Solar Probe Plus: Humanity's First Visit to Our Star

Solar Probe Plus A NASA Mission to Touch the Sun

Solar Probe Plus: Humanity’s First Visit to Our Star Nicola J. Fox, N.E. Raouafi, R. Decker, S. Bale, R. Howard, J.C. Kasper, D. McComas, M. Velli. Solar Probe Plus Project Scientist [email protected] A Brief History of the Solar Wind

. 1859: Richard C. Carrington first discovered Hα flare, which was followed by the strongest geomagnetic storm in recorded history. He suggested a connection between solar flares & geomagnetic activity. . 1910: British astrophysicist Arthur Eddington suggested the existence of a solar wind, without naming it, in a footnote to an article on Comet Morehouse. . 1916: Norwegian physicist Kristian Birkeland suggested that the solar wind was composed of both ions and electrons. . 1930s: scientists inferred from eclipse observations that the the solar corona must be > a million degree hot through observations of emissions from highly ionized ions. . Mid-1950s: British mathematician Sydney Chapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. . Also in the 1950s: German scientist Ludwig Biermann postulated that the anti-solar orientation of comet tails results from a steady stream of particles emitted by the Sun. . 1958: Eugene Parker developed the theory of hot coronal plasma evolving into what he termed the "solar wind”. . 1962: Marsha Neugebauer and Conway Snyder confirmed the existence of the solar wind through in-situ measurements. IUGG Solar Probe Plus How is the Corona Heated?

Reference: Cranmer & van Ballegooijen, ApJ, 2005

SPP

Electrons and different ion species are heated differently; theoretical work has shown that single‐fluid theories are clearly not sufficient to explain this. SPP will provide measurements in the region of space where observations are most needed

SPP will bridge the measurement gap between the low corona (i.e., spectroscopic observations (SOHO/SUMER & UVCS) and heliospheric in‐situ measurements from Helios.

IUGG Solar Probe Plus How is the Solar Wind Accelerated?

. ‘Alfvén point’: Within this point, the magnetic energy density dominates, and the gas is forced to flow along the field lines. Beyond this point, kinetic energy acquired by the flowing gas prevails and the field is forced to follow the flow. . In a magnetized plasma, the Alfvén point (colored circles in the figure below) determines radial extent of the lower (sub‐Alfvénic) corona

Reference: Kasper et al. 2010, SWEAP Proposal

It is important to measure the solar wind as close to the solar surface (below the Alfven critical point) as possible while it is still undergoing most of its acceleration. IUGG Solar Probe Plus 50 years into the space age and we still don’t understand the corona and solar wind

. The concept for a “Solar Probe” dates back to “Simpson’s Committee” of the Space Science Board (National Academy of Sciences, 24 October 1958) ‒ The need for extraordinary knowledge of Sun from remote observations, theory, and modeling to answer the questions: – Why is the solar corona so much hotter than the photosphere? – How is the solar wind accelerated? . The answers to these questions can be obtained only through in-situ measurements of the solar wind down in the corona and been of top priority in multiple Roadmaps and Decadal Surveys.

IUGG Solar Probe Plus SPP Over-arching Science Objective

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 mechanisms accelerate and transport energetic particles.

IUGG Solar Probe Plus Spacecraft Overview

. NASA selected instrument suites . 685 kg max launch wet mass . Reference Dimensions:  S/C height: 3 m  TPS max diameter: 2.3 m  S/C bus diameter: 1 m . C-C Thermal protection system . Hexagonal prism s/c bus configuration . Actively cooled solar arrays  388 W electrical power at encounter  Solar array total area: 1.55 m2  Radiator area under TPS: 4 m2 . 0.6 m HGA, 34 W TWTA Ka-band science DL . Science downlink rate: 167 kb/s at 1AU . Blowdown monoprop hydrazine propulsion . Wheels for attitude control

