The Influence of Fluctuations of the Solar Emission Line Profileon the Doppler Shift of Interplanetary HLyα Lines Observed by the Hubble–Space–Telescope

In an earlier research the employment of a radiation transport model with angle-dependent partial frequency redistribution, self-absorption by interplanetary hydrogen, realistic solar H_Lyαemission profile, and a time dependent `hot' hydrogen model to analyze 5 interplanetary H_Lyα glow spectra obtained with theHubble–Space–Telescope–GHRS spectrometer, has not resulted in unequivocal determination of a set of thermodynamical parameters of the interstellar hydrogen The residual discrepancies between the model and the data concern the observations performed within an interval of 1 year close to the solar minimum from very similar lines of sight. In this paper we investigate by calculating interplanetary H_Lyα lines with the use of a one hydrogen distribution and several solar H_Lyα line profiles whether this residual may be caused by possible variations in time of the shape of the solar H_Lyα emission line profile which cause variable illuminations of the interplanetary gas. These variations of illuminations cause variations in Doppler shift of the resonant interplanetary H_Lyα line that can amount to ≃ 4 km s^-1in the line peak. Consequently we conclude that without adequate knowledge of the solar H_Lyα emission line profile during spectral observations of the interplanetary hydrogen gas it is impossible to obtain an agreement between models and observations better than by this value. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sample return of interstellar matter (SARIM)

The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth. SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important constraints for subsequent laboratory analysis. The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area of 1 m². At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule. SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar samples by latest laboratory technologies.     

Symmetries in the Optimal Control of Solar Sail Spacecraft

The theory of optimal control is applied to obtain minimum-time trajectories for solar sail spacecraft for interplanetary missions. We consider the gravitational and solar radiation forces due to the Sun. The spacecraft is modelled as a flat sail of mass m and surface area A and is treated dynamically as a point mass. Coplanar circular orbits are assumed for the planets. We obtain optimal trajectories for several interrelated problem families and develop symmetry properties that can be used to simplify the solution-finding process. For the minimum-time planet rendezvous problem we identify different solution branches resulting in multiple solutions to the associated boundary value problem. We solve the optimal control problem via an indirect method using an efficient cascaded computational scheme. The global optimizer uses a technique called Adaptive Simulated Annealing. Newton and Quasi-Newton Methods perform the terminal fine tuning of the optimization parameters.     

Meteor Hazard for Interplanetary Flights in the Ecliptic Plane

Solar System Research - To increase the safety of interplanetary missions, it is necessary to have estimates of the meteor hazard along the flight trajectory. Meteoroid particles of known meteor...     

MODELING THE SPORADIC METEOROID BACKGROUND CLOUD

The orbital distributions of dust particles in interplanetary space are revised in the ESA meteoroid model to incorporate more observational data and to comply with the constraints due to the long-term particle dynamics under the planetary gravity and Poynting–Robertson effect. Infrared observations of the zodiacal cloud by the COBE Earth-bound observatory, flux measurements by the dust detectors on board Galileo and Ulysses spacecraft, and the crater size distributions on lunar rock samples retrieved by the Apollo missions are fused into a single model. Within the model, the orbital distributions are expanded into a sum of contributions due to a number of known sources, including the asteroid belt with the emphasis on the prominent families Themis, Koronis, Eos and Veritas, as well as comets on Jupiter-encountering orbits. An attempt to incorporate the meteor orbit database acquired by the Advanced Meteor Orbit Radar at Christchurch is also discussed. Work was done during D. Galligan’s stay at the University of Canterbury.     

Effect of Planetary Eccentricity on Ballistic Capture in the Solar System

Ballistic capture of spacecraft and celestial bodies by planets of the solar system is studied considering the elliptic restricted three body model. A preferential region, due to the eccentricity of the planet and the Sun-gravity-gradient effect is found for the capture phenomenon. An analytical formula is derived which determines the limiting value of the satellite capture eccentricity e_c as a function of the pericenter distance x_p and planet’s true anomaly. The analytic values e_c are tested by a numerical propagator, which makes use of planetary ephemeris, and only a small difference with respect to numerical integration is found. It turns out that lower values of e_c occur when the planet anomaly is close to zero; that is, capture is easier when the planet is at its perihelion. This fact is confirmed by the capture of celestial bodies. It is shown that Jupiter comets are generally captured when Jupiter is in its perihelion region. Ballistic capture is also important in interplanetary missions. The propellant saved using the minimum ballistic capture eccentricity is evaluated for different missions and compared with respect to the case in which the insertion orbit is a parabola: a significant saving can be accomplished.     

