Results of TV imaging of phobos (experiment VSK-FREGAT)

doi:10.1016/0032-0633(91)90150-9

Planetary and Space Science

Volume 39, Issues 1–2, January–February 1991, Pages 281-295

https://doi.org/10.1016/0032-0633(91)90150-9 Get rights and content

Abstract

From February to March 1989 the Phobos 2 spacecraft took 37 TV images of Phobos at a distance of 190–1100 km. These images complement Mariner-9 and Viking data by providing higherresolution coverage of a large region West of the crater Stickney (40–160°W) and by providing disk-resolved measurements of surface brightness at a greater range of wavelengths and additional phase angles. These images have supported updated mapping and characterization of large craters and grooves, and have provided additional observations of craters' and grooves' bright rims. Variations in surface visible/nearinfrared color ratio of almost a factor of 2 have been recognized ; these variations appear to be associated with the ejecta of specific large impact craters. Updated determinations of satellite mass and volume allow calculation of a more accurate value of bulk density, 1.90 ± 0.1 g cm⁻³. This is significantly lower than the density of meteoritic analogs to Phobos' surface, suggesting a porous interior perhaps containing interstitial ice.

References (40)

A. Dobrovolskis et al.
Life near the Roche limit: behavior of ejecta from satellites close to planets
Icarus
(1980)
T.C. Duxbury
The figure of Phobos
Icarus
(1989)
T.C. Duxbury
An analytic model for the Phobos surface
Planet. Space Sci.
(1991)
J. Goguen et al.
Marsshine on Phobos
Icarus
(1979)
L. Ksanfomality et al.
Phobos: spectrophotometry between 0.3 and 0.6 μm and IR-radiometry
Planet. Space Sci.
(1991)
T. McCord et al.
Spectral reflectance of Martian areas during the 1973 opposition: photoelectric filter photometry 0.33–1.10 mcm
Icarus
(1977)
M. Noland et al.
Photometric function of Phobos and Deimos, III. Surface photometry of Phobos
Icarus
(1977)
J.I. Peltoniemi et al.
Interpretation of the surface brightness of Phobos
Planet. Space Sci.
(1991)
Yu. Shkuratov et al.
A possible interpretation of bright features on the surface of Phobos
Planet. Space Sci.
(1991)
P. Thomas
Surface features of Phobos
Icarus
(1979)

R.J. Turner

A model of Phobos

Icarus

(1978)

B.H. Zellner et al.

Photometric properties of the Martian satellites

Icarus

(1974)

G.A. Avanesov et al.

Television observations of Phobos: first results

Nature

(1989)

R. Batson et al.

Maps of Phobos

(1989)

J.-P. Bibring et al.

First results of the ISM experiment

Nature

(1989)

D. Britt et al.

The origin of Phobos: implications of compositional properties

Astron. Vest.

(1988)

F. Fanale et al.

Loss of water from Phobos

Geophys. Res. Lett.

(1989)

J. Head

The geology of Phobos and Deimos and the origin of grooves on Phobos: scientific questions for Phobos mission

J. Head et al.

Grooves on Phobos: evidence for possible secondary cratering origin

T. Johnson et al.

Optical properties of carbonaceous chondrites and their relationship to asteroids

J. geophys. Res.

(1973)

Cited by (40)

