209 research outputs found
A Search for Water Masers in the Saturnian System
We searched for H2O 6(1,6)-5(2,3) maser emission at 22.235 GHz from several
Saturnian satellites with the Nobeyama 45m radio telescope in May 2009.
Observations were made for Titan, Hyperion, Enceladus and Atlas, for which
Pogrebenko et al. (2009) had reported detections of water masers at 22.235 GHz,
and in addition for Iapetus and other inner satellites. We detected no emission
of the water maser line for all the satellites observed, although sensitivities
of our observations were comparable or even better than those of Pogrebenko et
al.. We infer that the water maser emission from the Saturnian system is
extremely weak, or sporadic in nature. Monitoring over a long period and
obtaining statistical results must be made for the further understanding of the
water maser emission in the Saturnian system.Comment: 8 pages, 2 figures, accepted for publication in PASJ (Letter
The origin of planetary impactors in the inner solar system
New insights into the history of the inner solar system are derived from the
impact cratering record of the Moon, Mars, Venus and Mercury, and from the size
distributions of asteroid populations. Old craters from a unique period of
heavy bombardment that ended 3.8 billion years ago were made by asteroids
that were dynamically ejected from the main asteroid belt, possibly due to the
orbital migration of the giant planets. The impactors of the past 3.8
billion years have a size distribution quite different from the main belt
asteroids, but very similar to the population of near-Earth asteroids.Comment: 12 pages (including 4 figures
The invasion of a free floating planet and the number asymmetry of Jupiter Trojans
This paper extends our previous study (Li et al. 2023) of the early evolution
of Jupiter and its two Trojan swarms by introducing the possible perturbations
of a free floating planet (FFP) invading the Solar System. In the framework of
the invasion of a FFP, we aim to provide some new scenarios to explain the
number asymmetry of the L4 and L5 Jupiter Trojans, and some other observed
features. We investigate two different cases: (i) The indirect case, where
Jupiter experiences a scattering encounter with the FFP and jumps outwards at a
speed that is much higher than that considered in(Li et al. 2023), resulting in
a change in the numbers of the L4 (N4) and L5 (N5) Trojans swarms. (ii) The
direct case, in which the FFP traverses the L5 region and affects the stability
of the local Trojans. In the indirect case, the outward migration of Jupiter
can be fast enough to make the L4 islands disappear temporarily, inducing a
resonant amplitude increase of the local Trojans. After the migration is over,
the L4 Trojans come back to the re-appeared and enlarged islands. As for the L5
islands, they always exist but expand even more considerably. Since the L4
swarm suffers less excitation in the resonant amplitude than the L5 swarm, more
L4 Trojans are stable and could survive to the end. In the direct case, the FFP
could deplete a considerable fraction of the L5 Trojans, while the L4 Trojans
at large distances are not affected and all of them could survive. Both the
indirect and direct cases could result in a number ratio of R45=N4/N5~1.6 that
can potentially explain the current observations. The latter has the advantage
of producing the observed resonant amplitude distribution. For achieving these
results, we propose that the FFP should have a mass of at least of a few tens
of Earth masses and its orbital inclination is allowed to be as high as 40
degrees.Comment: Accepted for publication in A&A, 13 pages, 7 figures, 5 table
Time-series photometry of Earth flyby asteroid 2012 DA14
Context. The object 2012 DA14 is a near-Earth asteroid with a size of several
tens of meters. It had approached closely the Earth on 15 February, 2013 UT,
providing an opportunity for precise measurements of this tiny asteroid. Aims.
The solar phase angle of 2012 DA14 had varied widely around its closest
approach but was almost constant during the following night. We performed
time-series photometric observations on those two nights to determine the
rotational properties and phase effect. Methods. The observations were carried
out using the 0.55-m telescope at Saitama University, Japan. The R-band images
were obtained continuously over a 2 hr period at the closest approach and for
about 5 hr on the next night. Results. The lightcurve data from the second
night indicates a rotational period of 11.0 +1.8/-0.6 hr and a peak-to-peak
amplitude of 1.59 +/- 0.02 mag. The brightness variation before and after the
closest approach was separated into two components that are derived from the
rotation and phase effect. We found that the phase curve slope of this asteroid
is significantly shallower than those of other L-type asteroids. Conclusions.
We suggest that 2012 DA14 is coated with a coarse surface that lacks fine
regolith particles and/or a high albedo surface.Comment: 4 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
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