Polar wander on Mars: Evidence in the geoid

The geoid of Mars is dominated by its equilibrium figure and by the effect of the Tharsis rise. To investigate the rotational stability of Mars prior to the rise of Tharsis, we produced a residual non-hydrostatic geoid without Tharsis. First the hydrostatic component of the present-day flattening was removed. This procedure was performed using a 6% non-hydrostatic component of flattening, a value set by the spin axis precession rate of Mars. Then zonal spherical harmonics up to degree 6 centered on Tharsis were removed. Finally, the resultant residual geoid was evaluated for rotational stability by comparing polar and equatorial moments at 4050 trial pole positions. If the spin axis of ancient Mars was secularly stable, our analysis indicates that substantial polar wander has occurred with the rise of Tharsis. Stable spin axis positions on the non-hydrostatic residual figure of Mars are 15° to 90° from the present-day poles. This result is consistent with previously proposed paleopoles based on magnetic anomalies, geomorphology, and grazing impacts.     

Meteoroid streams and the sporadic background

Summary There is a general agreement that meteoroid streams form through the ejection of dust grains, or meteoroids, up to a few centimeters in size from comets and possibly asteroids. After ejection these meteoroids are subject to forces arising from Solar radiation and the gravitational fields of the planets. Meteoroids may also break up into smaller ones through collisions and other effects. In many cases meteor showers have been observed for millennia, with material being fed into the stream throughout this period from the parent and material lost through the external effects mentioned. Much of the lost material forms the general sporadic background. This paper will review our state of knowledge of the processes involved above and will also aim to give some insight into the structure of the sporadic background     

Vibrationally excited molecular hydrogen in circumstellar clouds and the interstellar CH+ abundance

The production of CH⁺ in dense interstellar clouds under intense UV irradiation is discussed. A model applicable to the cloud towards the star 20 Tau is described.     

Publication of new and revised taxa: a guide to the International Code of Botanical Nomenclature for Diatomists

As revision of diatom taxonomy has become crucial to many recent palaeolimnological studies, the number of nomenclatural changes required has increased. Publication and validation of new names for diatoms is governed by a set of principles published periodically and known collectively as the International Code of Botanical Nomenclature. Creation of a computerised taxonomic database, designed to record recent nomenclatural changes, has revealed many of the names published to be invalid as they fail to comply with all requirements of the code. This paper outlines briefly the criteria needed to validly publish new or revised taxa.