Addresses can be committed to the contract in exchange for sparks. The contract then holds those addresses, until someone burns a spark in exchange for them.

We're not sure exactly when or precisely how that market will get initialized — but you get the basic idea. Your star ownership will get mirrored in the contracts.

It seems that if you bought a star earlier then Tlon will "[...] write [Ethereum smart-] contracts that help galaxies and stars distribute their stars and planets" such that the "[...] star owner configures the planet sale contract with two parameters: the price in ether of a planet, and the number of planets available."

Basically, star owners will be handed a mechanism to run their own mini-ICO, where planets represent ICO tokens.

Why would you want to buy a planet from star owner X? I presume the answer lies somewhere in the statement: "Galaxies and stars are network infrastructure. Regular users have planets."

It means they're hosed.

Urbit is on about the same level as the next Zoë Quinn game in terms of hype-to-actual-value-delivered ratio.