The geology and geophysics of Kuiper Belt object (486958) Arrokoth

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contact binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters diameter) within a radius of 8000 km, and has a lightly-cratered smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism

The MESSENGER Venus Flybys: Opportunities for Synergy with Venus Express

The trajectory of the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft, launched by NASA on 3 August 2004 and destined to be the first probe to orbit Mercury, includes two flybys of Venus during the period that the ESA Venus Express mission is operational in Venus orbit. MESSENGER's first Venus flyby occurred on 24 October 2006, at a closest approach distance of 3140 km, but no scientific observations were made because Venus was at superior conjunction and no direct communication with the MESSENGER spacecraft (or with Venus Express) was possible for an extended period. All MESSENGER instruments, however, will be trained on Venus during the spacecraft's second flyby on 6 June 2007, when closest approach will be at 300 km altitude over 12°S, 107°E, in the uplands of Ovda Regio. The Mercury Dual Imaging System will image the night side in near-infrared bands, and color and higher-resolution monochrome mosaics will be made of both the approaching and departing hemispheres. The Ultraviolet and Visible Spectrometer on the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument will make profiles of atmospheric species on the day and night sides as well as observations of the exospheric tail on departure. The Visible and Infrared Spectrograph on MASCS will observe the planet near closest approach to sense cloud chemical properties and near-infrared returns from the lower atmosphere and surface. The laser altimeter will serve as a passive 1064-nm radiometer and will measure the range to one or more cloud decks for several minutes near closest approach. The combined observations of Venus Express and MESSENGER will permit simultaneous and complementary observations of particular value for characterization of the particle and field environment at Venus. MESSENGER's Energetic Particle and Plasma Spectrometer (EPPS) will observe charged particle acceleration at the Venus bow shock and elsewhere. The Magnetometer will provide measurements of the interplanetary magnetic field (IMF), bow shock signatures, and pickup ion waves as a reference for EPPS and Venus Express observations. The encounter will enable two-point measurements of IMF penetration into the Venus ionosphere, primary plasma boundaries, and the near-tail region. During the MESSENGER flyby the instruments on Venus Express will be operated to maximize the synergy between the two spacecraft for this unique opportunit

Energetic Electron Observations by Parker Solar Probe/ISo˙IS during the First Widespread SEP Event of Solar Cycle 25 on 2020 November 29

At the end of 2020 November, two coronal mass ejections (CMEs) erupted from the Sun and propagated through the interplanetary medium in the direction of Parker Solar Probe while the spacecraft was located at ∼0.81 au. The passage of these interplanetary CMEs (ICMEs) starting on November 29 (DOY 334) produced the largest enhancement of energetic ions and electrons observed by the Integrated Science Investigation of the Sun (ISo˙IS) energetic particle instrument suite on board Parker Solar Probe during the mission's first eight orbits. This was also the first spatially widespread solar energetic particle event observed in solar cycle 25. We investigate several key characteristics of the energetic electron event including the time profile and anisotropy distribution of near-relativistic electrons as measured by ISo˙IS's low-energy Energetic Particle Instrument (EPI-Lo) and compare these observations with contextual data from the Parker Solar Probe Fields Experiment magnetometer. These are the first electron anisotropy measurements from ISo˙IS/EPI-Lo, demonstrating that the instrument can successfully produce these measurements. We find that the electron count rate peaks at the time of the shock driven by the faster of the two ICMEs, implying that the shock parameters of this ICME are conducive to the acceleration of electrons. Additionally, the angular distribution of the electrons during the passage of the magnetic clouds associated with the ICMEs shows significant anisotropy, with electrons moving primarily parallel and antiparallel to the local magnetic field as well as bidirectionally, providing an indication of the ICME's magnetic topology and connectivity to the Sun or magnetic structures in the inner heliosphere. © 2021. The Author(s). Published by the American Astronomical Society..Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Parker Solar Probe observations of helical structures as boundaries for energetic particles

Energetic particle transport in the interplanetary medium is known to be affected by magnetic structures. It has been demonstrated for solar energetic particles in near-Earth orbit studies, and also for the more energetic cosmic rays. In this paper, we show observational evidence that intensity variations of solar energetic particles can be correlated with the occurrence of helical magnetic flux tubes and their boundaries. The analysis is carried out using data from Parker Solar Probe orbit 5, in the period 2020 May 24 to June 2. We use FIELDS magnetic field data and energetic particle measurements from the Integrated Science Investigation of the Sun (IS⊙IS) suite on the Parker Solar Probe. We identify magnetic flux ropes by employing a real-space evaluation of magnetic helicity, and their potential boundaries using the Partial Variance of Increments method. We find that energetic particles are either confined within or localized outside of helical flux tubes, suggesting that the latter act as transport boundaries for particles, consistent with previously developed viewpoints. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Comparative Analysis of the 2020 November 29 Solar Energetic Particle Event Observed by Parker Solar Probe

We analyze two specific features of the intense solar energetic particle (SEP) event observed by Parker Solar Probe (PSP) between 2020 November 29 and 2020 December 2. The interplanetary counterpart of the coronal mass ejection (CME) on 2020 November 29 that generated the SEP event (hereafter ICME-2) arrived at PSP (located at 0.8 au from the Sun) on 2020 December 1. ICME-2 was preceded by the passage of an interplanetary shock at 18:35 UT on 2020 November 30 (hereafter S2), that in turn was preceded by another ICME (i.e., ICME-1) observed in situ on 2020 November 30. The two interesting features of this SEP event at PSP are the following: First, the presence of the intervening ICME-1 affected the evolution of the ≲8 MeV proton intensity-time profiles resulting in the observation of inverted energy spectra throughout the passage of ICME-1. Second, the sheath region preceding ICME-2 was characterized by weak magnetic fields compared to those measured immediately after the passage of the shock S2 and during the passage of ICME-2. Comparison with prior SEP events measured at 1 au but with similar characteristics indicates that (1) low-energy particles accelerated by S2 were excluded from propagating throughout ICME-1, and (2) the low magnetic fields measured in the sheath of ICME-2 resulted from the properties of the upstream solar wind encountered by ICME-2 that was propagated into the sheath, whereas the energy density of the high-energy particles in the sheath did not play a dominant role in the formation of these low magnetic fields. © 2021. The American Astronomical Society. All rights reserved.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]