Outer Planets

A ~1500-year periodicity has been reported in paleoclimate proxy data and claims have been made that this rhythm persists through glacial and interglacial periods. It has been suggested that the periodicity is driven by solar cycles, though solar cycles longer than 200 years are not well-documented. Here this periodicity is investigated in the context of a 1542-year recurring series of conjunctions of Saturn, Uranus and Neptune. Correlations with solar irradiance, galactic cosmic ray flux, and global temperatures suggest that these conjunctions may drive a regular periodicity in climate regimes that are inherently unstable, but only punctuate stable climate regimes that are following longer orbital periodicities. Keywords: Holocene, barycenter, BP (before present), IRD (ice rafted debris), THC (thermohaline circulation), solar irradiance, GCR (galactic cosmic ray) flux, TSI (total solar irradiance), proxy data, cosmogenic isotopes 10 Be and 14 C,

A Monte Carlo model has been constructed to describe the energization and energy degradation of low-energy protons in an H2 atmosphere in the presence of parallel electric field. The energy spectrum of Ly a collision events is employed to determine the volume emission rate (VER) of H Ly a emissions. Numerical experiments have been performed to study the effect of initial proton energy, electric field, neutral number density, initial pitch angle, and cutoff limit on H Ly a VER. The present study demonstrates that energization of solar EUV-generated low-energy protons by parallel electric fields is incapable of producing optically thin Ly a emissions on Uranus through direct collision with H2. However, nonthermal H atoms, produced through acceleration of protons in parallel electric fields, play an important role in enhancing the Ly a intensity through resonant scattering of solar Ly a flux: resulting emissions are consistent with the broadening of the Ly a line observed on Jupiter by IUE. The Monte Carlo model is also applied to the problem of Doppler-shifted H Ly a emissions from the auroral atmosphere of Jupiter. Energetic neutral H precipitation from the ring current is discussed as a possible source of optically thin H Ly a emissions on outer planets. Estimates are also given for Ha, H/ • , and H2 band emissions resulting from the impact of fast H (of ring current origin) on H2. The input energies and fluxes of precipitating ring current particles are, however, too uncertain to permit definite conclusions.

This paper describes two space science missions that could take advantage of the proposed Ares-V heavy lift launch vehicle; the first, a Titan sample return mission, would leverage the Ares-V's injected mass capability and the second, a new large space telescope mission, would leverage its 8-10 meter shroud diameter. A direct trajectory sample return mission is described that features aerocapture at Titan, which is considered a relatively easy destination for aerocapture because of its dense nitrogen atmosphere and its low gravity. The Ares-V's ability to boost 12 mt on a 6 year Titan trajectory enables this exciting mission. The Advanced Technology Large Aperture Space Telescope (ATLAST), placed into Sun-Earth Lagrange Point 2 (SEL2), would take advantage of the Ares-V's useable payload volume of 860 m, a space big enough to hold 8 school buses, offering significantly greater optical capability than the Humble Telescope. The Ares-V could prove to be a national asset, opening the door to many new, flagship high science value exploration missions.