Context. Since its rendezvous with comet 67P/Churyumov-Gerasimenko (67P), the Rosetta spacecraft has provided invaluable information contributing to our understanding of the cometary environment. On ...board, the VIRTIS and ROSINA instruments can both measure gas parameters in the rarefied cometary atmosphere, the so-called coma, and provide complementary results with remote sensing and in situ measurement techniques, respectively. The data from both ROSINA and VIRTIS instruments suggest that the source regions of H2O and CO2 are not uniformly distributed over the surface of the nucleus even after accounting for the changing solar illumination of the irregularly shaped rotating nucleus. The source regions of H2O and CO2 are also relatively different from one another. Aims. The use of a combination of a formal numerical data inversion method with a fully kinetic coma model is a way to correlate and interpret the information provided by these two instruments to fully understand the volatile environment and activity of comet 67P. Methods. In this work, the nonuniformity of the outgassing activity at the surface of the nucleus is described by spherical harmonics and constrained by ROSINA-DFMS data. This activity distribution is coupled with the local illumination to describe the inner boundary conditions of a 3D direct simulation Monte-Carlo (DSMC) approach using the Adaptive Mesh Particle Simulator (AMPS) code applied to the H2O and CO2 coma of comet 67P. Results. We obtain activity distribution of H2O and CO2 showing a dominant source of H2O in the Hapi region, while more CO2 is produced in the southern hemisphere. The resulting model outputs are analyzed and compared with VIRTIS-M/-H and ROSINA-DFMS measurements, showing much better agreement between model and data than a simpler model assuming a uniform surface activity. The evolution of the H2O and CO2 production rates with heliocentric distance are derived accurately from the coma model showing agreement between the observations from the different instruments and ground-based observations. Conclusions. We derive the activity distributions for H2O and CO2 at the surface of the nucleus described in spherical harmonics, which we couple to the local solar illumination to constitute the boundary conditions of our coma model. The model presented reproduces the coma observations made by the ROSINA and VIRTIS instruments on board the Rosetta spacecraft showing our understanding of the physics of 67P’s coma. This model can be used for further data analyses, such as dust modeling, in a future work.
Context. Studying the coma environment of comet 67P/Churyumov-Gerasimenko (67P) is one of the primary scientific goals of the VIRTIS experiment on the ESA Rosetta mission. Aims. The distribution and ...variability of water vapour and carbon dioxide in the comet’s coma are needed to estimate their production rate, abundances in the nucleus, and the spatial distribution of the active regions. Methods. Infrared emission lines from vibrational bands of water and carbon dioxide at 2.67 and 4.27 μm, respectively, were observed by the VIRTIS-M imaging channel and mapped from close to the nucleus up to ~10 km altitude with a resolution of ~40 m/px. A dataset consisting of 74 observations in the 1−5 μm spectral range acquired from 8 to 14 April 2015 when 67P was at a heliocentric distance of 1.9 AU is analysed in this work. A statistical correlation between the gas distribution and the surface’s active regions was performed. Results. The maximum H2O emission is observed within 3 km from the nucleus and is mainly concentrated above two active regions, Aten-Babi and Seth-Hapi, while the CO2 distribution appears more uniform with significant emissions coming from both the “head” and southern latitude regions. In the equatorial region, the column densities of both species decrease with altitude, although CO2 decreases more rapidly than H2O. The calculated CO2/H2O column density ratios above Aten-Babi and Seth-Hapi are 2.4 ± 0.6% and 3.0 ± 0.7%, respectively. A value equal to 3.9 ± 1.0% is observed at equatorial latitudes in the region encompassing Imothep. Conclusions. VIRTIS-M has mapped the distribution of water vapour and carbon dioxide around the nucleus of 67P with unprecedented spatial resolution. The different water and carbon dioxide outgassing above the surface, seen in the VIRTIS-M data, might be indicative of a different thermal history of the northern and southern hemispheres of 67P.
The Visible, InfraRed, and Thermal Imaging Spectrometer (VIRTIS) on Rosetta obtained hyperspectral images, spectral reflectance maps, and temperature maps of the asteroid 21 Lutetia. No absorption ...features, of either silicates or hydrated minerals, have been detected across the observed area in the spectral range from 0.4 to 3.5 micrometers. The surface temperature reaches a maximum value of 245 kelvin and correlates well with topographic features. The thermal inertia is in the range from 20 to 30 joules meter⁻² kelvin⁻¹ second⁻⁰.⁵, comparable to a lunarlike powdery regolith. Spectral signatures of surface alteration, resulting from space weathering, seem to be missing. Lutetia is likely a remnant of the primordial planetesimal population, unaltered by differentiation processes and composed of chondritic materials of enstatitic or carbonaceous origin, dominated by iron-poor minerals that have not suffered aqueous alteration.
