have only observed its equatorial regions in detail. The Ulysses probe was launched in 1990 to study the Sun's polar regions. It first traveled to Jupiter, to "slingshot" into an orbit that would take it far above the plane of the ecliptic. Once Ulysses was in its scheduled orbit, it began observing the solar wind and magnetic field strength at high solar latitudes, finding that the solar wind from high latitudes was moving at about 750 km/s, which was slower than expected, and that there were large magnetic waves emerging from high latitudes that scattered galactic cosmic rays. Elemental abundances in the photosphere are well known from spectroscopic studies, but the composition of the interior of the Sun is more poorly understood. A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material. Solar Terrestrial Relations Observatory (STEREO) mission was launched in October 2006. Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections. Parker Solar Probe was launched in 2018 aboard a Delta IV Heavy rocket and will reach a perihelion of in 2025, making it the closest-orbiting manmade satellite as the first spacecraft to fly low into the solar corona. Solar Orbiter mission (SolO) was launched in 2020 and will reach a minimum perihelion of 0.28 AU, making it the closest satellite with sun-facing cameras. CubeSat for Solar Particles (CuSP) was launched as a rideshare on Artemis 1 on 16 November 2022 to study particles and magnetic fields. Indian Space Research Organisation has scheduled the launch of a satellite named Aditya-L1 for 2023. Its main instrument will be a coronagraph for studying the dynamics of the solar corona. Unsolved problems Coronal heating The temperature of the photosphere is approximately 6,000 K, whereas the temperature of the corona reaches . The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere. It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating. The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection