NAVIGATING MARS: ALTITUDE AND LONGITUDE ISSUES

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The rules have changed for naming altitudes and longitudes. (Updated 5/14/2014)

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 (0O) to 180O 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 180O.  In the case of Viking 1 it looks like the 49.97O West correlates with the plotted longitude of about 310O (360-49.97O West).     
     For MPF, the table given longitude of 33.22O West correlates well with  the plotted value of about 327 (360-33.22O 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 225.74O 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) 


 
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
 
 
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.