The Composition of Phobos: Evidence for Carbonaceous Chondrite Surface from Spectral Analysis

Pang, Kevin D.; Pollack, James B.; Veverka, J.; Lane, A. L.; Ajello, J. M.

doi:10.1126/science.199.4324.64

Cited by 73 publications

(33 citation statements)

References 26 publications

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“…Based on their colors and albedos, they have been historically classified as C-type (carbonaceous) asteroids (Pang et al 1978), although recent visible and near-IR spectroscopy (Rivkin et al 2002) find that their colors and spectral shapes are probably inconsistent with C-type asteroids. Regardless of what their best-fit asteroid type may be, the satellites clearly have low visible albedos, in the range of 0.06Y0.07.…”

Section: Introductionmentioning

confidence: 98%

Infrared Spectra of Deimos (1-13 μm) and Phobos (3-13 μm)

et al. 2007

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The 3Y13 m spectra of Deimos and Phobos were obtained on the nights of 2003 August 19, 20, and 21 UT, within a week of opposition (August 28). Spectra in the 1.5Y2.5 m region were taken a few weeks earlier on July 26. Observations were made near greatest elongation for each satellite in order to minimize scattered light from Mars. The L, M, and narrowband N (10.2 m) magnitudes for Deimos were 7:7 AE 0:1, 4:9 AE 0:1, and 0:79 AE 0:09, respectively. The L, M, and narrowband N (10.2 m) magnitudes for Phobos were 6.4, 3.8, and À0.52, respectively, all AE0.07. The 5Y12 m color temperatures of Deimos and Phobos were 344 AE 5 and 357 AE 5 K, respectively, significantly higher than the blackbody thermal equilibrium temperature for either a fast rotator at Mars's heliocentric distance (237 K) or a slow rotator (282 K). The high brightness temperatures of Deimos and Phobos in the thermal infrared of 310Y330 and 320Y340 K, respectively, are not understood, but they are somewhat consistent with the high color temperatures. Within the errors, there was little evidence for spectral features indicative of surface composition, although there were some 1Y2 variations that warrant further observations.

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Section: Introductionmentioning

confidence: 98%

Infrared Spectra of Deimos (1-13 μm) and Phobos (3-13 μm)

et al. 2007

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“…The latter two publications addressed the dynamics as seen in a non-inertial frame associated with the planet's equator of date. The analysis was carried out in terms of the so-called "contact" Kepler elements, i.e., in terms of the Kepler elements satisfying a condition different 1 Phobos and Deimos give every appearance of being captured asteroids of the carbonaceous chondritic type, with cratered surfaces older than ∼ 10 9 years (Veverka 1977;Pang et al 1978;Pollack et al 1979;Tolson et al 1978). If they were captured by gas drag (Burns 1978), this must have occurred early in the history of the solar system while the gas disk was substantial enough.…”

Section: Mathematical Toolsmentioning

confidence: 99%

Long-term evolution of orbits about a precessing oblate planet: 3. A semianalytical and a purely numerical approach

