Lake District pioneers – the earliest footprints on land

New evidence reveals that the first arthropods colonized dry land over 450 million years ago, more than 20 million years before the appearance of vascular plants. Traditionally, it was thought that animals only emerged on to land after plants had become established, thus providing a plentiful new food source. The earliest known terrestrial trace fossils occur in volcanogenic sediments from the English Lake District. The trace fossils are thought to have been made on land by a small millipede-like creature. These rocks contain no other fossils.     

The luminosity function and surface brightness distribution of H i selected galaxies

We measure the     B -band optical luminosity function (LF) for galaxies selected in a blind H  i survey. The total LF of the H  i selected sample is flat, with Schechter parameters     and     , in good agreement with LFs of optically selected late-type galaxies. Bivariate distribution functions of several galaxy parameters show that the H  i density in the local Universe is more widely spread over galaxies of different size, central surface brightness and luminosity than the optical luminosity density is. The number density of very low surface brightness (LSB ) (>24.0 mag arcsec⁻²) gas-rich galaxies is considerably lower than that found in optical surveys designed to detect dim galaxies. This suggests that only a part of the population of LSB galaxies is gas-rich and that the rest must be gas-poor. However, we show that this gas-poor population must be cosmologically insignificant in baryon content. The contribution of gas-rich LSB galaxies (>23.0 mag arcsec⁻²) to the local cosmological gas and luminosity density is modest     and     per cent respectively); their contribution to Ω_matter is not well-determined, but probably <11 per cent. These values are in excellent agreement with the low redshift results from the Hubble Deep Field.     

Upper Devonian tetrapod palaeoecology in the light of new discoveries in East Greenland

For the first time, new material of one of the world's oldest known tetrapods, Acanthostega, has been studied in its sedimentological context. The reported evidence suggests that Acanthostega was primarily aquatic and inhabited active fluvial channels in fluvial-dominated environments.     

Results from the Eso Large Program on Transneptunian Objects and Centaurs

BVRI photometry of 107 TNOs and Centaurs establishes the range of spectral gradients to be between –5 to 55%/100 nm (with one exception). A cluster of very red Cubewanos is firmly identified in orbits of low inclination and eccentricity beyond 40 AU from the Sun. Further correlations between surface colours and dynamical parameters (inclination and perihelion distance) are suggested for Cubewanos and scattered disk objects, but lack complete confidence for their reality. Plutinos and Centaurs do not show any clear correlation between surface colours and orbital parameters. We present in this paper 12 spectra obtained in the visible region and nine of them for which we obtained also near infrared spectra up to 2.4 microns. A few other objects have been observed, but the data are still under reduction and analysis. The principal reported results obtained are: (i) a wide range of visible slopes; (ii) evidence for surface variations on 2001 PT₁₃; and (iii) possible detection of few percent of water ice (1999 TC_36}, 2000 EB₁₇₃, 1999 DE₉, 2001 PT₁₃, 2000 QC₂₄₃, 1998 SG₃₅).     

Analyses of the chondritic meteorite Orvinio (H6): Insight into the origins and evolution of shocked H chondrite material

Abstract— We have studied the petrography, reflectance spectra, and Ar‐Ar systematics of the Orivinio meteorite. Orvinio is an H chondrite not an L chondrite as sometimes reported. The material in the meteorite was involved in several impact events. One impact event produced large swaths of impact melt from H chondrite material surrounding relict clasts of chondrule‐bearing material. Not only were portions of a bulk H chondrite planestesimal melted during the impact event, but shock redistribution of metal and sulfide phases in the meteorite dramatically altered its reflectance spectra. Both the melt and relict clasts are darker than unshocked H chondrite material, bearing spectral similarities to some C‐class asteroids. Such shock metamorphism, which lowers the albedo of an object without increasing its spectral slope, may partially explain some of the variation among S‐class asteroids and some of the trends seen on asteroid 433 Eros. Noble gases record the evidence of at least two, and perhaps three, impact events in the meteorite and its predecessor rocks. The most significant evidence is for an event that occurred 600 Ma ago or less, perhaps ?325 Ma ago or less. There is also a signature of 4.2 Ga in the Ar‐Ar systematics, which could either reflect complete degassing of the rock at that time or partial degassing of even the most retentive sites in the more recent event.     

