ABSTRACT
Asteroids smaller than 10 km are thought to be rubble piles formed from the reaccumulation of fragments produced in the catastrophic disruption of parent bodies. Ground-based observations reveal that some of these asteroids are today binary systems, in which a smaller secondary orbits a larger primary asteroid. However, how these asteroids became binary systems remains unclear. Here, we report the analysis of boulders on the surface of the stony asteroid (65803) Didymos and its moonlet, Dimorphos, from data collected by the NASA DART mission. The size-frequency distribution of boulders larger than 5 m on Dimorphos and larger than 22.8 m on Didymos confirms that both asteroids are piles of fragments produced in the catastrophic disruption of their progenitors. Dimorphos boulders smaller than 5 m have size best-fit by a Weibull distribution, which we attribute to a multi-phase fragmentation process either occurring during coalescence or during surface evolution. The density per km2 of Dimorphos boulders ≥1 m is 2.3x with respect to the one obtained for (101955) Bennu, while it is 3.0x with respect to (162173) Ryugu. Such values increase once Dimorphos boulders ≥5 m are compared with Bennu (3.5x), Ryugu (3.9x) and (25143) Itokawa (5.1x). This is of interest in the context of asteroid studies because it means that contrarily to the single bodies visited so far, binary systems might be affected by subsequential fragmentation processes that largely increase their block density per km2. Direct comparison between the surface distribution and shapes of the boulders on Didymos and Dimorphos suggest that the latter inherited its material from the former. This finding supports the hypothesis that some asteroid binary systems form through the spin up and mass shedding of a fraction of the primary asteroid.
ABSTRACT
The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.
ABSTRACT
The Ma_MISS miniaturized spectrometer is integrated within the Drilling System of the ExoMars Rosalind Franklin Rover for Mars exploration. Here we focus on the on ground calibration campaign to obtain radiometric and linearity calibrations of the Ma_MISS instrument, while the first paper dealt with the spectral calibration [De Angelis et al., Rev. Sci. Instrum. 93, 123704 (2022)]. The experimental setup used to carry out radiometric calibration is described, as are the methods used for data processing and key parameter retrieval. In particular, the Spectrometer Transfer Function (Responsivity), Signal-to-Noise Ratio, and detector linearity are determined. In a third paper [De Sanctis et al., Planet. Sci. J. 3, 142 (2022)], validation of the Ma_MISS calibration results through spectral measurements performed on rock and synthetic targets during the radiometric calibration campaign is described.
ABSTRACT
The Ma_MISS spectrometer is integrated within the drilling system of the Rosalind Franklin ExoMars rover. This paper reports the on-ground calibration campaign performed on the spectrometer. Here, we focus on the spectral calibration of the instrument. The experimental setup used to carry out calibration is described, and the methods used for data processing and key parameters retrieval are explained. In particular, the spectral parameters such as (i) pixel central wavelengths, (ii) spectral response function, (iii) spectral resolution, (iv) sampling, and (v) range are determined. In a follow-up paper, the linearity and radiometric calibrations are described, while in De Sanctis et al. [Planet. Sci. J. 3, 142 (2022)], the validation of spectral measurements performed on synthetic and natural rock targets is presented.
ABSTRACT
Usually dreaded, annual meetings can provide a crucial, powerful, but often neglected context for reviewing the "vital signs" of a group practice: mission, membership, marketplace strategy and infrastructure. We propose that regular and thoughtful attention to essential issues of cohesion and effectiveness significantly increases the likelihood of group vitality and group member satisfaction. We suggest a methodology for embedding these essential conversations into the ritual of the annual meeting.
Subject(s)
Congresses as Topic/organization & administration , Facility Regulation and Control/organization & administration , Group Practice/standards , Physicians/psychology , Attitude of Health Personnel , Communication , Forecasting , Group Processes , Humans , Interprofessional Relations , Job Satisfaction , Marketing of Health Services , Organizational ObjectivesABSTRACT
Part I of this series described a research project--a survey of more than 300 physician executives. Asked to share their personal experiences of unsuccessful consultations, our correspondents painted a clear picture of what can go wrong when organizational consultants enter health care systems, and described the lasting destructive sequelae to failed consultations. The two issues responsible for most failed consultations were the intrusion of internal politics into the process and the failure to clearly establish and maintain consensual goals. In Part 2, the consultation process is explored from a very different perspective. What are the issues that often trigger requests for consultation services, as well as the dynamics that can foreshadow success or failure before consultants are even engaged? What are the pitfalls and pointers for the successful use of consultation services?
Subject(s)
Consultants , Decision Making , Evaluation Studies as Topic , Guidelines as Topic , Humans , Leadership , Organizational Objectives , Physician Executives , Politics , Practice Management, Medical , United StatesABSTRACT
The first article in this series describes a research project--a survey of more than 300 physician executives. Asked to share their personal experiences of unsuccessful consultations, our correspondents painted a picture of what can go wrong when organizational consultants enter health care systems, and described the lasting destructive sequelae to failed consultations. The two issues responsible for most failed consultations were the intrusion of internal politics into the consultation process and the failure to clearly establish and maintain consensual goals. Part 2 of this series will explore the consultation process from a different perspective, examining the issues that often trigger requests for consultation services and the dynamics that can foreshadow success or failure before consultants are even engaged.