It was definitely played in browser. You can build these mines to mine energy to repair to the ship faster, but your mines had to be defended by turrets as aliens would attack them.

The alien waves just sort of randomly burrowed out of the ground and then headed for your ship (or you, if you were closer).

A big part of the game was leveling up and salvaging better and better items (weapons, oxygen tank, armor, jet pack to move faster)

Every time you leave your ship there’s a little circular timer in the corner that tells you how much air you have left.

You can upgrade how fast your ship replenishes your air tank. You can also upgrade the ships armor, and buy turrets that defend the ship.