On 2015 July 18, near perihelion at a heliocentric distance of 1.28 au, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-M) on board the Rosetta spacecraft had the opportunity of observing ...dust activity in the inner coma with a view of the night side (shadowed side) of comet 67P/Churyumov-Gerasimenko. At the time of the measurements we present here, we observe a dust plume that originates on the far side of the nucleus. We are able to identify the approximate location of its source at the boundary between the Hapi and Anuket regions, and we find that it has been in darkness for some hours before the observation. Assuming that this time span is equal to the conductive time scale, we obtain a thermal inertia in the range 25–36 W K−1 m−2 s−1/2. These thermal inertia values can be used to verify with a 3D finite-element method (FEM) numerical code whether the surface and subsurface temperatures agree with the values found in the literature. We explored three different configurations: (1) a layer of water ice mixed with dust beneath a dust mantle of 5 mm with thermal inertia of 36 J m−2 K−1 s−0.5; (2) the same structure, but with thermal inertia of 100 J m−2 K−1 s−0.5; (3) an ice-dust mixture that is directly exposed. Of these three configurations, the first seems to be the most reasonable, both for the low thermal inertia and for the agreement with the surface and subsurface temperatures that have been found for the comet 67P/Churyumov-Gerasimenko. The spectral properties of the plume show that the visible dust color ranged from 16 ± 4.8%/100 nm to 13 ± 2.6%/100 nm, indicating that this plume has no detectable color gradient. The morphology of the plume can be classified as a narrow jet that has an estimated total ejected mass of between 6 and 19 tons when we assume size distribution indices between −2.5 and −3.
Preoperative chemotherapy in patients with gastroesophageal cancer is hampered by the lack of reliable predictors of tumor response. This study evaluates whether positron emission tomography (PET) ...using fluorine-18 fluorodeoxyglucose (FDG) may predict response early in the course of therapy.
Forty consecutive patients with locally advanced adenocarcinomas of the esophagogastric junction were studied by FDG-PET at baseline and 14 days after initiation of cisplatin-based polychemotherapy. Clinical response (reduction of tumor length and wall thickness by > 50%) was evaluated after 3 months of therapy using endoscopy and standard imaging techniques. Patients with potentially resectable tumors underwent surgery, and tumor regression was assessed histopathologically.
The reduction of tumor FDG uptake (mean +/- 1 SD) after 14 days of therapy was significantly different between responding (-54% +/- 17%) and nonresponding tumors (-15% +/- 21%). Optimal differentiation was achieved by a cutoff value of 35% reduction of initial FDG uptake. Applying this cutoff value as a criterion for a metabolic response predicted clinical response with a sensitivity and specificity of 93% (14 of 15 patients) and 95% (21 of 22), respectively. Histopathologically complete or subtotal tumor regression was achieved in 53% (eight of 15) of the patients with a metabolic response but only in 5% (one of 22) of the patients without a metabolic response. Patients without a metabolic response were also characterized by significantly shorter time to progression/recurrence (P =.01) and shorter overall survival (P =.04).
PET imaging may differentiate responding and nonresponding tumors early in the course of therapy. By avoiding ineffective and potentially harmful treatment, this may markedly facilitate the use of preoperative therapy, especially in patients with potentially resectable tumors.
We present a study of the current state of knowledge concerning spacecraft operations and potential hazards while operating near a comet nucleus. Starting from simple back of the envelope ...calculations comparing the cometary coma environment to benign conditions on Earth, we progress to sophisticated engineering models of spacecraft behavior, and then confront these models with recent spacecraft proximity operations experience (e.g., Rosetta). Finally, we make recommendations from lessons learned for future spacecraft missions that enter into orbit around a comet for long-term operations. All of these considerations indicate that, with a proper spacecraft design and operations planning, the near-nucleus environment can be a relatively safe region in which to operate, even for an active short period comet near perihelion with gas production rates as high as 1029 molecules/s. With gas densities similar to those found in good laboratory vacuums, dust densities similar to Class 100 cleanrooms, dust particle velocities of 10's of m/s, and microgravity forces that permit slow and deliberate operations, the conditions around a comet are generally more benign than a typical day on Mars. Even in strong dust jets near the nucleus' surface, dust densities tend to be only a few grains/cm3, about the same as in a typical interior room on Earth. Stochastic forces on a modern spacecraft with tens of square meters of projected surface area can be accounted for using modern Attitude Control Systems to within tens of meters' navigation error; surface contamination issues are only important for spacecraft spending months to years within a few kilometers of the nucleus' surface; and the issues the Rosetta spacecraft faced, confusion of celestial star trackers by sunlit dust particles flying past the spacecraft, will be addressed using the next generation of star trackers implementing improved transient rejection algorithms.
