Luke Dones - Academia.edu (original) (raw)
Papers by Luke Dones
Circumstellar Habitable Zones, 1996
Enceladus and the Icy Moons of Saturn, 2018
Origin of the Earth and Moon, 2000
... We review the current understanding of the accumulation of spin angular momentum by a growing... more ... We review the current understanding of the accumulation of spin angular momentum by a growing terrestrial planet and the evolution of planetary spin subsequent to the accretionary epoch. Considerable progress toward understanding the origin of planetary rotation has ...
Comets II, 2004
In this chapter, we review the enormous progress that has been made in our understanding of the d... more In this chapter, we review the enormous progress that has been made in our understanding of the dynamical evolution of these bodies. We begin by reviewing the evidence that Jupiter-family comets (JFCs; those with 2 < T < 3) form a dynamically distinct class of comets that originate in a flattened disk beyond Neptune. We present a model for the distribution of comets throughout the JFC and Centaur regions that is consistent with current observations, although further observations and numerical simulations in the Centaur region are called for. We then discuss dynamical results (since confirmed by observations) that a significant amount of material that was scattered by Neptune during the early stages of planet formation could persist today in the form of a "scattered disk" of bodies with highly eccentric orbits beyond Neptune. We describe the dynamical mechanisms believed responsible for the longevity of the surviving bodies and argue that if objects in the Kuiper belt and scattered disk have similar size distributions, then the scattered disk is likely to be the primary source of JFCs and Centaurs. Finally, we describe the importance of understanding the ecliptic comet population for the purposes of determining impact rates on the satellites of the giant planets and of age determinations of the satellite surfaces. We present tables of impact rates based on the best currently available analyses. Further refinements of these rates and age determinations await better observations of the Centaur population (including its size distribution), as well as a better understanding of the formation and early dynamical evolution of the outer solar system.
Origin of the Earth and Moon, 2000
Abstract The accretion of planets involved a high flux of planetesimal impactors in the first 107... more Abstract The accretion of planets involved a high flux of planetesimal impactors in the first 107 108 yr, a flux on the order of 109× the present flux. Dynamical models suggest that the early planetesimals would be used up by impacting planets or the Sun, or by being ...
Comets II, 2004
The Oort cloud is the primary source of the "nearly isotropic" comets, which include new and retu... more The Oort cloud is the primary source of the "nearly isotropic" comets, which include new and returning long-period comets and Halley-type comets. We focus on the following topics: (1) the orbital distribution of known comets and the cometary "fading" problem; (2) the population and mass of the Oort cloud, including the hypothetical inner Oort cloud; (3) the number of Oort cloud comets that survive from the origin of the solar system to the present time, and the timescale for building the Oort cloud; (4) the relative importance of different regions of the protoplanetary disk in populating the Oort cloud; and (5) current constraints on the structure of the Oort cloud and future prospects for learning more about its structure.
&lt;p&gt;Centaurs &amp;#8211; planet-crossing bodies in the region of the... more &lt;p&gt;Centaurs &amp;#8211; planet-crossing bodies in the region of the giant planets that mainly originate in the Kuiper Belt/Scattered Disk [1, 2] &amp;#8211; are thought to be the primary impactors on the giant planets and their satellites [3-8]. As part of an effort to interpret the cratering records of the saturnian satellites, we are developing a dynamical-physical model for the size distribution of potential impactors on the moons.&lt;/p&gt; &lt;p&gt;Most models of the orbital distribution of "observable" comets&lt;sup&gt;[1]&lt;/sup&gt; assume that the size of the nucleus does not change with time. These models treat physical evolution only by assuming a lifetime, after which comets are considered inactive or "faded". These models do not specify a fading mechanism, but assume an expression for the probability that a comet remains active after some amount of time [10-14]. Fading can result from loss of all volatiles, formation of a nonvolatile mantle on the surface of the nucleus, or splitting [15, 16].