Endogenous CO2 ice mixture on the surface of Europa and no detection of plume activity

Jupiter's moon Europa has a subsurface ocean beneath an icy crust. Conditions within the ocean are unknown, and it is unclear whether it is connected to the surface. We observed Europa with the James Webb Space Telescope (JWST) to search for active release of material by probing its surface and atmosphere. A search for plumes yielded no detection of water, carbon monoxide, methanol, ethane, or methane fluorescence emissions. Four spectral features of carbon dioxide (CO2) ice were detected; their spectral shapes and distribution across Europa's surface indicate that the CO2 is mixed with other compounds and concentrated in Tara Regio. The 13CO2 absorption is consistent with an isotopic ratio of 12C/13C = 83 ± 19. We interpret these observations as indicating that carbon is sourced from within Europa.

Production of Hydronium Ion (H3O)+ and Protonated Water Clusters (H2O)nH+ after Energetic Ion Bombardment of Water Ice in Astrophysical Environments

Water ice exists on many objects in space. The most abundant icy species, among them water, are present in the icy satellites of the outer Solar System giant planets. The nuclei of comets, which are mainly composed of water ice, give another example of its abundance. In the interstellar medium (ISM), ice mantles, formed by molecular species sticking on dust grains, consist mainly of water ice. All these objects are exposed to ionizing radiation like ions, UV photons, and electrons. Sputtering of atoms, molecules, ions, and radicals from icy surfaces may populate and maintain exospheres of icy objects in the Solar System. In other respects, ionized hydrides such as OH⁺, H₂O⁺, and H₃O⁺ have been detected in the gas phase in star-forming regions. Interactions with cosmic rays could be an additional explanation to the current models for the formation of those species. In fact, laboratory simulations showed that the main components of the sputtered ionic species from water ice are oxygen hydrides. In this work, water ice targets were irradiated at several temperatures (10-200 K) by 90 keV O⁶⁺ ions, yielding an electronic stopping power of about 12 eV/Å, when the nuclear stopping power is comparable to the electronic stopping power. Sputtering of secondary ions after bombardment of the ice target was analyzed by time-of-flight mass spectrometry (TOF-SIMS). Besides hydrogen ions (H⁺, H₂⁺, H₃⁺), also O⁺, O²⁺, OH⁺, (H₂O)⁺, and clusters of (H₂O)_nH⁺ with n = 1-8 are emitted. Our results show a progressive yield decrease with increasing temperature of all of the detected species. This is related to the structure of the ice: the ionic sputtering yield for crystalline ice is much lower than for an amorphous ice. For instance, amorphous ice at 10 K exhibits a yield of the order of 2 × 10^-6 secondary (H₂O)_nH⁺ hydride ions/projectile (with n = 1-8). As the temperature is increasing toward the phase transition to crystalline ice, the yields decrease by about one order of magnitude.

Photolysis of Cometary Organic Dust Analogs on the EXPOSE-R2 Mission at the International Space Station

We describe the results obtained on a set of organic samples that have been part of the experiment "Photochemistry on the Space Station (PSS)" on the EXPOSE-R2 mission conducted on the EXPOSE-R facility situated outside the International Space Station (ISS). The organic samples were prepared in the Catania laboratory by 200 keV He⁺ irradiation of N₂:CH₄:CO icy mixtures deposited at 17 K, on vacuum UV (VUV) transparent MgF₂ windows. This organic material contains different chemical groups, including triple CN bonds, that are thought to be of interest for astrobiology. It is widely accepted that materials similar to that produced in the laboratory by ion irradiation of frozen ices could be present in some astrophysical environments such as comets. Once expelled from comets, these materials are exposed to solar radiation during their interplanetary journey. In the young Solar System, some of these processed materials could have reached early Earth and contributed to its chemical and prebiotic evolution. The samples were exposed for 16 months to the unshielded solar UV photons. It was found that, if an interplanetary dust particle (IDP) containing organic material (50% vol) is large enough (>20-30 μm), relevant chemical groups, such as those containing the CN triple bond, can survive for many years (>10⁴ years) in the interplanetary medium.

