| 1. |
- Grun, E., et al.
(author)
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The 2016 Feb 19 outburst of comet 67P/CG : an ESA Rosetta multi-instrument study
- 2016
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S220-S234
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Journal article (peer-reviewed)abstract
- On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09: 40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors > 100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors > 10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from similar to-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta ( 34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (similar to 25 m s(-1)) while 100 mu m radius particles were detected by the GIADA dust instrument similar to 1 h later at a speed of 6 m s(-1). The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
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| 2. |
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| 3. |
- Barucci, M. A., et al.
(author)
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Detection of exposed H2O ice on the nucleus of comet 67P/Churyumov-Gerasimenko as observed by Rosetta OSIRIS and VIRTIS instruments
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 595
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Journal article (peer-reviewed)abstract
- Context. Since the orbital insertion of the Rosetta spacecraft, comet 67P/Churyumov-Gerasimenko (67P) has been mapped by OSIRIS camera and VIRTIS spectro-imager, producing a huge quantity of images and spectra of the comet's nucleus. Aims. The aim of this work is to search for the presence of H2O on the nucleus which, in general, appears very dark and rich in dehydrated organic material. After selecting images of the bright spots which could be good candidates to search for H2O ice, taken at high resolution by OSIRIS, we check for spectral cubes of the selected coordinates to identify these spots observed by VIRTIS. Methods. The selected OSIRIS images were processed with the OSIRIS standard pipeline and corrected for the illumination conditions for each pixel using the Lommel-Seeliger disk law. The spots with higher I/F were selected and then analysed spectrophotometrically and compared with the surrounding area. We selected 13 spots as good targets to be analysed by VIRTIS to search for the 2 mu m absorption band of water ice in the VIRTIS spectral cubes. Results. Out of the 13 selected bright spots, eight of them present positive H2O ice detection on the VIRTIS data. A spectral analysis was performed and the approximate temperature of each spot was computed. The H2O ice content was confirmed by modeling the spectra with mixing (areal and intimate) of H2O ice and dark terrain, using Hapke's radiative transfer modeling. We also present a detailed analysis of the detected spots.
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| 4. |
- Davidsson, Björn, et al.
(author)
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The primordial nucleus of comet 67P/Churyumov-Gerasimenko
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Journal article (peer-reviewed)abstract
- Context. We investigate the formation and evolution of comet nuclei and other trans-Neptunian objects (TNOs) in the solar nebula and primordial disk prior to the giant planet orbit instability foreseen by the Nice model. Aims. Our goal is to determine whether most observed comet nuclei are primordial rubble-pile survivors that formed in the solar nebula and young primordial disk or collisional rubble piles formed later in the aftermath of catastrophic disruptions of larger parent bodies. We also propose a concurrent comet and TNO formation scenario that is consistent with observations. Methods. We used observations of comet 67P/Churyumov-Gerasimenko by the ESA Rosetta spacecraft, particularly by the OSIRIS camera system, combined with data from the NASA Stardust sample-return mission to comet 81P/Wild 2 and from meteoritics; we also used existing observations from ground or from spacecraft of irregular satellites of the giant planets, Centaurs, and TNOs. We performed modeling of thermophysics, hydrostatics, orbit evolution, and collision physics. Results. We find that thermal processing due to short-lived radionuclides, combined with collisional processing during accretion in the primordial disk, creates a population of medium-sized bodies that are comparably dense, compacted, strong, heavily depleted in supervolatiles like CO and CO2; they contain little to no amorphous water ice, and have experienced extensive metasomatism and aqueous alteration due to liquid water. Irregular satellites Phoebe and Himalia are potential representatives of this population. Collisional rubble piles inherit these properties from their parents. Contrarily, comet nuclei have low density, high porosity, weak strength, are rich in supervolatiles, may contain amorphous water ice, and do not display convincing evidence of in situ metasomatism or aqueous alteration. We outline a comet formation scenario that starts in the solar nebula and ends in the primordial disk, that reproduces these observed properties, and additionally explains the presence of extensive layering on 67P/Churyumov-Gerasimenko (and on 9P/Tempel 1 observed by Deep Impact), its bi-lobed shape, the extremely slow growth of comet nuclei as evidenced by recent radiometric dating, and the low collision probability that allows primordial nuclei to survive the age of the solar system. Conclusions. We conclude that observed comet nuclei are primordial rubble piles, and not collisional rubble piles. We argue that TNOs formed as a result of streaming instabilities at sizes below similar to 400 km and that similar to 350 of these grew slowly in a low-mass primordial disk to the size of Triton, Pluto, and Eris, causing little viscous stirring during growth. We thus propose a dynamically cold primordial disk, which prevented medium-sized TNOs from breaking into collisional rubble piles and allowed the survival of primordial rubble-pile comets. We argue that comets formed by hierarchical agglomeration out of material that remained after TNO formation, and that this slow growth was a necessity to avoid thermal processing by short-lived radionuclides that would lead to loss of supervolatiles, and that allowed comet nuclei to incorporate similar to 3 Myr old material from the inner solar system.
