ESA Science & Technology - Publication Archive

As the inner end-member of the planetary system, Mercury plays an important role in constraining and testing dynamical and compositional theories of planetary formation. The exploration of Mercury is of fundamental importance for answering questions of astrophysical and philosophical significance, such as: 'Are terrestrial bodies a common feature of most planetary systems in the Galaxy?'.

Two years after the launch of the XMM-Newton Observatory saw a gathering of about 350 scientists at ESTEC for the Conference 'New Vision of the X-ray Universe'. This huge interest in the mission and the rapidly increasing number of scientific papers published as a result of XMM-Newton observations show the importance of ESA's latest observatory for astrophysics in the 21st century.

The term 'Target of Opportunity' (ToO) is used in astronomy to identify unpredictable events whose study is of the highest scientific interest. For Xmm-Newton a ToO is an astronomical event observable by its instruments, which cannot be predicted and scheduled on the time scale of one year, yet is scientifically significant enough to justify the interruption of the ongoing observing programme. Here we discuss the kinds of objects that are suitable for observation as ToOs with XMM-Newton, their scientific interest, and how they are incorporated into the overall observing schedule in terms of target selection and mission planning. What has been done so far and the preliminary results for a few ToO examples are then presented

Water, the basic substance essential for life, has been detected by the Infrared Space Observatory (ISO) in many places throughout the Universe, including our planetary neighbours in the Solar System, clouds circling or pouring out of stars, the vast spaces between stars, and distant galaxies. We show here how these observations enable us to reconstruct the cosmic cycling of water, and its relevance to the presence of water on the Earth.

The XMM-Newton space observatory - a Cornerstone mission in ESA's Horizon 2000 Programme and originally referred to as the High- Throughput X-ray Spectroscopy Mission - was placed into a 48-hour orbit by the first commercial Ariane-5 launch (V504) on 10 December 1999. This brief survey of the scientific results obtained during the first year of XMM-Newton operations clearly illustrates that the observatory is more than living up to expectations and already providing unique and promising results, even before full scientific data analysis gets officially underway.

Last Christmas Eve was very special one for ESA astronauts Claude Nicollier and Jean-François Clervoy: together with their American colleagues, they spent it aboard the Space Shuttle 'Discovery', after concluding the latest scheduled repair mission to the orbiting Hubble Space Telescope (HST). This third Shuttle refurbishment mission to HST was, like its two predecessors, a resounding success. Only days later, as Hubble entered the new millennium, came the first beautiful images of a complex gravitationally lensing cluster of galaxies. The astronauts' visit took place shortly before the 10th Anniversary of the launch of Hubble, which was first placed in orbit on 26 April 1990. Since then, HST has become the leading tool in ultraviolet, optical and near-infrared astronomy and is now looking forward to another decade of exciting discoveries and sharp views of the Universe.

The studies that were carried out in 2001 around the possibility of re-using the Mars Express platform have proven the effectiveness of a fast approach between ESA and the scientific community. It was only in March 2001 that ESA issued a 'Call for Ideas' to react to the identified possibility of a low-cost mission based on the re-use of the platform developed for Mars Express, which will be launched in 2003. A strict schedule was imposed, in order to benefit from these special circumstances, aiming at a launch date for the new mission in 2005, which is the next 'window' for missions to Mars. In response to the Call for Ideas, the scientific community presented a wealth of interesting and challenging proposals.The studies that were carried out in 2001 around the possibility of re-using the Mars Express platform have proven the effectiveness of a fast approach between ESA and the scientific community. It was only in March 2001 that ESA issued a 'Call for Ideas' to react to the identified possibility of a low-cost mission based on the re-use of the platform developed for Mars Express, which will be launched in 2003. A strict schedule was imposed, in order to benefit from these special circumstances, aiming at a launch date for the new mission in 2005, which is the next 'window' for missions to Mars. In response to the Call for Ideas, the scientific community presented a wealth of interesting and challenging proposals.

Few enterprises are more difficult or hazardous than space travel. Yet, even when compared with the achievements of its illustrious predecessors, ESA's Rosetta mission to orbit Comet Wirtanen and deploy a lander on its pristine surface must be regarded as one of the most challenging ventures ever undertaken in more than four decades of space exploration.

The International Rosetta Mission was approved as a Cornerstone mission within ESA's Horizon 2000 Science Programme in November 1993. Even at this early stage, it was envisaged that the ambitious mission would be scheduled for launch in the 2003 timeframe and a number of comet rendezvous opportunities were identified. Although the original target, Comet Schwassman Wachmann 3, has since been superseded by another periodic intruder into the inner Solar System, Comet Wirtanen, there has been little shift in the original launch schedule.

On the night of 12-13 January 2003, one of the most powerful rockets in the world will blast off from Kourou spaceport in French Guiana. On top of the giant Ariane-4, cocooned inside a protective fairing, will be the Rosetta comet chaser, the most ambitious scientific spacecraft ever built in Europe.

