What we have not learned from the troubles with the Hubble

The Hubble space-based telescope is a great tribute to our progress in space. The ability to place an optical telescope at a significant distance from the Earth's surface, away from the interference of the planet's unsteady atmosphere, have already paid off by producing magnificent records of astronomical activities in the depths of outer space. In the past the problems with the alignment of the Hubble's optics were blamed on the manufacturers of it's optical components. The hastily set investigation concluded that the problem is a spherical aberration of the primary mirror (the primary mirror is said to be 2 microns too flat at the edges). It is suggested that the real culprit is the Parker Effect. Since the time of Galileo Galilei, all telescopes were built, aligned, and used on the Earth's surface. Hubble is the first telescope to be built and aligned on Earth for use in space. Because of this we have to consider the fundamental differences between the alignment of surface-based and space-based telescopes. For those who missed our article “The Parker Effect and Navigation in Space” published in the January issue. The Parker Effect describes the result of interaction between inertial bodies (anything that has mass) and non-inertial media (light or other E/M fields)     

The Magnetic Field of Mercury

The magnetic field strength of Mercury at the planet’s surface is approximately 1% that of Earth’s surface field. This comparatively low field strength presents a number of challenges, both theoretically to understand how it is generated and observationally to distinguish the internal field from that due to the solar wind interaction. Conversely, the small field also means that Mercury offers an important opportunity to advance our understanding both of planetary magnetic field generation and magnetosphere-solar wind interactions. The observations from the Mariner 10 magnetometer in 1974 and 1975, and the MESSENGER Magnetometer and plasma instruments during the probe’s first two flybys of Mercury on 14 January and 6 October 2008, provide the basis for our current knowledge of the internal field. The external field arising from the interaction of the magnetosphere with the solar wind is more prominent near Mercury than for any other magnetized planet in the Solar System, and particular attention is therefore paid to indications in the observations of deficiencies in our understanding of the external field. The second MESSENGER flyby occurred over the opposite hemisphere from the other flybys, and these newest data constrain the tilt of the planetary moment from the planet’s spin axis to be less than 5°. Considered as a dipole field, the moment is in the range 240 to 270 nT-R _M ³ , where R _M is Mercury’s radius. Multipole solutions for the planetary field yield a smaller dipole term, 180 to 220 nT-R _M ³ , and higher-order terms that together yield an equatorial surface field from 250 to 290 nT. From the spatial distribution of the fit residuals, the equatorial data are seen to reflect a weaker northward field and a strongly radial field, neither of which can be explained by a centered-dipole matched to the field measured near the pole by Mariner 10. This disparity is a major factor controlling the higher-order terms in the multipole solutions. The residuals are not largest close to the planet, and when considered in magnetospheric coordinates the residuals indicate the presence of a cross-tail current extending to within 0.5R _M altitude on the nightside. A near-tail current with a density of 0.1 μA/m² could account for the low field intensities recorded near the equator. In addition, the MESSENGER flybys include the first plasma observations from Mercury and demonstrate that solar wind plasma is present at low altitudes, below 500 km. Although we can be confident in the dipole-only moment estimates, the data in hand remain subject to ambiguities for distinguishing internal from external contributions. The anticipated observations from orbit at Mercury, first from MESSENGER beginning in March 2011 and later from the dual-spacecraft BepiColombo mission, will be essential to elucidate the higher-order structure in the magnetic field of Mercury that will reveal the telltale signatures of the physics responsible for its generation.     

The Relativistic Proton Spectrometer (RPS) for the Radiation Belt Storm Probes Mission

The Relativistic Proton Spectrometer (RPS) on the Radiation Belt Storm Probes spacecraft is a particle spectrometer designed to measure the flux, angular distribution, and energy spectrum of protons from ～60 MeV to ～2000 MeV. RPS will investigate decades-old questions about the inner Van Allen belt proton environment: a nearby region of space that is relatively unexplored because of the hazards of spacecraft operation there and the difficulties in obtaining accurate proton measurements in an intense penetrating background. RPS is designed to provide the accuracy needed to answer questions about the sources and losses of the inner belt protons and to obtain the measurements required for the next-generation models of trapped protons in the magnetosphere. In addition to detailed information for individual protons, RPS features count rates at a 1-second timescale, internal radiation dosimetry, and information about electrostatic discharge events on the RBSP spacecraft that together will provide new information about space environmental hazards in the Earth’s magnetosphere.     

Voyager 2 Solar Wind Observations in the Outer Heliosphere

We discuss the solar wind parameters measured in the distant heliosphere from the Voyager 2 spacecraft. Periodic variations in the speed of the wind observed at roughly the solar rotation period may correspond to interaction regions between slower and faster streams of wind. Since the interplanetary magnetic field is enhanced in such regions, they are important for the study of modulation of cosmic rays. Unfortunately, direct observation of the enhanced magnetic field from Voyager 2 has been made difficult by spacecraft-associated noise since 1989.     

In memoriam Julius Bartels

Ohne Zusammenfassung

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In memoriam Julius Bartels