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Solar Probe PlusA NASA Mission to Touch the Sun
Solar Probe PlusA NASA Mission to Touch the SunA NASA Mission to Touch the Sun
Kelly KorreckSWEAP Science and Operations Lead
Smithsonian Astrophysical [email protected]
Exploring the Sun Up Close: The Solar Wind Electron, Alphas, and
Protons (SWEAP) Instrument Suite aboard Solar Probe Plus
Solar Probe PlusA NASA Mission to Touch the Sun
Outline
Solar Physics background and current unanswered questions Solar Probe Plus Mission What measurements do we need to solve solar mysteries? SWEAP Instruments SWEAP Technology Advancement Summary
SOLAR PHYSICS BACKGROUND AND UNANSWERED QUESTIONS
Why is the Sun yellow?• The surface of the Sun is
hot because energy released through fusion in the solar core radiates and convects up to the surface
• What is the spectrum of light from an object so hot it glows?
• An ideal object without any intrinsic color emits light in a “Blackbody radiation curve” with a peak at one wavelength
• Most of the solar surface is at 6000C
Is there anything above the surface?
THE SOLAR ATMOSPHEREThe Solar Corona
How can you see the solar corona?• The photosphere of the Sun is
too bright to look for signatures of an atmosphere
• We can use solar eclipses, when the Moon blocks the Sun, to search for anything beyond the disk
• Astronomers have used solar eclipses to study the Moon and the Sun for thousands of years
• Earliest recorded observations of eclipses date back to 6000BC
• "Astronomers Studying an Eclipse," a 1571 painting by Antoine Caron, oil on panel
Solar eclipse, as seen from the International Space Station over Turkey, March 2006
Druckmuller, Aniol, Rusin
SOLAR MYSTERIESWhy so big?
The Scale Height Problem• The scale height of an atmosphere is the distance
in altitude you have to travel for the density to drop by a third
• In a simple atmosphere with one temperature and one type of particle, there is a pretty simple relationship for the scale height of:
• Using 6000 degrees C as a temperature and assuming the atmosphere is made of hydrogen then H = 175 km (110 miles)
• Instead, from the eclipses the scale height is clearly like the radius of the Sun, or H = 695,500 km (430,000 miles)
• We have a problem! The solar atmosphere is either:
– 1000+ times hotter than the surface of the Sun– Made up of a new form of matter, 1000 times lighter
than hydrogen
Mass
eTemperaturHeight
New Matter or High Temperature?
• By 1905, scientists thought they had discovered a new form of matter, which they called “Coronium”– A thousand times lighter than hydrogen– Only found in the atmosphere of the Sun– Other evidence (mysterious green lines), and a
precedent…
Evidence for a hot corona• By the 1940s, we realized
that the mysterious green lines were consistent with iron heated to millions of degrees
• The interpretation was that the corona is extremely hot is slowly accepted
• Today we can see this easily from space, by looking at x-rays from the Sun
Modern Images of the Hot Corona
Modern Artificial Eclipses
Going into the Eclipse
18
Solar Probe Plus closest
approach
SOLAR PROBE PLUS MISSION Mission to Touch the Sun
Solar Probe PlusA NASA Mission to Touch the Sun
The Rationale for Solar Probe Plus is Five Decades Old
Current study in line of studies dating back to “Simpson’s Current study in line of studies dating back to “Simpson’s Committee” of the Space Science Board (National Academy of Committee” of the Space Science Board (National Academy of Sciences, 24 October 1958)Sciences, 24 October 1958)
Why is the solar corona so much hotter than the photosphere? Why is the solar corona so much hotter than the photosphere? And how is the solar wind accelerated?And how is the solar wind accelerated?
The answers to these questions can be obtained only through in-The answers to these questions can be obtained only through in-situ measurements of the solar wind down in the corona.situ measurements of the solar wind down in the corona.
20
Solar Probe PlusA NASA Mission to Touch the Sun
The Spacecraft SPC
SPAN-A
FIELDS
WISPR
SPAN-B
ISIS
Solar Probe PlusA NASA Mission to Touch the Sun
SPP Instrument Suites Electromagnetic Fields (FIELDS)
Investigation PI. S. Bale, University of California Space
Sciences Laboratory, Berkeley, CA Integrated Science Investigation of
the Sun Energetic Particle Instruments (ISIS-EPI), PI. D. McComas, South West Research
Institution, San Antonio, TX Solar Wind Electrons Alphas and
Protons (SWEAP) Investigation PI. J. Kasper, Smithsonian Astrophysical
Observatory, Cambridge, MA Wide field Imager for Solar Probe
(WISPR) PI. R. Howard Naval Research Laboratory,
Washington, DC
Heliospheric Origins with Solar Probe Plus - Observatory Scientist (HeliOSPP) PI. M. Velli, Jet Propulsion Laboratory,
Pasadena, CA
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
Solar Probe PlusA NASA Mission to Touch the Sun
Final Orbit Near-Sun Trajectory
MEASUREMENTS NEEDED
Solar Probe PlusA NASA Mission to Touch the Sun
Magnetic measurements that hints at the heating of the solar corona and acceleration of the solar wind
Bruno & Carbone 2006
FIELDS Measurements
Solar Probe PlusA NASA Mission to Touch the Sun
ISIS Energetic Particle Suite
Energetic Particle are produced in flaring active regions on the Sun as well as in shocks between the Sun and Earth.