•The cometary near-nucleus environment is safe for remotely operated spacecraft to operate in.•This environment is more benign than a day on Mars or a Class 100 clean room.•The highly successful Rosetta mission experienced minimal side effects due to operations in the near-nucleus comet environment.•The minimal side effects can be ameliorated by flying instrument covers, avoiding active jet regions, and implementing modern star trackers with advanced false positive rejection algorithms.
The VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe for Planetary Exploration. VIRTIS, developed in cooperation among Italy, ...France and Germany, has been already selected as a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison – using the same combination of sophisticated experiments – of targets that are poorly differentiated and are representative of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the “in situ” measurements will provide “ground-truth” for the remote sensing information, and, in turn, the locally collected data will be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures – such as the typical spectral bands of minerals and molecules – arising from surface components and from materials dispersed in the coma. The identification of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied.
A summary is presented of our spectroscopic survey of comets extending for roughly 19 years from 1985 to 2004 comprising data for 92 comets of which 50 showed good emissions. All data were ...re-analyzed using consistent reduction techniques. Our observations of comets over several apparitions and comets observed over an extended period indicate no major changes in compositional classification. To our regret, no major unidentified cometary features were found in our surveyed spectral region of 5200–10400 Å. Absolute production rates for the dominant parent molecule H
2O and the daughter species C
2, NH
2 and CN are determined within the limits of the Haser model as are values for the dust continuum,
Afρ. From these data, production rate ratios are calculated for C
2/H
2O, NH
2/H
2O, CN/H
2O and
Afρ/H
2O. Excluding the odd Comets Yanaka (1988r), 43P/Wolf–Harrington and 19P/Borrelly, with unusual spectra, our set of comets exhibited relatively uniform composition. Detailed analyses of our data resulted in four taxonomic classes:
–
Comets of typical composition (∼70%); exhibiting typical ratios with respect to water of C
2, NH
2, and CN.
–
Tempel 1 type (∼22%); having a deficiency in C
2 but normal NH
2 abundance.
–
G–Z type (∼6%); having both low C
2 and NH
2 ratios.
–
The unusual object Yanaka (1988r) (∼2%?); no detectable C
2 or CN emission but normal NH
2.
It is uncertain whether there is a clear separation between the comets of typical composition and those with C
2 depletion, or whether the latter consists of a group showing a continuum of decreasing C
2/CN ratios. Our spectroscopic investigations result in a visual record of the various compositional classes, which are illustrated in a number of figures. Production rate comparisons with the comet photometry program of Schleicher and A'Hearn A'Hearn, M.F., and 4 colleagues, 1995. Icarus 118, 223–270 for 13 comets in common yielded good agreement once the different scale lengths are taken into account. An investigation into the possible origin of our compositional groups with respect to dynamical families of comets shows that the Halley family exhibits essentially no C
2 depletion. These objects were presumably formed in the region of Saturn and Uranus and scattered into the Oort cloud. Comets formed in the space near Neptune, responsible for the scattered Kuiper Belt show a mixture of “typical” and C
2 depleted objects, while we associate comets formed in-situ in the classical Kuiper belt with our C
2 depleted group.
Background This phase II study was initiated to determine the efficacy and safety of gemcitabine plus cisplatin in patients with pancreatic cancer. Patients and methods Gemcitabine 1000 mg/m2 was ...given on days 1, 8, and 15 of a 28-day schedule, and cisplatin 50 mg/m2 on days 1 and 15 to chemonaive patients with locally advanced or metastatic pancreatic cancer. Results Of the 41 patients enrolled (median age 57, and 61% male), median Karnofsky performance status was 80%. Patients received a median of 4.2 cycles (range 1–11). In 35 evaluable patients, one complete response (CR) and three partial responses (PR) were observed, for an overall response rate of 11% (95% confidence interval (95% CI): 3.2%–26.7%). Stable disease (SD) >3 months occurred in 20 (57%) patients; 6 survived ≥ 1 year. Median time to progressive disease was 4.3 months (95% CI: 3.0–5.7 months). For all patients, median survival was 8.2 months (95% CI: 6.1–10.6 months) with a one-year survival rate of 27%. Therapy was well tolerated. Grade 3–4 neutropenia (no grade 3–4 infection), thrombocytopenia (no bleeding), nausea/vomiting, and alopecia were reported in 29%, 13%, and 2.6% of patients, respectively. Conclusions The combination of gemcitabine and cisplatin is a moderately active treatment for patients with locally advanced and metastatic pancreatic cancer without compromising tolerability.
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