اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMercurys geochronology revised by applying Model Production Functions to Mariner 10 data: geological implications
53
0
0.0
(
0
)
تأليف
M. Massironi
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Model Production Function chronology uses dynamic models of the Main Belt Asteroids (MBAs) and Near Earth Objects (NEOs) to derive the impactor flux to a target body. This is converted into the crater size-frequency-distribution for a specific planetary surface, and calibrated using the radiometric ages of different regions of the Moons surface. This new approach has been applied to the crater counts on Mariner 10 images of the highlands and of several large impact basins on Mercury. MPF estimates for the plains show younger ages than those of previous chronologies. Assuming a variable uppermost layering of the Hermean crust, the age of the Caloris interior plains may be as young as 3.59 Ga, in agreement with MESSENGER results that imply that long-term volcanism overcame contractional tectonics. The MPF chronology also suggests a variable projectile flux through time, coherent with the MBAs for ancient periods and then gradually comparable also to the NEOs.
قيم البحث
اقرأ أيضاً
We describe the current state of knowledge about Mercurys interior structure. We review the available observational constraints, including mass, size, density, gravity field, spin state, composition, and tidal response. These data enable the construc
tion of models that represent the distribution of mass inside Mercury. In particular, we infer radial profiles of the pressure, density, and gravity in the core, mantle, and crust. We also examine Mercurys rotational dynamics and the influence of an inner core on the spin state and the determination of the moment of inertia. Finally, we discuss the wide-ranging implications of Mercurys internal structure on its thermal evolution, surface geology, capture in a unique spin-orbit resonance, and magnetic field generation.
Determining which small exoplanets have stony-iron compositions is necessary for quantifying the occurrence of such planets and for understanding the physics of planet formation. Kepler-10 hosts the stony-iron world Kepler-10b (K10b), and also contai
ns what has been reported to be the largest solid silicate-ice planet, Kepler-10c (K10c). Using 220 radial velocities (RVs), including 72 precise RVs from Keck-HIRES of which 20 are new from 2014-2015, and 17 quarters of Kepler photometry, we obtain the most complete picture of the Kepler-10 system to date. We find that K10b (Rp=1.47 Re) has mass 3.72$pm$0.42 Me and density 6.46$pm$0.73 g/cc. Modeling the interior of K10b as an iron core overlaid with a silicate mantle, we find that the iron core constitutes 0.17$pm$0.11 of the planet mass. For K10c (Rp=2.35 Re) we measure Mp=13.98$pm$1.79 Me and $rho$=5.94$pm$0.76 g/cc, significantly lower than the mass computed in Dumusque et al. (2014, 17.2$pm$1.9 Me). Internal compositional modeling reveals that at least $10%$ of the radius of Kepler-10c is a volatile envelope composed of hydrogen-helium ($0.2%$ of the mass, $16%$ of the radius) or super-ionic water ($28%$ of the mass, $29%$ of the radius). Analysis of only HIRES data yields a higher mass for K10b and a lower mass for K10c than does analysis of the HARPS-N data alone, with the mass estimates for K10c formally inconsistent by 3$sigma$. Splitting the RVs from each instrument leads to inconsistent measurements for the mass of planet c in each data set. This suggests that time-correlated noise is present and that the uncertainties in the planet masses (especially K10c) exceed our formal estimates. Transit timing variations (TTVs) of K10c indicate the likely presence of a third planet in the system, KOI-72.X. The TTVs and RVs are consistent with KOI-72.X having an orbital period of 24, 71, or 101 days, and a mass from 1-7 Me.
The Milky Way is filled with the tidally-disrupted remnants of globular clusters and dwarf galaxies. Determining the properties of these objects -- in particular, initial masses and density profiles -- is relevant to both astronomy and dark matter ph
ysics. However, most direct measures of mass cannot be applied to tidal debris, as the systems of interest are no longer in equilibrium. Since phase-space density is conserved during adiabatic phase mixing, Liouvilles theorem provides a connection between stellar kinematics as measured by observatories such as Gaia and the original mass of the disrupted system. Accurately recovering the phase-space density is complicated by uncertainties resulting from measurement errors and orbital integration, which both effectively inject entropy into the system, preferentially decreasing the measured density. In this paper, we demonstrate that these two issues can be overcome. First, we measure the phase-space density of the globular cluster M4 in Gaia data, and use Liouvilles theorem to derive its mass. We then show that, for tidally disrupted systems, the orbital parameters and thus phase-space density can be inferred by minimizing the phase-space entropy of cold stellar streams. This work is therefore a proof of principle that true phase-space density can be measured and the original properties of the star cluster reconstructed in systems of astrophysical interest.
Of the solar systems four terrestrial planets, the origin of Mercury is perhaps the most mysterious. Modern numerical simulations designed to model the dynamics of terrestrial planet formation systematically fail to replicate Mercury; which possesses
just 5% the mass of Earth and the highest orbital eccentricity and inclination among the planets. However, Mercurys large iron-rich core and low volatile inventory stand out among the inner planets, and seem to imply a violent collisional origin. Because most algorithms used for simulating terrestrial accretion do not consider the effects of collisional fragmentation, it has been difficult to test these collisional hypotheses within the larger context of planet formation. Here, we analyze a large suite of terrestrial accretion models that account for the fragmentation of colliding bodies. We find that planets with core mass fractions boosted as a result of repeated hit-and-run collisions are produced in 90% of our simulations. While many of these planets are similar to Mercury in mass, they rarely lie on Mercury-like orbits. Furthermore, we perform an additional batch of simulations designed to specifically test the single giant impact origin scenario. We find less than a 1% probability of simultaneously replicating the Mercury-Venus dynamical spacing and the terrestrial systems degree of orbital excitation after such an event. While dynamical models have made great strides in understanding Mars low mass, their inability to form accurate Mercury analogs remains a glaring problem.
Between 2004 and 2017, spectral observations have been gathered by the Visual and Infrared Mapping Spectrometer (VIMS) on-board Cassini (Brown et al., 2004) during 23 Enceladus close encounters, in addition to more distant surveys. The objective of t
he present study is to produce a global hyperspectral mosaic of the complete VIMS data set of Enceladus in order to highlight spectral variations among the different geological units. This requires the selection of the best observations in terms of spatial resolution and illumination conditions. We have carried out a detailed investigation of the photometric behavior at several key wavelengths (1.35, 1.5, 1.65, 1.8, 2.0, 2.25, 2.55 and 3.6 ${mu}$m), characteristics of the infrared spectra of water ice. We propose a new photometric function, based on the model of Shkuratov et al. (2011). When combined, corrected mosaics at different wavelengths reveal heterogeneous areas, in particular in the terrains surrounding the Tiger Stripes on the South Pole and in the northern hemisphere around 30{deg}N, 90{deg}W. Those areas appear mainly correlated to tectonized units, indicating an endogenous origin, potentially driven by seafloor hotspots.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