Gurfil

Lainey

Efroimsky

2007

Celestial Mech Dyn Astr

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Construction of an accurate theory of orbits about a precessing and nutating oblate planet, in terms of osculating elements defined in a frame associated with the equator of date, was started in Efroimsky & Goldreich (2004) and Efroimsky (2004bEfroimsky ( , 2005Efroimsky ( , 2006. Here we continue this line of research by combining that analytical machinery with numerical tools. Our model includes three factors: the J 2 of the planet, its nonuniform equinoctial precession described by the Colombo formalism, and the gravitational pull of the Sun. This semianalytical and seminumerical theory, based on the Lagrange-type planetary equations for the Keplerian elements, is then applied to Deimos on very long time scales (up to 1 billion of years). In parallel with the said semianalytical theory for the Keplerian elements defined in the co-precessing equatorial frame, we have also carried out a completely independent, purely numerical, integration in a fixed inertial Cartesian frame. The results agree to within 10 −3 − 10 −2 (from 0.3%, for near-polar orbits, through 1.3% for near-equatorial ones), for over 20 Myr, thus demonstrating the applicability of our semianalytical model over long * We use the term "precession" in its general meaning, which includes any change of the instantaneous spin axis. So generally defined precession embraces the entire spectrum of spin-axis variations -from the polar wander and nutations through the Chandler wobble through the equinoctial precession. 1timescales. This will enable us to employ the semianalytical model at the further stages of the project, enriching this model with the tides and the planet's triaxiality. (Lainey, Efroimsky & Gurfil 2007) Another goal of this work was to make an independent check of whether the equinoctial precession of Mars, as predicted for a rigid Mars, could have been sufficient to repel the orbits away from the equator. The answer to this question, in combination with our knowledge of the current position of Phobos and Deimos, will help us to understand whether this precession could indeed have always been as large as predicted or whether it ought to have been less in the past. It has turned out that, both for high and low initial inclinations, the orbit inclination reckoned from the precessing equator of date is subject only to small variations (from about 10 −3 deg, for near-equatorial satellites, to about 2 deg, for polar ones). This is an extension, to non-uniform equinoctial precession given by the Colombo model and to an arbitrary initial inclination, of an old result obtained by Goldreich (1965) for the case of uniform precession and a low initial inclination. Such "inclination locking", or the "Goldreich lock", confirms that an oblate planet can, indeed, afford a large equinoctial precession for billions of years, without repelling its near-equatorial satellites away from the equator of date: the satellite inclination oscillates but does not show a secular increase. Nor does it show secular decrease, a fact that is relevant to the discu...

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“…Spectrophotometric measurements suggest a surface composition close to that of carbonaceous chondrites (Pang et al, 1978(Pang et al, , 1980. Thus, there are grounds to assume that the overall composition of the two satellites also corresponds to type Cl primitive carbonaceous chondrites (Tolson et al, 1978).…”

Section: Introductionmentioning

confidence: 98%

The origin and specific features of the martian satellites in the context of the euruption concept

Drobyshevski

1988

Earth Moon Planet

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The numerous problems related to the origin and evolution of Phobos and Deimos, as well as to specific features of their topography, are readily accounted for in the context of a concept presupposing the possibility of detonation (or burning) of electrolyzed ices.The explosion of an 'icy' asteroid of rnass mA -> Id3 g within the gravitational sphere of Mars resulted in the capture of secondary fragments into satellite orbits and the formation of a ring of icy and rocky particles. The motion of satellites in the ring reduced the eccentricities of their orbits and rendered their mutual collisions impossible. The thick regolith of Deimos is the material captured from the ring.The impact responsible for the Stickney crater on Phobos initiated a detonation in the material in the crater, and the detonation, in its turn, ignited the products of electrolysis in the bulk of the satellite. Phobos lost its regolith because of detonation-induced acceleration. As a result of the burning out of Phobos's ices, its density somewhat exeeds that of Deimos.Different grooves on Phobos have differing origins. The grooves of groups B, E, D (as specified by P.Thomas et a/., J. Geophys. Res., 84, 1979) are due to fracturing caused by the Sickney event;group C (which is normal to the minor axis of the Phobos ellipsoid) reflects the layered nature of the parent asteroid; while the closely arranged group A grooves, which are normal to Phobos's major axis, were formed during the contraction of the satellite as a result of the loss of burnt-out ices. A number of conclusions are drawn which can be tested by future missions to the satellites.

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The Composition of Phobos: Evidence for Carbonaceous Chondrite Surface from Spectral Analysis

Cited by 73 publications

References 26 publications

Infrared Spectra of Deimos (1-13 μm) and Phobos (3-13 μm)

Infrared Spectra of Deimos (1-13 μm) and Phobos (3-13 μm)

Long-term evolution of orbits about a precessing oblate planet: 3. A semianalytical and a purely numerical approach

The origin and specific features of the martian satellites in the context of the euruption concept

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