&lt;/p&gt; &lt;p&gt;A model of the erosion of 67P/Churyumov-Gerasimenko and 46P/Wirtanen due to sublimation of water ice throughout their orbital evolution estimates that 67P&amp;#8217;s nucleus has shrunk from a radius of 2.5 km to 2 km, while 46P&amp;#8217;s has decreased from 1 km to 0.6 km [17]. This calculation assumes that 10% of the nucleus is active and that its density is 500 kg/m&lt;sup&gt;3&lt;/sup&gt;. These estimates are uncertain because comets follow chaotic orbits, but in general, erosion has a bigger effect on smaller nuclei.&lt;/p&gt; &lt;p&gt;Some comets are active well beyond the water-ice sublimation zone within 3 au. Eighteen active Centaurs are currently known [18, 19]. 29P/Schwassmann-Wachmann, which follows a near-circular orbit at 6 au, is a copious source of dust and CO [20-22] and undergoes significant dust outbursts 7 or more times a year [23]. 174P/Echeclus underwent an outburst 13 au from the Sun that released &amp;#8776; 300 kg/s of dust for about two months [24], a rate comparable to the 530 kg/s of dust released by 67P at its peak near 1.3 au [25]. Echeclus also underwent several more outbursts near perihelion (&amp;#8776;6 au) with CO outgassing at &amp;#8776; 10% the rate of 29P at the same heliocentric distance and dust mass loss rates of 10 - 700 kg/s [20]. 2060 Chiron is another Centaur that is sporadically active in gas and dust, consistent with a more depleted state, like Echeclus [20].&lt;/p&gt; &lt;p&gt;Di Sisto et al. (2009) constructed a model of the orbital distributions of Jupiter-family comets (JFCs) that incorporated planetary perturbations, nongravitational forces, sublimation, and splitting. They considered nuclei with initial radii of 10, 5, and 1 km [26]. Di Sisto et al. found that 5- and 10-km comets usually evolved onto Centaur orbits, while 1-km comets were most likely to shrink below 100 m. Inspired by their work, we are developing a model for the dynamical-physical evolution of JFCs and Centaurs. We will use the orbital distribution found by Nesvorny et al. as our baseline model [14, 27].&lt;/p&gt; &lt;p&gt;We will first focus on modeling the evolution of the size distribution of JFCs. The model will eventually account for mass loss by both JFCs and Centaurs, with activity driven by H&lt;sub&gt;2&lt;/sub&gt;O, CO, or other volatiles. The fraction of the nucleus that is active will be allowed to vary with size, since smaller nuclei are typically more active [28-30]. We will then implement a model for cometary splitting with these inputs: the frequency of splitting as a function of perihelion distance; the fraction of the comet&amp;#8217;s mass released as fragments; the size distribution of the fragments; and the velocity imparted to the fragments by the splitting event. We will present preliminary results of our simulations.&lt;/p&gt; &lt;p&gt;We thank Raphael Marschall for discussions and the Cassini Data Analysis Program for support.&lt;/p&gt; &lt;p&gt;References&lt;/p&gt; &lt;p&gt;[1] Volk, K.; Malhotra, R. ApJ 687, 714&amp;#8211;725, 2008.&lt;/p&gt; &lt;p&gt;[2] Di Sisto, R. P.; Rossignoli, N. L. CMDA, in press (arXiv:2006.09657), 2020.&lt;/p&gt; &lt;p&gt;[3] Zahnle, K.; Dones, L.; Levison, H. F. Icarus 136, 202&amp;#8211;222, 1998.&lt;/p&gt; &lt;p&gt;[4] Zahnle, K.; Schenk, P.; Levison, H.; Dones, L. Icarus 163, 263&amp;#8211;289, 2003.&lt;/p&gt; &lt;p&gt;[5] Di Sisto, R. P.; Zanardi, M. A&amp;A 553, id. A79, 2013.&lt;/p&gt; &lt;p&gt;[6] Di Sisto, R. P.; Zanardi, M. Icarus 264, 90&amp;#8211;101, 2016.&lt;/p&gt; &lt;p&gt;[7] Rossignoli, N. L.; Di Sisto, R. P.; Zanardi, M.; Dugaro, A.…
Reviews of Geophysics, 1991
Abstract This review discusses each planetary ring system and describes recent theoretical develo... more Abstract This review discusses each planetary ring system and describes recent theoretical developments and models of ring evolution. The distribution of the inner rings and satellites of all four giant planets reduced to a uniform scale of'planetary units', normalized by the ...
Astrobiology, Jan 11, 2017
We analyzed Cassini Imaging Science Subsystem (ISS) images of the plume of Enceladus to derive pa... more We analyzed Cassini Imaging Science Subsystem (ISS) images of the plume of Enceladus to derive particle number densities for the purpose of comparing our results with those obtained from other Cassini instrument investigations. Initial discrepancies in the results from different instruments, as large as factors of 10-20, can be reduced to ∼2 to 3 by accounting for the different times and geometries at which measurements were taken. We estimate the average daily ice production rate, between 2006 and 2010, to be 29 ± 7 kg/s, and a solid-to-vapor ratio, S/V > 0.06. At 50 km altitude, the plume's peak optical depth during the same time period was τ ∼ 10(-3); by 2015, it was ∼10(-4). Our inferred differential size distribution at 50 km altitude has an exponent q = 3. We estimate the average geothermal flux into the sea beneath Enceladus' south polar terrain to be comparable to that of the average Atlantic, of order 0.1 W/m(2). Should microbes be present on Enceladus, concentra...
