NAVIGATING MARS: ALTITUDE AND LONGITUDE ISSUES

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The rules have changed for naming altitudes and longitudes. (Updated 4/16/2019)

Anyone who attempts to seriously crosscheck information about Mars published over the years that we have been sending probes there is likely to get confused because the rules for establishing altitude and longitude have both changed. This article will attempt to clarify the issues involved. Obviously altitudes will greatly affect pressures.

Figure 1 - There are widely different altitudes published for Olympus Mons.

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LONGITUDE SYSTEMS IN USE AND MARS LANDING COORDINATES.

To find specific sites on Mars, you can now use Google Mars. The landing sites for Mars landers are given below; however the topography (MOLA) map included further below appears to use a different coordinate system for denoting longitudes. On Earth longitude coordinates are given from the Prime Meridian (0^O) to 180^O East or West. Phoenix was plotted by this writer, but for Viking 1, Viking 2, and PathFinder (MPF) there are West longitudes in excess of 180^O. In the case of Viking 1 it looks like the 49.97^O West correlates with the plotted longitude of about 310^O (360-49.97^O West).
For MPF, the table given longitude of 33.22^O West correlates well with the plotted value of about 327 (360-33.22^O West). The Google map shows Isidis, which is where the British Beagle was supposed to land, but that probe failed. So the map must have been produced before that failure and the landing of Phoenix that I had to add. This leaves us with one problem, Viking 2. It is plotted at about 135 (East), but the chart lists it as landing at 225.74^O West. However, these longitude positions are basically equal. There are two systems in use for longitudes on Mars:

(1) Planetographic latitude with West longitude. This is the coordinate system originally used in the Gazetteer of Planetary Nomenclature, and the system used for maps produced before approximately 2002. An ellipsoidal equatorial radius of 3,396.0 km and polar radius of 3,376.8 km are assumed.

(2) Planetocentric latitude with East longitude. This is the coordinate system used for maps produced after approximately 2002, although the planetographic latitudes and west longitudes are also shown on printed maps for reference, and the radii on which these are based are different (3,396.19 and 3,376.20 km).

LANDER	DATE LANDED	LATITUDE	LONGITUDE
VIKING 1	JULY 20, 1976	22.48 N (Smith et al. states 22.2692 N)	49.97 W (Smith et al. states 311.8113 E)
VIKING 2	SEP 3, 1976	47.97 N (Smith et al. states 47.6680 N)	225.74 W (Smith et al. states 134.0430 E)
PATHFINDER	JULY 4, 1997	19.13 N (Smith et al. states 19.0949 N)	33.22 W (Smith et al. states 326.5092 E)
SPIRIT at Gusev Crater	JAN 4, 2004	14.5718 S	175.4785 W (Mars globe shows 184.5W, 14.7 S)
OPPORTUNITY	JAN 25, 2004	1.95 S	354.47 E
PHOENIX	MAY 25, 2008	68 N	234 E
MARS SCIENCE LAB	AUG 6, 2012	4.59 S	137.44 E (222.56W)
INSIGHT	NOV 26, 2018	4.5 N	135 E (225 W)

Smith figures from Smith, D. E., et al. (2001), Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars, J. Geophys. Res., 106, 23,689–23,722, doi:10.1029/2000JE001364. http://www-geodyn.mit.edu/mola.summary.pdf

MARTIAN QUADRANGLES

Name^[4]	Number^[4]	Area^[4]
Mare Boreum (North Pole)	MC-01	Latitude 65° to 90°, Longitude 0° to 360°
Diacria	MC-02	Latitude 30° to 65°, Longitude 120° to 180°
Arcadia	MC-03	Latitude 30° to 65°, Longitude 60° to 120°
Mare Acidalium^[5]	MC-04	Latitude 30° to 65°, Longitude 0° to 60°
Ismenius Lacus	MC-05	Latitude 30° to 65°, Longitude 300° to 360°
Casius^[6]	MC-06	Latitude 30° to 65°, Longitude 240° to 300°
Cebrenia	MC-07	Latitude 30° to 65°, Longitude 180° to 240°
Amazonis	MC-08	Latitude 0° to 30°, Longitude 135° to 180°
Tharsis	MC-09	Latitude 0° to 30°, Longitude 90° to 135°
Lunae Palus	MC-10	Latitude 0° to 30°, Longitude 45° to 90°
Oxia Palus	MC-11	Latitude 0° to 30°, Longitude 0° to 45°
Arabia^[7]	MC-12	Latitude 0° to 30°, Longitude 315° to 360°
Syrtis Major^[8]	MC-13	Latitude 0° to 30°, Longitude 270° to 315°
Amenthes	MC-14	Latitude 0° to 30°, Longitude 225° to 270°
Elysium	MC-15	Latitude 0° to 30°, Longitude 180° to 225°
Memnonia	MC-16	Latitude -30° to 0°, Longitude 135° to 180°
Phoenicis Lacus	MC-17	Latitude -30° to 0°, Longitude 90° to 135°
Coprates	MC-18	Latitude -30° to 0°, Longitude 45° to 90°
Margaritifer Sinus	MC-19	Latitude -30° to 0°, Longitude 0° to 45°
Sinus Sabaeus	MC-20	Latitude -30° to 0°, Longitude 315° to 360°
Iapygia	MC-21	Latitude -30° to 0°, Longitude 270° to 315°
Mare Tyrrhenum	MC-22	Latitude -30° to 0°, Longitude 225° to 270°
Aeolis	MC-23	Latitude -30° to 0°, Longitude 180° to 225°
Phaethontis	MC-24	Latitude -65° to -30°, Longitude 120° to 180°
Thaumasia	MC-25	Latitude -65° to -30°, Longitude 60° to 120°
Argyre	MC-26	Latitude -65° to -30°, Longitude 0° to 60°
Noachis^[9]	MC-27	Latitude -65° to -30°, Longitude 300° to 360°
Hellas	MC-28	Latitude -65° to -30°, Longitude 240° to 300°
Eridania	MC-29	Latitude -65° to -30°, Longitude 180° to 240°
Mare Australe (South Pole)	MC-30	Latitude -90° to -65°, Longitude 0° to 360°

The Relationship of the MOLA Topography of Mars to the Mean Atmospheric Pressure

Internet Source: http://adsabs.harvard.edu/abs/1999DPS....31.6702S

Smith, D. E.; Zuber, M. T. American Astronomical Society, DPS meeting #31, #67.02

The MOLA topography of Mars is based on a new mean radius of the planet and new equipotential surface for the areoid. The mean atmospheric pressure surface of 6.1mbars that has been used in the past as a reference level for topography does not apply to the zero level of MOLA elevations. The MOLA mean radius of the planet is 3,389,508 meters and the mean equatorial radius is 3,396,000 meters (Zuber incorrectly gives it as 339,600 meters). The areoid of the zero level of the MOLA altimetry is defined to be the potential surface with the same potential as the mean equatorial radius. The MOLA topography differs from the USGS digital elevation data by approximately 1.6 km, with MOLA higher. The average pressure on the MOLA reference surface for Ls =0 is approximately 5.1 mbars and has been derived from occultation data obtained from the tracking of Viking, Mariner, and MGS spacecraft and interpolated with the aid of the Ames Mars GCM. The new topography and the new occultation data are providing a more reliable relationship between elevation and surface pressure.