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 The Late Ordovician is the third and final epoch of the Ordovician period, lasting million years and spanning from around 458.2 to 443.1 million years ago. The rocks associated with this epoch are referred to as the Upper Ordovician Series. At ...

). 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