On the rate of ancient meteoroidal flux: Studies of the pre-mare crater population on the Moon

According to radiometric dating of lunar rocks, meteoroidal bombardment and accompanying cratering on the Moon were intensive in the first 0.7×10⁹ y, the so-calledterra stage. Recently the hypothesis of a terminal cataclysm has been gaining acceptance, meaning that a sharp increase in the bombardment followed by a steep decay occurred at the end of theterra stage.The purpose of this paper is to investigate possible variations in the intensity of the bombardment during theterra stage by analyzing the population of large (3–1000 km)terra craters and comparing it with results obtained by theoretical models. The proportion of fresh craters is specifically used.Observational data were obtained by studying the craters on an oldterra surface photographed by Zond 8 and/or covered by LTO and LM maps and by conducting a statistical study of theterra listed in the Lunar and Planetary Laboratory Catalog. Mathematical models were developed in such a way as to make them dimensionless, and as such applicable even without the knowledge of the physical constants and variables involved. Particularly powerful is the method of measuring time as multiples of the average lifetime of a crater of that size.The following conclusions and/or interpretations are reached. (1) A crater remains fresh for less than 20% of the average life of a crater of that size. (2) A condition of equilibrium (i.e., on the average, a new impact does not cause a net increase in the total number of craters) is reached or almost reached on lunarterrae. (3) The age of theterra surface is more than three average lifetimes of the 2 km to at least 20 km size craters (4) The observedterra crater population isnot the result of two cataclysms, one at the beginning of the stage and one at the end. (5) This population, however, could be the result of a constant or slowly decaying flux continuing until the end of the stage, when the terminal cataclysms occurred. This sequence of events cannot be proven or disproven. (6) If no terminal cataclysm occurred, then the meteoroidal flux during theterra stage was slowly decaying or constant. (7) The formation of all the large multi-ringed basins essentially contemporaneously is doubtful.     

Auroral recombination of N and O: A possible source for emission in the γ and δ bands of NO

Radiative recombination of N and O provides a significant source for auroral emission in the γ and δ bands of NO with selective population of vibrational levels in the A²Σ⁺ and C²Π states. This mechanism may account for emissions detected near 2150 Å. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 10⁸ cm^?1 near 140 km in an IBC III aurora. The corresponding density for N is about 5 × 10⁷cm^?3 and the concentration ratio $\text{NO}{}^{\mathrm{+}}\text{O}{}_2{}^{\mathrm{+}}$ has a value of about 5.5.     

The Jovian surface condition and cooling rate

A theory which is almost fully analytic is used to investigate Jupiter's cooling rate. We find that a simple model of contraction with adiabatic interior structure gives a total cooling time to the present which is in good agreement with the age of the solar system. The interplay between the surface condition and the cooling rate is exhibited and discussed. The current rate of change of the effective temperature is calculated to be ?1°K/0.145×10⁹ yr. Discrepancies with fully numerical investigations of the Jovian age and cooling rate are noted.     

Photochemistry of nitrogen in the Martian atmosphere

Models are developed for the photochemistry of a CO₂H₂ON₂ atmosphere on Mars and estimates are given for the concentrations of N, NO, NO₂, NO₃, N₂O₅, HNO₂, HNO₃, and N₂O as a function of altitude. Nitric oxide is the most abundant form of odd nitrogen, present with a mixing ratio relative to CO₂ of order 10^?8. Deposition rates for nitrite and nitrate minerals could be as large as 3× 10⁵ N equivalent atoms cm^?2 sec^?1 under present conditions and may have been higher in the past.     

Torsional waves on the Sun and the activity cycle

Some properties of the recently-discovered torsional oscillations of the Sun are presented. The detailed relation of this velocity feature to magnetic activity gives evidence that these motions represent a fundamental oscillation within the Sun that is responsible for the solar activity cycle and that they are not a natural consequence of an - dynamo. A new torsional oscillation with wave number 1 hemisphere^–1 is demonstrated to exist on the Sun.     