Ejecta distribution from impact craters on Ryugu: Possible origin of the bluer units
2021, Icarus
Citation Excerpt :
For example, on the Martian moon, Phobos, bluer regions are distributed around or east of the Stickney crater. These regions are referred to as the blue units (Bibring et al., 1989; Ksanfomality et al., 1990; Avanesov et al., 1991; Patsyn et al., 2012; Pieters et al., 2014). Asteroid (243) Ida also exhibits redder and bluer spectral units (Veverka et al., 1996; Carlson et al., 1994).
Asteroid (162173) Ryugu was the first spinning-top-shaped asteroid to be closely approached by a probe, the Hayabusa2 spacecraft, which sent numerous high-resolution images of Ryugu to the Earth and revealed the nature of this type of asteroid. One of the notable features of Ryugu is the equatorial ridge, which is considered the result of rapid spin in the past. Despite the advanced age of the ridge, indicated by the presence of numerous craters, the ridge exhibits a bluish color, indicating that it is covered with fresh material. In addition to Ryugu, many other asteroids have similar blue areas, which are considered the result of ejecta emplacement. We examined the distribution of ejecta blankets from actual craters on Ryugu to assess ejecta emplacement as a possible origin of Ryugu's bluer units. We determined that when Ryugu's rotation was fast, ejecta from craters formed at lower latitudes accumulated along the equator, which may explain the bluish color of the equatorial ridge. On the other hand, ejecta emplacement does not fully explain the bluish color of Tokoyo Fossa, although we attempted to find the corresponding ejecta blankets.
Origin of Phobos grooves: Testing the Stickney Crater ejecta model
2019, Planetary and Space Science
The model of Wilson and Head (1989, 2005, 2015) interprets the grooves of Phobos as the product of sliding, rolling, and bouncing ejecta boulders from the Stickney Crater impact. To test the model of Wilson and Head (1989, 2005, 2015) we apply a dynamical physics simulation to a three-dimensional shape model of Phobos and systematically assess six specific objections to the rolling boulder model. Our simulation calculates the motions of Stickney Crater ejecta boulders under the influence of Mars gravitation, the post-Stickney-impact desynchronized rotation of Phobos and altered orbit of Phobos, a spherically symmetrical gravity field of Phobos, and a collision system that simulates the effects of surface friction. We also take the orbital history of Phobos into account and test the rolling boulder model at three semimajor axes greater than the present day (10,000 km, 12,000 km, and 14,000 km). At a Phobos semimajor axis of 12,000 km, we find that boulder motions are generally consistent with observed grooves – specifically 1) Test boulders travel in linear/parallel patterns that are consistent with observed grooves, including grooves that are not radially aligned with Stickney Crater; 2) test boulders drift into suborbital flights over the trailing hemisphere of Phobos and do not travel on the surface of Phobos in this region; 3) grooves inside Stickney Crater are produced by Stickney ejecta boulders that return to Stickney Crater; 4) boulders that travel around Phobos >180° from Stickney Crater crosscut the motions of other boulders that travel >180° from Stickney; 5) at boulder ejection velocities ≲6 m/s, test boulders moving in contact with Phobos typically follow the contours of local terrain. We also find that 6) a spike of Stickney secondary impacts likely destroyed missing groove-producing boulders and removed grooves with widths ≲80 m; 7) with respect to the motion of test boulders, the two possible pre-Stickney-impact tidal-lock orientations of Phobos produce the same boulder motion effects; and 8) where our 12,000 km semimajor axis testing model is consistent with observed grooves, this supports a ∼150 Ma prediction for the age of Phobos grooves and Stickney Crater.
DePhine – The Deimos and Phobos Interior Explorer
2018, Advances in Space Research
Citation Excerpt :
Our current knowledge about the interiors of Deimos and Phobos is almost entirely based on indirect conclusions from estimates of mass, shape, and rotation. From the improved mass and the volume of Phobos and Deimos, the bulk densities of the two satellites have been estimated as 1.860 ± 0.02 g/cm3 (Willner et al., 2014) and 1.48 ± 0.22 g/cm3 (Rosenblatt, 2011) respectively, suggesting that their interiors have a high porosity and/or contain water ice (Avanesov et al., 1991; Murchie et al., 1991). The respective required porosity ranges are between 10–30% (Murchie et al., 1991) and 33–66% (Rosenblatt, 2011), which are comparable with porosities of small-sized asteroids (Britt et al., 2002).
