What is the 14-ton bomb that could destroy Iran's nuclear facility and will Trump use it?

Israel has made no secret of its desire to destroy Iran's nuclear program, but the only bomb believed to be powerful enough to penetrate Iran's Fordow facility is an American "bunker-busting" bomb that the Israelis do not yet have.

As President Donald Trump appears to be switching between calling on Iran to negotiate and threatening retaliation "at levels never seen before," the US will inevitably be drawn into another conflict in the Middle East - something the president has repeatedly said he does not want.

What are bunker busting bombs?

Simply put, bunker busting bombs are designed to explode twice. Once to breach the ground's surface and again after the bomb has sunk to a certain depth.

They are used to reach military headquarters, bunkers, and other facilities buried deep underground.

"They're big, very heavy. There's a lot of explosives in them," says military analyst Michael Clarke.

The Israeli military has a number of bunker-busting bombs, but it does not have the vaunted GBU-57, a 14-ton bomb so heavy that it can only be dropped by the US fleet of heavy bombers.

It is the GBU-57 that is believed to be the only one capable of destroying the heavily defended plant at Fordow.

Analysts say it could only be delivered by a stealth American B-2 bomber. Its weight of 30,000 lb (13,600 kg) means its kinetic force allows it to reach deeply buried targets.

It is understood that it can penetrate about 200 ft (61 m) below the surface before exploding.

What are Iran's main nuclear facilities?

Prime Minister Benjamin Netanyahu has made clear his desire to destroy Iran's nuclear program and any hint of a nuclear weapons threat - something Iran has long denied seeking.

In the days since Israel launched its surprise attack on Iran, much attention has been paid to how well they would be able to disrupt Iran's nuclear program, much of which is buried deep underground.

"The three places they really want are Natanz, Isfahan and Fordow," says Prof. Clarke.

Natanz and Fordow are uranium enrichment sites, and Isfahan is one of the largest nuclear research centers in Iran.

What damage has Israel caused to Iran's nuclear program?

The Natanz enrichment plant has been hit by Israel in recent days, with its underground centrifuge hall believed to have been damaged but not destroyed.

Rafael Grossi, head of the International Atomic Energy Agency, told the BBC that the Natanz plant suffered extensive damage, likely destroying 15,000 centrifuges.

This was probably due to an Israeli airstrike that cut off the centrifuges' power supply, rather than actual physical damage to the centrifuge hall, he said. 

However, no damage was observed in Fordow. Mr Grossi added: "There is very limited, if any, damage recorded (there)."

In Isfahan, Iran's third key nuclear site, there was damage to buildings, including the central chemical laboratory and a uranium conversion plant.

Mr. Grossi said: "In Isfahan you also have underground spaces, which do not appear to have been affected."

What will Israel do now?

Professor Clarke says Israel is likely to continue its bombing campaign against Iran's nuclear facilities.

"I think they're going to keep visiting Natanz again," he said. "They're going to want to keep aiming down with more bunker bombs until they hit the centrifuge hall itself."

Fordow, on the other hand, seems very deep even about Israel's bunker bombs.

"It's the most important because it's the one the Iranians think they can protect," he adds. "You have to blow up the mountain to get there."

It is possible, says Professor Clarke, that Israel could try to damage it in a way similar to what happened to Natanz - by cutting off the power supply - which could have the cumulative effect of rendering the centrifuges inoperable.

"What Netanyahu wants to say is: look at the devastation we've caused to Iran. Their weapons program is destroyed, it would take them 30 years to rebuild it... we've taken them off the table as a threat to us for a generation."

But it remains to be seen whether this is possible without direct American intervention - something President Trump may want to avoid at all costs. Adapted from Sky News