113 research outputs found
Surface Thermophysical Properties determination of OSIRIS-REx target asteroid (101955) Bennu
In this work, we investigate the thermophysical properties of OSIRIS-REx
target asteroid (101955) Bennu (hereafter, Bennu), where thermal inertia plays
an important role in understanding the nature of the asteroid's surface, and
will definitely provide substantial information for the sampling return
mission. Using a thermophysical model incorporating the recently updated 3D
radar-derived shape model \citep{Nolan2013} and mid-infrared observations of
Spitzer-PUI, Spitzer-IRAC, Herschel/PACS and ESO VLT/VISIR
\citep{Muller2012,Emery2014}, we derive the surface thermophysical properties
of Bennu. The asteroid has an effective diameter of m, a
geometry albedo of , a roughness fraction of
, and thermal inertia of
for a best-fit solution at
1 level. The best-estimate thermal inertia indicates that fine-grained
regolith may cover a large area of Bennu's surface, with a grain size that may
range from to ~mm, and our outcome further supports that Bennu would
be a suitable target for the OSIRIS-REx mission to return samples from the
asteroid to Earth.Comment: 10 pages, 7 figures, 5 tables, accepted to MNRA
Thermophysical Characteristics of OSIRIS-REx Target Asteroid (101955) Bennu
In this work, we investigate the thermophysical properties, including thermal
inertia, roughness fraction and surface grain size of OSIRIS-REx target
asteroid (101955) Bennu by using a thermophysical model with the recently
updated 3D radar-derived shape model (\cite[Nolan et al., 2013]{Nolan2013}) and
mid-infrared observations (\cite[Mller et al, 2012]{Muller2012},
\cite[Emery et al., 2014]{Emery2014}). We find that the asteroid bears an
effective diameter of m, a geometric albedo of
, a roughness fraction of ,
and thermal inertia of for our
best-fit solution. The best-estimate thermal inertia suggests that fine-grained
regolith may cover a large portion of Bennu's surface, where a grain size may
vary from to ~mm. Our outcome suggests that Bennu is suitable for the
OSIRIS-REx mission to return samples to Earth.Comment: 3 pages, 1 figures, accepted to IAU Symposium 318: Asteroids: New
Observations, New Model
Using Chebyshev polynomials interpolation to improve the computation efficiency of gravity near an irregular-shaped asteroid
In asteroid rendezvous missions, the dynamical environment near the
asteroid's surface should be made clear prior to the mission launch. However,
most of the asteroids have irregular shapes, which lower the efficiency of
calculating their gravitational field by adopting the traditional polyhedral
method. In this work, we propose a method to partition the space near the
asteroid adaptively along three spherical coordinates and use Chebyshev
polynomials interpolation to represent the gravitational acceleration in each
cell. Moreover, we compare four different interpolation schemes to obtain the
best precision with the identical initial parameters. An error-adaptive octree
division is combined to improve the interpolation precision near the surface.
As an example, we take the typical irregular-shaped near-Earth asteroid 4179
Toutatis to show the advantage of this method, as a result, we show that the
efficiency can be increased by hundreds to thousands times with our method. In
a word, this method can be applicable to other irregular-shaped asteroids and
can greatly improve the evaluation efficiency.Comment: 17 pages, 10 figures, 3 tables, accepted to Research in Astronomy and
Astrophysic
Near 3:2 and 2:1 mean motion resonances formation in the systems observed by Kepler
The Kepler mission has released ~4229 transiting planet candidates. There are
approximately 222 candidate systems with three planets. Among them, the period
ratios of planet pairs near 1.5 and 2.0 reveal that two peaks exist for which
the proportions of the candidate systems are ~7.0% and 18.0%, respectively. In
this work, we study the formation of mean motion resonance (MMR) systems,
particularly for the planetary configurations near 3:2 and 2:1 MMRs, and we
concentrate on the interplay between the resonant configuration and the
combination of stellar accretion rate, stellar magnetic field, speed of
migration and additional planets. We perform more than 1000 runs by assuming a
system with a solar-like star and three surrounding planets. From the
statistical results, we find that under the formation scenario, the proportions
near 1.5 and 2.0 can reach 14.5% and 26.0%, respectively. In addition, is propitious toward the formation
of 3:2 resonance, whereas
contributes to the formation of 2:1 resonance. The speed-reduction factor of
type I migration facilitates 3:2 MMRs, whereas
facilitates 2:1 MMRs. If additional planets are present in orbits within the
innermost or beyond the outermost planet in a three-planet system, 3:2:1 MMRs
can be formed, but the original systems trapped in 4:2:1 MMRs are not affected
by the supposed planets. In summary, we conclude that this formation scenario
will provide a likely explanation for Kepler candidates involved in 2:1 and 3:2
MMRs.Comment: 13 pages, 8 figures, accepted for publication in Ap
Near Mean-motion Resonances in the Systems Observed by Kepler: Affected by Mass Accretion and Type I Migration
The Kepler mission has released over 4496 planetary candidates, among which
3483 planets have been confirmed as of April 2017. The statistical results of
the planets show that there are two peaks around 1.5 and 2.0 in the
distribution of orbital period ratios. The observations indicate that a plenty
of planet pairs could have firstly been captured into mean motion resonances
(MMRs) in planetary formation. Subsequently, these planets depart from exact
resonant locations to be near MMRs configurations. Through type I migration,
two low-mass planets have a tendency to be trapped into first-order MMRs (2:1
or 3:2 MMRs), however two scenarios of mass accretion of planets and potential
outward migration play an important role in reshaping their final orbital
configurations. Under the scenario of mass accretion, the planet pairs can
cross 2:1 MMRs and then enter into 3:2 MMRs, especially for the inner pairs.
With such formation scenario, the possibility that two planets are locked into
3:2 MMRs can increase if they are formed in a flat disk. Moreover, the outward
migration can make planets have a high likelihood to be trapped into 3:2 MMRs.
We perform additional runs to investigate the mass relationship for those
planets in three-planet systems, and we show that two peaks near 1.5 and 2.0
for the period ratios of two planets can be easily reproduced through our
formation scenario. We further show that the systems in chain resonances (e.g.,
4:2:1, 3:2:1, 6:3:2 and 9:6:4 MMRs), have been observed in our simulations.
This mechanism can be applicable to understand the formation of systems of
Kepler-48, Kepler-53, Kepler-100, Kepler-192, Kepler-297, Kepler-399, and
Kepler-450.Comment: 12 pages, 6 figures, accepted for publication in A
The scattering outcomes of Kepler circumbinary planets: planet mass ratio
Recent studies reveal that the free eccentricities of Kepler-34b and
Kepler-413b are much larger than their forced eccentricities, implying that the
scattering events may take place in their formation. The observed orbital
configuration of Kepler-34b cannot be well reproduced in disk-driven migration
models, whereas a two-planet scattering scenario can play a significant role of
shaping the planetary configuration. These studies indicate that circumbinary
planets discovered by Kepler may have experienced scattering process. In this
work, we extensively investigate the scattering outcomes of circumbinary
planets focusing on the effects of planet mass ratio. We find that the
planetary mass ratio and the the initial relative locations of planets act as
two important parameters which affect the eccentricity distribution of the
surviving planets. As an application of our model, we discuss the observed
orbital configurations of Kepler-34b and Kepler-413b. We first adopt the
results from the disk-driven models as the initial conditions, then simulate
the scattering process occurred in the late evolution stage of circumbinary
planets. We show that the present orbital configurations of Kepler-34b and
Kepler-413b can be well reproduced when considering two unequal-mass planet
ejection model. Our work further suggests that some of the currently discovered
circumbinary single-planet systems may be the survivals of original
multiple-planet systems. The disk-driven migration and the scattering events
occurring in the late stage both play an irreplaceable role in sculpting the
final systems.Comment: 18 pages, 9 figures, accepted for publication in A
Formation of S-type planets in close binaries: scattering induced tidal capture of circumbinary planets
Although several S-type and P-type planets in binary systems were discovered
in past years, S-type planets have not yet been found in close binaries with an
orbital separation not more than 5 au. Recent studies suggest that S-type
planets in close binaries may be detected through high-accuracy observations.
