Comet

"Ragnarok, The Age of Fire and Gravel, proposes that a comet impacted the Earth several tens of thousands of years ago; the impact produced the 'Drift' layers of gravel which have been attributed to the Ice ages; this event destroyed a civilization which had high technology, a civilization which vanished completely except for some myths; the disaster was accompanied by catastrophic fire followed by years-long cloud cover and extreme cold. Humanity survived only by hiding in deep caves; when they re-emerged they had to restart civilization from scratch." (From Introduction by J.B. Hare.)

A pathogen is defined as a bacterial, viral or other microbial agent that causes disease. It might therefore be a surprise that studies with a number of pathogens have, in recent years, yielded some of the most exciting new insights into the regulation of actin polymerization in the ...

Mega-tsunami have affected much of the coastline of Australia over the past millennium. Such catastrophic waves have left an imprint consisting predominently of bedrock sculpturing of the rocky coastline and deposition of marine sediments to elevations reaching 130 m above sea level. One of the largest of these events occurred in eastern Australia in the fifteenth century. This event may be related to the Mahuika impact crater found at 48.3 S, 166.4 E on the continental shelf 250 km south of New Zealand. A comet at least 500 m in diameter formed the crater. Maori and Aboriginal legends allude to significant cosmogenic events in the region, while Aboriginal legends about tsunami are common along the eastern Australian coast. Evidence for legends that could describe the impact of a cosmogenic tsunami also exists in NW Australia. Here geological evidence of a single mega-tsunami as recent as in the seventeenth century covers 1500 km of coastline. We term this event Wandjina after the a...

Time variations in velocities and relative amount of observed particles (mainly icy particles with diameter d<3 μm) ejected from Comet 9P/Tempel 1 are studied based on analysis of the images made by Deep Impact (DI) cameras during the first 13 minutes after the collision of the DI impactor with the comet. Analysis of maxima or minima of plots of the time variations in distances of contours of constant brightness from the place of ejection allowed us to estimate the characteristic velocities of particles at several moments in time te of ejection after impact for te≤115 s. Other approaches for estimates of the velocities were also used. All these estimates are in accordance with the same exponential decrease in velocity. The estimates of time variations in the relative amount of ejected particles were based also on results of the analysis of time variations in the size of the bright region of ejected material. At te~10 s, the morphology of the ejecta (e.g. the location and brightne...

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.

... Hughes (1979) has rightly criticized this theory (and withdrawn his own earlier theory, Hughes 1976) as having the 'almost insurmountable difficulty' that the star the Magi saw when they set out, and the star they saw in Jerusalem, should have been one and the same star not a ...

Time-variations in velocities and relative amount of observed particles (mainly icy particles with diameter d < 3 μm) ejected from Comet 9P/Tempel 1 are studied based on analysis of the images made by Deep Impact (DI) cameras during the first 13 min after the collision of the DI impactor with the comet. Analysis of maxima or minima of plots of the time-variations in distances of contours of constant brightness from the place of ejection allowed us to estimate the characteristic velocities of particles at several moments in time, t e , of ejection after impact for t e ≤ 115 s. Other approaches for estimates of the velocities were also used. All these estimates are in accordance with the same exponential decrease in velocity. The estimates of time-variations in the relative amount of ejected particles were also based on results of the analysis of time-variations in the size of the bright region of ejected material. At t e ∼ 10 s, the morphology of the ejecta (e.g. the location and brightness of the brightest pixel) changed and the rate, r te , of ejection of observed material increased. Between 1 and 3 s after the impact and between 8 and 60 s after the impact, more small bright particles were ejected than expected from crater excavation alone. An outburst triggered by the impact could cause such a difference. The sharp (by a factor of 1.6) decrease in the rate of ejection at 55 < t e < 72 s could be caused by a decrease in the outburst that began at 10 s. Analysis of observations of the DI cloud and of the outbursts from some comets testifies in favour of the proposition that there can be large cavities, with material under gas pressure, below a considerable fraction of a comet's surface. Internal gas pressure and material in the cavities can produce natural and triggered outbursts and can cause splitting of comets.

Context. The Rosetta spacecraft escorted Comet 67P/Churyumov-Gerasimenko for 2 yr along its journey through the Solar System between 3.8 and 1.24 au. Thanks to the high resolution mass spectrometer on board Rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time. Aims. Previous cometary missions, such as Giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. In contrast, the Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis on board Rosetta (ROSINA), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions. Methods. We calibrated and analysed the set of spectra acquired by DFMS in ion mode from October 2014 to April 2016. In particular, we focused on the range ...