## Cosmic rays

This diagram shows the mounting of PAMELA on the Resurs-DK1 satellite. Credit: -=HyPeRzOnD=- as modified by Aldebaran66.

The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) is an operational cosmic ray research module attached to the Resurs-DK1 commercial Earth observation satellite. PAMELA is the first satellite-based experiment dedicated to the detection of cosmic rays, with a particular focus on their antimatter component, in the form of positrons and antiprotons. Other objectives include long-term monitoring of the solar modulation of cosmic rays, measurements of energetic particles from the Sun, high-energy particles in Earth's magnetosphere and Jovian electrons.

The instrument is built around a permanent magnet spectrometer with a silicon microstrip tracker that provides rigidity and dE/dx information. At its bottom is a silicon-tungsten imaging calorimeter, a neutron detector and a shower tail scintillator to perform lepton/hadron discrimination. A Time of Flight (ToF), made of three layers of plastic scintillators, is used to measure the beta and charge of the particle. An anticounter system made of scintillators surrounding the apparatus is used to reject false triggers and albedo particles during off-line analysis.[1]

## Solar wind spectrometers

"Because the Solar Wind Spectrometer made continuous measurements, it was possible to measure how the Earth's magnetic field affects arriving solar wind particles. For about two-thirds of each orbit, the Moon is outside of the Earth's magnetic field. At these times, a typical proton density was 10 to 20 per cubic centimeter, with most protons having velocities between 400 and 650 kilometers per second. For about five days of each month, the Moon is inside the Earth's geomagnetic tail, and typically no solar wind particles were detectable. For the remainder of each lunar orbit, the Moon is in a transitional region known as the magnetosheath, where the Earth's magnetic field affects the solar wind but does not completely exclude it. In this region, the particle flux is reduced, with typical proton velocities of 250 to 450 kilometers per second. During the lunar night, the spectrometer was shielded from the solar wind by the Moon and no solar wind particles were measured."[2][3]

## Antiheliums

AMS-02 is a RICH detector for analyzing cosmic rays. Credit: NASA.
Overlap of projected occurrences of anti hydrogen, anti deuterium, and anti helium are related to AMS sensitivities. Credit: Vivian Poulin, Pierre Salati, Ilias Cholis, Marc Kamionkowski, and Joseph Silk.{{fairuse}}

The Alpha Magnetic Spectrometer device AMS-02, recently mounted on the International Space Station uses a Ring-imaging Cherenkov (RICH) detector in combination with other devices to analyze cosmic rays.

"[A]ntihelium-3 and -4 events [were] possibly detected by AMS-02. [...] spallation from primary hydrogen and helium nuclei onto the ISM predicts a [antihelium-3] ${\displaystyle {\bar {^{3}He}}}$ typically one to two orders of magnitude below the sensitivity of AMS-02 after 5 years, and a ${\displaystyle {\bar {^{4}He}}}$ flux roughly 5 orders of magnitude below the AMS-02 sensitivity."[4]

These "events [may] originate from antimatter-dominated regions in the form of anticlouds or antistars. In the case of anticlouds, we show how the isotopic ratio of antihelium nuclei might suggest that [Big Bang nucleosynthesis] BBN has happened in an inhomogeneous manner, resulting in antiregions with a antibaryon-to-photon ratio ${\displaystyle {\bar {\eta }}}$ ≃ 10−3η. [The] anticlouds [must] be almost free of normal matter. [Part] of the unidentified sources in the 3FGL catalog can originate from anticlouds or antistars."[4]

The image on the left displays possible overlap of projected occurrences of anti-hydrogen, anti-deuterium, and anti-helium possibly originating from anticlouds or antistars related to AMS sensitivities.[4]

## Neutron spectrometers

This is an image of the neutron spectrometer aboard the MESSENGER spacecraft in orbit around Mercury. Credit: NASA/JHU/APL.
The image shows the hydrogen concentrations on the Moon detected by the Lunar Prospector. Credit: NASA.
This image contains polar maps of thermal and epithermal neutrons as detected by the Mars Odyssey spacecraft in orbit around Mars. The images are from July 22, 2009. Credit: NASA/JPL-Caltech.

The neutron spectrometer on the MESSENGER spacecraft determines the hydrogen mineral composition to a depth of 40 cm by detecting low-energy neutrons that result from the collision of cosmic rays and the minerals.[5][6]

"During large solar flares, the region near Mercury may be strongly illuminated with solar neutrons."[7]

At right is the result of an all Moon survey by the Lunar Prospector using an onboard neutron spectrometer (NS). Cosmic rays impacting the lunar surface generate neutrons which in turn lose much of their energy in collisions with hydrogen atoms trapped within the Moon's surface.[8] Some of these thermal neutrons collide with the helium atoms within the NS to yield an energy signature which is detected and counted.[8] The NS aboard the Lunar Prospector has a surface resolution of 150 km.[8] Several neutron detectors and spectrometers have been and are currently being used to measure surface properties associated with neutron emission. The Dynamic Albedo of Neutrons (DAN) spectrometer is aboard the Curiosity rover.

"The Dynamic Albedo of Neutrons (DAN) is an active/passive neutron spectrometer that measures the abundance and depth distribution of H- and OH-bearing materials (e.g., adsorbed water, hydrated minerals) in a shallow layer (~1 m) of Mars' subsurface along the path of the MSL rover. In active mode, DAN measures the time decay curve (the "dynamic albedo") of the neutron flux from the subsurface induced by its pulsing 14 MeV neutron source."[9] "The science objectives of the DAN instrument are as follows: 1) Detect and provide a quantitative estimation of the hydrogen in the subsurface throughout the surface mission; 2) Investigate the upper <0.5 m of the subsurface and determine the possible layering structure of hydrogen-bearing materials in the subsurface; 3) Track the variability of hydrogen content in the upper soil layer (~1 m) during the mission by periodic analysis; and 4) Track the variability of neutron radiation background (neutrons with energy < 100 keV) during the mission by periodic analysis."[9]

Both the neutron spectrometer, from Los Alamos National Laboratories in New Mexico, and the High Energy Neutron Detector (HEND), from the Russian Aviation and Space Agency, are operating aboard the Odyssey spacecraft in orbit around Mars since 2001.

## Proton spectrometers

"The initial solar wind conditions at the inner boundary at 1 AU are radial outward speed V = 441 km/s, solar wind proton density N = 7.0/cc and temperature T = 9.8 × 104 K, and interplanetary magnetic field = 7.0 × 10−5 Gauss. The interstellar hydrogen atoms at the solar wind termination shock are taken to have speed 20 km/s and temperature 1 × 104 K, while H0 density, and the energy partition ratio for ions, are varied to give good fits to radial speed and temperature profiles measured by the operational plasma spectrometer on Voyager 2. Good fits are obtained for a neutral density of 0.09/cc and a partition ratio of 0.05, which means that five percent of the total energy from the pickup process goes into solar wind protons. For the LISM plasma ions, which are not included in the Wang and Richardson model, we compute convecting maxwellian (Vasyliunas, 1971) distributions for the LISM parameters T ∼ 7000 K, u ∼ 26 km/s, and N ∼ 0.1/cc of interstellar protons as derived from Wood and Linsky (1997)."[10]

## Gamma-ray spectrometers

This is a spectrum of 60Co, with peaks at 1.17 and 1.33 MeV from a spectrometer.

A Gamma-Ray Spectrometer, or (GRS), is an instrument for measuring the distribution (or spectrum—see figure) of the intensity of gamma radiation versus the energy of each photon.

This diagram depicts the generation of gamma rays by cosmic ray exposure. Credit: JPL, NASA.

Using Germanium detectors - a crystal of hyperpure germanium that produces pulses proportional to the captured photon energy; while more sensitive, it has to be cooled to a low temperature, requiring a bulky cryogenic apparatus. When exposed to cosmic rays (charged particles in space that come from the stars, including our sun), chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. The gamma ray spectrometer looks at these signatures, or energies, coming from the elements present in the target soil. By measuring gamma rays coming from the target body, it is possible to calculate the abundance of various elements and how they are distributed around the planet's surface. Gamma rays, emitted from the nuclei of atoms, show up as sharp emission lines on the instrument's spectrum output. While the energy represented in these emissions determines which elements are present, the intensity of the spectrum reveals the elements concentrations. Spectrometers are expected to add significantly to the growing understanding of the origin and evolution of planets like Mars and the processes shaping them today and in the past.

## Atmospheres

This is a computer generated model of the Lunar Atmosphere and Dust Environment Explorer (LADEE). Credit: NASA.

