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M. Landgraf

Publications and source records attributed to M. Landgraf.

18 recordsLinked to original sources
arXiv2006

The Sky in Dust -- Methods and Prospects of Dust Astronomy

Information about the make-up of the galaxy arrives in the Solar system in many forms: photons of different energies, classically collected by ground- and space-based telescopes, neutral and charged atomic particles, and solid macroscopic particles: cosmic dust particles. Dust particles, like photons, carry information from remote sites in space and time. This information can be analysed in order to understand the processes and mechanisms that are involved in the formation and evolution of solid matter in the galaxy. This approach is called ``Dust Astronomy'' which is carried out by means of a dust telescope on a dust observatory in space. The analysis of cosmic grains collected in the high atmosphere of the Earth has shown that each dust grain is a small world with various sub-grains featuring different galactic origin and evolution, which is identified on the basis of elementary and isotopic analysis. Independent information about the origin and evolution of the grains coming from the kinematic properties of the arrival trajectory would be invaluable for linking the isotopic signature of the formation of heavy elements in old stars and supernovae to distinctive regions in our galaxy, e.g. known star-forming regions. Here we present a skymap of potential dust sources together with a report on already existing lab hardware of a trajectory sensor and a large-area mass spectrometre.

astro-ph↗
arXiv2004

Mission design for LISA Pathfinder

Here we describe the mission design for SMART-2/LISA Pathfinder. The best trade-off between the requirements of a low-disturbance environment and communications distance is found to be a free-insertion Lissajous orbit around the first co-linear Lagrange point of the Sun-Earth system L1, 1.5x 10^6 km from Earth. In order to transfer SMART-2/LISA Pathfinder from a low Earth orbit, where it will be placed by a small launcher, the spacecraft carries out a number of apogee-raise manoeuvres, which ultimatively place it to a parabolic escape trajectory towards L1. The challenges of the design of a small mission are met, fulfilling the very demanding technology demonstration requirements without creating excessive requirements on the launch system or the ground segment.

gr-qc↗
arXiv2003

Comparison of EISCAT Radar Data on Space Debris with Model Prediction by the MASTER Model of ESA

In the effort to obtain low cost routine space debris observations in low Earth orbit, ESA plans to utilise the radar facilities of the European Incoherent Scatter Scientific Association. First demonstration measurements were performed from 11 to 23 February 2001. In total $16{\rm hours}$ of radar signals were collected. Here we compare these initial measurements with the predictions of the ESA MASTER/PROOF'99 model in order to assess the sensitivity as well as the reliability of the data. We find that while the determination of object size needs to be reviewed, the altitude distribution provides a good fit to the model prediction. The absolute number of objects detected in the various altitude bins indicates that the coherent integration method indeed increases the detection sensitivity when compared to incoherent integration. In the data presented here integration times from 0.1 to $0.3{\rm s}$ were used. As expected, orbit information cannot be obtained from the measurements if they are linked to ionospheric measurements as planned. In addition routine space debris observations provide also useful information for the validation of large-object catalogues.

astro-ph↗
arXiv2002

Origins of Solar System Dust Beyond Jupiter

The measurements of cosmic interplanetary dust by the instruments on board the Pioneer 10 and 11 spacecraft contain the dynamical signature of dust generated by Edgeworth-Kuiper Belt objects, as well as short period Oort Cloud comets and short period Jupiter family comets. While the dust concentration detected between Jupiter and Saturn is mainly due to the cometary components, the dust outside Saturn's orbit is dominated by grains originating from the Edgeworth-Kuiper Belt. In order to sustain a dust concentration that accounts for the Pioneer measurements, short period external Jupiter family comets, on orbits similar to comet 29P/Schwassmann-Wachmann-1, have to produce $8\times 10^4:{\rm g}:{\rm s}^{-1}$ of dust grains with sizes between 0.01 and $6:{\rm mm}$. A sustained production rate of $3\times 10^5:{\rm g}:{\rm s}^{-1}$ has to be provided by short period Oort cloud comets on 1P/Halley-like orbits. The comets can not, however, account for the dust flux measured outside Saturn's orbit. The measurements there can only be explained by a generation of dust grains in the Edgeworth-Kuiper belt by mutual collisions of the source objects and by impacts of interstellar dust grains onto the objects' surfaces. These processes have to release in total $5\times 10^7:{\rm g}:{\rm s}^{-1}$ of dust from the Edgeworth Kuiper belt objects in order to account for the amount of dust found by Pioneer beyond Saturn, making the Edgeworth-Kuiper disk the brightest extended feature of the Solar System when observed from afar.

astro-ph↗
arXiv2001

Contemporary interstellar meteoroids in the solar system - in situ measurements and clues on composition