Circumstellar Habitable Zones, 1996
Enceladus and the Icy Moons of Saturn, 2018
Origin of the Earth and Moon, 2000
... We review the current understanding of the accumulation of spin angular momentum by a growing... more ... We review the current understanding of the accumulation of spin angular momentum by a growing terrestrial planet and the evolution of planetary spin subsequent to the accretionary epoch. Considerable progress toward understanding the origin of planetary rotation has ...
Comets II, 2004
In this chapter, we review the enormous progress that has been made in our understanding of the d... more In this chapter, we review the enormous progress that has been made in our understanding of the dynamical evolution of these bodies. We begin by reviewing the evidence that Jupiter-family comets (JFCs; those with 2 < T < 3) form a dynamically distinct class of comets that originate in a flattened disk beyond Neptune. We present a model for the distribution of comets throughout the JFC and Centaur regions that is consistent with current observations, although further observations and numerical simulations in the Centaur region are called for. We then discuss dynamical results (since confirmed by observations) that a significant amount of material that was scattered by Neptune during the early stages of planet formation could persist today in the form of a "scattered disk" of bodies with highly eccentric orbits beyond Neptune. We describe the dynamical mechanisms believed responsible for the longevity of the surviving bodies and argue that if objects in the Kuiper belt and scattered disk have similar size distributions, then the scattered disk is likely to be the primary source of JFCs and Centaurs. Finally, we describe the importance of understanding the ecliptic comet population for the purposes of determining impact rates on the satellites of the giant planets and of age determinations of the satellite surfaces. We present tables of impact rates based on the best currently available analyses. Further refinements of these rates and age determinations await better observations of the Centaur population (including its size distribution), as well as a better understanding of the formation and early dynamical evolution of the outer solar system.
Origin of the Earth and Moon, 2000
Abstract The accretion of planets involved a high flux of planetesimal impactors in the first 107... more Abstract The accretion of planets involved a high flux of planetesimal impactors in the first 107 108 yr, a flux on the order of 109× the present flux. Dynamical models suggest that the early planetesimals would be used up by impacting planets or the Sun, or by being ...
Comets II, 2004
The Oort cloud is the primary source of the "nearly isotropic" comets, which include new and retu... more The Oort cloud is the primary source of the "nearly isotropic" comets, which include new and returning long-period comets and Halley-type comets. We focus on the following topics: (1) the orbital distribution of known comets and the cometary "fading" problem; (2) the population and mass of the Oort cloud, including the hypothetical inner Oort cloud; (3) the number of Oort cloud comets that survive from the origin of the solar system to the present time, and the timescale for building the Oort cloud; (4) the relative importance of different regions of the protoplanetary disk in populating the Oort cloud; and (5) current constraints on the structure of the Oort cloud and future prospects for learning more about its structure.
&lt;p&gt;Centaurs &amp;#8211; planet-crossing bodies in the region of the... more &lt;p&gt;Centaurs &amp;#8211; planet-crossing bodies in the region of the giant planets that mainly originate in the Kuiper Belt/Scattered Disk [1, 2] &amp;#8211; are thought to be the primary impactors on the giant planets and their satellites [3-8]. As part of an effort to interpret the cratering records of the saturnian satellites, we are developing a dynamical-physical model for the size distribution of potential impactors on the moons.&lt;/p&gt; &lt;p&gt;Most models of the orbital distribution of "observable" comets&lt;sup&gt;[1]&lt;/sup&gt; assume that the size of the nucleus does not change with time. These models treat physical evolution only by assuming a lifetime, after which comets are considered inactive or "faded". These models do not specify a fading mechanism, but assume an expression for the probability that a comet remains active after some amount of time [10-14]. Fading can result from loss of all volatiles, formation of a nonvolatile mantle on the surface of the nucleus, or splitting [15, 16].