Without getting too deep into it, the idea is planet hopping at around 20% of the speed of light.
I can't begin to imagine how that would work. Have to say that once ideas are put put forward, as I posted above, it results in more questions. As you've answered it in the context of Jelster's post which relates to aliens and not microbes/bacteria, when you say planet-hopping do you mean they stop-off on various planets ? Travelling at 20% the speed of light ? That's still 37,200 mps. Just taking our solar system the furthest 'planet' away from us is Pluto and that's 4.67 billion miles from us. As you're probably aware it's now classed as a dwarf planet so that leaves Jupiter which, at its closest, is 365 million miles away at its farthest 601 million miles. The nearest.at times,is Venus but due to orbits Mercury is really the nearest most of the time and distances for them are Venus at 38 million miles and Mercury 48 million miles. To the best of my knowledge none of the planets in our solar system ,apart from Earth, has conditions for any substantial form of life due to extremes. Either too hot..Venus gets to 465C... too cold ..Uranus gets down to -224C ,Neptune not quite as cold at -214C and with winds of more than 700mph. Anyway, planet-hopping within the solar system is a non-starter so it seems to me a reasonable assumption that the planets of other stars have similar hostile environments. No planet has been discovered yet that has any form of life on it. I'm sure there must be but so far we don't know.
Re the actual planet-hopping can you imagine the calculations required to do that across the Milky Way as planets move and at very fast speeds ?
Naturally, we can only imnagine what so-called aliens look like and it's always a variation of us. ET ? Putting that aside here are some mind-blowing facts.
There are 125 billion galaxies in the observable Universe...courtesy of Hubble. It's going to be fascinating to learn what the JW telescope discovers. The Milky Way is 100,000 light -years across. It has 50 satellite galaxies, the largest being the Large Megellanic Cloud and that's 14,000 light-years in diameter, btw..it's 158,200 light-years away from Earth.The Small Magellanic Cloud is 199,000 light-years away.
Better not start on the nearest galaxy Andromeda.

That's approximately 2.5 million light years away.
In no way do I claim to know all this stufff off the top of my head but I'm aware of enough to know what data to look at. They say that a lawyer doesn't know all there is to know about law for each case but does know in what area to do the research which is often case law.
You've started your reply to Jelster with.."Without getting too deep into it"... etc.. There's a thread dedicated to all this .'The Space and Astronomy' thread in the Out of Focus/General Discussion section..well, you posted in it yourself on Christmas Day re the live footage of the launch of the JW Telescope and there's a good level of interest in it not to mention all the contributions in this one so, with that in mind, could you expand on this planet-hopping theory ? If you get 'too deep' into it I'm sure someone will ask for a simplified explanation.My guess is that it would really be appreciated as you indicate that you have some depth of knowledge that most of us don't have.