Meteoroids originating from the local interstellar medium, traverse the solar system. This has been proven by in situ measurements by interplanetary spacecraft as well as highly sensitive radar measurements. Early attempts to detect interstellar meteoroids using the instruments on board the Pioneer 8 and 9 spacecraft failed. More sensitive detectors on board the joint ESA/NASA mission Ulysses as well as on board the NASA spacecraft Galileo, however, unambiguously detected meteoroids of interstellar origin. This discovery has started efforts to compare the results from the in situ measurements with highly sophisticated models of interstellar dust properties derived from astronomical absorption and extinction measurements. It was found that, at least locally, is more mass locked up in meteoroids than expected from the astronomical measurements. So far the in situ measurements only allow to derive composition information indirectly via the meteoroid's dynamics.

astro-ph↗
arXiv2001

Four years of Ulysses dust data: 1996 to 1999

The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse ($ i = 79^{\circ}$, perihelion distance 1.3 AU, aphelion distance 5.4 AU). Between January 1996 and December 1999 the spacecraft was beyond 3 AU from the Sun and crossed the ecliptic plane at aphelion in May 1998. In this four-year period 218 dust impacts were recorded with the dust detector on board. We publish and analyse the complete data set of both raw and reduced data for particles with masses $\rm 10^{-16} g$ to $\rm 10^{-8}$ g. Together with 1477 dust impacts recorded between launch of Ulysses and the end of 1995 published earlier \cite{gruen1995c,krueger1999b}, a data set of 1695 dust impacts detected with the Ulysses sensor between October 1990 and December 1999 is now available. The impact rate measured between 1996 and 1999 was relatively constant with about 0.2 impacts per day. The impact direction of the majority of the impacts is compatible with particles of interstellar origin, the rest are most likely interplanetary particles. The observed impact rate is compared with a model for the flux of interstellar dust particles. The flux of particles several micrometers in size is compared with the measurements of the dust instruments on board Pioneer 10 and Pioneer 11 beyond 3 AU (Humes 1980, JGR, 85, 5841--5852, 1980). Between 3 and 5 AU, Pioneer results predict that Ulysses should have seen five times more ($\rm \sim 10 μm$ sized) particles than actually detected.

astro-ph↗
arXiv2001

Space Debris Hazards from Explosions in the collinear Sun-Earth Lagrange points

The collinear Lagrange points of the Sun-Earth system provide an ideal environment for highly sensitive space science missions. Consequently many new missions are planed by ESA and NASA that require satellites close to these points. For example, the SOHO spacecraft built by ESA is already installed in the first collinear Lagrange point. Neither uncontrolled spacecraft nor escape motors will stay close to the Lagrange points for a long time. In case an operational satellite explodes, the fragmentation process will take place close to the Lagrange point. Apparently a number of spacecraft will accumulate close to the Lagrange points over the next decades. We investigate the space debris hazard posed by these spacecraft if they explode and fall back to an Earth orbit. From our simulation we find that, as expected, about half of the fragments drift towards the Earth while the other half drifts away from it. Around 2% of the simulated fragments even impact the Earth within one year after the explosion.

astro-ph↗
arXiv2001

Interstellar Dust Module for the ESA Meteoroid Model

The ESA meteoroid model predicts impacts of meteoroids in the mass range between $10^{-18}$ to $10^0$ g on spacecraft surfaces. It covers heliocentric distances from 0.3 to 20 AU. Measurements of the dust detector on board the highly successful joint ESA/NASA mission Ulysses have shown, that the flux of meteoroids with masses between $10^{-15}$ and $10^{-12}$ g is, at least in the outer Solar System, dominated by interstellar dust grains that traverse the Solar System as it travels through the local interstellar cloud. We present a simple semi-analytic interstellar dust model that can easily be included in the ESA meteoroid model, together with a more precise determination of the flux direction of the interstellar dust stream. The model is based on the assumption that interstellar dust dynamics have two effects: solar gravitation and radiation pressure determines the spatial distribution, and Lorentz-interaction of the charged particles creates a temporal variation.

