The major observational results of the detection of the nucleus of Comet Halley will be summarized with some emphasis on the images. A comparison to or context with ground based observations will be discussed. The paradigm set by the first observations of a cometary nucleus should be critically reviewed. The results of the VEGA missions and the recent observations of the nucleus of Comet Borrelly by DS-1 will also be considered.

On 22 Sept 2001 at 22h 29m 33s UTC the Deep Space 1 (DS1) spacecraft encountered the comet 19P/Borrelly at a distance of 2171 km. Measurements were undertaken by two dedicated science instruments on the spacecraft and by the spacecraft’s ion propulsion system diagnostic sensors (IDS). The images are the highest resolution ever obtained of a cometary nucleus and show topography and albedo differences on the surface at a resolution of 47m. The disk averaged geometric albedo is less than 0.03, among the lowest of any solar system object observed. The surface reflectance varies by a factor of three; the most absorbing areas having a normal reflectance of less than 0.01. Material is being emitted of from localized regions on the nucleus generally in the sunward direction. These regions are cylindrically shaped about 0.5 km in diameter and about 5 km in length. The cometary bow shock and other features associated with the cometary environs are asymmetrically offset from the sun-Borrelly axis. This suggests that the localized emission regions seen in the images may cause the coma to be asymmetrically offset from the sun-nucleus line. Such an offset has not been reported in previous spacecraft encounters with other comets.

The new scenario of the Rosetta mission to comet 67/P Churyumov-Gerasimenko (launch on February 2004), includes as baseline the fly-by of one or two asteroids. Several asteroids are now possible fly-by candidates (single or double) within the available resources. Other candidates whose fly-bys require a larger Δv can be also considered if the Rosetta interplanetary orbit insertion will cost less Δv.

All the up to date available information on the possible targets are discussed in this report.

MUSES-C is launched in May 2003, and arrives in the vicinity of a near-Earth asteroid (25143)1998 SF36 in June 2005. The spectral type is S and its diameter is 300-600 m. During four months stay multi-band imaging, near-infrared spectra, and X-ray spectra will be taken at the nominal altitude of about 6km above the asteroid surface.. Sampling of the surface material will be made at two different locations. The total mass collected will be about 1 g. A miniature hopping lander on which imaging cameras are boarded will be dropped onto the surface. The sample will be returned to the earth in June 2007. These methods, the close-up global observation from the spacecraft, in situ observation from the lander, and detailed analysis of the returned sample, can, as well as ground-based observation of the targeted asteroid, provide information of surface material distribution in various scales, and also provide powerful benchmarks to interpretation of spectroscopic data obtained through ground-based observation of S-type asteroids.

The Dawn mission, the ninth in the series of NASA Discovery missions, is scheduled for launch in late May 2006 on a voyage to both Vesta and Ceres. The mission carries a framing camera, visible and infrared mapping spectrometer, gamma ray and neutron spectrometer, laser altimeter and magnetometer to understand and contrast these two very different bodies. Vesta apparently accreted dry, differentiated, and formed an iron core. Ceres apparently contains much water and ice and has remained relatively cool over its lifetime. The community of 1AU observers can help optimize the Dawn mission by improving the knowledge of Vesta and Ceres rotation axes, thus improving our knowledge of when regions and features will be best illuminated. The detection of any satellites would not just identify a potential hazard, and a secondary target of interest, but would also determine the mass of the primaries, enabling better mission planning. Characterization of the surface in any way, including identifying potential targets for detailed study, is also most welcome.

The ESA space astrometry mission has a great potential of observation and discovery on the solar system objects. GAIA is due for launch in 2010 and the survey mission will last five years. In addition to accurate astrometry of about 1 billion stars, the mission will survey all solar system objects brighter than 20th magnitude, in astrometry and with multicolor photometry. Each object will be observed about a hundred times during the five year mission. It is expected that more than 500 000 asteroids will be repeatedly measured by the mission.

ISHTAR (Internal Structure High-resolution Tomography by Asteroid Rendezvous) is a mission developed through ESA General Studies programme. The study, led by Astrium in cooperation with several scientific institutes throughout Europe, has produced a spacecraft design capable of performing multiple asteroid rendezvous and to characterize them with a focussed set of instruments. The ISHTAR concept is centred around a Radar Tomography paylod able to probe the internal structure of a small asteroid to depths of few hundred meters, combined with a small camera for investigation of the surface properties and a radio science experiment for gravity field measurement. This combination will allow the first detailed characterization of a NEO and will give valuable insights into the origin and evolution processes that govern the NEO population. In particular, ISHTAR will be able to visit at least 2 NEOs belonging to two different spectral classes, thereby allowing us to probe the diversity of the NEO population.

Comet 67P/Churyumov-Gerasimenko has been chosen as the new target of the Rosetta mission. A concise overview of the basic properties of the new target comet is given.

The Deep Impact mission aims at understanding the third dimension of a cometary nucleus, the physical and chemical properties as a function of depth below the surface. General wisdom holds that comets, because they are small and spend most of their lives far from the sun, hold primordial ices in their interiors. However, it is universally agreed that the surface layers have evolved, whether from cosmic rays while residing in the Oort cloud or from solar heating during previous perihelion passages. Clearly, in order to interpret surface observations and outgassing, we must understand how the surface layers differ from the interior. Deep Impact is the first mission to carry out a macroscopic experiment on a planetary body since the Apollo program dropped a lunar module on the moon and measured the seismic response.

