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  • 1
    Publication Date: 2012-03-23
    Description: Laser altimetry by the MESSENGER spacecraft has yielded a topographic model of the northern hemisphere of Mercury. The dynamic range of elevations is considerably smaller than those of Mars or the Moon. The most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains. Within this lowland is a broad topographic rise that experienced uplift after plains emplacement. The interior of the 1500-km-diameter Caloris impact basin has been modified so that part of the basin floor now stands higher than the rim. The elevated portion of the floor of Caloris appears to be part of a quasi-linear rise that extends for approximately half the planetary circumference at mid-latitudes. Collectively, these features imply that long-wavelength changes to Mercury's topography occurred after the earliest phases of the planet's geological history.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zuber, Maria T -- Smith, David E -- Phillips, Roger J -- Solomon, Sean C -- Neumann, Gregory A -- Hauck, Steven A 2nd -- Peale, Stanton J -- Barnouin, Olivier S -- Head, James W -- Johnson, Catherine L -- Lemoine, Frank G -- Mazarico, Erwan -- Sun, Xiaoli -- Torrence, Mark H -- Freed, Andrew M -- Klimczak, Christian -- Margot, Jean-Luc -- Oberst, Jurgen -- Perry, Mark E -- McNutt, Ralph L Jr -- Balcerski, Jeffrey A -- Michel, Nathalie -- Talpe, Matthieu J -- Yang, Di -- New York, N.Y. -- Science. 2012 Apr 13;336(6078):217-20. doi: 10.1126/science.1218805. Epub 2012 Mar 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. zuber@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22438510" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2012-03-23
    Description: Radio tracking of the MESSENGER spacecraft has provided a model of Mercury's gravity field. In the northern hemisphere, several large gravity anomalies, including candidate mass concentrations (mascons), exceed 100 milli-Galileos (mgal). Mercury's northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/MR(2) = 0.353 +/- 0.017, where M and R are Mercury's mass and radius, and a ratio of the moment of inertia of Mercury's solid outer shell to that of the planet of C(m)/C = 0.452 +/- 0.035. A model for Mercury's radial density distribution consistent with these results includes a solid silicate crust and mantle overlying a solid iron-sulfide layer and an iron-rich liquid outer core and perhaps a solid inner core.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, David E -- Zuber, Maria T -- Phillips, Roger J -- Solomon, Sean C -- Hauck, Steven A 2nd -- Lemoine, Frank G -- Mazarico, Erwan -- Neumann, Gregory A -- Peale, Stanton J -- Margot, Jean-Luc -- Johnson, Catherine L -- Torrence, Mark H -- Perry, Mark E -- Rowlands, David D -- Goossens, Sander -- Head, James W -- Taylor, Anthony H -- New York, N.Y. -- Science. 2012 Apr 13;336(6078):214-7. doi: 10.1126/science.1218809. Epub 2012 Mar 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22438509" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 365 (1993), S. 788-789 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE planets in the Solar System are believed to have accumulated in a dusty gaseous disk, where internal dissipative processes caused the disk material to be flattened and relaxed into circular motion around the Sun. As a consequence, most have orbits that are near-circular and nearly coplanar. But ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 206 (1965), S. 1240-1241 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] For a planet with substantial orbital eccentricity the condition is different, however, and synchronous rotation with the orbital period need not then be expected. With the 1/r6 dependence the tidal torque at perihelion will exceed that at other times, and the angular velocity of the planet will ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 262 (1976), S. 765-766 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Siegfried and Solomon3 have calculated two thermal histories for Mercury leading to a differentiated and an undifferentiated planet respectively. In the latter models, of course, Mercury would have no core. Even in the differentiated model a once molten core tends to solidify as the planet cools. ...
