Predicting the Strength of Leonid Outbursts

Abstract. A simple model is described that predicts the time of occurrences and peak activity of Leonid shower outbursts. It is assumed that the ejection speeds of escaping particles at each return of the parent comet near perihelion are very small, but solar radiation pressure acting differently on different particles causing a spread of particles into different period orbits. Earlier papers predicted the position of the resulting dust trails. This paper sets forth to better predict the strength of the expected outbursts by considering the role of non-isotropic effects in the interaction with the solar radiation on the dispersion of particles away from the dust trail center. This paper determines the approximate magnitude of the relevant effects. Predictions for the next few years are presented that include such considerations, for reasonable assumptions of particle properties. For example, earlier predictions for the 1999 storm of ZHR = 6,000–7,000 are now reduced by a factor of two, which is in better agreement with the observed ZHR ~ 4,000. The success of the technique, when applied to historic meteor storms and outbursts without need of additional free parameters, lends confidence to the soundness of the underlying model and to its application for future predictions. We predict that the best encounters of this return of the parent-comet will occur in the years 2001 and 2002

THERMAP: a mid-infrared spectro-imager for space missions to small bodies in the inner solar system

We present THERMAP, a mid-infrared (8-16 μm) spectro-imager for space missions to small bodies in the inner solar system, developed in the framework of the MarcoPolo-R asteroid sample return mission. THERMAP is very well suited to characterize the surface thermal environment of a NEO and to map its surface composition. The instrument has two channels, one for imaging and one for spectroscopy: it is both a thermal camera with full 2D imaging capabilities and a slit spectrometer. THERMAP takes advantage of the recent technological developments of uncooled microbolometers detectors, sensitive in the mid-infrared spectral range. THERMAP can acquire thermal images (8-18 μm) of the surface and perform absolute temperature measurements with a precision better than 3.5 K above 200 K. THERMAP can acquire mid-infrared spectra (8-16 μm) of the surface with a spectral resolution Δλ of 0.3 μm. For surface temperatures above 350 K, spectra have a signal-to-noise ratio >60 in the spectral range 9-13 μm where most emission features occur

Low-latitude glaciation and rapid changes in the earth's obliquity explained by obliquity-oblateness feedback

Palaeomagnetic data suggest that the Earth was glaciated at low latitudes during the Palaeoproterozoic (about 2.4-2.2 Gyr ago) and Neoproterozoic (about 820-550 Myr ago) eras, although some of the Neoproterozoic data are disputed. If the Earth's magnetic field was aligned more or less with its spin axis, as it is today, then either the polar ice caps must have extended well down into the tropics-the 'snowball Earth' hypothesis-or the present zonation of climate with respect to latitude must have been reversed. Williams has suggested that the Earth's obliquity may have been greater than 54 degrees during most of its history, which would have made the Equator the coldest part of the planet. But this would require a mechanism to bring the obliquity down to its present value of 23.5 degrees. Here we propose that obliquity-oblateness feedback could have reduced the Earth's obliquity by tens of degrees in less than 100 Myr if the continents were situated so as to promote the formation of large polar ice sheets. A high obliquity for the early Earth may also provide a natural explanation for the present inclination of the lunar orbit with respect to the ecliptic (5 degrees), which is otherwise difficult to explain