1.   But the lunar gravity field was then so poorly mapped that the chances of achieving a successful preprogrammed landing were very small.

2.   For example, the gravity field on the lunar surface is about one seventh as strong as on Earth.

3.   In effect, the debris is captured and contained locally by the Martian gravity field.

4.   It seemed to geophysicists that the continents should shape the gravity field in some way.

5.   We should also recall that asteroids have very weak gravity fields.

6.   Due to variations in the density and types of materials that make up the Earth, its resulting gravity field is lumpy.

7.   Two missions to observe the forests and gravity field of earth have been approved by the National Aeronautics and Space Administration, officials said Wednesday.