Unusual coronal activity following the flare of 6 November 1980

For almost 30 hr after the major (gamma-ray) two-ribbon flare on 6 November 1980, 03:30 UT, the Hard X-Ray Imaging Spectrometer (HXIS) aboard the SMM satellite imaged in > 3.5 keV X-rays a gigantic arch extending above the active region over the limb. Like a similar configuration on 22 May 1980, this arch formed the lowest part of a stationary post-flare radio noise storm recorded at metric wavelengths at Nançay and Culgoora. 6.5 hr after the flare a coronal region below the arch started quasi-periodic pulsations in X-ray brightness, observed by several SMM instruments. These brightness variations had no response in the chromosphere (H), very little in the transition layer (O v), but they clearly correlated with similar variations in brightness at 169 MHz. There were 13 pulses of this kind, with apparent periodicity of about 20 min, until another flare occurred in the active region at 15:00 UT. All the brightenings appeared within a localized area of about 30000 km² in the northern part of the active region, but they definitely did not occur all at the same place.The top of the X-ray arch, at an altitude of 155 000 km, was continuously and smoothly decaying, taking no part in the striking variations below it. Therefore, the area variable in brightness does not seem to be the footpoint of the arch, as we supposed for similar variations on 22 May. More likely, it is a separate region connected directly with the source of the radio storm; particles accelerated in the storm may be dumped into the low corona and cause the X-ray enhancements. The X-ray arch was enhanced by two orders of magnitude in 3.5–5.5 keV X-ray counts and the temperature increased from 7.3 × 10⁶ to 9 × 10⁶ K when the new two-ribbon flare occurred at 15:00 UT. Thus, it is possible that energy is brought into the arch via the upper parts of the reconnecting flare loops - a process that can continue for hours.     

TREK: A cosmic-ray experiment on the Russian space station MIR

The goals of the TREK experiment, now in place on the MIR Space Station, are to resolve and measure the composition of both odd-Z and even-Z cosmic-ray nuclei up to uranium, to measure the isotopic composition of Fe-group nuclei, and to search for transuranic nucleic and exotic particles such as strangelets. To collect tracks of ultraheavy cosmic rays, exterior panels holding an array of BP-1 phosphate glass 1.2m² in area and 16 plates thick are now mounted outside the Kvant-2 module on MIR. Heaters and relays regulate the temperature of the glass at 25°±5°C. The detectors will record 10³ cosmic-ray tracks withZ50 during 2.5 years. An interior panel consisting of an array 0.09 m² in area and 32 plates thick and mounted on the inside wall of the Soyuz spacecraft (attached to the Space Station) will collect tracks of about 13000 Fe and 500 Ni nuclei.     

Re-analysis of close binary systems

Line-forming regions around close binaries with strong winds ( /4r _* v 10^–4 g cm^–2) are large in extent compared with the stars, large enough to screen them. Their orbitally-modulated Doppler shifts can overestimate the mass function, because of a larger rotational lever arm. In particular, most of the black-hole candidates need not involve companions more massive than a neutron star.The solar-wind problem is reconsidered. An extrapolation to Wolf-Rayet stars suggests that their winds are centrifugally driven. Their mass-loss rates tend to have been overestimated.Seemingly single (massive) stars can hide a (compact) companion.     

The resolution of the compact core of quasars and active galaxies with the gravitational lens effect

The central energy source of quasars and active galactic nuclei cannot be resolved by observation. When such a compact source is affected by gravitational micro-lensing (lensing of stars in a distant galaxy), brightness changes of the order of magnitudes may occur. Since it is an eclipse-like effect, it gives the possibility of calculating the one-dimensional source profile from the lightcurve. We present the method and the results of its application on simulated lightcurves. It should be possible to obtain information on the structure of the source on a scale smaller than 10^–3 pc. The micro gravitational lens effect gives, therefore, the only known possibility of observing directly the central energy source of quasars and active galactic nuclei.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Diffuse extragalactic gamma-radiation above ‘black-body cutoff’

The possible contribution of gamma-rays predicted within the universal cosmic-ray (CR) hypothesis to the energy range of CR spectrum above black-body cutoff is calculated. These gamma-rays arise from the relativistic electromagnetic cascade generated in the field of microwave background radiation (MBR). The ultra-high energy photons and electrons that initiate the cascade are produced at the decay of -mesons created in interactions of photons with the MBR. Simple analytic expression for cascade gamma-ray spectrum is obtained from the solution of kinetic equations for electrons and photons as well as for protons propagating in the MBR field. It is shown that at certain values of magnetic field and radio-wave density in the intergalactic space te flux of cascade gamma-rays may at least partly mask the black-body cutoff in the CR spectrum.Deceased, August 13, 1989.