Search

Space weather phenomena threaten the space assets that bring us services via space technologies, such as the Global Positioning System, communication systems with satellite relays, and most global TV broadcast networks, which have provided unprecedented convenience to everyday life and opportunities to businesses. A hazard among phenomena1 is the population of relativistic electrons in the region called Van Allan radiation belts2. These electrons can be trapped for years once produced by either natural3 or artificial processes4 and can damage the electronics and degrade the solar panels on satellites. Intense investigations have begun with recently launched NASA satellites, Van Allen Belt Probes A and B in 20125-13. To remedy the threat and reduce the resulting damage, artificial processes can be introduced to shorten the lifetime of these particles14 with mechanisms such as pitch-angle diffusion through wave-particle interaction15-17 by transmitting very-low-frequency (VLF) waves into radiation belts. To directly transmit the VLF waves in space is an extremely challenging task, and previous theoretical and numerical predictions of the radiation impedance differ more than five orders in magnitude18-23. Here we show the measurements of radiation impedance from high-power VLF wave transmission experiments in the radiation belts to help settle the dispute of the previous studies. The measured radiation reactance disagrees with the most influential theoretical model18,19,22 and the vacuum model, but proves the plasma sheath model and simulation of the antenna-plasma interaction20,21,23. A new discovery is that the measured radiation resistance decreases as the transmission frequency increases. Our results demonstrate the possibility to transmit high power in space and validated the design and technology for further high-power space-borne VLF transmitters. The physical understanding obtained in this study will also provide a guide to laboratory whistler mode wave injection experiments24, especially in controlled fusion25.

FIREBIRD-II (Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics) is a National Science Foundation CubeSat mission exploring relativistic electron microbursts. The mission consists of two identically instrumented CubeSats that were launched into a near polar orbit on January 31, 2015. Each spacecraft has two solid state detectors that return high cadence (10's of ms) measurements of the electron population. Both units operated continuously for almost 5 years and one unit continues to operate and return high quality data over 6 years after launch.

One component of the REX instrument on NASA's New Horizons spacecraft was an investigation of the radio continuum radiation from Pluto and Charon during the flyby on 14 July 2015. The planetary thermal emission was recorded at a wavelength of 4.17 cm (7.18 GHz) during approach, departure, and specifically on the non-illuminated hemispheres of Pluto and Charon during the respective intervals between occultation ingress and egress. We derive the brightness temperatures for these disk-resolved and unresolved observations. The mean values and 1σ deviations of brightness temperature for the unresolved sunlit disk are 33.2 ± 1.4 K and 47.2 ± 5.3 K for Pluto and Charon, respectively, consistent with the global albedos of the two bodies as well as with previous ground-based estimates at smaller wavelengths. A slightly colder temperature of 29.0 ± 2.5 K was determined for the disk-integrated nightside of Pluto and a larger drop in temperature was observed for Charon (40.9 ± 0.9 K), implying a smaller thermal inertia for Charon than Pluto. The measured brightness temperature of Pluto across the nightside diametric scan reached a maximum of 29.0 ± 1.5 K in the center of the disk. The profile shape is attributed to an emissivity effect, which favors thermal emission toward higher elevation angles. As a first approximation, the effective emissivity for thermal emission is calculated for the case when Pluto and Charon are uniformly smooth homogenous spheres. Under this assumption, the effective emissivity for these observations is close to unity for all probable surface constituents, implying that the effective temperature of the Pluto subsurface is only a few percent higher than the observed brightness temperature. A considerably lower subsurface emissivity is implied, however, if the higher atmospheric temperatures near the surface determined from the REX occultation measurements are also valid for the subsurface.

We discuss in a thermodynamic, geologically empirical way the long-term nature of the stable majority ices that could be present in Kuiper Belt Object 2014 MU69 after its 4.6 Gyr residence in the EKB as a cold classical object. Considering the stability versus sublimation into vacuum for the suite of ices commonly found on comets, Centaurs, and KBOs at the average ~40K sunlit surface temperature of MU69 over Myr to Gyr, we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability). NH3 and H2CO ices are marginally stable and may be removed by any positive temperature excursions in the EKB, as produced every 1e8 - 1e9 yrs by nearby supernovae and passing O/B stars. To date the NH team has reported the presence of abundant CH3OH and evidence for H2O on MU69s surface (Lisse et al. 2017, Grundy et al. 2020). NH3 has been searched for, but not found. We predict that future absorption feature detections will be due to an HCN or poly-H2CO based species. Consideration of the conditions present in the EKB region during the formation era of MU69 lead us to infer that it formed "in the dark", in an optically thick mid-plane, unable to see the nascent, variable, highly luminous Young Stellar Object-TTauri Sun, and that KBOs contain HCN and CH3OH ice phases in addition to the H2O ice phases found in their Short Period comet descendants. Finally, when we apply our ice thermal stability analysis to bodies/populations related to MU69, we find that methanol ice may be ubiquitous in the outer solar system; that if Pluto is not a fully differentiated body, then it must have gained its hypervolatile ices from proto-planetary disk sources in the first few Myr of the solar systems existence; and that hypervolatile rich, highly primordial comet C/2016 R2 was placed onto an Oort Cloud orbit on a similar timescale., Comment: 34 Pages, 5 Figures, 2 SOM Tables