"The Lunar Atmosphere and Dust Environment Explorer (LADEE, at left) launched 07 September 2013 at 03:27 UT (06 September 11:27 EDT) on a Minotaur-V from Wallops Flight Facility. LADEE is designed to characterize the tenuous lunar atmosphere and dust environment from orbit. The scientific objectives of the mission are:(1) determine the global density, composition, and time variability of the fragile lunar atmosphere; and, (2) determine the size, charge, and spatial distribution of electrostatically transported dust grains and assess their likely effects on lunar exploration and lunar-based astronomy. Further objectives are to determine if the Apollo astronaut sightings of diffuse emission at 10s of km above the surface were Na glow or dust and document the dust impactor environment (size-frequency) to help guide design engineering for outpost and future robotic missions."[11]

"The orbiter will carry a Neutral Mass Spectrometer (NMS), an Ultraviolet/Visible Spectrometer (UVS), and a Lunar Dust Experiment (LDEX)."[11]

"The NMS is a quadrupole mass spectrometer designed ot detect species up to 150 amu and will look for CH4, S, O, Si, Kr, Xe, Fe, Al, Ti, Mg, OH, and H2O. The UVS will detect Al, Ca, Fe, K, Li, Na, Si, T, Ba, Mg, H2O, and O and will monitor the dust composition. The LDEX is an impact ionization dust detector designed to measure particles down to 0.3 microns at the spacecraft altitude. The LLCD is a test of a high data-rate optical (laser) communications system."[11]

## References

1. P.Picozza et al., "Launch of the space experiment PAMELA", http://arxiv.org/abs/0708.1808
2. Apollo 11 Mission. Lunar and Planetary Institute. 2009. Retrieved 2009-06-12.
3. Space Travel and Cancer Linked? Stony Brook Researcher Secures NASA Grant to Study Effects of Space Radiation. Brookhaven National Laboratory. 12 December 2007. Retrieved 2009-06-12.
4. Vivian Poulin; Pierre Salati; Ilias Cholis; Marc Kamionkowski; Joseph Silk (28 January 2019). "Where do the AMS-02 antihelium events come from?". Physical Review D 99 (2-15): 023016. doi:10.1103/PhysRevD.99.023016. Retrieved 13 July 2019.
5. Goldsten, John O.; Edgar A. Rhodes, William V. Boynton, William C. Feldman, David J. Lawrence, Jacob I. Trombka, David M. Smith, Larry G. Evans, Jack White and Norman W. Madden, et al. (November 8, 2007). "The MESSENGER Gamma-Ray and Neutron Spectrometer". Space Science Reviews 131: 339–391. doi:10.1007/s11214-007-9262-7.
6. Gamma-Ray and Neutron Spectrometer (GRNS). NASA / National Space Science Data Center. Retrieved 2011-02-19.
7. C. T. Russell; D. N. Baker; J. A. Slavin (January 1, 1988). Faith Vilas. ed. The Magnetosphere of Mercury, In: Mercury. Tucson, Arizona, United States of America: University of Arizona Press. pp. 514-61. ISBN 0816510857. Bibcode: 1988merc.book..514R. Retrieved 2012-08-23.
8. David R. Williams (November 2011). Lunar Prospector Neutron Spectrometer (NS). Goddard Space Flight Laboratory: National Aeronautics and Space Administration. Retrieved 2012-01-11.
9. Igor Mitrofanov. Dynamic Albedo of Neutrons (DAN). Jet Propulsion Laboratory, Pasadena, California: NASA. Retrieved 2012-08-17.
10. John F. Cooper; Eric R. Christian; John D. Richardson; Chi Wang (2004). Davies J.K.. ed. Proton irradiation of Centaur, Kuiper Belt, and Oort Cloud objects at plasma to cosmic ray energy, In: The First Decadal Review of the Edgeworth-Kuiper Belt. 92. Dordrecht: Springer. pp. 261-277. doi:10.1007/978-94-017-3321-2_24. Retrieved 19 June 2019.
11. Richard C. Elphic; Sarah Noble; P. Butler Hine III (September 7, 2013). Lunar Atmosphere and Dust Environment Explorer (LADEE). Washington, DC USA: National Space Science Data Center, NASA. Retrieved 2014-01-07.