astro-ph↗
arXiv2001

IRSI-DARWIN: How to see through the interplanetary dust cloud

ESA has identified interferometry as one of the major goals of the Horizon 2000+ programme. Infrared interferometers are a highly sensitive astronomical instruments that enable us to observe terrestrial planets around nearby stars. In this context the Infrared Space Interferometry Mission (IRSI)/ DARWIN is studied. The current design calls for a constellation of 6 free flying telescopes using 1.5m mirrors, plus one hub and one master spacecraft. As the baseline trajectory an orbit about the second collinear libration point of the Earth-Sun system has been selected. The thermal radiation from the interplanetary dust cloud that surrounds the Sun, the so-called zodiacal infrared foreground, is a major concern for any high-sensitivity infrared mission. The most reliable information about this radiation comes from the measurements by NASA's Cosmic Background Explorer (COBE) mission. There are various ways to detect faint terrestrial planets despite the bright foreground. We find that, using integration times in the order of 30h, the baseline mission scenario is capable of detecting earth-sized exo-planets out to 14pc. We seize the suggestion that increasing the heliocentric distance of the instrument would make the observing conditions even better. A dust model that was fitted to the COBE measurements shows that an observing location of DARWIN in the outer solar system would potentially reduce the zodiacal foreground by a factor of 100, effectively increasing the number of potential target stars by almost a factor of 30.

astro-ph↗
arXiv2001

Zodiacal Infrared Foreground Prediction for Space Based Infrared Interferometer Missions

The zodiacal foreground for a highly sensitive space infrared interferometer is predicted for various observing locations. For the predictions we use a model that was derived from measurements of the Cosmic Background Explorer (COBE). We find that at a wavelength of $10{\rm μm}$ 96% of the sky is darker than $1{MJy}{\rm sr}^{-1}$ for observations in the ecliptic plane at $5{\rm AU}$, and 83% is darker than $0.1{\rm MJy}{\rm sr}^{-1}$. At $1{\rm AU}$, however, always more than 50% of the sky are brighter than $1{\rm MJy}{\rm sr}^{-1}$, even if the observations are made from $30^\circ$ or $60^\circ$ of latitude above the ecliptic plane, at 10 or $20{\rm μm}$. Thus, according to the employed model, the foreground reduction by increasing the heliocentric distance of the observing location is more effective than by increasing the latitude.

astro-ph↗
arXiv1999

The Galactic Environments of Cool Stars - part I: Modeling Interstellar Dust around the Sun and Nearby Cool Stars

We present a model of the interaction of interstellar dust grains with a stellar environment, that predicts the distribution of interstellar dust grains in the size range between $0.1 {\rm μm}$ and $1 {\rm μm}$ around a star for the whole stellar cycle. Comparisons of the model results with in-situ dust measurements by the Ulysses spacecraft in the Solar System validate the model. We show that in the case of the Sun, interstellar dust grains can produce large regions of infrared emission that can be confused with a circumsolar dust disk when observed from afar. Our model can determine the shape of interstellar dust concentrations close to nearby stars, if we have information on the relative velocty of the stars with respect to the surrounding interstellar medium, and the properties of the stellar wind.

astro-ph↗
arXiv1999

Collisional Consequences of Big Interstellar Grains

Identification by the Ulysses spacecraft of interstellar grains inside the planetary system provides a new window for the study of diffuse interstellar matter. Dust particles observed by Ulysses and confirmed by Galileo are more massive ($\geq 10^{-13} {\rm g}$) than the 'classical' interstellar grains. Even bigger grains ($\approx 10^{-7} {\rm g}$) were observed in form of interstellar meteors. We analyze the consequences of the plentiful existence of massive grains in the diffuse interstellar medium. Astronomically observed 'classical' interstellar grains can be described by a size distribution ranging from about 5 to 250 nm in radius (about $10^{-18}$ to $10^{-13} {\rm g}$). Lifetimes of these particles, due to mutual collisions in interstellar space, can be as short as $10^{5} f$ years, where f = 10 to 1000, is the fraction of total lifetime to the time when grains are exposed to supernova shocks. Shattering is a source of the smallest of these grains, but grains more massive than about $10^{-16} {\rm g}$ of the classical interstellar grain population are rapidly destroyed. When applying the same shattering mechanism to the more massive grains found recently, we suggest that collisions of particles bigger than about $10^{-15} {\rm g}$ provide a source for smaller grains. Because massive grains couple to the interstellar gas only over large (100 to 1000 pc) length scales, the cosmic abundance ratio of gas-to-dust needs only to be preserved averaged over corresponding volumes of space.

astro-ph↗
arXiv1999

Aspects of the Mass Distribution of Interstellar Dust Grains in the Solar System from In-Situ Measurements