&lt;/p&gt; &lt;p&gt;A model of the erosion of 67P/Churyumov-Gerasimenko and 46P/Wirtanen due to sublimation of water ice throughout their orbital evolution estimates that 67P&amp;#8217;s nucleus has shrunk from a radius of 2.5 km to 2 km, while 46P&amp;#8217;s has decreased from 1 km to 0.6 km [17]. This calculation assumes that 10% of the nucleus is active and that its density is 500 kg/m&lt;sup&gt;3&lt;/sup&gt;. These estimates are uncertain because comets follow chaotic orbits, but in general, erosion has a bigger effect on smaller nuclei.&lt;/p&gt; &lt;p&gt;Some comets are active well beyond the water-ice sublimation zone within 3 au. Eighteen active Centaurs are currently known [18, 19]. 29P/Schwassmann-Wachmann, which follows a near-circular orbit at 6 au, is a copious source of dust and CO [20-22] and undergoes significant dust outbursts 7 or more times a year [23]. 174P/Echeclus underwent an outburst 13 au from the Sun that released &amp;#8776; 300 kg/s of dust for about two months [24], a rate comparable to the 530 kg/s of dust released by 67P at its peak near 1.3 au [25]. Echeclus also underwent several more outbursts near perihelion (&amp;#8776;6 au) with CO outgassing at &amp;#8776; 10% the rate of 29P at the same heliocentric distance and dust mass loss rates of 10 - 700 kg/s [20]. 2060 Chiron is another Centaur that is sporadically active in gas and dust, consistent with a more depleted state, like Echeclus [20].&lt;/p&gt; &lt;p&gt;Di Sisto et al. (2009) constructed a model of the orbital distributions of Jupiter-family comets (JFCs) that incorporated planetary perturbations, nongravitational forces, sublimation, and splitting. They considered nuclei with initial radii of 10, 5, and 1 km [26]. Di Sisto et al. found that 5- and 10-km comets usually evolved onto Centaur orbits, while 1-km comets were most likely to shrink below 100 m. Inspired by their work, we are developing a model for the dynamical-physical evolution of JFCs and Centaurs. We will use the orbital distribution found by Nesvorny et al. as our baseline model [14, 27].&lt;/p&gt; &lt;p&gt;We will first focus on modeling the evolution of the size distribution of JFCs. The model will eventually account for mass loss by both JFCs and Centaurs, with activity driven by H&lt;sub&gt;2&lt;/sub&gt;O, CO, or other volatiles. The fraction of the nucleus that is active will be allowed to vary with size, since smaller nuclei are typically more active [28-30]. We will then implement a model for cometary splitting with these inputs: the frequency of splitting as a function of perihelion distance; the fraction of the comet&amp;#8217;s mass released as fragments; the size distribution of the fragments; and the velocity imparted to the fragments by the splitting event. We will present preliminary results of our simulations.&lt;/p&gt; &lt;p&gt;We thank Raphael Marschall for discussions and the Cassini Data Analysis Program for support.&lt;/p&gt; &lt;p&gt;References&lt;/p&gt; &lt;p&gt;[1] Volk, K.; Malhotra, R. ApJ 687, 714&amp;#8211;725, 2008.&lt;/p&gt; &lt;p&gt;[2] Di Sisto, R. P.; Rossignoli, N. L. CMDA, in press (arXiv:2006.09657), 2020.&lt;/p&gt; &lt;p&gt;[3] Zahnle, K.; Dones, L.; Levison, H. F. Icarus 136, 202&amp;#8211;222, 1998.&lt;/p&gt; &lt;p&gt;[4] Zahnle, K.; Schenk, P.; Levison, H.; Dones, L. Icarus 163, 263&amp;#8211;289, 2003.&lt;/p&gt; &lt;p&gt;[5] Di Sisto, R. P.; Zanardi, M. A&amp;A 553, id. A79, 2013.&lt;/p&gt; &lt;p&gt;[6] Di Sisto, R. P.; Zanardi, M. Icarus 264, 90&amp;#8211;101, 2016.&lt;/p&gt; &lt;p&gt;[7] Rossignoli, N. L.; Di Sisto, R. P.; Zanardi, M.; Dugaro, A.…
Reviews of Geophysics, 1991
Abstract This review discusses each planetary ring system and describes recent theoretical develo... more Abstract This review discusses each planetary ring system and describes recent theoretical developments and models of ring evolution. The distribution of the inner rings and satellites of all four giant planets reduced to a uniform scale of'planetary units', normalized by the ...
Astrobiology, Jan 11, 2017
We analyzed Cassini Imaging Science Subsystem (ISS) images of the plume of Enceladus to derive pa... more We analyzed Cassini Imaging Science Subsystem (ISS) images of the plume of Enceladus to derive particle number densities for the purpose of comparing our results with those obtained from other Cassini instrument investigations. Initial discrepancies in the results from different instruments, as large as factors of 10-20, can be reduced to ∼2 to 3 by accounting for the different times and geometries at which measurements were taken. We estimate the average daily ice production rate, between 2006 and 2010, to be 29 ± 7 kg/s, and a solid-to-vapor ratio, S/V > 0.06. At 50 km altitude, the plume's peak optical depth during the same time period was τ ∼ 10(-3); by 2015, it was ∼10(-4). Our inferred differential size distribution at 50 km altitude has an exponent q = 3. We estimate the average geothermal flux into the sea beneath Enceladus' south polar terrain to be comparable to that of the average Atlantic, of order 0.1 W/m(2). Should microbes be present on Enceladus, concentra...