Active Cryovolcanism on Europa? Sparks, W. B.; Schmidt, B. E.; McGrath, M. A. ...
Astrophysical journal. Letters,
04/2017, Letnik:
839, Številka:
2
Journal Article
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Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two different observing techniques. Roth et al. found line emission from the dissociation ...products of water. Sparks et al. found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal anomaly, its depth is 1.8-2 km, under simple modeling assumptions, consistent with scenarios in which a liquid water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial characterization of Europa's internal water and ice and for seeking evidence of Europa's habitability.
ABSTRACT Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude region on Europa: spectroscopic detection of off-limb line emission from the dissociation ...products of water. Here, we present Hubble Space Telescope direct images of Europa in the far-ultraviolet (FUV) as it transited the smooth face of Jupiter to measure absorption from gas or aerosols beyond the Europa limb. Out of 10 observations, we found 3 in which plume activity could be implicated. Two observations showed statistically significant features at latitudes similar to Roth et al., and the third at a more equatorial location. We consider potential systematic effects that might influence the statistical analysis and create artifacts, and are unable to find any that can definitively explain the features, although there are reasons to be cautious. If the apparent absorption features are real, the magnitude of implied outgassing is similar to that of the Roth et al. feature; however, the apparent activity appears more frequently in our data.
Volcanic eruptions are the dominant cause of natural variability in climate forcing on timescales up to multidecadal. Large volcanic eruptions lead to global-scale climate effects and influence the ...carbon cycle on long timescales. However, estimating the frequency of eruptions is challenging. Here we assess the frequency at which eruptions with particular deposition fluxes are observed in the EPICA Dome C ice core over the last
200 kyr. Using S isotope analysis we confirm that most of the largest peaks recorded at Dome C are from stratospheric eruptions. The cumulative
frequency through 200 kyr is close to linear, suggesting an approximately
constant rate of eruptions. There is no evidence for an increase in the rate of events recorded in Antarctica at either of the last two deglaciations. Millennial variability is at the level expected from recording small numbers of eruptions, while multimillennial variability may be partly due to changes in transport efficiency through the Brewer–Dobson circulation. Our record of events with sulfate deposition rates > 20 and >50 mg m−2 contains 678 and 75 eruptions, respectively, over the last 200 kyr. Calibration with data on historic eruptions and analysis of a global Quaternary dataset of terrestrial eruptions indicates that sulfate peaks with deposition rates > 20 and >50 mg m−2 correspond to explosive eruptions of magnitude ≥ 6.5 and ≥7, respectively. The largest recorded eruption deposited just over 300 mg m−2.
The ∼74 ka Toba eruption was one of the
largest volcanic events of the Quaternary. There is much interest in
determining the impact of such a large event, particularly on the climate
and hominid ...populations at the time. Although the Toba eruption has been
identified in both land and marine archives as the Youngest Toba Tuff, its
precise place in the ice core record is ambiguous. Several volcanic sulfate
signals have been identified in both Antarctic and Greenland ice cores and
span the Toba eruption 40Ar/39Ar age uncertainty. Here, we measure
sulfur isotope compositions in Antarctic ice samples from the Dome C
(EDC) and Dronning Maud Land (EDML)
ice cores at high temporal resolution across 11 of these potential Toba
sulfate peaks to identify candidates with sulfur mass-independent
fractionation (S-MIF), indicative of an eruption whose plume reached
altitudes at or above the stratospheric ozone layer. Using this method, we
identify several candidate sulfate peaks that contain stratospheric sulfur.
We further narrow down potential candidates based on the isotope signatures
by identifying sulfate peaks that are due to a volcanic event at tropical
latitudes. In one of these sulfate peaks at 73.67 ka, we find the largest
ever reported magnitude of S-MIF in volcanic sulfate in polar ice, with a
Δ33S value of −4.75 ‰. As there is a
positive correlation between the magnitude of the S-MIF signal recorded in
ice cores and eruptive plume height, this could be a likely candidate for
the Toba super-eruption, with a plume top height in excess of 45 km. These
results support the 73.7±0.3 ka (1σ) 40Ar/39Ar
age estimate for the eruption, with ice core ages of our candidates with the
largest magnitude S-MIF at 73.67 and 73.74 ka. Finally, since these
candidate eruptions occurred on the transition into Greenland Stadial 20,
the relative timing suggests that Toba was not the trigger for the large
Northern Hemisphere cooling at this time although we cannot rule out an
amplifying effect.
