will still support growth of plants, if they're "shade loving" species).

Both of these stars would look white to the naked eye unless there was a similarly strong, hotter source for comparison.  Both would support a large fraction of Earth's green life, other factors being amenable.  Both would likely give you a sunburn with long enough exposure, though Proxima would take a lot of exposure on unacclimated skin to do it, even at a distance where insolation matches that of Earth by our Sun.

I've also read that Proxima is a relatively old red dwarf, and as such has "settled down" -- become less prone to flares.  That leaves tide-locking as (in my mind, at least) the biggest obstacle to the presence of life on a planet orbiting Proxima in the liquid-water zone.

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2 hours ago, Zeiss Ikon said:

halogen lamp

... Which is tungsten and is filtered by an atmosphere of halogen. They're not representative of stars...

13 hours ago, Diche Bach said:

Thanks YNM. Somewhat disheartening.

Earth really is a gem, isn't it?

... Nah, don't be too dissappointed.

There's still a continuum where life could exists. All our searches of life have centered on life as we know it on Earth. It doesn't stave off possibility for other creations of life.

For instance, despite the questioning, PS I and PS II in plants use 680 nm and 700 nm wavelength each. They're still in the range where there would be emitted well. So it's still possible for such mechanism to occur - albeit a bit more slowly.

Basically, as you're getting less energy, things go a bit slow. And that's where people are voicing their concern - how slow ?

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On 11/3/2017 at 10:40 PM, YNM said:

Okay, I'll answer this according to OP's questioning.

1) You know that Proxima Centauri is a red dwarf right ? They don't normally emit UV and X-ray - in fact, their emission is such of a low-energy one that many have questioned whether photochemical water breaking process found in chlorophyll back on Earth is possible on such bodies.

2) As with above, not much.

1, 2 & 3) Red dwarfs are known to have "tantrums" every now and then. Star Flares so to speak. The biggest problem a close-orbiting-planet faces is that they're more vulnerable to get a hit of these flares at maximum energy.

Is there anything one can do to avoid them ?

Well, not much. Even a magnetic field as strong as the Earth's isn't strong enough to hold some historical solar flares. Now, getting some 30 magnitude greater than that (almost 10^30) ? Really ?

4) Actually, that have some probability of becoming "safer". The only problem is, sometimes, you end up being the "butterfly net" catching up these particles. See Io.

Agreeing with much of what you say. During tantrums the spectra does shift somewhat, and it has been theorized that these tantrums can cause close orbiting planets to be degassed.

The problem with excessive unprotected UV and X-radiation is in the lighter elements (Hydrogen, helium) Xrays in particular are known to exert nuclear force (it is the xradiation in an H-bomb that compresses the nucleus of the bomb allowing detonation with a much lower critical mass) of fissile material. It is believed that the exposure of Venus to higher levels of solar radiation depleted the atmosphere of hydrogen, water, some carbon and oxygen until it was stabilized by sulfate. The absorption spectrum for hydrogen has strong and weak bands. UV hitting a strong band can kick off an electron cause the proton to repel other protons. If you kick the electron off a sulfate molecule or hit it with an X-ray its not going to react nearly as strongly (in terms of acceleration) as a hydrogen or helium might.

The thing that we have to remember that in the early days of a potentially habitable planet the hydrogen is in many forms, hydrogen, methane, ammonia, etc. In a two step process the hydrogen can be kicked from the molecule and then kicked from the atmosphere of the planet by ionization and then interaction with magnetic storms or being pummeled by xrays.

Quote

Proxima CentauriEdit

The Sun's nearest stellar neighbor Proxima Centauri is a flare star that undergoes occasional increases in brightness because of magnetic activity.[5] The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. - https://en.m.wikipedia.org/wiki/Flare_star

This is a problem for stars closer to proxima centuari than venus is to the sun. For most small stars the habitable zone is just such close to its star and thus the habitable zone of most M class stars would be in the zone were flares could strip the atmosphere of its lightest gases.

 

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11 hours ago, Green Baron said:

New work on Proxima C.:

https://arxiv.org/abs/1711.00578

 

I think a paper is about being published in the Astrophysical Journal.

