1,083 research outputs found
Use of Linear Perspective Scene Cues in a Simulated Height Regulation Task
As part of a long-term effort to quantify the effects of visual scene cuing and non-visual motion cuing in flight simulators, an experimental study of the pilot's use of linear perspective cues in a simulated height-regulation task was conducted. Six test subjects performed a fixed-base tracking task with a visual display consisting of a simulated horizon and a perspective view of a straight, infinitely-long roadway of constant width. Experimental parameters were (1) the central angle formed by the roadway perspective and (2) the display gain. The subject controlled only the pitch/height axis; airspeed, bank angle, and lateral track were fixed in the simulation. The average RMS height error score for the least effective display configuration was about 25% greater than the score for the most effective configuration. Overall, larger and more highly significant effects were observed for the pitch and control scores. Model analysis was performed with the optimal control pilot model to characterize the pilot's use of visual scene cues, with the goal of obtaining a consistent set of independent model parameters to account for display effects
Dynamics of the Kuiper Belt
Our current knowledge of the dynamical structure of the Kuiper Belt is
reviewed here. Numerical results on long term orbital evolution and dynamical
mechanisms underlying the transport of objects out of the Kuiper Belt are
discussed. Scenarios about the origin of the highly non-uniform orbital
distribution of Kuiper Belt objects are described, as well as the constraints
these provide on the formation and long term dynamical evolution of the outer
Solar system. Possible mechanisms include an early history of orbital migration
of the outer planets, a mass loss phase in the outer Solar system and
scattering by large planetesimals. The origin and dynamics of the scattered
component of the Kuiper Belt is discussed. Inferences about the primordial mass
distribution in the trans-Neptune region are reviewed. Outstanding questions
about Kuiper Belt dynamics are listed.Comment: 22 pages plus 8 figures added footnote, figure
An Oort cloud origin for the high-inclination, high-perihelion Centaurs
We analyse the origin of three Centaurs with perihelia in the range 15 AU to
30 AU, inclinations above 70 deg and semi-major axes shorter than 100 AU. Based
on long-term numerical simulations we conclude that these objects most likely
originate from the Oort cloud rather than the Kuiper Belt or Scattered Disc. We
estimate that there are currently between 1 and 200 of these high-inclination,
high-perihelion Centaurs with absolute magnitude H<8.Comment: Accepted for publication in MNRA
Models for the Effects of G-seat Cuing on Roll-axis Tracking Performance
Including whole-body motion in a flight simulator improves performance for a variety of tasks requiring a pilot to compensate for the effects of unexpected disturbances. A possible mechanism for this improvement is that whole-body motion provides high derivative vehicle state information whic allows the pilot to generate more lead in responding to the external disturbances. During development of motion simulating algorithms for an advanced g-cuing system it was discovered that an algorithm based on aircraft roll acceleration producted little or no performance improvement. On the other hand, algorithms based on roll position or roll velocity produced performance equivalent to whole-body motion. The analysis and modeling conducted at both the sensory system and manual control performance levels to explain the above results are described
Mapping the stability field of Jupiter Trojans
Jupiter Trojans are a remnant of outer solar system planetesimals captured into stable or quasistable libration about the 1:1 resonance with the mean motion of Jupiter. The observed swarms of Trojans may provide insight into the original mass of condensed solids in the zone from which the Jovian planets accumulated, provided that the mechanisms of capture can be understood. As the first step toward this understanding, the stability field of Trojans were mapped in the coordinate proper eccentricity, e(sub p), and libration amplitude, D. To accomplish this mapping, the orbits of 100 particles with e(sub p) in the range of 0 to 0.8 and D in the range 0 to 140 deg were numerically integrated. Orbits of the Sun, the four Jovian planets, and the massless particles were integrated as a full N-body system, in a barycentric frame using fourth order symplectic scheme
On The Effect of Giant Planets on the Scattering of Parent Bodies of Iron Meteorite from the Terrestrial Planet Region into the Asteroid Belt: A Concept Study
In their model for the origin of the parent bodies of iron meteorites, Bottke
et al proposed differentiated planetesimals that were formed in the region of
1-2 AU during the first 1.5 Myr, as the parent bodies, and suggested that these
objects and their fragments were scattered into the asteroid belt as a result
of interactions with planetary embryos. Although viable, this model does not
include the effect of a giant planet that might have existed or been growing in
the outer regions. We present the results of a concept study where we have
examined the effect of a planetary body in the orbit of Jupiter on the early
scattering of planetesimals from terrestrial region into the asteroid belt. We
integrated the orbits of a large battery of planetesimals in a disk of
planetary embryos, and studied their evolutions for different values of the
mass of the planet. Results indicate that when the mass of the planet is
smaller than 10 Earth-masses, its effects on the interactions among
planetesimals and planetary embryos is negligible. However, when the planet
mass is between 10 and 50 Earth-masses, simulations point to a transitional
regime with ~50 Earth-mass being the value for which the perturbing effect of
the planet can no longer be ignored. Simulations also show that further
increase of the mass of the planet strongly reduces the efficiency of the
scattering of planetesimals from the terrestrial planet region into the
asteroid belt. We present the results of our simulations and discuss their
possible implications for the time of giant planet formation.Comment: 20 pages, 7 figures, accepted for publication in Ap
Albedos of Main-Belt Comets 133P/Elst-Pizarro and 176P/LINEAR
We present the determination of the geometric R-band albedos of two main-belt
comet nuclei based on data from the Spitzer Space Telescope and a number of
ground-based optical facilities. For 133P/Elst-Pizarro, we find an albedo of
p_R=0.05+/-0.02 and an effective radius of r_e=1.9+/-0.3 km (estimated
semi-axes of a~2.3 km and b~1.6 km). For 176P/LINEAR, we find an albedo of
p_R=0.06+/-0.02 and an effective radius of r_e=2.0+/-0.2 km (estimated
semi-axes of a~2.6 km and b~1.5 km). In terms of albedo, 133P and 176P are
similar to each other and are typical of other Themis family asteroids, C-class
asteroids, and other comet nuclei. We find no indication that 133P and 176P are
compositionally unique among other dynamically-similar (but inactive) members
of the Themis family, in agreement with previous assertions that the two
objects most likely formed in-situ. We also note that low albedo (p_R<0.075)
remains a consistent feature of all cometary (i.e., icy) bodies, whether they
originate in the inner solar system (the main-belt comets) or in the outer
solar system (all other comets).Comment: 11 pages, 3 figures, accepted for publication in ApJ
Constructing the secular architecture of the solar system II: The terrestrial planets
We investigate the dynamical evolution of the terrestrial planets during the
planetesimal-driven migration of the giant planets. A basic assumption of this
work is that giant planet migration occurred after the completion of
terrestrial planet formation, such as in the models that link the former to the
origin of the Late Heavy Bombardment. The divergent migration of Jupiter and
Saturn causes the g5 eigenfrequency to cross resonances of the form g5=gk with
k ranging from 1 to 4. Consequently these secular resonances cause
large-amplitude responses in the eccentricities of the terrestrial planets. We
show that the resonances g5=g_4 and g5=g3 do not pose a problem if Jupiter and
Saturn have a fast approach and departure from their mutual 2:1 mean motion
resonance. On the other hand, the resonance crossings g5=g2 and g5=g1 are more
of a concern as they tend to yield a terrestrial system incompatible with the
current one. We offer two solutions to this problem. The first uses the fact
that a secular resonance crossing can also damp the amplitude of a Fourier mode
if the latter is large originally. A second scenario involves a 'jumping
Jupiter' in which encounters between an ice giant and Jupiter, without ejection
of the former, cause the latter to migrate away from Saturn much faster than if
migration is driven solely by encounters with planetesimals. In this case, the
g5=g2 and g5=g1 resonances can be jumped over, or occur very briefly.Comment: Astronomy & Astrophysics (2009) in pres
A Possible Stellar Metallic Enhancement in Post-T Tauri Stars by a Planetesimal Bombardment
The photospheres of stars hosting planets have larger metallicity than stars
lacking planets. In the present work we study the possibility of an earlier
metal enrichment of the photospheres by means of impacting planetesimals during
the first 20-30Myr. Here we explore this contamination process by simulating
the interactions of an inward migrating planet with a disc of planetesimal
interior to its orbit. The results show the percentage of planetesimals that
fall on the star. We identified the dependence of the planet's eccentricity
() and time scale of migration () on the rate of infalling
planetesimals. For very fast migrations (yr and yr) there
is no capture in mean motion resonances, independently of the value of .
Then, due to the planet's migration the planetesimals suffer close approaches
with the planet and more than 80% of them are ejected from the system. For slow
migrations (yr and yr) the percentage of collisions with
the planet decrease with the increase of the planet's eccentricity. For
and most of the planetesimals were captured in the 2:1 resonance and
more than 65% of them collided with the star. Whereas migration of a Jupiter
mass planet to very short pericentric distances requires unrealistic high disc
masses, these requirements are much smaller for smaller migrating planets. Our
simulations for a slowly migrating 0.1 planet, even demanding
a possible primitive disc three times more massive than a primitive solar
nebula, produces maximum [Fe/H] enrichments of the order of 0.18 dex. These
calculations open possibilities to explain hot Jupiters exoplanets
metallicities.Comment: Accepted for publication by Monthly Notices of the Royal Astronomical
Societ
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