Can Surveyor 7 See It Change?
1A space agency is planning Surveyor 7, a satellite that will watch Earth's surface from orbit. Before the design is final, the mission team must answer one question: which changes will it actually be able to see? At a briefing, mission geologist Dr. Ayesha Moreau reminded the team's student interns that Earth's surface changes at very different speeds and sizes. Some changes are over in minutes, and others take millions of years. Some cover one hillside, and others cover a whole region.
2Each pixel in a picture from Surveyor 7's camera covers a square 10 m on a side, so the camera cannot show anything smaller than about 10 m across. The satellite passes over the same place every 5 days. It also carries a radar that can tell whether the ground has moved up or down by 5 mm or more since an earlier pass, but the radar cannot show what the ground looks like.
3To test the design, the team studied four recent changes (Table 1). On Crag Mountain, a slope soaked by days of rain gave way in a landslide. On Marrow Island, a volcano poured lava into the sea, and the lava cooled into new land. The front of Ice Creek Glacier keeps melting back up its valley. Around Tern Bay, the land is still slowly rising because a thick ice sheet that once pressed it down melted about 10,000 years ago. Lines of rounded beach pebbles, left by waves long ago, now sit on hillsides high above the bay.
4The team also looked at three landforms that took much longer to build (Table 2). Marrow Island's volcano has grown up from the sea floor in many eruptions, with long quiet times between them, while rain and waves wear its rock away. Ice Creek's valley is U-shaped because glaciers filled it again and again during many ice ages, scraping its floor deeper each time.