QUESTION:
Will it be winter, spring, summer, or autumn at 19 deg N when Pathfinder
lands on Mars?

ANSWER from Mary Urquhart on June 30, 1997:
A good question.  On July 4th, when Pathfinder lands on Mars, it will be
late summer in the northern hemisphere.  The Sun will be higher in the sky
than during most other times of the Martian year, and this will help Mars
Pathfinder get more of the energy it needs from the solar panels.

You can check out the seasons on Mars for yourself on the "Mars Today" web
site at:

http://humbabe.arc.nasa.gov/

which has a great deal of useful information.  One piece of information on
the Web page is a number called Ls which indicates where Mars is in its
orbit around the Sun.  (The orbit is divided into 360 degrees.) Mars is
tilted on its axis (just like the Earth).  At one part of the orbit the
North pole of Mars is pointed towards the Sun and it is summer in the
northern hemisphere.  The maximum tilt toward the Sun for the North pole
occurs at an Ls of 90 degrees.  On the opposite side of the orbit, the
northern hemisphere (Ls of 270 degrees) will be tilted away from the Sun and
the northern hemisphere will be in winter.

So, if you know Ls, you know the season in the season in the Martian
northern hemisphere. Ls= 0 at the vernal equinox (or the beginning of
spring), 90 at the summer solstice (or the beginning of summer), 180 at the
autumnal equinox (or the beginning of fall), and 270 at the winter solstice
(or the beginning of winter).  The seasons are just the opposite in the
southern hemisphere for the same Ls.

If you look at the bottom of the "Mars Today" web page you will see the Ls
for today's date.  Now you know what season it is in the northern AND
southern hemispheres on Mars today.  If you look on July 4, 1997 (the day
Pathfinder lands) you will see Ls = 142 or so.  Since 142 is a little more
than half way between the beginning of summer (Ls = 90) and the beginning of
fall (Ls = 180), we know that Pathfinder will land in late summer at 19 deg
N!