ESA Science & Technology - Publication Archive

Proceedings of the Fifth IAA International Conference on Low-Cost planetary Missions

Geosail is a small, low cost, innovative mission designed to exploit the versatility of solar sail propulsion for the exploration of magnetic reconnection and electron dynamics in the earth's magnetotail. The GeoSail mission requires only a very low performance solar sail to precess the major axis of an otherwise inertially fixed orbit, thus maintaining payload alignment within the geomagnetic tail. This constant rotation enables a near continuous observation window with the opportunity to probe the rapid dynamic evolution of energetic particle distributions in this critical region of geospace. An end-to-end system design study has been concluded and the key performance requirements identified. The level of solar sail performance required for GeoSail is typical of that currently being discussed within Europe for a near-term technology demonstration mission. GeoSail is therefore capable of providing both technology validation within the cost restrictions of a SMART mission while also returning unique science data from a first solar sail mission.

The last few months have proved to be a time when both the Hubble project and the ST-ECF are considering the transition period when Hubble will end its life and the James Webb Space Telescope (JWST) will begin operations.

Planck is the third Medium-Sized Mission (M3) of ESA's Horizon 2000 Scientific Programme. It is designed to image the anisotropies of the Cosmic Microwave Background (CMB) over the whole sky, with unprecedented sensitivity (DeltaT/T ~ 2 x 10^-6) and angular resolution (better than 10 arcminutes). Planck will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early universe and the origin of cosmic structure. The ability to measure to high accuracy the angular power spectrum of the CMB fluctuations will allow the determination of fundamental cosmological parameters such as the density parameter (Omega₀) and the Hubble constant H₀, with an uncertainty of order a few percent. In addition to the main cosmological goals of the mission, the Planck sky survey will be used to study in detail the very sources of emission which "contaminate" the signal due to the CMB, and will result in a wealth of information on the properties of extragalactic sources, and on the dust and gas in our own galaxy. One specific notable result will be the measurement of the Sunyaev-Zeldovich effect in many thousands of galaxy clusters. We will present an overview of the Planck mission, its scientific objectives, the key elements of its technical design, and its current status.

In this paper we define and describe morphological features that have colloquially been termed "spiders" and map their distribution in the south polar region of Mars. We show that these features go through a distinct seasonal evolution, exhibiting dark plumes and associated fan-shaped deposits during the local defrosting of the seasonal cap. We have documented the seasonal evolution of the cryptic region and have found that spiders only occur within this terrain. These observations are consistent with a geyser-like model for spider formation. Association with the transparent (cryptic) portion of the seasonal cap is consistent with basal sublimation and the resulting venting of CO₂ gas. Also consistent with such venting is the observation of dark fan-shaped deposits apparently emanating from spider centers. Spiders are additionally confined to the polar layered deposits presumably due to the poorly consolidated and easily eroded nature of their upper surface.

Eds. Marsden, R., Scherer, K. and Heber, B.

Launched from Cape Canaveral more than 13 years ago, Ulysses is well on its way to completing two full circuits of the Sun in a unique orbit that takes it over the north and south poles of our star. In doing so, the European-built space probe and its payload of scientific instruments have added a fundamentally new perspective to our knowledge of the bubble in space in which the Sun and the Solar System exist, called 'the heliosphere'.

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a truly international enterprise. While ESA is responsible for the overall mission, the satellite's development and the flight operations, the launcher is provided by the Russian Space Agency and the second ground station is provided by NASA. The scientific instruments and the Science Data Centre are provided by the mission's Principal Investigators, with funding from national organisations.

GRS 1747-312 is a bright transient X-ray source in the globular cluster Terzan 6 with quasi-periodic outbursts approximately every 4.5 months. We carried out 260 keV target-of-opportunity observations during eight outbursts with the Proportional Counter Array on the RXTE satellite, for a total exposure time of 301 ks, and detect the first unambiguous thermonuclear X-ray bursts from this source.

Measurements of the Lyman alpha column brightness by the Geocoronal Imager (GEO), part of the FUV imaging system on board the IMAGE satellite, have been used to derive an empirical model of the neutral hydrogen density distribution at high altitudes (>3.5 R_E geocentric distance) on the night-side of the Earth. The model presented is an effort to provide the density profiles needed to analyze the energetic neutral atom imaging data at ring current altitudes and above. The variable solar Lyman alpha flux is obtained from the UARS/SOLSTICE measurements and the scattered solar Lyman alpha emissions from interplanetary hydrogen are obtained from a model. Assuming that the exosphere at high altitudes (>3.5 R_E geocentric distance) can be considered as an optical thin medium and that the hydrogen density profile can be expressed as a double exponential we show that the Lyman alpha column brightness can be converted to hydrogen density profiles. The hydrogen density above 5 R_E is found to be slightly higher for large solar zenith angles than for 90° solar zenith angle. The hydrogen density shows temporal variations which are not controlled by any solar quantity or geomagnetic parameter alone. Our Lyman alpha profiles and derived hydrogen density profiles are close to what was observed by Dynamics Explorer 1 [Rairden et al., 1986]. Above 8 R_E we find higher densities than they did for all solar zenith angles >90°. We do not find any evidence of depletion due to charge exchange with solar wind protons outside the magnetopause. Our results are only valid above 3.5 R_E

