Former Indiana Sen. Dan Coats (R-Ind.) said Wednesday that he is moving forward with a challenge to Sen. Evan Bayh (D-Ind.).

Coats didn't say he's definitely in, but he will need to move fast if he is to make the ballot. He will need to collect 500 signatures from each of the state's nine congresional districts over the next two weeks.

Sources close to the situation say he is all but certain to run.

"After much thoughtful consideration, I have authorized my supporters to begin gathering signatures as I test the waters for a potential challenge to Evan Bayh in 2010," Coats said in a statement. "Over the next few weeks, I will be talking to Hoosiers from all walks of life, and I will make a formal announcement regarding my intentions in the near future."

Coats, a former ambassador to Germany who retired from the Senate in 1998, said his desire to serve in public life has returned.

"After coming back from Germany I was content to return to the private sector," he said. "But like many Hoosiers, I have become increasingly alarmed and frustrated about the direction of our country and the failure by leaders in Washington to listen to those they were elected to represent."

Bayh's seat has emerged as a target in recent weeks, but Rep. Mike Pence (R-Ind.) and Indiana Secretary of State Todd Rokita both passed on the race. Coats's name came out of nowhere late Tuesday night, when Indiana political analyst Brian Howey first reported he would run for Senate.