Television observations of Phobos

Avanesov, G. A.; Murray, Bruce C.

doi:10.1038/341585a0

Cited by 42 publications

(7 citation statements)

References 11 publications

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“…Using the theory of Woolard [1944], Sharpless [1945] estimated an along‐track acceleration of (1.82 ± 0.17) × 10 −3 deg/yr 2 . Subsequent observations have refined the estimate and models generated in support of the Russian Phobos mission [ Sagdeev and Zakharov , 1989; Avensov et al , 1989; Morley , 1989] all give concordant estimates, as indicated in Table 1. Given the long time span of the observations, and relatively high accuracy of the models, it might be supposed that little additional progress would occur.…”

Section: Introductionmentioning

confidence: 86%

Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos

et al. 2005

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[1] We report on new observations of the orbital position of Phobos, the innermost natural satellite of Mars, and show that these observations provide an improved estimate of the rate of tidal dissipation within Mars. The observations were made with the Mars Orbiter Laser Altimeter instrument on the Mars Global Surveyor spacecraft. The secular acceleration in along-track orbital motion is conventionally expressed in terms of a quadratic term in mean orbital longitude, which yields s = (dn/dt)/2 = (136.7 ± 0.6) Â 10 À5 deg/yr 2 , where n is the mean motion. The corresponding fractional rate of change in orbital angular velocity is (dn/dt)/n = (6.631 ± 0.029) Â 10 À9 /yr, the highest measured for any natural satellite in the solar system. The energy dissipation rate is (3.34 ± 0.01) MW. Because Phobos is so close to Mars, there are nonnegligible contributions to the tidal evolution from harmonic degrees 2, 3, and 4. However, the elastic tidal Love numbers are observationally constrained only at degree two. The observed acceleration is consistent with that for a homogeneous Maxwell viscoelastic model of Mars with effective viscosity of (8.7 ± 0.6) Â 10 14 Pa s.

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Section: Introductionmentioning

confidence: 86%

Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos

et al. 2005

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“…We adopt C ej =0.3 and ν =1.2. Using equation (1) and a Phobos density of 1.9 g cc −1 (refs 42 , 43 ), the mass ejected within each velocity bin is calculated. For the Stickney impact, of the 1.5 × 10 13 kg ejected faster than the Phobos escape velocity, only 1.2 × 10 12 kg (8%) is ejected faster than 100 m s −1 .…”

Section: Methodsmentioning

confidence: 99%

Sesquinary catenae on the Martian satellite Phobos from reaccretion of escaping ejecta

Nayak

Asphaug

2016

Nat Commun

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The Martian satellite Phobos is criss-crossed by linear grooves and crater chains whose origin is unexplained. Anomalous grooves are relatively young, and crosscut tidally predicted stress fields as Phobos spirals towards Mars. Here we report strong correspondence between these anomalous features and reaccretion patterns of sesquinary ejecta from impacts on Phobos. Escaping ejecta persistently imprint Phobos with linear, low-velocity crater chains (catenae) that match the geometry and morphology of prominent features that do not fit the tidal model. We prove that these cannot be older than Phobos' current orbit inside Mars' Roche limit. Distinctive reimpact patterns allow sesquinary craters to be traced back to their source, for the first time across any planetary body, creating a novel way to probe planetary surface characteristics. For example, we show that catena-producing craters likely formed in the gravity regime, providing constraints on the ejecta velocity field and knowledge of source crater material properties.

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“…We adopt = 0.3 and = 1.2. For Phobos' density we use 1.9 g/cc (Avanesov et al, 1989;Rosenblatt et al, 2008;Schmedemann et al, 2014). From (11), the mass ejected within each velocity bin is calculated ( Figure 6).…”

Section: Mass Transfer Between Martian Satellitesmentioning

confidence: 99%

Effects of mass transfer between Martian satellites on surface geology

Nayak

Nimmo

Udrea

2016

Icarus

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Impacts on planetary bodies can lead to both prompt secondary craters and projectiles that reimpact the target body or nearby companions after an extended period, producing so-called "sesquinary" craters. Here we examine sesquinary cratering on the moons of Mars. We model the impact that formed Voltaire, the largest crater on the surface of Deimos, and explore the orbital evolution of resulting high-velocity ejecta across 500 years using four-body physics and particle tracking. The bulk of mass transfer to Phobos occurs in the first 10 2 years after impact, while reaccretion of ejecta to Deimos is predicted to continue out to a 10 4 year timescale (cf. Soter, Studies of the Terrestrial Planets, Cornell U., 1971). Relative orbital geometry between Phobos and Deimos plays a significant role; depending on the relative true longitude, mass transfer between the moons can change by a factor of five. Of the ejecta with a velocity range capable of reaching Phobos, 25-42% by mass reaccretes to Deimos and 12-21% impacts Phobos. Ejecta mass transferred to Mars is <10%. We find that the characteristic impact velocity of sesquinaries on Deimos is an order of magnitude smaller than those of background (heliocentric) hypervelocity impactors and will likely result in different crater morphologies. The time-averaged flux of Deimos material to Phobos can be as high as 11% of the background (heliocentric) direct-to-Phobos impactor flux. This relatively minor contribution suggests that spectrally red terrain on Phobos (Murchie and Erard, Icarus 123, 63-86, 1996) is not caused by Deimos material. However the high-velocity ejecta mass reaccreted to Deimos from a Voltaire-sized impact is comparable to the expected background mass accumulated on Deimos between Voltaire-size events. Considering that the high-velocity ejecta contains only 0.5% of the total mass sent into orbit, sesquinary ejecta from a Voltaire-sized impact could feasibly resurface large parts of the moon, erasing the previous geological record. Dating the surface of Deimos may be more challenging than previously suspected.

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Television observations of Phobos

Cited by 42 publications

References 11 publications

Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos

Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos

Sesquinary catenae on the Martian satellite Phobos from reaccretion of escaping ejecta

Effects of mass transfer between Martian satellites on surface geology

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