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I'm currently working on a world for a fantasy novel. For the sake of this discussion, we can assume it's low to no magic at all, and has no higher-intelligence interference, such as creator races, aliens, or gods. The technological level of this world is similar to our Bronze Age.

Structurally, we can imagine our solar system, Earth, and its moon.

My question: I plan on having my moon coated in mushrooms or other living organisms that could shoot something, be it spores or debris or anything else in between, towards the host planet in order to spread spores there. How plausible would this be? I'm not looking for 100% scientific accuracy here, just enough to make it plausible. The nature of the flora inhabiting this moon, and the way through which it shoots off planet is not vitally important, I'm good with most options.

  • What situation would I need to create in order to have a moon with an atmosphere that could be infested with fungus and other life-forms, that could be capable of "seeding" the host planet on a cyclical basis?

My research:

Some discuss heavy numbers, which is something that in general confuses me a lot, and I have problems understanding. Others concern themselves with living planets and the way they could potentially move across space, which is not exactly what I'm looking for. Another one is quite close to what I intend, but not quite, as it discusses how a planet of this sort could shoot its spores to other solar systems, while I'm simply aiming for a Moon to Earth situation.

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  • $\begingroup$ Are your asking is a moon that shoots spores plausible, what would cause a moon to be infested with fungus or other lifeforms, or would a moon be capable of seeding it's planet on a cyclical basis? We have a strict one-question per post policy. Can you edit your post so that you're asking a single question? $\endgroup$
    – sphennings
    Commented May 26, 2022 at 21:49
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    $\begingroup$ Does this answer your question? Could plants spread their seed to other planets? $\endgroup$
    – Escaped dental patient.
    Commented May 26, 2022 at 22:54
  • $\begingroup$ I don't really have time to write a full answer - and anyone else is welcome to do so from this comment; But would geyser-like plumes similar to those detected on Europa (real life) work? Imagine a similar moon but with fungi all over. Some would definitely be in the seas, oceans w/e, and that could get ejected into space through other mechanisms of the moon. That would leave a bunch of secondary questions (would the spore survive in space) etc... but I think yes, the moon could eject fungi into space. $\endgroup$
    – Spacemonkey
    Commented May 26, 2022 at 23:27
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    $\begingroup$ Does it matter if it's plausible? Anne McCaffery's famous Dragonriders of Pern series of books had as its central plot element a rogue planet in a solar system with a spoor lifeform that jumped between planets when they grew closer together. Scientifically the entire premise of her books was completely implausible - but they're a great read, won awards, and made here a ton of money. Plausible is boring, especially when all you likely need is satisfactory suspension of disbelief. $\endgroup$
    – JBH
    Commented May 27, 2022 at 5:06

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Escape Velocity

The escape velocity of the Moon is 2.4 km/s. That is 8,500 km/h. This is a few times faster than the Blackbird spy plane but a few times slower than the ISS orbit speed. Much slower than the space shuttle taking off.

That means the spores need to be launched at a speed of 8,500 km/h to escape the Moon's gravity and have any hope of reaching Earth. They need something to launch them this fast and also need to survive the trip.

Now an orbiting asteroid would be easier than the Moon, since the escape velocity is negligible. But the spores still need to survive landing.

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  • $\begingroup$ I thought escape velocity is the speed at which an object must travel in order to enter orbit. The OP isn't concerned about orbiting the moon — just fast enough to make it to the region of space where the Earth's gravity becomes dominant. You could slow down to walking speed relative to the moon, and still make it to earth. Of course this lengthens the time spent in space, but if water bears can do it, why not fungal spores? $\endgroup$
    – Greg Burghardt
    Commented May 28, 2022 at 15:51
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    $\begingroup$ @GregBurghardt Escape velocity of the moon is the speed you have to throw a rock upwards from the surface and it will never fall back down. $\endgroup$
    – Daron
    Commented May 28, 2022 at 15:52
  • $\begingroup$ And even if you are launched from the Moon at lunar surface escape velocity, the result of that is that you're in an Earth orbit very similar to that of the Moon, to actually hit Earth from a single impulse, you have to be launched a little faster than that, with the combination of speed and direction that puts you in an earth orbit whose perigee intersects the Earth's surface. The energy budget required for biological un-aimed orbital mechanics shots is...astronomical. $\endgroup$
    – notovny
    Commented May 29, 2022 at 2:38
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This happened to us (maybe).

Mars is bigger than a typical moon. Nonetheless, the zodiacal light ("false dawn") has been determined to originate at Mars. It is dust from that planet's atmosphere that flies right up out of the planet's orbit, though it remains trapped by the Sun's gravity for a long time in the zone of the Solar system that extends outward from Mars orbit.

Some of this dust also heads in Earth's direction. Some scientists believe Earth life originated from Mars, because Mars was a small planet further from the Sun, quicker to cool down and form liquid water than Earth.

I'm not sure I buy that, but current consensus cannot rule out that your spores not merely are plausible but are the mother of us all.

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Geysers could carry spores

Jupiter's moon Europa has sweet water geysers that eject watery material into space. It seems quite plausible that these plumes could carry masses of small spores.

Europa is roughly the same size as the Moon, although it is much less massive (~10%) and has weaker surface gravity (~80%).

Crucially, Europa seems to be covered in water, and its surface temperature is always below freezing, so the planet's whole surface seems to be ice. Meanwhile, the interior is heated by tidal deformation. That is what makes the geyser situation work: the ice crust "shrink-wraps" the liquid ocean, and then the heating creates pressure that eventually punches through the ice with enough force to launch a spray "more than 20 times the height of Mt. Everest."

If there is life in Europa's ocean, it is probably already spewing biological material into space.

Your moon could be similar. For this to work, I think it cannot be a jungle-like world: the whole surface must be water and the surface temperature must be below freezing. It definitely must be extra sweet.

I don't know if this is compatible with fungus. Maybe there are organically created "geodes," made by ocean-dwelling plants, drifting in the comparatively warm depths, and filled with a kind of fungus. These geodes eventually break open (collisions, overgrowth, predation), disgorging their spores into the ocean water. Rinse and repeat for millions of years, and probably every geyser spews ocean-geode fungal spores into space.

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Solar wind

Solar winds can pick up spores descending from the mushroom. Some of these spores might end up on earth.

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I suggest reading Camelot 30K. Spoiler for major plot point:

The aliens reproduce by means of spores flung off the world by a hydrogen bomb. While I believe his aliens could never evolve the Plumbbob Pascal A test showed that you can certainly throw stuff that way--without the atmosphere interfering the well cap would have been thrown clear out of the solar system.

Also, does it have to be throw? Larry Niven's stage trees come to mind--bioengineered plants whose reproductive method is to grow a "tree" that's really a solid rocket booster.

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