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Register a new userThe Phenomenon of Shape Evolution due to Solar Driven Outgassing for Analogues of Small Kuiper Belt Objects
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One of the key findings of the Rosettas mission to the Jupiter family comet 67P/Churyumov-Gerasimenko was its peculiar bilobed shape along with the apparent north/south dichotomy in large scale morphology. This has re-ignited scientific discussions on the topic of origin, evolution and age of the nucleus. In this work we set up a general numerical investigation on the role of solar driven activity on the overall shape change. Our goal is to isolate and study the influence of key parameters for solar driven mass loss, and hopefully obtain a classification of the final shapes. We consider five general classes of three-dimensional (3D) objects for various initial conditions of spin-axis and orbital parameters, propagating them on different orbits accounting for solar driven CO ice sublimation. A detailed study of the coupling between sublimation curve and orbital parameters (for CO and H$_{2}$O ices) is also provided. The idealizations used in this study are aimed to remove the ad-hoc assumptions on activity source distribution, composition, and/or chemical inhomogeneities as applied in similar studies focusing on explaining a particular feature or observation. Our numerical experiments show that under no condition a homogeneous nucleus with solar driven outgassing can produce concave morphology on a convex shape. On the other hand, preexisting concavities can hardly be smoothed/removed for the assumed activity. In summary, the coupling between solar distance, eccentricity, spin-axis and its orientation, as well as effects on shadowing and self-heating do combine to induce morphology changes that might not be deducible without numerical simulations.
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Here we measure the absolute magnitude distributions (H-distribution) of the dynamically excited and quiescent (hot and cold) Kuiper Belt objects (KBOs), and test if they share the same H-distribution as the Jupiter Trojans. From a compilation of all useable ecliptic surveys, we find that the KBO H-distributions are well described by broken power-laws. The cold population has a bright-end slope, $alpha_{textrm{1}}=1.5_{-0.2}^{+0.4}$, and break magnitude, $H_{textrm{B}}=6.9_{-0.2}^{+0.1}$ (r-band). The hot population has a shallower bright-end slope of, $alpha_{textrm{1}}=0.87_{-0.2}^{+0.07}$, and break magnitude $H_{textrm{B}}=7.7_{-0.5}^{+1.0}$. Both populations share similar faint end slopes of $alpha_2sim0.2$. We estimate the masses of the hot and cold populations are $sim0.01$ and $sim3times10^{-4} mbox{ M$_{bigoplus}$}$. The broken power-law fit to the Trojan H-distribution has $alpha_textrm{1}=1.0pm0.2$, $alpha_textrm{2}=0.36pm0.01$, and $H_{textrm{B}}=8.3$. The KS test reveals that the probability that the Trojans and cold KBOs share the same parent H-distribution is less than 1 in 1000. When the bimodal albedo distribution of the hot objects is accounted for, there is no evidence that the H-distributions of the Trojans and hot KBOs differ. Our findings are in agreement with the predictions of the Nice model in terms of both mass and H-distribution of the hot and Trojan populations. Wide field survey data suggest that the brightest few hot objects, with $H_{textrm{r}}lesssim3$, do not fall on the steep power-law slope of fainter hot objects. Under the standard hierarchical model of planetesimal formation, it is difficult to account for the similar break diameters of the hot and cold populations given the low mass of the cold belt.
In its 16 years of scientific measurements, the Spitzer Space Telescope performed a number of ground breaking and key infrared measurements of Solar System objects near and far. Targets ranged from the smallest planetesimals to the giant planets, and have helped us reform our understanding of these objects while also laying the groundwork for future infrared space-based observations like those to be undertaken by the James Webb Space Telescope in the 2020s. In this first Paper, we describe how the Spitzer Space Telescope advanced our knowledge of Solar System formation and evolution via observations of small outer Solar System planetesimals, i.e., Comets, Centaurs, and Kuiper Belt Objects (KBOs). Relics from the early formation era of our Solar System, these objects hold important information about the processes that created them. The key Spitzer observations can be grouped into 3 broad classes: characterization of new Solar System objects (comets D/ISON 2012 S1, C/2016 R2, 1I/`Oumuamua); large population surveys of known object sizes (comets, Centaurs, and KBOs); and compositional studies via spectral measurements of body surfaces and emitted materials (comets, Centaurs, and KBOs).
The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters less than approximately 13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (less than 1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely greater than 4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.
We present the results of a Herschel survey of 21 late-type stars that host planets discovered by the radial velocity technique. The aims were to discover new disks in these systems and to search for any correlation between planet presence and disk properties. In addition to the known disk around GJ 581, we report the discovery of two new disks, in the GJ 433 and GJ 649 systems. Our sample therefore yields a disk detection rate of 14%, higher than the detection rate of 1.2% among our control sample of DEBRIS M-type stars with 98% confidence. Further analysis however shows that the disk sensitivity in the control sample is about a factor of two lower in fractional luminosity than for our survey, lowering the significance of any correlation between planet presence and disk brightness below 98%. In terms of their specific architectures, the disk around GJ 433 lies at a radius somewhere between 1 and 30au. The disk around GJ 649 lies somewhere between 6 and 30au, but is marginally resolved and appears more consistent with an edge-on inclination. In both cases the disks probably lie well beyond where the known planets reside (0.06-1.1au), but the lack of radial velocity sensitivity at larger separations allows for unseen Saturn-mass planets to orbit out to $sim$5au, and more massive planets beyond 5au. The layout of these M-type systems appears similar to Sun-like star + disk systems with low-mass planets.
The four longest period Kuiper belt objects have orbital periods close to integer ratios with each other. A hypothetical planet with orbital period $sim$17,117 years, semimajor axis $sim$665 AU, would have N/1 and N/2 period ratios with these four objects. The orbital geometries and dynamics of resonant orbits constrain the orbital plane, the orbital eccentricity and the mass of such a planet, as well as its current location in its orbital path.
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