Hellas Planitia

From Wikipedia, the free encyclopedia

Hellas Planitia, also known as the Hellas Impact Basin, is a roughly circular impact crater located in the southern hemisphere of the planet Mars. With a diameter of about 2,300 km (1437 Miles)^[1], it is the largest impact structure on the planet. The basin is thought to have been formed during the Late Heavy Bombardment period of the Solar System, > 3.9 billion years ago, when a large asteroid impacted Mars ^[2].

To get an idea of its size, if all the material excavated from it were spread evenly on the continental United States, there would be a 3.5 km (2 miles) thick layer of debris.^[3] If the ejecta were distributed evenly over the surface of Mars, which has 15 times the surface area of the continental United States, there would be a layer over 200 meters thick.

Due to its size and contrasting light colour, Hellas Planitia was one of the first Martian features discovered from Earth by telescope. It was at one point known as 'Lockyer Land' before Giovanni Schiaparelli gave the feature the name Hellas ('Greece'). Richard Anthony Proctor had named it in 1867 in honour of Sir Joseph Norman Lockyer, an English astronomer who, using a 6.25-inch (16-cm) refractor, produced "the first really truthful representation of the planet" (in the estimation of E. M. Antoniadi).

The altitude difference between the rim and the bottom is ~9 km (5.6 Miles). The depth of the crater (~7 km^[4], or 3.7 to 4.3 miles, below the topographic datum, or "sea level" of Mars) explains the atmospheric pressure at the bottom: 1155 Pa^[4] (11.55 mbar) (.34375 InHG). This is 89% higher than the pressure at the topographical datum (610 Pa, or 6.1 mbar or .18 InHG). The pressure is above the triple point of water, suggesting that the liquid phase would be stable when the temperature is above ~0 C (32 F)

[edit] See also

• Argyre Planitia
• List of plains on Mars
• Geography of Mars

[edit] References

1. ^ Schultz, R.A., and H.V. Frey, A new survey of multiring impact basins on Mars, J. Geops. Res., 95, pp. 14175-14189, 1990.
2. ^ Acuña et al., Science, 284, 790-793, 1999 [1]
3. ^ http://rst.gsfc.nasa.gov/Sect19/Sect19_12.html
4. ^ ^{a b} Martian Weather Observation MGS radio science measured 11.50 mbar at 34.4 degrees S 59.6 degrees E -7152 meters

• J. N. Lockyer, Observations on the Planet Mars (Abstract), Monthly Notices of the Royal Astronomical Society, Vol. 23, p. 246
• E. M. Antoniadi, The Hourglass Sea on Mars, Knowledge, July 1, 1897, pp. 169-172.
• A NASA site that writes of Hellas Planitia
• The Hellas Of Catastroph