Deep-sea Crusts Research Articles

An X-Ray-dim “Isolated” Neutron Star in a Binary?

We report the discovery of a dark companion to 2MASS J15274848+3536572 with an orbital period of 6.14 hr. Combining the radial velocity from LAMOST observations and modeling of the multiband light curve, one obtains a mass function of ≃0.131 M ⊙, an inclination of , and a mass ratio of , which demonstrate the binary nature of the dark companion with a mass of 0.98 ± 0.03M ⊙ and a main-sequence K9-M0 star of 0.62 ± 0.01 M ⊙. LAMOST optical spectra at a range of orbital phases reveal extra-peaked H α emission that suggests the presence of an accretion disk. The dark companion does not seem to be a white dwarf because of the lack of any observed dwarf nova outbursts in the long-term data archive, although a magnetic white dwarf cannot be excluded. Alternatively, we propose a scenario wherein the dark companion is a neutron star, but we have not detected radio pulsations or a single pulse from the system with the FAST (Five-hundred-meter Aperture Spherical radio Telescope), which hints at a radio-quiet compact object. If the dark companion is identified as a neutron star, it will be the nearest (∼118 pc) and lightest neutron star. Furthermore, kinematic analysis of the system’s orbit in the galaxy may suggest its supernova event is associated with the radionuclide 60Fe signal observed from deep-sea crusts. This radio-quiet and X-ray-dim nearby neutron star may resemble an XDINS (X-ray-dim isolated neutron star) but in a binary.

The Dyadic Radionuclide System 60Fe / 53Mn to Distinguish Interstellar from Interplanetary 60Fe

The discovery of live 60Fe in a deep-sea crust with proposed interstellar origin followed by evidence for elevated interplanetary 3He in the same crust raised the question on how to unambiguously identify the true production site of the identified 60Fe. Here, we show the implementation of the dyadic radionuclide system 60Fe / 53Mn to serve as a tool for the identification of surplus interstellar 60Fe over interplanetary production. The recent updates in experimental 60Fe and 53Mn data from iron meteorites as well as in production rate models confirm the validity and robustness of this dyadic system for future applications.

60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae.

Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust-iron-60 (60Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (244Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 million years and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.

Natural plutonium from supernovae

Nuclear Astrophysics The rapid neutron capture process (r-process) produces many of the heavy chemical elements, but the astrophysical settings where it occurs remain unclear. Leading candidates are neutron star mergers and some types of supernovae. Wallner et al. analyzed the plutonium content of a deep-sea crust sample, identifying a few dozen atoms of the r-process isotope plutonium- 244 that were delivered to Earth within the past few million years. There was a simultaneous signal of iron-60, which is known to be produced in supernovae. Comparing the ratios of these isotopes constrains the relative contributions of supernovae and neutron star mergers to r-process nucleosynthesis. Science , this issue p. [742][1] [1]: /lookup/doi/10.1126/science.aax3972

Interstellar Dust and Gas in the Heliosphere

Interstellar dust and gas that enter the heliosphere provide us with important clues about both the heliosphere and the local interstellar medium (LISM). The picture we have of the LIC from both in situ detections and absorption line data presents questions that have important implications for the origins and evolution of the cloud. New detections of 60Fe on Earth in deep sea crusts and Antarctic snow cores provide evidence for the role of supernovae in shaping the LISM. We discuss our models for the evolution of the LIC inside the Local Bubble and possible explanations for the source of the supernova produced dust.

Numerical studies on the link between radioisotopic signatures on Earth and the formation of the Local Bubble

The discovery of radionuclides like 60Fe with half-lives of million years in deep-sea crusts and sediments offers the unique possibility to date and locate nearby supernovae. We want to quantitatively establish that the 60Fe enhancement is the result of several supernovae which are also responsible for the formation of the Local Bubble, our Galactic habitat. We performed three-dimensional hydrodynamic adaptive mesh refinement simulations (with resolutions down to subparsec scale) of the Local Bubble and the neighbouring Loop I superbubble in different homogeneous, self-gravitating environments. For setting up the Local and Loop I superbubble, we took into account the time sequence and locations of the generating core-collapse supernova explosions, which were derived from the mass spectrum of the perished members of certain stellar moving groups. The release of 60Fe and its subsequent turbulent mixing process inside the superbubble cavities was followed via passive scalars, where the yields of the decaying radioisotope were adjusted according to recent stellar evolution calculations. The models are able to reproduce both the timing and the intensity of the 60Fe excess observed with rather high precision, provided that the external density does not exceed 0.3 cm-3 on average. Thus the two best-fit models presented here were obtained with background media mimicking the classical warm ionised and warm neutral medium. We also found that 60Fe (which is condensed onto dust grains) can be delivered to Earth via two physical mechanisms: either through individual fast-paced supernova blast waves, which cross the Earth's orbit sometimes even twice as a result of reflection from the Local Bubble's outer shell, or, alternatively, through the supershell of the Local Bubble itself, injecting the 60Fe content of all previous supernovae at once, but over a longer time range.

The locations of recent supernovae near the Sun from modelling 60Fe transport

The signature of (60)Fe in deep-sea crusts indicates that one or more supernovae exploded in the solar neighbourhood about 2.2 million years ago. Recent isotopic analysis is consistent with a core-collapse or electron-capture supernova that occurred 60 to 130 parsecs from the Sun. Moreover, peculiarities in the cosmic ray spectrum point to a nearby supernova about two million years ago. The Local Bubble of hot, diffuse plasma, in which the Solar System is embedded, originated from 14 to 20 supernovae within a moving group, whose surviving members are now in the Scorpius-Centaurus stellar association. Here we report calculations of the most probable trajectories and masses of the supernova progenitors, and hence their explosion times and sites. The (60)Fe signal arises from two supernovae at distances between 90 and 100 parsecs. The closest occurred 2.3 million years ago at present-day galactic coordinates l = 327°, b = 11°, and the second-closest exploded about 1.5 million years ago at l = 343°, b = 25°, with masses of 9.2 and 8.8 times the solar mass, respectively. The remaining supernovae, which formed the Local Bubble, contribute to a smaller extent because they happened at larger distances and longer ago ((60)Fe has a half-life of 2.6 million years). There are uncertainties relating to the nucleosynthesis yields and the loss of (60)Fe during transport, but they do not influence the relative distribution of (60)Fe in the crust layers, and therefore our model reproduces the measured relative abundances very well.

Recent near-Earth supernovae probed by global deposition of interstellar radioactive (60)Fe.

The rate of supernovae (SNe) in our local galactic neighborhood within a distance of ~100 parsec from Earth (1 parsec (pc)=3.26 light years) is estimated at 1 SN every 2-4 million years (Myr), based on the total SN-rate in the Milky Way (2.0±0.7 per century1,2). Recent massive-star and SN activity in Earth’s vicinity may be evidenced by traces of radionuclides with half-lives t1/2 ≤100 Myr3-6, if trapped in interstellar dust grains that penetrate the Solar System (SS). One such radionuclide is 60Fe (t1/2=2.6 Myr)7,8 which is ejected in supernova explosions and winds from massive stars1,2,9. Here we report that the 60Fe signal observed previously in deep-sea crusts10,11, is global, extended in time and of interstellar origin from multiple events. Deep-sea archives from all major oceans were analyzed for 60Fe deposition via accretion of interstellar dust particles. Our results, based on 60Fe atom-counting at state-of-the-art sensitivity8, reveal 60Fe interstellar influxes onto Earth 1.7–3.2 Myr and 6.5–8.7 Myr ago. The measured signal implies that a few percent of fresh 60Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ~10 Myr at nearby distances ≤100 pc.

Tracer-Based Estimates of Drilling-Induced Microbial Contamination of Deep Sea Crust

Keywords: Contamination Deep-BIOSPHERE Joides Resolution Ocean Drilling Program Leg 185 Oceanic Crust

Quaternary crusts on slopes of the Mediterranean Sea: A tentative explanation for their genesis

Quaternary deep-sea crusts, i.e. lithified omission surfaces, are widespread on slopes and subsea relief features in the Western and, especially, the Eastern Mediterranean Sea. The lithification is induced by the early precipitation of a magnesian calcite cement in the uppermost few centimetres of a calcareous ooze. Based on their thickness and degree of hardening, the collected samples have been divided into three main types, each of them corresponding to a different degree of lithification. Except in rare, probably old crusts collected at water depths below 2000–2500 m, and in infills of some sponge skeletons or in the case of inferred internal tension, recrystallization and (generally) mineral alterations are very limited. The precipitation mechanisms appear to be essentially physicochemically controlled, and ions involved in cementation come from the seawater reservoir by means of an inward diffusion of solutions. Diffusion is enhanced by bottom currents, these currents maintaining a low or zero rate of sedimentation. Moreover, lithification also depends on the chemical characteristics of the seawater; i.e. supersaturation with respect to low-magnesian calcite, and low contents of phosphates and dissolved organic matter which would inhibit crystal growth. Local factors and primary composition of the original sediment also appear to influence the speed of early lithification. When conditions of lithification are favourable, a few hundreds of years to a few thousand years at the most seem sufficient for the first two stages of lithification to be reached. The submarine lithification was active during the last glacial episode and, as exhibited by numerous samples, especially towards the end of this period. The previous cold stages were probably also episodes of efficient lithification. This correlation with Quaternary climatic cycles certainly reflects an intensification of thermohaline and bottom-current circulations during periods of severe climatic conditions. There is also some evidence of Holocene and even present-day crusts.

Tectonics, Bathymetry, and Geomagnetism of the Southern Continental Borderland West of Baja California, Mexico

Bathymetric and magnetic ship surveys of the southern continental borderland (the southern portion of a submarine province of ridges and basins west of northern Baja California) reveal the following structural features: (1) a fault zone trending south-southeast from Islas Los Coronados to Bahia Todos Santos, (2) southeast-northwest faults within the borderland, especially a trend toward San Clemente Island, (3) the Santo Tomas fault zone trending west-southwest across the borderland from Bahfa Soledad [(1), (2) (?), and (3) are associated with the continental Agua Blanca fault], (4) several east-west fault zones, (5) faults along the seaward margin of the borderland, (6) very large geomagnetic anomalies associated with the present coast line, (7) north-south geomagnetic anomalies in the deep-sea crust, (8) many minor faults, and (9) broad folding of the borderland. The recorded seismicity is associated only with the first three. Most (if not all) of the faults are observed or interpreted to dip steeply. Many are observed or interpreted to have large strike-slip components of displacement in addition to obvious dip-slip components. Heat-flow measurements by Von Herzen (1964) reveal that heat flow increases to the east and probably indirectly causes the strength of the crust under the borderland to diminish to half the strength of the oceanic crust to the west where heat flow is normal. This largely explains the severe deformation of the borderland crust relative to the oceanic crust. The high heat flow helps to explain the ubiquitous volcanic rocks. Isostatic computations suggest a test for determining some structure and history of the underlying mantle. The development of the continental borderland apparently began in the Mesozoic and reached its peak during the Miocene Epoch. It is still proceeding. The borderland results from a combination of many processes including right-lateral faulting between the oceanic basin and the continent plus east-west dilation.