First results are presented of an effort to model the storm-time distortion of the magnetic field in the inner magnetosphere using space magnetometer data. Strong geomagnetic storms are relatively rare events, represented by only a small fraction of the data used in the derivation of existing empirical geomagnetic field models. Hence using those models for the mapping of the storm-time magnetosphere is at most an extrapolation based on trends, obtained from quiet and moderately disturbed data. To overcome that limitation, a set of data was created, containing only clear-cut events with Dst <= -65 nT, with the goal to derive models of the inner and near geomagnetic field (R < 15 R_E), representing strongly disturbed geomagnetic configurations and their evolution during the storm cycle. The final data set included about 143,000 records with 5-min average B-vectors, covering 37 major storms between 1996 and 2000. Most of the data came from GOES-8, -9, -10, Polar, and Geotail spacecraft, and two storms in February-March of 1998 were also partially covered by the data of Equator-S. In all cases, only those storms were selected for which concurrent solar wind and IMF data were available for the entire duration of the event. Interplanetary medium data were provided by Wind, ACE, and, to a lesser extent, by IMP 8 and Geotail. The inner magnetospheric field was represented using the newly developed T01 model [Tsyganenko, 2002a, 2002b], with a duskside partial ring current with variable amplitude and scale size, an essential part of the storm-time current system.

Ulysses is now completing its second solar polar orbit, dropping back down in latitude as the Sun passes through its post-maximum phase of the solar cycle. A mid-sized circumpolar coronal hole that formed around solar maximum in the northern hemisphere has persisted and produced a highly inclined CIR, which was observed from ~70°N down to ~30°N. We find that the speed maxima in the high-speed streams follow the same slow drop in speed with decreasing latitude observed in the large polar coronal holes around solar minimum. These results suggest a solar wind acceleration effect that is related to heliolatitude or solar rotation. We also find that the solar wind dynamic pressure is significantly lower in the post-maximum phase of this solar cycle than during the previous one, indicating that while the heliosphere is larger than near solar minimum, it should be smaller than during or after the previous maximum.

The launch of the X-ray Multi-Mirror (XMM) telescope on flight V119, the first commercial launch of Ariane-5, will mark another important milestone for European Space and the Agency's Scientific Programme. The mission, conceived in the late 1970s, entered the assessment-study phase in 1982 and was adopted as a 'Cornerstone Mission' in the then new Horizon 2000 Programme approved by the Science Programme Committee in 1984. The industrial studies were completed in 1988 and the scientific payload selected in 1989.

"As the first spacecraft to use primary electric propulsion in conjunction with gravity manoeuvres, and as Europe's first mission to the Moon, SMART-1 opens up new horizons in space engineering and scientific discovery. Moreover,we promise frequent news and pictures, so that everyone can share in our lunar adventure."

The spectroscopic study of atomic and molecular lines in the infrared, optical and ultraviolet regions of the electromagnetic spectrum has provided us with knowledge and understanding of the physics of normal stars. Spectrallines in the gamma-ray region are produced by new and different processes. These include radioactivity, nuclear excitation, electron- positron annihilation and radiation in the vicinity of magnetic fields. Gamma-ray lines are indicators of all these processes and have now been observed at astrophysical sites.They provide powerful diagnostics for the high-energy processes occurring in some of the most violent and exotic objects in the Universe. The key features of the Integral satellite will allow us to study in great detail these, and other sites of key interest in today's astrophysical research, with high sensitivity combined with very good energy resolution and very good imaging capabilities (in order to avoid source confusion) using two main instruments, an 'Imager' and a 'Spectrometer'.

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, beta_i ~ 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V_x ~ 700 km/s and a diameter of ~1 R_e. The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were ~15-19 nA m^-2. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA m^-2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

The SOHO mission is a major element of the joint ESA/NASA International Solar Terrestrial Programme (ISTP). ESA was responsible for the spacecraft's procurement, integration and testing. NASA provided the launcher, launch services and ground-segment system and is responsible for in-flight operations following the launch on 2 December 1995. The SOHO mission operations are therefore conducted under a NASA/Goddard Space Flight Center (GSFC) contract with Allied-Signal Technology Corporation (ATSC). Following the spacecraft's in-orbit checkout and the transit from low Earth orbit to its operational halo orbit around the Lagrangian point (L1) between the Earth and the Sun, the SOHO mission was declared fully operational in April 1996. SOHO then completed its two-year primary mission and entered an extended-mission phase in May 1998. On 25 June 1998, all contact with SOHO was lost.

Experimental evidence is provided for the existence of slow-mode magnetosonic solitons in the collisionless plasma at the magnetopause boundary layer. The solitons were detected by the fleet of Cluster spacecraft at the dusk flank of the magnetosphere as magnetic field depressions (up to 85%) accompanied with enhancement of the plasma density and temperature by a factor of 2. The solitons propagate 250 km/s with respect to the satellites and have perpendicular size of 1000-2000 km, which is a few ion inertial scale lengths. The comparison with numerical solutions of a theoretical model shows quantitative agreement between the model and observations.

The Faint Sky Variability Survey is aimed at finding photometric and/or astrometric variable objects in the brightness range between ~16th and ~24th magnitude on timescales between tens of minutes and years with photometric precisions ranging from 3 millimagnitudes for the brightest to 0.2 magnitudes for the faintest objects. An area of ~23 square degrees, located at mid and high Galactic latitudes, has been covered using the Wide Field Camera on the 2.5m Isaac Newton Telescope on La Palma. Here we describe the main goals of the Faint Sky Variability Survey and the data reduction process.

Cataclysmic Variables' (CVs) are a distinct class of interacting binaries, transferring mass from a donor star to a degenerate accretor, a white dwarf (WD). In all observational determinations, and as is required by theory for stable mass transfer, the donor star is of lower mass than the accretor.