Solar Probe Plus: Small Car-Sized Spacecraft Will Plunge Directly Into The Sun's Atmosphere

NASA has begun development of a mission to visit and study the sun closer than ever before. The unprecedented project, named Solar Probe Plus, is slated to launch no later than 2018.

The small car-sized spacecraft will plunge directly into the sun's atmosphere approximately four million miles from our star's surface. It will explore a region no other spacecraft ever has encountered. NASA has selected five science investigations that will unlock the sun's biggest mysteries.

"The experiments selected for Solar Probe Plus are specifically designed to solve two key questions of solar physics -- why is the sun's outer atmosphere so much hotter than the sun's visible surface and what propels the solar wind that affects Earth and our solar system? " said Dick Fisher, director of NASA's Heliophysics Division in Washington. "We've been struggling with these questions for decades and this mission should finally provide those answers." 

The sun is a star with a diameter of approximately 864,000 miles (1,390,000 kilometers), about 109 times the diameter of Earth. The largest stars have a diameter about 1,000 times that of the sun.

 

Image credit: NASA/NSSDC

As the spacecraft approaches the sun, its revolutionary carbon-composite heat shield must withstand temperatures exceeding 2550 degrees Fahrenheit and blasts of intense radiation. The spacecraft will have an up close and personal view of the sun enabling scientists to better understand, characterize and forecast the radiation environment for future space explorers.

NASA invited researchers in 2009 to submit science proposals. Thirteen were reviewed by a panel of NASA and outside scientists. The total dollar amount for the five selected investigations is approximately $180 million for preliminary analysis, design, development and tests.
The selected proposals are:

-- Solar Wind Electrons Alphas and Protons Investigation: principal investigator, Justin C. Kasper, Smithsonian Astrophysical Observatory in Cambridge, Mass.

This investigation will specifically count the most abundant particles in the solar wind -- electrons, protons and helium ions -- and measure their properties. The investigation also is designed to catch some of the particles in a special cup for direct analysis.

-- Wide-field Imager: principal investigator, Russell Howard, Naval Research Laboratory in Washington. This telescope will make 3-D images of the sun's corona, or atmosphere. The experiment actually will see the solar wind and provide 3-D images of clouds and shocks as they approach and pass the spacecraft. This investigation complements instruments on the spacecraft providing direct measurements by imaging the plasma the other instruments sample.

-- Fields Experiment: principal investigator, Stuart Bale, University of California Space Sciences Laboratory in Berkeley, Calif. This investigation will make direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the sun's atmospheric plasma. The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft's antenna.

-- Integrated Science Investigation of the Sun: principal investigator, David McComas of the Southwest Research Institute in San Antonio. This investigation consists of two instruments that will take an inventory of elements in the sun's atmosphere using a mass spectrometer to weigh and sort ions in the vicinity of the spacecraft.

-- Heliospheric Origins with Solar Probe Plus: principal investigator, Marco Velli of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Velli is the mission's observatory scientist, responsible for serving as a senior scientist on the science working group. He will provide an independent assessment of scientific performance and act as a community advocate for the mission.

"This project allows humanity's ingenuity to go where no spacecraft has ever gone before," said Lika Guhathakurta, Solar Probe Plus program scientist at NASA Headquarters, in Washington. "For the very first time, we'll be able to touch, taste and smell our sun." 

The sun is one of over 100 billion stars in the Milky Way Galaxy. It is about 25,000 light-years from the center of the galaxy, and it revolves around the galactic center once about every 250 million years. One light-year, the distance that light travels in a vacuum in a year, equals about 5.88 trillion miles (9.46 trillion kilometers).

 

Image credit: NASA/Transition Region & Coronal Explore

Our First Visit to a Star

Two of the transformative advances in our understanding of the Sun and its influence on the solar system were the discovery that the corona is several hundreds of times hotter than the visible solar surface (the photosphere) and the development—and observational confirmation—of the theory of the corona’s supersonic expansion into interplanetary space as a “solar wind.”

In the decades that have followed these important milestones in solar and space physics, the composition, properties, and structure of the solar wind have been extensively measured, at high heliolatitudes as well as in the ecliptic and at distances far beyond the orbit of Pluto. The corona and the transition region above the photosphere have been imaged with unprecedentedly high resolution, revealing a complex architecture of loops and arcades, while photospheric magnetography has uncovered the “magnetic carpet” of fine-scale flux bundles that underlies the corona. Observational advances have been accompanied by advances in theory and modeling, with a broad range of models offering plausible and competing scenarios to explain coronal heating and solar wind acceleration.

We now know more about the corona and the solar wind than ever before. And yet the two fundamental questions, raised in the 1940s by the discovery of the corona’s million-degree temperature and in the early 1960s by the proof of the supersonic solar wind’s existence, remain unanswered: Why is the solar corona so much hotter than the photosphere? And 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. A mission to provide these measurements, to probe the near-Sun particles-andfields environment, was first recommended in 1958, at the dawn of the space age, by the National Academy of Science’s “Simpson Committee.” Since then, NASA has conducted several studies of possible implementations of a Solar Probe mission, and a Solar Probe has remained at the top of various National Academy and NASA science priority lists.

The Solar Probe Plus mission is part of NASA's Living with a Star Program. The program is designed to understand aspects of the sun and Earth's space environment that affect life and society. The program is managed by NASA'S Goddard Space Flight Center in Greenbelt, Md., with oversight from NASA's Science Mission Directorate's Heliophysics Division. The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., is the prime contractor for the spacecraft. 

Contacts and sources:

NASA news release
For more information about the Solar Probe Plus mission, visit:
http://solarprobe.gsfc.nasa.gov/

For more information about the Living with a Star Program, visit:
http://science.nasa.gov/about-us/smd-programs/living-with-a-star/