Engineering topics

Mottola, Stefano

Publications and source records attributed to Mottola, Stefano.

6 records

DOE OSTI2018

Light Curves of Lucy Targets: Leucus and Polymele

We present new observations from 2016 of two Jupiter Trojan asteroids that are targets for the Lucy Discovery mission. The extremely long rotation period of (11351) Leucus is confirmed and refined to a secure value of 445.732 ± 0.021 hr with photometric parameters of H {sub r} = 11.046 ± 0.003 and G {sub r} = 0.58 ± 0.02 in the SDSS r′ filter. This leads to a geometric albedo of p {sub V} = 4.7%. The amplitude of the light curve was measured to be 0.61 mag, unchanged from the value of one-fourth of a revolution earlier, suggesting a low obliquity. The first light-curve observations for (15094) Polymele are also presented. This object is revealed to have a much shorter rotation period of 5.8607 ± 0.0005 hr with a very low amplitude of 0.09 mag. Its photometric parameters are H {sub r} = 11.691 ± 0.002 and G {sub r} = 0.22 ± 0.02. These values lead to a refined geometric albedo of p {sub V} = 7.3%. This object is either nearly spherical or was being viewed nearly pole-on in 2016. Further observations are required to fully determine the spin pole orientation and convex-hull shapes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

SURFACE ALBEDO AND SPECTRAL VARIABILITY OF CERES

Previous observations suggested that Ceres has active, but possibly sporadic, water outgassing as well as possibly varying spectral characteristics over a timescale of months. We used all available data of Ceres collected in the past three decades from the ground and the Hubble Space Telescope, as well as the newly acquired images by the Dawn Framing Camera, to search for spectral and albedo variability on Ceres, on both a global scale and in local regions, particularly the bright spots inside the Occator crater, over timescales of a few months to decades. Our analysis has placed an upper limit on the possible temporal albedo variation on Ceres. Sporadic water vapor venting, or any possibly ongoing activity on Ceres, is not significant enough to change the albedo or the area of the bright features in the Occator crater by >15%, or the global albedo by >3% over the various timescales that we searched. Recently reported spectral slope variations can be explained by changing Sun–Ceres–Earth geometry. The active area on Ceres is less than 1 km{sup 2}, too small to cause global albedo and spectral variations detectable in our data. Impact ejecta due to impacting projectiles of tens of meters in size like those known to cause observable changes to the surface albedo on Asteroid Scheila cannot cause detectable albedo change on Ceres due to its relatively large size and strong gravity. The water vapor activity on Ceres is independent of Ceres’ heliocentric distance, ruling out the possibility of the comet-like sublimation process as a possible mechanism driving the activity.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2011

Imaging Asteroid 4 Vesta Using the Framing Camera

The Framing Camera (FC) onboard the Dawn spacecraft serves a dual purpose. Next to its central role as a prime science instrument it is also used for the complex navigation of the ion drive spacecraft. The CCD detector with 1024 by 1024 pixels provides the stability for a multiyear mission and its high requirements of photometric accuracy over the wavelength band from 400 to 1000 nm covered by 7 band-pass filters. Vesta will be observed from 3 orbit stages with image scales of 227, 63, and 17 m/px, respectively. The mapping of Vesta s surface with medium resolution will be only completed during the exit phase when the north pole will be illuminated. A detailed pointing strategy will cover the surface at least twice at similar phase angles to provide stereo views for reconstruction of the topography. During approach the phase function of Vesta was determined over a range of angles not accessible from earth. This is the first step in deriving the photometric function of the surface. Combining the topography based on stereo tie points with the photometry in an iterative procedure will disclose details of the surface morphology at considerably smaller scales than the pixel scale. The 7 color filters are well positioned to provide information on the spectral slope in the visible, the depth of the strong pyroxene absorption band, and their variability over the surface. Cross calibration with the VIR spectrometer that extends into the near IR will provide detailed maps of Vesta s surface mineralogy and physical properties. Georeferencing all these observation will result in a coherent and unique data set. During Dawn s approach and capture FC has already demonstrated its performance. The strong variation observed by the Hubble Space Telescope can now be correlated with surface units and features. We will report on results obtained from images taken during survey mode covering the whole illuminated surface. Vesta is a planet-like differentiated body, but its surface gravity and escape velocity are comparable to those of other asteroids and hence much smaller than those of the inner planets or

Keller, H. Uwe↗

DOE OSTI2011

ROTATIONAL PROPERTIES OF JUPITER TROJANS. I. LIGHT CURVES OF 80 OBJECTS

We present the results of a Jupiter Trojans' light curve survey aimed at characterizing the rotational properties of Trojans in the approximate size range 60-150 km. The survey, which was designed to provide reliable and unbiased estimates of rotation periods and amplitudes, resulted in light curves for a total of 80 objects, 56 of which represent the first determinations published to date and nine of which supersede previously published erroneous values. Our results more than double the size of the existing database of rotational properties of Jovian Trojans in the selected size range. The analysis of the distributions of the rotation periods and light curve amplitudes is the subject of companion papers.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1992

A photometric survey of outer belt asteroids

Since 1989, we have been conducting a research program devoted to the study of the Trojans and outer belt asteroids (Hilda and Cybele groups), in order to characterize their rotational properties and shapes. As an outcome of several observational campaigns, we determined rotational periods and lightcurve amplitudes for 23 distant asteroids, using both CCD and photoelectric photometry. In this paper, we compare the rotational properties of main belt asteroids and Trojans, based on the preliminary results of this survey.

Dimartino, M.↗

NASA NTRS1992

Ground-based observations of 951 Gaspra: CCD lightcurves and spectrophotometry with the Galileo filters

This paper reports the observations of 951 Gaspra carried out at the European Southern Observatory (La Silla, Chile) during the 1991 apparition, using the DLR CCD Camera equipped with a spare set of the Galileo SSI filters. Time-resolved spectrophotometric measurements are presented. The occurrence of spectral variations with rotation suggests the presence of surface variegation.

Mottola, Stefano↗