The in-situ detection of interstellar dust grains in the Solar System by the dust instruments on-board the Ulysses and Galileo spacecraft as well as the recent measurements of hyperbolic radar meteors give information on the properties of the interstellar solid particle population in the solar vicinity. Especially the distribution of grain masses is indicative of growth and destruction mechanisms that govern the grain evolution in the interstellar medium. The mass of an impacting dust grain is derived from its impact velocity and the amount of plasma generated by the impact. Because the initial velocity and the dynamics of interstellar particles in the Solar System are well known, we use an approximated theoretical instead of the measured impact velocity to derive the mass of interstellar grains from the Ulysses and Galileo in-situ data. The revised mass distributions are steeper and thus contain less large grains than the ones that use measured impact velocities, but large grains still contribute significantly to the overall mass of the detected grains. The flux of interstellar grains with masses $> 10^{-14} {\rm kg}$ is determined to be $1\cdot 10^{-6} {\rm m}^{-2} {\rm s}^{-1}$. The comparison of radar data with the extrapolation of the Ulysses and Galileo mass distribution indicates that the very large ($m > 10^{-10} {\rm kg}$) hyperbolic meteoroids detected by the radar are not kinematically related to the interstellar dust population detected by the spacecraft.

astro-ph↗
arXiv1999

Modeling the Motion and Distribution of Interstellar Dust inside the Heliosphere

The interaction of dust grains originating from the local interstellar cloud with the environment inside the heliosphere is investigated. As a consequence of this interaction the spatial distribution of interstellar dust grains changes with time. Since dust grains are charged in the interplanetary plasma and radiation environment, the interaction of small grains with the heliosphere is dominated by their coupling to the solar wind magnetic field. The change of the field polarity with the solar cycle imposes a temporal variation of the spatial distribution and the flux of small (radius smaller than $0.4 μm$) interstellar dust grains in the Solar System, whereas the flux of large grains is constant because of their negligible coupling to the solar wind magnetic field. The flux variation observed by in-situ measurements of the Galileo and Ulysses spacecraft are reproduced by simulating the interaction of interstellar grains with charge-to-mass ratios between $0.5 C/kg^{-1}$ and $1.4 C/kg$ with the interplanetary environment.

astro-ph↗
arXiv1999

Dust in the Local Interstellar Wind

The gas-to-dust mass ratios found for interstellar dust within the Solar System, versus values determined astronomically for the cloud around the Solar System, suggest that large and small interstellar grains have separate histories, and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange with nearby interstellar gas. Observations by the Ulysses and Galileo satellites of the mass spectrum and flux rate of interstellar dust within the heliosphere are combined with information about the density, composition, and relative flow speed and direction of interstellar gas in the cloud surrounding the solar system to derive an in situ value for the gas-to-dust mass ratio, $R_{g/d} = 94^{+46}_{-38}$. Hubble observations of the cloud surrounding the solar system yield a gas-to-dust mass ratio of Rg/d=551+61-251 when B-star reference abundances are assumed. The exclusion of small dust grains from the heliosheath and heliosphere regions are modeled, increasing the discrepancy between interstellar and in situ observations. The shock destruction of interstellar grains is considered, and comparisons are made with interplanetary and presolar dust grains.

astro-ph↗
arXiv1998

Three years of Ulysses dust data: 1993 to 1995

The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse ($i = 79^{\circ}$). After its Jupiter flyby in 1992 at a heliocentric distance of 5.4 AU, the spacecraft reapproached the inner solar system, flew over the Sun's south polar region in September 1994, crossed the ecliptic plane at a distance of 1.3 AU in March 1995, and flew over the Sun's north polar region in July 1995. We report on dust impact data obtained with the dust detector onboard Ulysses between January 1993 and December 1995. We publish and analyse the complete data set of 509 recorded impacts of dust particles with masses between $10^{-16}$ g to $10^{-7}$ g. Together with 968 dust impacts from launch until the end of 1992 published earlier (Grün et al., 1995, {\em Planet. Space Sci}, Vol. 43, p. 971-999), information about 1477 particles detected with the Ulysses sensor between October 1990 and December 1995 is now available. The impact rate measured between 1993 and 1995 stayed relatively constant at about 0.4 impacts per day and varied by less than a factor of ten. Most of the impacts recorded outside about 3.5 AU are compatible with particles of interstellar origin. Two populations of interplanetary particles have been recognised: big micrometer-sized particles close to the ecliptic plane and small sub-micrometer-sized particles at high ecliptic latitudes. The observed impact rate is compared with a model for the flux of interstellar dust particles which gives relatively good agreement with the observed impact rate. No change in the instrument's noise characteristics or degradation of the channeltron could be revealed during the three-year period.

astro-ph↗
arXiv1997

In Situ Measurements of Interstellar Dust

We present the mass distribution of interstellar grains measured in situ by the Galileo and Ulysses spaceprobes as cumulative flux. The derived in situ mass distribution per logarithmic size interval is compared to the distribution determined by fitting extinction measurements. Large grains measured in situ contribute significantly to the overall mass of dust in the local interstellar cloud. The problem of a dust-to-gas mass ratio that contradicts cosmic abundances is discussed.

astro-ph↗