Observations Of Zodiacal Light Research Articles

Heliocentric distance dependence of zodiacal light observed by Hayabusa2#

Zodiacal light (ZL) is sunlight scattered by interplanetary dust particles (IDPs) at optical wavelengths. The spatial distribution of IDPs in the Solar System may hold an important key to understanding the evolution of the Solar System and material transportation within it. The number density of IDPs can be expressed as n(r) sim r^{-alpha }, and the exponent alpha sim 1.3 was obtained by previous observations from interplanetary space by Helios 1/2 and Pioneer 10/11 in the 1970s and 1980s. However, no direct measurements of alpha based on ZL observations from interplanetary space outside Earth’s orbit have been performed since then. Here, we introduce initial results for the radial profile of the ZL at optical wavelengths observed over the range 0.76-1.06 au by ONC-T aboard the Hayabusa2# mission in 2021-2022. The ZL brightness we obtained is well reproduced by a model brightness, although there is a small excess of the observed ZL brightness over the model brightness at around 0.9 au. The radial power-law index we obtained is alpha = 1.30 pm 0.08, which is consistent with previous results based on ZL observations. The dominant source of uncertainty arises from the uncertainty in estimating the diffuse Galactic light (DGL).Graphical

Detection and measurement of micrometeoroids with LISA Pathfinder

The Solar System contains a population of dust and small particles originating from asteroids, comets, and other bodies. These particles have been studied using a number of techniques ranging from in-situ satellite detectors to analysis of lunar microcraters to ground-based observations of zodiacal light. In this paper, we describe an approach for using the LISA Pathfinder (LPF) mission as an instrument to detect and characterize the dynamics of dust particles in the vicinity of Earth-Sun L1. Launching in late 2015, LPF is a dedicated technology demonstrator mission that will validate several key technologies for a future space-based gravitational-wave observatory. The primary science instrument aboard LPF is a precision accelerometer which we show will be capable of sensing discrete momentum impulses as small as $4\times 10^{-8}\,\textrm{N}\cdot\textrm{s}$. We then estimate the rate of such impulses resulting from impacts of micrometeoroids based on standard models of the micrometeoroid environment in the inner solar system. We find that LPF may detect dozens to hundreds of individual events corresponding to impacts of particles with masses $> 10^{-9}\,$g during LPF's roughly six-month science operations phase in a $5\times 10^5\,\textrm{km}$ by $8\times 10^5\,\textrm{km}$ Lissajous orbit around L1. In addition, we estimate the ability of LPF to characterize individual impacts by measuring quantities such as total momentum transferred, direction of impact, and location of impact on the spacecraft. Information on flux and direction provided by LPF may provide insight as to the nature and origin of the individual impact and help constrain models of the interplanetary dust complex in general. Additionally, this direct in-situ measurement of micrometeoroid impacts will be valuable to designers of future spacecraft targeting the environment around L1.

Interplanetary dust distribution and temporal variability of Mercury's atmospheric Na

The interplanetary dust (IPD) distribution in the inner solar system is not yet well understood because of lack of direct dust measurements in the inner solar system and so one needs to rely on zodiacal light observations that are difficult to interpret. Mercury has an unstable atmosphere, and the source processes of Na in its atmosphere are unclear. Results of past observations have revealed that the atmospheric Na density has no or low correlation with the solar flux, sunspot number, heliocentric distance, or solar radiation pressure. We show that the variability of Mercury's atmospheric Na density depends strongly on the IPD distribution. That is, Na density is low (high) when Mercury is far away from (close to) the symmetry plane of IPD, and so one can infer the IPD distribution near Mercury orbit from the temporal variability of Na density in Mercury's atmosphere.

