Tvären is a circular bay close to

Studsvik Studsvik is a supplier of nuclear analysis software and specialised services to the international nuclear industry. The company is headquartered in Nyköping, Sweden, and has five divisions: Sweden, United Kingdom, Germany, the United States, and ...

, Sweden. Within the bay is an ancient buried

impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...

about in diameter. It was first identified using

reflection seismology Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflection (physics), reflected seismic waves. The method requir ...

. The crater is estimated to be about 455 million years old ( Late Ordovician). Asteroid 7771 Tvären is named after the bay.

References

Impact craters of Sweden Ordovician impact craters Ordovician Sweden Sandbian Landforms of Södermanland County {{Earth-crater-stub