The Mass of Dwarf Planet Eris

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Science (Impact Factor: 33.61). 07/2007; 316(5831):1585. DOI: 10.1126/science.1139415
Source: PubMed


The discovery of dwarf planet Eris was followed shortly by the discovery of its satellite, Dysnomia, but the satellite orbit, and thus the system mass, was not known. New observations with the Keck Observatory and the Hubble Space Telescopes show that Dysnomia has a circular orbit with a radius of 37,350 +/- 140 (1-sigma) kilometers and a 15.774 +/- 0.002 day orbital period around Eris. These orbital parameters agree with expectations for a satellite formed out of the orbiting debris left from a giant impact. The mass of Eris from these orbital parameters is 1.67 x 10(22) +/- 0.02 x 10(22) kilograms, or 1.27 +/- 0.02 that of Pluto.

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    • "The Quaoar-Weywot system presented a further peculiarity; Weywot appeared to be on an eccentric orbit (Fraser and Brown, 2010). This was unexpected, as it seemed most likely that tidal evolution would circularize the orbits of the small satellites on short timescales consistent with the satellite of Eris, Dysnomia, which is found on a nearly circular orbit (Brown and Schaller, 2007). These two strange properties of the Quaoar- Weywot system warrant further investigation. "
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    ABSTRACT: Here we present new adaptive optics observations of the Quaoar-Weywot system. With these new observations we determine an improved system orbit. Due to a 0.39 day alias that exists in available observations, four possible orbital solutions are available with periods of $\sim11.6$, $\sim12.0$, $\sim12.4$, and $\sim12.8$ days. From the possible orbital solutions, system masses of $1.3-1.5\pm0.1\times10^{21}$ kg are found. These observations provide an updated density for Quaoar of $2.7-5.0{g cm$^{-3}$}$. In all cases, Weywot's orbit is eccentric, with possible values $\sim0.13-0.16$. We present a reanalysis of the tidal orbital evolution of the Quoaor-Weywot system. We have found that Weywot has probably evolved to a state of synchronous rotation, and have likely preserved their initial inclinations over the age of the Solar system. We find that for plausible values of the effective tidal dissipation factor tides produce a very slow evolution of Weywot's eccentricity and semi-major axis. Accordingly, it appears that Weywot's eccentricity likely did not tidally evolve to its current value from an initially circular orbit. Rather, it seems that some other mechanism has raised its eccentricity post-formation, or Weywot formed with a non-negligible eccentricity.
    Icarus 11/2012; 222(1). DOI:10.1016/j.icarus.2012.11.004 · 3.04 Impact Factor
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    • "Orbits for these systems have been reported by Veillet et al. (2002), Noll et al. (2004a,b), Brown and Schaller (2007), Grundy et al. (2007, 2008, 2009), Brown et al. (2010), and Stansberry et al. (2011) "
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    ABSTRACT: We present three improved and five new mutual orbits of transneptunian binary systems (58534) Logos-Zoe, (66652) Borasisi-Pabu, (88611) Teharonhiawako-Sawiskera, (123509) 2000 WK183, (149780) Altjira, 2001 QY297, 2003 QW111, and 2003 QY90 based on Hubble Space Telescope and Keck 2 laser guide star adaptive optics observations. Combining the five new orbit solutions with 17 previously known orbits yields a sample of 22 mutual orbits for which the period P, semimajor axis a, and eccentricity e have been determined. These orbits have mutual periods ranging from 5 to over 800 days, semimajor axes ranging from 1,600 to 37,000 km, eccentricities ranging from 0 to 0.8, and system masses ranging from 2 x 10^17 to 2 x 10^22 kg. Based on the relative brightnesses of primaries and secondaries, most of these systems consist of near equal-sized pairs, although a few of the most massive systems are more lopsided. The observed distribution of orbital properties suggests that the most loosely-bound transneptunian binary systems are only found on dynamically cold heliocentric orbits. Of the 22 known binary mutual or-bits, orientation ambiguities are now resolved for 9, of which 7 are prograde and 2 are retro-grade, consistent with a random distribution of orbital orientations, but not with models predicting a strong preference for retrograde orbits. To the extent that other perturbations are not dominant, the binary systems undergo Kozai oscillations of their eccentricities and inclinations with periods of the order of tens of thousands to millions of years, some with strikingly high amplitudes.
    Icarus 03/2011; 213(2). DOI:10.1016/j.icarus.2011.03.012 · 3.04 Impact Factor
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    • "Observational evidence indicates that the largest KBOs are of different composition than the regular satellites of the giant planets. Triton (ρ = 2.061 ± 0.007 g cm −3 ; Person et al. 2006), Eris (ρ = 2.3±0.3 g cm 3 ; Brown and Schaller 2007), and Pluto-Charon (ρ = 1.94±0.09 g cm −3 ; Buie et al. 2006) have densities that imply a rock/water-ice ratio of approximately 70/30 by mass. "
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    ABSTRACT: Here we show that Iapetus can serve to discriminate between satellite formation models. Its accretion history can be understood in terms of a two-component gaseous subnebula, with a relatively dense inner region, and an extended tail out to the location of the irregular satellites, as in the SEMM model of Mosqueira and Estrada (2003a,b). Following giant planet formation, planetesimals in the feeding zone of Jupiter and Saturn become dynamically excited, and undergo a collisional cascade. Ablation and capture of planetesimal fragments crossing the gaseous circumplanetary disks delivers enough collisional rubble to account for the mass budgets of the regular satellites of Jupiter and Saturn. This process can result in rock/ice fractionation provided the make up of the population of disk crossers is non-homogeneous, thus offering a natural explanation for the marked compositional differences between outer solar nebula objects and those that accreted in the subnebulae of the giant planets. Consequently, our model leads to an enhancement of the ice content of Iapetus, and to a lesser degree those of Ganymede, Titan and Callisto, and accounts for the (non-stochastic) compositions of these large, low-porosity outer regular satellites of Jupiter and Saturn. (abridged)
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