There are other subtle clues to look for. The impact might have displaced ancient, extremely deep layers of soil, or paleo-soils, and placed them at a higher level than normal.

"If there was this big explosion," Killeen explains, "there would have been a big splash, so that splash should have slopped over a lot of soil to the areas adjacent to the crater."

Three or four meters of newer soil that was formed since the impact would then cover the displaced paleo-soils. Scientists will float the river in motorized canoes searching for areas where water cuts into the riverbanks and the paleo-soils might be revealed. Dating the paleo-soils and the soil levels that sandwich them can also narrow down when the impact occurred.

Killeen will also participate in the biologists' efforts to collect samples of the flora and fauna in and around the crater. Besides contributing to their understanding of the region's biodiversity (which is Killeen's primary work for Conservation International) they are trying to characterize the subtle differences in vegetation detected by Landsat.

To make a crater the size of Iturralde, the impacting object would be roughly the size of a bus and the event would release energy equivalent to thousands of megatons of dynamite, according to James Garvin, an impact crater expert at NASA. In comparison, the largest hydrogen bomb ever made had the power of 100 megatons of dynamite, but the Soviet Union never detonated it.

"The global impact would have been equivalent to that of a large volcanic eruption, like Pinatubo," Garvin says.

Dust could have been carried through the atmosphere and deposited in places as far away as Greenland, the Andes mountains, or even Antarctica. Any data gathered at Iturralde can then be correlated with ice cores taken at these frozen locations.

But on a local level around the blast, the energy released would heat the surrounding dust and material to a plasma-like state. As the material cools, the magnetic field realigns differently from the original direction and can form a conspicuous pattern distinct from the underlying magnetic field of the Earth.

"It's like if you drop a pebble in the water and you see the waves coming out, with rings that define different magnetic measurements," says Patrick Coronado, a senior engineer at Goddard.

Miniature Cessna

Coronado led the team that developed the MagPlane, or Magnetometer Plane, a one-third-scale Cessna with a 12-foot wingspan, fitted with a highly sensitive hand-made magnetometer. "The same quality and sensitivity as spacecraft magnetometers," Coronado says. It runs on a modified weed-whacker engine that should power the 44-pound plane for three hours on a half-gallon of standard gasoline. "Trying to get special fuel down there is not trivial so we had to use the regular stuff."

Each MagPlane cost about $50,000 to make. The first one went from concept to finished product in six months. "Even if we had all the money in the world it wouldn't really have helped because a lot of it was new," Coronado says.

The MagPlane was born when Tucker and the expedition organizer, Peter Wasilewski, a Goddard astrophysicist, were consulting with Goddard’s Office of University Programs, which provided most of their funding through the director’s discretionary fund, about maximizing their magnetic field measurements.

"The [University Programs] office is just down the hall from me," Coronado says. They told Tucker and Wasilewski about "this guy down the hallway who has little planes for remote sensing, so they perked their ears and opened their eyes and came down and talked to me," Coronado recounts. "This was six months ago, and we started working the next day. We were behind schedule the day after we started."

Coronado says the project was similar to the Skunkworks, "like the old days at Lockheed when you crammed a bunch of engineers in a room and you put food and water under the door and they worked until they dropped."

When Coronado spoke with SPACE.com, he and his team were still constructing the magnetometer for a backup MagPlane.  "My engineer is taking it down with him to install on the second plane in case the first one goes down.  Otherwise all there is is a pretty plane flying around taking pictures." Because of the tight schedule, however, the MagPlane has not been fully tested.  "A lot of the testing will occur as it's doing its job." 

Still, the MagPlane is more than was originally planned. The trek was supposed to start last fall but was postponed because of the terror attacks last year.

The expedition officially started this year on Sept. 10, and the MagPlane flight is scheduled for Wednesday, Sept. 25. In case it doesn’t work out, the scientists have also brought along ground-based magnetometers.