Multiwavelength focusing with the Sun as gravitational lens

The light deviation caused by the gravitational potential in the vicinity of the sun could be used as a means of focussing radiation that cannot be focussed easily otherwise. The gravitational lens formed by the sun is not stigmatic, but does have the advantage of being achromatic and acts identically on all types of mass-less radiations. For a source at infinity, its geometrical characteristics present a “caustic” line starting at 550 astronomical units (UA) downstream from the sun. In a plane perpendicular to that caustic line, images of distant objects are formed.The perturbations by the solar corona plasma will significantly blur electromagnetic radiation for wavelengths longer than those of the IR domain. At shorter wavelengths, for example the γ domain, the focussing process could lead to 10⁸ amplification factors. In order to reach the regions where images are formed, long distance space missions are necessary. Once launched, missions of this type would be dedicated to a single field. Some possible targets are considered, such as Sagitarius A observed in X and γ rays.In this paper we study the point spread function (PSF) of the sun as a gravitational lens. Taking into account perturbations by the planets, the non sphericity of the sun and coronal plasma index, we derive limits within which such observations could be possible.     

4π Models of CMEs and ICMEs (Invited Review)

Coronal mass ejections (CMEs), which dynamically connect the solar surface to the far reaches of interplanetary space, represent a major manifestation of solar activity. They are not only of principal interest but also play a pivotal role in the context of space weather predictions. The steady improvement of both numerical methods and computational resources during recent years has allowed for the creation of increasingly realistic models of interplanetary CMEs (ICMEs), which can now be compared to high-quality observational data from various space-borne missions. This review discusses existing models of CMEs, characterizing them by scientific aim and scope, CME initiation method, and physical effects included, thereby stressing the importance of fully 3D (??4????) spatial coverage.     

基于PSP观测的行星际Ⅲ型射电爆发的研究进展

与太阳射电爆发相比,通常认为频率较低的行星际射电爆发产生于远离低日冕的行星际空间.地球电离层的截止导致地基设备无法对其进行观测.美国国家航空航天局(National Aeronautics and Space Administration, NASA)发射的帕克太阳探测器(Parker Solar Probe, PSP)是迄今为止距离太阳最近的空间探测器.其搭载的射电频谱仪能够对10 k Hz–19.17 MHz频段范围内的射电辐射进行观测. PSP能够靠近甚至可能穿越行星际III型射电爆发的辐射源区,因此使用PSP对行星际射电爆发进行观测具有前所未有的优势.简要介绍了目前为止使用PSP的射电观测数据对行星际III型射电爆发的多方面研究,包括爆发的发生率、偏振、散射、截止频率、可能的辐射机制和相关的辐射源区等方面的研究进展,并讨论了其未来的研究前景.     

Coronal Field Opens at Lower Height During the Solar Cycles 22 and 23 Minimum Periods: IMF Comparison Suggests the Source Surface Should Be Lowered

The solar cycle 23 minimum period has been characterized by a weaker solar and interplanetary magnetic field. This provides an ideal time to study how the strength of the photospheric field affects the interplanetary magnetic flux and, in particular, how much the observed interplanetary fields of different cycle minima can be understood simply from differences in the areas of the coronal holes, as opposed to differences in the surface fields within them. In this study, we invoke smaller source surface radii in the potential-field source-surface (PFSS) model to construct a consistent picture of the observed coronal holes and the near-Earth interplanetary field strength as well as polarity measurements for the cycles 23 and 22 minimum periods. Although the source surface value of 2.5 R _⊙ is typically used in PFSS applications, earlier studies have shown that using smaller source surface heights generates results that better match observations during low solar activity periods. We use photospheric field synoptic maps from Mount Wilson Observatory (MWO) and find that the values of ≈ 1.9 R _⊙ and ≈ 1.8 R _⊙ for the cycles 22 and 23 minimum periods, respectively, produce the best results. The larger coronal holes obtained for the smaller source surface radius of cycle 23 somewhat offsets the interplanetary consequences of the lower magnetic field at their photospheric footpoints. For comparison, we also use observations from the Michelson Doppler Imager (MDI) and find that the source surface radius of ≈ 1.5 R _⊙ produces better results for cycle 23, rather than ≈ 1.8 R _⊙ as suggested from MWO observations. Despite this difference, our results obtained from MWO and MDI observations show a qualitative consistency regarding the origins of the interplanetary field and suggest that users of PFSS models may want to consider using these smaller values for their source surface heights as long as the solar activity is low.     

On the backscatter of solar HeII, 304åradiation from interplanetary He +

Backscatter of solar HeII, 304Åradiation by interplanetary He ⁺ is shown to be insufficient to account for recent observations.     

The “Floor” in the Interplanetary Magnetic Field: Estimation on the Basis of Relative Duration of ICME Observations in Solar Wind During 1976 – 2000

Measurement of the floor in the interplanetary magnetic field and estimation of the time-invariant open magnetic flux of the Sun require knowledge of closed magnetic flux carried away by coronal mass ejections (CMEs). In contrast with previous papers, we do not use global solar parameters to estimate such values: instead we identify different large-scale types of solar wind for the 1976 – 2000 interval to obtain the fraction of interplanetary CMEs (ICMEs). By calculating the magnitude of the interplanetary magnetic field B averaged over two Carrington rotations, the floor of the magnetic field can be estimated from the B value at a solar cycle minimum when the number of ICMEs is minimal. We find a value of 4.65±0.6 nT, in good agreement with previous results.     

Single-point position estimation in interplanetary trajectories using star trackers

This study provides a single-point position estimation technique for interplanetary missions by observing visible planets using star trackers. Closed-form least-squares solution is obtained by minimizing the sum of the expected object-space squared distance errors. A weighted least-squares solution is provided by an iterative procedure. The weights are evaluated using the distances to the planets estimated by the least-squares solution. It is shown that the weighted approach only requires one iteration to converge and results in significant accuracy gains compared to simple least squares approach. The light-time correction is taken into account while the star-light aberration cannot be implemented in single-point estimation as it requires knowledge of the observer velocity. The proposed method is numerically validated through a statistical scenario as follows. A three-dimensional grid of test cases is generated: two dimensions sweep through the ecliptic plane and the third dimension sweeps through time from January 1, 2018 to January 1, 2043 in 5-year increments. The observer position is estimated at each test case and the estimate error is recorded. The results obtained show that a large majority of positions are well suited to position estimation by using star trackers pointing to visible planets, and reliable and accurate single-point position estimations can be provided in interplanetary missions. The proposed approach is suitable to be used to initiate a filtering technique to increase the estimation accuracy.     

The Solar Ionization Rate of the Interplanetary Hydrogen as a Function of a Heliomagnetic Latitude: A New Model for the Interplanetary Lyman Alpha Studies

In this work we have modelled the solar wind proton flux which varies as a function of distance to the heliomagnetic equator and its effects on the interplanetary Lyman α radiation. The results imply that a groove observed in Lyman α intensity patterns toward the upwind direction Bertaux et al. disappears when the tilt angle of the heliomagnetic equator is larger than 20^°.The observations by Bertaux et al. were measured during the solar wind minimum when the tilt angle of the streamer belt is low. During the solar wind maximum when the tilt angle of the streamer belt is large the Lyman α groove should disappear according to our results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radio scintillations due to plasma irregularities with power law spectra: The interplanetary medium

The scintillation effects which are produced when radiation is incident on a medium containing phase changing irregularities which have power law spectra are discussed. The results are then applied to the interplanetary medium and it is concluded that the small scale sizes (≈100 km) for irregularities measured by interplanetary scintillation represent a genuine ‘outer scale’ distinct from the 10⁶ km scales detected by space probes. It is also shown that the small scale irregularities contain discontinuities which are finite or almost finite, with a sharpness as yet undetermined.     

