Planetary tides and sunspot cycles

There is an empirical function of the heights of tides on the Sun produced by Venus, Earth, and Jupiter whose period is nearly equal to that of the 11-yr sunspot cycle (Wood, 1972). This period match has been used in suggestions that planetary tides cause sunspots and, indirectly, terrestrial climate changes and earthquakes. We derive the period of the tidal function in terms of the planetary orbital periods and show that it is artificially lengthened by aliasing. Furthermore, there exists a class of functions whose measure in frequency space is so great that, in the absence of a physical justification for preferring one member, no statistically significant period match can possibly be made with current sunspot data.     

Are Planetary Tides on the Sun and the Birthplace of Sunspots Related?

We study whether the birthplaces of sunspots (defined as the location of first appearance in the photosphere) are related to the planetary tides on the Sun. The heliocentric longitudes of newly emerging sunspots are statistically compared to the longitudes of tidal peaks caused by the tidal planets Mercury, Venus, Earth, and Jupiter. The longitude differences between new sunspots and tidal planets (and their conjugate locations) as well as the magnitudes of the vertical and horizontal tidal forces at the birthplace of new sunspots are calculated. The statistical distributions are compared with simulation results calculated using a random sunspot distribution. The results suggest that the birthplaces of sunspots (in the photosphere) are independent of the positions of tidal planets and the strength of tidal forces caused by them. However, since the sunspots actually originate near the tachocline (well below the photosphere) and it takes considerable time for the disturbances to reach photosphere, we hesitate to conclude that the formation of sunspots are not related to planetary positions.     

Mass loss from the region of Mars and the asteroid belt

Models of the solar nebula suggest that the mass of solid matter which condensed in the region of Mars and the asteroids was much greater than the amount now present. Bombardment by a primordial population of asteroidal bodies originating near Jupiter's orbit could preferentially remove matter from this region, without significant effects in the Earth's zone. A “critical velocity” exists, for which they can be ejected from the solar system by Jupiter. The minimum perihelion attainable at this velocity lies between the orbits of Mars and the Earth. The lifetimes of Mars-crossing bodies are limited by collisions with Jupiter; Earth-crossers are ejected on a much shorter time scale. The total bombardment flux was at least two orders of magnitude greater in the zone of Mars than in that of the Earth. The flux at Venus and Mercury from this source was negligible. The cratering rate for Mars may have differed greatly from those of the other terrestrial planets for a significant fraction of the age of the solar system.     

The mid-term and long-term solar quasi-periodic cycles and the possible relationship with planetary motions

This work investigates the solar quasi-periodic cycles with multi-timescales and the possible relationships with planetary motions. The solar cycles are derived from long-term observations of the relative sunspot number and microwave emission at frequency of 2.80 GHz. A series of solar quasi-periodic cycles with multi-timescales are registered. These cycles can be classified into three classes: (1) the strong PLC (PLC is defined as the solar cycle with a period very close to the ones of some planetary motions, named as planetary-like cycle) which is related strongly with planetary motions, including nine periodic modes with relatively short period (P<12 yr), and related to the motions of the inner planets and of Jupiter; (2) the weak PLC, which is related weakly to planetary motions, including two periodic modes with relatively long period (P>12 yr), and possibly related to the motions of outer planets; (3) the non-PLC, for which so far there has been found no clear evidence to show the relationship with any planetary motions. Among the planets, Jupiter plays a key role in most periodic modes due to its sidereal motion or spring tidal motions associated with other planets. Among planetary motions, the spring tidal motion of the inner planets and of Jupiter dominates the formation of most PLCs. The relationships between multi-timescale solar periodic modes and the planetary motions will help us to understand the essential nature and prediction of solar activities.     

Détermination quantitative de l'effect de phase dans la mesure des longitudes sur Jupiter

We have quantitatively determined the phase exaggeration effect (Phillips effect) as a function of the planet's phase angle for the correction of the longitude of spots on the Jupiter disk. This was done on the basis of over 1000 visual observations of the longitude of permanent details of Jupiter's surface compared with photographic observations. We also propose the existence of a systematic error (+0°.6 zenographic) in our visual observations. As this error is probably caused by unidirectional motion of the detail over the planetary disk, we named it the “shift effect”.     

Models of Jupiter and Saturn after Galileo mission

New models of Jupiter are based on observational data provided by the Galileo spaceprobe, which considerably improved previously existing estimates of the helium abundance in the atmosphere of Jupiter. These data yield for Jupiter’s atmosphere 20% of the solar oxygen abundance and do not agree with the results of the analysis of the collision of comet Shoemaker-Levy 9 with Jupiter (10 times the solar value). Therefore, both the models of Jupiter with water-depleted and water-enriched atmosphere are considered. By analogy with Jupiter, trial models of Saturn with a water-depleted external envelope are also developed. The molecular-metallic phase transition pressure of hydrogen P_m was taken to be 1.5, 2 and 3 Mbar. Since Saturn’s internal molecular envelope is noticeably enriched in the IR-component (its weight concentration, 0.25–0.30, being by a factor of 3–4 higher than in Jupiter), the phase transition pressure in Saturn can be lower than in Jupiter. In the constructed models, the IR-core masses are 3–3.5 M_⊕ for Jupiter and 3–5.5 M_⊕ for Saturn. Jupiter’s and Saturn’s IR-cores can be considered embryos onto which the accretion of the gas occurred during the formation of the planets. The mass of the hydrogen–helium component dispersed in the zone of planetary formation constitutes ≈2–5 planetary masses for Jupiter and ≈11–14 planetary masses for Saturn.     

Change in the orbital period of a binary system due to dynamical tides for main-sequence stars

We investigate the change in the orbital period of a binary system due to dynamical tides by taking into account the evolution of a main-sequence star. Three stars with masses of one, one and a half, and two solar masses are considered. A star of one solar mass at lifetimes t = 4.57 × 10⁹ yr closely corresponds to our Sun. We show that a planet of one Jupiter mass revolving around a star of one solar mass will fall onto the star in the main-sequence lifetime of the star due to dynamical tides if the initial orbital period of the planet is less than P _orb ≈ 2.8 days. Planets of one Jupiter mass with an orbital period P _orb ≈ 2 days or shorter will fall onto a star of one and a half and two solar masses in the mainsequence lifetime of the star.     

Metallicity of Sun-like G-stars that have Exoplanets

By considering the physical and orbital characteristics of G type stars and their exoplanets, we examine the association between stellar mass and its metallicity that follows a power law. Similar relationship is also obtained in case of single and multiplanetary stellar systems suggesting that, \(\hbox {Sun}^{\prime }\)s present mass is about 1% higher than the estimated value for its metallicity. Further, for all the stellar systems with exoplanets, association between the planetary mass and the stellar metallicity is investigated, that suggests planetary mass is independent of stellar metallicity. Interestingly, in case of multiplanetary systems, planetary mass is linearly dependent on the stellar absolute metallicity, that suggests, metal rich stars produce massive (\(\ge \)1 Jupiter mass) planets compared to metal poor stars. This study also suggests that there is a solar system planetary missing mass of \({\sim }\)0.8 Jupiter mass. It is argued that probably 80% of missing mass is accreted onto the Sun and about 20% of missing mass might have been blown off to the outer solar system (beyond the present Kuiper belt) during early history of solar system formation. We find that, in case of single planetary systems, planetary mass is independent of stellar metallicity with an implication of their non-origin in the host star’s protoplanetary disk and probably are captured from the space. Final investigation of dependency of the orbital distances of planets on the host stars metallicity reveals that inward migration of planets is dominant in case of single planetary systems supporting the result that most of the planets in single planetary systems are captured from the space.     

