Neighborhood Of Earth Research Articles

Asteroid retrieval missions enabled by invariant manifold dynamics

Near Earth Asteroids are attractive targets for new space missions; firstly, because of their scientific importance, but also because of their impact threat and prospective resources. The asteroid retrieval mission concept has thus arisen as a synergistic approach to tackle these three facets of interest in one single mission. This paper reviews the methodology used by the authors (2013) in a previous search for objects that could be transported from accessible heliocentric orbits into the Earth's neighbourhood at affordable costs (or Easily Retrievable Objects, a.k.a. EROs). This methodology consisted of a heuristic pruning and an impulsive manoeuvre trajectory optimisation. Low thrust propulsion on the other hand clearly enables the transportation of much larger objects due to its higher specific impulse. Hence, in this paper, low thrust retrieval transfers are sought using impulsive trajectories as first guesses to solve the optimal control problem. GPOPS-II is used to transcribe the continuous-time optimal control problem to a nonlinear programming problem (NLP). The latter is solved by IPOPT, an open source software package for large-scale NLPs. Finally, a natural continuation procedure that increases the asteroid mass allows to find out the largest objects that could be retrieved from a given asteroid orbit. If this retrievable mass is larger than the actual mass of the asteroid, the asteroid retrieval mission for this particular object is said to be feasible. The paper concludes with an updated list of 17 EROs, as of April 2016, with their maximum retrievable masses by means of low thrust propulsion. This ranges from 2000tons for the easiest object to be retrieved to 300tons for the least accessible of them.

Do Inner Planets Modulate the Solar Wind Velocity at 1 AU from the Sun?

Quite recently, it has been suggested that the interaction of the solar wind with Mercury results in the variation in the solar wind velocity in the Earth's neighborhood during inferior conjunctions with Mercury. This suggestion has important implications both on the plasma physics of the interplanetary space and on the space weather forecast. In this study we have attempted to answer a question of whether the claim is properly tested. We confirm that there are indeed ups and downs in the profile of the solar wind velocity measured at the distance of 1 AU from the Sun. However, the characteristic attribute of the variation in the solar wind velocity during the inferior conjunctions with Mercury is found to be insensitive to the phase of the solar cycles, contrary to an earlier suggestion. We have found that the cases of the superior conjunctions with Mercury and of even randomly chosen data sets rather result in similar features. Cases of Venus are also examined, where it is found that the ups and downs with a period of ~ 10 to 15 days can be also seen. We conclude, therefore, that those variations in the solar wind velocity turn out to be a part of random fluctuations and have nothing to do with the relative position of inner planets. At least, one should conclude that the solar wind velocity is not a proper observable modulated by inner planets at the distance of 1 AU from the Sun in the Earth's neighborhood during inferior conjunctions.

Easily retrievable objects among the NEO population

Asteroids and comets are of strategic importance for science in an effort to understand the formation, evolution and composition of the Solar System. Near-Earth Objects (NEOs) are of particular interest because of their accessibility from Earth, but also because of their speculated wealth of material resources. The exploitation of these resources has long been discussed as a means to lower the cost of future space endeavours. In this paper, we consider the currently known NEO population and define a family of so-called Easily Retrievable Objects (EROs), objects that can be transported from accessible heliocentric orbits into the Earth's neighbourhood at affordable costs. The asteroid retrieval transfers are sought from the continuum of low energy transfers enabled by the dynamics of invariant manifolds; specifically, the retrieval transfers target planar, vertical Lyapunov and halo orbit families associated with the collinear equilibrium points of the Sun-Earth Circular Restricted Three Body problem. The judicious use of these dynamical features provides the best opportunity to find extremely low energy Earth transfers for asteroid material. A catalogue of asteroid retrieval candidates is then presented. Despite the highly incomplete census of very small asteroids, the ERO catalogue can already be populated with 12 different objects retrievable with less than 500 m/s of {\Delta}v. Moreover, the approach proposed represents a robust search and ranking methodology for future retrieval candidates that can be automatically applied to the growing survey of NEOs.

