Snowden's first tweet: 'Can you hear me now?'

Edward Snowden has joined the Twittersphere.

Snowden, the former National Security Agency contractor who leaked details of U.S. surveillance programs, tweeted: "Can you hear me now?" at about noon ET Tuesday.

Twitter verified the account.

Snowden was quickly greeted on social media by famed astrophysicist Neil deGrasse Tyson. Snowden's response: ".@neiltyson Thanks for the welcome. And now we've got water on Mars! Do you think they check passports at the border? Asking for a friend."

Former three-term New York governor George Pataki, now running for the GOP presidential nomination, quickly tweeted harsh words for Snowden: "Some say you have courage, I saw real courage on #Sept11 You are just a traitor who put American lives at risk."

Snowden amassed more than 300,000 followers in two hours. He was following one account — the NSA. The NSA did not immediately follow him back.

Snowden, now 31, is a North Carolina native who once spent four months in the Army. He was a contractor for Booz Allen Hamilton when he leaked details of U.S. surveillance programs to The Guardian and The Washington Post. The first reports were published in June 2013, setting off an immediate global firestorm.

He was in hiding in Hong Kong at the time but fled to Moscow. Facing charges of violating the Espionage Act and theft of government property, he stayed in Russia when the U.S. revoked his passport. Now he works in IT in Moscow, consults for several U.S. companies — and is learning Russian, his lawyer, Anatoly Kucherena, has said.

Snowden's lawyers have been attempting to negotiate a deal that would allow him to return to the United States. Tyson followed up on Snowden's Mars mention: "Ed @Snowden, If you visit Mars, I'd bet any life forms there will greet you with a sip of that water – and a tourist visa."

Snowden said he was staying busy with "secret" projects for the Freedom of the Press Foundation but added that he "still finds time for cat pictures."

Tyson noted that Snowden is called a hero by some, traitor by others. Snowden's response: "Hero, traitor – I'm just a citizen with a voice."

Kucherena said earlier this year that it is no secret that Snowden wants to return to the U.S. Kucherena said Snowden just wants to be guaranteed a fair trial.

In July, petitioners on the website "We The People" called Snowden "a national hero," and said he "should be immediately issued a full, free, and absolute pardon for any crimes he has committed or may have committed related to blowing the whistle on secret NSA surveillance programs."

Lisa Monaco, President Obama's homeland security adviser, rejected the request in the official White House response. She said Snowden should return to the U.S. and "be judged by a jury of his peers – not hide behind the cover of an authoritarian regime. Right now, he's running away from the consequences of his actions."

She added:

"We live in a dangerous world. We continue to face grave security threats like terrorism, cyber attacks and nuclear proliferation that our intelligence community must have all the lawful tools it needs to address."

Earlier this month, actor Joseph Gordon-Levitt revealed that he secretly met with Snowden in Russia to research his role in the biopic Snowden. The film has not yet been released.