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We analyze data from multiple flybys by the Solar Orbiter, BepiColombo, and Parker Solar Probe (PSP) missions to study the interaction between Venus' plasma environment and the solar wind forming the induced magnetosphere. Through examination of magnetic field and plasma density signatures we characterize the spatial extent and dynamics of Venus' magnetotail, focusing mainly on boundary crossings. Notably, we observe significant differences in boundary crossing location and appearance between flybys, highlighting the dynamic nature of Venus' magnetotail. In particular, during Solar Orbiter's third flyby, extreme solar wind conditions led to significant variations in the magnetosheath plasma density and magnetic field properties, but the increased dynamic pressure did not compress the magnetotail. Instead, it is possible that the increased EUV flux at this time rather caused it to expand in size. Key findings also include the identification of several far downstream bow shock (BS), or bow wave, crossings to at least 60 RV ${\mathrm{R}}_{V}$ (1 RV ${\mathrm{R}}_{V}$ = 6,052 km is the radius of Venus), and the induced magnetospheric boundary to at least ∼ ${\sim} $ 20 RV ${\mathrm{R}}_{V}$. These crossings provide insight into the extent of the induced magnetosphere. Pre‐existing models from Venus Express were only constrained to within ∼ ${\sim} $ 5 RV ${\mathrm{R}}_{V}$ of the planet, and we provide modifications to better fit the far‐downstream crossings. The new model BS is now significantly closer to the central tail than previously suggested, by about 10 RV ${\mathrm{R}}_{V}$ at 60 RV ${\mathrm{R}}_{V}$ downstream. Plain Language Summary: We studied data from the missions Solar Orbiter, BepiColombo, and Parker Solar Probe to understand Venus' magnetotail. We focused on how Venus' magnetic environment interacts with the solar wind to create its magnetosphere. By looking at magnetic fields and plasma density, we figured out the size and movement of Venus' magnetotail, and found where its boundaries are. We noticed that these boundaries change a lot between missions, showing that Venus' magnetotail is very dynamic. Our main discoveries include finding boundary crossings like the bow shock 60 times Venus' radius downstream, and the magnetospheric boundary about 20 times Venus' radius downstream. This helps us understand how far the magnetosphere extends and improve our models of its shape. We also saw that the solar wind affects the magnetotail: during one mission, even though the solar wind was strong, it didn't squish the magnetotail; instead, it made it bigger because of increased solar radiation. Key Points: Venus' magnetotail is observed during nine spacecraft flybys revealing a dynamic structure reaching at least 60 RV downstreamAn improved bow shock model is presented for the deep tail regionThe pre‐existing model of the induced magnetospheric boundary is valid downstream to at least 20 RV [ABSTRACT FROM AUTHOR]

We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 R s and 20 R s , respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. Furthermore, protons were energized to super-thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust.

In the present work, the kinetic exospheric model of the solar wind is improved by considering regularized Kappa distributions that have no diverging moments through consideration of a cut-off at relativistic velocities. The model becomes valid even for kappa indices lower than 2, which is important since low values of kappa are observed in the fast solar wind. The exospheric model shows that the electric potential accelerates the wind to supersonic velocities. The presence of suprathermal Strahl electrons at the exobase can further increase the velocity to higher values, leading to profiles comparable to the observations in the fast and slow wind at all radial distances. The kappa index is not the only parameter that influences the acceleration of the wind: the difference in the altitude of the exobase also makes a significant difference between the fast and slow wind. The exobase is located at lower altitudes in the coronal holes where the density is smaller than in the other regions of the corona, allowing the wind originating from the holes to be accelerated to higher velocities. The new observations of Parker Solar Probe are used to constrain the model. The observations at low radial distances show suprathermal electrons already well present in the Strahl in the antisunward direction and a deficit in the sunward direction, confirming the exospheric feature of almost no incoming particles. For proton distributions, we observe that the proton tail parallel to the magnetic field is already present at 17.2 Rs.