Organics in cometary and interplanetary dust

AbstractWhile gaseous carbon-rich species in cometary comae (coming from the nuclei icy component) are extensively studied by spectroscopic remote observations, so-called CHONs dust particles, i. e. organic compounds coming from the nuclei refractory component, have mostly been studied by dust mass spectrometers flying through the comae of comets 1P/Halley and 81P/Wild 2. However, remote observations of the light scattered by dust in cometary comae and in the interplanetary medium, coupled with both numerical and experimental simulations, have recently allowed us to confirm that such particles harbor a significant fraction of absorbing material, presumably consisting of organic compounds (Levasseur-Regourd et al. PSS 2007, Lasue et al. A&A 2007).We estimate the fraction of absorbing material present in cometary dust for extensively observed comets (e.g., 1P/Halley, C/1995 O1 Hale-Bopp) and in the interplanetary dust (from zodiacal light observations). We also establish that, besides compact particles, fluffy aggregates are definitely present in these media. The properties (e.g., size distribution, morphology, composition) of the cometary and interplanetary dust particles, as inferred from light scattering data analysis, are compared with those of the IDPS collected in the upper Earth atmosphere and of the unique samples returned by the Stardust mission at Wild 2. The results are discussed in terms of the formation of comets in the protosolar nebula, and of the possible survival, at the epoch of late early bombardment, of cometary organics embedded in fluffy aggregates.

Planet-C: Venus Climate Orbiter mission of Japan

The Venus Climate Orbiter mission (PLANET-C), one of the future planetary missions of Japan, aims at understanding the atmospheric circulation of Venus. Meteorological information will be obtained by globally mapping clouds and minor constituents successively with four cameras at ultraviolet and infrared wavelengths, detecting lightning with a high-speed imager, and observing the vertical structure of the atmosphere with radio science technique. The equatorial elongated orbit with westward revolution fits the observation of the movement and temporal variation of the atmosphere which as a whole rotates westward. The systematic, continuous imaging observations will provide us with an unprecedented large data set of the Venusian atmospheric dynamics. Additional targets of the mission are the exploration of the ground surface and the observation of zodiacal light. The mission will complement the ESA's Venus Express, which also explores the Venusian environment with different approaches.

Optical properties of fluffy aggregates as analogue of interplanetary dust particles

Based on the appearance of chondritic porous aggregates collected from stratosphere, we have modeled interplanetary dust particles as fluffy aggregates consisting of submicron-sized spherical monomers. The optical properties are calculated by a modified version of the discrete dipole approximation where the dipole polarizability is determined by the first term of scattering coefficient in the Mie theory. The accuracy of our calculations is confirmed through the comparison with the rigorous solutions for cluster of spherical monomers. It is found that fluffy aggregates have larger cross sections and less resonant structures in the scattering profiles in comparison with the volume-equivalent sphere. Our model results in consistent behaviors with the observation of zodiacal light, i.e., slow rise towards the backward direction and negative polarization between the scattering angles 160° ≤ θ ≤ 180°. For two sets of optical constants of dielectric materials, these properties are not sensitive to the size of an aggregate as long as the monomer size is smaller than the incident wavelength.

Disentangling the main populations of the Zodiacal Cloud from Zodiacal Light observations

Photometric surveys of the Zodiacal Light (ZL) already allowed to retrieve features of interplanetary dust space distribution and optical behaviour. Of the brightness “gathering” function dZ = D(α)/m along each line of sight (LOS), (α being the phase angle, m the subsolar distance of the LOS, D) the local scattering coefficient), two approximate values could be derived, based on the constraints provided by the two observed values of its integral Z, when the LOS is in-ecliptic. This “nodes of lesser uncertainty” method (Dumont, Levasseur-Regourd, Renard, 1985 to 1996), however, lowered but did not rule out question marks upon the phase function. To improve this inversion, additional constraints can be found in ZL surveys from deep space probes. We show that both the Pioneer 10 (Toller and Weinberg, 1985) and (despite their lack of in-ecliptic scans) the Helios (Leinert et al., 1982) data imply the phase function to weakly depart from isotropy, at least in the 30°–150° range. The latitudinal dependence f(β⊙, r = cst) of the space density (less well known than the heliocentric, D(r, β⊙ = 0)) can be tracked through the brightness ratio, at the same elongation ε, aiming in the helioecliptic meridian, against in the ecliptic. At ε = 90°, this ratio 0.3 would lead—in the improper assumption of a single, homogeneous cloud—to fit the latitudinal density drop by a — cos12β⊙ function. The resulting brightness ratio at ε < 90°, which should be equal to ∫LOS cos12 β⊙(α)D(α)· dα/∫LOS D(α)dα turns out to be much lower than the ratio observed in the 60° > ε > 15° range (again ≃0.3). This contradiction is solved with a steeper exponent (20–22?) for cos/gb⊙, and by assuming the flattened cloud to coexist with another one, spherically symmetrical, which contributes 15–25 S10 at ε = 90°, 50–80 S10 at ε = 60°, 100–160 S10 at ε = 45° and 250–450 S10 at ε = 30°.

Temperatures of Zodiacal dust

Temperatures of interplanetary dust particles have been determined by calculating the termal emission from dust concentrations according to the “Five Populations of Interplanetary Meteroids” model by Divine ( J. geophys. Res., in press, 1993) and matching it with the observed zodiacal thermal emission. Properties of the meteoroid populations are describned by comparing them with the meteoroid mas distribution measured at 1 a.u., and with zodiacal light observations ranging from 0.3 to 4 a.u. Particle temperatures are assumed as a function of heliocentric distance and particle size. An IR emissivity of 1 has been assumed for aprticles bigger than-one tenth of the considered wavelength and zero for smaller particles. The intensity contributions of the five meteoroid populations are evaluated. The resulting total IR intensity is compared with the intensity of the zoidcal emission as determined either by the Infrared Astronomical Satellite IRAS or by the Zodiacal Infrared Project ZIP. At I a.u., temperatures have been obtained which range from 130 to 190 K and from 380 to 390 K for particles of diameters 10 −4 and 10 −6 m, respectively. Compared with Mie calculations the particle temperatures are between those of a dielectric (obsidian) and a strongly absorbing material (graphite).

On a possible use of total solar eclipse below the horizon for observations of the inner zodiacal light (as applied to the eclipse of 30 June, 1992)

The Moon's umbral shadow, tangentially penetrating the Earth's atmosphere, appreciably reduces the brightness of the twilight sky at points located under the shadow axis. This should yield favourable conditions for observation of the zodiacal light for small altitudes of the Sun below the horizon. The location of the projection of the Moon's shadow axis at the Earth's surface under the above conditions is calculated for the case of the total solar eclipse of 30 June, 1992.

Solar dust ring observation at the total solar eclipse in Mexico

There are dust grains in interplanetary space. Zodiacal light observations show a distribution of dust grains in the ecliptic plane, but cannot show how close to the Sun dust grains survive. Dust grains close to the Sun are heated by solar radiation and are evaporated. Thus, a dust free zone is formed. There is a question as to how large this dust free zone may be.

The Zodiacal Cloud Complex

AbstractThe physical properties of the interplanetary dust grains are, out of the ecliptic plane, mainly derived from observations of zodiacal light in the visual or infrared domains. The bulk optical properties (polarization, albedo) of the grains are demonstrated to depend upon their distance to the Sun (at least in a 0.1 AU to 1.7 AU range in the symmetry plane) and upon the inclination of their orbits (at least up to 22°). Classical models assuming the homogeneity of the zodiacal cloud are no longer acceptable. A hybrid model, with a mixture of two populations, is proposed. It suggests that various sources (periodic comets, asteroids, non periodic comets...) play an important role in the replenishment of the zodiacal cloud complex.

Optical Properties of Interplanetary Dust in the Tangential Plane

AbstractLocal intensity and emissivity, and consequently local polarization degree, temperature and albedo, can be retrieved from optical and thermal observations of zodiacal light. The local polarization degree (normalized at constant solar distance and phase angle) is found to decrease with elevation above the symmetry plane of the zodiacal cloud. The heterogeneity of the cloud, established towards the symmetry pole, is here demonstrated in the tangential plane (almost perpendicular to the ecliptic plane at 1 AU). We present a map of the local polarization degree in this plane.

