46 research outputs found
Dependence of the Martian radiation environment on atmospheric depth: Modeling and measurement
The energetic particle environment on the Martian surface is influenced by
solar and heliospheric modulation and changes in the local atmospheric pressure
(or column depth). The Radiation Assessment Detector (RAD) on board the Mars
Science Laboratory rover Curiosity on the surface of Mars has been measuring
this effect for over four Earth years (about two Martian years). The
anticorrelation between the recorded surface Galactic Cosmic Ray-induced dose
rates and pressure changes has been investigated by Rafkin et al. (2014) and
the long-term solar modulation has also been empirically analyzed and modeled
by Guo et al. (2015). This paper employs the newly updated HZETRN2015 code to
model the Martian atmospheric shielding effect on the accumulated dose rates
and the change of this effect under different solar modulation and atmospheric
conditions. The modeled results are compared with the most up-to-date (from 14
August 2012 to 29 June 2016) observations of the RAD instrument on the surface
of Mars. Both model and measurements agree reasonably well and show the
atmospheric shielding effect under weak solar modulation conditions and the
decline of this effect as solar modulation becomes stronger. This result is
important for better risk estimations of future human explorations to Mars
under different heliospheric and Martian atmospheric conditions
Measurements of Forbush decreases at Mars: both by MSL on ground and by MAVEN in orbit
The Radiation Assessment Detector (RAD), on board Mars Science Laboratory's
(MSL) Curiosity rover, has been measuring ground level particle fluxes along
with the radiation dose rate at the surface of Mars since August 2012. Similar
to neutron monitors at Earth, RAD sees many Forbush decreases (FDs) in the
galactic cosmic ray (GCR) induced surface fluxes and dose rates. These FDs are
associated with coronal mass ejections (CMEs) and/or stream/corotating
interaction regions (SIRs/CIRs). Orbiting above the Martian atmosphere, the
Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has also been
monitoring space weather conditions at Mars since September 2014. The
penetrating particle flux channels in the Solar Energetic Particle (SEP)
instrument onboard MAVEN can also be employed to detect FDs. For the first
time, we study the statistics and properties of a list of FDs observed in-situ
at Mars, seen both on the surface by MSL/RAD and in orbit detected by the
MAVEN/SEP instrument. Such a list of FDs can be used for studying
interplanetary CME (ICME) propagation and SIR evolution through the inner
heliosphere. The magnitudes of different FDs can be well-fitted by a power-law
distribution. The systematic difference between the magnitudes of the FDs
within and outside the Martian atmosphere may be mostly attributed to the
energy-dependent modulation of the GCR particles by both the pass-by ICMEs/SIRs
and the Martian atmosphere
Modeling the variations of Dose Rate measured by RAD during the first MSL Martian year: 2012-2014
The Radiation Assessment Detector (RAD), on board Mars Science Laboratory's
(MSL) rover Curiosity, measures the {energy spectra} of both energetic charged
and neutral particles along with the radiation dose rate at the surface of
Mars. With these first-ever measurements on the Martian surface, RAD observed
several effects influencing the galactic cosmic ray (GCR) induced surface
radiation dose concurrently: [a] short-term diurnal variations of the Martian
atmospheric pressure caused by daily thermal tides, [b] long-term seasonal
pressure changes in the Martian atmosphere, and [c] the modulation of the
primary GCR flux by the heliospheric magnetic field, which correlates with
long-term solar activity and the rotation of the Sun. The RAD surface dose
measurements, along with the surface pressure data and the solar modulation
factor, are analysed and fitted to empirical models which quantitatively
demonstrate} how the long-term influences ([b] and [c]) are related to the
measured dose rates. {Correspondingly we can estimate dose rate and dose
equivalents under different solar modulations and different atmospheric
conditions, thus allowing empirical predictions of the Martian surface
radiation environment
Comparison of Martian Surface Radiation Predictions to the Measurements of Mars Science Laboratory Radiation Assessment Detector (MSL/RAD)
For the analysis of radiation risks to astronauts and planning exploratory space missions, detailed knowledge of particle spectra is an important factor. Detailed measurements of the energetic particle radiation environment on the surface of Mars have been made by the Mars Science Laboratory Radiation Assessment Detector (MSL-RAD) on the Curiosity rover since August 2012, and particle fluxes for a wide range of ion species (up to several hundred MeV/u) and high energy neutrons (8 - 1000 MeV) have been available for the first 200 sols. Although the data obtained on the surface of Mars for 200 sols are limited in the narrow energy spectra, the simulation results using the Badhwar-O'Neill galactic cosmic ray (GCR) environment model and the high-charge and energy transport (HZETRN) code are compared to the data. For the nuclear interactions of primary GCR through Mars atmosphere and Curiosity rover, the quantum multiple scattering theory of nuclear fragmentation (QMSFRG) is used, which includes direct knockout, evaporation and nuclear coalescence. Daily atmospheric pressure measurements at Gale Crater by the MSL Rover Environmental Monitoring Station are implemented into transport calculations for describing the daily column depth of atmosphere. Particles impinging on top of the Martian atmosphere reach the RAD after traversing varying depths of atmosphere that depend on the slant angles, and the model accounts for shielding of the RAD by the rest of the instrument. Calculations of stopping particle spectra are in good agreement with the RAD measurements for the first 200 sols by accounting changing heliospheric conditions and atmospheric pressure. Detailed comparisons between model predictions and spectral data of various particle types provide the validation of radiation transport models, and thus increase the accuracy of the predictions of future radiation environments on Mars. These contributions lend support to the understanding of radiation health risks to astronauts for the planning of various mission scenarios
Comparisons Between Model Predictions and Spectral Measurements of Charged and Neutral Particles on the Martian Surface
Detailed measurements of the energetic particle radiation environment on the surface of Mars have been made by the Radiation Assessment Detector (RAD) on the Curiosity rover since August 2012. RAD is a particle detector that measures the energy spectrum of charged particles (10 to approx. 200 MeV/u) and high energy neutrons (approx 8 to 200 MeV). The data obtained on the surface of Mars for 300 sols are compared to the simulation results using the Badhwar-O'Neill galactic cosmic ray (GCR) environment model and the high-charge and energy transport (HZETRN) code. For the nuclear interactions of primary GCR through Mars atmosphere and Curiosity rover, the quantum multiple scattering theory of nuclear fragmentation (QMSFRG) is used. For describing the daily column depth of atmosphere, daily atmospheric pressure measurements at Gale Crater by the MSL Rover Environmental Monitoring Station (REMS) are implemented into transport calculations. Particle flux at RAD after traversing varying depths of atmosphere depends on the slant angles, and the model accounts for shielding of the RAD "E" dosimetry detector by the rest of the instrument. Detailed comparisons between model predictions and spectral data of various particle types provide the validation of radiation transport models, and suggest that future radiation environments on Mars can be predicted accurately. These contributions lend support to the understanding of radiation health risks to astronauts for the planning of various mission scenario
Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover
The Radiation Assessment Detector (RAD) on the Mars Science Laboratory’s Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the Martian surface for ~300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars, and provide an anchor point to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient Martian environment