The martian hemispheric dichotomy may be due to a giant impact

@article{Wilhelms1984TheMH,
  title={The martian hemispheric dichotomy may be due to a giant impact},
  author={Don E. Wilhelms and Steven W. Squyres},
  journal={Nature},
  year={1984},
  volume={309},
  pages={138-140}
}
Mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1–3. The more southerly province is heavily cratered, contains relatively old geological units, and superficially resembles the lunar and mercurian highlands. The northern province is relatively lightly cratered and contains younger geological units, including extensive plains, volcanic edifices, and volcanic calderas. Except for the Tharsis and Elysium regions and other large volcanoes… 
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References

SHOWING 1-10 OF 20 REFERENCES
Lunar basin formation and highland stratigraphy
Multiring impact basins, formed after solidification of the lunar crust, account for most or all premare regional deposits and structures expressed in the lunar landscape and for major topographic
Martian Cratering, 4, Mariner 9 initial analysis of cratering chronology
Mars contains a range of crater types similar to the types found on the earth and on the moon and in varying states of preservation. Positive evidence of erosive loss of kilometer scale craters comes
Tectonic evolution of Mars
Any model for the tectonic evolution of Mars must account for two major crustal elements: the Tharsis bulge and the topographically low and lightly cratered northern third of the planet. Ages
Comparison of Martian and lunar multiringed circular basins
The Martian multiringed circular basins Argyre, Hellas, Libya, ‘Martian Schrodinger,’ Edom, and Iapygia resemble lunar basins of comparable size. There is a similar relation between basin size and
The structure and evolution of ancient impact basins on Mars
The number of Martian impact basins, once thought deficient owing to a low number of impactors, has been significantly increased through the identification of structural imprints that remain even
Impact crater and basin control of igneous processes on Mars
Numerous martian impact craters have been heavily modified by processes restricted to the crater interior. A common expression of this modification is the presence of extensive fractures arranged in
Bouguer gravity profiles across the highland-lowland escarpment on Mars
Selected Bouguer gravity profiles crossing the highland-lowland boundary of Mars are calculated. Density-depth models are presented for two areas. All profiles show an isostatic behaviour of the
...
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