Blue and Red Brightnesses of the Integrated Starlight Obtained by Star-Counts in 24 Regions

Star-counts on the Palomar Sky Survey Atlas were made in 1968-87 in order to estimate the background brightness in zodiacal light and airglow observations. Measured diameters of blue and red images of each star were converted to the magnitude with empirical diameter-magnitude relations. The resultant blue and red brightnesses and colors of the integrated starlight are presented for 24 sky regions, including 4 polar (North Celestial, North Ecliptic, North and South Galactic) and 10 ecliptic regions.

Are There Many More Small Meteors Than Hitherto Detected?

AbstractVisual meteors, due to impinging meteoroids of radius about 1 cm, appear at a rate of a few per hour during non-shower periods. Smaller meteoroids (100 μm – 1 cm) give rise to less bright trails, but are much more abundant. These are usually detected by radars of about 10 m wavelength which, over the past 40 years, have produced a plethora of information concerning mass and height distributions, orbits, etc.Using such ‘conventional radars’, the peak of the measured height distribution is found at about 95 km, with few meteors detected above 105 km. However, the flux detected is only a few percent of the total flux (a) measured using a large (10 m) optical collector, and (b) expected from a comparison with measurements by satellite impacts and zodiacal light observations (radii &lt; 100 μm). One possibility is that the radars detect few low-velocity (V &lt; ~25 km s-1) meteors since these produce little ionization and thus limit their detectability: the ionizing efficiency of meteors varies as ~ V7/2. In direct opposition, our alternative hypothesis is that the undetected flux is held in a faint high-velocity component which ablates at high altitude. These are not detected by conventional radars because meteor trails have ‘initial widths’ of about 3 m at 105 km; for a radar wavelength of 10 m, components scattered from different regions of the trail therefore destructively interfere, and the probability of detecting any meteor above 105 km is small.In order to test our hypothesis we have measured the height distribution with a 150 m radar, and we are commencing ancillary observations at 50 m; compared to these wavelengths the initial width is small to at least 140 km. The results show a peak at 105 km with most meteors being above this, significant numbers occurring right up to 140 km. This suggests that the true flux is at least 10 or 20 times that previously deduced, having implications for the number of cornets in the recent past and the balance of material between the smaller bodies in the solar System.

Collisional balance of the meteoritic complex

Taking into account meteoroid measurements by in situ experiments, zodiacal light observations, and oblique angle hypervelocity impact studies, it is found that the observed size distributions of lunar microcraters usually do not represent the interplanetary meteoroid flux for particles with masses ⪅10 −10g. From the steepest observed lunar crater size distribution a “lunar flux” is derived which is up to 2 orders of magnitude higher than the interplanetary flux at the smallest particle masses. New models of the “lunar” and “interplanetary” meteoroid fluxes are presented. The spatial mass density of interplanetary meteoritic material at 1 AU is ∼10 −16g/m 3. A large fraction of this mass is in particles of 10 −6 to 10 −4 g. A detailed analysis of the effects of mutual collisions (i.e., destruction of meteoroids and production of fragment particles) and of radiation pressure has been performed which yielded a new picture of the balance of the meteoritic complex. It has been found that the collisional lifetime at 1 AU is shortest (∼10 4years) for meteoroids of 10 −4 to 1 g mass. For particles with masses m > 10 −5g, Poynting-Robertson lifetimes are considerably larger than collisional lifetimes. The collisional destruction rate of meteoroids with masses m ⪆ 10 −3 g is about 10 times larger than the rate of collisional production of fragment particles in the same mass range. About 9 tons/sec of these “meteor-sized” ( m > 10 −5g) particles are lost inside 1 AU due to collisions and have to be replenished by other sources, e.g., comets. Under steady-state conditions, most of these large particles are “young”; i.e., they have not been fragmented by collisions and their initial orbits are not altered much by radiation pressure drag. Many more micrometeoroids of masses m ⪅ 10 −5g are generated by collisions from more massive particles than are destroyed by collisions. The net collisional production rate of intermediate-sized particles 10 −10g ⪅ m ⪅ 10 −5g is found to be about 16 times larger at 1 AU than the Poynting-Robertson loss rate. The total Poynting-Robertson loss rate inside 1 AU is only about 0.26 tons/sec. The smallest fragment particles ( m ⪅ 10 −10g) will be largely injected into hyperbolic trajectories under the influence of radiation pressure (β meteoroids). These particles provide the most effecient loss mechanism from the meteoritic complex. When it is assumed that meteoroids fragment similarly to experimental impact studies with basalt, then it is found that interplanetary meteoroids in the mass range 10 −10g ⪅ m ⪅ 10 −5g cannot be in temporal balance under collisions and Poynting-Robertson drag but their spatial density is presently increasing with time.