For the first time in history, Parker Solar Probe touched the Sun in April 2021 when it entered the Sun's corona—humanity's first mission ever that reached the Sun—for a scientific in-situ study to unlock the mystery of our star. To reach the Sun is extremely difficult because, unlike any other space exploration destination, the Sun is the solar system's central body, around which Earth and other planets revolve. Earth orbits the Sun at a velocity of about 30 km/s, so for a spacecraft to reach the Sun from Earth the spacecraft must cancel out its velocity in the Earth orbit so it can fall to the Sun. That requires an excessively large energy higher than that required to reach any destination in the solar system, which is beyond the capability of current rockets. This paper describes how Parker Solar Probe is delivered to the Sun through a unique V7GA trajectory that enables it to attain the excessive energy through planetary gravity assists of Venus, flying by Venus seven times to ultimately come within 9.86 solar radii (R S) of the Sun. An emphasis is on in-flight trajectory control of the probe through the intricate V7GA trajectory in actual operation in an unprecedented space environment around the Sun, where unpredictable orbit perturbations plus their ripple effects on the consecutive seven Venus flybys could easily drive the flight trajectory out of control. A novel systematic 2-level control method is developed and has been applied to solve the complicated trajectory control problem in flight operation, using in-flight trajectory re-optimization to select the targets of Venus flybys as trajectory control points and then using trajectory correction maneuvers to target a Venus flyby at the control point. This method enables effective and efficient control of the intricate V7GA trajectory and has resulted in significantly better than pre-launch anticipated flight performance, saving tremendous ΔV. Four years from launch, Parker Solar Probe has completed 5 of the 7 Venus gravity-assist flybys and 12 of the 24 planned solar encounters, passing by the Sun at 13 R S in its orbit. Flight results and performance of the completed flight to date are also described. • How Parker Solar Probe was flown and touched the Sun for the first time in history. • Getting to the Sun is extremely difficult and is enabled by a unique V7GA trajectory. • A novel systematic 2-level control method for complex in-flight trajectory control. • In-flight trajectory re-optimization, trajectory correction maneuver and performance. • Flight results of 5 Venus gravity-assist flybys and record-braking solar encounters. [ABSTRACT FROM AUTHOR]

The editorial discusses the significance of solar wind turbulence in heating and accelerating solar winds, as well as its role in space weather modeling. Recent advancements in computational power and spacecraft deployment have allowed for unprecedented studies on solar wind turbulence. The editorial highlights various studies on wave-wave interactions, magnetic reconnection, numerical simulations, and in-situ measurements by the Parker Solar Probe. Additionally, research on heavy-ion composition in the solar wind and interplanetary coronal mass ejections is discussed, with the aim of improving space weather prediction models. [Extracted from the article]

The search‐coil magnetometer (SCM) aboard Parker Solar Probe (PSP) measures the 3 Hz to 1 MHz magnetic field fluctuations. During Encounter 1, the SCM operated as expected; however, in March 2019, technical issues limited subsequent encounters to two components for frequencies below 1 kHz. Detrimentally, most whistler waves are observed in the affected frequency band where established techniques cannot extract the wave polarization properties under these conditions. Fortunately, the Electric Field Instrument aboard PSP measures two electric field components and covers the affected bandwidth. We propose a technique using the available electromagnetic fields to reconstruct the missing components by neglecting the electric field parallel to the background magnetic field. This technique is applicable with the assumptions of (a) low‐frequency whistlers in the plasma frame relative to the electron cyclotron frequency; (b) a small propagation angle with respect to the background magnetic field; and (c) a large wave phase speed relative to the cross‐field solar wind velocity. Critically, the method cannot be applied if the background magnetic field is aligned with the affected SCM coil. We have validated our method using burst mode measurements made before March 2019. The reconstruction conditions are satisfied for 80% of the burst mode whistlers detected during Encounter 1. We apply the method to determine the polarization of a whistler event observed after March 2019 during Encounter 2. Our novel method is an encouraging step toward analyzing whistler properties in affected encounters and improving our understanding of wave‐particle interactions in the young solar wind. Key Points: We present a method to determine whistler wave polarization without a magnetic field component (Parker Solar Probe regime after March 2019)This allows us to expand whistler wave statistical databases; this is an essential step to better understanding wave‐particle interactionsWe demonstrate that this method applies to 80% of whistler waves observed in burst‐mode data from the first encounter [ABSTRACT FROM AUTHOR]

