It's up to Gov. Chris Christie to pick a replacement for New Jersey U.S. Senator Frank Lautenberg, who passed away from complications of viral pneumonia Monday morning at the age of 89.

Governor Chris Christie shakes hands with Senator Frank Lautenberg at a Statehouse meeting about Superstorm Sandy in November (Governor's Office, Tim Larsen)

Christie can appoint a temporary Senator to replace Lautenberg, and then order a special election to be held this year- with a special primary - but beforehand, both parties must select their candidates.

So who will Christie pick?

"The name at the top of the list for republicans is State Senator Joe Kyrillos - who ran and lost against Senator Bob Menendez last year - he's a close friend of the governor's," said Montclair State political science professor Dr. Brigid Harrison.

However, she says the problem with Kyrillos is many republicans in the state were kind of disappointed in his performance.

"Not just in the number of votes that he got - no one really expected him to win against Menendez, but that he really wasn't able to make significant headway, and perhaps more importantly, many people were disappointed in his performance on the campaign trail," Dr. Harrison said.

Full Coverage:  Frank Lautenberg Dies at 89

Harrison said moving beyond Kyrillos, there are three other state legislators, including Tom Kean Jr., the son of the former Gov., Bill Baroni, who's now on the Port Authority of New York and New Jersey and Kevin O'Toole from the State Senate.

However, Harrison said it's possible that Gov. Christie could actually appoint Cory Booker, the democratic mayor of Newark who announced his intention to seek the nomination for U.S Senate a few months ago.

"It certainly would be a rather shocking development, but the reality is both the governor and Booker enjoy a close personal relationship and Cory Booker is the favorite to win this seat.  And by doing something so bold and daring, Gov. Christie first off has the ability to ingratiate himself with democrats in his own re-election bid. He has the ability to ingratiate himself with voters in one of the State's largest cities in Newark, and he actually has the chance to ingratiate himself with African-American voters in the State of New Jersey."

If Christie decides to toss his hat into the Presidential ring in 2016, appointed Booker could help him. "What a remarkable feat to have appointed one of only three African-American U.S. Senators.  Such a move might not be enormously popular with the conservative republican primary constituency, but in terms of a general election constituency, I think that is a very, very strong selling point," said Harrison.