Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNanodust detection between 1 and 5 AU by using Cassini wave measurements
485
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The solar system contains solids of all sizes, ranging from km-size bodies to nano-sized particles. Nanograins have been detected in situ in the Earths atmosphere, near cometary and giant planet environments, and more recently in the solar wind at 1 AU. These latter nano grains are thought to be formed in the inner solar system dust cloud, mainly through collisional break-up of larger grains and are then picked-up and accelerated by the magnetized solar wind because of their large charge-to-mass ratio. In the present paper, we analyze the low frequency bursty noise identified in the Cassini radio and plasma wave data during the spacecraft cruise phase inside Jupiters orbit. The magnitude, spectral shape and waveform of this broadband noise is consistent with the signature of nano particles impinging at nearby the solar wind speed on the spacecraft surface. Nanoparticles were observed whenever the radio instrument was turned on and able to detect them, at different heliocentric distances between Earth and Jupiter, suggesting their ubiquitous presence in the heliosphere. We analyzed the radial dependence of the nano dust flux with heliospheric distance and found that it is consistent with the dynamics of nano dust originating from the inner heliosphere and picked-up by the solar wind. The contribution of the nano dust produced in asteroid belt appears to be negligible compared to the trapping region in the inner heliosphere. In contrast, further out, nano dust are mainly produced by the volcanism of active moons such as Io and Enceladus.
rate research
Read More
Nanodust grains of a few nanometer in size are produced near the Sun by collisional break-up of larger grains and picked-up by the magnetized solar wind. They have so far been detected at 1 AU by only the two STEREO spacecraft. Here we analyze the spectra measured by the radio and plasma wave instrument onboard Cassini during the cruise phase close to Earth orbit; they exhibit bursty signatures similar to those observed by the same instrument in association to nanodust stream impacts on Cassini near Jupiter. The observed wave level and spectral shape reveal impacts of nanoparticles at about 300 km/s, with an average flux compatible with that observed by the radio and plasma wave instrument onboard STEREO and with the interplanetary flux models.
Current models of Titan ionosphere have difficulties in explaining the observed electron density and/or temperature. In order to get new insights, we re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science (RPWS) instrument. This is the first of two papers that present the new analysis method (current paper) and statistics on the whole dataset. We suggest that between 2 and 4 electron populations are necessary to fit the data. Each population is defined by a potential, an electron density and an electron temperature and is easily visualized by a dinstinct peak in the second derivative of the electron current, which is physically related to the electron energy distribution function (Druyvesteyn method). The detected populations vary with solar illumination and altitude. We suggest that the 4 electron populations are due to photo-ionization, magnetospheric particles, dusty plasma and electron emission from the probe boom, respectively.
New measurements using radio and plasma-wave instruments in interplanetary space have shown that nanometer-scale dust, or nanodust, is a significant contributor to the total mass in interplanetary space. Better measurements of nanodust will allow us to determine where it comes from and the extent to which it interacts with the solar wind. When one of these nanodust grains impacts a spacecraft, it creates an expanding plasma cloud, which perturbs the photoelectron currents. This leads to a voltage pulse between the spacecraft body and the antenna. Nanodust has a high charge/mass ratio, and therefore can be accelerated by the interplanetary magnetic field to speeds up to the speed of the solar wind: significantly faster than the Keplerian orbital speeds of heavier dust. The amplitude of the signal induced by a dust grain grows much more strongly with speed than with mass of the dust particle. As a result, nanodust can produce a strong signal, despite their low mass. The WAVES instruments on the twin Solar TErrestrial RElations Observatory spacecraft have observed interplanetary nanodust particles since shortly after their launch in 2006. After describing a new and improved analysis of the last five years of STEREO/WAVES Low Frequency Receiver data, a statistical survey of the nanodust characteristics, namely the rise time of the pulse voltage and the flux of nanodust, is presented. Agreement with previous measurements and interplanetary dust models is shown. The temporal variations of the nanodust flux are also discussed.
Saturns main rings exhibit variations in both their opacity and spectral properties on a broad range of spatial scales, and the correlations between these parameters can provide insights into the processes that shape the composition and dynamics of the rings. The Visual and Infrared Mapping Spectrometer (VIMS) instrument onboard the Cassini Spacecraft has obtained spectra of the rings between 0.35 and 5.2 microns with sufficient spatial resolution to discern variations on scales below 200 km. These relatively high-resolution spectral data reveal that both the depths of the near-infrared water-ice absorption bands and the visible spectral slopes are often correlated with structural parameters such as the rings optical depth. Using a simplified model for the ring-particles regolith properties, we have begun to disentangle the trends due to changes in the gross composition of the ring particles from those that may be due to shifts in the texture of the ring particles regolith. Consistent with previous studies, this analysis finds that the C ring and the Cassini Division possess enhanced concentrations of a contaminant that absorbs light over a broad range of wavelengths. On the other hand, a second contaminant that preferentially absorbs at short visible and near-ultraviolet wavelengths is found to be more evenly distributed throughout the rings. The optical activity of this short-wavelength absorber increases in the inner B ring inwards of 100,000 km from Saturn center, which may provide clues to the origin of this contaminant. The spectral variations identified as shifts in the regolith texture are in some places clearly correlated with the rings optical depth, and in other locations they appear to be associated with the disturbances generated by strong mean-motion resonances with Saturns various moons.
The Lunar University Network for Astrophysics Research (LUNAR) undertakes investigations across the full spectrum of science within the mission of the NASA Lunar Science Institute (NLSI), namely science of, on, and from the Moon. The LUNAR teams work on science of and on the Moon, which is the subject of this white paper, is conducted in the broader context of ascertaining the content, origin, and evolution of the solar system.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