The distribution of sunspots over the Sun

The distribution of the sunspots for the period 1967–1987 (solar cycles 20 and 21) is presented here. We find that the ±11–20° latitude belt is most prolific for the occurrence of various spot types irrespective of magnetic-field ranges. Furthermore, longitudinally sunspots occur most prolifically at six or more places on the Sun. Spatially 7–9 zones are present in each hemisphere (north or south) of the Sun where about 50% sunspots occur and occupy only about 4% area of the Sun. During the above cycles at least 5 flare zones were regularly present in each hemisphere. The existing models cannot explain these active zones on the Sun. Thus, the present analysis emphasizes the need for a new magnetic models of the Sun.     

A search for the origin of very low electron temperatures

VLET's (Very Low Electron Temperature) are regions in the solar wind (lasting 12–30 h) in which the electron temperature is abnormally low. Because it is generally believed that the thermal conductivity parallel to the interplanetary magnetic field lines is high for electrons, i.e. the contact with the Sun should be ideal, VLET's are surprising observations. In this work a statistical analysis of many of these events is made with respect to the dependence of this phenomenon on interplanetary plasma and field parameters. In contrast with earlier work it was found that VLET's exist not only after a shock front. The statistical analysis showed further that a VLET is always associated with a VLPT (Very Low Proton Temperature) event and that, whilst on average the temperature of the electrons and protons outside the low temperature regions is about the same, the mean proton temperature inside is three times lower than that of the electrons.A particular model for VLET's is investigated in detail; the closed magnetic loop or “blob” model. By assuming: (a) pure adiabatic expansion in a radially streaming solar wind without pressure equalization across the “blob” boundary, and (b) rapid pressure equalization across the boundary, an attempt was made to quantitatively investigate the feasibility of the “blob” model in the light of plasma and field data. It can be shown that the closed magnetic loop model is unlikely to be the major cause of VLET's.     

Does Io have an ammonia atmosphere?

An atmosphere containing 0.5 cm atm of ammonia is assumed on Io. Such an atmosphere will be frozen at the unilluminated pole during the solstices, but will evaporate at the equinoctial seasons. The ammonia atmosphere will explain: (1) the posteclipse brightenings and their observed times of occurrence and nonocurrence; (2) the observed departure from a two-layer model beating curve upon emergence from eclipse; (3) the discordant temperatures obtained at 10 and 20 μm; and (4) discordant temperatures obtained at 10 and 20 μm during the total phase of an eclipse by Jupiter.In order to explain items 3 and 4 above, a proton flux in Jupiter's magnetosphere of 1.1 × 10⁹ cm^?2s^? at an energy of 0.5MeV at io's distance from Jupiter is assumed. This flux is 40 times the flux in Divine's (1972) “upper-limit” model of the Jovian radiation belts, while the proton energy is eight times less. The proton flux, plus the solar ultraviolet and infrared flux absorbed by the ammonia, will heat the atmosphere to 245 ± 10°K. At this temperature the occultation atmospheric upper limit allows the addition of 4 cmatm of nitrogen.     

Jupiter's outer atmosphere

The current state of the theory of Jupiter's outer atmosphere is briefly reviewed. The similarities and dissimilarities between the terrestrial and Jovian upper atmospheres are discussed, including the interaction of the solar wind with the planetary magnetic fields. Estimates of Jovian parameters are given, including magnetosphere and auroral zone sizes, ionospheric conductivity, energy inputs, and solar wind parameters at Jupiter. The influence of the large centrifugal force on the cold plasma distribution is considered. The Jovian Van Alien belt is attributed to solar wind particles diffused in towards the planet by dynamo electric fields from ionospheric neutral winds and consequences of this theory are given.     

