Retired (mostly!) Professor of Space Sciences. I was involved in a variety of high profile Space Science missions including Hubble Space Telescope, Giotto, Cassini/Huygens
The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the densit... more The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the density and mass spectrum (in the range 10 -20 −10 -8 kg) of the dust near comet Halley. Profiles of the dust spectrum obtained at a distance of 291,000 km from the Halley nucleus show a ...
The Open University's repository of research publications and other research outputs The mercury ... more The Open University's repository of research publications and other research outputs The mercury imaging X-ray spectrometer (MIXS) on BepiColombo
The GIADA (Grain Impact Analyser and Dust Accumulator) instrument aboard the Rosetta spacecraft a... more The GIADA (Grain Impact Analyser and Dust Accumulator) instrument aboard the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P/C-G) measures dust grain number, mass, momentum and velocity [1,2]. GIADA is composed of three sub-systems: the Grain Detection System (GDS), detecting dust grains based on light scattering; an Impact Sensor (IS), providing momentum measurements from the impact on a plate connected to five piezoelectric sensors; and the MicroBalances System (MBS), made up of five Quartz Crystal Microbalances (QCMs), to yield cumulative deposited dust mass through the shift in resonance frequency
The Grain Impact Analyzer and Dust Accumulator (GIADA) instrument on board ESA’s Rosetta mission ... more The Grain Impact Analyzer and Dust Accumulator (GIADA) instrument on board ESA’s Rosetta mission is constraining the origin of the dust particles detected within the coma of comet 67 P/Churyumov–Gerasimenko (67P). The collected particles belong to two families: (i) compact particles (ranging in size from 0.03 to 1 mm), witnessing the presence of materials that underwent processing within the solar nebula and (ii) fluffy aggregates (ranging in size from 0.2 to 2.5 mm) of sub-micron grains that may be a record of a primitive component, probably linked to interstellar dust. The dynamics of the fluffy aggregates constrain their equivalent bulk density to <1kg m. These aggregates are charged, fragmented, and decelerated by the spacecraft negative potential and enter GIADA in showers of fragments at speeds<1m s. The density of such optically thick aggregates is consistent with the low bulk density of the nucleus. The mass contribution of the fluffy aggregates to the refractory compo...
The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, is detecting individu... more The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, is detecting individual dust particles of mass larger than 10 −10 kg by means of the GIADA dust collector and the OSIRIS WAC and NAC cameras since August, 2014, till September, 2016. Single dust particle detections allow us to estimate the anisotropic dust flux from 67P, infer the dust loss rate and size distribution at the sunlit nucleus surface, and look if 67P dust size distribution evolves in time. The Rosetta orbiter velocity, relative to 67P, is much lower than the dust velocity measured Subject headings: comets: general-comets: individual (67P/Churyumov-Gerasimenko)-space vehicles: instruments
Space in the vicinity of atmosphereless bodies in the Solar system is often populated by dust ori... more Space in the vicinity of atmosphereless bodies in the Solar system is often populated by dust originating from the surface. Fragments of the surface are ejected mostly due to hypervelocity meteoroid impacts. It is also possible that material from sub-surface layers may be vented through cracks in the ice (as detected near Enceladus). The understanding of Europa's dust cloud (and dust clouds of this sort in general) is done by mimicking micrometeoroid impact into simulated Europan regolith/ice using the light gas gun at the Open University. The research is complemented with impact modelling using the finite element hydrocode, ANSYS Autodyn 3D. The results are implemented in IDL in order to calculate the approximate dust cloud population (size and spatial density) of the surface fragments at different altitudes above Europa’s surface. It is, therefore, investigated whether orbit-based detection and analysis of material ejected from the surface may provide an alternative method fo...
The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to... more The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed.
The capabilities of combining Aerogel (A) as a passive target and position-sensitive impact sensi... more The capabilities of combining Aerogel (A) as a passive target and position-sensitive impact sensing (PSIS) are examined; experimental performance factors are established from tests on Hypervelocity Impact Facilities at the University of Kent and previous space deployment. Results of system requirements analysis favour the deployment of large area detectors. Analysis of the in-flight impact sensor signals yields the position, time and exposure pointing direction of the tracks containing the impactor residues, which are analysed after retrieval.
