1
|
Nikoukar R, Lawrence DJ, Peplowski PN, Dewey RM, Korth H, Baker DN, McNutt RL. Statistical Study of Mercury's Energetic Electron Events as Observed by the Gamma-Ray and Neutron Spectrometer Instrument Onboard MESSENGER. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2018; 123:4961-4978. [PMID: 30167351 PMCID: PMC6108406 DOI: 10.1029/2018ja025339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Revised: 04/17/2018] [Accepted: 05/11/2018] [Indexed: 06/08/2023]
Abstract
We present results from a statistical analysis of Mercury's energetic electron (EE) events as observed by the gamma-ray and neutron spectrometer instrument onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The main objective of this study is to investigate possible anisotropic behavior of EE events using multiple data sets from MESSENGER instruments. We study the data from the neutron spectrometer (NS) and the gamma-ray spectrometer anticoincidence shield (ACS) because they use the same type of borated plastic scintillator and, hence, they have very similar response functions, and their large surface areas make them more sensitive to low-intensity EE events than MESSENGER's particle instrumentation. The combined analysis of NS and ACS data reveals two different classes of energetic electrons: "Standard" events and "ACS-enhanced" events. Standard events, which comprise over 90% of all events, have signal sizes that are the same in both the ACS and NS. They are likely gyrating particles about Mercury's magnetic field following a 90° pitch angle distribution and are located in well-defined latitude and altitude regions within Mercury's magnetosphere. ACS-enhanced events, which comprise less than 10% of all events, have signal sizes in the ACS that are 10 to 100 times larger than those observed by the NS. They follow a beam-like distribution and are observed both inside and outside Mercury's magnetosphere with a wider range of latitudes and altitudes than Standard events. The difference between the Standard and ACS-enhanced event characteristics suggests distinct underyling acceleration mechanisms.
Collapse
Affiliation(s)
- Romina Nikoukar
- Applied Physics LaboratoryJohns Hopkins UniversityLaurelMDUSA
| | | | | | - Ryan M. Dewey
- Department of Climate and Space Sciences and EngineeringUniversity of MichiganAnn ArborMIUSA
| | - Haje Korth
- Applied Physics LaboratoryJohns Hopkins UniversityLaurelMDUSA
| | - Daniel N. Baker
- Laboratory for Atmospheric and Space PhysicsUniversity of ColoradoBoulderCOUSA
| | - Ralph L. McNutt
- Applied Physics LaboratoryJohns Hopkins UniversityLaurelMDUSA
| |
Collapse
|
2
|
Lawrence DJ, Feldman WC, Peplowski PN, Solomon SC. The 4 June 2011 neutron event at Mercury: A defense of the solar origin hypothesis. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2015; 120:5284-5289. [PMID: 26937331 PMCID: PMC4758620 DOI: 10.1002/2015ja021069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 06/01/2015] [Accepted: 06/03/2015] [Indexed: 06/05/2023]
Abstract
We address claim that neutrons from a 4 June 2011 event at Mercury are nonsolarThe claim is based on an erroneous assumption about instrument singles countsThe best interpretation of the neutron event is that the neutrons have a solar origin.