X-ray Emission from the Pre-Main Sequence Systems FU Orionis and T Tauri

We present new results from recent X-ray observations of the accreting pre-main sequence stars FU Orionis and T Tauri. XMM-Newton observations of the close binary system FU Ori reveal an unusual X-ray spectrum consisting of a cool moderately-absorbed component and a hot component viewed through much higher absorption. The two components thus originate in physically distinct regions. The double absorption spectrum is qualitatively different than observed in typical coronal sources and may signal either non-coronal emission or separate unresolved X-ray contributions from more than one star in the system. High-resolution Chandra imaging of the T Tau triple system shows that its X-ray emission is dominated by the optically-revealed northern component T Tau N. X-ray spectra of T Tau obtained with XMM can be acceptably fitted with a moderately absorbed two-temperature thermal plasma model. Its spectral properties are similar to those seen in coronal X-ray sources.     

Arsenic and mercury contamination in 31 cores taken in 1965, St. Anna Trough, Kara Sea, Arctic Ocean

 Several cores of 31 collected in 1965 in the St. Anna Trough, Kara Sea, have very high concentrations of Hg and As in surface/near-surface samples. Mercury contents range from 94 to 3915 ppb with a mean of 444 ppb and a baseline value of 314 ppb. Arsenic contents range from 5 to 710 ppm with a mean of 51 ppm and a baseline value of 23 ppm. The Hg and part of the As loading is likely anthropogenic from industrial activities in Siberia via atmospheric emission and deposition onto catchments. This is followed by mobilization into fluvial systems and is added to by industrial effluent discharge. Post-depositional diagenesis from depth in the cores contributes to high As values. A north-flowing bottom current transports Hg- and As-bearing suspended material from the Ob River sea discharge zone to depositional environments in the St. Anna Trough. Dumping of military materials and other wastes into the Kara Sea from the late 1940s to 1991 has likely added to Hg and As loading in the trough sediments. The bioavailability of mercury from suspended materials may be the reason why higher than normal levels of these potentially toxic elements are found in European Arctic seabirds, ringed seal and polar bear. Received: 12 December 1999 · Accepted: 23 May 2000     

Probing the dark ages with the Square Kilometer Array

The epoch of reionization (EoR) sets a fundamental benchmark in cosmic structure formation, corresponding to the formation of the first luminous objects that act to ionize the neutral intergalactic medium (IGM). Recent observations at near-IR and radio wavelengths imply that we are finally probing into this key epoch of galaxy formation at z 6. The Square Kilometer Array (SKA) will provide critical insight into the EoR, in a number of ways. First, the ability of the SKA to image the neutral IGM in 21-cm emission is a truly unique probe of the process of reionization, and is recognized as the next necessary and fundamental step in our study of the evolution of large scale structure and cosmic reionization. Second, study of HI 21-cm absorption toward the first radio loud objects probes small to intermediate scale structure in the neutral ‘cosmic web’, as well as HI in the first collapsed structures (proto-disks and mini-halos). And third, the incomparable sensitivity of the SKA allows for the study of the molecular gas, dust, and star formation activity in the first galaxies, as well as the radio continuum emission from the first accreting massive black holes. Such objects will be obscured at optical wavelengths due to absorption by the neutral IGM.     

Mass anomalies on Ganymede

Radio Doppler data, generated with NASA's Galileo spacecraft during its second encounter with Jupiter's moon Ganymede, are used to infer the locations and magnitudes of mass anomalies on Ganymede. We construct models for both surface and buried anomalies. With only one flyby and no global coverage, a solution for mass anomalies cannot be uniquely determined. However, we are able to constrain acceptable solutions for mass anomalies to four broad regions—a near polar region and three that are roughly equatorial. If the mass anomalies are constrained to lie at the surface, the centers of the regions are located near the coordinates (77° N, 333° W), (36° N, 0° W), (33° N, 130° W), and (7° N, 194° W). If the mass anomalies are located at the deep ice-rock interface 800 km below the surface, the regions' centers are approximately (65° N, 17° W), (32° N, 30° W), (37° N, 175° W), and (15° N, 211° W). For both models, the regions are up to a few thousand kilometers across. The magnitude of mass anomalies on the surface is on the order of 10¹⁷ kg. Mass anomalies at the ice-rock interface are on average no more than an order of magnitude larger (10¹⁸ kg). There are two positive and two negative mass anomalies in both the surface and ice-rock interface models. One of the positive mass anomalies at the surface is associated with Galileo Regio. The other positive surface mass anomaly is located at high northern latitudes with no obvious geological association. Negative surface mass anomalies lie near Uruk Sulcus and between Perrine Regio and Barnard Regio near Sicyan Sulcus and Phrygia Sulcus. The locations of the ice-rock interface mass anomalies lie approximately radially below the surface anomalies. Positive mass anomalies at the surface could be associated with the silicate-rich ice or accumulated silicate layers of the dark regions. Negative mass anomalies at the surface could be associated with the relatively clean, low-lying ice of sulci. Alternatively, Ganymede's mass anomalies could be associated with the topography or other mass concentrations at the deep ice-rock interface.