How does it work?

Level 9 guy finds a level ~69 guys planet.

It has no defensive buildings. 125 total population. It's Very Large / Abundant in all three things.

Would I be able to claim it?
Would he be able to immediately take it back?

You should be able to take it if your are out of the 2 week protection period. Make sure you get your attack as high as possible. If you had a flux you could make it disappear from his list so he could not take it back. You could also have legion members help guard the planet and use artifacts to help defend it.

My suggestion is to attack the planet once then come back the next day to see if he put up any defenses. If he did not then he may be inactive or does not care if you take it.

Keep in mind that the planet building that are on it might not produce anything for you if you have not researched to that level yet. So you will probably not get the same production out of the planet if you take it.

i doubt a level 9 would have a flux, you would need a legion to help you.

I have attacked and captured many a planet without a flux. I have actually never had a flux. Plus if the player is inactive why use it.

I know it is unlikely for the player to have a flux unless he pays for it. I was giving all the possible options. I would not take the planet unless the owner does not put up any defenses after a test shot on the planet.

Ooo! Hehehe, right, thats hwo you check ^^ BTW you should hack some planet locals from me... XD

Oh, I was actually wondering about that with one of my planets, somebody hit it with three Ion Storm Charges throughout a day, but only attacked it once or twice and I never figured out what was going on.

When planet fluxes were more common I used to do an attack on enemy planets a couple of days before a scan blitz hoping that the owner would flux it. Now that is unlikely to happen. It could also be a new player who has not figured out how to invade a planet yet. You could set a trap to figure out who it is.