Collapse
Affiliation(s)
- David J Lawrence
- The Johns Hopkins University Applied Physics Laboratory Laurel Maryland USA
| | | | | | - Sean C Solomon
- Department of Terrestrial Magnetism Carnegie Institution of Washington Washington District of Columbia USA; Lamont-Doherty Earth Observatory Columbia University Palisades New York USA
| |
Collapse
|
3
|
Köhler J, Ehresmann B, Zeitlin C, Wimmer-Schweingruber RF, Hassler DM, Reitz G, Brinza DE, Appel J, Böttcher S, Böhm E, Burmeister S, Guo J, Lohf H, Martin C, Posner A, Rafkin S. Measurements of the neutron spectrum in transit to Mars on the Mars Science Laboratory. LIFE SCIENCES IN SPACE RESEARCH 2015; 5:6-12. [PMID: 26177845 DOI: 10.1016/j.lssr.2015.03.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 03/16/2015] [Accepted: 03/19/2015] [Indexed: 06/04/2023]
Abstract
The Mars Science Laboratory spacecraft, containing the Curiosity rover, was launched to Mars on 26 November 2011. Although designed for measuring the radiation on the surface of Mars, the Radiation Assessment Detector (RAD) measured the radiation environment inside the spacecraft during most of the 253-day, 560-million-kilometer cruise to Mars. An important factor for determining the biological impact of the radiation environment inside the spacecraft is the specific contribution of neutrons with their high biological effectiveness. We apply an inversion method (based on a maximum-likelihood estimation) to calculate the neutron and gamma spectra from the RAD neutral particle measurements. The measured neutron spectrum (12-436 MeV) translates into a radiation dose rate of 3.8±1.2 μGy/day and a dose equivalent of 19±5 μSv/day. Extrapolating the measured spectrum (0.1-1000 MeV), we find that the total neutron-induced dose rate is 6±2 μGy/day and the dose equivalent rate is 30±10 μSv/day. For a 360 day round-trip from Earth to Mars with comparable shielding, this translates into a neutron induced dose equivalent of about 11±4 mSv.
Collapse
Affiliation(s)
- J Köhler
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany.
| | - B Ehresmann
- Southwest Research Institute, Space Science and Engineering Division, Boulder, USA
| | - C Zeitlin
- Southwest Research Institute, Earth, Oceans & Space Department, Durham, NH, USA
| | | | - D M Hassler
- Southwest Research Institute, Space Science and Engineering Division, Boulder, USA
| | - G Reitz
- Aerospace Medicine, Deutsches Zentrum für Luft- und Raumfahrt, Köln, Germany
| | - D E Brinza
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - J Appel
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - S Böttcher
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - E Böhm
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - S Burmeister
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - J Guo
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - H Lohf
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - C Martin
- Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany
| | - A Posner
- NASA Headquarters, Science Mission Directorate, Washington DC, USA
| | - S Rafkin
- Southwest Research Institute, Space Science and Engineering Division, Boulder, USA
| |
Collapse
|
4
|
Lawrence DJ, Feldman WC, Goldsten JO, Maurice S, Peplowski PN, Anderson BJ, Bazell D, McNutt RL, Nittler LR, Prettyman TH, Rodgers DJ, Solomon SC, Weider SZ. Evidence for water ice near Mercury's north pole from MESSENGER Neutron Spectrometer measurements. Science 2012. [PMID: 23196909 DOI: 10.1126/science.1229953] [Citation(s) in RCA: 149] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Measurements by the Neutron Spectrometer on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show decreases in the flux of epithermal and fast neutrons from Mercury's north polar region that are consistent with the presence of water ice in permanently shadowed regions. The neutron data indicate that Mercury's radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 30 cm thick that is less rich in hydrogen. Combined neutron and radar data are best matched if the buried layer consists of nearly pure water ice. The upper layer contains less than 25 weight % water-equivalent hydrogen. The total mass of water at Mercury's poles is inferred to be 2 × 10(16) to 10(18) grams and is consistent with delivery by comets or volatile-rich asteroids.
Collapse
Affiliation(s)
- David J Lawrence
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Share GH, Murphy RJ, Tylka AJ, Kozlovsky B, Ryan JM, Gwon C. Physics of solar neutron production: Questionable detection of neutrons from the 31 December 2007 flare. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja015930] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Gerald H. Share
- Department of Astronomy; University of Maryland; College Park Maryland USA
| | - Ronald J. Murphy
- Space Science Division; Naval Research Laboratory; Washington D.C. USA
| | - Allan J. Tylka
- Space Science Division; Naval Research Laboratory; Washington D.C. USA
| | - Benz Kozlovsky
- School of Physics and Astronomy; Tel Aviv University; Tel Aviv Israel
| | - James M. Ryan
- Space Science Center; University of New Hampshire; Durham New Hampshire USA
| | - Chul Gwon
- Space Science Division; Naval Research Laboratory; Washington D.C. USA
| |
Collapse
|