The concept of putting a neutrino detector in close orbit of the sun has been unexplored until very recently. The primary scientific return is to vastly enhance our understanding of the solar interior, which is a major NASA goal. Preliminary calculations show that such a spacecraft, if properly shielded, can operate in space environments while taking data from neutrino interactions. These interactions can be distinguished from random background rates of solar electromagnetic emissions, galactic charged cosmic-rays, and gamma-rays by using a double pulsed signature. Early simulations of this project have shown this veto schema to be successful in eliminating background and identifying the neutrino interaction signal in upwards of 75% of gamma ray interactions and nearly 100% of other interactions. Hence, we propose a new instrument to explore and study our sun. Due to inverse square scaling, this instrument has the potential to outperform earth-based experiments in several domains such as making measurements not accessible from the earth's orbit.

Charon's exosphere may exhibit extreme seasonal dynamics, with centuries of quiescence punctuated by short lived (∼4 earth years) exospheric surges near the equinoxes, as spring sunrise bi‐annually drives frozen methane off the polar night zones. Charon's pole‐centric red spot has been proposed to be the product of Ly‐α photolysis of frozen methane into refractory hydrocarbon “tholins”, but the role of exospheric dynamics in the red material's formation has not been investigated. We show with exospheric modeling that methane “polar‐swap”, in which exospheric CH4 sublimated from the spring polar zone is rapidly re‐frozen onto the autumn hemisphere, deposits ∼30 μm polar frosts too thick for Ly‐α light to penetrate. Ethane, the primary methane photoproduct under these conditions, may unlike methane remain frozen decades after polar sunrise under solar wind exposure. Solar wind radiolysis of polar ethane frost synthesizes higher‐order refractories that may contribute to the coloration of Charon's polar zones.

We have characterized the far‐ultraviolet (FUV) spectro‐photometric response of lunar soil simulants JSC‐1A and LMS‐1, reporting notable differences from our previous results for Apollo soil 10084 (Raut et al., 2018, https://doi.org/10.1029/2018JE005567 ). While JSC‐1A and LMS‐1 were designed to emulate the geotechnical and compositional properties of a low‐Ti and high‐Ti mare soil respectively, these terrestrial simulants lack “space weathering” attributes such as the nanophase iron present in the weathered rims of Apollo grains and glassy agglutinates. Photometric analyses of the JSC‐1A phase curves reveal a ∼3–4 fold increase in single scattering albedo (SSA) and a forward scattering behavior compared to 10084. LMS‐1 is shown to have SSA nearly twice that of 10084 and a near isotropic reflectance. Additionally, both JSC‐1A and LMS‐1 spectra present a blue slope in the FUV, with the JSC‐1A slope ∼10× larger than that reported for the 10084 soil. Our analyses imply that low‐Ti content corroborated using energy dispersive x‐ray spectroscopy, correlates to brighter FUV reflectance and a greater spectral blue slope for JSC‐1A, while space weathering components likely contribute to the backscattering of FUV light by the Apollo soil relative to both simulants. Further work with an extended set of Apollo soils is warranted to deconvolute the relative contributions of weathering and composition to their FUV spectro‐photometric response.

Folder "CharonCode": Charon model code in MATLAB script, used in "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot", Geophysical Research Letters, 2022, by Ben Teolis, Ujjwal Raut, Joshua A. Kammer, Caleb J. Gimar, Carly J. A. Howett, G. Randall Gladstone, Kurt D. Retherford. File "Fig2plotData.txt": Data for Figure 2 bottom plot, in "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot", Geophysical Research Letters, 2022, by Ben Teolis, Ujjwal Raut, Joshua A. Kammer, Caleb J. Gimar, Carly J. A. Howett, G. Randall Gladstone, Kurt D. Retherford. Data gives the total CH4 molecules in the exospheric model and on the surface versus time, and the cumulative number of CH4 molecules photo-converted to surface photoproducts over one Pluto orbit. File "Fig4plotData.txt": Data for Figure 4 bottom plot, in "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot", Geophysical Research Letters, 2022, by Ben Teolis, Ujjwal Raut, Joshua A. Kammer, Caleb J. Gimar, Carly J. A. Howett, G. Randall Gladstone, Kurt D. Retherford. Data gives the time-averaged frozen methane and photo-product distributions versus latitude at three different thermal inertias. The results are averaged over Pluto perihelion longitude to capture the estimated distributions over geologic time.

We combine novel laboratory experiments and exospheric modeling to reveal that “dynamic” Ly-α photolysis of Plutonian methane generates a photolytic refractory distribution on Charon that increases with latitude, consistent with poleward darkening observed in the New Horizons images. The flux ratio of the condensing methane to the interplanetary medium Ly-α photons, φ, controls the distribution and composition of Charon’s photoproducts. Mid-latitude regions are likely to host complex refractories emerging from low-φ photolysis, while high-φ photolysis at the polar zones primarily generate ethane. However, ethane being colorless does not contribute to the reddish polar hue. Solar wind radiolysis of Ly-α–cooked polar frost past spring sunrise may synthesize increasingly complex, redder refractories responsible for the unique albedo on this enigmatic moon.

We report on our study of the design of a neutrino detector, shielding and veto array needed to operate a neutrino detector in space close to the Sun. This study also took into account the expected rates of Galactic gamma and cosmic rays in addition to the particles from the Sun.These preliminary studies show that we can devise a detector such that a small signal of neutrino interactions can be extracted from a large random number of events from the background sources using a double timing method from the conversion electron produced in the neutrino interaction and a secondary delayed signal from the nuclear excited state produced from the initial neutrino interaction; in our case the conversion of Ga 69 or 71 into Ge 69 or 71, but this method could apply to other nuclei with large neutrino cross sections such as Ir 115. Although these types of events need to be above 0.405 megaelectronvolt (MeV) neutrino energy and are only 66 percent of all conversion neutrino interactions on Gallium, this is a small price to pay for an increase of 10,000 by going close to the Sun to enhance the neutrino rate over the background combatorical fake-signal events. The conclusion of this Phase-1 study is very positive in that we can get the backgrounds less than 20 percent fake signals, and in addition to this we have devised another shielding method that makes the Galactic gamma-ray rate a hundred fold less which will make further improvements over these initial estimates. Although these studies are very encouraging it suggests that the next step is a NIAC Phase-II to actually build a test device,measuring basic principles such as light attention within the scintillator with high dopants and to take data in the lab with a cosmic-ray test stand and triggered X-ray source for comparison with simulated expected performance of the detector. This would be the perfect lead into a future proposal beyond a NIAC (NASA Innovative Advanced Concepts) Phase-II for a test flight of a small one-pint detector in orbit of the detector concept beyond Earth outside of the radiation belts.

Neutrinos—weakly interacting subatomic particles often resultant of nuclear processes, including hydrogen fusion—are the only direct insight into the core of the Sun. Previously constructed neutrino detection experiments have successfully detected solar-origin neutrinos, proving hydrogen fusion to be the Sun’s energy production mechanism; however, these experiments’ large size and Earth-based location limit their capabilities. A solar neutrino detection satellite orbiting the sun with a close approach distance of 7 to 3 solar radii could revolutionize solar interior studies. At such proximity, the neutrino flux increases by several orders of magnitude allowing for a much smaller detector design than Earth-based devices. An off-ecliptic orbital location also allows for fusion core geometry studies. To pursue these improvements, a scintillation detector using gallium-doped liquid scintillator and veto array methods has been devised. Interactions between neutrinos and gallium nuclei can result in a sequentially released electron and gamma-ray/X-ray, giving distinct double-pulse signals in the detector. The veto array is a secondary detection assembly to filter external-source charged particles. Presented here are the methods and results from Monte Carlo simulations of particle events visible to the detector. This code incorporates background event rates obtained from Geant4 simulations of the detector assembly, and neutrino interaction rates based on scaling of similar, Earth-based experiments’ performance to the detector’s parameters. The code output is examined to find the number of true double-pulse signals versus those of false signals. Establishing experiment parameters necessary for a false event detection rate less than 20% is a primary goal of these simulations.