These particles are hazardous to our space assets.
The acceleration mechanisms of these high energy particles are of interest throughout astronomy and physics.
ISIS
EPI-Lo EPI-Hi
Solar Probe PlusA NASA Mission to Touch the Sun
Wide field Imager for Solar Probe Imaging
The Solar Wind Structures and Fluctuations Directly. CME and Shock Propagation and Evolution and Their
Connection to the Site of Production of SEPs. Provides the Links Between the
Solar Wind Structure and SPP in-situ Instruments Solar Orbiter and Solar Probe Plus Missions
Characteristic Value
Image Type White Light Broadband
Aperture and Focal Length 3.78 cm diameter, 1.78 cm focal length
Spatial Resolution 6.25 arc min
Maximum Cadence – Full Frame <2 min
Sensor APS – new design
Format 2K x 2K, 10 µ square
Solar Probe PlusA NASA Mission to Touch the Sun
Overview of STEREO’s Heliospheric Imager
29
Solar Probe PlusA NASA Mission to Touch the Sun
WISPR Observations
• Images over an encounter used to determine large scale structure, inverted to produce electron density profile
• High time resolution images used to study variable structures near the spacecraft: shocks, streams, reconnection exhausts, turbulence
Polar Wind
SWEAP INSTRUMENT SUITEElectrons, Alphas and Protons
Solar Probe PlusA NASA Mission to Touch the Sun
The Role of SWEAP SWEAP makes detailed measurements of the electrons,
alpha-particles (fully ionized helium), and protons (fully ionized hydrogen) that make up 99% of the solar corona and solar wind
SWEAP observations map out the number of particles moving at different velocities. These maps are then used to determine, e.g.: Velocities, densities, temperatures, anisotropies Electron temperature, anisotropy, heat flux Interactions between particles and electromagnetic waves
Solar Probe PlusA NASA Mission to Touch the Sun
Overview – SWEAP Suite SWEAP Consists of Two
Instruments (SPC & SPAN) and an Electronics Module (SWEM)
SPC – Solar Probe Cup Sun-viewing Faraday Cup
SPAN – Solar Probe Analyzers SPAN-A, ion and electron
electrostatic analyzers (ESAs) on ram-side of spacecraft bus
SPAN-B, electron ESA on anti-ram size of spacecraft bus
SWEM – SWEAP Electronics Module (not shown) Single electrical interface to
SPP, distributes power, commands instruments, formats and buffers data products, interfaces with FIELDS
SPAN-B
SPC
Ram
Dire
ctio
nSPAN-A
Solar Probe PlusA NASA Mission to Touch the Sun
Overview – SWEAP Science (1/4)Objective 1: Trace the flow of energy that heats and accelerates the solar corona and solar wind.
How is magnetic energy converted into heating ions and electrons?
How does thermal and kinetic energy of plasma change with distance?
NASA/SDO/AIA
Reconnection?Wave/Turbulence?
Hinode/XRT
Solar Probe PlusA NASA Mission to Touch the Sun
Overview – SWEAP Science (2/4)
SPP
Hinode/SOT
G-band bright points
SUMER/SOHO
Helios &
Ulysses
UVCS/SOHO
Undamped (WKB) wavesDamped (non-WKB)waves
SPP
Solar Probe PlusA NASA Mission to Touch the Sun
Overview – SWEAP Science (3/4)Objective 2: Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind.
What is the fraction of closed magnetic field lines? How do solar wind sources evolve with time? How does coronal structure evolve into the solar wind?
Solar Probe PlusA NASA Mission to Touch the Sun
Overview – SWEAP Science (4/4) Objective 3: Explore
mechanisms that accelerate and transport energetic particles. What are the roles of
shocks, reconnection, waves, and turbulence in the acceleration of energetic particles?
What are the source populations and physical conditions necessary for energetic particle acceleration?NASA/SDO/AIA
Flare and corona mass ejection
WHAT SWEAP MEASUREMENTS DO WE NEED TO SOLVE SOLAR MYSTERIES?
