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Sure enough, when I passed, camera in hand, over Korea early in the mission, I spotted the green ring of the crater easily. Snapping away, I caught the crater (if that's really what it is) peeking through the cloud cover below. A few days later I was scanning the ground in Siberia, east of the huge freshwater lake Baikal, when I saw another crater-like formation dusted with early winter snow. That may also prove to be an undiscovered impact feature. Other scientists are working with me now to see if either of these features has been studied before, and to go after the evidence that will prove these circular scars were created by cosmic impacts. I'm sure there are many similar surprises waiting to be revealed by those who keep a keen eye on our planet's surface.

This suspected Seoul impact structure is located about 32 km north of Seoul, the capital of South Korea. The crater location is 37 degrees 49' North, 127 degrees 03' East. This features, while not proven to be caused by an asteroid or comet impact, appears similar to many other impact craters on Earth, the Moon, Venus, and Mars. The suspected crater has a sharply elevated rim, a flat floor, and an uplifted set of hills at the center. The shuttle photographs also show a roughly circular region of forested hills surrounding the sharp rim; the impact that formed the crater may have also influenced this area's appearance through fracturing of the surrounding rock.

The crater's rim lies just at the outer reaches of Seoul's suburbs. Urban development--roads and buildings--reaches to the southern rim of the structure, but the crater floor is mostly farmland. The rim ridges are rugged and forested; this contrast of the green, circular rim with the fields on the crater floor was what caught the eye of the astronaut photographers on STS-59 and STS-68. The town of Tongducheon is just north of the rim, near the demilitarized zone, and the small village of Tokchong is nested in the central uplift. The town of Uijongbu lies outside the southern rim along a major north-south highway. This road was the axis along which North Korean forces advanced during the June 1950 invasion of South Korea. The ridges of the Seoul impact structure saw heavy fighting during the see-saw campaigns back and forth across the demilitarized zone from 1950-1953.

Now that our suspicions have been aroused, planetary scientists must visit the area and obtain rocks for study from the rim and central uplift. Those rocks should tell us whether the structure is, in fact, a true impact crater, and when the impact explosion occurred. Other circular features in Korea are visible in space photographs, some very similar to the Seoul feature. Are they all impacts, or is there something about Korean rocks that produces circular uplifts throughout the peninsula? The answers are not know. The few samples we've obtained from our friends in Korea do not show the shocked quartz crystals within the rocks that prove an impact shook the bedrock here. Another field trip to the site will be necessary to confirm our suspicions and tell us more about the history of the feature. Judging from our space images, erosion has operated on the suspected crater structure for millions of years. A visit to study the geology of the site will tell us much about the formation and subsequent history of this feature. The Seoul feature reminds us that Earth's surface still holds undiscovered secrets about the history of our planet. Space-based observations of Earth will give us the global view we need to understand Earth's violent past, the present state of its surface, and dramatic natural and human-induced changes to our environment.