IUGG Solar Probe Plus Reference Mission: Launch and Mission Design Overview

Launch 1st Min Launch . Dates: Jul 31 – Aug 19, 2018 (20 Perihelion 7/31/2018 days) at 9.86 RS . Max. Launch C3: 154 km2/s2 12/19/2024 . Delta IV-Heavy with Upper Stage Trajectory Design . 24 Orbits

. 7 Venus gravity assist flybys Sun Final Solar Orbits

. Closest approach: 9.86 Rsun (3.83 Mercury million miles) Venus . Speed ~450,000 miles per hour (~125 miles per second) Earth . Orbit period: 88 days Mission duration: 6 yrs, 11 months 1st Perihelion at 35.7 RS 11/1/2018

IUGG Solar Probe Plus SPP Rapidly Explores the Inner Heliosphere

Orbit # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Period (d) 168 150 150 140 121 112 107 102 102 100 96 96 96 96 96 96 96 92 92 92 87 88 88 88 A1

A2 A3 A4 Venus Flyby A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16 A17 A18 A19 A20 A21 A22 A23 A24 A25

P1 P2 P3 P4 P5 P6 P7 P8 P9 P11 P14 P15 P16 P10 P12 P13 P17 P18 P19 P20 P21 P22 P23 P24

. Max solar distance is 1.018 AU, and min solar distance is 0.04587 AU (9.86 RS) . 1st perihelion (0.16 AU) 3 months after launch; 19 passes below 20 Rs . Perihelia gradually decreases. Science measurements will commence at the first Perihelion

IUGG Solar Probe Plus Reference Vehicle: Concept of Operations

IUGG Solar Probe Plus Reference Vehicle: Anti-Ram Facing View

SWEAP PI Justin Kasper University of Michigan

At closest approach, the front the heat shield will be at 1,400°C (2500 oF), but the payload will be near room temperature

IUGG Solar Probe Plus Reference Vehicle: Ram Facing View

FIELDS PI Stuart Bale (UC, Berkeley) ISIS PI David McComas (Southwest Research Inst.) WISPR PI Russ Howard (Naval Research Lab)

IUGG Solar Probe Plus Solar Probe Plus Science Investigations (1/5)

. Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: This Solar Probe Cup (SPC) 2 Solar Probe ANalyzers (SPAN) investigation will count the most abundant particles in the solar wind ‐‐ electrons, protons and helium ions ‐‐ and SPC

measure their properties such as SPAN-B SPAN-A+ velocity, density, and temperature.

SWEAP Investigation

SWEAP PI Prof. Justin Kasper University of Michigan/ Smithsonian Astrophysics Observatory

IUGG Solar Probe Plus Solar Probe Plus Science Investigations (2/5)

. Fields Experiment (FIELDS): FIELDS Investigation

‐ Five voltage sensors This investigation will make V1‐V4 electric antennas ‐ Two Fluxgate magnetometers ‐ One search‐coil magnetometer direct measurements of ‐ Main Electronics Package electric and magnetic fields and waves, Poynting flux,

absolute plasma density and MAGi, MAGo

electron temperature, SCM spacecraft floating potential and density fluctuations, and V1‐V4 electric antennas V5 electric antenna radio emissions. FIELDS PI Prof. Stuart Bale University of California, Berkeley

IUGG Solar Probe Plus olar Probe Plus Science vestigations (3/5) grated Science Investigation of the High energy Energetic Particle Instrument (EPI‐Hi) (ISIS): This investigation makes EPI-Lo Low energy Energetic Particle Instrument (EPI‐Lo) rvations of energetic electrons, 8 Sensor ons and heavy ions that are Wedges lerated to high energies (10s of keV 00 MeV) in the Sun's atmosphere nner heliosphere, and correlates LET1 m with solar wind and coronal HET tures. ISIS Bracket

EPI-Hi LET2 ISIS Investigation ISIS PI Dr David McComas olar Probe Plus Science vestigations (4/5) e‐field Imager for Solar PRobe PR): These telescopes will take images White light imager e solar corona and inner heliosphere. experiment will also provide images of Inner Telescope olar wind, shocks and other structures Outer Telescope ey approach and pass the spacecraft. nvestigation complements the other uments on the spacecraft providing t measurements by imaging the ma the other instruments sample.