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 8 (1973), S. 515-531 
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A general Hamiltonian for a rotating Moon in the field of the Earth is expanded in terms of parameters orienting the spin angular momentum relative to the pricipal axes of the Moon and relative to coordinate axes fixed in the orbital plane. The effects of elastic distortion are included as modifications of the moment of inertia tensor, where the magnitude of the distortion is parameterized by the Love numberk 2. The principal periodic terms in the longitude of a point on the Moon due to variations of the tide caused by the Earth are shown to have amplitudes between 3″.9 × 10−3 and 1″.6 × 10−2 with a period of an anomalistic month, 3″.0 × 10−4 and 1″.2 × 10−3 with a period of one-half an anomalistic month and 2″.4 × 10−4 and 9″.6 × 10−4 with a period of one-half of a nodical month. The extremes in the amplitudes correspond to rigidities of 8 × 1011 cgs and 2 × 1011 cgs, respectively, the former rigidity being comparable to that of the Earth. Only the largest amplitude given above is comparable to that detectable by the projected precision of the laser ranging to the lunar retrorereflectors, and this amplitude corresponds to an improbably low rigidity for the Moon. A detailed derivation of the free wobble of the lunar spin axis about the axis of maximum moment of inertia is given, where it is shown that elasticity can alter the period of the free wobble of 75.3 yr by only 3 × 10−4 to 10−3 of this period. Also, the effect of elasticity on the period of free libration is completely negligible by many orders of magnitude. If the Moon's rigidity is close to that of the Earth there is no effect of elasticity on the rotation which can be measured with the laser ranging and, therefore, no elastic properties of the Moon can be determined from variations in the rotation.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1572-9478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Several unsolved problems in the evolutionary histories leading to current dynamical configurations of the planets and their systems of satellites are discussed. These include the possibilities of rather tight constraints on the primordial rotation states of Mercury and Venus and the stabilizing mechanism for the latter's retrograde spin, a brief mention of the problem of origin of the moons of Earth and Mars, the excessive heat flow from Jupiter's satellite lo which is not compatible with an otherwise self-consistent model of origin of the Laplace three-body libration, the mechanism for the long history of resurfacing of Saturn's satellite Enceladus and the possibly short lifetime of the A ring and the mechanisms for resurfacing the satellites of Uranus, especially Ariel, if the high stability of the mean motion orbital resonances at the 2/1 commensurability involving Ariel and Umbriel precludes a long term occupancy of the resonance. Finally, excessive times of accumulation of the outer planets in current models may possibly be reducible from the effects of nebular gas drag.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 14 (1973), S. 412-423 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The constraints placed on models of the interiors of the major planets by the non-spherical components of their gravitational fields are explained, and several methods of determining these non-spherical components are described and evaluated.
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  • 9
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Unambiguous detection of the consequences of mutual perturbations of the hypothesized planets about the pulsar PSR1257+12 would be unassailable proof of their existence. Nearly all of the residuals in the times of arrival (TOA) of the pulses after subtraction of the TOA predicted from the best fit constant period model are accounted for by including the effects of two orbiting planets with constant orbital parameters. The nature and magnitude of additional residuals in the TOA due to the gravitational interactions between the planets are determined by numerically calculating the TOA residuals for the orbital motion including the perturbations and subtracting the TOA residuals from analytic expressions of the orbital motion with orbital parameters fixed at averaged values. The TOA residual differences so obtained oscillate with periods comparable to the orbital periods with the oscillations varying in amplitude as a function of epoch within any given observational period. The signature of the perturbations is thus a quasiperiodic modulation of the residual differences obtained after removal of the effects of the orbital motion with best fit, constant orbital parameters. The amplitudes of this modulation reach about 10μsec for observational periods exceeding 1000 days for the minimum planetary masses with sini = 1, and they increase as 1 / sini for 1 / sini 〈 5, wherei is the inclination of the orbit plane to that of the sky. Greater accumulated phase differences between the effects of perturbed and unperturbed orbital motions are available in the times of zero values in the observed and predicted TOA residuals and these comprise a second signature of the perturbations. The perturbation signatures should become detectable as the observation interval approaches 1000 days.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
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