22 research outputs found
Upper atmospheres and ionospheres of planets and satellites
The upper atmospheres of the planets and their satellites are more directly
exposed to sunlight and solar wind particles than the surface or the deeper
atmospheric layers. At the altitudes where the associated energy is deposited,
the atmospheres may become ionized and are referred to as ionospheres. The
details of the photon and particle interactions with the upper atmosphere
depend strongly on whether the object has anintrinsic magnetic field that may
channel the precipitating particles into the atmosphere or drive the
atmospheric gas out to space. Important implications of these interactions
include atmospheric loss over diverse timescales, photochemistry and the
formation of aerosols, which affect the evolution, composition and remote
sensing of the planets (satellites). The upper atmosphere connects the planet
(satellite) bulk composition to the near-planet (-satellite) environment.
Understanding the relevant physics and chemistry provides insight to the past
and future conditions of these objects, which is critical for understanding
their evolution. This chapter introduces the basic concepts of upper
atmospheres and ionospheres in our solar system, and discusses aspects of their
neutral and ion composition, wind dynamics and energy budget. This knowledge is
key to putting in context the observations of upper atmospheres and haze on
exoplanets, and to devise a theory that explains exoplanet demographics.Comment: Invited Revie
Earth: Atmospheric Evolution of a Habitable Planet
Our present-day atmosphere is often used as an analog for potentially
habitable exoplanets, but Earth's atmosphere has changed dramatically
throughout its 4.5 billion year history. For example, molecular oxygen is
abundant in the atmosphere today but was absent on the early Earth. Meanwhile,
the physical and chemical evolution of Earth's atmosphere has also resulted in
major swings in surface temperature, at times resulting in extreme glaciation
or warm greenhouse climates. Despite this dynamic and occasionally dramatic
history, the Earth has been persistently habitable--and, in fact,
inhabited--for roughly 4 billion years. Understanding Earth's momentous changes
and its enduring habitability is essential as a guide to the diversity of
habitable planetary environments that may exist beyond our solar system and for
ultimately recognizing spectroscopic fingerprints of life elsewhere in the
Universe. Here, we review long-term trends in the composition of Earth's
atmosphere as it relates to both planetary habitability and inhabitation. We
focus on gases that may serve as habitability markers (CO2, N2) or
biosignatures (CH4, O2), especially as related to the redox evolution of the
atmosphere and the coupled evolution of Earth's climate system. We emphasize
that in the search for Earth-like planets we must be mindful that the example
provided by the modern atmosphere merely represents a single snapshot of
Earth's long-term evolution. In exploring the many former states of our own
planet, we emphasize Earth's atmospheric evolution during the Archean,
Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of
potential atmospheric trajectories into the distant future, many millions to
billions of years from now. All of these 'Alternative Earth' scenarios provide
insight to the potential diversity of Earth-like, habitable, and inhabited
worlds.Comment: 34 pages, 4 figures, 4 tables. Review chapter to appear in Handbook
of Exoplanet
Testing common habitat-based surrogates of invertebrate diversity in a semi-arid rangeland
Habitat-based surrogates are a low cost alternative to intensive biodiversity surveys, though they have been poorly investigated in semi-arid ecosystem compared to others such as temperate woodlands. In this study we tested potential habitat-based surrogates of invertebrate richness in a semi-arid rangeland in northwest Australia. Potential surrogates were: distance from artificial watering-point; soil hardness; habitat complexity; and individual complexity components. Generalised additive models (GAMs) were used to relate abundance and richness of selected invertebrates with environmental factors and cluster analysis was used to examine similarity in species composition. The most frequently selected factor was soil hardness, but taxa varied as to whether biodiversity was higher in soft or hard soils. Where distance from watering-point was an important predictor, there were generally higher abundances and richness closer to watering-points than further away. Abundance and species richness could be partially explained using individual complexity components, but relationships were weak and there were no consistent trends among taxa. Therefore, although habitat complexity has been correlated with species richness under some circumstances, our results cast doubt on the generality of this relationship. There are also dangers in assuming that all taxa respond in a manner similar to indicator taxa, as we observed that different taxa had higher richness at opposite extremes of some environmental gradients. Grazing may have a negative impact on biodiversity in some environments, but in regions where water is limiting, the net effect may be positive due to the creation of waterholes
Piezonuclear fission reactions: evidences from microchemical analysis, neutron emission, and geological transformation
Neutron emission measurements, by means of He3 devices and bubble detectors, were performed during three different kinds of compression tests on brittle rocks: (1) under monotonic displacement control, (2) under cyclic loading, and (3) by ultrasonic vibration. The material used for the tests was Luserna Stone. Since the analyzed material contains iron, our conjecture is that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. This hypothesis is confirmed by the direct evidence of energy dispersive X-ray spectroscopy tests conducted on Luserna Stone specimens. It is also interesting to emphasize that the anomalous chemical balances of the major events that have affected the geomechanical and geochemical evolution of the Earth's crust should be considered as an indirect evidence of the piezonuclear fission reactions considered abov