Through a recently developed thermophysical model, observations from the Infrared Space Observatory (ISO) were combined with visual photometry, lightcurves, close-up observations and direct measurement. In this way, many applications were possible, ranging from simple diameter and albedo determination of serendipitously seen asteroids to sophisticated studies of mineralogic aspects and regolith properties, like emissivity, roughness or thermal inertia for well-known asteroids. The possibility to combine all sources of information in one single model lead also to a better understanding of thermophysical effects, like beaming or the before/after opposition effect. Thus, the mineralogic signatures can be recognized easier and asteroid data from infrared surveys and individual IR photometry can be interpreted more accurately, even in cases where shape or rotational behaviour are not known. Some well-studied asteroids are now even considered as excellent far-infrared calibrators.

Many physical parameters of asteroids can be inferred from remote measurements at optical wavelengths. These observations constitute the bulk of the information we have about these objects, and nicely complement the detailed physical studies which are made possible by in situ explorations of a few selected targets. The discovery of many binary systems for which mass determinations become possible, the identification of hydration features in asteroid spectra, including unexpectedly many M-types, the detection of space-weathering phenomena affecting S-type near-Earth objects, as well as improved estimates of sizes, albedos, and spin properties for many objects are among the major results obtained in recent years by means of remote-sensing techniques. These data can be used to infer important properties of the internal structures of the asteroids.

The availability of highly accurate synthetic proper elements for a large number of asteroids made possible detailed studies of the structure of asteroid families. The entire region of the Vesta family is dominated by bodies with D < 7 km. The large spread of family members appears to be primarily due to Yarkovsky mobility, a strongly size-dependent. The proper elements of the asteroids the region (except close to mean motion resonances) are stable over very long time spans; thus chaotic diffusion could not play a significant role. The total volume of the family members with diameter less than 7 km amounts approximately to 6 x 104 cubic km, the volume of a crater with 100 km diameter and average depth 7 km. If the albedo feature, visible in the Hubble Space Telescope images, is really a crater its volume could be even larger. Thanks to the recently computed catalogs of proper elements for 1167 trojans, there are now confirmed dynamical families in the trojan swarms. This allows to begin to study the collisional evolution with constraints from observations.

The recent upgrade of the Arecibo planetary radar system, combined with the huge increase in the near-Earth asteroid (NEA) discovery rate by large survey programs, has greatly increased our ability to observe these objects with radar. Radar provides size, shape, rotation, and trajectory information, and in most cases is the only ground-based technique that spatially resolves near-Earth objects. While the resolution of radar images (typically 7.5m) is not as high as for the very best spacecraft images, spacecraft can visit only a few such objects, and radar observations greatly increase our understanding of the diversity of near-Earth objects, at orders of magnitude lower cost. The single clearest result of these observations is the great variety of near-Earth objects, with binary systems, very fast and very slow rotations, spheres, “bifurcated” objects, and “shards”, suggesting that a similar variety of production and delivery mechanisms deliver these objects to near-Earth orbit. Spacecraft mission planning should take into account this variety, and concentrate on broad coverage of a wide range of objects.

The first detailed characterization of a near-Earth binary (2000 DP107) provided significant insights into the formation mechanism, orbital evolution, and physical properties of the system. Near-Earth Asteroid (NEA) binaries are tidally evolved with synchronously rotating secondaries, providing constraints on asteroid mechanical properties (tidal Q and rigidity). It is expected that radar observations will permit measurements of orbital precession, with corresponding implications for the distribution of mass within asteroids.

The Infrared Space Observatory (ISO) offered us the opportunity to observe celestial bodies from 2.4 to 196 microns. A wealth of new results were obtained for comets. Spectroscopic investigations have shown band fluorescence emissions for H2O, CO and CO2, and rotational line emissions for H2O. High resolution spectra of water vapor around 2.7 microns in comets C/1995 01 (Hale-Bopp) and 103P/Hartley 2 have permitted measurement of the water rotational temperature and ortho-to-para ratio. The thermal region of the spectra showed the signatures of crystalline, Mg-rich olivine and emission features attributed to water ice. Broad band photometry of the coma allowed to investigate several properties of cometary dust, such has color temperature, size distribution and production rate. For several comets, it was possible to separate the nuclear and coma contribution in infrared images obtained from the ISO camera. Inferences concerning the nucleus size and albedo were obtained.

Earth-based observations of comets far surpass the ability of in situ observations to understand the range of cometary properties and thus provide unique insight into the relationship between comets and the formation of the solar system. Recent developments in composition have emphasized near-IR and mm-wave data, although optical and ultraviolet data still play crucial roles. Observers now realize the importance of chemistry in the coma. Surveys of nuclear sizes are beginning to provide a real size distribution and we have recent examples of breakup that provide important information on structure.

Nine comets have been detected with either the Arecibo (12.6 cm wavelength) or Goldstone (3.5 cm) radar systems. Included are six nucleus detections and five detections of echoes from coma grains. The radar backscatter cross sections measured for the nuclei correlate well with independent estimates of their sizes and are indicative of surface densities in the range of 0.5 to 1.0 g cm-3. Like most asteroids, comets appear to have surfaces that are very rough at scales much larger than the radar wavelength. Coma echo models can explain the radar cross sections using grain size distributions that include a substantial population of cm-sized grains. A long term goal of the cometary radar program has been the high resolution imaging of a cometary nucleus. Eleven short period comets are potentially detectable over the next two decades a few of which may be suitable for imaging. We are always waiting for the arrival of a new comet with an orbit that brings it within 0.1 AU of the earth.

This paper introduces the rationale and program of Joint Discussion 20, Frontiers of High Resolution Spectroscopy, which took place on 2003 July 23-24 during the IAU General Assembly in Sydney Australia.

Gamma-ray spectroscopy has made important progress with the observations of the OSSE and COMPTEL telescopes aboard CGRO, and has entered the domain of high-resolution spectroscopy with the launch of the SPI telescope aboard the INTEGRAL satellite. Recent science highlights in this field are presented, and an outlook is given to future promising projects.