Zodiacal Light: A Probe of the Properties and Evolution of Interplanetary Dust

AbstractA brief discussion is presented on the use of zodiacal light observations to derive information on the optical and physical properties of interplanetary dust and its spatial distribution.

Dynamics of Micrometeoroids

Recent observations of zodiacal light have established a reliable and consistent picture of the spatial distribution of interplanetary dust in the ecliptic plane. The spatial density nr varies with heliocentric distance r according to a power law nr ∝ r−ν. From Helios observations an exponent v = 1.3 is derived for the distance interval from 0.08 A.U. to 1 A.U. (Link et al. 1976). Outside the earth's orbit the Pioneer 10 and 11 results suggest a higher exponent v = 1.5 for the distance interval from 1 A.U. to 3.3. A.U. (Hanner et al., 1976). Giese and Grün (1976) showed that the results from zodiacal light observations are compatible with the micrometeoroid fluxes derived from in situ measurements and lunar crater statistics. They found that micrometeoroids in the size range from 10 μm to 100 μm radii (corresponding roughly to 10−8g to 10−5g) contribute most to the zodiacal light brightness.The orbital distribution of large interplanetary particles (10−6 g &lt; m &lt; 10−3g) is known from meteor observations. Sekanina and Southworth (1975) reported average orbital elements of these particles: ā ∼ 1.25 A.U., ē ∼ 0.4 and ī ∼ 20°. Orbital information on micrometeoroids (m &lt; 10−8g) is obtained from in situ detectors on board the Pioneer 8 and 9 and Helios 1 spaceprobes and the HEOS-2 satellite. Characteristics of the different micrometeoroid experiments are given in Table 1. There is almost no time overlap in the data taking intervals of the experiments. Therefore one has to assume that there are no time variations of the meteoroid flux on the time scale of 1 to 10 years if one compares the results from the different experiments. This assumption may be violated for the smallest of the observed particles (m &lt; 10−13g) due to strong electromagnetic interaction of these particles with the interplanetary magnetic field (Morfill and Grün 1979).

Four Years of Zodiacal Light Observations from the Helios Space Probes: Evidence for a Smooth Distribution of Interplanetary Dust

The zodiacal light experiments on Helios 1 and Helios 2 have been continually operating since launch in December 1974 and January 1976, respectively. The data support the view that the distribution of interplanetary dust is rather simple in space and quite constant in time. Instrument and data reduction have been described by Leinert et al. (1978). In the following we present Helios 2 data only.

The Symmetry Plane of the Zodiacal Cloud Near 1 AU

Analysis of zodiacal light observations from Mt. Haleakala, Hawaii show that the symmetry plane of the zodiacal cloud near 1 A.U. is close to the invariable plane of the solar system. Since the symmetry plane of the inner zodiacal cloud is close to the orbital plane of Venus (Misconi and Weinberg, 1978; Leinert et al., 1979), we suggest that the symmetry plane changes inclination with heliocentric distance.

Is Venus Concentrating Interplanetary Dust Toward Its Orbital Plane?

By use of observations of zodiacal light, the symmetry plane or plane of maximum density of interplanetary dust at elongations of 32 degrees to 50 degrees from the sun has been found to be closer to the orbital plane of Venus than to the invariable plane. This suggests that the plane of maximum density in this region is being gravitationally perturbed closer to the orbital plane of Venus.