Browsing by Subject "SATELLITES"

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  • Fedorets, Grigori; Micheli, Marco; Jedicke, Robert; Naidu, Shantanu P.; Farnocchia, Davide; Granvik, Mikael; Moskovitz, Nicholas; Schwamb, Megan E.; Weryk, Robert; Wierzchos, Kacper; Christensen, Eric; Pruyne, Theodore; Bottke, William F.; Ye, Quanzhi; Wainscoat, Richard; Devogele, Maxime; Buchanan, Laura E.; Djupvik, Anlaug Amanda; Faes, Daniel M.; Fohring, Dora; Roediger, Joel; Seccull, Tom; Smith, Adam B. (2020)
    We report on our detailed characterization of Earth's second known temporary natural satellite, or minimoon, asteroid 2020 CD3. An artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the S or V complex in asteroid taxonomy. The discovery of 2020 CD3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. The estimated diameter of 1.2(-0.2)(+0.4) m and geocentric capture approximately a decade after the first known minimoon, 2006.RH120, are in agreement with theoretical predictions. The capture duration of 2020 CD3 of at least 2.7 yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020 CD3's atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. More discoveries and a detailed characterization of the population can be expected with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.
  • Campbell, David J. R.; Frenk, Carlos S.; Jenkins, Adrian; Eke, Vincent R.; Navarro, Julio F.; Sawala, Till; Schaller, Matthieu; Fattahi, Azadeh; Oman, Kyle A.; Theuns, Tom (2017)
    The observed stellar kinematics of dispersion-supported galaxies are often used to measure dynamical masses. Recently, several analytical relationships between the stellar line-of-sight velocity dispersion, the projected (2D) or deprojected (3D) half-light radius and the total mass enclosed within the half-light radius, relying on the spherical Jeans equation, have been proposed. Here, we use the APOSTLE cosmological hydrodynamical simulations of the Local Group to test the validity and accuracy of such mass estimators for both dispersion and rotation-supported galaxies, for field and satellite galaxies, and for galaxies of varying masses, shapes and velocity dispersion anisotropies. We find that the mass estimators of Walker et al. and Wolf et al. are able to recover the masses of dispersion-dominated systems with little systematic bias, but with a 1 sigma scatter of 25 and 23 per cent, respectively. The error on the estimated mass is dominated by the impact of the 3D shape of the stellar mass distribution, which is difficult to constrain observationally. This intrinsic scatter becomes the dominant source of uncertainty in the masses estimated for galaxies like the dwarf spheroidal (dSph) satellites of the Milky Way, where the observational errors in their sizes and velocity dispersions are small. Such scatter may also affect the inner density slopes of dSphs derived from multiple stellar populations, relaxing the significance with which Navarro-Frenk-White profiles may be excluded, depending on the degree to which the relevant properties of the different stellar populations are correlated. Finally, we derive a new optimal mass estimator that removes the residual biases and achieves a statistically significant reduction in the scatter to 20 per cent overall for dispersion-dominated galaxies, allowing more precise and accurate mass estimates.
  • Solin, Otto; Granvik, Mikael (2018)
    Aims. We present an automated system called neoranger that regularly computes asteroid-Earth impact probabilities for objects on the Minor Planet Center's (MPC) Near-Earth-Object Confirmation Page (NEOCP) and sends out alerts of imminent impactors to registered users. In addition to potential Earth-impacting objects, neoranger also monitors for other types of interesting objects such as Earth's natural temporarily-captured satellites. Methods. The system monitors the NEOCP for objects with new data and solves, for each object, the orbital inverse problem, which results in a sample of orbits that describes the, typically highly-nonlinear, orbital-element probability density function (PDF). The PDF is propagated forward in time for seven days and the impact probability is computed as the weighted fraction of the sample orbits that impact the Earth. Results. The system correctly predicts the then-imminent impacts of 2008 TC3 and 2014 Lambda Lambda based on the first data sets available. Using the same code and configuration we find that the impact probabilities for objects typically on the NEOCP, based on eight weeks of continuous operations, are always less than one in ten million, whereas simulated and real Earth-impacting asteroids always have an impact probability greater than 10% based on the first two tracklets available.