Cryogenic Synthesis of Molecules of Astrobiological Interest: Catalytic Role of Cosmic Dust Analogues

We have studied the effects of the substrate, namely amorphous olivine (MgFeSiO(4)) cosmic dust analogues (CDAs), in synthesis of molecules obtained after 200 keV proton irradiation of formamide (NH(2)COH). Formamide has been deposited on the olivine substrate at 20 K. The abundances of new molecular species formed after an irradiation dose of 12 eV/16 amu in formamide pure (i.e. deposited on an inert silicon substrate) and deposited on CDAs have been compared. Specifically, MgFeSiO(4) amorphous olivine is a selective catalyst preventing formation of NH(3) and CN(-) molecules and changing the relative abundances of NH4(+)OCN(-), CO(2), HNCO, CO. We have shown that the role of CDAs has to be taken into account in experiments simulating processes occurring in astronomical environments.

Production of oxidants by ion irradiation of water/carbon dioxide frozen mixtures

We present new experimental results on the formation of oxidants, such as hydrogen peroxide, ozone, and carbonic acid, under ion irradiation of icy mixtures of water/carbon dioxide at different ratios and temperatures (16 and 80 K). Pure water ice layers and mixtures with carbon dioxide were irradiated by 200 keV He+ ions. We found that the CO(2)/H(2)O ratio progressively decreased to a value of about 0.1, the H(2)O(2) production increased with increasing CO(2) abundance at both 16 and 80 K, and the CO and H(2)CO(3) production increased with increasing CO(2) abundance at 16 K. At 80 K, the synthesis of CO was less efficient because of the high volatility of the molecule that partially sublimed from the target. The production of carbonic acid was connected with the production of CO(3). O(3) was detected only after ion irradiation of CO(2)-rich mixtures. The experimental results are discussed with regard to the relevance they may have in the production of an energy source for a europan or a martian biosphere.

Vibrational spectroscopy of ion-irradiated ices

In the last 20 years we have studied some effects induced by fast ions (E approximately keV-MeV) impinging on solid materials (mainly ices) with a view to their astrophysical relevance. The main techniques used have been infrared and Raman spectroscopy. Here we review some of the results obtained so far concerning, in particular, the formation of new species not present in the original sample. When hydrocarbons are an important constituent of the target ion irradiation gives rise also to a refractory residue which is left over after warming up. In addition we present some preliminary results of a new study, still in progress, on the infrared properties of the organic residue formed after irradiation of an icy mixture with H-, C-, N- and O-bearing species. Furthermore we present the micro-Raman spectra of some fragments of Orgueil a carbonaceous chondrite meteorite. Some astrophysical applications of these laboratory results are also discussed.

Organics produced by ion irradiation of ices: some recent results

Some results, recently obtained from laboratory experiments of ion irradiation of ice mixtures containing H, C, N, and O, are here summarized. They are relevant to the formation and evolution of complex organics on interstellar dust, comets and other small bodies in the external Solar System. In particular the formation of CN-bearing species is discussed. Interstellar dust incorporated into primitive Solar System bodies and subsequently delivered to the early Earth, may have contributed to the origin of life. The delivery of CN-bearing species seems to have been necessary because molecules containing the cyanogen bond are difficult to be produced in an environment that is not strongly reducing as that of the early Earth probably was. Moreover we report on an ongoing research program concerning the interaction between refractory materials produced by ion irradiation of simple ices and biological materials (amino acids, proteins, cells).

R-O-C(triple bond)N species produced by ion irradiation of ice mixtures: comparison with astronomical observations

We have investigated the effects induced by ion bombardment of mixtures containing nitrogen-bearing compounds at low temperatures. The results show the formation of a band at 2080 cm-1 in binary mixtures, NH3:CH4 and N2:CH4, which we attribute to HCN embedded in the organic residue formed by ion irradiation. In addition to this band, ternary mixtures containing an oxygen-bearing species (i.e., H2O) form a compound with a prominent absorption band at about 2165 cm-1 (4.62 microns). We ascribe this band to a nitrile compound containing O that is bonded to the organic residue. A detailed comparison of the laboratory results with astronomical data of the 4.62 microns absorption band in protostellar spectra shows good agreement in peak position and profile. Our experimental studies show that N2, which is a more likely interstellar ice component than NH3, can be the molecular progenitor of the carrier of the interstellar band. This is an alternative to the pathway by which UV photolysis of NH3-containing ices produces the 4.62 microns band and implies that ion bombardment may well play an important role in the evolution of interstellar ices. Here, we discuss the implications of our studies for the chemical route by which the carrier of the 4.62 microns band is formed in these laboratory experiments.

Ion irradiation: its relevance to the evolution of complex organics in the outer solar system

Ion irradiation of carbon containing ices produces several effects among which the formation of complex molecules and even refractory organic materials whose spectral color and molecular complexity both depend on the amount of deposited energy. Here results from laboratory experiments are summarized. Their relevance for the formation and evolution of simple molecules and complex organic materials on planetary bodies in the external Solar System is outlined.

Acute effects of physiological increments of brain natriuretic peptide in humans

To investigate the effects of physiological increases in plasma brain natriuretic peptide concentration in humans, we studied six healthy volunteers who received incremental infusions (0.25 pmol/kg per minute in the first hour and 0.50 pmol/kg per minute in the second) of synthetic human brain natriuretic peptide-32 in a placebo-controlled, crossover study. Peptide plasma levels were 1.69 +/- 0.39 pmol/L at baseline and rose 1.5- and 3-fold with the lower and higher doses, respectively. These values were within the normal range and also comparable to those reported in patients with mild essential hypertension. The urinary excretion rate of cGMP also increased during brain natriuretic peptide infusion, indicating stimulation of natriuretic peptide receptors. Peptide administration induced a significant 1.7-fold increase in urinary sodium excretion without affecting renal plasma flow (para-aminohippurate clearance), glomerular filtration rate (creatinine clearance), and urine flow rate. Fractional proximal sodium reabsorption (lithium clearance method) was unchanged, and fractional distal sodium reabsorption significantly decreased. Brain natriuretic peptide caused no changes in arterial pressure, heart rate, hematocrit, and serum proteins, but it exerted an inhibitory effect on the renin-aldosterone axis, as indicated by the significant 50% or more decrease of plasma renin activity and urinary excretion rate of aldosterone. These results suggest that brain natriuretic peptide may be involved in the overall regulation of body fluid and cardiovascular homeostasis in humans, mainly through its natriuretic and endocrine effects.

Cardiovascular effects of brain natriuretic peptide in essential hypertension

We evaluated the cardiovascular effects of pathophysiological plasma levels of brain natriuretic peptide in seven patients with mild to moderate essential hypertension by performing equilibrium radionuclide angiocardiography at baseline and during brain natriuretic peptide infusion at increasing doses (4, 8, 10, and 12 pmol/kg per minute for 20 minutes each). Brain natriuretic peptide induced a progressive reduction of left ventricular end-diastolic volume (from 107.5 +/- 10.3 to 89.0 +/- 11.0 mL at the end of all infusion periods) and end-systolic volume, whereas stroke volume did not show any significant change (from 64.9 +/- 5.9 to 62.7 +/- 7.8 mL). Cardiac output, arterial pressure, and peripheral vascular resistance did not change significantly. The lack of effects on systemic hemodynamics was probably due to compensatory activation of the sympathetic nervous system, as indicated by the significant increase in plasma norepinephrine levels (from 1.75 +/- 0.18 to 2.19 +/- 0.21 nmol/L), heart rate (from 68 +/- 6 to 81 +/- 6 beats per minute), peak ejection rate, and peak filling rate. These results indicate that brain natriuretic peptide, at the pathophysiological plasma concentrations reached in this study, influences cardiovascular homeostasis mainly by reducing cardiac preload.

Production and evolution of carbonaceous material by ion irradiation in space

We review recent experimental studies concerning the evolution, driven by ion irradiation, of carbonaceous material from frozen gas to a refractory molecular solid. Under further irradiation the latter changes to a polymer-like material and ultimately to amorphous carbon. Most of the results have been obtained by "in situ" and remote IR and Raman spectroscopy. The results have been applied to demonstrate that molecular solids may be easily formed by irradiation of frozen mantles in dense interstellar clouds. Polymer-like material and amorphous carbons may result by further irradiation of organic mantles on grains in the diffuse interstellar medium. Those grains, during the aggregation to form extended bodies like comets (T-Tau phase of the Sun), are further modified. These latter are also irradiated, after the comet formation, during their long stay in the Oort cloud. In particular it has been suggested that comet may develop an ion-produced cometary organic crust that laboratory evidences show to be stable against temperature increases experienced during passages near the Sun. The comparison between the Raman spectra of some IDP (Interplanetary Dust Particles) and the Raman spectra of some ion-produced amorphous carbons, is also discussed.

Cardiovascular function during brain natriuretic peptide infusion in man

To investigate the cardiovascular effects of pathophysiological levels of brain natriuretic peptide (BNP), 7 healthy subjects were submitted to equilibrium radionuclide angiocardiography in baseline conditions and during BNP infusion at increasing doses (4, 8, 10 and 12 pmol/kg.min for 20 min each). BNP induced a progressive, significant reduction in left ventricular end diastolic volume, stroke volume and end systolic volume and an increase in ejection fraction and heart rate. Cardiac output, arterial pressure and peripheral vascular resistance were unchanged. Activation of the sympathetic nervous system, as indicated by the significant increase in plasma norepinephrine levels, probably played a contributory role in the maintenance of cardiovascular homeostasis. These results indicate that BNP, at pathophysiological plasma concentrations, influences cardiovascular homeostasis in man.

Radiation chemistry of ices of planetological interest at low temperature

We present the results of recent experiments on some physico-chemical effects induced by fast ion colliding with solids of relevance for the physics of planetary objects. The production of molecular solids, polymer-like materials and amorphous carbon by irradiation of frozen hydrocarbons and pentacene is discussed. We also report on a set of experimental results obtained irradiating methanol and water-methanol mixtures. Because of bombardment different species form. The techniques used for the analysis are "in situ" infrared (IR) and Raman spectroscopy. The experimental results are finally discussed in the light of their relevance for planetary physics.

Renal effects of atrial natriuretic peptide during dopa-decarboxylase inhibition in patients with essential hypertension

To assess whether intrarenal dopamine synthesis could contribute to the renal response to ANP in essential hypertension, the effects of alpha-human ANP infusion (50 ng.min-1.kg-1 b.w. for 30 min) on the urinary excretion of dopamine and sodium, urine flow rate and arterial pressure were evaluated in 7 patients with mild-moderate essential hypertension before (control period) and during DOPA-decarboxylase inhibition with carbidopa (carbidopa period). In the control period, urinary dopamine excretion was 400 pg.min-1 in baseline conditions and 340 pg.min-1 during ANP infusion. Carbidopa significantly decreased urinary dopamine excretion both before (210 pg.min-1) and during ANP (99 pg.min-1). In contrast, carbidopa did not affect sodium excretion (control from 184 to 460 mu Eq.min-1; carbidopa period from 140 to 390 mu Eq.min-1) or urine flow rate (control from 5.35 to 11.21 ml.min-1; carbidopa period from 4.29 to 11.54 ml.min-1). Arterial pressure fell significantly during ANP infusion in both periods, and no significant difference was observed between the two study days, i.e. in the absence of and during carbidopa administration. We conclude that DOPA-decarboxylase inhibition does not influence the diuretic and natriuretic response to alpha-human ANP infusion in patients with essential hypertension.

[The effects of the acute administration of atrial natriuretic peptide on the mechanisms regulating diuresis and natriuresis in the essential hypertension patient]

The authors investigated the role of atrial natriuretic peptide (alpha-hANP 99-126) in essential hypertension by evaluating some hemodynamic and renal effects of acute peptide infusion (1 micrograms/kg for 1 min + 50 ng/kg for the following 20 min) in fourteen subjects: eight mild to moderate, untreated, essential hypertensives (EH) and six normotensive (N) controls, during 2 hour-clearance periods, the 1st after ANP infusion, the 2nd during placebo (PL) administration. The double-blind study was carried out after the patients had rested and fasted overnight. It showed no significant changes in heart rate (HR); instead, compared with placebo, mean blood pressure (MBP) decreased significantly in both groups, beginning from the 3rd min after ANP infusion was begun (N: PL = 87.04 +/- 1.7 mmHg, ANP = 80.9 +/- 3.7 mmHg, p less than 0.0001; EH: PL = 102.6 +/- 3.2 mmHg, ANP = 97.7 +/- 5.9 mmHg, p less than 0.01). Among the urinary parameters we considered, cyclic GMP (cGMP) increased after ANP infusion in all subjects (N: PL = 129.1 +/- 56.3 pmol/mL, ANP = 199.2 +/- 85.4 pmol/mL; EH: PL = 106.55 +/- 56.2 pmol/mL, ANP = 220.03 +/- 92.7 pmol/mL, p less than 0.05); diuresis showed a prompt and significant increase in EH (N: PL = 837 +/- 368 mL, ANP = 1066 +/- 340 mL; EH: PL = 713 +/- 286 mL, ANP = 1043 +/- 280 mL, p less than 0.005), and so did natriuresis (N: PL = 23 +/- 14.3 mEq/L, ANP = 33 +/- 14.6 mEq/L; EH: PL = 25.6 +/- 8.9 mEq/L, ANP = 41.9 +/- 13.8 mEq/L, p less than 0.01); urinary potassium excretion was significantly reduced in EH (N: PL = 18.7 +/- 12.9 mEq/L, ANP = 14.2 +/- 6.9 mEq/L; EH: PL = 16.5 +/- 7.9 mEq/L, ANP = 10.7 +/- 4.8 mEq/L, p less than 0.005), while no changes were noted in glomerular filtration rate (GFR), estimated as creatinine clearance, urinary magnesium, albumin and aldosterone excretion. To investigate other potential mechanisms involved in renal effects of ANP, the urinary excretion of both prostaglandins 6-cheto PGF1-alpha and thromboxane B2 (TXB2), and dopamine were studied. The results showed only a significant decrease of dopamine urinary excretion in EH after ANP administration (N: PL = 50.4 +/- 28.7 micrograms/L, ANP = 45.0 +/- 29.7 micrograms/L; EH: PL = 47.3 +/- 21.5 micrograms/L, ANP = 27.1 +/- 12.7 micrograms/mL, p less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Left ventricular diastolic filling improvement obtained by intravenous verapamil in mild to moderate essential hypertension: a complex effect

In order to try and evaluate through what prevailing mechanism verapamil (V) can induce an improvement in left ventricular (LV) diastolic early filling in mild to moderate essential hypertension, 43 properly classified essential hypertensives, aged 41-74 years (mean age 58.1 +/- 10.3), and 20 age-matched normotensives were studied. All subjects underwent both echocardiographic evaluation and 99mTc radionuclide angiocardiography in basal conditions between 8.00 a.m. and noon, after an overnight rest. In essential hypertensives gated equilibrium angiocardiography was repeated 3 and 30 min after i.v. V (0.1-mg/kg bolus, followed by 0.005 mg/kg/min for the period of radionuclide data acquisition). Simultaneously, supine arterial pressure was measured with a cuff manometer. In 36 essential hypertensives a phono-echo evaluation was obtained, both at 3 and 30 min after V, deriving a LV isovolumetric relaxation index (IRTI). Among diastolic early filling indices, we particularly considered the ratio of peak filling rate (PFR) to peak ejection rate (PER) in order to take into account the interaction of systolic performance with LV relaxation and diastolic early filling. Three minutes after V the increase in PFR (from 2.47 +/- 0.5 to 3.04 +/- 0.8 EDV/s, p less than 0.001) and the upwards tendency of PFR/PER were coupled with the enhancement in ejection fraction (from 61.1 +/- 13.3 to 63.9 +/- 13.8%, p less than 0.001) and heart rate (from 70.3 +/- 12.6 to 77.7 +/- 12.2 b/min, p less than 0.001) and with the reduction in mean arterial pressure (from 122 +/- 16 to 107 +/- 14 mm Hg, p less than 0.001), systemic arterial resistance index (from 3,234 +/- 968 to 2,432 +/- 678 dyn s cm-5 m2, p less than 0.001) and end-systolic volume index (from 32.9 +/- 17.1 to 31.5 +/- 18.3 ml/m2, p less than 0.02). On the contrary, 30 min after V, when systolic indices, heart rate, mean arterial pressure and systemic arterial resistance index had returned towards baseline values, PFR/PER showed a persistent improvement when compared with basal values (0.71 +/- 0.12 vs. 0.63 +/- 0.08, p less than 0.005). No changes were observed in LV volumes and IRTI, either at 3 or 30 min. Moreover, also the pulmonary blood volume ratio was unchanged. A weak negative correlation was found between delta % of IRTI and delta % of PFR/PER 30 min after drug administration (r = 0.58, p less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Calcitonin increases peripheral plasma somatostatin-like immunoreactivity levels in humans

Even though the inhibitory effects of CT on both hormone secretion and gastrointestinal functions have been well established, the exact mechanism of action still remains unclear. Since the effects of CT can be reproduced by somatostatin, we studied in man the effect of SCT on peripheral plasma SLI levels. Immediately after the onset of CT infusion SLI rose from its mean basal value of 45 +/- 5.5 pg/ml to a peak value of 91 +/- 11 pg/ml (p less than 0.005). SLI levels were still significantly elevated at 30 (p less than 0.05), 45 (p less than 0.05), 90 (p less than 0.005) and 120 min (p less than 0.02). Our results, in good agreement with the previous report by Chiba et al. on isolated perfused rat stomach, suggest that CT effects may, at least in part, be mediated by endogenous somatostatin release.

[Reactivation of the allogenous component of experimental skin inflammation after exposure to ultraviolet rays]

The effects of U.V. radiation induced cutaneous erythema on an experimental inflammation focus in another part of the body have been studied. The skin inflammation caused by carbon dioxide snow was used as a model. The onset of erythema is followed by reactivation of the diminishing inflammation process. It is therefore deduced that such effects are transmitted humorally and that reactivation is caused by histamine circulation. Histamine is released locally from the U.V. induced erythema and, entering into the circulation, increased the permeability of the microvessels in the inflamed area. This sends inactive chemical mediators to the interstitial sector where the appropriate conditions for their activation exist.

[Reactivation of the algogenic component in experimental inflammation induced by histamine administration]

The action of i.v. histamine on human skin inflammation experimentally induced with carbon dioxide snow in man is described. Histamine was injected when the skin reaction was on the wane to determine its possible reactivation of inflammation. Complete recrudescence of erythralgia was noted (reappearance of pain and of erythralgic halo, with a fresh spread of secondary hyperalgesia). It is felt that histamine was responsible. Its arrival to the reaction site through microvessels in a state of increased permeability during the remission of inflammation may be assumed to promote the passage of chemical mediators in the preactive stage from the vascular to the interstitial sector, and thus to pave the way for their activation.