On the Relationship of the 27-day Variations of the Solar Wind Velocity and Galactic Cosmic Ray Intensity in Minimum Epoch of Solar Activity

We study the relationship of the 27-day variations of the galactic cosmic ray intensity with similar variations of the solar wind velocity and the interplanetary magnetic field based on observational data for the Bartels rotation period # 2379 of 23 November 2007 – 19 December 2007. We develop a three-dimensional (3-D) model of the 27-day variation of galactic cosmic ray intensity based on the heliolongitudinally dependent solar wind velocity. A consistent, divergence-free interplanetary magnetic field is derived by solving Maxwell’s equations with a heliolongitudinally dependent 27-day variation of the solar wind velocity reproducing in situ observations. We consider two types of 3-D models of the 27-day variation of galactic cosmic ray intensity, i) with a plane heliospheric neutral sheet, and ii) with the sector structure of the interplanetary magnetic field. The theoretical calculations show that the sector structure does not significantly influence the 27-day variation of galactic cosmic ray intensity, as had been shown before, based on observational data. Furthermore, good agreement is found between the time profiles of the theoretically expected and experimentally obtained first harmonic waves of the 27-day variation of the galactic cosmic ray intensity (with a correlation coefficient of 0.98±0.02). The expected 27-day variation of the galactic cosmic ray intensity is inversely correlated with the modulation parameter ζ (with a correlation coefficient of −0.91±0.05), which is proportional to the product of the solar wind velocity V and the strength of the interplanetary magnetic field B (ζ∼VB). The high anticorrelation between these quantities indicates that the predicted 27-day variation of the galactic cosmic ray intensity mainly is caused by this basic modulation effect.     

Guidelines for Future UV Observatories

Ultra-violet image sensors and UV optics have been developed for a variety of space borne UV astronomy missions. Technology progress has to be made to improve the performance of future UV space missions. Throughput is the most important technology driver for the future. Required developments for different UV detector types – detectors are one of the most problematic and critical parts of a space born mission – and for optical components of the instruments are given in these guidelines. For near future missions we need high throughput optics with UV sensors of large formats, which show simultaneously high quantum efficiency and low noise performance.     

A Study of the Frequency of Occurrence of Large-Fluence Solar Proton Events and the Strength of the Interplanetary Magnetic Field

It has been shown previously that the number of very-large-fluence solar proton events inferred for the period since 1561 were more frequent at times of low solar activity (e.g., following the recovery from the Maunder minimum), than in the present epoch of high solar activity. An inverse dependence is demonstrated between the probability of observation of the very large-fluence solar proton events and the strength of the interplanetary magnetic field derived from empirical predictions. Using the observed dependence, it is predicted and demonstrated that large-fluence solar proton events have been observed at Earth more frequently near the recurrent minima of the solar activity cycle in the past than during the present epoch. We show that these results are explicable in terms of the linear dependence of the Alfvén velocity upon the strength of the interplanetary magnetic field, leading to higher shock compression ratios in the past. These results indicate that this aspect of “solar weather” will be significantly influenced by the prevailing strength of the interplanetary magnetic field, and that recurrence of solar conditions similar to those of the solar activity minimum of solar cycles 12–14 (1878.9–1913.6) would be accompanied by a factor of ∼4 increase in the occurrence of large-fluence solar proton events.     

Interplanetary dust particles: Disintegration and orbital motion

Abrupt or gradual disintegration of the interplanetary dust particle causes increase of its distance from the Sun due to the solar radiation pressure. The problem of the orbital evolution of the interplanetary dust particles under such disintegration processes is discussed. The process of gradual disintegration due to the solar wind particles is calculated in detail. Obtained results represent corrections to the changes of orbital elements for the Poynting-Robertson effect and effect of the solar wind.     

Experimental aqueous alteration of cometary dust

Abstract– Recent spacecraft missions to comets have reopened a long‐standing debate about the histories and origins of cometary materials. Comets contain mixtures of anhydrous minerals and ices seemingly unaffected by planetary processes, yet there are indications of a hydrated silicate component. We have performed aqueous alteration experiments on anhydrous interplanetary dust particles (IDPs) that likely derived from comets. Hydrated silicates rapidly formed from submicrometer amorphous silicates within the IDPs at room temperature in mildly alkaline solution. Hydrated silicates may thus form in the near‐surface regions of comets if liquid water is ever present. Our findings provide insight into origins of cometary IDPs containing both anhydrous and hydrated minerals and help reconcile the seemingly inconsistent observations of hydrated silicates from the Stardust and Deep Impact missions.