Monthly Notices of the Royal Astronomical Society, 2016
GIADA (Grain Impact Analyzer and Dust Accumulator) on-board the Rosetta space probe is designed t... more GIADA (Grain Impact Analyzer and Dust Accumulator) on-board the Rosetta space probe is designed to measure the momentum, mass and speed of individual dust particles escaping the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P). From 2014 August to 2016 June, Rosetta escorted comet 67P during its journey around the Sun. Here, we focus on GIADA data taken between 2015 January and 2016 February which included 67P's perihelion passage. To better understand cometary activity and more specifically the presence of dust structures in cometary comae, we mapped the spatial distribution of dust density in 67P's coma. In this manner, we could track the evolution of high-density regions of coma dust and their connections with nucleus illumination conditions, namely tracking 67P's seasons. We also studied the link between dust particle speeds and their masses with respect to heliocentric distance, i.e. the level of cometary activity. This allowed us to derive a global and a local correlation of the dust particles' speed distribution with respect to the H 2 O production rate.
Context. During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft ... more Context. During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft accomplished the circular orbit phase around the nucleus of comet 67P/Churyumov-Gerasimenko (67P). The Grain Impact Analyzer and Dust Accumulator (GIADA) onboard Rosetta monitored the 67P coma dust environment for the entire period. Aims. We aim to describe the dust spatial distribution in the coma of comet 67P by means of in situ measurements. We determine dynamical and physical properties of cometary dust particles to support the study of the production process and dust environment modification. Methods. We analyzed GIADA data with respect to the observation geometry and heliocentric distance to describe the coma dust spatial distribution of 67P, to monitor its activity, and to retrieve information on active areas present on its nucleus. We combined GIADA detection information with calibration activity to distinguish different types of particles that populate the coma of 67P: compact particles and fluffy porous aggregates. By means of particle dynamical parameters measured by GIADA, we studied the dust acceleration region. Results. GIADA was able to distinguish different types of particles populating the coma of 67P: compact particles and fluffy porous aggregates. Most of the compact particle detections occurred at latitudes and longitudes where the spacecraft was in view of the comet's neck region of the nucleus, the so-called Hapi region. This resulted in an oscillation of the compact particle abundance with respect to the spacecraft position and a global increase as the comet moved from 3.36 to 2.43 AU heliocentric distance. The speed of these particles, having masses from 10 −10 to 10 −7 kg, ranged from 0.3 to 12.2 m s −1. The variation of particle mass and speed distribution with respect to the distance from the nucleus gave indications of the dust acceleration region. The influence of solar radiation pressure on micron and submicron particles was studied. The integrated dust mass flux collected from the Sun direction, that is, particles reflected by solar radiation pressure, was three times higher than the flux coming directly from the comet nucleus. The awakening 67P comet shows a strong dust flux anisotropy, confirming what was suggested by on-ground dust coma observations performed in 2008.
The entry, descent and landing of ExoMars offer a rare (once-per-mission) opportunity to perform ... more The entry, descent and landing of ExoMars offer a rare (once-per-mission) opportunity to perform in situ investigation of the martian environment over a wide altitude range. We present an initial assessment of the atmospheric science that can be performed using sensors of the Entry, Descent and Landing System (EDLS), over and above the expected engineering information. This is intended to help fulfill the concept of an Atmospheric Parameters Package (APP), as mentioned
ABSTRACT Analysis of the data from Giotto&#39;s Dust Impact Detection System experiment (DIDS... more ABSTRACT Analysis of the data from Giotto&#39;s Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (&gt;10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.
The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the densit... more The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the density and mass spectrum (in the range 10 -20 −10 -8 kg) of the dust near comet Halley. Profiles of the dust spectrum obtained at a distance of 291,000 km from the Halley nucleus show a ...
The knowledge of Martian airborne dust properties and about mechanisms of dust settling/raising t... more The knowledge of Martian airborne dust properties and about mechanisms of dust settling/raising to/from the surface are important to determine climate and surface evolution on Mars. Water is an important tracer of climatic changes on long time-scales and is strictly related to the presence of life forms. The study in situ of dust and water vapour properties and evolution in
Dust devil data from Mars is limited by a lack of data relating to diurnal dust devil behaviour. ... more Dust devil data from Mars is limited by a lack of data relating to diurnal dust devil behaviour. Previous work looking at the Viking Lander meteorological data highlighted seasonal changes in temporal occurrence of dust devils and gave an indication of typical dust devil diameter, size, and internal dynamics. The meteorological data from Viking Lander 2 for sols 1 to 60 have been revisited to provide detailed diurnal dust devil statistics. Results of our analysis show that the Viking Lander 2 experienced a possible 38 convective vortices in the first 60 sols of its mission with a higher occurrence in the morning compared to Earth, possibly as a result of turbulence generated by the Lander body. Dust devil events have been categorised by statistical confidence and intensity. Some initial analysis and discussion of the results is also presented. Assuming a similar dust loading to the vortices seen by Mars Pathfinder, it is estimated that the amount of dust lofted in the locality of the Lander is approximately 800 Ϯ 10 kgsol Ϫ1 km Ϫ2 .
On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was... more On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was mainly nitrogen, with some methane, but its temperature and pressure profiles were poorly constrained because of uncertainties in the detailed composition. The extent of atmospheric electricity ('lightning') was also hitherto unknown. Here we report the temperature and density profiles, as determined by the Huygens Atmospheric Structure Instrument (HASI), from an altitude of 1,400 km down to the surface. In the upper part of the atmosphere, the temperature and density were both higher than expected. There is a lower ionospheric layer between 140 km and 40 km, with electrical conductivity peaking near 60 km. We may also have seen the signature of lightning. At the surface, the temperature was 93.65^0.25 K, and the pressure was 1,467^1 hPa.
TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Ca... more TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini–Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini–Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere. Keywords TandEM Titan Enceladus Saturnian system Landing probes
The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the densit... more The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the density and mass spectrum (in the range 10 -20 −10 -8 kg) of the dust near comet Halley. Profiles of the dust spectrum obtained at a distance of 291,000 km from the Halley nucleus show a ...
The Open University's repository of research publications and other research outputs The mercury ... more The Open University's repository of research publications and other research outputs The mercury imaging X-ray spectrometer (MIXS) on BepiColombo
The GIADA (Grain Impact Analyser and Dust Accumulator) instrument aboard the Rosetta spacecraft a... more The GIADA (Grain Impact Analyser and Dust Accumulator) instrument aboard the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P/C-G) measures dust grain number, mass, momentum and velocity [1,2]. GIADA is composed of three sub-systems: the Grain Detection System (GDS), detecting dust grains based on light scattering; an Impact Sensor (IS), providing momentum measurements from the impact on a plate connected to five piezoelectric sensors; and the MicroBalances System (MBS), made up of five Quartz Crystal Microbalances (QCMs), to yield cumulative deposited dust mass through the shift in resonance frequency
The Grain Impact Analyzer and Dust Accumulator (GIADA) instrument on board ESA’s Rosetta mission ... more The Grain Impact Analyzer and Dust Accumulator (GIADA) instrument on board ESA’s Rosetta mission is constraining the origin of the dust particles detected within the coma of comet 67 P/Churyumov–Gerasimenko (67P). The collected particles belong to two families: (i) compact particles (ranging in size from 0.03 to 1 mm), witnessing the presence of materials that underwent processing within the solar nebula and (ii) fluffy aggregates (ranging in size from 0.2 to 2.5 mm) of sub-micron grains that may be a record of a primitive component, probably linked to interstellar dust. The dynamics of the fluffy aggregates constrain their equivalent bulk density to <1kg m. These aggregates are charged, fragmented, and decelerated by the spacecraft negative potential and enter GIADA in showers of fragments at speeds<1m s. The density of such optically thick aggregates is consistent with the low bulk density of the nucleus. The mass contribution of the fluffy aggregates to the refractory compo...
