Snowden followed a single Twitter account: the US National Security Agency, from which he stole electronic documents revealing the agency's secret surveillance programs.
"Can you hear me now?" he asked in his first tweet, which was quickly resent by Twitter users tens of thousands of times.
In his second, Snowden noted the recent news about the planet Mars and then quipped about the difficulty he had finding asylum after the US government fingered him as the source of the NSA leaks.
"And now we have water on Mars!" he wrote. "Do you think they check passports at the border? Asking for a friend."