Data Needed
Solar Probe PlusA NASA Mission to Touch the Sun
Kinetic Physics We are driven by two main questions and puzzling observations
Why is the solar corona so hot? Plasma in corona 100-1000x hotter than photosphere (apparently
violating 2nd law of thermodynamics) Temperature anisotropies (10-100x hotter in one direction than
another) How is the solar wind accelerated so efficiently?
Too much mass escaping at too high a speed Why are these questions so hard to answer?
Kinetic physics f(time, space, velocity) is needed, but we do not understand it well - 7 dimensions!
We cannot make the needed measurements remotely, we cannot reproduce the environment in a laboratory, and we cannot simulate it on a computer
What can Solar Probe Plus do? Enter the corona and make direct observations Capture the particle distributions and electromagnetic field fluctuations
with high precision and cadence to get to the kinetic physics
Solar Probe PlusA NASA Mission to Touch the Sun
Background: Physics of a Classical Gas
It is too difficult to describe the motion of every single particle in a gas or plasma, so we adopt statistical approaches
If there are many collisions, then the distribution of particles with speed follows a Bell Curve
However, in the Solar Wind, there are very few collisions. Leading to Temperature anisotropies and wave propagation and
instabilities
A gas of particles Maxwell-Boltzmann distribution (the Bell Curve)
Rel
ativ
e nu
mbe
r of
par
ticle
sSpeed
Solar Probe PlusA NASA Mission to Touch the Sun
SWEAP Measurements SWEAP measures velocity distribution
functions Need to determine velocity (speed and
direction), density, and temperature of the solar wind.
Why not just fly an anemometer and a weather vane?
Because the solar wind is not in equilibrium Relative densities change Species have different velocities Species have different temperatures Temperature can be hard to define
A SWEAP measurement is a map of the number of electrons, alphas, and protons as a function of direction and energy
Speed#
of P
artic
les
density
velocity (speed and direction)
temperature
Hydrogen(protons)
Helium(alphas)
Solar Probe PlusA NASA Mission to Touch the Sun
SPC Operating Principle
HV Waveform
AC-Coupled Current
Convert signal to voltage and amplifyMeasure amplitude with digital lock-in amplifier
Move on to next energy window
HV Grid
Four collector plates
Solar Probe PlusA NASA Mission to Touch the Sun
SPAN Operating Principle
All three electrostatic analyzers in SPAN begin with top hat hemispherical analyzers Voltage across pair of
deflector plates selects elevation angle
Voltage across pair of curved plates selects energy/charge
Anodes arranged in a ring determine the azimuth angle of each particle
Counters record flux of particles as a function of energy/charge, elevation, and azimuth
Symmetry axis
Deflectors
Curved Plates
SWEAP TECHNOLOGY ADVANCEMENTSSolar Research in the Laboratory
Solar Probe PlusA NASA Mission to Touch the Sun
The Faraday Cup on Voyager I & II
Star Trek: The Motion Picture
Solar Probe PlusA NASA Mission to Touch the Sun
Faraday CupsMore than 20 Faraday cups built by members of the SWEAP team have flown on a variety of
spacecraft in a wide range of environmentse.g. Wind, Voyager, SOLRAD A-B,
Pioneer 6-7
How do we build this to survive close to the Sun?
How do we know we got it right?
Solar Probe PlusA NASA Mission to Touch the Sun
SPC Technology AdvancementMission: Bring Solar Probe Cup to TRL6
Driving Requirement TRL 6=Show instrument operates in the
thermal and particle environment of solar encounters
Key Development Milestones High temperature/high solar intensity
material testing in solar furnace Exposure of SPC thermal test model in
solar furnace Exposure to simulated solar photon and
particle environments
Experimental Practices Use multiple facilities for measurement of
materials properties Use multiple facilities for solar simulator
You can clearly see the furnace from the highway.
The control room we were in where you steer the
mirrors
The laboratory with the vacuum chamberThe focusing parabola
The mirrors
The “iris”: a pair of doors that open and close to adjust the amount of sunlight that hits the
chamber
Solar Furnace
This is the view from the operations center. At the moment the mirrors are all stowed pointing straight forward.
In this example, the center 32 mirrors have just been commanded to move from
standby to projecting the Sun onto the focusing parabola. As the mirrors tilt downward, the Sun shines into the
window of the control center and then to the center of the parabola. The light is
bright but not dangerous because we are not at any kind of focus. This entire
sequence of images took place in less than 60 seconds.
Solar Probe PlusA NASA Mission to Touch the Sun
Summary
There are outstanding mysteries about our Sun Why is the corona so hot? Why is the solar wind so fast?
The Solar Probe Plus mission will enter the atmosphere of our Sun in 2018 Using measurements ranging from white light images to proton
distribution functions, we will help answer the outstanding solar mysteries.
Follow our adventure! http://twitter.com/TheSWEAPLife