The UVCS can be used to map neutral species in the outer atmosphere and atmospheric tail of Venus (and possibly) Mercury at the occasions when these planets cross the field of view of UVCS.
Obviously one would have to look at neutral or weakly ionized species. The
prime target would be Ly--
. Other lines are of similar interest,
eg. C III, N II, O II and O III, He I for Venus which has a thick
atmosphere. For Mercury one would like to look at lines for Na I, Na II and
K I and K II (Na has been observed previously, K might also exist in
sufficient amounts to be detected).
Paul Wild and Urs Hugentobler from the Astronomisches Institut, University
of Bern, have made some preliminary computation on possible occasions for
such observations. There seems to be only one occasion when Venus apparently
approaches the Sun to less than 5 R
within the next few years.
We are lucky
as this will already be on June 10, 1996 at 16h UT when the distance (as
observed from the Earth) will be 1.9 R
. Then there will be opportunities
every eight years. Of course one should make the computations using the
trajectory of SOHO but there will not be a large difference as SOHO remains
within 6 10
km from the Earth--Sun line. Other lower conjunctions of Venus
with distances < 6 R
will be at the following dates:
Lower conjunctions of Venus with Sun
we could hopefully produce a picture of the Venus atmosphere with good resolution. Furthermore, one could even do some good science with such a picture. It has to be anticipated, that the instrument will no longer work, for the second and third encounter.
The upper conjunctions when Venus could pass our field of
view but will be much farther away (behind the Sun) have also been
added.
Upper conjunctions of Venus with Sun
Lower conjunctions of Mercury with Sun
Upper conjunctions of Mercury with Sun
