Transfer of Rocks Between Planetary Systems: Panspermia Revisited

Motivated by the recent discovery of interstellar objects passing through the solar system, and by recent developments in dynamical simulations, this article reconsiders the likelihood for life-bearing rocks to be transferred from one planetary system to another. The astronomical aspects of this lithopanspermia process can now be estimated, including the cross sections for rock capture, the velocity distributions of rocky ejecta, the survival times for captured objects, and the dynamics of the solar system in both its birth cluster and in the field. The remaining uncertainties are primarily biological, that is, the probability of life developing on a planet, the time required for such an event, and the efficiency with which life becomes seeded in a new environment. Using current estimates for the input quantities, we find that the transfer rates are enhanced in the birth cluster, but the resulting odds for success are too low for panspermia to be a likely occurrence. In contrast, the expected inventory of alien rocks in the solar system is predicted to be substantial (where the vast majority of such bodies are not biologically active and do not interact with the Earth).

A giant planet candidate transiting a white dwarf

Astronomers have discovered thousands of planets outside the Solar System¹, most of which orbit stars that will eventually evolve into red giants and then into white dwarfs. During the red giant phase, any close-orbiting planets will be engulfed by the star², but more distant planets can survive this phase and remain in orbit around the white dwarf^3,4. Some white dwarfs show evidence for rocky material floating in their atmospheres⁵, in warm debris disks^6-9 or orbiting very closely^10-12, which has been interpreted as the debris of rocky planets that were scattered inwards and tidally disrupted¹³. Recently, the discovery of a gaseous debris disk with a composition similar to that of ice giant planets¹⁴ demonstrated that massive planets might also find their way into tight orbits around white dwarfs, but it is unclear whether these planets can survive the journey. So far, no intact planets have been detected in close orbits around white dwarfs. Here we report the observation of a giant planet candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4 days. We observed and modelled the periodic dimming of the white dwarf caused by the planet candidate passing in front of the star in its orbit. The planet candidate is roughly the same size as Jupiter and is no more than 14 times as massive (with 95 per cent confidence). Other cases of white dwarfs with close brown dwarf or stellar companions are explained as the consequence of common-envelope evolution, wherein the original orbit is enveloped during the red giant phase and shrinks owing to friction. In this case, however, the long orbital period (compared with other white dwarfs with close brown dwarf or stellar companions) and low mass of the planet candidate make common-envelope evolution less likely. Instead, our findings for the WD 1856+534 system indicate that giant planets can be scattered into tight orbits without being tidally disrupted, motivating the search for smaller transiting planets around white dwarfs.

A triple-star system with a misaligned and warped circumstellar disk shaped by disk tearing

Young stars are surrounded by a circumstellar disk of gas and dust, within which planet formation can occur. Gravitational forces in multiple star systems can disrupt the disk. Theoretical models predict that if the disk is misaligned with the orbital plane of the stars, the disk should warp and break into precessing rings, a phenomenon known as disk tearing. We present observations of the triple-star system GW Orionis, finding evidence for disk tearing. Our images show an eccentric ring that is misaligned with the orbital planes and the outer disk. The ring casts shadows on a strongly warped intermediate region of the disk. If planets can form within the warped disk, disk tearing could provide a mechanism for forming wide-separation planets on oblique orbits.

An Earth-sized planet in the habitable zone of a cool star

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.

Lithopanspermia in star-forming clusters

This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections <sigma(cap)> for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime.

New peat bog record of atmospheric lead pollution in Switzerland: Pb concentrations, enrichment factors, isotopic composition, and organolead species

A peat core collected at Etang de la Gruère, an ombrotrophic bog in the Jura Mountains of Switzerland, was analyzed for organolead species (DEL, TEL, DML, and TML) using GC-MIP AES, Pb isotopes using TIMS, and total Pb using XRF and age-dated using 210Pb. The earliest occurrence of quantifiable alkyllead is found at a depth of 24 cm, which is dated at AD 1946 +/- 3; this finding is consistent with the introduction of leaded gasoline in Switzerland in 1947. The maximum concentration of alkyllead (2.89 ng/g) is found at 5 cm, which is dated at AD 1988 +/- 2. This same sample yielded 206Pb/207Pb = 1.1254, which is the least radiogenic value in the entire 2K core and comparable to the isotopic composition of Pb in leaded gasoline. The highest concentrations of DML (906 ng/g) and DEL (1906 ng/g) also were found in this sample. Total alkyllead never accounts for more than 0.02% of total Pb in any given sample. The spatial and temporal variations in organolead species is matched by the changes in the isotopic composition of Pb over the same interval. Despite this, the decline in anthropogenic Pb pre-dates the maximum in total alkyllead and minimum 206Pb/207Pb, indicating that atmospheric Pb emissions had already begun their decline prior to the introduction of unleaded gasoline. In fact the decline in anthropogenic Pb was probably in response to the introduction of legislation, first in Germany and later in the European Union, establishing a maximum allowable concentration of Pb in gasoline.