However, nowadays planet formation theories imply that it is difficult for
S-type planets in close binaries systems to form in situ. In this work, we
extensively perform numerical simulations to explore scenarios of planet-planet
scattering among circumbinary planets and subsequent tidal capture in various
binary configurations, to examine whether the mechanism can play a part in
producing such kind of planets. Our results show that this mechanism is robust.
The maximum capture probability is , which can be comparable to the
tidal capture probability of hot Jupiters in single star systems. The capture
probability is related to binary configurations, where a smaller eccentricity
or a low mass ratio of the binary will lead to a larger probability of capture,
and vice versa. Furthermore, we find that S-type planets with retrograde orbits
can be naturally produced via capture process. These planets on retrograde
orbits can help us distinguish in situ formation and post-capture origin for
S-type planet in close binaries systems. The forthcoming missions (PLATO) will
provide the opportunity and feasibility to detect such planets. Our work
provides several suggestions for selecting target binaries in search for S-type
planets in the near future.Comment: 12 pages, 6 figures, accepted for publication in MNRA
Revisit of rotational dynamics of Asteroid 4179 Toutatis from Chang'e-2's flyby
This paper presents analysis of the rotational parameters of Toutatis based
on the observational results from Chang'e-2's close flyby. The 3-D shape model
derived from ground-based radar observation is used to calculate the 3-1-3
Euler angles at the flyby epoch, which are evaluated to be
, and . The
large amplitude of Toutatis' tumbling attitude is demonstrated to be the result
of the large deviation of the angular momentum axis and the rotational axis.
Two rotational periods are evaluated to be days for rotation
about the long axis and days for precession of the long axis
about the angular momentum vector based on Fourier analysis. These results
provide a further understanding of rotational state of Toutatis.Comment: 4 pages, 3 figures, accepted to IAU Symposium 318: Asteroids: New
Observations, New Model
Investigation of Thermal Inertia and Surface Properties for Near-Earth Asteroid (162173) 1999 JU3
In order to obtain the substantial information about the surface physics and
thermal property of the target asteroid (162173) 1999 JU3, which will be
visited by Hayabusa 2 in a sample return mission, with the Advanced Thermal
Physical Model (ATPM) we estimate the possible thermal inertia distribution
over its surface, and infer the major material composition of its surface
materials. In addition, the effective diameter and geometric albedo are derived
to be , , respectively,
and the average thermal inertia is estimated to be about . According to the derived thermal inertia
distribution, we infer that the major area on the surface of the target
asteroid may be covered by loose materials, such as rock debris, sands, and so
on, but few bare rocks may exist in a very small region. In this sense, the
sample return mission of Hayabusa 2 is feasible, when it is performed
successfully, it will certainly bring significant scientific information to the
research of asteroids.Comment: 15 pages, 7 figures, published in Chinese Astronomy and Astrophysic
Dynamical evolution and stability maps of the Proxima Centauri system
Proxima Centauri was recently discovered to host an Earth-mass planet of
Proxima b, and a 215-day signal which is probably a potential planet c. In this
work, we investigate the dynamical evolution of the Proxima Centauri system
with the full equations of motion and semi-analytical models including
relativistic and tidal effects. We adopt the modified Lagrange-Laplace secular
equations to study the evolution of eccentricity of Proxima b, and find that
the outcomes are consistent with those from the numerical simulations. The
simulations show that relativistic effects have an influence on the evolution
of eccentricities of planetary orbits, whereas tidal effects primarily affects
the eccentricity of Proxima b over long timescale. Moreover, using the MEGNO
(the Mean Exponential Growth factor of Nearby Orbits) technique, we place
dynamical constraints on orbital parameters that result in stable or
quasi-periodic motions for coplanar and non-coplanar configurations. In the
coplanar case, we find that the orbit of Proxima b is stable for the semi-major
axis ranging from 0.02 au to 0.1 au and the eccentricity being less than 0.4.
This is where the best-fitting parameters for Proxima b exactly fall.
Additional simulations show that the robust stability of this system would
favor an eccentricity of Proxima b less than 0.45 and that of Proxima c below
0.65. In the non-coplanar case, we find that mutual inclinations of two planets
must be lower than in order to provide stability. Finally, we
estimate the mass of Proxima c to be when , if
and .Comment: 11 pages, 11 figures, accepted for publication in MNRA
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