That seems to be the abstract for the blurb in one of the links I posted in the OP.

Haven't read the PDF yet. When you say "Proxima C" do you mean the "Cold dust belt" or the "unknown source" that they identified just on the inside edge of that intermediate position cold belt?

I'm leaning toward a very small dense planet with a core disproportionately made of osmium or some other very high density metal, very volcanic, permanent ice age with only relict oceans, very seismically active, no native vertebrates, though some simple animals forms and quite a few plant/fungi forms. Insufficient atmosphere but breathable for brief periods (perhaps about like being above Base Camp III on Everest? . . . not sure if 21% O2 composition but lower pressure, or lower O2 or a combination of both is better . . .). That all fits nicely with the project objectives and doesn't seem like it stretches plausibly horrifically . . . end of the day, it is sci-fi, so some "stretching" is inherent.

Still haven't decided on the orbit. That "habitable" zone is quite close and the logic that tidal locking is inherent at that range from the star seems fairly "law like." But then 40K for that "cold dust" belt, is clearly not warm enough for anything that couldn't evolve in a ice cube

Edited by Diche Bach
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9 hours ago, Diche Bach said:

That seems to be the abstract for the blurb in one of the links I posted in the OP.

Haven't read the PDF yet. When you say "Proxima C" do you mean the "Cold dust belt" or the "unknown source" that they identified just on the inside edge of that intermediate position cold belt?

I'm leaning toward a very small dense planet with a core disproportionately made of osmium or some other very high density metal, very volcanic, permanent ice age with only relict oceans, very seismically active, no native vertebrates, though some simple animals forms and quite a few plant/fungi forms. Insufficient atmosphere but breathable for brief periods (perhaps about like being above Base Camp III on Everest? . . . not sure if 21% O2 composition but lower pressure, or lower O2 or a combination of both is better . . .). That all fits nicely with the project objectives and doesn't seem like it stretches plausibly horrifically . . . end of the day, it is sci-fi, so some "stretching" is inherent.

Still haven't decided on the orbit. That "habitable" zone is quite close and the logic that tidal locking is inherent at that range from the star seems fairly "law like." But then 40K for that "cold dust" belt, is clearly not warm enough for anything that couldn't evolve in a ice cube

I say its completely lifeless spare the odd bacteria living in a gravitationally heated underground crevace 10 to 20 miles underground.

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21 hours ago, Diche Bach said:

I'm leaning toward a very small dense planet with a core disproportionately made of osmium or some other very high density metal, very volcanic, permanent ice age with only relict oceans, very seismically active, no native vertebrates, though some simple animals forms and quite a few plant/fungi forms.

No.

That's not how planets work, and 1.6 AU is well beyond the habitable zone of Proxima.

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Proxima Centauri is not the right place to look for or construct potentially habitable planets.

Unrelated: would it be possible to scan the recently fabricated star catalogues for the dispersed members of the cluster our sun is from ? I know they exist and some have been identified by relative movement. I would speculate that among those might be candidates that might have a similar composition and history to our solar system and thus (wildly speculating) maybe there is a higher probability for you know what i mean. Also, wouldn't it make for a nice story ?

But, really, i do not know.

Edited by Green Baron
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9 hours ago, Green Baron said:

Proxima Centauri is not the right place to look for or construct potentially habitable planets.

Unrelated: would it be possible to scan the recently fabricated star catalogues for the dispersed members of the cluster our sun is from ? I know they exist and some have been identified by relative movement. I would speculate that among those might be candidates that might have a similar composition and history to our solar system and thus (wildly speculating) maybe there is a higher probability for you know what i mean. Also, wouldn't it make for a nice story ?

But, really, i do not know.

I don't quite follow what you are referring to.

ADDIT: Well, correct me if I'm wrong but . . . the Moon, Mars, and even some of the Moons in the outer solar system are all "potentially habitable" aren't they!? Not to mention many of the larger asteroids.

Edited by Diche Bach
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10 hours ago, _Augustus_ said:

No.