The influx rate of long-period comets in the Earth's neighborhood and their debris contribution to the interplanetary medium

AbstractWe analyze the flux of new and evolved long-period comets (LPCs) reaching the Earth's neighborhood (perihelion distances q < 1.3 AU), their physical lifetimes, and their implications as regards to the amount of meteoritic matter that is being deposited in the near-Earth region. The flux of LPCs with q < 1.3 au is found to be of about 340 ± 40, brighter than absolute total magnitude 8.6 (radius R ~ 0.6 km) (Fernández and Sosa 2012). Bearing in mind that most of these comets disintegrate into meteoritic matter, this represents a large contribution to the interplanetary dust complex which requires an amount of matter of about 10 tons s−1 to keep it in steady state. These aspects, as well as the impact rate with Earth of meteoroids of LPC origin, will be discussed in this presentation.

SAMPEX to Reenter Atmosphere: Twenty‐Year Mission Will End

SAMPEX to Reenter Atmosphere: Twenty‐Year Mission Will End

Parallels among the “music scores” of solar cycles, space weather and Earth's climate

AbstractSolar variability and its effects on the physical variability of our (space) environment produces complex signals. In the indicators of solar activity at least four independent cyclic components can be identified, all of them with temporal variations in their timescales.Time-frequency distributions (see Kolláth & Oláh 2009) are perfect tools to disclose the “music scores” in these complex time series. Special features in the time-frequency distributions, like frequency splitting, or modulations on different timescales provide clues, which can reveal similar trends among different indices like sunspot numbers, interplanetary magnetic field strength in the Earth's neighborhood and climate data.On the pseudo-Wigner Distribution (PWD) the frequency splitting of all the three main components (the Gleissberg and Schwabe cycles, and an ≈5.5 year signal originating from cycle asymmetry, i.e. the Waldmeier effect) can be identified as a “bubble” shaped structure after 1950. The same frequency splitting feature can also be found in the heliospheric magnetic field data and the microwave radio flux.

China NEO Survey Telescope and its preliminary achievement

AbstractIn recent years, there has been an increasing appreciation for the hazards posed by Near Earth Objects (NEOs), those asteroids and periodic comets whose motions can bring them into the Earth's neighborhood. An NEO Survey Telescope (NEOST) was built in China to be taken part in the international NEO joint survey. This telescope is a 1.0/1.2m Schmidt telescope, equipped with a 4K by 4K CCD detector with a drift-scanning function. After adjusting the telescope and test observations, in December 2006 the NEOST began its NEO survey program. We have found 188 new asteroids including an NEO – 2007 JW2 and one periodic comet –P/2007 S1 (Zhao).

Transfers between the Earth–Moon and Sun–Earth systems using manifolds and transit orbits

The L 1 and L 2 libration points have been proposed as gateways granting inexpensive access to interplanetary space. The lunar libration points, in conjunction with the collinear libration points in the Sun–Earth system, may also become primary hubs for future human activities in the Earth's neighborhood. The associated manifold tubes have been introduced by a number of researchers as the basis for design strategies to produce trajectories that shift between different systems. Intersections may ultimately be sought between many tubes from many different libration point orbits in each system; the complexity forces a new look at the computations. Individual transfers between three-body systems have been the focus of some recent investigations. This paper presents an approach to solve the general problem for transfers between the Earth–Moon system (lunar orbits and/or lunar libration point orbits) and Sun–Earth/Moon L 2 libration point orbits. The solutions are transitioned to the full ephemeris models with additional perturbations and the transfers can be determined for various lunar phases. The solution process also seeks the particular Lissajous trajectory in each system to accomplish the transfer at a low cost. Some results are presented for various types of transfer problems.

A Map of the Universe

We have produced a new conformal map of the universe illustrating recent discoveries, ranging from Kuiper belt objects in the Solar system, to the galaxies and quasars from the Sloan Digital Sky Survey. This map projection, based on the logarithm map of the complex plane, preserves shapes locally, and yet is able to display the entire range of astronomical scales from the Earth's neighborhood to the cosmic microwave background. The conformal nature of the projection, preserving shapes locally, may be of particular use for analyzing large scale structure. Prominent in the map is a Sloan Great Wall of galaxies 1.37 billion light years long, 80% longer than the Great Wall discovered by Geller and Huchra and therefore the largest observed structure in the universe.

