QUESTION:
When I see an analysis of the Martian atmosphere I do not find nitrogen
listed as a significant component. Oxygen apparently has been, for the most
part, assimilated into componds in the soil but nitrogen being much less
reactive should still be on Mars. What is the current explanation for its
absence in the Martian atmosphere and would Viking or the next lander be
able to detect nitrogeous compounds in the soil?

ANSWER from Bruce Jakosky on May 28, 1997:
Nitrogen is about 2.5 % of the martian atmosphere, but you're right that
that still means there is very little nitrogen in the atmosphere.  There
is evidence that a substantial amount of the nitrogen has been lost to
space.  This comes from the ratio of nitrogen-15 to nitrogen-14.  Nitrogen-15
has one more neutron than nitrogen-14, and because it is heavier it will
escape to space with more difficulty.  As a result, escape to space will
increase the ratio of nitrogen-15 to nitrogen-14.  As measured by the
Viking spacecraft, the ratio is about 1.7 times the terrestrial value,
indicating that about 90 % of the nitrogen has been lost to space.

In addition, nitrogen (and other gases) could have been lost to space
very early, as a result of the impact of planetesimals or asteroids onto
the surface during the planet's formation.  We see the impact craters that
were left behind.  This type of ejection to space would not remove the
heavier nitrogen preferentially (it would remove both equally), so that
the loss from this process adds on to the loss described above.  Our most
recent calculations suggest that 50-90 % of the atmopshere that was
present when the oldest martian surfaces were formed could have been
lost to space, and that even more could have been lost before the surface
features formed.

As a result, it looks like more than 95 %, and as much as 99 %, of the martian
nitrogen has been lost to space.

One thing that is uncertain is that this still may not account for all of the
nitrogen that ever was on Mars.  It is not clear whether some has formed
nitrates in the soil or whether some might never have been outgassed into
the atmosphere.  Also, it is not known how much nitrogen Mars originally
had.