WISPR Investigation

WISPR PI Dr. Russell Howard Naval Research Laboratory ervations from 10‐20 Rs are required chieve the SPP Science Objectives oronal magnetic ructure still channels he flow and determines ngular momentum loss Solar Orbiter Waves, turbulence rongest emperature maximum ollisional‐Collisionless ransition Magnetic–Kinetic P Level‐1 Science Objectives

• Trace the flow of energy that heats the corona and accelerates the solar wind • Determine the structure and dynamics of the magnetic fields at the sources of the fast and slow solar wind • Determine what mechanisms accelerate and transport energetic particles

There are three detailed science sub‐questions stemming from each of these objectives. ailed Science Sub‐Questions Example: 1st Science Objective

IUGG Solar Probe Plus Example: 1st Science Objective Observation Strategy

• SPP, with 75 hrs inside 12 Rs /400 inside 15 Rs (sub‐Alfvénic), will measure more than 20 hrs (<12 Rs) 100 hrs (< 15 Rs) of fast wind. • SPP will provide direct measurements of Alfvén Wave Poynting fluxes and of ion and electron thermal and kinetic energy fluxes, allowing detailed energy flow analysis. • SPP will fly inside regions where Alfvénic turbulence is expected to peak, allowing definite confirmation/exclusion of the role played by low‐frequency fluctuations in heating and acceleration. • SPP radial and longitudinal scans will allow us to determine the roles of reconnection and jets and instabilities in the heating and acceleration of the slow wind.

IUGG Solar Probe Plus SPP Participation

• 31 institutions participate in SPP science teams • 23 in the US, 8 foreign • 17 educational, 5 non‐profit, 8 government labs • 106 science team members • 69 PIs and Co‐Is • 37 additional scientists • Next generation graduate students and post‐docs

IUGG Solar Probe Plus Opportunity for World‐Wide Community to Collaborate in SPP!

• Full‐disk magnetograms of the photosphere and chromosphere • Solar Orbiter, NSO Mount Wilson Observatory, GONG, Wilcox Solar Observatory, SDO, SOHO • High‐resolution spectro‐polarimetry and imaging spectroscopy of dynamic solar atmosphere (photosphere to corona) • Solar Orbiter, ATST; GREGOR; NJIT’s Big Bear Solar Observatory New Solar Telescope (NST), • Coronagraph observations • Solar Orbiter, MLSO White light coronagraph, STEREO, SOHO • UV/X‐ray imaging and spectroscopy • Solar Orbiter, SDO, IRIS, SOHO • In‐situ solar wind measurements • Solar Orbiter, SOHO, ACE, DSCVR, STEREO • Radio observations • VLA, Green Bank Solar Radio Burst Spectrometer, Nançay radioheliograph, Nobeyama Radioheliograph; Owens Valley Solar Array, Siberian Solar Radiotelescope; Atacama Large Millimeter Array, FASR • Interplanetary scintillation for tomography of solar wind and ICMEs; • Differential Faraday rotation of background sources constraining magnetic field strength of outer corona and SW. –EISCAT, LWA, MWA, ORT

IUGG Solar Probe Plus Physics of the Corona: Making The Link - Summary

• Solar Probe Plus provides: – Statistical survey of outer corona – 1st perihelion (0.16 AU 0r ~15 million miles) 3 months after launch

– Closest approach below 10 Rs (0.04 AU or 4 million miles) – Excellent sampling of all types of solar wind – Measurements from within the region where all the action happens – Particle measurements from the lowest energy plasma through the most energetic particles associated with solar flares – Measurements of plasma waves that enable energy and momentum flow – Coronal imaging “from the inside out” bridges local to global scales by providing the context

0Action Region 20406080100

IUGG Solar Probe Plus SPP Conclusions • Solar Probe Plus will be an extraordinary and historic mission, exploring what is arguably the last region of the solar system to be visited by a spacecraft, the Sun’s corona. • SPP will repeatedly sample the near‐Sun environment, revolutionizing our knowledge and understanding of coronal heating and of the origin and evolution of the solar wind and answering critical questions in heliophysics that have been ranked as top priorities for decades. • By making direct, in‐situ measurements of the region where some of the most hazardous solar energetic particles are energized, SPP will make a fundamental contribution to our ability to characterize and forecast the radiation environment in which future space explorers will work and live. • Fantastic mission of discovery to the Sun • Only opportunity to understand basic plasma physics mechanisms where the magnetic field dominates • Trace the flow of energy that heats the corona and accelerates the solar wind • Determine structure and dynamics of the B fields at sources of the fast & slow solar wind • Determine what mechanisms accelerate and transport energetic particles • Great collaborative opportunities

IUGG Solar Probe Plus It has been 50+ years since the Solar Probe Concept was introduced. . .

We are on our way! olar Probe Plus ASA Mission to Touch the Sun

Back-up rmine the structure and dynamics of the ma and magnetic fields at the sources of olar wind ow does the magnetic field in the solar wind source regions onnect to the photosphere and the heliosphere? Potential Field Source Surface models show that the magnetic field expansion up to the source‐surface plays a crucial role in determining global solar wind outflow properties, including the terminal velocity, which is inversely correlated to the expansion factor itself. re the sources of the solar wind steady or intermittent? To date it has not been possible to determine the origin and variability of the fast solar wind as connections between solar events and high‐speed wind features have not been adequately measured. ow do the observed structures in the corona evolve into the olar wind? Structures emanating from active regions and coronal holes can be traced to several solar radii above the solar surface, but it is unclear how they evolve into the solar wind. Their respective contributions to the solar wind has proven to be hard to quantify from distant (e.g., 1 AU) rmine the structure and dynamics of the netic fields at the sources of the solar xtended measurements of equatorial extensions of high‐ titude coronal holes as well as equatorial coronal holes. peeds of 110 km/s for perihelia at 20 Rs and ~190 km/s below 0 Rs— allows sampling of the structures, such as plumes, inside he equatorial extensions of the coronal holes. t a radial distance of ~31.5 Rs, there are two periods (one bound, one outbound) where Solar Probe Plus will be in quasi‐ orotation and will cross a given longitudinal sector slowly. In hese intervals, the spacecraft will be able to sample the solar ind for significant radial distances along a field line before oving across the sector. olar Probe Plus, orbiting in the ecliptic, will remain inside the reamer belt for a significant fraction of the 3 encounters inside ( h) d h bl ( h) rmine what mechanisms accelerate transport energetic particles

hat are the roles of shocks, reconnection, waves, and turbulence in the celeration of energetic particles? Identifying the specific SEP acceleration process is a fundamental goal for the SPP mission. Measurements made near SEP acceleration sites will reduce uncertainties due to modifications of angular distributions by propagation and thus provide the timing needed to differentiate specific acceleration processes. hat are the source populations and physical conditions necessary for nergetic particle acceleration? Continuous monitoring of the intensity and composition of suprathermal seed particles in the high corona and inner heliosphere (along with the plasma conditions) are needed to constrain the physical conditions necessary for particle acceleration, their intensity, energy spectrum, and composition. ow are energetic particles transported in the corona and heliosphere? Good pitch‐angle coverage during the observation of these small events close to the Sun is necessary to determine whether the longitudinal spreading of SEP events is due to a direct magnetic connection to the particle source or because of other transport mechanism(s) (e.g., cross‐field diffusion). rmine what mechanisms accelerate transport energetic particles ong observing times in the inner heliosphere enable extensive ampling of shocks and particle acceleration and transport rocesses. apid scans in longitude allow direct exploration of the spatial xtent of particle acceleration sites olar Probe Plus, orbiting in the ecliptic, will remain inside the reamer belt for a significant fraction of the 3 encounters inside 0 Rs (15 hrs) and the previous 5 below 12 Rs (50 hrs). xtensive radial exploration of the inner heliosphere will clarify he origin of the “ubiquitous” power‐law supra‐thermal tails. addition, the synergy of SEP measurements from SPP and 1 U spacecraft will help constrain the role of cross‐field transport ithin 1 AU. rticipating Organizations

lifornia Institute of Technology • Royal Observatory of Belgium ntre Spatiale de Liege, BELSPO • Smithsonian Astrophysical rvard University Observatory perial College • Southwest Research Institute t Propulsion Laboratory • Swedish Institute of Space Physics hns Hopkins University / APL • University of Alabama, Huntsville boratoire d'Astrophysique de • University of Arizona arseille - CNRS • University of California, Berkeley s Alamos National Laboratory • University of Chicago assachusetts Institute of • University of Colorado, Boulder chnology • University of Delaware ax Planck Institute for Solar System • University of Gottingen - DLR udies - DLR • University of Maryland, College Park ASA Goddard Space Flight Center • University of Michigan ASA Marshall Space Flight Center • University of Minnesota val Research Laboratory • University of New Hampshire ris Observatory LESIA-CNRS Ui it fOl CNRS ar Probe Plus Timeline ssion Confirmation: March 14 tical Design Review (CDR): rch 2015 unch: July 2018 on Delta IV‐ avy with Upper Stage st perihelion (r = 34 Rs): tober 2018 st perihelion with r < 10 Rs: cember 2024 icle Instrument capabilities meet el 1 requirements with margin

Particle Sensors SWEAP/SPAN SWEAP/SPC SWEAP-SPAN ons SWEAP-SPC ISIS/EPI-Lo ISIS-EPI-Lo ISIS/EPI-Hi L1 Requirement ISIS-EPI-Hi

SWEAP-SPAN ons SWEAP-SPC ISIS-EPI-Lo ISIS-EPI-Hi

SWEAP-SPAN m SWEAP-SPC ISIS-EPI-Lo ISIS-EPI-Hi s ISIS-EPI-Lo ISIS-EPI-Hi

1eV 1keV 1MeV 1GeV ds & Waves Instrument capabilities t Level 1 requirements with margin

gnetic FIELDS FGM L1 Requirement gnetic FIELDS SCM ectric FIELDS EFI asma aves Fields & Waves FIELDS PWI Sensors FIELDS/FGM adio FIELDS/SCM FIELDS PWI FIELDS/EFI ermal FIELDS/PWI e FIELDS PWI ~DC 10Hz 1kHz 1MHz ds and Waves Measurement Tables

Measurement Dynamic Range Cadence Bandwidth Magnetic Field 140 dB 100k vectors/s DC - 50 kHz Electric Field 140 dB 2M vectors/s DC - 1 MHz Plasma Waves 140 dB 1 spectrum/s ~ 5 Hz - 1 MHz Quasi-Thermal 100 dB for QTN 1 spectrum/4 s QTN 10-2500 kHz QTN Noise/Radio 80 dB for radio 1 spectrum/16 s radio 1-16 MHz radio

Meas. Energy Energy FOV Ang. VDF Mass Res.(3) range(1) Res. Res.(2) cadence Thermal 10 eV – < 20% nadir and ram 10ox25o 1 Hz d(m/q)/(m/q) Ions 20 keV directions < 25% Thermal 5 eV – < 20% > 75% of the 10ox10o 1 Hz n/a Electrons 20 keV sky rmal Particle Measurement uirements Tables seline

Meas. Energy Energy FOV Ang. VDF Mass Res.(3) range(1) Res. Res.(2) cadence Thermal 100 eV – < 30% nadir and ram 20ox25o 1 Hz None Ions 10 keV directions Thermal 5 eV – 2 < 30% > 65% of the 20ox20o 1 Hz n/a Electrons keV sky rgy range not required in all directions ite Light Baseline Measurement quirements Tables

Meas. Cadence FOV Inner Spatial Photometric FOV res. sensitivity bound. (SNR/pixel) Visible ≤16.5 min ≥76° radial x ≥20° ≤ 14° ≤ 6.4 ≥ 20 Broadband transverse at 14° arcmin elongation to ≥44° transverse at 90° elongation

Meas. Energy range Highest FOV (3) Angular Composition (1) cadence (2) sector (4) Energetic ≥1.5 decade in ≤10 sec ≥π/4 sr in sunward vs n/a electrons the range from sunward & anti- 0.02 - 6 MeV anti-sunward sunward hemispheres Energetic ≥2 decades in ≤10s, ≥π/4 sr in sunward vs protons, heavy protons the range from protons; 1 sunward & anti- ion groups and heavy 0.02 to 100 min, ion anti-sunward sunward (He, CNO, ergetic Particle Measurement quirements Tables seline Meas. Energy Highest FOV (3) Angular Composition range (1) cadence sector (4) (2) Energetic ≤0.05 to ≤1 sec ≥π/2 sr in sunward ≤45° n/a electrons ≥3 MeV (select & anti-sunward sectors rates) hemispheres Energetic ≤0.05 to ≤5 sec ≥π/2 sr in sunward ≤30° at least H, He, protons and ≥50 (selected & anti-sunward sectors 3He, C, O, Ne, heavy ions MeV/nuc rates) hemispheres Mg, Si, Fe reshold Meas. Energy range Highest FOV (3) Angular Composition (1) cadence (2) sector (4) Energetic ≥1.5 decade in ≤10 sec ≥π/4 sr in sunward vs n/a electrons the range from sunward & anti- 0.02 - 6 MeV anti-sunward sunward hemispheres Energetic ≥2 decades in ≤10s, ≥π/4 sr in sunward vs protons, heavy protons the range from protons; 1 sunward & anti- ion groups P High Level Organizational Chart

NASA Science Mission Directorate Heliophysics Division Director: S. Clarke Program Scientist: M. Guhathakurta Program Executive: J. Lee

GSFC LWS Program Office APL/SES Management Program Manager: N. Chrissotimos PM for APL Projects: M. Goans Mission Scientist: A. Szabo HELIOSPP – JPL* PI: M. Velli, Obs Sci Solar Probe Plus Project Office Project SAM: L. Becker Project Manager: A. Driesman EPO Deputy Project Manager: P. Hill EV Manager: H. Hunter D. Turney Deputy PM for Instruments: K. Cooper Planning Manager: C. Battista Production Planning Mgr: C. Battista Financial Manager: S. Diamond

ISIS – SwRI R – NRL* PI: D. McComas Mission System Project Scientist Howard PM: S. Weidner Engineer N. Fox Plunkett MSE: J. Kinnison DMSE: M. Lockwood FIELDS – UCB P SAO PI S B l ker’s ‘solar wind’ model - 1958

Sun's corona is strongly attracted by solar gravity, but it is such a good ductor of heat that it is still very hot at large distances. Since gravity kens as distance from the Sun increases, the outer coronal atmosphere pes supersonically into interstellar space. weakening effect of the A ‘solar wind’ is accelerated from the corona ity has the same effect on odynamic flow as a de Laval le (or jet engine): it incites nsition from subsonic to ersonic flow. uires energy input at the

. kTph is not nearly enough! uires non‐thermal energy predicts a critical point e solar wind is heated continuously

s spacecraft urements from 0.3 U ger spacecraft urements outward /r batic cooling cts a much more decay ires continuous, buted energy input Waves/turbulence vs reconnection

otpoint shuffling of open Reconnection injects d lines generates Alfvén energy from closed field ves. Waves propagate regions ward and damp (Cranmer cartoon) ere are we today?

e corona requires a non-thermal source of heat A sufficiently heated corona will expand super-sonically and super- Alfvénically to form a ‘solar wind’ The expanding solar wind requires additional heating e large coronal magnetic energy density is a sufficient energy source. s is our ‘dark energy’. But problems remain: How are the magnetic fields created and transported How is the magnetic energy converted to thermal energy: magnetic reconnection, shocks, waves and turbulence What is the role of ambipolar electric fields?