DePhine – Deimos and Phobos Interior Explorer – is a mission proposed in the context of ESA’s Cosmic Vision program, for launch in 2030. The mission will explore the origin and the evolution of the two Martian satellites, by focusing on their interior structures and diversity, by addressing the following open questions: Are Phobos and Deimos true siblings, originating from the same source and sharing the same formation scenario? Are the satellites rubble piles or solid bodies? Do they possess hidden deposits of water ice in their interiors? The DePhine spacecraft will be inserted into Mars transfer and will initially enter a Deimos quasi-satellite orbit to carry out a comprehensive global mapping. The goal is to obtain physical parameters and remote sensing data for Deimos comparable to data expected to be available for Phobos at the time of the DePhine mission for comparative studies. As a highlight of the mission, close flybys will be performed at low velocities, which will increase data integration times, enhance the signal strength and data resolution. 10–20 flyby sequences, including polar passes, will result in a dense global grid of observation tracks. The spacecraft orbit will then be changed into a Phobos resonance orbit to carry out multiple close flybys and to perform similar remote sensing as for Deimos. The spacecraft will carry a suite of remote sensing instruments, including a camera system, a radio science experiment, a high-frequency radar, a magnetometer, and a Gamma Ray/Neutron Detector. A steerable antenna will allow simultaneous radio tracking and remote sensing observations (which is technically not possible for Mars Express). Additional instrumentation, e.g. a dust detector and a solar wind sensor, will address further science goals of the mission. If Ariane 6–2 and higher lift performance are available for launch (the baseline mission assumes a launch on a Soyuz Fregat), we expect to have greater spacecraft mobility and possibly added payloads.
Groove formation on Phobos: Testing the Stickney ejecta emplacement model for a subset of the groove population
2015, Planetary and Space Science
Citation Excerpt :
These include (1) original primary layering (Veverka and Duxbury, 1977), (2) drag forces generated during capture of the satellite (Pollack and Burns, 1977), (3) tidal distortion (Soter and Harris, 1977), (4) impact fracturing (Fujiwara and Asada, 1983), (5) impact fracturing accompanied by degassing, (6) impact fracturing accompanied by regolith drainage (Thomas et al., 1979), (7) impact fracturing followed by regolith drainage (Horstman and Melosh, 1989), (8) ejecta emplacement and secondary cratering associated with the Stickney event (Head and Cintala, 1979; Wilson and Head, 1989; Hamelin, 2011; Duxbury et al., 2010; Head and Wilson, 2010), (9) crater ejecta from Mars intersecting Phobos to form secondary chains (Murray, 2011; Murray et al., 1992, 1994, 2006; Murray and Iliffe, 1995, 2011; Murray and Heggie, 2014; Ramsley and Head, 2013a,b), and (10) a combination of several of these processes (Illes and Horvárth, 1980). Additional observations and interpretations have been reported from the Soviet Phobos, ESA Mars Express, and the NASA Viking and Mars Reconnaissance Orbiter missions (Avanesov et al. 1989, 1991; Duxbury and Veverka, 1979; Duxbury, 1989; Head, 1986; Murchie et al., 1991, 2013; Murray, 2010). Two factors have motivated us to reassess theories for the origin of grooves on Phobos.
Numerous theories have been proposed for the formation of grooves on Phobos, and no single explanation is likely to account fully for the wide variety of observed groove morphologies and orientations. One set of grooves is geographically associated with the impact crater Stickney. We test the hypothesis that these grooves were formed by clasts that were ejected from the Stickney crater interior at velocities such that they were able to slide, roll, and/or bounce to distances comparable to observed groove lengths (of the order of one-quarter of the circumference of Phobos), partly crushing the regolith and partly pushing it aside as they moved. We show that this mechanism is physically possible and is consistent with the sizes, shapes, lengths, linearity, and distribution of Stickney-related grooves for plausible values of the material properties of both the regolith and the ejecta clasts. Because the escape velocity from Phobos varies by more than a factor of two over the surface of the satellite, it is possible for ejecta clasts to leave the surface again after generating grooves. We make predictions for the surface characteristics and distributions of such grooves and their deposits on the basis of this model, and then compare them with remotely sensed observations of Phobos׳ grooves. We find that many of their characteristics can be accounted for by a model in which grooves are formed by rolling and bouncing boulders ejected from Stickney. As a further test of this hypothesis, we examine a wide range of lunar boulder tracks, and find that they have considerable similarities to grooves on Phobos in terms of morphology, structure, and relationships with underlying topography. We therefore find that the emplacement of very low-velocity ejecta associated with the Stickney cratering event is a candidate mechanism for the formation of grooves on Phobos. This model and these predictions can be further tested by analysis of high-resolution image data from current and upcoming missions to this and other small airless bodies.
The Phobos geodetic control point network and rotation model
2014, Planetary and Space Science
Citation Excerpt :
We also included 10 images from the Phobos-2 mission, which provided observations from additional viewing angles of covered areas. Phobos-2 had a close approach to Phobos in 1989 and acquired a total of 37 TV images from a distance of 190–1100 km (32–76 m/pixel) using its onboard framing camera (Avanesov et al., 1989, 1991). The camera with its focal length of 100 mm was equipped with a 505-288 (non-square) pixel sensor.
A new global control point network was derived for Phobos, based on SRC (Mars Express), Phobos-2, and Viking Orbiter image data. We derive 3-D Cartesian coordinates for 813 control points as well as improved pointing data for 202 SRC and Viking images in the Phobos-fixed coordinate system. The point accuracies vary from 4.5 m on the Phobos nearside, to up to 67.0 m on the farside, where we rely on Viking images (average point accuracy: 13.7 m). From tracking of the control points we detect a librational motion synchronous to the Phobos orbital period and measure libration amplitude of 1.09°, in agreement with predictions from shape information assuming a uniform interior. This suggests that the interior of Phobos is homogeneous – but small local mass anomalies, e.g., associated with crater Stickney, cannot be ruled out. Our new control point network has a higher number of data points and higher point accuracy than previous data products and will be an important basis for accurate shape models and maps.
Photometry of meteorites
2012, Icarus
We have measured the bi-directional reflectance phase function on selected meteorite samples (1 howardite, 1 eucrite, 1 diogenite, Orgeuil (CI), Tagish Lake (CC), Allende (CV), Lunar meteorite (MAC 88105), Forest Vale (H4)) covering part of the geochemical and petrologic diversity expected for asteroid surfaces. Samples were measured as powders, for which we achieved reflectance measurements from phase angles down to 3°, and up to 150°, at five different wavelengths covering the VIS–NIR spectral region. The data were fitted by the photometric model of Hapke (Hapke, B. [1993]. Theory of reflectance and emittance spectroscopy. Cambridge University Press, Cambridge). The physical sense of the retrieved Hapke’s parameters seems unclear but they permit to interpolate the data to any observation geometry. Strong opposition effects were observed for all samples. The absolute intensity of this effect appears moderately variable among our sample suite, and is not correlated with the average sample reflectance. We interpret this observation as Shadow-Hiding Opposition Effect (SHOE). In the case of samples presenting intense absorption bands (the Fe crystal field band at 1 μm of HED and the ordinary chondrite), we observe significant dependence of band depth to phase angle, up to 70°, even for moderate variation of phase angle. In addition, a general trend of spectral reddening with phase angle is observed. This reddening, linear with phase angle, is present in all meteorites studied. This behavior is not predicted by classical radiative theories. We propose that small-scale roughness (of the order of or below the wavelength) may induce such a behavior.

View all citing articles on Scopus

View full text

Results of TV imaging of phobos (experiment VSK-FREGAT)

Abstract

Icarus

Icarus

Planet. Space Sci.

Icarus

Planet. Space Sci.

Icarus

Icarus

Planet. Space Sci.

Planet. Space Sci.

Icarus

Icarus

Icarus

Television observations of Phobos: first results

Nature

Maps of Phobos

First results of the ISM experiment

Nature

The origin of Phobos: implications of compositional properties

Astron. Vest.

Loss of water from Phobos

Geophys. Res. Lett.

The geology of Phobos and Deimos and the origin of grooves on Phobos: scientific questions for Phobos mission

Grooves on Phobos: evidence for possible secondary cratering origin

Optical properties of carbonaceous chondrites and their relationship to asteroids

J. geophys. Res.