I understand an interstellar dust cloud as "an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, (ISM), the matter and radiation that exists in the space between the star systems in a galaxy."

(I'm assuming it would be possible for Earth to cross one of these interstellar clouds, but tell me if I'm wrong, please)

  • $\begingroup$ This may help: discovermagazine.com/2008/whole-universe/… $\endgroup$ – Morris The Cat Aug 12 '19 at 18:34
  • $\begingroup$ @MorrisTheCat Thank you for the link! I'll check it. $\endgroup$ – Renan Aug 12 '19 at 18:38
  • $\begingroup$ If it's an interstellar cloud then we have far bigger problems than a bit of dust. $\endgroup$ – Separatrix Aug 12 '19 at 18:45
  • $\begingroup$ Then I'm afraid the question is too broad, an interstellar cloud is anything from a thin smear of ions we'd hardly notice except for the radiance to a swarm of meteoric debris that could potentially add a noticeable percentage to the mass of the solar system in collisions on the way through. $\endgroup$ – Ash Aug 12 '19 at 19:02
  • $\begingroup$ This seems to be more of an astronomy/space science question than worldbuilding. $\endgroup$ – rek Aug 13 '19 at 2:33

Probably nothing at all as a "dense" cloud of matter in space is still not nearly as dense as planetary atmospheres surrounding an earth like planet. Those pretty pictures of nebulas that you see are spanning areas of multiple stars, each likely to have some planetary orbits. In fact, any video game in which space is colored in some way to show it's in a nebula is not realistic. You would see the same black field of space if you were looking out from a nebula as you would see looking into it. In fact, the NASA photos you see with pretty colors are artificially colored to represent differing parts of the non-visible light spectrum and the general areas of concentration of a particular chemical or a composite of both renderings of non-visible light and chemical composition. Nebula aren't visible to the human eye unassisted and the visibility that radio or other non-visible spectrum telescopes can see is only because we are looking at a massive area of space from a massive distance away from said area.

Edit: Forgot, by comparison, the Asteroid Belt is the densest area of space that is closest to the Earth and is filled with massive rocks of various land mass sizes... It's also not a hindrance for space ships passing through it, as the gaps between these rocks are typically wider by orders of magnitude when compared to the rock. If you're lost at sea in a life boat, you could find a small island eventually... But you'll find a lot more stretches of ocean surface before shouting Land Hoe! Even in the Pacific, which is the ocean with the densest concentration of islands.... It's still got a lot more "not Islands" that you're far more likely to go from the Americas to Asia and never see a single one unless you specifically know where to look.

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  • $\begingroup$ I'd argue that the densest area of space near us is the centre of Sol. $\endgroup$ – Ash Aug 12 '19 at 18:45
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    $\begingroup$ Ash I think that hszmv doesn't consider the centers of astronomical bodies to be outer space, but inner space. Hszmy probable considers space to be the vacuum that begin at the surfaces or tops of atmospheres of astronomical bodies. $\endgroup$ – M. A. Golding Aug 12 '19 at 18:49
  • $\begingroup$ @hszmv Actually you can see a nebula, although they don't look dense or opaque when you see them with telescopes. Instead they are transparent or translucent with pale, delicate colors. It takes long exposure photography to make them look dense and opaque. And when you see such a pale and translucent nebula in a telescope, that blocks hardly any light from the stars beyond, you may looking though many trillions of miles of nebula that has almost no effect on the light passing through it, much less effect that a hundred feet of dense fog on Earth. $\endgroup$ – M. A. Golding Aug 12 '19 at 18:53
  • $\begingroup$ @M.A.Golding The vacuum in our solar system counts as an interstellar cloud in terms of particle density though. $\endgroup$ – Ash Aug 12 '19 at 19:05
  • $\begingroup$ Does the Pacific really have a higher concentration of islands than the South China Sea? $\endgroup$ – Ash Aug 12 '19 at 19:10

Any interstellar material would be redirected by the Heliopause in the Heliosphere (https://en.m.wikipedia.org/wiki/Heliosphere). The solar winds travel for a pretty long time and only get slowed down at the Heliopause (or mark the Heliopause by slowing down there, if you want to look at it that way). Besides creating a strong magnetic field, which deflects interstellar ions, the density of particle interaction would lead to the deflection of most uncharged interstellar atoms as well. If an interstellar cloud was able to get a detectable amount of matter towards Earth, it would be pretty bad news. I guess the upper atmosphere would be getting stripped away, continuing with lower parts of the atmosphere, then mountains depending on the density. Like using rougher and rougher abrasive paper on wood.

EDIT: Okay it seems like only large scale objects can surpass the Heliosphere. Interstellar dust gets electrically charged after passing through the Heliopause and deflected by the lorenz force. An insterstellar dust or gas cloud could never damage earths atmosphere due to this effect. (arxiv.org/ftp/arxiv/papers/1107/1107.0283.pdf Page 3, "Between the heliopause and termination shock,...") (If large scale astroids are contained inside the interstellar gas/dust cloud they could, as mentioned, travel to earth and damage it, if they are considered part of the cloud.)

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    $\begingroup$ I'm not sure this is accurate. Interstellar dust clouds can approach densities of 1000 molecules/cm^3, whereas the solar wind is something like 6 atoms/cm^2. A sufficiently dense dust cloud would probably push back the solar wind. That being said, the atmosphere is around 13 orders of magnitude denser than that, so the dust cloud would probably pass before inflicting any relevant damage on our atmosphere. $\endgroup$ – ckersch Aug 12 '19 at 20:11
  • $\begingroup$ @ckersch Most deflection seems to be due to inital electrically charging of the grains of interstellar dust after passing through the heliopause and later change of course due to the lorenz force. So density doesnt have much of a say in it. And you seem to be absolutly right that no interstellar dust could ever damage the earths atmosphere due to this effect. (arxiv.org/ftp/arxiv/papers/1107/1107.0283.pdf Page 3, "Between the heliopause and termination shock,...") $\endgroup$ – r3dapple Aug 12 '19 at 20:51
  • $\begingroup$ What do you mean with "Speed of Sound"? That doesn't make sense if we are talking about space. $\endgroup$ – DarthDonut Aug 13 '19 at 6:17
  • $\begingroup$ @DarthDonut You are correct. I edited the answer. $\endgroup$ – r3dapple Aug 16 '19 at 2:37
  • $\begingroup$ @DarthDonut Slow, low-frequency sound waves do propagate through the interstellar medium, and more so through dust clouds and nebulae, and a speed of sound can be calculated for them. In fact, such large-scale pressure waves are critical to new star formation, and the speed of sound in the local interstellar medium partially determines the shape of the solar bow shock. $\endgroup$ – Logan R. Kearsley Aug 16 '19 at 3:55

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