Examining Arrokoth The New Horizons spacecraft flew past the Kuiper Belt object (486958) Arrokoth (also known as 2014 MU 69 ) in January 2019. Because of the great distance to the outer Solar System and limited bandwidth, it will take until late 2020 to downlink all the spacecraft's observations back to Earth. Three papers in this issue analyze recently downlinked data, including the highest-resolution images taken during the encounter (see the Perspective by Jewitt). Spencer et al. examined Arrokoth's geology and geophysics using stereo imaging, dated the surface using impact craters, and produced a geomorphological map. Grundy et al. investigated the composition of the surface using color imaging and spectroscopic data and assessed Arrokoth's thermal emission using microwave radiometry. McKinnon et al. used simulations to determine how Arrokoth formed: Two gravitationally bound objects gently spiraled together during the formation of the Solar System. Together, these papers determine the age, composition, and formation process of the most pristine object yet visited by a spacecraft. Science , this issue p. eaay3999 , p. eaay3705 , p. eaay6620 ; see also p. 980

Very-long baseline interferometry (VLBI) allows for exceptionally high-resolution imaging in radio astronomy. Ultimately the angular resolution of radio interferometers and telescopes is determined by the separation between antennas in the array. Building on this fundamental concept, potential uses of existing spacecraft radio systems for VLBI are explored. Coherent observations performed between ground radio telescopes (GRT) and spacecraft require stringent drift tolerances for timing and synchronization between the GRT and spacecraft. Observed data using the spacecraft antenna is then recorded and stored on-board before downlink. Among candidate spacecraft, a promising contender and focus of this paper is New Horizons. Currently at a distance greater than 45 AU, New Horizons offers an outstanding baseline for astronomical radio observation and provides necessary, configurable instrumentation for performing an extended baseline observation in conjunction with a GRT or other spacecraft. Communications with New Horizons are synchronized with a 30 MHz clock signal using an ultra-stable oscillator (USO), providing an exceptional Allan Deviation of $3\times 10^{-13}$ per one second integration time. Of the instruments on-board New Horizons, the Radio Science Experiment (REX) is of particular interest for its potential towards VLBI application. Developed for atmospheric measurements during occultations between the 7.182 GHz uplink from the 70 meter NASA Deep Space Network (DSN) antenna and Pluto/Charon, REX also successfully performed axial radiometric measurements of the Cygnus-A and Cassiopeia-A galaxies using the New Horizons high-gain antenna (HGA). The REX instrument's infusion with the New Horizons HGA allows for any radio measurement to be recorded, stored on-board, and ultimately to be downlinked to the DSN. For VLBI, New Horizons could receive command data for timed three-dimensional alignment synchronous to a ground-based observation. The observed data would then be recorded, downlinked, correlated, and processed for synthesized imaging. Using New Horizons for VLBI would be a proof-of-concept. With a fixed observation frequency, narrow bandwidth and receiver sensitivity of −177 dBm, New Horizons is limited as an extension for long-baseline radio interferometry. Given these restrictions, a successful VLBI measurement using New Horizons would still result in the highest angular resolution for any radio observation ever, at an astonishing 1.34 nanoarcseconds. Expanding the applications of New Horizons to VLBI observations encourages collaboration within the growing infrastructure for space-based astronomy.

We used existing data from the New Horizons LORRI camera to measure the optical-band ($0.4\lesssim\lambda\lesssim0.9{\rm\mu m}$) sky brightness within seven high galactic latitude fields. The average raw level measured while New Horizons was 42 to 45 AU from the Sun is $33.2\pm0.5{\rm ~nW ~m^{-2} ~sr^{-1}}.$ This is $\sim10\times$ darker than the darkest sky accessible to the {\it Hubble Space Telescope}, highlighting the utility of New Horizons for detecting the cosmic optical background (COB). Isolating the COB contribution to the raw total requires subtracting scattered light from bright stars and galaxies, faint stars below the photometric detection-limit within the fields, and diffuse Milky Way light scattered by infrared cirrus. We remove newly identified residual zodiacal light from the IRIS $100\mu$m all sky maps to generate two different estimates for the diffuse galactic light (DGL). Using these yields a highly significant detection of the COB in the range ${\rm 15.9\pm 4.2\ (1.8~stat., 3.7~sys.) ~nW ~m^{-2} ~sr^{-1}}$ to ${\rm 18.7\pm 3.8\ (1.8~stat., 3.3 ~sys.)~ nW ~m^{-2} ~sr^{-1}}$ at the LORRI pivot wavelength of 0.608 $\mu$m. Subtraction of the integrated light of galaxies (IGL) fainter than the photometric detection-limit from the total COB level leaves a diffuse flux component of unknown origin in the range ${\rm 8.8\pm4.9\ (1.8 ~stat., 4.5 ~sys.) ~nW ~m^{-2} ~sr^{-1}}$ to ${\rm 11.9\pm4.6\ (1.8 ~stat., 4.2 ~sys.) ~nW ~m^{-2} ~sr^{-1}}$. Explaining it with undetected galaxies requires the galaxy-count faint-end slope to steepen markedly at $V>24$ or that existing surveys are missing half the galaxies with $V< 30.$, Comment: 32 pages, 20 figures. Accepted for publication in ApJ

The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We studied its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, which suggests that Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 ± 5 kelvin. ©2020, NASA (contract no. NASW-02008), NASA (grant no. NAS5-97271 / TaskOrder30)

On 14 July 2015 New Horizons performed a radio occultation (RO) that sounded Pluto’s neutral atmosphere and ionosphere. The solar zenith angle was 90.2° (sunset) at entry and 89.8° (sunrise) at exit. We examined the data for evidence of an ionosphere, using the same method of analysis as in a previous investigation of the neutral atmosphere (Hinson et al., 2017). No ionosphere was detected. The measurements are more accurate at occultation exit, where the 1-sigma sensitivity in integrated electron content (IEC) is 2.3 × 1011 cm − 2 . The corresponding upper bound on the peak electron density at the terminator is about 1000 cm − 3 . We constructed a model for the ionosphere and used it to guide the analysis and interpretation of the RO data. Owing to the large abundance of CH4 at ionospheric heights, the dominant ions are molecular and the electron densities are relatively small. The model predicts a peak IEC of 1.8 × 1011 cm − 2 for an occultation at the terminator, slightly smaller than the threshold of detection by New Horizons.

NASA's New Horizons mission within the New Frontiers program; NASA's Mars Data Analysis Program [NNX15AM48G]

The radio thermal emission from Pluto was observed from the New Horizons spacecraft at a wavelength of 4.2 cm along two scans across the planetary disk shortly after closest approach to Pluto on 14 July 2015. The measurements were performed as part of the New Horizons Radio Science Experiment (REX) using the 2.1 m High Gain Antenna (HGA) and the spacecraft's X-Band receiver. The HGA boresight first scanned along a diametric chord across the Pluto disk and then reversed direction to traverse a chord that crossed close to Pluto's winter pole. The diametric scan reveals a “hot spot” on the Pluto nightside associated with an optically bright region centered roughly at the planetocentric coordinates 280° E, 55° S, imaged in 2002–03 with the Hubble Space Telescope. The nightside was also found to be warmer than the dayside during the polar scan. The highest emission was not observed at the maximum southern latitude, however, but rather near the outbound Pluto limb at lower latitude. The REX emission profile from the polar scan is qualitatively consistent with a bright U-shaped polar cap observed on Pluto's Charon-facing hemisphere during the recurring Pluto/Charon mutual events in the late 1980's. The REX radiometer measurements show distinct variations in microwave brightness that constrain volatile transport models and provide unique information on the thermal structure and composition on the regions in winter night during the New Horizons encounter at Pluto.

On 14 July 2015 New Horizons performed a radio occultation (RO) that sounded Pluto’s atmosphere down to the surface. The sensitivity of the measurements was enhanced by a unique configuration of ground equipment and spacecraft instrumentation. Signals were transmitted simultaneously by four antennas of the NASA Deep Space Network, each radiating 20 kW at a wavelength of 4.2 cm. The polarization was right circular for one pair of signals and left circular for the other pair. New Horizons received the four signals and separated them by polarization for processing by two independent receivers, each referenced to a different ultra-stable oscillator. The two data streams were digitized, filtered, and stored on the spacecraft for later transmission to Earth. The results reported here are the first to utilize the complete set of observations. We calibrated each signal to remove effects not associated with Pluto’s atmosphere, including the limb diffraction pattern. We then applied a specialized method of analysis to retrieve profiles of number density, pressure, and temperature from the combined phase measurements. Occultation entry sounded the atmosphere at sunset at 193.5°E, 17.0°S — on the southeast margin of an ice-filled basin known informally as Sputnik Planitia (SP); occultation exit occurred at sunrise at 15.7°E, 15.1°N — near the center of the Charon-facing hemisphere. Above 1215 km radius (∼25 km altitude) there is no discernible difference between the measurements at entry and exit, and the RO profiles are consistent with results derived from ground-based stellar occultation measurements. At lower altitudes the RO measurements reveal horizontal variations in atmospheric structure that had not been observed previously, and they are the first to reach the ground. The entry profile has a strong temperature inversion that ends 3.5 km above the surface, and the temperature in the cold boundary layer beneath the inversion is nearly constant, 38.9 ± 2.1 K, and close to the saturation temperature of N 2 . The exit profile has a much weaker inversion that extends all the way to the ground, where the air temperature is 51.6 ± 3.8 K. Three factors appear to be responsible for the presence of a cold boundary layer in the entry profile (Forget et al., 2017): a substantial diurnal cycle of sublimation and condensation of N 2 ice in SP, the local time of the RO observation, and confinement within SP by the surrounding topography and katabatic winds. We have also determined the surface pressure and the local radius at both entry and exit. The best pressure reference is the mean value: 11.5 ± 0.7 microbar at 1189.9 ± 0.2 km.

NASA's New Horizons flyby mission of the Pluto-Charon binary system and its four moons provided humanity with its first spacecraft-based look at a large Kuiper Belt Object beyond Triton. Excluding this system, multiple Kuiper Belt Objects (KBOs) have been observed for only 20 years from Earth, and the KBO size distribution is unconstrained except among the largest objects. Because small KBOs will remain beyond the capabilities of ground-based observatories for the foreseeable future, one of the best ways to constrain the small KBO population is to examine the craters they have made on the Pluto-Charon system. The first step to understanding the crater population is to map it. In this work, we describe the steps undertaken to produce a robust crater database of impact features on Pluto, Charon, and their two largest moons, Nix and Hydra. These include an examination of different types of images and image processing, and we present an analysis of variability among the crater mapping team, where crater diameters were found to average ± 10% uncertainty across all sizes measured (∼0.5–300 km). We also present a few basic analyses of the crater databases, finding that Pluto's craters' differential size-frequency distribution across the encounter hemisphere has a power-law slope of approximately –3.1 ± 0.1 over diameters D ≈ 15–200 km, and Charon's has a slope of –3.0 ± 0.2 over diameters D ≈ 10–120 km; it is significantly shallower on both bodies at smaller diameters. We also better quantify evidence of resurfacing evidenced by Pluto's craters in contrast with Charon's. With this work, we are also releasing our database of potential and probable impact craters: 5287 on Pluto, 2287 on Charon, 35 on Nix, and 6 on Hydra.

The Kuiper Belt is a distant region of the Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a Cold Classical Kuiper Belt Object, a class of objects that have never been heated by the Sun and are therefore well preserved since their formation. Here we describe initial results from these encounter observations. MU69 is a bi-lobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color and compositional heterogeneity. No evidence for satellites, ring or dust structures, gas coma, or solar wind interactions was detected. By origin MU69 appears consistent with pebble cloud collapse followed by a low velocity merger of its two lobes., 43 pages, 8 figure

We augment the heliospheric network of galactic cosmic ray (GCR) monitors using 2012–2017 penetrating radiation measurements from the New Horizons (NH) Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), obtaining intensities of ≳75 MeV particles. The new, predominantly GCR observations provide critical links between the Sun and Voyager 2 and Voyager 1 (V2 and V1), in the heliosheath and local interstellar medium (LISM), respectively. We provide NH, Advanced Composition Explorer (ACE), V2, and V1 GCR observations, using them to track solar cycle variations and short-term Forbush decreases from the Sun to the LISM, and to examine the interaction that results in the surprising, previously reported V1 LISM anisotropy episodes. To investigate these episodes and the hitherto unexplained lagging of associated in situ shock features at V1, propagating disturbances seen at ACE, NH, and V2 were compared to V1. We conclude that the region where LISM magnetic field lines drape around the heliopause is likely critical for communicating solar disturbance signals upstream of the heliosheath to V1. We propose that the anisotropy-causing physical process that suppresses intensities at ∼90° pitch angles relies on GCRs escaping from a single compression in the draping region, not on GCRs trapped between two compressions. We also show that NH suprathermal and energetic particle data from PEPSSI are consistent with the interpretation that traveling shocks and corotating interaction region (CIR) remnants can be distinguished by the existence or lack of Forbush decreases, respectively, because turbulent magnetic fields at local shocks inhibit GCR transport while older CIR structures reaching the outer heliosphere do not.

Global Lightning and Sprite Measurements on Japanese Experiment Module (JEM-GLIMS) started the nadir observations of lightning discharges and transient luminous events (TLEs) from the International Space Station (ISS) since November 2012. In the nadir observations, JEM-GLIMS optical instruments have to simultaneously detect incomparably intense lightning emissions and weak TLE emissions. To distinguish TLEs, especially sprite events, from lightning events, combined data analytical methods are adopted: (1) a subtraction of the wideband camera image from the narrowband camera image, (2) a calculation of the intensity ratio between different photometer channels, and (3) an estimation of the polarization and charge moment changes for the TLE-producing lightning discharges. We succeeded in identifying numbers of sprite events using the combined analytical methods, and here we report three sprite events detected by JEM-GLIMS as a case study. In the subtracted images, sprite emissions are located over the area of the sprite-producing lightning emissions. However, these sprites and sprite-producing lightning discharges did not occur at the nadir point of the ISS. For this reason, the geometry conversion of the sprite and sprite-producing lightning emissions as observed from the point just over the sprite-producing lightning discharges is performed. In the geometry-converted images, the locations of the sprite emissions are clearly displaced by 8–20 km from the peak positions of the sprite-producing lightning emissions. Thus, the first quantitative spatial distributions of sprites and sprite-producing lightning discharges from the JEM-GLIMS nadir observations are revealed.

Recent observations of interplanetary medium (IPM) atomic hydrogen Lyman-{\alpha} (Ly{\alpha}) emission in the outer solar system, made with the Alice ultraviolet spectrograph on New Horizons (NH), are presented. The observations include regularly spaced great-circle scans of the sky and pointed observations near the downstream and upstream flow directions of interstellar H atoms. The NH Alice data agree very well with the much earlier Voyager UVS results, after these are reduced by a factor of 2.4 in brightness, in accordance with recent re-analyses. In particular, the falloff of IPM Ly{\alpha} brightness in the upstream-looking direction as a function of spacecraft distance from the Sun is well-matched by an expected 1/r dependence, but with an added constant brightness of ~40 Rayleighs. This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant background. Ongoing observations are planned at a cadence of roughly twice per year., Comment: 21 pages, 5 figures, 1 table, accepted for publication in Geophys. Res. Lett

The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N_2, CH_4, C_2H_2, C_2H_4, C_2H_6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: (1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65–68 K. The inferred enhanced Jeans escape rates were (3–7) × 10^(22) N_2 s^(−1) and (4–8) × 10^(25) CH_4 s^(−1) at the exobase (at a radius of ∼ 2900 km, or an altitude of ∼1710 km). (2) We measured CH_4 abundances from 80 to 1200 km above the surface. A joint analysis of the Alice CH_4 and Alice and REX N_2 measurements implied a very stable lower atmosphere with a small eddy diffusion coefficient, most likely between 550 and 4000 cm^2 s^(−1). Such a small eddy diffusion coefficient placed the homopause within 12 km of the surface, giving Pluto a small planetary boundary layer. The inferred CH_4 surface mixing ratio was ∼ 0.28–0.35%. (3) The abundance profiles of the “C_2H_x hydrocarbons” (C_2H_2, C_2H_4, C_2H_6) were not simply exponential with altitude. We detected local maxima in line-of-sight abundance near 410 km altitude for C_2H_4, near 320 km for C_2H_2, and an inflection point or the suggestion of a local maximum at 260 km for C_2H_6. We also detected local minima near 200 km altitude for C_2H_4, near 170 km for C_2H_2, and an inflection point or minimum near 170–200 km for C_2H_6. These compared favorably with models for hydrocarbon production near 300–400 km and haze condensation near 200 km, especially for C_2H_2 and C_2H_4 (Wong et al., 2017). (4) We found haze that had an extinction coefficient approximately proportional to N_2 density.

Global Lightning and Sprite Measurements on Japanese Experiment Module (JEM-GLIMS) is a space mission to conduct the nadir observations of lightning discharges and transient luminous events (TLEs). The main objectives of this mission are to identify the horizontal distribution of TLEs and to solve the occurrence conditions determining the spatial distribution. JEM-GLIMS was successfully launched and started continuous nadir observations in 2012. The global distribution of the detected lightning events shows that most of the events occurred over continental regions in the local summer hemisphere. In some events, strong far-ultraviolet emissions have been simultaneously detected with N2 1P and 2P emissions by the spectrophotometers, which strongly suggest the occurrence of TLEs. Especially, in some of these events, no significant optical emission was measured by the narrowband filter camera, which suggests the occurrence of elves, not sprites. The VLF receiver also succeeded in detecting lightning whistlers, which show clear falling-tone frequency dispersion. Based on the optical data, the time delay from the detected lightning emission to the whistlers was identified as ∼10 ms, which can be reasonably explained by the wave propagation with the group velocity of whistlers. The VHF interferometer conducted the spaceborne interferometric observations and succeeded in detecting VHF pulses. We observed that the VHF pulses are likely to be excited by the lightning discharge possibly related with in-cloud discharges and measured with the JEM-GLIMS optical instruments. Thus, JEM-GLIMS provides the first full set of optical and electromagnetic data of lightning and TLEs obtained by nadir observations from space.

Methane ice dunes on Pluto Wind-blown sand or ice dunes are known on Earth, Mars, Venus, Titan, and comet 67P/Churyumov-Gerasimenko. Telfer et al. used images taken by the New Horizons spacecraft to identify dunes in the Sputnik Planitia region on Pluto (see the Perspective by Hayes). Modeling shows that these dunes could be formed by sand-sized grains of solid methane ice transported in typical Pluto winds. The methane grains could have been lofted into the atmosphere by the melting of surrounding nitrogen ice or blown down from nearby mountains. Understanding how dunes form under Pluto conditions will help with interpreting similar features found elsewhere in the solar system. Science , this issue p. 992 ; see also p. 960

Suprathermal ions form from interstellar gas that is first ionized into pickup ions and then accelerated to tens and hundreds of keV in energy. The resulting suprathermal ion spectra with hundreds of keV have been previously observed throughout the heliosphere; however, measurements at lower energies, around the pickup ion cutoff energy where they are accelerated from, were limited to New Horizons spacecraft, which recorded observations at a wide range of heliocentric distances, and compare these measurements to charge energy mass spectrometer (CHEMS) observations on Cassini, which cruised to and remained at Saturn. We find that the power-law exponents of suprathermal ion intensity over energy are between −1 and −2, change abruptly close to discontinuities that are likely corotating merged interaction regions, correlate with the solar wind bulk speed, and show a long-term evolution on the timescale of the solar cycle. The independent measurements from New Horizons and Cassini are consistent, confirming the first fully calibrated measurements from the New Horizons/PEPSSI instrument.

New Horizons unveils the Pluto system In July 2015, the New Horizons spacecraft flew through the Pluto system at high speed, humanity's first close look at this enigmatic system on the outskirts of our solar system. In a series of papers, the New Horizons team present their analysis of the encounter data downloaded so far: Moore et al. present the complex surface features and geology of Pluto and its large moon Charon, including evidence of tectonics, glacial flow, and possible cryovolcanoes. Grundy et al. analyzed the colors and chemical compositions of their surfaces, with ices of H 2 O, CH 4 , CO, N 2 , and NH 3 and a reddish material which may be tholins. Gladstone et al. investigated the atmosphere of Pluto, which is colder and more compact than expected and hosts numerous extensive layers of haze. Weaver et al. examined the small moons Styx, Nix, Kerberos, and Hydra, which are irregularly shaped, fast-rotating, and have bright surfaces. Bagenal et al. report how Pluto modifies its space environment, including interactions with the solar wind and a lack of dust in the system. Together, these findings massively increase our understanding of the bodies in the outer solar system. They will underpin the analysis of New Horizons data, which will continue for years to come. Science , this issue pp. 1284 , 10.1126/science.aad9189 , 10.1126/science.aad8866 , 10.1126/science.aae0030 , & 10.1126/science.aad9045

The New Horizons spacecraft mapped colors and infrared spectra across the encounter hemispheres of Pluto and Charon. The volatile ices CH$_4$, CO, and N$_2$, that dominate Pluto's surface, have complicated spatial distributions resulting from sublimation, condensation, and glacial flow acting over seasonal and geological timescales. Pluto's H$_2$O ice "bedrock" is also mapped, with isolated outcrops occurring in a variety of settings. Pluto's surface exhibits complex regional color diversity associated with its distinct provinces. Charon's color pattern is simpler, dominated by neutral low latitudes and a reddish northern polar region. Charon near infrared spectra reveal highly localized areas with strong NH$_3$ absorption tied to small craters with relatively fresh-appearing impact ejecta., Comment: in Science 351, aad9189 (2016)

The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of $\approx$40 km for Nix and Hydra and ~10 km for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of $\approx$2. All four moons have high albedos ( $\approx$50-90 %) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages $\gtrsim$ 4 Ga. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary., Comment: in Science 351, aae0030 (2016)

第29回大気圏シンポジウム（2016年3月7日-8日. 宇宙航空研究開発機構宇宙科学研究所（JAXA)(ISAS)）, 相模原市, 神奈川県, 29th Atmospheric Science Symposium (March 7-8, 2016. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000051028, レポート番号: V-2

We present an approach to the common problem in data analysis namely to detect interesting phenomena without a priori knowledge. In an earlier work [1,2] we put forth method of decomposition in one dimension based on a notion we called degree of symmetry. In this work we present a decomposition model in two dimensions based as well on degree of symmetry. We associate degree of symmetry with fractional order of derivatives and represent each feature along each axis as a linear combination of fractionally differentiated symmetric Schwartz functions. The fractional derivatives for each component complement each other such that the sum of their orders is an odd integer. The parameters of this model, namely the fractional degree of the derivatives, the widths of the Schwartz functions and the ratio of the weights in the linear combination of each component induce a multidimensional representation space to detect, classify and characterize shapes. We present a numerical method using wavelet transform coefficients for determining the parameters of the representation model given a two dimensional shape.

© 2016 Elsevier Inc. We discuss two semi-independent calibration techniques used to determine the inflight radiometric calibration for the New Horizons’ Multi-spectral Visible Imaging Camera (MVIC). The first calibration technique compares the measured number of counts (DN) observed from a number of well calibrated stars to those predicted using the component-level calibration. The ratio of these values provides a multiplicative factor that allows a conversation between the preflight calibration to the more accurate inflight one, for each detector. The second calibration technique is a channel-wise relative radiometric calibration for MVIC's blue, near-infrared and methane color channels using Hubble and New Horizons observations of Charon and scaling from the red channel stellar calibration. Both calibration techniques produce very similar results (better than 7% agreement), providing strong validation for the techniques used. Since the stellar calibration described here can be performed without a color target in the field of view and covers all of MVIC's detectors, this calibration was used to provide the radiometric keyword values delivered by the New Horizons project to the Planetary Data System (PDS). These keyword values allow each observation to be converted from counts to physical units; a description of how these keyword values were generated is included. Finally, mitigation techniques adopted for the gain drift observed in the near-infrared detector and one of the panchromatic framing cameras are also discussed.

Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto's atmosphere. While the lower atmosphere (at altitudes, in Science 351, aad8866 (2016)

This paper details initial results from a study of electrical effects resulting from hypervelocity impacts at a Van de Graaff dust accelerator. Iron particles between 10 −15 g and 10 −10 g in mass were impacted on several different metallic targets at speeds of 1 km/s to 50 km/s. The goal of this study is to characterize the impact-generated plasma and associated RF emission. Results are presented from data collected using retarding potential analyzers. The rate of signal detection was found to have a dependence both on material and on target bias. From a single analyzer, some signal waveforms exhibited oscillatory behavior which is significant in determining the effect of impacts on spacecraft. Using two analyzers at different distances from the target, the expansion speed of the impact plasma was measured to be between 10 km/s and 30 km/s.

We have developed an on-chip RF filter in 130 nm BiCMOS for SAW-less GPS receivers. The filter is implemented as a cascode amplifier stage with reactive resonant tanks. The filter employs two Q-enhanced LC tanks to create a transfer function with steep roll-off characteristic and narrow passband. The image rejection filter achieves a 3 dB bandwidth of less than 12 MHz at the GPS L1 center frequency of 1575.42 MHz. The resulting magnitude response exhibits a notch at 1540 MHz and at 1610 MHz, attenuating noise and interference 30 MHz away from the center frequency by more than 30 dB. The NF of the RF filter is 4.0 dB. A competitive power consumption of only 5.7 mW is achieved.

This paper presents a design framework for soft-error-resilient sequential cells, by introducing a new sequential cell called LEAP-DICE and evaluating it against existing circuit techniques in the “soft error resilience-power-delay-area” design space in an 180 nm CMOS test chip. LEAP-DICE, which employs both circuit and layout techniques, achieved the best soft error performance with a 2,000X improvement over the reference D flip-flop with moderate design costs. This study also discovered new soft error effects related to operating conditions.

We propose to model shapes and features in order to recognize the unusual, or novel, in the presence of the ordinary especially when we lack a basis set of known patterns with which to conduct a search for the unknown. Our method is based on a novel abstraction called degree of symmetry and suggests that any feature or shape can be decomposed into two orthogonal components: one associated with a fractional degree of symmetry, and the other with a mirror, fractional degree of anti-symmetry. In this framework, we associate the measure of symmetry with fractional-order derivatives, and propose that every feature can be represented as f ( x ) = A G σ 1 α ( x ) + B G σ 2 n ∓ α ( ± x ) where n∈Nodd and G σ α denotes the αth order fractional derivative of a symmetric Schwartz function G with width σ. A/B, α, and σ1/σ2 are our parameters. These parameters induce a 3-D representation space to detect, classify and characterize features. We show that the footprint of wavelet transform coefficients particularly their decay characteristics help us determine the parameters of our model. We have processed 21 cm interstellar neutral hydrogen spectra collected synoptically by the 150-foot Stanford Radio Telescope to search for unusual structures, and examples obtained using our fractional symmetry transformations illustrate the utility of our approach.

Lightning and sprite measurement sensors on the International Space Station (ISS) are introduced in this paper. Lightning is an electrical discharge which neutralizes the charge inside thunderstorm. In the early 1990s, optical transient luminous events (TLEs) occurring just above the thunderstorm were firstly reported by the US scientists and are associated with positive cloud-to-ground discharges with a large amount of charge. Though the luminous events so-called sprite, elves and jets have been investigated by numerous researchers all over the world based mainly on the ground observations, some important problems have not been fully understood yet such as generation mechanisms of columniform fine structure and horizontal offset of some sprites from the parent lightning discharges. In the JEM-GLIMS mission, observations from our synchronized sensors are going to shed light on above-mentioned unsolved problems regarding TLEs as well as causative lighting discharges. Our goals are (1) to detect and locate lightning and sprite within storm scale resolution over a large region of the Earth's surface along the orbital track of the ISS without any bias, (2) to clarify the generation mechanism of sprite, and (3) to identify the occurrence conditions of TLEs.

Global Lightning and sprIte MeasurementS (GLIMS) is a mission on the International Space Station (ISS) to detect and locate optical transient luminous events (TLEs) and associated lightning simultaneously from the non-sun-synchronous orbit. It is scheduled to be launched from Japan in January, 2012 as part of the multi-mission consolidated equipment on the Japanese Exposure Module (JEM). Our mission's goals are (1) to detect and locate lightning and sprites within storm scale resolution over a large region of the Earth's surface along the orbital track of the ISS without any bias, (2) to clarify the mechanism by which sprites are generated, and (3) to identify the conditions under which TLEs occur. To achieve these goals, two CMOS cameras, six Photometers, a VLF receiver and VHF interferometer with two antennas are installed at the bottom of the module to observe the TLEs, as well as causative lightning discharges at nadir direction during day and night time. Though the luminous events' so-called sprites, elves and jets have been investigated by numerous researchers all over the world based mainly on ground observations, some important problems have not been fully understood yet. These include the generation mechanisms of columniform fine structures and horizontal offset of some sprites from the parent lightning discharges. In the JEM-GLIMS mission, observations from our synchronized sensors will shed light on the unsolved problems mentioned above regarding TLEs and causative lightning discharges. In this presentation scientific background, instrumentation, and project summaries are given.

The New Horizons (NH) Radio Science Experiment, REX, is designed to determine the atmospheric state at the surface of Pluto and in the lowest few scale heights. Expected absolute accuracies in n, p, and T at the surface are 4⋅1019 m−3, 0.1 Pa, and 3 K, respectively, obtained by radio occultation of a 4.2 cm-λ signal transmitted from Earth at 10–30 kW and received at the NH spacecraft. The threshold for ionospheric observations is roughly 2⋅109 e− m−3. Radio occultation experiments are planned for both Pluto and Charon, but the level of accuracy for the neutral gas is expected to be useful at Pluto only. REX will also measure the nightside 4.2 cm-λ thermal emission from Pluto and Charon during the time NH is occulted. At Pluto, the thermal scan provides about five half-beams across the disk; at Charon, only disk integrated values can be obtained. A combination of two-way tracking and occultation signals will determine the Pluto system mass to about 0.01 percent, and improve the Pluto–Charon mass ratio. REX flight equipment augments the NH radio transceiver used for spacecraft communications and tracking. Implementation of REX required realization of a new CIC-SCIC signal processing algorithm; the REX hardware implementation requires 1.6 W, and has mass of 160 g in 520 cm3. Commissioning tests conducted after NH launch demonstrate that the REX system is operating as expected.

The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition, its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected., 8 pages - Initial Science paper from NASA's New Horizons Pluto Encounter