Automated design of gravity-assist trajectories to Mars and the outer planets

In this paper, a new approach to planetary mission design is described which automates the search for gravity-assist trajectories. This method finds all conic solutions given a range of launch dates, a range of launch energies and a set of target planets. The new design tool is applied to the problems of finding multiple encounter trajectories to the outer planets and Venus gravity-assist trajectories to Mars. The last four-planet grand tour opportunity (until the year 2153) is identified. It requires an Earth launch in 1996 and encounters Jupiter, Uranus, Neptune, and Pluto. Venus gravity-assist trajectories to Mars for the 30 year period 1995–2024 are examined. It is shown that in many cases these trajectories require less launch energy to reach Mars than direct ballistic trajectories.Assistant Professor, School of Aeronautics and AstronauticsGraduate Student, School of Aeronautics and Astronautics     

Ion winds in Saturn's southern auroral/polar region

We present profiles of the line-of-sight (l.o.s.) ionospheric wind velocities in the southern auroral/polar region of Saturn. Our velocities are derived from the measurement of Doppler shifting of the H₃⁺ν₂Q(1,0⁻) line at 3.953 microns. The data for this study were obtained using the facility high-resolution spectrometer CSHELL on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, during the night of February 6, 2003 (UT). The l.o.s. velocity profiles finally derived are consistent with an extended region of the upper atmosphere sub-corotating with the planet: the ion velocities in the inertial reference are only 1/3 of those expected for full planetary corotation. We discuss the results in the light of recent proposals for the kronian magnetosphere, and suggest that, in this region, Saturn's ion winds may be under solar wind control.     

Hubble Space Telescope imaging polarimetry of Mars during the 2003 opposition

We report results of polarimetric imaging observations of Mars with the Hubble Space Telescope during the 2003 opposition. Through careful calibration, the observations with the ACS camera allow measurements of the polarization degree with an absolute accuracy better than 0.5% and detection of features with polarization degree contrast as small as 0.2%. The general distribution of linear polarization parameters over the Mars disk and their dependence on phase angle and wavelength are well explained qualitatively by a combination of scattering separately by the martian surface and atmosphere. We have discovered transient polarization phenomena interpreted as clouds that are best observed in ultraviolet light. These clouds are optically thin but strongly polarizing, and their origin may be related to atmospheric ice condensation processes.     

Effective collision strengths for fine-structure forbidden transitions among the 3s23p4 levels of Cl ii

The ab initio R -matrix method is used to calculate effective collision strengths for electron-impact excitation of the sulphur-like ion Cl  ii in the close-coupling approximation. All 10 astrophysically important fine-structure forbidden transitions within the 3s²3p⁴     ,     ,     ground configuration levels are considered. The 12 lowest LS target states are included in the calculation. Effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. Results are presented for electron temperatures in the range  log  T (K)=3.3  to  log  T (K)=5.5  , appropriate for astrophysical applications. These are the only effective collision strength data that are currently available.     

The 2dF Galaxy Redshift Survey: luminosity dependence of galaxy clustering

We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range     . The clustering of     galaxies in real space is well-fitted by a correlation length     and power-law slope     . The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M *, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between     and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.     

ASOCAM Observations of CYG X-3: Search for a Hot Stellar Wind

Six CAM observations have been made in the 4 - 14 μm wavelength region to search for further evidence of emission from a hot stellar wind. Initial results suggest that the spectrum detected by Fender et al. using UKIRT extends into the wavelength region covered by ISOCAM. There is also evidence that the source is variable on timescales of ≈ 70 seconds. This revised version was published online in August 2006 with corrections to the Cover Date.     

Environmental changes on Yugorski Peninsula, Kara Sea, Russia, during the last 12,800 radiocarbon years

New pollen and radiocarbon data from an 8.6-m coastal section, Cape Shpindler (69°43′N; 62°48′E), Yugorski Peninsula, document the latest Pleistocene and Holocene environmental history of this low Arctic region. Twelve AMS ¹⁴C dates indicate that the deposits accumulated since about 13,000 until 2000 radiocarbon years BP. A thermokarst lake formed ca. 13,000–12,800 years BP, when scarce arctic tundra vegetation dominated the area. By 12,500 years BP, a shallow lake existed at the site, and Arctic tundra with Poaceae, Cyperaceae, Salix, Saxifraga, and Artemisia dominated nearby vegetation. Climate was colder than today. Betula nana became dominant during the Early Preboreal period about 9500 years BP, responding to a warm event, which was one of the warmest during the Holocene. Decline in B. nana and Salix after 9500 years BP reflects a brief event of Preboreal cooling. A subsequent increase in Betula and Alnus fruticosa pollen percentages reflects amelioration of environmental conditions at the end of Preboreal period (ca. 9300 years BP). A decline in arboreal taxa later, with a dramatic increase in herb taxa, reflects a short cold event at about 9200 years BP. The pollen data reflect a northward movement of tree birch, peaking at the middle Boreal period, around 8500 years BP. Open Betula forest existed on the Kara Sea coast of the Yugorski Peninsula during the Atlantic period (8000–4500 years BP), indicating that climate was significantly warmer than today. Deteriorating climate around the Atlantic–Subboreal boundary (ca. 4500 years BP) is recorded by a decline in Betula percentages. Sedimentation slowed at the site, and processes of denudation and/or soil formation started at the beginning of the Subatlantic period, when vegetation cover on Yugorski Peninsula shifted to near-modern assemblages.