656 research outputs found
Asteroid detection at millimetric wavelengths with the Planck survey
The Planck mission, originally devised for cosmological studies, offers the
opportunity to observe Solar System objects at millimetric and submillimetric
wavelengths. We concentrate in this paper on the asteroids of the Main Belt. We
intend to estimate the number of asteroids that can can be detected during the
mission and to evaluate the strength of their signal. We have rescaled the
instrument sensitivities, calculated by the LFI and HFI teams for sources fixed
in the sky, introducing some degradation factors to properly account for moving
objects. In this way a detection threshold is derived for asteroidal detection
that is related to the diameter of the asteroid and its geocentric distance. We
have developed a numerical code that models the detection of asteroids in the
LFI and HFI channels during the mission. This code perfoprms a detailed
integration of the orbits of the asteroids in the timespan of the mission and
identifies those bodies that fall in the beams of Planck and their signal
stenght. According to our simulations, a total of 397 objects will be observed
by Planck and an asteroidal body will be detected in some beam in 30% of the
total sky scan--circles. A significant fraction (in the range from ~50 to 100
objects) of the 397 asteroids will be observed with a high S/N ratio. Flux
measurements of a large sample of asteroids in the submillimeter and millimeter
range are relevant since they allow to analyze the thermal emission and its
relation to the surface and regolith properties. Furthermore, it will be
possible to check on a wider base the two standard thermal models, based on a
nonrotating or rapidly rotating sphere. Our method can also be used to separate
Solar System sources from cosmological sources in the survey. This work is
based on Planck LFI activities.Comment: Contact person [email protected]. Accepted for pubblication in
New Astronomy (2002). 1 figure in .eps format. Needs elsart.cls style +
harvard.st
1999 Quadrantids and the lunar Na atmosphere
Enhancements of the Na emission and temperature from the lunar atmosphere
were reported during the Leonids meteor showers of 1995, 1997 and 1998. Here we
report a search for similar enhancement during the 1999 Quadrantids, which have
the highest mass flux of any of the major streams. No enhancements were
detected. We suggest that different chemical-physical properties of the Leonid
and Quadrantid streams may be responsible for the difference.Comment: 5 pages, 1 figure, accepted for publication in MNRA
The 1999 Quadrantids and the lunar Na atmosphere
Enhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonid meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical-physical properties of the Leonid and Quadrantid streams may be responsible for the differenc
Geometrical Calibration for the Panrover: a Stereo Omnidirectional System for Planetary Rover
Abstract. A novel panoramic stereo imaging system is proposed in this paper. The system is able to carry out a 360° stereoscopic vision, useful for rover autonomous-driving, and capture simultaneously a high-resolution stereo scene. The core of the concept is a novel "bifocal panoramic lens" (BPL) based on hyper hemispheric model (Pernechele et al. 2016). This BPL is able to record a panoramic field of view (FoV) and, simultaneously, an area (belonging to the panoramic FoV) with a given degree of magnification by using a unique image sensor. This strategy makes possible to avoid rotational mechanisms. Using two BPLs settled in a vertical baseline (system called PANROVER) allows the monitoring of the surrounding environment in stereoscopic (3D) mode and, simultaneously, capturing an high-resolution stereoscopic images to analyse scientific cases, making it a new paradigm in the planetary rovers framework.Differently from the majority of the Mars systems which are based on rotational mechanisms for the acquisition of the panoramic images (mosaicked on ground), the PANROVER does not contain any moving components and can rescue a hi-rate stereo images of the context panorama.Scope of this work is the geometric calibration of the panoramic acquisition system by the omnidirectional calibration methods (Scaramuzza et al. 2006) based on Zhang calibration grid. The procedures are applied in order to obtain well rectified synchronized stereo images to be available for 3D reconstruction. We applied a Zhang chess boards based approach even during STC/SIMBIO-SYS stereo camera calibration (Simioni et al. 2014, 2017). In this case the target of the calibration will be the stereo heads (the BPLs) of the PANROVER with the scope of extracting the intrinsic parameters of the optical systems. Differently by previous pipelines, using the same data bench the estimate of the extrinsic parameters is performed
PERFORMANCE EVALUATION OF 3DPD, THE PHOTOGRAMMETRIC PIPELINE FOR THE CASSIS STEREO IMAGES
A novel photogrammetric pipeline has been designed by INAF-Padova for the processing of the recent stereo images of CaSSIS and it will be a starting point for the future procedures that will be applied to Stereo Camera (STC) (Cremonese, 2009; Da Deppo, 2010) images for the BepiColombo mission to Mercury. The large number of stereo pairs being generated has made it necessary that several teams attempt to generate products. The presented procedures are the two strategies (proposed by INAF-PADOVA and by EPFLLausanne) available nowadays in an international attempt to generate 3D products from the CaSSIS images. The comparisons here presented will be the first of several such efforts and are important to make the planetary community aware of the accuracy of the 3D data available. Furthermore, the possibility to consider higher accuracy DTMs as the ones of HiRISE makes the quality assessment of stereo products of CaSSIS robust and important for the assessment of data to be provided to the scientific community. The performance evaluation of the INAF-Padova pipeline (3DPD software) is the main objectives of this work. Additionally, the comparison between the correlation phase of 3DPD and of ASP (Moratto, 2010) that is integrated in the EPFL pipeline has been considered
Warming permafrost and active layer variability at Cime Bianche, Western European Alps
