Brett Gladman

The Exchange of Impact Ejecta Between Terrestrial Planets

Orbital histories of ejecta from the terrestrial planets were numerically integrated to study their transfer to Earth. The properties of the lunar and martian meteorites are consistent with a recurrent ejection of small meteoroids as a result of impacts on their parent bodies. Long-range gravitational effects, especially secular resonances, strongly influence the orbits of many meteoroids, increasing their collision rates with other planets and the sun. These effects and collisional destruction in the asteroid belt result in shortened time scales and higher fluxes than previously believed, especially for martian meteorites. A small flux of mercurian ejecta appears possible; recovery of meteorites from the Earth and Venus is less likely.

The Structure of the Kuiper Belt: Size Distribution and Radial Extent

The size distribution in the Kuiper Belt records physical processes operating during the formation and subsequent evolution of the solar system. This paper reports a study of the apparent magnitude distribution of faint objects in the Kuiper Belt, obtained via deep imaging on the Canada-France-Hawaii Telescope and the ESO Very Large Telescope UT1. We —nd that the entire range of observed objects (magnitudes is well represented by an unbroken power law, with the number of objects per m R D 20¨27) square degree brighter than magnitude R being of the form with a 0.69 and &(m R R) 10a(R~R0),

Evidence for an Extended Scattered Disk

Abstract By telescopic tracking, we have established that the transneptunian object (TNO) 2000 CR 105 has a semimajor axis of 220±1 AU and perihelion distance of 44.14±0.02 AU, beyond the domain which has heretofore been associated with the “scattered disk” of Kuiper Belt objects interacting via gravitational encounters with Neptune. We have also firmly established that the TNO 1995 TL 8 has a high perihelion (of 40.08±0.02 AU). These objects, and two other recent discoveries which appear to have perihelia outside 40 AU, have probably been placed on these orbits by a gravitational interaction which is not strong gravitational scattering off of any of the giant planets on their current orbits. Their existence may thus have profound cosmogonic implications for our understanding of the formation of the outer Solar System. We discuss some viable scenarios which could have produced these objects, including long-term diffusive chaos and scattering off of other massive bodies in the outer Solar System. This discovery implies that there must be a large population of TNOs in an “extended scattered disk” with perihelia above the previously suggested 38 AU boundary. The total population is difficult to estimate due to the ease with which such objects would have been lost. This illustrates the great value of frequent and well time-sampled recovery observations of trans-neptunian objects within their discovery opposition.

Production of the Extended Scattered Disk by Rogue Planets

We show that if the early outer solar system contained one or more additional planets of an Earth mass or larger, these planets are likely to be temporarily emplaced in the Kuiper Belts scattered disk. While on an orbit of large semimajor axis, such a rogue planet may efficiently raise either (1) the perihelia of other scattered-disk objects, emplacing them in the extended scattered disk, or (2) their orbital inclinations, to the levels currently observed in the Kuiper Belt. With even a single rogue planet present, the probability of producing extended scattered disk objects is 20%-50%. After the rogue is removed from the system (on a characteristic timescale of 200 Myr), most extended scattered disk orbits are not appreciably modified over the age of the solar system. Objects with large orbital inclinations like the outliers 2004 XR190, 2003 UB313, 2000 CR105, and Sedna are also produced.

Discovery of two distant irregular moons of Uranus

The systems of satellites and rings surrounding the giant planets in the Solar System have remarkably similar architectures. Closest to each planet are rings with associated moonlets, then larger ‘regular’ satellites on nearly circular orbits close to the planets equatorial plane, and finally one or more distant, small ‘irregular’ satellites on highly elliptical or inclined orbits. Hitherto, the only departure from this broad classification scheme was the satellite system around Uranus, in which no irregular satellites had been found. Here we report the discovery of two satellites orbiting Uranus at distances of several hundred planetary radii. These satellites have inclined, retrograde orbits of moderate eccentricity that clearly identify them as irregular. The satellites are extremely faint (apparent red magnitudes mR = 20.4 and 21.9), with estimated radii of only 60 and 30u2009km. Both moons are unusually red in colour, suggesting a link between these objects—which were presumably captured by Uranus early in the Solar Systems history—and other recently discovered bodies orbiting in the outer Solar System.

Risks threatening viable transfer of microbes between bodies in our solar system

Abstract A fraction of the number of ejecta expelled from a planet by comet or asteroid impacts end up landing on another planet. If microorganisms were living in the ground before impact, they would be transported inside ejecta to the target planet. During that perilous trip, they would be subject to four main categories of threat to their survival: dynamical stress, excess temperature, radiation, chemical attack and vacuum. The effect of these, in the form of survival fractions as a function of time, as well as approximate numbers of arriving ejecta with viable flight times, have been investigated in a quantitative study we have made. The result shows that viable transfer from Mars to Earth and vice versa was highly probable during the first 0.5 Ga, and also probable, but with lower frequency, thereafter. Here we follow up with considerations about the consequences of the result regarding the question of whether the ancestor cell of all life on Earth must have originated on Earth, or whether it could have originated on Mars, its descendants thereafter moving to Earth. Some other possible consequences are also discussed.

Discovery of a Low-Eccentricity, High-Inclination Kuiper Belt Object at 58 AU

We report the discovery of the first trans-Neptunian object, designated 2004 XR190, with a low-eccentricity orbit beyond the 2 : 1 mean motion resonance. Fitting an orbit to 23 astrometric observations spread out over 12 months yields an orbit of a = 57.2 ± 0.4, e = 0.08 ± 0.04, and i = 466. All viable orbits have perihelia distances q > 49 AU. The very high orbital inclination of this extended scattered disk object might be explained by several models, but its existence again points to a large as-yet undiscovered population of trans-Neptunian objects with large orbital perihelia and inclination.

Dynamically depleted zones for Cassinis safe passage beyond Saturns rings

Abstract Motivated by concern for the safety of the Cassini orbiter, we explore the orbital histories and reaccretion of circumplanetary particles in the Saturnian system. Our goal is to find regions near the satellites that might be dynamically cleared of orbital debris. Including the gravitational effects of all the classical satellites out to Titan, we numerically integrate the orbits of test particles in the Saturnian system, examining the region from 2.4–24 R S (Saturn radii), for 1000 years. Particles are followed until they impact a moon, enter the main ring, or travel well beyond Hyperions orbit. Our numerical simulations demonstrate that the orbital eccentricities and inclinations of test particles are appreciably influenced only in the immediate neighborhoods of the satellites, and at the 2 :1 and (to a much lesser degree) 3 :1 resonances of Titan ; the effects of a secular resonance appear just near Rhea. Simulations of material in Mimas vicinity show that particles, whether launched from the satellite or placed in an originally uniform distribution across semimajor axis, are swept clear within a (theoretically predicted) region where particle orbits eventually cross the satellites ; Mimass orbital eccentricity broadens this sweep-up region. The timescale over which particles are removed by the satellites is of order a hundred years ; the few members that remain in the cleared zone are identified as moving on stable horseshoe orbits.

Relaxation Oscillations in Tidally Evolving Satellites

AbstractWe study the rotational evolution under tidal torques of axisymmetric natural satellites in inclined, precessing orbits. In the spin- and orbit-averaged equations of motion, we find that a global limit cycle exists for parameter values near the stability limit of Cassini state n