Utilization of libration points for human exploration in the Sun–Earth–Moon system and beyond

A plan to use the Sun–Earth L2 libration point as the primary hub for future human space activities in the Earth's neighborhood is described. It is expected that the Sun–Earth L2 point will be the location of choice for a number of large astronomical observatories over the next 20 years. These observatories will probably require some level of servicing and/or repair by astronauts. To provide human access to the L2 point, the early development of a reusable vehicle called a Deep-Space Shuttle (DSS) is proposed. The DSS, based in low-Earth orbit, would be able to transport astronauts to and from the L2 point in about 35 days (including a 5-day stay time at L2). The Sun–Earth L2 point is also useful as a staging node for missions to near-Earth asteroids and Mars. For instance, a reusable interplanetary transfer vehicle (ITV) stationed at the L2 point could be used for the round-trip journey. The ITV would use lunar gravity-assists and a perigee Δ V maneuver to enter the desired interplanetary transfer trajectory. Just prior to the Earth-escape maneuver, a DSS “taxi” would transfer the crew to the ITV. A reverse procedure would be used to return the ITV to the libration point with the crew leaving the ITV just before the Earth-capture maneuver, and returning directly to Earth via an Apollo-style re-entry capsule. Using this technique, the L2-based ITV would save approximately 6.3 km/ s in Δ V cost compared with an ITV stationed in low-Earth orbit.

The AMOR radar: an efficient tool for meteoroid research

The Advanced Meteor Orbit Radar (AMOR) is a multi-station HF system in continuous operation that measures both the geophysical parameters associated with meteoroid ablation and the heliocentric orbits of Earth-impacting particles to a limiting size of ∼ 40 μm. With a directional accuracy of ∼ 2° the facility is an incisive probe of the directional characteristics of material in the Earth's neighbourhood and the orbital spatial distribution of inner solar system dust.

International coordination of solar terrestrial science

A broad, international, cooperative effort is under way to study and develop quantitative understanding of the fundamental electrodynamic processes in the solar-terrestrial environment. Japan, Europe, Russia, the United States, and other countries are providing spacecraft to be placed in key regions with the aim of utilizing coordinated, multipoint spaceflight measurements, ground-based observations, and theory to study the global energy budget of geospace. The U.S. contribution began in the late 1970's as the OPEN program (Origin of Plasmas in Earth's Neighborhood) and was reconstituted in the 1980's as the Global Geospace Science (GGS) program. The international effort, known in the U. S. as the International Solar Terrestrial Physics program (ISTP), began with the launch of the Japanese GEOTAIL in 1992, and will continue with the U. S. spacecraft WIND and POLAR in 1994–1995, and the European four-spacecraft Cluster fleet and its Solar and Heliospheric Observatory (SOHO) in 1995. Russia will launch its Interball set of four spacecraft in 1995. The Inter-Agency Consultative Group (IACG) is promoting the coordination of the spacecraft observations by means of scientific campaigns aimed at addressing scientific questions that can only be answered by observations from the multiple spacecraft. The Solar Terrestrial Energy Program (STEP) is coordinating the involvement of the broad scientific community and especially the correlative ground observations.

Global Energy Flow in the Magnetosphere-Ionosphere System.

Planning for the OPEN (Origin of Plasmas in the Earth's Neighborhood) program in 1977-1978 was representative of early concepts to obtain a quantitative estimate of the energy flow through the magnetosphere-ionosphere system. The magnetosphere was the focus of those early planning discussions and the OPEN program was defined to address global issues of mass, momentum, and energy flow. The STEP program that we are celebrating at this conference is in many ways a direct evolution of the early work that led to the OPEN program. One of the main characteristics of those early discussions was the desire to obtain a global view of the magnetosphere. This pursuit of a global view not only has persisted through the evolution of OPEN through STEP, but it has been a consistent pursuit of space physics from its very beginnings. In fact, ground-based scientific activities prior to the space age had already recognized the importance of establishing observation networks designed to provide global views of the parameters being observed. In this paper, we review briefly both the early attempts at obtaining a global view of the magnetosphere and the initial arguments for obtaining a global measure of the energy flow through the magnetosphere. We then show, through realistic simulations, what now can be accomplished in the arena of measuring the global energy flow through the magnetosphere and its component parts. We discuss both qualitative and quantitative results, stressing the manner in which global observations play a vital role in furthering our understanding of the magnetosphere and its dynamics. Finally we present an example constructed from a video shown at the symposium that illustrates what might be seen of global magnetosphere dynamics with presently existing instrumentation.

