scholarly journals Sample collection from asteroid (162173) Ryugu by Hayabusa2: Implications for surface evolution

Science ◽  
2020 ◽  
Vol 368 (6491) ◽  
pp. 654-659 ◽  
Author(s):  
T. Morota ◽  
S. Sugita ◽  
Y. Cho ◽  
M. Kanamaru ◽  
E. Tatsumi ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Solar Heating ◽  
Space Weathering ◽  
The Sun ◽  
Surface Material ◽  
Exposed Surface ◽  
Sample Collection ◽  
Surface Evolution ◽  
Earth Asteroid ◽  
Short Period

The near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu’s surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2’s thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.

Discussion following the presentation by F. Deubner

1977 ◽  
Vol 36 ◽  
pp. 69-74
Keyword(s):  
List Type ◽  
The Sun ◽  
Type Number ◽  
Harmonic Motion ◽  
Locally Excited ◽  
Long Period ◽  
Coherent Wave ◽  
Short Period ◽  
Global Modes

The discussion was separated into 3 different topics according to the separation made by the reviewer between the different periods of waves observed in the sun :1) global modes (long period oscillations) with predominantly radial harmonic motion.2) modes with large coherent - wave systems but not necessarily global excitation (300 s oscillation).3) locally excited - short period waves.

scholarly journals PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data

2020 ◽  
Vol 499 (3) ◽  
pp. 3738-3748
Author(s):  
R H Østensen ◽  
C S Jeffery ◽  
H Saio ◽  
J J Hermes ◽  
J H Telting ◽  
...  
Keyword(s):  
Heavy Metal ◽  
Helium Abundance ◽  
The Sun ◽  
The Third ◽  
Short Period ◽  
Standard Models ◽  
Hot Subdwarfs ◽  
Amplitude Mode ◽  
Rare Group

ABSTRACT The Kepler spacecraft observed the hot subdwarf star PHL 417 during its extended K2 mission, and the high-precision photometric light curve reveals the presence of 17 pulsation modes with periods between 38 and 105 min. From follow-up ground-based spectroscopy, we find that the object has a relatively high temperature of 35 600 K, a surface gravity of $\log g / {\rm cm\, s^{-2}}\, =\, 5.75$ and a supersolar helium abundance. Remarkably, it also shows strong zirconium lines corresponding to an apparent +3.9 dex overabundance compared with the Sun. These properties clearly identify this object as the third member of the rare group of pulsating heavy-metal stars, the V366-Aquarii pulsators. These stars are intriguing in that the pulsations are inconsistent with the standard models for pulsations in hot subdwarfs, which predicts that they should display short-period pulsations rather than the observed longer periods. We perform a stability analysis of the pulsation modes based on data from two campaigns with K2. The highest amplitude mode is found to be stable with a period drift, $\dot{P}$, of less than 1.1 × 10−9 s s−1. This result rules out pulsations driven during the rapid stages of helium flash ignition.

Evolution of Comets into Asteroids?

1971 ◽  
Vol 12 ◽  
pp. 413-421 ◽  
Author(s):  
B.G. Marsden
Keyword(s):  
Solar Radiation ◽  
Solar Nebula ◽  
Oort Cloud ◽  
Original Version ◽  
Terrestrial Planets ◽  
Minor Planets ◽  
The Sun ◽  
Physical Difference ◽  
Short Period ◽  
The One

There has long been speculation as to whether comets evolve into asteroidal objects. On the one hand, in the original version of the Oort (1950) hypothesis, the cometary cloud was supposed to have formed initially from the same material that produced the minor planets; and an obvious corollary was that the main physical difference between comets and minor planets would be that the latter had long since lost their icy surfaces on account of persistent exposure to strong solar radiation (Öpik, 1963). However, following a suggestion by Kuiper (1951), it is now quite widely believed that, whereas the terrestrial planets and minor planets condensed in the inner regions of the primordial solar nebula, icy objects such as comets would have formed more naturally in the outer parts, perhaps even beyond the orbit of Neptune (Cameron, 1962; Whipple, 1964a). Furthermore, recent studies of the evolution of the short-period comets indicate that it is not possible to produce the observed orbital distribution from the Oort cloud, even when multiple encounters with Jupiter are considered (Havnes, 1970). We must now seriously entertain the possibility that most of the short-period orbits evolved directly from low-inclination, low-eccentricity orbits with perihelia initially in the region between, say, the orbits of Saturn and Neptune, and that these comets have never been in the traditional cloud at great distances from the Sun.