A theoretical model of the bow shock and the magnetosphere of Jupiter

Using the data obtained from the Pioneer 10 and 11 observations, a theoretical model is proposed for the bow shock and the magentosphere of Jupiter. This indicates that the distance of the magnetopause from Jupiter on the sunlit side is (50–55) × r_J (r_J: Jupiter radius, = 7 × 10⁹ cm) and that the ratio of the stand-off distance to this distance is about equal to or slightly larger than unity. Hence the Mach number of the solar wind seems to be less than 1.5 at Jupiter's orbit. This result necessarily leads to a blunt body model of the Jovian magnetosphere, the tail region of which is not as extended as observed in the Earth's case.     

X-rays from solar system objects

During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at energies below 2 keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies.At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1–2 keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles.This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun. Processes of production of solar system X-rays are discussed and an overview is provided of the main source mechanisms of X-ray production at each object. A brief account on recent development in the area of laboratory studies of X-ray production is also provided.     

A former asteroidal planet as the origin of comets

The idea of a missing planet between Mars and Jupiter has been with us since the formulation of the Titius-Bode law. The discovery of the asteroid belt in that location led to speculation about a planetary breakup event. Both ideas remained conjectures until Ovenden's finding in 1972, from which it could be derived that the mass of the missing planet was about 90 Earth masses and that its breakup was astronomically recent. Apparently much of that mass was blown out of the solar system during the disruption of the planet. Because of the action of planetary perturbations, only two types of orbits of surviving fragments could remain at present-asteroid orbits and once-around very-long-period elliptical orbits. Objects in the latter type of orbit are known to exist-the very-long-period comets. A large number of these are on elliptical trajectories with periods of revolution of 5 million years; yet they are known to have made no more than one revolution in an orbit passing close to the Sun. By direct calculation it is possible to predict the distribution of the orbital elements of objects moving on long-period ellipses which might have originated in a breakup event in the asteroid belt 5 million years ago. The comet orbits have the predicted distribution in every case where a measure is possible. Some of the distribution anomalies, such as a bias in the directions of perihelion passage, are statistically strong and would be difficult to explain in any other uncontrived way. In addition, a relative deficiency of orbits with perihelia less than 1 AU indicates that the comets must have had small perihelion distances since their origin, rather than that they have been perturbed into small perihelion orbits from a distant “cloud” of comets by means of stellar encounters. The comet orbital data lead to the conclusion that all comets originated in a breakup event in the asteroid belt (5.5±0.6) × 10⁶ years ago. Asteroid and meteoritic evidence can now be interpreted in a way which not only is supportive but also provides fresh insights into understanding their physical, chemical, and dynamical properties. Particularily noteworthy are the young cosmic-ray exposure ages of meteorites, evidence of a previous high-temperature/pressure environment and of chemical differentiation of the parent body, and compositional similarities among comets, asteroids, and meteorites. Certain “explosion signatures” in asteroid orbital element distributions are likewise indicative. Tektites may also have originated in the same event; but if so, there are important implications regarding the absolute accuracy of certain geological dating methods. Little is known about possible planetary breakup mechanisms of the requisite type, though some speculations are offered. In any case, the asteroid belt is an existing fact; and the arguments presented here that a large planet did disintegrate 5 million years ago must be judged on their merits, even in the absence of a suitable theory of planetary explosions.     

Plasma interactions of exoplanets with their parent star and associated radio emissions