That's not how planets work, and 1.6 AU is well beyond the habitable zone of Proxima.

Well what is the "most hospitable" planet you could imagine around Proxima? When you say "not how planets" work: (a) what specifically are you referring to and (b) what evidence are you referring to?

Making it as _close_ to plausible is a goal. In fact, the planet does not necessarily need to be any more habitable than Mars for the story to forge ahead.

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4 hours ago, Diche Bach said:

I don't quite follow what you are referring to.

Morning :-)

I simply wanted to say that stars with the same origin and a similar history might have developed systems with similar features compared to our system. But that is only a very basic thought of mine based on the view that the sun didn't form alone, it was part of an open cluster that has since then dispersed but members are still identifiable.

Quote

ADDIT: Well, correct me if I'm wrong but . . . the Moon, Mars, and even some of the Moons in the outer solar system are all "potentially habitable" aren't they!? Not to mention many of the larger asteroids.

I must because this impression may arise when browsing through the forum.

The Moon is not habitable at all and has never been. Nobody regards it as potentially habitable. The Mars is not habitable at all but it can be speculated that it has been in its early history. Too little is known about the moons of the gas giants, but they all are regarded dead places. Speculations about Europa having an ocean under its icy shell still have to be confirmed, and the cause for the fountains in the southern area that have led to wild speculation about vents and life analogous to earth(!) is unclear, probable shifts in the icy shell where the last i read about it.

Same with speculations about Ganimede's postulated subsurface ocean. The surfaces of all the moons are cold and radiated, no life can be there. It is only tat a long row of speculations and analogies may construct the possibilities of subglacial life on 2 or 3 of them, but there is no evidence in that direction yet.

Not one asteroid is regarded potentially habitable, where is that from ? Asteroids are dead rocks without atmospheres exposed to interplanetary temperature and radiation levels.

 

Edit: well, with the help of a set of fictitious technology everything is "habitable". Until the technology needs repair.

Concerning technology: aren't people constructing space ships to fly around the moon in the coming years ? :-)

 

Edited by Green Baron
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I think we must be using different terminology. I'm using "habitable" to refer to whether humans (and their animals and plants) could, under ANY reasonable technology INHABIT a celestial body. Admittedly, the closed-loop arcological designs that would require for sustainable self-sufficient moon bases (not to mention the enormous cost, time and resources necessary to build such a thing at a scale that made any sense) remain out of our grasp. Proponents of such things have yet to successful create them in the most forgiving of settings (e.g., rural Arizona) much less antarctica or the Gobi desert or 100m under the surface of the ocean or in orbit.

The Sun on the other hand is clearly UNINHABITABLE, as is I gather Jupiter and I would assume Saturn and Neptune: meaning it is not conceivable based on the physical and chemical rules we presently see ourselves bound by, that human inhabitants will EVER dwell on any of these bodies.

What you seem to be referring to by the term "inhabitable" is what I would refer to as "capacity for sustainable in situ life" if not "natal territory in which life evolved" (the former leaving open the possibility for some sort of exotic panspermia event in the distant past which seems highly unlikely but probably cannot be ruled out completely).

-=-=-=-

As to the question of "Habitable" Planets in our Solar System (and I'm not asserting my perfect accuracy and open to debate)

Mars, many asteroids, Luna, many Jovian and Saturnian and possibly Neptunian moons: inhabitable

Many orbital or Lagrange positions within the solar system: inhabitable!

Venus, and Mercury, Neptune and Saturn: probably not inhabitable

Sun, Jupiter and probably a large fraction of every other rock in the system: not inhabitable.

-=-=-=-

As to the question of "capacity to provide a home for local life"

Mars, and some of the outer planet moons (I can never keep them straight and the seem to be fairly numerous): could conceivably have some local life clinging to existence somewhere on board. That is probably just about it . . .

The discovery of amino acids on a comet strikes me as rather stunning and it tempts me to speculate that extremophile very simple life MIGHT exist on some of the larger minor planets or asteroids. But that strikes me as highly unlikely.

Edited by Diche Bach
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