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I think you are pushing the boundary of believability a little too far, at least for someone who is somewhat familiar with orbital mechanics. (That may or may not be a problem for your intended audience.)

Space isn't high up, like:

Space is fast, like:

Now, in principle, you could get around this by having your volcanic eruptions take place at an angle somehow (not sure how realistic that is), but just tossing material straight up will have one of two outcomes:

It will reach escape velocity and leave the planet's sphere of influence. It may still remain in a relevant orbit, like how you can gain enough velocity to break free of Earth's gravity only to find yourself still stuck in the Sun's gravity well.
It will fail to reach escape velocity, and simply fall back down. In this case, the object will likely trace approximately a ballistic trajectory. Keep in mind that in low Earth orbit, despite apparent weightlessness, gravity is about 90% of that on the surface.

The only reason why a satellite doesn't simply fall down is that the launch has imparted a great (approximately 7,000 m/s or more, in the case of the Earth) forward velocity. This forward velocity exactly (to within small error) compensates for the downward pull effected by the gravity of the Earth, in any given orbit. Compare for example Why is geosynchronous orbit an altitude, rather than a velocity? over on Space Exploration SE, or more generally their orbital-mechanics tag.

As others have already pointed out, absent additional energy inputs, orbits are closed, which means you can't toss material into an orbit. However, with suitably lucky atmospheric skips and low enough gravity, it just might be possible to toss material at an angle that eventually results into a (most likely highly elliptic) orbit. Such material would likely need to be launched at angles that are almost parallell to the ground, and obviously with sufficient velocity to maintain orbital velocity at orbital altitudes.

An alternative solution:

However, this might be easy to work around without altering your setting too much. You stated in a comment that:

In my novel, a crew sails through the clouds of such a planet and find a spacecraft wreckage containing some important information for the rest of the plot. Some people said it wasn't believable since such clouds are just impossible to form without the debris accreting into a disc, like Saturn.

(This has the added problem that such a "cloud" would create drag, which will quickly cause anything caught in it to deorbit. Even the ISS experiences drag and needs periodic reboosts to maintain its approximately 400 km high orbit.)

Consider instead of making this a natural phenomenon, simply making it an extreme runaway case of space debris, known as the Kessler syndrome or effect. Have the timing reasonably right, and it's plausible for a spacecraft to be disabled by space debris but not yet destroyed by it when your crew comes along.

posted almost 9 years ago