The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, is detecting individu... more The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, is detecting individual dust particles of mass larger than 10 −10 kg by means of the GIADA dust collector and the OSIRIS WAC and NAC cameras since August, 2014, till September, 2016. Single dust particle detections allow us to estimate the anisotropic dust flux from 67P, infer the dust loss rate and size distribution at the sunlit nucleus surface, and look if 67P dust size distribution evolves in time. The Rosetta orbiter velocity, relative to 67P, is much lower than the dust velocity measured Subject headings: comets: general-comets: individual (67P/Churyumov-Gerasimenko)-space vehicles: instruments
Space in the vicinity of atmosphereless bodies in the Solar system is often populated by dust ori... more Space in the vicinity of atmosphereless bodies in the Solar system is often populated by dust originating from the surface. Fragments of the surface are ejected mostly due to hypervelocity meteoroid impacts. It is also possible that material from sub-surface layers may be vented through cracks in the ice (as detected near Enceladus). The understanding of Europa's dust cloud (and dust clouds of this sort in general) is done by mimicking micrometeoroid impact into simulated Europan regolith/ice using the light gas gun at the Open University. The research is complemented with impact modelling using the finite element hydrocode, ANSYS Autodyn 3D. The results are implemented in IDL in order to calculate the approximate dust cloud population (size and spatial density) of the surface fragments at different altitudes above Europa’s surface. It is, therefore, investigated whether orbit-based detection and analysis of material ejected from the surface may provide an alternative method fo...
The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to... more The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed.
The capabilities of combining Aerogel (A) as a passive target and position-sensitive impact sensi... more The capabilities of combining Aerogel (A) as a passive target and position-sensitive impact sensing (PSIS) are examined; experimental performance factors are established from tests on Hypervelocity Impact Facilities at the University of Kent and previous space deployment. Results of system requirements analysis favour the deployment of large area detectors. Analysis of the in-flight impact sensor signals yields the position, time and exposure pointing direction of the tracks containing the impactor residues, which are analysed after retrieval.
Monthly Notices of the Royal Astronomical Society, 2016
GIADA (Grain Impact Analyzer and Dust Accumulator) on-board the Rosetta space probe is designed t... more GIADA (Grain Impact Analyzer and Dust Accumulator) on-board the Rosetta space probe is designed to measure the momentum, mass and speed of individual dust particles escaping the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P). From 2014 August to 2016 June, Rosetta escorted comet 67P during its journey around the Sun. Here, we focus on GIADA data taken between 2015 January and 2016 February which included 67P's perihelion passage. To better understand cometary activity and more specifically the presence of dust structures in cometary comae, we mapped the spatial distribution of dust density in 67P's coma. In this manner, we could track the evolution of high-density regions of coma dust and their connections with nucleus illumination conditions, namely tracking 67P's seasons. We also studied the link between dust particle speeds and their masses with respect to heliocentric distance, i.e. the level of cometary activity. This allowed us to derive a global and a local correlation of the dust particles' speed distribution with respect to the H 2 O production rate.
Context. During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft ... more Context. During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft accomplished the circular orbit phase around the nucleus of comet 67P/Churyumov-Gerasimenko (67P). The Grain Impact Analyzer and Dust Accumulator (GIADA) onboard Rosetta monitored the 67P coma dust environment for the entire period. Aims. We aim to describe the dust spatial distribution in the coma of comet 67P by means of in situ measurements. We determine dynamical and physical properties of cometary dust particles to support the study of the production process and dust environment modification. Methods. We analyzed GIADA data with respect to the observation geometry and heliocentric distance to describe the coma dust spatial distribution of 67P, to monitor its activity, and to retrieve information on active areas present on its nucleus. We combined GIADA detection information with calibration activity to distinguish different types of particles that populate the coma of 67P: compact particles and fluffy porous aggregates. By means of particle dynamical parameters measured by GIADA, we studied the dust acceleration region. Results. GIADA was able to distinguish different types of particles populating the coma of 67P: compact particles and fluffy porous aggregates. Most of the compact particle detections occurred at latitudes and longitudes where the spacecraft was in view of the comet's neck region of the nucleus, the so-called Hapi region. This resulted in an oscillation of the compact particle abundance with respect to the spacecraft position and a global increase as the comet moved from 3.36 to 2.43 AU heliocentric distance. The speed of these particles, having masses from 10 −10 to 10 −7 kg, ranged from 0.3 to 12.2 m s −1. The variation of particle mass and speed distribution with respect to the distance from the nucleus gave indications of the dust acceleration region. The influence of solar radiation pressure on micron and submicron particles was studied. The integrated dust mass flux collected from the Sun direction, that is, particles reflected by solar radiation pressure, was three times higher than the flux coming directly from the comet nucleus. The awakening 67P comet shows a strong dust flux anisotropy, confirming what was suggested by on-ground dust coma observations performed in 2008.