Simultaneous observation of a traveling vortex structure in the morning sector and a field line resonance in the postnoon sector

Radar observations suggesting ULF field line resonances impulsively excited via a cavity or waveguide mode were obtained simultaneously in the dawn (Bistatic Auroral Radar System (BARS)) and postnoon (Sweden and Britain Radar‐Auroral Experiment (SABRE)) sectors. The primary data used to study this event are from both the European Incoherent Scatter magnetometer cross and Subauroral Magnetometer Network magnetometer arrays in the postnoon sector and from the Canadian Auroral Network for the Origin of Plasmas in the Earth's Neighborhood Program Unified Study (CANOPUS), MAgnetometer, RIometer and tellurics Array (MARIA), the GOES 7 magnetometer, and the neural network classification of Defense Meteorological Satellite Program (DMSP) particle data in the dawn sector. In the postnoon sector (Scandinavia) a decaying field line resonance was observed following a more complicated initial interval. The resonance period was 326 s (3.07 mHz). However, in the dawn sector the response was dominated by the initial interval in which the characteristics of a traveling vortex system were observed. The subsequent disturbance in this sector was of lesser amplitude and without discerned pattern. The field‐aligned current(s) of the traveling vortex structure was (were) at about 65° Eccentric Dipole Field Line (EDFL) latitude (approximately 68° International Geomagnetic Reference Field (IGRF)). The DMSP neural network data, however, indicate this position to have been well within the magnetosphere. GOES 7 was on a field line which was connected to the ionosphere near the MARIA meridian line at about 62.5° EDFL latitude (approximately 65.5° IGRF), just equatorward of the traveling vortex structure. It observed a magnetic disturbance which was initially driven and followed directly by a damped sinusoid signature of the azimuthal component. The frequency during this decay was 4.45 mHz (225‐s period). Values of ∑p, the height‐integrated Pedersen conductivity for both the postnoon and GOES 7 damped segments were deduced. These were low, particularly if the disturbances were in the second harmonic along the field line as suggested by GOES 7 data, and perhaps imply an additional loss mechanism. Although substantially understood, this pulsation event had distinctly different characteristics in the two time sectors and displayed many puzzling features. In particular, it was significantly more complicated than our initial anticipation of global excitation of field line resonances via a cavity or waveguide mode.

Auroral latitude Pc 5 field line resonances: Quantized frequencies, spatial characteristics, and diurnal variation

On the basis of observations with the Goose Bay Radar, several stations of the the Canadian Auroral Network for the Origin of Plasmas in the Earth's Neighborhood (OPEN) Unified Study (CANOPUS) magnetometer array, and a CANOPUS meridian scanning photometer, recent work has indicated the existence of Pc 5 ULF waves with discrete and remarkably stable frequencies (1.3, 1.9, 2.7 and 3.3 mHz with <10% variation) in the local midnight and early morning (predawn) sectors. These ULF waves were interpreted as the consequence of field line resonances driven by MHD waveguide/cavity modes, possibly excited by impulsive stimulation of the magnetopause or by Kelvin‐Helmholtz instabilities in the low‐latitude boundary layer. However, the reported stability of these frequencies over long periods of time remains a puzzle, as it seems to be inconsistent with the dynamic behavior of the magnetosphere. In order to establish if these frequencies are also observed in the dayside magnetosphere, where one of the proposed source mechanisms predicts they should be seen, we have examined the temporal and spatial characteristics of Pc 5 pulsations recorded recently with the CANOPUS magnetometer array. Pure state filtering techniques were used to determine the Pc 5 signal characteristics and their temporal and spatial variation. The results show that ULF wave signals with quantized frequencies seem to be observed throughout the dayside and dusk magnetosphere. However, frequencies both higher than and between previously reported values were also seen. The difficulty in correctly determining fundamental frequencies and their stability in the presence of polychromatic, highly amplitude‐modulated signals is noted. The signal characteristics observed in the postnoon sector were found to be significantly different compared with those seen at prenoon. While local morning and noon Pc 5 revealed typical field line resonance characteristics, toroidal mode signal characteristics prevailed in the local afternoon and evening. The reason for this asymmetry is unknown. The azimuthal wave numbers were generally small and showed a linear dependence on the Pc 5 signal frequency, implying antisunward phase velocities independent of the wave frequency.