scholarly journals Dynamics of Comets

1992 ◽  
Vol 152 ◽  
pp. 255-268 ◽  
Author(s):  
A. Carusi ◽  
G.B. Valsecchi
Keyword(s):  
Molecular Clouds ◽  
Vertical Component ◽  
The Sun ◽  
Giant Molecular Clouds ◽  
Mean Motion Resonances ◽  
Galactic Field ◽  
Mean Motion ◽  
Short Period ◽  
Gravitational Processes

The gravitational processes affecting the dynamics of comets are reviewed. At great distances from the Sun the motion of comets is primarily affected by the vertical component of the galactic field, as well as by encounters with stars and giant molecular clouds. When comets move in the region of the planets, encounters with these can strongly affect their motion. A good fraction of all periodic comets spend some time in temporary libration about mean motion resonances with Jupiter; some comets can be captured by this planet as temporary satellites. Finally, there is a small number of objects with orbital characteristics quite different from those of all other short-period comets.

scholarly journals The Polar Fields and Time Fluctuations of the General Magnetic Field of the Sun

1971 ◽  
Vol 43 ◽  
pp. 675-695 ◽  
Author(s):  
A. B. Severny
Keyword(s):  
Magnetic Field ◽  
Close Agreement ◽  
Present Knowledge ◽  
Short Time Scale ◽  
The Sun ◽  
Statistical Nature ◽  
General Magnetic Field ◽  
Short Period ◽  
The Mean ◽  
Short Time

In an attempt to summarize the present knowledge on the general magnetic field (gmf) of the Sun we pointed out the fine structure and the statistical nature of the gmf as one of its most important properties. The dipole-like behaviour of the mean polar field strengths is combined sometimes (since 1964) with a bias of the S-polarity flux for both poles. Highly uneven distribution of gmf with latitude and longitude, the disappearance of gmf at the South pole for months, and short period, almost synchronous at both poles, variations in the sign of gmf are pointed out. The fluctuations with time of the mean magnetic field of the Sun seen as a star (as well as mf at different latitudes) shows periodicity connected with the rotation of the Sun and very close agreement with the fluctuations of the interplanetary field (sector structure). The effect of faster rotation of N-polarities as compared with S-polarities as well as the bias of mean solar as well as interplanetary S-polarity fields are also pointed out. The possibility of short time-scale (hours) intrinsic changes in the local pattern of gmf is demonstrated.

scholarly journals Jupiter’s decisive role in the inner Solar System’s early evolution

2015 ◽  
Vol 112 (14) ◽  
pp. 4214-4217 ◽  
Author(s):  
Konstantin Batygin ◽  
Greg Laughlin
Keyword(s):  
Solar System ◽  
Dynamical Evolution ◽  
Decisive Role ◽  
Terrestrial Planets ◽  
The Sun ◽  
Mean Motion Resonances ◽  
The Earth ◽  
Short Period ◽  
Orbital Periods ◽  
Gas Drag

The statistics of extrasolar planetary systems indicate that the default mode of planet formation generates planets with orbital periods shorter than 100 days and masses substantially exceeding that of the Earth. When viewed in this context, the Solar System is unusual. Here, we present simulations which show that a popular formation scenario for Jupiter and Saturn, in which Jupiter migrates inward from a > 5 astronomical units (AU) to a ≈ 1.5 AU before reversing direction, can explain the low overall mass of the Solar System’s terrestrial planets, as well as the absence of planets with a < 0.4 AU. Jupiter’s inward migration entrained s ≳ 10−100 km planetesimals into low-order mean motion resonances, shepherding and exciting their orbits. The resulting collisional cascade generated a planetesimal disk that, evolving under gas drag, would have driven any preexisting short-period planets into the Sun. In this scenario, the Solar System’s terrestrial planets formed from gas-starved mass-depleted debris that remained after the primary period of dynamical evolution.