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| 5. |
- El-Marry, M. R., et al.
(author)
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Regional surface morphology of comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images : The southern hemisphere
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 593
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Journal article (peer-reviewed)abstract
- Aims. The OSIRIS camera on board the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P)'s nucleus since August 2014. Starting in May 2015, the southern hemisphere gradually became illuminated and was imaged for the first time. Here we present the regional morphology of the southern hemisphere, which serves as a companion to an earlier paper that presented the regional morphology of the northern hemisphere. Methods. We used OSIRIS images that were acquired at orbits similar to 45-125 km from the center of the comet (corresponding to spatial resolutions of similar to 0.8 to 2.3 m/pixel) coupled with the use of digital terrain models to define the different regions on the surface, and identify structural boundaries accurately. Results. Seven regions have been defined in the southern hemisphere bringing the total number of defined regions on the surface of the nucleus to 26. These classifications are mainly based on morphological and/or topographic boundaries. The southern hemisphere shows a remarkable dichotomy with its northern counterpart mainly because of the absence of wide-scale smooth terrains, dust coatings and large unambiguous depressions. As a result, the southern hemisphere closely resembles previously identified consolidated regions. An assessment of the overall morphology of comet 67P suggests that the comet's two lobes show surface heterogeneities manifested in different physical/mechanical characteristics, possibly extending to local (i.e., within a single region) scales.
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| 6. |
- Giacomini, L., et al.
(author)
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Geologic mapping of the Comet 67P/Churyumov-Gerasimenko's Northern hemisphere
- 2016
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S352-S369
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Journal article (peer-reviewed)abstract
- The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), the scientific imaging system onboard the Rosetta mission, has been acquiring images of the nucleus of the comet 67P/Churyumov-Gerasimenko since 2014 August with a resolution which allows a detailed analysis of its surface. Indeed, data reveal a complex surface morphology which is likely the expression of different processes which occurred at different times on the cometary nucleus. In order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67P Northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. For this purpose, we used narrow-angle camera images acquired in 2014 August and September with a spatial scale ranging from 1.2 to 2.4 m pixel(-1). Several different geologic units have been identified on the basis of their different surface textures, granulometry and morphology. Some of these units are distinctive and localized, whereas others are more common and distributed all over the Northern hemisphere. Moreover, different types of linear features have been distinguished on the basis of their morphology. Some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. The geologic mapping results presented here will allow us to better understand the processes which affected the nucleus' surface and thus the origin and evolutionary history of comet 67P/Churyumov-Gerasimenko.
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| 7. |
- Graff, RE, et al.
(author)
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2Pre-diagnostic circulating sex hormone levels and risk of prostate cancer by TMPRSS2:ERG status.
- 2016
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In: JOURNAL OF CLINICAL ONCOLOGY. - : American Society of Clinical Oncology (ASCO). - 0732-183X .- 1527-7755. ; 34:2
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Conference paper (other academic/artistic)abstract
- 93 Background: Experimental studies have shown that androgen receptor stimulation can facilitate formation of the TMPRSS2:ERG gene fusion in prostate cell lines. No study has tested whether higher pre-diagnostic circulating sex hormone levels in men increase the risk of developing TMPRSS2:ERG positive prostate cancer specifically. Methods: We conducted a nested case-control study of 200 prostate cancer cases and 1,057 controls from the Physicians’ Health Study and Health Professionals Follow-up Study. We examined associations between pre-diagnostic circulating levels of total testosterone, free testosterone, DHT, androstanediol glucuronide, estradiol, and SHBG and risk of prostate cancer by TMPRSS2:ERG status. TMPRSS2:ERG was assessed by ERG immunohistochemistry. We used multivariable unconditional polytomous logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for risk of fusion-positive (n = 94) and, separately, fusion-negative (n = 106) disease. Results: Free testosterone was significantly associated with the risk of ERG-positive prostate cancer (OR: 1.37, 95% CI: 1.05-1.77), but not ERG-negative prostate cancer (OR: 1.09, 95% CI: 0.86-1.38) (p-diff: 0.17). None of the remaining hormones evaluated showed clear differential associations with ERG-positive versus ERG-negative disease. Conclusions: These findings provide some suggestive evidence that higher pre-diagnostic free testosterone levels are associated with an increased risk of developing TMPRSS2:ERG positive prostate cancer but are not associated with prostate cancer that lacks TMPRSS2:ERG.