Plasma Motions in Planetary Magnetospheres

Before direct exploration by spacecraft, Jupiter was the only planet other than Earth that was known to have a magnetic field, as revealed by its nonthermal radio emissions. The term "magnetosphere" did not exist because there was no clear concept of such an entity. The space age provided the opportunity to explore Earth's neighborhood in space and to send instruments to seven of the other eight planets. It was found that interplanetary space is pervaded by a supersonic "solar wind" plasma and that six planets, including Earth, have magnetic fields of sufficient strength to deflect this solar wind and form a comet-shaped cavity called a magnetosphere. Comparative study of these magnetospheres aims to elucidate both the general principles and characteristics that they share in common, and the specific environmental factors that cause the important, and sometimes dramatic, differences in behavior between any two of them. A general understanding of planetary magnetospheres holds the promise of wide applicability in astrophysics, which, for the indefinite future, must rely solely on remote sensing for experimental data.

ASTEROID AND COMET BOMBARDMENT OF THE EARTH

Two classes of solid bodies large enough to be detected by telescopes occur in orbits that overlap that of the Earth. These bodies are the Earth-crossing asteroids and comet nuclei. Although their orbits only rarely intersect the Earth's, the probabilities of their collision with the Earth are nevertheless finite and calculable. Systematic telescopic surveys carried out over the past two decades show that the flux of asteroids and comet nuclei in the Earth's neighborhood is sufficiently high that the effects of occasional collisions should be recognizable in the geological record. During these same two decades, an intensive international search for ancient impact structures has gone forward. The actual rate of bombardment of the Earth during the last half-billion years has been found to be roughly consistent with the present rate predicted from astronomical observations. Within a factor of about two, the average rate of bombardment of the Earth during the last half­ billion years also appears to be consistent with the average rate of bombardment of the Moon over the last 3.3 billion years. Spectacular new lines of study have developed in recent years leading to the recognition of rare large impact events that produce geochemical anomalies on a global scale. The possible effects of these large impacts on the Earth's biota have become the subject of vigorous debate. In this paper, I first review the astronomical and geologic evidence concerning the history of bombardment and then discuss the physical effects of large impacts, as they may apply to both the inorganic and organic worlds.

Global nature of field‐aligned currents and their relation to auroral phenomena

Low‐ and high‐altitude spacecraft carrying scientific magnetometers have probed the magnetic fields of the terrestrial magnetosphere. These measurements reveal that field‐aligned currents, possibly powered by dynamo action, flow over large regions of the earth's neighborhood. The purpose of this paper is to report on highlights of the U.S. contributions to the IMS effort in the area of understanding the global nature of the field‐aligned currents and their relation to auroral and ionospheric phenomena. It has been established now that field‐aligned currents flow on the same field lines connecting distant regions to low ionospheric altitudes. Similarly, currents flow on L shells extending over several hours of local time. However, it is becoming increasingly apparent that the sources of the currents in the various latitudes and longitudes are not the same. For this reason we discuss separately the following current‐laden regions: (1) the noon sector, (2) the dawn and dusk sectors, (3) the midnight sector, and (4) the polar cap. Special attention is paid to polar cap ionospheric irregularities and the relation of auroral kilometric radiation to field‐aligned currents and optical auroral emissions.

OPEN team selected

The Office of Space Science Applications of the National Aeronautics and Space Administration (NASA) has completed the selection of the scientific team that will work on the science definition for the Origins of Plasma in Earth's Neighborhood (OPEN) mission. These scientists will define the instrument packages that will fly aboard the four‐spacecraft mission proposed for later in the decade. The mission, although not currently authorized, is expected to provide detailed information about the sun's energy and its transfer from the solar wind through the earth's magnetosphere down through the ionosphere, according to NASA.

Multi-ion resonances in finite temperature plasma

Dispersion properties of electrostatic waves in a multi-ion plasma are examined, with an analysis that incorporates the effects of finite temperature, finite parallel wavenumber, and wave growth/damping in a systematic development of equations. Numerical solutions and analytic formulas are given for an ion plasma consisting of H(+), O(+), and S(+) for application to Jupiter's magnetosphere. It is demonstrated how observations of plasma resonance lines may be used as a diagnostic of ion composition in magnetospheric plasma. This potential use of high-sensitivity/high-resolution plasma wave instrumentation may provide information necessary to resolve issues concerning the origin of plasmas in the earth's neighborhood.