The entry, descent and landing of ExoMars offer a rare (once-per-mission) opportunity to perform ... more The entry, descent and landing of ExoMars offer a rare (once-per-mission) opportunity to perform in situ investigation of the martian environment over a wide altitude range. We present an initial assessment of the atmospheric science that can be performed using sensors of the Entry, Descent and Landing System (EDLS), over and above the expected engineering information. This is intended to help fulfill the concept of an Atmospheric Parameters Package (APP), as mentioned
ABSTRACT Analysis of the data from Giotto&#39;s Dust Impact Detection System experiment (DIDS... more ABSTRACT Analysis of the data from Giotto&#39;s Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (&gt;10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.
The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the densit... more The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the density and mass spectrum (in the range 10 -20 −10 -8 kg) of the dust near comet Halley. Profiles of the dust spectrum obtained at a distance of 291,000 km from the Halley nucleus show a ...
The knowledge of Martian airborne dust properties and about mechanisms of dust settling/raising t... more The knowledge of Martian airborne dust properties and about mechanisms of dust settling/raising to/from the surface are important to determine climate and surface evolution on Mars. Water is an important tracer of climatic changes on long time-scales and is strictly related to the presence of life forms. The study in situ of dust and water vapour properties and evolution in
Dust devil data from Mars is limited by a lack of data relating to diurnal dust devil behaviour. ... more Dust devil data from Mars is limited by a lack of data relating to diurnal dust devil behaviour. Previous work looking at the Viking Lander meteorological data highlighted seasonal changes in temporal occurrence of dust devils and gave an indication of typical dust devil diameter, size, and internal dynamics. The meteorological data from Viking Lander 2 for sols 1 to 60 have been revisited to provide detailed diurnal dust devil statistics. Results of our analysis show that the Viking Lander 2 experienced a possible 38 convective vortices in the first 60 sols of its mission with a higher occurrence in the morning compared to Earth, possibly as a result of turbulence generated by the Lander body. Dust devil events have been categorised by statistical confidence and intensity. Some initial analysis and discussion of the results is also presented. Assuming a similar dust loading to the vortices seen by Mars Pathfinder, it is estimated that the amount of dust lofted in the locality of the Lander is approximately 800 Ϯ 10 kgsol Ϫ1 km Ϫ2 .
On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was... more On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was mainly nitrogen, with some methane, but its temperature and pressure profiles were poorly constrained because of uncertainties in the detailed composition. The extent of atmospheric electricity ('lightning') was also hitherto unknown. Here we report the temperature and density profiles, as determined by the Huygens Atmospheric Structure Instrument (HASI), from an altitude of 1,400 km down to the surface. In the upper part of the atmosphere, the temperature and density were both higher than expected. There is a lower ionospheric layer between 140 km and 40 km, with electrical conductivity peaking near 60 km. We may also have seen the signature of lightning. At the surface, the temperature was 93.65^0.25 K, and the pressure was 1,467^1 hPa.
TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Ca... more TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini–Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini–Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere. Keywords TandEM Titan Enceladus Saturnian system Landing probes
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TandEM Titan Enceladus Saturnian system Landing probes
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TandEM Titan Enceladus Saturnian system Landing probes