How do you unlock these locked chests in Europa?

I understand that the accepted answer implies that you will learn how to unlock these weirdly locked chests as you progress through the campaign; however, I'd still like to add a solid answer covered by a spoiler:

These chests are locked by Stasis. You can see a unique blue symbol in the action prompt when you move close to these chests, which is a Stasis symbol. In order to unlock the chests, you must first use your Splinter of Darkness (which is simply a quest step) while progressing through the campaign and attune the respective symbol at the Ziggurat. Then, commune with a Crux of Darkness (marked as a waypoint on your map). Once you finish this step, you can unlock chests sealed by that symbol.

To avoid any spoilers, you should just progress the campaign, as you do so each of the locked chests will become capable of being unlocked.

Complete the quests as they come up and you'll even be tasked with hunting down specific chests.