ELECTRICITY DEREGULATION: WHAT'S IN STORE FOR THE ENVIRONMENT?

We test the: degree to which electricity consumers will trade off price and environmental attributes, effectiveness of environmental certification, and effectiveness of voluntary versus mandatory environmental disclosure. The type and consistency of information, the degree of difference in environmental attributes and the individual's characteristics all impact the choice of electricity product.Environmental Economics and Policy,

Lifetime of cm-sized zodiacal dust from the physical and dynamical evolution of meteoroid streams

peer reviewedWhile comets eject mass mostly at cm-sizes and larger, that size range of particles is mostly absent from the interplanetary medium. Such particles are thought to be lost from the solar system by grain-grain collisions. Here, we investigate the lifetime of cm-sized meteoroids from their abundance in meteoroid streams of different age. For 487 streams, we measured the orbital element dispersions, the magnitude size distribution index, the ratio of fluffy and dense materials in the stream and their bulk densities, and the meteor light curve shape-parameter. We find that older long-period comet meteoroid streams tend to be more dispersed and evolve towards smaller semi-major axis, higher magnitude size distribution index, and contain relatively more high-density material. Meteoroids that approach the Sun closer than 0.2-0.3 AU are mostly young and composed of denser materials poor in sodium. We compare the observed properties of the streams to age estimates from the literature and to a set of new age estimates for long-period comet streams based on observed dispersions. We find that streams broaden with age inversely proportional to the perihelion distance (q). By selecting narrow ranges of age, we find that their magnitude distribution index changes proportional to 1/√q, less steep than expected from meteoroid destruction by collisions. Instead, this shallow dependence suggests a lifetime inversely proportional to the peak grain temperature along its orbit, with the lifetime limited by thermal stresses if 0.3 < q < 1.02 AU and by sublimation if q < 0.2 AU

Properties of outer solar system pebbles during planetesimal formation from meteor observations

peer reviewedObservations of proto-planetary disks, as well as theoretical modeling, suggest that in the late stages of accretion leading up to the formation of planetesimals, particles grew to pebbles the size of 1-mm to tens of cm, depending on the location and ambient conditions in the disk. That is the same size range that dominates the present-day comet and primitive asteroid mass loss. Meteoroids that size cause visible meteors on Earth. Here, we hypothesize that the size distribution and the physical and chemical properties of young meteoroid streams still contain information about the conditions in the solar nebula during these late stages of accretion towards planetesimal formation. If so, they constrain where long-period (Oort Cloud) comets, Jupiter-family (Scattered Disk Kuiper Belt) comets, and primitive asteroids (Asteroid Belt) formed. From video and visual observations of 47 young meteor showers, we find that freshly ejected meteoroids from long-period comets tend to have low bulk density and are distributed with equal surface area per log-mass interval (magnitude distribution index χ ∼ 1.85), suggesting gentle accretion conditions. Jupiter-family comets, on the other hand, mostly produce meteoroids twice as dense and distributed with a steeper χ ∼ 2.15 or even χ ∼ 2.5, which implies that those pebbles grew from particles fragmenting in a collisional cascade or by catastrophic collisions, respectively. Some primitive asteroids show χ > 2.5, with most mass in small particles, indicating an even more aggressive fragmentation by processes other than mutual collisions. Both comet populations contain an admixture of compact materials that are sometimes sodium-poor, but Jupiter-family comets show a higher percentage (∼8% on average) than long-period comet showers (∼4%) and a wider range of percentages among comets. While there are exceptions in both groups, the implication is that most long-period comets formed under gentle particle growth conditions, possibly near the 30 AU edge of the Trans Neptunian Disk, while most Jupiter family comets formed closer to the Sun where pebbles reached or passed the fragmentation barrier, and primitive asteroids formed in the region where the cores of the giant planets formed. This is possible if the Scattered Disk represents all objects scattered by Neptune during its migration, while the present-day outer Oort cloud formed only during and after the time of the planet instability, well after the Sun had moved away from sibling stars

ELECTRICITY DEREGULATION: WHAT'S IN STORE FOR THE ENVIRONMENT?

We test the: degree to which electricity consumers will trade off price and environmental attributes, effectiveness of environmental certification, and effectiveness of voluntary versus mandatory environmental disclosure. The type and consistency of information, the degree of difference in environmental attributes and the individual's characteristics all impact the choice of electricity product

Meteor showers from known long-period comets

peer reviewedWhat long-period comets with orbital periods >250 years cause detectable meteor showers on Earth? Low-light video cameras are used to track the motion of +4 to -5 magnitude meteors in our atmosphere by triangulation and calculate the meteoroid orbit in space. In recent years, the CAMS (Cameras for Allsky Meteor Surveillance) low-light video camera network was greatly expanded and, together with other video networks, now has increased the total video meteoroid orbit database to over 2.2 million orbits. Here, we searched this database for meteor showers associated with known long-period comets. Previously, five associations were known. Now, we find 14, as well as six uncertain but likely associations. These showers show a change of longitude of perihelion with node that is a strong function of inclination. Showers of longer duration show a steeper magnitude distribution index, presumably due to aging of the meteoroid population. Showers are generally detected only if the orbital period of the comet is less than 4000 years and the Earth-Comet orbital miss distance is ≤0.10 AU. The lack of an associated meteor shower sets lower limits on the orbital period of poorly observed comets