No Man's Sky allows players to affect planets in ways that subsequent visitors can see. You will, however, have to alter a planet a lot for the changes to be saved to the game's server. Developer Hello Games has implied that you'll need to do something drastic, like perhaps full-on terraforming or wiping out entire species.
Even though we can only speculate about this mechanic at this point, it both worries and intrigues me. It means, for instance, that players who want to leave their mark will have incentive to completely wreak havoc upon a planet. After all, even though you will be able to name things you discover, destroying everything in sight and taking an entire chunk out of a world might be the most dramatic way you can interact with other players.
But it also means that the game might end up being an experiment in human morality. No Man's Sky's universe is so unfathomably massive that each player will be virtually alone, with a limited system of holding them accountable for their actions. You'll probably never come across another player, nor stumble across a planet that another player had already found. You will, however, likely find really cool and interesting creatures, landscapes, and worlds. How, then, do we act when we are in a universe with no accountability, except what we impose on ourselves?
At some level, all sandbox games are like this because there aren't real-world consequences for in-game behavior. But our moral compasses still have some sway over what we do, even in video games. For example, in Mass Effect 3, a substantial majority of players picked the Paragon option over Renegade. It's a good bet that this trend holds true for other games with player choice.
However, virtually all of the sandbox games that give you the tools to sow mayhem nonetheless have some sort accountability system in place of in-game actions. Think about Grand Theft Auto V, for instance. I wouldn't be surprised if the vast majority of GTA V players have gone on at least one murderous rampage. But even though the massive arsenal given to you in GTA lets you destroy basically everything and everyone in sight, you can reload the map and everything will be back to the way it is, or you can stand up to virtual law enforcement. Same with most other sandbox games: things don't stay the same, and there are usually systems in place to prevent players from screwing things up too badly. Even titles like Skyrim that let you do things like murder almost every NPC or fill a poor citizen's house full of cabbages, you're faced with consequences that affect your own ability to play the game. In Skyrim, for instance, if you kill everyone you'll break many of the game's quests and anger most of the unkillable NPCs. But, if you do kill everyone, you can also just start the game over or reload and reset the world.
No Man's Sky doesn't have this ability to just turn back the clock. You'll essentially be the only actor in an colossal slice of an unbelievably huge universe, but at the same time each place you explore has permanence. Because of its immensity, there won't be anyone to stop you from creating chaos on the planets you visit except for the occasional hostile species. Even the Sentinels--the custodians of the game's worlds--will likely only show up on some of the planets. While they'll keep you in line sometimes, other times you might truly be on the frontier. Alone. With an arsenal equipped to destroy.
To explain what I mean, let's look at an analogy: consider a situation in which you were given the keys to an empty house and told to do whatever you wanted to it, without consequence. There might or might not be people living there. Some people might ransack the place, but I bet a lot of people wouldn't do anything too drastic.
Now imagine if that house looked only a little like a house as we know it, and there was only a miniscule chance of an intelligent creature residing in it. And it's one of 18 quintillion other houses in the neighborhood. Would we still restrain ourselves? Would we destroy those houses because it's fun, or would the freedom afforded to us encourage us to conserve and appreciate?
No Man's Sky seems to me like it'll be a virtual test of the theory that, to create human decency, we rely on governments and accountability structures. On Sentinel-less planets, the state of nature will reign. Players won't have accountability. But will life for native beings on those planets prove to be, as philosopher Thomas Hobbes theorized, "poor, nasty, brutish, and short" when players discover them?
In the real world, we generally like to conceive of "good" and "morality" as existing separately of laws, rules, and police. We intend our moral codes to apply universally, even when it's not necessarily good for ourselves. In games, however, it changes. We act in our own self-interest in video games, or at least in the interest of the end goal, because we play games for victory, completion, or simple enjoyment. The contextual vacuum of an alien planet that no other person may ever visit will test our capacity to place ourselves into a digital world. It's easy to feel something when you're making a choice in Mass Effect. It'll be entirely different when you're alone on a planet deep in a universe with the ability to wipe out an entire species without consequence.
It won't be too difficult to determine whether or not players moralize their actions in the game. We'll surely see some videos called things like "How to Be a Space Jerk in No Man's Sky" or "Destroying an Entire Planet in No Man's Sky," but the frequency of videos like this will give clues to how we end up conceiving of morality when applied to video games. On the flip side, if we see a concerted effort by players to chronicle and preserve the greatest sights and creatures, this might show that players are applying real-world moral considerations to the game.
I sincerely hope that we all become astrobiologists instead of space anarchists in No Man's Sky. If we end up embracing destruction and chaos, wreaking havoc on the planets we come across, then some truly amazing occurrences in the procedurally generated universe might be lost forever. After all, Hello Games says really special lifeforms exist, but they pop up on only 1 in 100 million planets. If these things are preserved and catalogued, it might be possible for players to engage in No Man's Sky tourism, traveling to the particularly cool planets out there to check them out.
But there's also the possibility that someone shows up looking to burn everything down.
There'd be something elegant about players assuming the role of explorers and pioneers rather than renegades. But even if we watch planet after planet destroyed by players hell-bent on leaving a mark, it'll still be an interesting result in a grand experiment in how we apply morality to digital worlds.