We present results from two Chandra/ACIS-I observations and one XMM-Newton observation of X-ray emission from the interstellar medium (ISM) and the inner radio lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial surface brightness profile that is well described by a beta-model profile with index beta = 0.40 ± 0.04 and a temperature of k_BT_ISM ~ 0.29 keV beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is coincident with the outer half of the southwest radio lobe, and a bright X-ray enhancement is detected along the edge of the lobe. On the basis of energetic and lifetime arguments, we reject a nonthermal explanation for this emission. We model this emission as a thin, hot shell or cap of X-ray-emitting plasma surrounding the radio lobe that was created by the supersonic inflation of the lobe. This plasma shell is both hotter than (k_BT_SH ~ 2.9 keV) and greatly overpressurized relative to the ambient ISM, indicating supersonic expansion. We estimate that the lobe is expanding into the ISM at approximately Mach 8.5, or 2400 km s^-1. We are not directly observing the bow shock, but rather the cooler, denser material that is accumulating ahead of the contact discontinuity. The thermal energy in the shell is a significant fraction of the thermal energy of the hot ISM, demonstrating the possibility that the hot ISM of early galaxies can be reenergized by outflows from nuclear activity. Interestingly, no similarly bright X-ray emission is detected in or along the edge of the northeast lobe, implying that there are differences in the dynamics and evolution of the kiloparsec-scale radio components.

We present a comprehensive lensing analysis of the rich cluster Cl0024+1654 (z=0.395) based on panoramic sparse-sampled imaging conducted with the WFPC2 and STIS cameras on board the Hubble Space Telescope. By comparing higher fidelity signals in the limited STIS data with the wider field data available from WFPC2, we demonstrate an ability to detect reliably weak lensing signals to a cluster radius of ~5 (h₆₅)^-1 Mpc where the mean shear is around 1%.

We discuss chorus emissions measured by the four Cluster spacecraft at close separations during a geomagnetically disturbed period on 18 April 2002. We analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 Earth's radii, within a 2000 km long source region located close to the equator. The characteristic wave vector directions in this region are nearly parallel to the field lines and the multipoint measurement demonstrates the dynamic character of the chorus source region, changing the Poynting flux direction at time scales shorter than a few seconds. The electric field waveforms of the chorus wave packets (forming separate chorus elements on power spectrograms) show a fine structure consisting of subpackets with a maximum amplitude above 30 mV/m. To study this fine structure we have used a sine-wave parametric model with a variable amplitude.

Coordinated data analyses from the initial in-ecliptic phase of the Ulysses mission are presented with special attention given to measurements of particles and fields in interplanetary space. The collection of papers presents the results of observations of large solar flares and effects related to solar wind, and some results are synopsized. The charged-particle instrumentation on the spacecraft is shown to have good dynamic range and energy coverage as demonstrated by a sample proton-energy spectrum.

The Ulysses spacecraft encountered Jupiter in February 1992, passing within 6.31 radii of the planet. For approximately 8 days it was inside the Jovian magnetosphere, and for several days before and after that, Ulysses was in the interaction regions formed by the solar wind (the magnetosheath and boundary layer).

Proceedings of the 28th ESLAB Symposium, held in Friedrichshafen, Germany, April 19-21, 1994. Ed. Marsden, R.G.

Article that appeared in the popular astronomy magazine Sky & Telescope. Unfortunately no preview of the publication exists online. The link from this page, however, will take you to the Sky Publishing website where you purchase a copy of the whole magazine.

For much of the past four decades, the scientific probes sent into space stayed relatively close to the equatorial plane of the Sun, which contains the orbits of Earth and other planets. But a few years ago a single craft, Ulysses, ventured out of that thin zone and into the 'polar regions' of interplanetary space.

Proceedings of the 34th ESLAB Symposium held 3-6 October 2000 at ESTEC, Noordwijk, The Netherlands. Ed. Marsden, R.G.

The Ulysses mission has explored and charted the heliosphere around the minimum in the 11-year cycle of solar activity from a high-latitude perspective. Here, for the first time, is a comprehensive review of the results of that mission. The book furthers our knowledge of the heliosphere near solar minimum and provides the basis for understanding the more complex state of the heliosphere around solar maximum. Amongst other topics, the book covers: the solar wind, the large- and small-scale structure of the heliosphere in 3 dimensions, cosmic rays and energetic particles, interstellar aspects, including cosmic dust. In "The Heliosphere Near Solar Minimum: The Ulysses Perspective", Eds. Balogh, A., Marsden, R.G. & Smith, E.J., Springer-Praxis, Chichester (2001) ISBN 1-85233-204-2, XXV + 411 pp.

Vilnius, Lithuania, 2-6 July 2001
Editors: Vladas Vansevicius, Arunas Kucinskas, Jokubas Sudzius
The proceedings are published in Astrophysics and Space Science Vol. 280, Issue 1-2, 2002 (see contents list online - restricted access) and are available online