In the early hours of 2021 April 25, the Solar Probe Cup on board Parker Solar Probe registered the passage of a solar wind structure characterized by a clear and constant He2+/H+ density ratio above 6% during three hours. The He2+ contribution remained present but fainting and intermittent within a twelve-hour window. Solar Orbiter and Parker Solar Probe were in nearly perfect quadrature, allowing for optimal observing configuration in which the material impacting the Parker Solar Probe was in the Solar Orbiter plane of the sky and visible off the limb. In this work, we report the journey of the helium-enriched plasma structure from the Sun to the Parker Solar Probe by combining multi-spacecraft remote-sensing and in situ measurements. We identify an erupting prominence as the likely source, behind the Sun relative to the Earth, but visible to multiple instruments on both the Solar-Terrestrial Relations Observatory-A and Solar Orbiter. The associated CME was also observed by coronagraphs and heliospheric imagers from both spacecrafts before reaching the Parker Solar Probe at 46 R⊙, 8 h after the spacecraft registered a crossing of the heliospheric current sheet. Except for extraordinary helium enhancement, the CME showed ordinary plasma signatures and a complex magnetic field with an overall strength enhancement. The images from the Wide-field Imager for Solar Probe (WISPR) aboard Parker Solar Probe show a structure entering the field of view a few hours before the in situ crossing, followed by repetitive transient structures that may be the result of flying through the CME body. We believe this to be the first example of a CME being imaged by WISPR directly before and during being detected in situ. This study highlights the potential of combining the Parker Solar Probe in situ measurements in the inner heliosphere with simultaneous remote-sensing observations in (near) quadrature from other spacecrafts.

Introduction: Intermittency is a property of turbulent astrophysical plasmas, such as the solar wind, that implies irregularity and fragmentation, leading to non-uniformity in the transfer rate of energy carried by nonlinear structures from large to small scales. We evaluated the intermittency level of the turbulent magnetic field measured by the Parker Solar Probe (PSP) in the slow solar wind in the proximity of the Sun during the probe’s first close encounter.Methods: A quantitative measure of intermittency could be deduced from the normalized fourth-order moment of the probability distribution functions, the flatness parameter. We calculated the flatness of the magnetic field data collected by the PSP between 1 and 9 November 2018. We observed that when dividing the data into contiguous time intervals of various lengths, ranging from 3 to 24 hours, the flatness computed for individual intervals differed significantly, suggesting a variation in intermittency from “quieter” to more intermittent intervals. In order to quantify this variability, we applied an elaborate statistical test tailored to identify nonlinear dynamics in a time series. Our approach is based on evaluating the flatness of a set of surrogate data built from the original PSP data in such a way that all nonlinear correlations contained in the dynamics of the signal are eliminated. Nevertheless, the surrogate data are otherwise consistent with the “underlying” linear process, i.e., the null hypothesis that we want to falsify. If a discriminating statistic for the original signal, such as the flatness parameter, is found to be significantly different from that of the ensemble of surrogates, then the null hypothesis is not valid, and we can conclude that the computed flatness reliably reflects the intermittency level of the underlying nonlinear processes.Results and discussion: We determined that the non-stationarity of the time series strongly influences the flatness of both the data and the surrogates and that the null hypothesis cannot be falsified. A global fit of the structure functions revealed a decrease in flatness at scales smaller than a few seconds: intermittency is reduced in this scale range. This behavior was mirrored by the spectral analysis, which was suggestive of an acceleration of the energy cascade at the high-frequency end of the inertial regime.

Flyby tours are challenging to design due to the extraordinarily large search space. A single algorithm is proposed to answer the question of what low-cost, post-flyby options exist for a spacecraft arriving at a flyby body. The algorithm a) considers the full domain of reachable bodies and transfer types including even- and odd-nπ resonant ballistic, nonresonant ballistic, and v -infinity leveraging; b) identifies families of solutions instead of just single points; and c) structures the search to only seek solutions within a Δv threshold. This algorithm extends and integrates these state-of-the-art characteristics, and is designed to rapidly inform an outer-loop pathfinding scheme for flyby tour design. Detailed examples of resulting solutions and families are provided for multiple variations of three different use case scenarios, including tours in the Jupiter, Saturn, and sun systems. As a representative example in the Jupiter system starting at Callisto, the algorithm takes on the order of 0.1 s to find over 500 solutions with Δv costs below 200  m/s organized into nearly 70 families, all either returning to Callisto or proceeding to Ganymede. [ABSTRACT FROM AUTHOR]

Launched on 12 Aug. 2018, NASA's Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The mission's primary science goal is to determine the structure and dynamics of the Sun's coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-Alfvénic solar wind, which is one of the mission's primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles. [ABSTRACT FROM AUTHOR]

The Parker Solar Probe is a spacecraft designed to study the Sun's corona from inside. It is providing unprecedented detailed information on the density and composition of the Sun's atmosphere as well as the electromagnetic fields, plasma and solar wind. On the other hand, this probe is to achieve record speeds in the International Celestial Reference Frame (ICRF) never obtained before in any previous mission. It is expected that in the last perihelion of 2025 it would move at 0.064 % of the speed of light with respect to the barycenter of the Solar System. By this time it will approach only 9.86 solar radii to the center of the Sun. These orbital conditions make the Parker's Solar Probe also an interesting experiment concerning the validity of General Relativity (GR). The combination of a high velocity and a relatively intense gravitational field increases the values of the post-Newtonian terms governing the orbital corrections by GR. In this paper, we consider an orbital model for the Parker Probe trajectory, including the important effect of radiation pressure, to calculate the relativistic corrections. From this model, we compare the magnitude of the corrections in order to evaluate the possibility of obtaining a test of GR from spacecraft missions orbiting close to the Sun. [ABSTRACT FROM AUTHOR]

Increasingly one interplanetary coronal mass ejection (ICME) structure can propagate across more than one spacecraft in the solar wind. This usually happens when two or more spacecraft are nearly radially aligned with a relatively small longitudinal separation angle from one another. This provides multi-point measurements of the same structure and enables better characterization and validation of modeling results of the structures embedded in these ICMEs. We report such an event during October 13-14, 2019 when the Solar TErrestrial RElations Observatory Ahead (STA) spacecraft and the Parker Solar Probe (PSP) crossed one ICME structure at two different locations with nominal separations in both heliocentric distances and the longitudinal angles. We first perform an optimal fitting to the STA in-situ measurements, based on an analytic quasi-three dimensional (3D) model, yielding a minimum reduced χ2 = 0.468. Then we further apply the optimization approach by combining the magnetic field measurements from both spacecraft along their separate paths across the ICME structure. We find that the output based on the optimization (with the minimum reduced χ2 = 3.15) of the combined two-spacecraft dataset yields a more consistent result, given the much improved agreement of the model output with PSP data. The result demonstrates a magnetic flux rope configuration with clear 3D spatial variations.

Scale-invariance has rapidly established itself as one of the most used concepts in space plasmas to uncover underlying physical mechanisms via the scaling-law behavior of the statistical properties of field fluctuations. In this work, we characterize the scaling properties of the magnetic field fluctuations in a sub-alfvénic region in contrast with those of the nearby super-alfvénic zone during the ninth Parker Solar Probe perihelion. With our observations, (i) evidence of an extended self-similarity (ESS) for both the inertial and the sub-ion/kinetic regimes during both solar wind intervals is provided, (ii) a multifractal nature of field fluctuations is observed across inertial scales for both solar wind intervals, and (iii) a mono-fractal structure of the small-scale dynamics is reported. The main novelty is that a universal character is found at the sub-ion/kinetic scale, where a unique rescaling exponent describes the high-order statistics of fluctuations during both wind intervals. Conversely, a multitude of scaling symmetries is observed at the inertial scale with a similar fractal topology and geometrical structures between the magnetic field components in the ecliptic plane and perpendicular to it, in contrast with a different level of intermittency, more pronounced during the super-alfvénic interval rather than the sub-alfvénic one, along the perpendicular direction to the ecliptic plane. The above features are interpreted in terms of the possible underlying heating and/or acceleration mechanisms in the solar corona resulting from turbulence and current sheet formation. [ABSTRACT FROM AUTHOR]

One of the major discoveries of NASA's 1979–1991 Pioneer Venus Orbiter is that the nightside ionosphere becomes filamentary at high altitude, forming comet‐like tail rays. Pioneer Venus Orbiter could not establish how much farther into the wake of Venus tail rays extend, nor understand how they form. Here we present plasma and fields data from the fourth flyby of Venus by NASA's Parker Solar Probe consistent with an intercept with an ionospheric tail ray. The observations unambiguously demonstrate that Venusian Ionotail Rays can extend to at least 7,800 km in altitude. Using the new Parker observations we are able to identify a tail ray encounter within the Venus Express dataset. We thus present a unified picture of the structure of the magnetotail of Venus based on combined Venus Express, Pioneer Venus Orbiter, and Parker observations, and recent hybrid modeling. Plain Language Summary: Like a comet, the planet Venus has a tail made of plasma. This tail was first discovered and explored by NASA's 1979–1991 Pioneer Venus Orbiter (PVO) mission. The next mission capable of measuring plasmas at Venus was the 2006–2014 ESA Venus Express (VEX) mission. However, by the time of VEX, the technology of space plasma analyzers had advanced so much that even if PVO and VEX flew through the same phenomenon, each would present data very differently. On February 20, 2021 NASA's Parker Solar Probe made its fourth close flyby of Venus, spending 10 min in the wake on the nightside. For two of these minutes, Parker encountered a plume of cold plasma escaping from Venus with all the properties of a Venusian tail ray. These measurements confirm the predictions of recent simulations which predict that tail rays can extend away from the nightside of Venus to an altitude equivalent to the radius of the planet. Furthermore, some of the modern instrumentation aboard Parker are similar to that flown aboard Venus Express enabling us to identify tail rays in that dataset as well, allowing us to directly compare and combine VEX and PVO datasets. Key Points: During its fourth flyby of Venus, NASA's Parker Solar Probe flew through a structure consistent with the tail rays discovered by Pioneer VenusTail rays are a distinct phenomenon that sometimes forms along the current sheet in the Venusian wake, extending to over 7,800 km altitudeThe tail rays discovered by Pioneer Venus Orbiter (PVO) and "Bursty Flows" later reported by Venus Express are likely one and the same phenomenon [ABSTRACT FROM AUTHOR]

On July 11, 2020, NASA's Parker Solar Probe made its third flyby of Venus. The upper hybrid resonance emission was observed below 1,100 km (a first at Venus), revealing electron densities an order of magnitude lower than at solar maximum. These observations are consistent with a substantial variation in the density and structure of the Venusian ionosphere over the Solar Cycle. Plain Language Summary: The planet Venus is in many ways the most Earth‐like planet known and is thus a perfect natural laboratory for understanding what makes Earth‐like planets habitable. It is often thought that Earth's magnetic field is important for life to exist, as it shields our atmosphere from being stripped away to space. If this is true then one might expect that Venus, with no protective magnetic field, would lose more atmosphere when the sun was more active. However, recent studies have shown the opposite to be true. To investigate this, we need measurements of the upper most part of the Venusian atmosphere (the ionosphere, the source of atmospheric escape. On July 11, 2020, NASA's Parker Solar Probe made a close flyby of Venus. During the 7 minutes around the closest approach, one of its scientific instruments detected low‐frequency radio emission of a type naturally generated by planetary ionospheres. By measuring the frequency of this emission, we can directly calculate the density of the ionosphere around Parker, finding it to be far less dense than previous missions have encountered. This supports the theory that the ionosphere of Venus varies substantially over the 11 year solar cycle. Key Points: We report the first detection of upper hybrid resonance emission at Venus, the first in situ measurement of the ionosphere at solar minimumElectron densities were an order of magnitude lower than at solar maximum, and asymmetrically denser toward the terminatorThe Venusian ionosphere varies significantly over the solar cycle, confirming past remote sensing experiments [ABSTRACT FROM AUTHOR]

Scale-invariance has rapidly established itself as one of the most used concepts in space plasmas to uncover underlying physical mechanisms via the scaling-law behavior of the statistical properties of field fluctuations. In this work, we characterize the scaling properties of the magnetic field fluctuations in a sub-alfvénic region in contrast with those of the nearby super-alfvénic zone during the ninth Parker Solar Probe perihelion. With our observations, (i) evidence of an extended self-similarity (ESS) for both the inertial and the sub-ion/kinetic regimes during both solar wind intervals is provided, (ii) a multifractal nature of field fluctuations is observed across inertial scales for both solar wind intervals, and (iii) a mono-fractal structure of the small-scale dynamics is reported. The main novelty is that a universal character is found at the sub-ion/kinetic scale, where a unique rescaling exponent describes the high-order statistics of fluctuations during both wind intervals. Conversely, a multitude of scaling symmetries is observed at the inertial scale with a similar fractal topology and geometrical structures between the magnetic field components in the ecliptic plane and perpendicular to it, in contrast with a different level of intermittency, more pronounced during the super-alfvénic interval rather than the sub-alfvénic one, along the perpendicular direction to the ecliptic plane. The above features are interpreted in terms of the possible underlying heating and/or acceleration mechanisms in the solar corona resulting from turbulence and current sheet formation.

The Parker Solar Probe (PSP) spacecraft completed its second Venus gravity assist maneuver (VGA2) on December 26, 2019. For a 20 min interval surrounding closest approach, the PSP/FIELDS Radio Frequency Spectrometer (RFS) was set to "burst mode," recording radio spectra from 1.3 to 19.2 MHz at sub‐second cadence. We analyze this burst mode data, searching for signatures of radio frequency "sferic" emission from lightning discharges. During the burst mode interval, only four spectra were observed with strong impulsive signals, and all four could be attributed to saturation of the RFS high gain stage by in situ electrostatic plasma waves. These RFS measurements during VGA2 are consistent with previous non‐detection of radio frequency lightning signals from Venus reported by Gurnett et al. (2001, https://doi.org/10.1038/35053009). Plain Language Summary: The Parker Solar Probe (PSP) studies the physics of the solar wind, using an elliptic solar orbit which brings it much closer to the Sun than any other spacecraft. PSP uses seven Venus flybys to change its orbital trajectory via gravitational assist, lowering the distance of closest solar approach after each flyby. During Venus Flyby 2 in December 2019, the PSP radio receiver was set to a special operating mode, which is sensitive to possible lightning signals from the Venus atmosphere. During the flyby, no lightning signals were detected. This is consistent with previous non‐detection of Venus lightning at radio frequencies reported by Gurnett et al. (2001). Key Points: During the second Parker Solar Probe (PSP) Venus gravity assist, the PSP/FIELDS radio receiver recorded high cadence "burst mode" spectraWe examined the burst mode data for lightning‐associated emission. No lightning events were observed, consistent with prior observationsWe can use this non‐detection to place an upper limit on possible lightning emission from Venus [ABSTRACT FROM AUTHOR]

The addition of Parker Solar Probe (PSP) to the Heliophysics System Observatory has allowed for the unprecedented ability to study Corotating Interaction Regions (CIRs) at multiple radial distances without significant temporal/longitudinal variations. On September 19, 2019, PSP observed a CIR at ∼0.5 au when it was nearly radially aligned with the Solar Terrestrial Relations Observatory‐Ahead (STEREO‐A) spacecraft at ∼1 au, allowing for an unambiguous assessment of the radial evolution of a single CIR. Bulk plasma and magnetic field signatures of the CIR evolve in a fashion characteristic to previous observations; however, the suprathermal ions are enhanced over a larger longitudinal range at PSP than at STEREO‐A, although at much lower intensities. The longitudinal spread appears to be largely a consequence of magnetic field line topology at CIRs between the compressed slow solar wind upstream and high‐speed stream following the CIR, underscoring the importance of the large‐scale topology of these structures. Key Points: A CIR was observed by PSP and STA when the spacecraft were near radially alignedThe plasma measurements suggest only radial evolution has occurred between observationsDifferences in fast and slow solar wind magnetic topology lead to a wider longitudinal extent of the suprathermal ion enhancement at PSP [ABSTRACT FROM AUTHOR]

Parker Solar Probe (PSP) was launched on August 12, 2018, on its way to enter the solar corona and "touch" the Sun for the first time. We utilize enormous planetary gravity assists from 7 repeated Venus flybys via a V7GA trajectory in 24 solar orbits over 7 years, to get within 8.86 solar radii from the Sun's surface. The probe successfully entered the V7GA trajectory and made the first Venus flyby only 52 days after launch. Five weeks later it flew by the Sun at a perihelion distance of 0.166 AU and flyby speed of 95.3 km/s, setting new records as the closest craft to the Sun and the fastest human-made object. In this paper, the overall strategy, plan, process, and early flight results and performance for PSP's flight execution including in-flight trajectory control and re-optimization, orbit determination and navigation, and trajectory correction maneuvers are presented. The unique challenges and operation constraints we encountered in flying a solar mission are described. • Flying to the sun's corona in an innovative V7GA trajectory with 24 solar flybys. • Unprecedented challenges and operation constraints in the sun's harsh environments. • In-flight trajectory control, re-optimization, orbit determination, and navigation. • Flight results of launch and first Venus gravity-assist flyby and solar encounters. [ABSTRACT FROM AUTHOR]

The search‐coil magnetometer (SCM) measures the magnetic signature of solar wind fluctuations with three components in the 3 Hz–50 kHz range and one single component in the 1 kHz–1 MHz range. This instrument is important for providing in situ observations of transients caused by interplanetary shocks and reconnection, for the identification of electromagnetic wave modes in plasmas and the determination of their characteristics (planarity, polarization, ellipticity, and k‐vector) and for studying the turbulent cascade in the kinetic range. Two similar triaxial search‐coils have been built for the Parker Solar Probe and Solar Orbiter missions. Here we describe the science objectives of both missions which led to the SCM design and present the characteristics of the two instruments.Key Points: The search‐coil magnetometer (SCM) measures AC magnetic fields onboard the Parker Solar Probe and Solar Orbiter satellitesThis instrument is important for addressing the problem of coronal heating, solar wind formation and particle acceleration by means of wave mode identificationBoth SCM instruments have been launched and are now operating [ABSTRACT FROM AUTHOR]

Electric fields are generally measured or calculated using two intuitive assumptions: (1) the electric field equals the voltage divided by the antenna length when the antenna is electromagnetically short (2) the antenna responds best to electric field along its length. Both assumptions are often incorrect for electrostatic fields because they scale as the Debye length or as the electron gyroradius, which may be smaller than the antenna length. Taking into account this little‐known fact enables us to complete or correct several recent papers on plasma spontaneous fluctuations in various solar system environments. Plain Language Summary: Electric fields are measured in space by detecting the voltage across an electric antenna and dividing this voltage by the antenna length (or an effective length taking into account geometry and receiver gain). The antenna is also assumed to respond best to electric field along its length. Both intuitive assumptions are correct for antennas shorter than the scale of variation of the field and therefore for measuring electromagnetic waves with electromagnetically short antennas. However, in space, the measured power often stems from electrostatic waves, scaling as the plasma Debye length or the electron gyroradius, which are generally much smaller than the electromagnetic wavelength. In that case, the electric antenna may not be short compared to the scale of the electric field, so that the voltage is no longer proportional to the antenna length nor maximum when the antenna lies along the field. This fact is generally ignored, producing incorrect results. We complete and correct several recent papers and discuss the adequate antenna response and directivity in various space environments. Key Points: Measured plasma wave spectra are determined by the antenna geometry in a nonintuitive wayWe correct several recent papers on plasma spontaneous fluctuations or quasi‐thermal noiseWe consider various space applications including Van Allen Probes and Parker Solar Probe [ABSTRACT FROM AUTHOR]

The interplanetary medium variability has been extensively studied by means of different approaches showing the existence of a wide variety of dynamical features, such as self-similarity, self-organization, turbulence and intermittency, and so on. Recently, by means of Parker solar probe measurements, it has been found that solar wind magnetic field fluctuations in the inertial range show a clear transition near 0.4 AU, both in terms of spectral features and multifractal properties. This breakdown of the scaling features has been interpreted as the evidence of a dynamical phase transition. Here, by using the Klimontovich S-theorem, we investigate how the process of self-organization is under way through the inner heliosphere, going deeper into the characterization of this dynamical phase transition by measuring the evolution of entropic-based measures through the inner heliosphere.

In 1958, Eugene Parker advanced that the solar wind must be produced through the thermal expansion of coronal gas. At the time, he introduced a dimensionless parameter, λ = GMSMH/2kbT0a, where G corresponds to the universal constant of gravitation, MS to the solar mass, MH to the mass of the hydrogen atom, kb to Boltzmann's constant, T0 to the temperature at the location of interest, and a is the distance to the effective surface, or the radial distance, to the outer solar corona, the location of interest, relative to the center of the Sun. It is straightforward to demonstrate that this equation stands in violation of the 0th and 2nd laws of thermodynamics by simply rearranging the expression in terms of temperature: T0 = GMSMH/2kBλa. In that case, then temperature, an intensive property, is now being defined in terms of an extensive property, MS, and the radial position, a, which is neither intensive nor extensive. All other terms in this expression are constants and unable to affect the character of a thermodynamic property. As a result, temperature in this expression is not intensive. Consequently, the expression advanced by Parker is not compatible with the laws of thermodynamics. This analysis demonstrates that solar winds cannot originate from the thermal expansion of coronal gas, as is currently accepted. [ABSTRACT FROM AUTHOR]

Electron photoemission influences spacecraft surface potentials and the surrounding plasma, and many modern spacecraft use new uncharacterized materials. The angle-dependent photoemission properties were measured for niobium C103 alloy, molybdenum TZM alloy, tantalum tungsten alloy, Elgiloy, graphite lubricant epoxy (DAG213) and titanium nitride at the Bending for Emission Absorption and Reflectivity beam line. The properties of tungsten were also studied to verify the method with past data. The materials were prepared similarly to flight materials. The properties were measured from 0 (normal) to 80 deg (grazing) incidence preannealed and postannealed conditioning of the samples. The yield was measured in all cases for both p and s polarization at each angle of incidence. Results are presented for the photoelectric threshold and photoelectron yield for photon energies up to 30 eV. The work function was also found for each material tested. An analytical equation was then used to fit the normal photoelectron yield for each material to help obtain photocurrents, which were calculated assuming solar illumination at 1 astronomical unit (AU) at normal incidence. [ABSTRACT FROM AUTHOR]

The interplanetary medium variability has been extensively studied by means of different approaches showing the existence of a wide variety of dynamical features, such as self-similarity, self-organization, turbulence and intermittency, and so on. Recently, by means of Parker solar probe measurements, it has been found that solar wind magnetic field fluctuations in the inertial range show a clear transition near 0.4 AU, both in terms of spectral features and multifractal properties. This breakdown of the scaling features has been interpreted as the evidence of a dynamical phase transition. Here, by using the Klimontovich S-theorem, we investigate how the process of self-organization is under way through the inner heliosphere, going deeper into the characterization of this dynamical phase transition by measuring the evolution of entropic-based measures through the inner heliosphere. [ABSTRACT FROM AUTHOR]