The relatively high contrast between planetary and solar low-frequency radio emissions suggests that the low-frequency radio range may be well adapted to the direct detection of exoplanets. We review the most significant properties of planetary radio emissions (auroral as well as satellite induced) and show that their primary engine is the interaction of a plasma flow with an obstacle in the presence of a strong magnetic field (of the flow or of the obstacle). Scaling laws have been derived from solar system planetary radio emissions that relate the emitted radio power to the power dissipated in the various corresponding flow–obstacle interactions. We generalize these scaling laws into a “radio-magnetic” scaling law that seems to relate output radio power to the magnetic energy flux convected on the obstacle, this obstacle being magnetized or unmagnetized. Extrapolating this scaling law to the case of exoplanets, we find that hot Jupiters may produce very intense radio emissions due to either magnetospheric interaction with a strong stellar wind or to unipolar interaction between the planet and a magnetic star (or strongly magnetized regions of the stellar surface). In the former case, similar to the magnetosphere–solar wind interactions in our solar system or to the Ganymede–Jupiter interaction, a hecto-decameter emission is expected in the vicinity of the planet with an intensity possibly 10³–10⁵ times that of Jupiter's low frequency radio emissions. In the latter case, which is a giant analogy of the Io–Jupiter system, emission in the decameter-to-meter wavelength range near the footprints of the star's magnetic field lines interacting with the planet may reach 10⁶ times that of Jupiter (unless some “saturation” mechanism occurs). The system of HD179949, where a hot spot has been tentatively detected in visible light near the sub-planetary point, is discussed in some details. Radio detectability is addressed with present and future low-frequency radiotelescopes. Finally, we discuss the interests of direct radio detection, among which access to exoplanetary magnetic field measurements and comparative magnetospheric physics.     

Sunspot and Auroral Activity During Maunder Minimum

The extremely low sunspot activity during the period of the Maunder minimum 1645–1715 was confirmed by group sunspot numbers, a new sunspot index constructed by Hoyt and Schatten (1998a,b). Neither sunspots nor auroral data time behavior indicate the presence of 11-year solar cycles as stated by Eddy (1976). The evidence for solar cycles was found in the butterfly diagram, constructed from observations made at Observatoire de Paris. After Clivier, Boriakoff, and Bounar (1998) the solar cycles were reflected also in geomagnetic activity. Results are supported by the variation of cosmogenic isotopes ¹⁰Be and ¹⁴C. The majority of the observed 14 naked-eye sunspots occurred on days when telescopic observations were not available. A part of them appeared in the years when no spot was allegedly observed. Two-ribbon flares appear in plages with only very small or no sunspots. Some of these flares are geoactive. Most aurorae (90%), which were observed during the Maunder minimum, appeared in years when no spot was observed. Auroral events as a consequence of proton flares indicate that regions with enhanced magnetic field can occur on the Sun when these regions do not produce any sunspots.     

Restricted problem stability and the solar system

Reference periodic orbits are determined accurately for the planets of the solar system, using a restricted problem model with the Sun and Jupiter as the two primaries. The prediction is verified that stability of the planetary orbits should imply stability of those reference orbits that are simple-periodic.     

Searching for nonsolar planets

Existing instruments are unable to detect planets about stars other than the Sun but such detection would be important for the theory of origin of our solar system and in the search for extraterrestrial intelligence. Infrared offers an advantage of about 10⁵ over visible light as regards the ratio of power received from star and planet. Infrared interferometry from Earth orbit would allow discrimination against the stellar infrared by the placement of an interference null on the star and a spinning infrared interferometer would modulate the planetary emission to permit extraction by synchronous detection from the background level. The limit to sensitivity will be set by thermal emission from the zodiacal light particles near the Earth's orbit unless the interferometer is launched out of the ecliptic or out to the orbit of Jupiter, in which case instrumental limitations will dominate. Technological developments in several fields will be required as also with astrometry, spectroscopic radial velocity measurement, and direct photography from orbit, three approaches with which infrared interferometry should be carefully compared.     

Solar wind interaction with interstellar helium

Solar wind interaction with neutral interstellar helium focused by the Sun's gravity in the downwind solar cavity is discussed in a hydrodynamical approach. Upon ionization the helium atoms “picked up” by the (single fluid) solar wind plasma cause a slight decrease in the wind speed and a corresponding marked temperature increase. For neutral helium density outside the cavity n_He^∞ = 0.01 atoms cm^?3 and for interstellar kinetic temperature T_He= 10,000 K, the reduction is speed of the solar wind on the downwind axis at 10 AU from the Sun amounts to about 2kms^?1; the solar wind temperature excess attains 7000 K. The resulting pressure excess leads to a non-radial flow of the order of 0.25 km s^?1. The possibility of experimental confirmation is discussed.