Radio Occultation Latitude Coverage
Radio occultation experiments with MGS began in January 1998.
This figure shows the distribution in
latitude and season of the profiles that are currently available
through this Web site. The measurement latitude is determined by
the position of Earth relative to the MGS orbit plane, and the
latitude varies continually due to the orbital motion of Earth and
Mars about the Sun. Occultations occur at high latitudes when Earth
is in or near the MGS orbit plane, but no occultations occur when
the MGS orbit is nearly face-on as viewed from Earth. Measurements
in the Southern Hemisphere are sporadic due to failure of a
spacecraft high-gain antenna gimbal.
The horizontal axis is solar longitude (Ls), an angular measure
of the position of Mars in its orbit about the Sun. By definition,
Ls = 0 at the vernal equinox of the Northern Hemisphere, and one
Martian year spans 360 degrees of Ls. Martian years are identified
by a year number near the bottom of the figure. In this convention,
Martian year 1 (MY 1) begins at Ls = 0 on 11 April 1955; MY 24
begins on 14 July 1998; MY 25 begins on 31 May 2000; MY 26 begins on
18 April 2002; and MY 27 begins on 05 March 2004.
Last updated: September 19, 2007