Borealis Basin
large basin in the northern hemisphere of Mars
The North Polar Basin, more commonly known as the Borealis Basin, is a large basin in the northern hemisphere of Mars that covers 40% of the planet. Some scientists have postulated that the basin formed during the impact of a single, large body roughly 2% of the mass of Mars, having a diameter of about 1,900 km (1,200 miles) early in the history of Mars, around 4.5 billion years ago. However, the basin is not currently recognized as an impact basin by the IAU. The basin is one of the flattest areas in the Solar System, and has an elliptical shape.
Large regions within the Borealis Basin
Because the Borealis Basin covers 40% of the surface of Mars, and much of the Northern Hemisphere, many currently recognized regions of Mars lie within it:
Acidalia Planitia
Arcadia Planitia
Planum Boreum
Utopia Planitia
Vastitas Borealis
Borealis impact
Formation of the Borealis Basin
One possible explanation for the basin's low, flat and relatively crater-free topography is that the basin was formed by a single large impact. Two simulations of a possible impact sketched a profile for the collision: low velocity—6 to 10 km (3.7 to 6.2 mi) per second—oblique angle and a diameter of 1,600–2,700 km (990–1,680 mi). Topographical data from Mars Global Surveyor are consistent with the models and also suggest that the elliptical crater has axes of length 10,600 km (6,600 mi) and 8,500 km (5,300 mi), centered on 67°N 208°E, though this has been partially obscured by later volcanic eruptions that created the Tharsis bulge along its rim. There is evidence for a secondary rim as well. This would make the North Polar Basin by far the largest impact crater in the Solar System, approximately four times the diameter of the next largest craters: Utopia Planitia, which is imbedded inside the North Polar Basin, the South Pole–Aitken basin on The Moon, and Hellas Planitia on Mars's southern hemisphere.
This impact would have resulted in significant crustal melting and a general increase in the rate of crustal formation for a period of 40 million years following the impact. Such a large impact would have disturbed the mantle, altering the normal convection currents and causing upwellings which further increase the amount of melting at the impact site.
The public source identifies “Borealis Basin” as large basin in the northern hemisphere of Mars. This brief keeps that definition visible, then builds a research path around Borealis, Basin and large.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Sep 25, 2026. The linked authority identifier is Q2887477. Authority coordinates are 67.000, 208.000. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
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