Design of Solar Tracker Based on Square Structure and Camera Device

2014 ◽  
Vol 672-674 ◽  
pp. 105-108
Author(s):  
Yan Liu ◽  
Jian Liu ◽  
Ying Wei Song ◽  
De Wei Zhao ◽  
Lin Zhao ◽  
...  
Keyword(s):  
Heating System ◽  
Solar Heating ◽  
The Sun ◽  
Photovoltaic Generation ◽  
Heating Systems ◽  
Solar Tracker

Solar tracker is an important part of photovoltaic generation and solar heating system. By solar tracker, the efficiency of solar utility can be significantly improved. Considering the camera device is widely applied in the photovoltaic generation and solar heating systems, based on the visual motoring equipment, a kind of solar tracker is designed. Using the proposed solar tracker, the height and the angle of the sun can be detected and be applied in solar tracker controller. Experiments show this design has relatively high accurate rate during a week’s period while the weather are partly cloudy or clear. It shows good application future in photovoltaic generation and solar heating industries.

scholarly journals Surface evolution in stable magnetic fields: the case of the fully convective dwarf V374 Peg

2010 ◽  
Vol 6 (S273) ◽  
pp. 460-464
Author(s):  
K. Vida ◽  
K. Oláh ◽  
Zs. Kővári
Keyword(s):  
Magnetic Field ◽  
Photometric Data ◽  
The Sun ◽  
Body Rotation ◽  
Active Nest ◽  
Poloidal Magnetic Field ◽  
Surface Evolution ◽  
Photometric Measurements ◽  
Time Changes ◽  
Short Time

AbstractWe present BV(RI)C photometric measurements of the dM4-type V374 Peg covering ~430 days. The star has a mass of ~0.28MSun, so it is supposed to be fully convective. Previous observations detected almost-rigid-body rotation and stable, axisymmetric poloidal magnetic field. Our photometric data agree well with this picture, one persistent active nest is found on the stellar surface. Nevertheless, the surface is not static: night-to-night variations and frequent flaring are observed. The flares seem to be concentrated on the brighter part of the surface. The short-time changes of the light curve could indicate emerging flux ropes in the same region, resembling to the active nests on the Sun. We have observed flaring and quiet states of V374 Peg changing on monthly timescale.

scholarly journals New Trends in the Discovery of Comets by Amateurs

1988 ◽  
Vol 98 ◽  
pp. 163-163 ◽  
Author(s):  
J.C. Merlin
Keyword(s):  
Strong Correlation ◽  
Considerable Proportion ◽  
The Sun ◽  
Long Period ◽  
Short Period

AbstractThe ways in which amateurs may increase their chances of discovering comets were described. Amateurs discover a considerable proportion of comets, but their contribution is greater among long-period comets. The relative proportions of short-period comets is revealing: 1 in 2 for professional astronomers, 1 in 8 for amateurs. Professional discoveries are largely a by-product of searches for asteroids: the comets have low inclinations (i < 30°) and are faint (m1 > 14). Amateurs are most successful in areas close (<60°) to the Sun. Typical apertures are 150-mm, and most comets are brighter than magnitude 10.Past results show that there is a strong correlation between number of observers and number of discoveries. Several amateurs have discovered comets at great elongations with larger telescopes (≥ 400 mm). The comets tend to be fainter (10 < m1 < 12). Several comets have been discovered with simple equipment (200- or 300-mm telephoto lenses) down to magnitude 13.Calculations of the distribution of discoverable comets show that an average of 14 comets (9 < m1 < 14) are missed per year.

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