Solar Probe: Mission to the Sun Donald M. Hassler/David J. McComas Southwest Research Institute

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)2 Why Solar Probe? Solar Probe is the single most important mission for the solar and heliospheric community to make breakthrough discovery science in the next decade! Why? Solar Probe is the last great flyby mission of discovery, providing the next great advance in understanding our star! A coronal fly-through is the ONLY way to make conclusive measurements to determine uniquely what heats the corona and accelerates the solar wind,... and solve the mysteries of the critical region where the solar wind is “born”.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)3 Solar Probe Science Objectives Group 1 Objectives: –Determine the acceleration processes and find the source regions of the fast and slow solar wind at maximum and minimum solar activity; –Locate the source and trace the flow of energy that heats the corona; –Construct the three-dimensional coronal density configuration from pole to pole and determine the subsurface flow pattern, the structure of the polar magnetic field, and their relationship with the overlying corona; and –Identify the acceleration mechanisms and locate the source regions of energetic particles, and determine the role of plasma waves and turbulence in the production of solar wind and energetic particles. Group 2 Objectives: –Investigate dust rings and particulates in the near-Sun environment; –Determine the outflow of atoms from the Sun and their relationship to the solar wind; and –Establish the relationship between remote sensing, near-Earth observations at 1 AU and plasma structures near the Sun. Group 3 Objectives: –Determine the role of x-ray microflares in the dynamics of the corona; and –Probe nuclear processes near the solar surface from measurements of solar gamma rays and slow neutrons.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)4

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9 “High-speed” Solar Wind Acceleration This plot shows the flow speed above polar coronal holes and indicates that the solar wind acceleration is relatively rapid, reaching velocities of the terminal speeds of about 800 km/s well below a distance of 10 R S. SOHO measurements have placed the velocities on the order of 100 to 150 km/s as maximal, at a distance of 2 to 3 R S. Solar Probe will cross the polar regions at 7 R S and if the coronal holes extend down to 30 degrees latitude at the time of its passage, it will extend the distance of Solar Probe down to 5 R S in the high-speed region. Solar Probe will cross the equatorial region at 4 R S, a distance believed to be inside the subsonic point.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)10

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)11

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)12 In-Situ Measurements High time resolution, synchronized plasma, energetic particle, and field measurements, including mass resolved ion distribution functions, will resolve: solar wind heating and acceleration macroscopic coronal structure and composition fine scale spatial structures –plasma and magnetic structures in the helmet streamer belt –plume/interplume structure

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)13 Direct In-situ measurements and tomographic imaging of Polar Plumes

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)14 The Hemispheric Imager’s 180 deg. FOV permits true tomographic reconstruction of 3-D coronal structure and context for the in-situ package A coronal fly-through is the ONLY way to reconstruct the 3-D coronal structure!

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)15 Reconstructed image of the heliosphere out to 1.5 AU, derived by tomographic reconstruction from HELIOS photometer data. Solar Probe will permit reconstruction of the corona and inner heliosphere with 1,000 times better spatial resolution.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)16 Observations of the Sun’s Poles: Polar Magnetic Field Solar Probe magnetograph will provide the first high resolution maps and time series evolution studies of the polar magnetic field. Solar Probe magnetograms will be the highest resolution magnetograms of the photosphere ever obtained.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)17 LEFT: An MDI full-disk magnetogram, reprojected to the pole. RIGHT: 32-minute averaged magnetogram. Current measurements of the polar magnetic field are severely foreshortened and sensitivity-limited due to our perspective from the ecliptic plane. Magnetograms of the Sun’s polar region (above 60 deg.) are not sufficient to detect small scale flux concentrations or offsets in the large scale magnetic field.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)18 Solar Probe will provide important constraints on theories of the Solar Dynamo The poloidal component of the magnetic field, a key ingredient to the dynamo mechanism, is predicted to be strongest at the poles. Models suggest that transport of magnetic flux by meridional circulation is crucial for the solar cycle and the operation of the dynamo, because it couples toroidal and poloidal field components, and links the surface field to the shear layer at the base of the convection zone.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)19 Solar Probe will solve fundamental mysteries related to the subsurface origins of the solar cycle.

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)20

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)21 Solar Probe will provide EUV imaging of the corona and solar surface with a resolution 10 times higher than TRACE. Ultra-high (35 km) resolution images of the corona and solar surface, including the poles!

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)22 SCIENCE IMPACT: Dramatic exploration of “new territory” in the solar system Comparable to the first planetary flybys ONLY way to determine uniquely what heats the corona and accelerates the solar wind Solar Probe is a mission of discovery - NOT incremental science!

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)23 Solar Probe Status/Update (1) Solar Probe was on track!!! –mature mission concept that has undergone years of design optimization –within budget and below initial projected cost –NASA ready to make instrument team selections - project ready to undertake mission –extended study phase at minimal cost to NASA reduces overall risk and total mission cost

Don Hassler/Dave McComas (SwRI)Decadal Survey Presentation (Boulder, 17 April 2001)24 Solar Probe Status/Update (2) SP is in jeopardy of cancellation under the current presidential budget. “The Solar Probe mission, slated to be NASA's first voyage to a star, was not determined to be a near-term budget priority for NASA, and is not funded in the FY 2002 budget. In the event that the Solar Probe is assigned a high priority by the solar and space physics science community, the mission could be funded out of the resources planned for other solar and space physics programs.” - OSS White Paper on Presidential Budget (9 April 2001) SP is the single most important mission for the solar and heliospheric community to make breakthrough, discovery science! The findings of the Decadal Survey Panel can make a difference!