Comparison of three coupled gas chromatographic detectors (MS, MIP-AES, ICP-TOFMS) for organolead speciation analysis

An automatic unit for the screening of rainwater is used for the determination of organolead compounds using different detectors coupled to a gas chromatograph. A systematic overview is given of the advantages and disadvantages of several detectors (electron ionization mass spectrometry, EI-MS; microwave induced plasma atomic emission spectrometry, MIP-AES; and inductively coupled plasma time-of-flight mass spectrometry, ICP-TOFMS, for the speciation of organolead compounds on the basis of sensitivity, selectivity and reliability. C60 fullerene and RP-C18 were used as sorbent materials for these compounds. The primary assets of the fullerene sorbent, as compared to C18 sorbent, are high sensitivity and selectivity resulting from efficient adsorption due to large surface area and interstitial volume. Among the detection systems, GC/ ICP-TOFMS is the most sensitive, with absolute detection limits of approximately 15 fg of organolead compounds (as lead) using 5-mL sample volumes. Except for diethyllead, similar sensitivities were obtained by MIP-AES. GC/MS is intrinsically the most specific option, because the species are detected directly from molecular information. The precision is similar for all detectors. The screening of rainwater from different locations showed that samples collected in countries in which leaded gasolines are now banned contain organolead species at concentrations below 2 pg/ mL, levels that can be detected only for sample volumes of 25 mL and using MIP-AES or ICP-TOFMS as detectors, their determination being impossible by GC/MS.

Gas chromatography--inductively coupled plasma--time-of-flight mass spectrometry for the speciation analysis of organolead compounds in environmental water samples

The application of inductively coupled plasma--time-of-flight mass spectrometry for the speciation analysis of organolead compounds in environmental waters is described. Construction of the transfer line was achieved by means of a relatively simple and rapid coupling procedure. Derivatization of the ionic lead species was achieved by in-situ propylation with sodium tetrapropylborate; simultaneous extraction of the derivatized compounds in hexane was followed by separation and detection by capillary gas chromatography hyphenated to inductively coupled plasma-time-of-flight mass spectrometry. Detection limits for the different organolead species ranged from 10 to 15 fg (as Pb), corresponding to procedural detection limits between 50 and 75 ng L(-1), on the basis of a 50 mL snow sample, extraction with 200 microL hexane, and subsequent injection of 1 microL of the organic extract on to the column. The accuracy of the system was confirmed by additional analysis of the water samples by capillary gas chromatography coupled with microwave-induced plasma-atomic-emission spectrometry and the analysis of a standard reference material CRM 605 (road dust) with a certified content of trimethyllead.

Low-molecular-weight organoiodine and organobromine compounds released by polar macroalgae--the influence of abiotic factors

The influence of temperature, light, salinity and nutrient availability on the release of volatile halogenated hydrocarbons was investigated in the Antarctic red macroalgal species Gymnogongrus antarcticus Skottsberg. Compared to standard culture condition, an increase in the release rates of iodocompounds was generally found for the exposure of the alga to altered environmental conditions. Macroalgae exhibited higher release rates after adaptation for two months to the changed factors, than after short-term exposure. Monitoring the release rates during a 24 h incubation period (8.25 h light, 15.75 h darkness) showed that changes between light and dark periods had no influence on the release of volatile halocarbons. Compounds like bromoform and 1-iodobutane exhibited constant release rates during the 24 h period. The formation mechanisms and biological role of volatile organohalogens are discussed. Although marine macroalgae are not considered to be the major source of biogenically-produced volatile organohalogens, they contribute significantly to the bromine and iodine cycles in the environment. Under possible environmental changes like global warming and uncontrolled entrophication of the oceans their significance may be increase.

Lead concentrations and isotopic signatures in vintages of French wine between 1950 and 1991

Vintages of French wine from 1950 to 1991 were analyzed for lead isotopes and concentrations to investigate whether they might be used to archive the isotopic composition of the anthropogenic lead in aerosols to which the vineyard was exposed. Early vintages (1950-1980) contained 78-227 ng/g of lead with 206Pb/207Pb ratios between 1.152 and 1.173, while the later vintages displayed significantly lower concentrations and a smaller range of isotopic ratios. The concentration of trimethyl lead, which is associated with automobile emissions, was found to be poorly correlated with total lead in the wines, suggesting that automobile aerosols were not a significant source of the lead. This result was supported by lead isotope data which showed a poor correlation with the available petrol and aerosol data. To identify its origin lead isotopes were measured in vineyard aerosols, soil particles, bottle caps, corks, and brass components used to dispense the wine. Although a dominant source could not be identified there was some evidence to suggest that brass which had a high lead concentration was a significant contributor. Because the lead contribution from the processing of wine was probably relatively high in the past it is unlikely that old vintages of wine will be a suitable archive for lead isotopes in aerosols.

Speciation analysis of organolead compounds in wine by capillary gas chromatography/microwave-induced-plasma atomic emission spectrometry

A method was developed for the speciation analysis of ionic organolead compounds in wine. The analytes were extracted as diethyldithiocarbamate complexes into hexane and propylated with a Grignard reagent. The derivatized extract was analyzed by capillary gas chromatography/microwave-induced-plasma atomic emission spectrometry. The method of standard additions was used for calibration to correct for variable recoveries and signal enhancements. Red, rosé, and white wines from southern France were analyzed. Trimethyllead was the ubiquitous species. The wines made from grapes grown close to industrial zones showed elevated concentrations of ethyllead species. The concentrations of methyllead and ethyllead found in wines were compared with the concentrations of organolead found in rain water and plant sap collected in the viticultural regions. The ratio of methyllead to ethyllead in wines greatly exceeded the same ratio found in atmospheric deposits.

Renal secretion of inactive renin and extraction of angiotensin II in renal artery stenosis in man: factors determining renal vein renin ratio

Triplicate blood samples were obtained, without stimulation, simultaneously from the aorta and both renal veins in 24 untreated hypertensive patients with unilateral renal artery stenosis. Across the affected kidney the plasma concentrations of active renin, inactive renin and angiotensin II increased by 363% (P less than 0.001), 80% (P less than 0.05) and 100% (P less than 0.05) respectively. Thus the affected kidney was secreting both active and inactive renin, while appreciable quantities of angiotensin II were generated across the renal circulation on that side. Across the contralateral unaffected kidney there were no significant changes in concentration of active or inactive renin, indicating net suppression of secretion of both forms of renin. Plasma angiotensin II concentration was however markedly reduced, to 50% of the arterial value (P less than 0.001), in the contralateral renal vein, demonstrating renal extraction of angiotensin II. In 14 patients renal plasma flow was also measured. The ratio of active renin concentration between the two renal veins correlated more closely with the renal plasma flow to the affected kidney (r = -0.81; P less than 0.01) than with renin secretion rate on that side (r = +0.37; NS). Thus reduction in renal blood flow rather than increase in renin secretion appeared to be the major determinant of renal vein renin ratio.

Changes in active and inactive renin and in angiotensin II across the kidney in essential hypertension and renal artery stenosis

Investigations were performed in 26 patients with essential hypertension and 24 with unilateral renal artery stenosis. In each patient blood was drawn simultaneously and in triplicate, from both renal veins and aorta, for measurement of plasma concentrations of active and inactive renin and of angiotensin II. In 19 patients estimates of individual renal plasma flow were obtained in order to calculate secretion rates for active and inactive renin, and to assess the contribution of renin secretion rate and of renal plasma flow to the renal vein renin ratio. In patients with essential hypertension there was evidence that the kidney secreted active renin (18% mean increase in renal vein concentration above that of arterial plasma; P less than 0.001), but no evidence of secretion of inactive renin (4% mean increase; NS). There was a tendency for the kidney to extract angiotensin II (8% mean decrease in renal vein concentration below that of arterial plasma; P = 0.07). The affected kidney in patients with renal artery stenosis showed marked secretion of active renin (364% mean increase; P less than 0.001) and also secreted inactive renin (80% mean increase; P less than 0.05) with net generation of angiotensin II across the renal circulation (100% mean increase; P less than 0.05). The contralateral kidney exhibited suppressed secretion of active renin (3% mean increase; NS) with no evidence of secretion of inactive renin (2% mean increase; NS), and marked extraction of angiotensin II (50% mean decrease; P less than 0.001). The correlation between combined secretion rate of active renin by both kidneys and the arterial concentration of active renin in patients with essential and renovascular hypertension taken together was strongly positive (r = 0.82; P less than 0.01). The same correlation for inactive renin was weak (r = 0.32; NS). The correlation between the combined secretion rates of active renin by both kidneys and the circulating plasma concentration of angiotensin II (r = +0.60; P less than 0.05) was both significant and positive. By contrast, the total 'secretion' rate of angiotensin II by both kidneys was inversely related to arterial plasma angiotensin II (r = -0.92; P less than 0.001). This latter relationship suggests an important role for the kidney in clearing angiotensin II from the circulation, this being more marked the higher the arterial angiotensin II concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Two families of abl-related transcripts in human haematopoietic cells differing in their homology to v-abl

The transforming gene of the Abelson murine leukaemia virus, v-abl, contains two open reading frames (orf). The 5' orf encodes a tyrosine-specific protein kinase while the 3' orf has the capacity to code for an 18,000 Mr protein. However, no 3' orf product has yet been identified. Using probes capable of distinguishing between the 5' and 3' orfs of v-abl, we have examined the abl-related transcripts present in human haematopoietic cells and leukaemia-derived cell lines, including the chronic myeloid leukaemia-derived cell line K562. Our results indicate that transcripts of 6 kb, 7 kb and 8 kb (kilobase, 10(3) base-pairs) show strong homology to v-abl 5' protein kinase-encoding orf sequences, but are devoid of any sequences from the v-abl 3' orf. In addition, transcripts of 5 kb, 3 kb, 1.6 kb and 1.4 kb, reacting with both 5' orf and 3' orf probes, were observed. The latter species, with coding sequences from both the tyrosine kinase and the putative 18,000 Mr protein, must be transcribed from the human c-abl gene as this is apparently the only human gene containing sequences homologous to the v-abl 3' orf. The 6 kb, 7 kb and 8 kb transcripts may arise either from the c-abl gene through differential splicing, or from one of the three other regions of the human genome with sequences homologous to the 5' orf of v-abl. Examination of genomic DNA from the K562 cell line revealed that the amplification of abl-related sequences, which is presumed to result in the elevated levels of the 8 kb transcript found in this cell line, does not involve sequences homologous to the v-abl 3' orf. This lends credence to the idea that the 8 kb transcript may derive from an abl-related gene other than c-abl. While the significance of the 3' orf of v-abl remains unknown, the data presented strongly suggest the existence of at least two distinct abl-related proteins in human haematopoietic cells.

Children's brain tumour cells produce RNA particles with incomplete retrovirus characteristics

Short-term cultures of cells from human rain tumours have been reported to synthesise RNA particles of density in the range characteristic of C type RNA retroviruses, with associated DNA polymerase activity. Fresh tumour cells obtained from 6 children with astrocytoma and 7 children with medulloblastoma, together with one sample of normal brain tissue and normal leukocytes from brain tumour patients were assayed by several characteristics for the primate retrovirus. 1 or 6 (17%) astrocytomas and 4 of 7 (57%) medulloblastomas released RNA particles which banded in sucrose gradients at a density of 1.16-1.18 g/cm3 together with a short segment of DNA, which was eliminated by prior ribonuclease treatment and two proteins of 28k and 16k daltons. These findings were compatible with the presence of a primate retrovirus. Immune coprecipitation of 125I-labelled proteins from the 1.16-1.18 g/cm3 gradient region failed to show any reactivity with antisera to p28 core antigens or the p70 reverse transcriptase antigens of simian sarcoma virus, baboon endogenous virus or Mason Pfizer virus. Assays for DNA polymerase activity in culture supernatant fluid showed only a low amount of activity with template preferences not characteristic of the retroviral reverse transcriptase enzyme.