The objective of this paper is to provide a first synthesis on the state and recent evolution of permafrost at the monitoring site of Cime Bianche (3100 m a.s.l.) on the Italian side of the Western Alps. The analysis is based on 7 years of ground temperature observations in two boreholes and seven surface points. The analysis aims to quantify the spatial and temporal variability of ground surface temperature in relation to snow cover, the small-scale spatial variability of the active layer thickness and current temperature trends in deep permafrost.Results show that the heterogeneity of snow cover thickness, both in space and time, is the main factor controlling ground surface temperatures and leads to a mean range of spatial variability (2.5 ± 0.1 °C) which far exceeds the mean range of observed inter-annual variability (1.6 ± 0.1 °C). The active layer thickness measured in two boreholes at a distance of 30 m shows a mean difference of 2.0 ± 0.1 m with the active layer of one borehole consistently deeper. As revealed by temperature analysis and geophysical soundings, such a difference is mainly driven by the ice/water content in the sub-surface and not by the snow cover regimes. The analysis of deep temperature time series reveals that permafrost is warming. The detected trends are statistically significant starting from a depth below 8 m with warming rates between 0.1 and 0.01 °C yrâ»Âč
Contrasting responses of forest growth and carbon sequestration to heat and drought in the Alps
>Climate change is expected to increase both the frequency and the intensity of climate extremes, consequently increasing the risk of forest role transition from carbon sequestration to carbon emission. These changes are occurring more rapidly in the Alps, with important consequences for tree species adapted to strong climate seasonality and short growing season. In this study, we aimed at investigating the responses of a high-altitude Larix decidua Mill. forest to heat and drought, by coupling ecosystem- and tree-level measurements. From 2012 to 2018, ecosystem carbon and water fluxes (i.e., gross primary production, net ecosystem exchange, and evapotranspiration) were measured by means of the eddy covariance technique, together with the monitoring of canopy development (i.e., larch phenology and normalized difference vegetation index). From 2015 to 2017 we carried out additional observations at the tree level, including stem growth and its duration, direct phenological observations, sap flow, and tree water deficit. Results showed that the warm spells in 2015 and 2017 caused an advance of the phenological development and, thus, of the seasonal trajectories of many processes, at both tree and ecosystem level. However, we did not observe any significant quantitative changes regarding ecosystem gas exchanges during extreme years. In contrast, in 2017 we found a reduction of 17% in larch stem growth and a contraction of 45% of the stem growth period. The growing season in 2017 was indeed characterized by different drought events and by the highest water deficit during the study years. Due to its multi-level approach, our study provided evidence of the independence between C-source (i.e., photosynthesis) and C-sink (i.e., tree stem growth) processes in a subalpine larch forest
Photometric observations of comet 81P/Wild 2 during the 2010 perihelion passage
Context. The Jupiter-family comet 81P/Wild 2, target of the NASA Stardust mission, is very important in the context of the studies of pristine objects in the solar system. First, it was only recently deflected into the present orbit, having spent at least 300 yr at higher heliocentric distance prior to the orbital change in 1974. It is therefore likely that the comet experienced a recent activation with consequent low alteration of its original material. Second, it is the only comet whose coma material was brought back to Earth for laboratory analysis. We observed the object between 2010 February 9 and September 9 for a total of 11 nights during the 2010 perihelion passage. Aims. The goals of the campaign were the characterization of the comet's dust activity and the comparison with previous apparitions to derive hints on the secular behavior of the object. Methods. Broadband R-and I-images were acquired using three instruments: ALFOSC, CAMELOT, and TCP. The first one is mounted at the Nordic Optical Telescope on La Palma, while the second and the third are mounted at the Instituto de Astrofisica de Canarias 0.82-m telescope on Tenerife. We analyzed the presence and variability of dust structures in the coma with image-enhancing techniques, the radial profile of the dust brightness, and we measured the dust production rate and the dust reddening. Results. We found evidence of a long-lasting sunward fan and anti-solar tail activity throughout all our observations up to a heliocentric distance of 2.42 AU. AfÏ measurements suggest a pre-perihelion peak of the activity, caused by a seasonal effect, plus two post-perihelion outbursts. Both spatial and AfÏ radial profiles indicate a steady-state coma at nucleocentric distances greater than ~1000-2000 km. The color analysis reveals a moderately reddened dust with a 6-9%/1000 reddening, consistent with the current picture of cometary dust. The second outburst emitted dust with lower reddening. Conclusions. The comparison with previous perihelion passages points toward a recurrent main activity always driven by the same areas on the nucleus, producing dust with similar characteristics and in similar coma structures in different years. Our AfÏ measurement at the longest heliocentric distance suggests the comet was less dust-productive in 2010, pointing toward a possible secular aging of the object and its activity. The change of dust colors during the unusual second outburst suggests that an internal part of the nucleus has different physical properties compared with those that produce the recurrent main activity, pointing toward a heterogeneous comet. © ESO, 2012
The Cratering History of Asteroid (2867) Steins
The cratering history of main belt asteroid (2867) Steins has been
investigated using OSIRIS imagery acquired during the Rosetta flyby that took
place on the 5th of September 2008. For this purpose, we applied current models
describing the formation and evolution of main belt asteroids, that provide the
rate and velocity distributions of impactors. These models coupled with
appropriate crater scaling laws, allow the cratering history to be estimated.
Hence, we derive Steins' cratering retention age, namely the time lapsed since
its formation or global surface reset. We also investigate the influence of
various factors -like bulk structure and crater erasing- on the estimated age,
which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted
scaling law and asteroid physical parameters. Moreover, a marked lack of
craters smaller than about 0.6km has been found and interpreted as a result of
a peculiar evolution of Steins cratering record, possibly related either to the
formation of the 2.1km wide impact crater near the south pole or to YORP
reshaping.Comment: Accepted by Planetary and Space Scienc
- âŠ