This week, the U.S. and its allies will sit down with some of their arch-nemeses: the Iranians. The meeting in Baghdad is the definition of high stakes, as 2012 has been characterized by frequent speculation that Israel would bomb Teheran to prevent it from going nuclear, launching a war that would inevitably draw the U.S. in. That's something the U.S. doesn't want – the Air Force chief of staff has publicly questioned the wisdom of a bombing campaign – but big, unresolved questions persist about Iran's nuclear program, which Iran swears exists just to produce peaceful nuclear energy. In particular, those questions primarily concern five installations that trouble the International Atomic Energy Agency (IAEA), the world's nuclear watchdog. And unless you're a nuclear wonk, you probably don't understand them. But you should. Granting the IAEA unfettered access to these five sites – some of which concern the IAEA more than others – is probably the most important step Iran could take to avert a war. Getting Iran to "Yes" will be an arduous diplomatic process that likely involves international economic sanctions, a U.S. military buildup off its shores, some prospect for improved relations with the world – and, arguably, the threat of a war. And there's an additional X-factor: nuclear sites that the IAEA doesn't know Iran even has. But watching what happens over the following five sites, during the Baghdad talks and afterward, will go a long way to determining if the U.S. will be dragged into its third mideastern war in a decade. Fordow (Qom) Fordow is a uranium enrichment facility not far from the clerical hotspot of Qom. (That's why the facility is often referred to as "Qom.") Under construction since 2009, when Iran was already under tight IAEA scrutiny, the existence of the facility was a secret until Western intelligence agencies uncovered it. Not surprisingly, in a November report, the IAEA said that "additional information from Iran is still needed in connection with this facility." Here's what the IAEA thinks it knows about Fordow. There are a variety of centrifuge cascades, or arrays of centrifuges for enriching uranium, totaling 696 centrifuges. The IAEA initially understood that Fordow would only enrich uranium to a 5 percent standard, which is too low for use in a bomb. But the IAEA had to confirm that the Iranians had a change of heart, and began enriching to 20 percent. To be clear, the enrichment process is a method to get rid of most of the atoms in uranium, yielding the fissile isotope Uranium-235. Twenty percent enrichment isn't sufficient for bomb-grade fuel, which is 90 percent enriched uranium. But as the Arms Control Association clarifies, "such material can be further enriched to weapons-grade levels relatively quickly." The U.S. called the extra enrichment a provocative act of bad faith, which will almost certainly be revisited in Baghdad. Photo: Institute for Science and International Security

Parchin Parchin, shown above, is a massive military R&D facility that works on rocket, ammo and high-explosives tech. All of which is important to the detonation of a bomb, so the IAEA wants to inspect the place again, as it did early in the '00s. No luck. After January's meeting between the IAEA and Iran, the nuclear watchdogs reported "Iran did not grant access to the site at that time." To be clear, nuclear fuel work doesn't appear to occur at Parchin. That's the rub. The Iranians say that the IAEA is out of its jurisdiction to inspect it. The IAEA says it can't be sure Iran's nuclear activities are peaceful unless it sees Parchin for itself. That's because Iran "constructed a large explosives containment vessel" at Parchin "in which to conduct hydrodynamic experiments." Like, for instance, detonating a bomb. More recently, the Institute for Science and International Security, a nuclear-weapons think tank, released satellite photography, shown above, indicating Iran has scrubbed Parchin down, which could either mean it's hiding evidence of nuclear-relevant work or practicing good sanitation. Either way, access to Parchin will surely be a key issue discussed in Baghdad. Photo: Institute for Science and International Security

Natanz The site that launched a decade-long panic over an Iranian a-bomb. Shown here in a 2006 satellite photo from GeoEye and annotated by the Institute for Science and International Security, it's a sprawling campus of nuclear development. A "pilot" plant does R&D on individual centrifuges, while a fuel enrichment plant holds over 9,100 centrifuges in 54 cascades. According to the IAEA's most recent report (.pdf), Natanz has produced 5,451 kilograms of 5 percent enriched uranium since 2007. The IAEA wants to keep monitoring Natanz, although at the pilot plant site, "the Agency has concluded that the facility has operated as declared by Iran." Photo: Institute for Science and International Security/GeoEye

Esfahan Iran is supposed to stop both enriching uranium and working on so-called heavy water, another step in processing nuclear fuel. But the IAEA's February report found that Iran is "conducting a number of activities at [its Uranium Conversion Facility] and the Fuel Manufacturing Plant (FMP) at Esfahan" that it considers "in contravention of those obligations." That month, Iran sent at least 8 kilograms of uranium enriched up to 20 percent to the Esfahan fuel plant -- in addition to 144.3 kilograms of uranium dioxide, another nuclear fuel, currently present at a facility that the IAEA is supposed to have under safeguard. Photo: Institute for Science and International Security/DigitalGlobe