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| 8. |
- Gutierrez, P. J., et al.
(author)
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Possible interpretation of the precession of comet 67P/Churyumov-Gerasimenko
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590
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Journal article (peer-reviewed)abstract
- Context. Data derived from the reconstruction of the nucleus shape of comet 67P/Churyumov-Gerasimenko (67P) from images of the OSIRIS camera onboard ROSETTA show evidence that the nucleus rotates in complex mode. First, the orientation of the spin axis is not fixed in an inertial reference frame, which suggests a precessing motion around the angular momentum vector with a periodicity of approximately 257 h +/- 12 h. Second, periodograms of the right ascension and declination (RA/Dec) coordinates of the body-frame Z axis show a very significant (higher than 99.99%) periodicity at 276 h +/- 12 h, different from the rotational period of 12.40 h as previously determined from light-curve analysis. Aims. The main goal is to interpret the data and associated periodicities of the spin axis orientation in space. Methods. We analyzed the spin axis orientation in space and associated periodicities and compared them with solutions of Euler equations under the assumption that the body rotates in torque-free conditions. Statistical tests comparing the observationally derived spin axis orientation with the outcome from simulations were applied to determine the most likely inertia moments, excitation level, and periods. Results. Under the assumption that the body is solid-rigid and rotates in torque-free conditions, the most likely interpretation is that 67P is spinning around the principal axis with the highest inertia moment with a period of about 13 h. At the same time, the comet precesses around the angular momentum vector with a period of about 6.35 h. While the rotating period of such a body would be about 12.4 h, RA/Dec coordinates of the spin axis would have a periodicity of about 270 h as a result of the combination of the two aforementioned motions. Conclusions. The most direct and simple interpretation of the complex rotation of 67P requires a ratio of inertia moments significantly higher than that of a homogeneous body.
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| 9. |
- Mucci, LA, et al.
(author)
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Precision prevention of TMPRSS2: ERG prostate cancer.
- 2016
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In: JOURNAL OF CLINICAL ONCOLOGY. - : American Society of Clinical Oncology (ASCO). - 0732-183X .- 1527-7755. ; 34:2
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Conference paper (other academic/artistic)abstract
- 78 Background: Increased integration of tumor biomarker data into prostate cancer epidemiology studies is needed to identify molecular subtypes that underlie its etiology and progression. We hypothesize that the TMPRSS2:ERG gene fusion is a unique prostate cancer subtype that is etiologically distinct from cancers lacking TMPRSS2:ERG. Methods: We leveraged the Physicians’ Health Study and Health Professionals Follow-up Study cohort data on pre- and post-diagnostic lifestyle factors, inherited genetic variants, circulating biomarkers, and clinical data and follow-up for 30 years. We have a tumor repository of men with prostate cancer and tumor tissue microarrays. Using immunohistochemistry, we characterized TMPRSS2:ERG status for 1,491 incident prostate cancer cases in these cohorts, and also have biomarker data on a range of additional markers from immunohistochemistry and mRNA expression profiling. Results: Fifty percent of prostate cancer cases were ERG-positive. ERG-positive cancers show much higher expression of insulin/IGF signaling, PTEN loss, higher VDR expression, as well as expression of mismatch repair genes. In contrast, ERG-negative prostate cancer is characterized by increased presence of chronic inflammation and atrophy. We found higher pre-diagnostic free testosterone levels, but not other sex hormones, were associated with increased risk of ERG-positive (OR = 1.4, 95% CI = 1.0-1.8) but not ERG-negative disease (OR = 0.9, 95% CI = 0.7-1.2). Of 39 known genetic risk loci, six were significantly associated (p < 0.05) with ERG+ versus ERG- cancer (2 expected by chance). Prostate cancer risk factors such as taller height (an indicator of growth factors in puberty) are uniquely associated with ERG-positive prostate cancer. Moreover, we observe a complex interaction of components of insulin/IGF and ERG-status on prostate cancer mortality. Conclusions: TMPRSS2:ERG is a highly prevalent somatic event in prostate cancer that likely defines a unique molecular subtype of this common disease. Understanding the differences between these two prostate cancer subtypes may enhance opportunities for prevention.
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