Hellas Planitia
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| Hellas | |
 NASA image of Hellas Planitia |
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| Region | Hellas quadrangle, south of Iapygia |
|---|---|
| Coordinates | 42.7° S, 70.0° E |
| Diameter | 2300 km |
| Depth | ~7 km |
Hellas Planitia, also known as the Hellas Impact Basin, is a huge, roughly circular impact basin located in the southern hemisphere of the planet Mars. It is known to be the largest visible impact crater in our Solar System due to its area, length and size. The basin floor is 3 km deeper than the moon's South Pole-Aitken basin, extends about 2300 km east to west,[1] and its debris field could be interpereted as extending about 7000 km across[2][3]. It is centered at .
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[edit] Description
With a diameter of about 2,300 km (1,400 mi)[4], it is the largest impact structure on the planet. If all the material excavated from it were spread evenly on the continental United States, there would be a 3.5 km (12,000 ft) thick layer of debris.[5] The basin is thought to have been formed during the Late Heavy Bombardment period of the Solar System, over 3.9 billion years ago, when a large asteroid hit the surface.[6]
The altitude difference between the rim and the bottom is ~9 km (30,000 ft). The depth of the crater (~7 km[7] (23,000 ft) below the standard topographic datum of Mars) explains the atmospheric pressure at the bottom: 1155 Pa[7] (11.55 mbar or 0.17 psi). This is 89% higher than the pressure at the topographical datum (610 Pa, or 6.1 mbar or 0.09 psi) and above the triple point of water, suggesting that the liquid phase would be transient (would evaporate over time) if the the temperature would rise above 0 °C (32 °F).[8]
Some of the low elevation outflow channels extend into Hellas from the volcanic complex Hadriaca Patera to the northeast, two of which Mars Orbiter Camera images show contain gullies: Dao Vallis and Reull Vallis. These gullies are also low enough for liquid water to be transient around Martian noon, if the temperature would rise above 0 Celsius.[9]
[edit] Discovery and naming
Due to its size and its light colouring, which contrasts with the rest of the planet, Hellas Planitia was one of the first Martian features discovered from Earth by telescope. Before Giovanni Schiaparelli gave it the name Hellas ('Greece'), it was known as 'Lockyer Land', having been named by Richard Anthony Proctor 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).[10]
[edit] See also
[edit] Notes
- ^ The part below zero datum, see Geography of Mars#Zero elevation
- ^ The part above zero datum, The part below zero datum, see Geography of Mars#Zero elevation
- ^ Remote Sensing Tutorial Page 19-12, NASA
- ^ Schultz, R.A., and H.V. Frey, A new survey of multiring impact basins on Mars, J. Geops. Res., 95, pp. 14175-14189, 1990.
- ^ Remote Sensing Tutorial Page 19-12
- ^ Acuña et al., Science, 284, 790-793, 1999 [1]
- ^ a b Martian Weather Observation MGS radio science measured 11.50 mbar at 34.4° S 59.6° E -7152 meters
- ^ Making a Splash on Mars, NASA, 2000-06-29
- ^ Heldmann et al., Jennifer L., para 3 page 2 Martian Gullies Mars#References DOI:10.1029/2004JE002261
- ^ William Sheehan. The Planet Mars: A History of Observation and Discovery. Retrieved on 2007-08-20.
[edit] References
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This article or section includes a list of references or external links, but its sources remain unclear because it lacks in-text citations. You can improve this article by introducing more precise citations. |
- 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.
[edit] External links
- The Hellas Of Catastroph, Peter Ravenscroft, 2000-08-16, Space Daily
- Google Mars scrollable map - centered on Hellas
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