The Outburst of HST-1 in the M87 Jet Harris, D. E; Cheung, C. C; Biretta, J. A ...
Astrophysical journal/The Astrophysical journal,
03/2006, Letnik:
640, Številka:
1
Journal Article
Recenzirano
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The X-ray intensity of knot HST-1,0".85 from the nucleus of the radio galaxy M87, has increased by more than a factor of 50 during the last 5 yr. The optical increase is similar, and our more limited ...radio data indicate a commensurate activity. We give the primary results of our Chandra X-Ray Observatory monitoring program and consider some of the implications of this extreme variability in a relativistic jet. We find that the data support a "modest beaming synchrotron" model as indicated in our earlier papers. Based on this model, the decay of the X-ray light curve appears to be dominated by the light-travel time across the emitting region of HST-1, rather than synchrotron loss timescales.
Context. Radio-loud active galactic nuclei with powerful relativistic jets are thought to be associated with rapidly spinning black holes (BHs). BH spin-up may result from a number of processes, ...including accretion of matter onto the BH itself, and catastrophic events such as BH-BH mergers. Aims. We study the intriguing properties of the powerful (Lbol ~ 1047 erg s-1) radio-loud quasar 3C 186. This object shows peculiar features both in the images and in the spectra. Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical spectra to study the kinematics of the source. Chandra X-ray data are also used to better constrain the physical interpretation. Results. HST imaging shows that the active nucleus is offset by 1.3 ± 0.1 arcsec (i.e. ~11 kpc) with respect to the center of the host galaxy. Spectroscopic data show that the broad emission lines are offset by −2140 ± 390 km s-1 with respect to the narrow lines. Velocity shifts are often seen in QSO spectra, in particular in high-ionization broad emission lines. The host galaxy of the quasar displays a distorted morphology with possible tidal features that are typical of the late stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged to account for the observed features. While the presence of a peculiar outflow cannot be completely ruled out, all of the observed features are consistent with those expected if the QSO is associated with a gravitational wave (GW) recoiling BH. Future detailed studies of this object will allow us to confirm this type of scenario and will enable a better understanding of both the physics of BH-BH mergers and the phenomena associated with the emission of GW from astrophysical sources.
During the 2010 eruption of Eyjafjallajökull, improvements were made to the modeling procedure at the Met Office, UK, enabling peak ash concentrations within the volcanic cloud to be estimated. In ...this paper we describe the ash concentration forecasting method, its rationale and how it evolved over time in response to new information and user requirements. The change from solely forecasting regions of ash to also estimating peak ash concentrations required consideration of volcanic ash emission rates, the fraction of ash surviving near‐source fall‐out, and the relationship between predicted mean and local peak ash concentrations unresolved by the model. To validate the modeling procedure, predicted peak ash concentrations are compared against observations obtained by ground‐based and research aircraft instrumentation. This comparison between modeled and observed peak concentrations highlights the many sources of error and the uncertainties involved. Despite the challenges of predicting ash concentrations, the ash forecasting method employed here is found to give useful guidance on likely ash concentrations. Predicted peak ash concentrations lie within about one and a half orders of magnitude of the observed peak concentrations. A significant improvement in the agreement between modeled and observed values is seen if a buffer zone, accounting for positional errors in the predicted ash cloud, is used. Sensitivity of the predicted ash concentrations to the source properties (e.g., the plume height and the vertical distribution of ash at the source) is assessed and in some cases, seemingly minor uncertainties in the source specification have a large effect on predicted ash concentrations.
Key Points
A method for forecasting peak volcanic ash concentrations is described
Method validated using observations from the 2010 Eyjafjallajokull eruption
Uncertainties in modeled ash concentrations are numerous and large
ABSTRACT We present new rest-frame UV and visible observations of 22 high-z (1 < z < 2.5) 3C radio galaxies and QSOs obtained with the Hubble Space Telescope's Wide Field Camera 3 instrument. Using a ...custom data reduction strategy in order to assure the removal of cosmic rays, persistence signal, and other data artifacts, we have produced high-quality science-ready images of the targets and their local environments. We observe targets with regions of UV emission suggestive of active star formation. In addition, several targets exhibit highly distorted host galaxy morphologies in the rest frame visible images. Photometric analyses reveal that brighter QSOs generally tend to be redder than their dimmer counterparts. Using emission line fluxes from the literature, we estimate that emission line contamination is relatively small in the rest frame UV images for the QSOs. Using archival VLA data, we have also created radio map overlays for each of our targets, allowing for analysis of the optical and radio axes alignment.
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