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This is an image of the surface of Mercury.
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Early Cratering of the Planets

When we look at images of many of the planets, we see all sorts of circular craters on the planet surfaces. Most of these craters were probably formed when the solar system was still very young.

Once the early solar system had planets about the size of the planets today, there were still probably a lot of smaller planetesimals and debri around, too. The gravity of the large planets would attract nearby planetesimals, which would hit the planets and leave a crater on the planet's surface.

Craters on the surfaces of the inner planets are up to 4 billion years old, and some craters seem to have been made by objects up to 200 km across!


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The Summer 2010 issue of The Earth Scientist, available in our online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA