On September 2, 2010 NASA announced that it has chosen the scientific instruments for the Solar Probe Plus. Planned for 2018 or sooner, Solar Probe Plus will be NASA's first mission to the Sun, or any star. Solar Probe Plus will approach the Sun more closely than any other space probe. The Sun will be the last major object in the solar system to be visited by a space probe.
Solar astronomers hope that data from Solar Probe Plus will answer two fundamental questions about the Sun that have puzzled astronomers for over half a century.
- Why is the Sun's corona hotter than the photosphere?
- What causes the solar wind?
The visible surface of the Sun is the photosphere. At a temperature of 5800 Kelvins, the photosphere is much cooler than the Sun's core. The solar chromosphere, just above the photosphere, is hotter than the photosphere. The Sun's outermost atmospheric layer is the corona, usually visible only during a solar eclipse. The very tenuous corona has a temperature of a few million Kelvins. Astronomers don't know why the corona is so hot.
The solar wind is a stream of particles, mostly protons, electrons, and alpha particles, flying outward from the Sun. Many stars also have stellar winds, so finally understanding the origin of the solar wind will help astronomers understand other stars.
SWEAP, Solar Wind Electrons Alphas and Protons, will measure the numbers and properties of these particles in the solar wind. The properties of the solar wind have been measured far from the Sun by many space missions, but the solar wind has never been studied directly so close to the Sun.
The WISPR, Wide-field Imager for Solar Probe Plus, telescope will directly image clouds and shock waves in the solar wind in three dimensions. Direct images will help astronomers visualize and understand structure in the solar wind.
The FIELDS, Fields Investigation for Solar Probe Plus, instrument will measure the electric and magnetic fields, shock waves, and radio emissions as the spacecraft approaches the Sun. Solar storms, sunspots, coronal mass ejections, and coronal heating are all tied to the Sun's magnetic field. Measuring these fields will help astronomers understand these phenomena.
ISIS, Integrated Science Investigation of the Sun, has instruments to monitor high speed charged particles accelerated by shock waves in the Sun's outer atmosphere. When these particles become part of the solar wind and reach Earth, they have enough energy to threaten astronauts and satellites as well as trigger aurora.
Solar Probe Plus will be designed to operate only 7 million kilometers from the Sun, less than 5 times the Sun's diameter. To protect the scientific instruments, Solar Probe Plus will have a 4.5 inch thick 8 foot diameter outer carbon composite heat shield. The shield will reach temperatures of over 2000 Kelvins.
If Solar Probe Plus goes as planned, it will help astronomers answer many long standing questions about the Sun.
Also of Interest:
Lowest mass extrasolar planet discovered, HD 10180 b has 1.4 times Earth's mass
NASA Kepler mission discovers hot stellar companions possible new class of astronomical objects
Astronomers discover planet outside solar system similar to Jupiter and Saturn
Astronomy 101: How astronomers discovered the water planet GJ 1214b
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