Capt. Richard Olson, 74th Expeditionary Fighter Squadron A-10 pilot, gets off an A-10 Warthog after his flight at Kandahar Airfield, Afghanistan, Sept. 2, 2011. (Photo by Senior Airman Corey Hook/ U.S. Air Force)

The impending mothballing of the A-10 Thunderbolt II attack jet has prompted outrage among its advocates in the active-duty military, hand-wringing on Capitol Hill and questions from analysts about whether the new F-35 Joint Strike Fighter can be operated cheaply enough to support ground troops on a regular basis.

But it also has sparked a question: Which plane could the U.S. military adopt if it ultimately decides it needs a new, designated plane to provide close-air support?

[RELATED: Close-air support mission to get new scrutiny as the A-10 retires]

The mission has been handled by a variety of aircraft in recent years, but it is the A-10, nicknamed the Warthog, that is beloved for its ability to loiter over a battlefield and target enemy fighters, tanks and vehicles. Even as its heads into retirement, it is carrying out about 11 percent of the combat sorties against the Islamic State militant group, Air Force Secretary Deborah James said in January.

Air Force Gen. Herbert “Hawk” Carlisle, commander of the Air Combat Command, left open the possibility on Friday that the service could eventually need another plane to fill the close-air support mission. He called it the “A-X,” with the “A” meaning its primary mission would be attacking enemy forces on the ground. (As opposed to fighter jets, which get the “F” prefix.)

But the Air Force isn’t planning to pay for that anytime soon. Rather, it plans to retire the A-10 and rely on other existing planes such as the F-15 Strike Eagle and F-16 Fighting Falcon to carry out close-air support. Defense officials want the F-35 to eventually take the mission over, but it isn’t clear how long that will take. Getting rid of the Air Force’s 283 A-10s will save $3.7 billion over five years, senior defense officials said.

[RELATED: Air Force to move A-10 jets into backup status despite congressional opposition]

Carlisle said that questions about “capacity” leave the door open to an “A-X” plane.” Each variant of the F-35 costs more than $30,000 per hour to fly, according to Pentagon estimates that some critics consider conservative. The cost to fly the A-10 is closer to $11,500, according to an analysis by The Atlantic.

The A-10 and possible successors wouldn’t fare well in dogfights with other advanced fighters. But against the variety of militant groups that have seized attention in the last year, they’d still be effective, and at a fraction of the price. Here are a few planes analysts discuss in the close-air support mission:

A-29 Super Tucano

Air Force Capt. Matthew Clayton, of the 81st Fighter Squadron, flies an A-29 Super Tucano on March 5, 2015, in the skies over Moody Air Force Base, Ga. The 81st FS is the only A-29 squadron in the Air Force. (Photo by Senior Airman Ryan Callaghan/ Air Force)

The U.S. military thought enough of this turboprop aircraft to purchase a number of them for the nascent Afghan air force, which the Pentagon is funding and training. The first 20 arrived at Moody Air Force Base in Georgia in September, as the service prepares to train Afghan pilots there.

The Super Tucano, called the A-29 by the Air Force, is made by Brazilian aviation firm Embraer, and has been used by militaries across the world. It typically costs about $1,000 an hour to fly. It could be outfitted with a variety of bombs and machine guns, and has drawn interest from a variety of African militaries facing insurgencies. The Afghan version is made in the United States by Embraer and Sierra Nevada Corp.

Afghanistan won’t receive its first Super Tucanos until December, Gen. Joseph Campbell, the top U.S. commander there, testified last week. The fact that the plane will not be available for fighting season this year is considered a setback for the Afghan military.

The Scorpion

The Textron Scorpion is a small jet that has been pitched by the company as an option for close-air support. (Photo released by Textron)

The Scorpion jet has been developed by Textron, which includes Bell Helicopter, Cessna and other major aviation companies. It was first introduced in 2013, and recently reached 300 hours in flight testing, company officials said. It costs about $3,000 per flight hour, and has been pitched by the company as a cheap option to perform maritime security, close-air support and surveillance missions.

Carlisle left open the possibility that the Air Force might pursue the Scorpion when asked about it Friday. But he said other planes also are in play, without naming any.

“We have to keep thinking about those things because, frankly, we haven’t been very good at predicting the future and what it’s going to look like,” the general said.

The aircraft has drawn interest from militaries across the world, and was displayed at an international airshow in Abu Dhabi, the International Defense Exhibition and Conference (IDEX), last month.

The AT-6

The Beechcraft AT-6 has competed with the Super Tucano for contracts in the past. (Photo released by Beechcraft)

Beechcraft’s AT-6 has been used by the Air Force as a trainer plane for years, and used by a variety of militaries abroad, including Iraq’s and Mexico’s. The single-prop plane can carry a variety of weapons on stations mounted on its wings, and has competed with the Super Tucano for contracts in the past.

The American version is sometimes known as the Texan II. Raytheon is integrating the 44-pound Griffin “mini-missile” onto it in the future, upping its firepower. The Griffin has been used on other U.S. aircraft, including the KC-130 gunship, which is equipped with a powerful Harvest Hawk weapons suite.

[RELATED: The B-1B bomber gets new missiles as it continues to strike in Iraq and Syria]