Space physics

Space physics is the study of naturally occurring plasmas. A plasma is a specific state of matter found in the upper atmosphere and the Solar System. This field includes many complex topics like aeronomy and aurorae. It also investigates planetary ionospheres and magnetospheres. Scientists study radiation belts and space weather within this discipline. They also look at the solar wind and the Sun. More recently, the field has expanded to include the interstellar medium. This science is vital for our modern world. It helps with radio transmission and spacecraft operations. It is also useful for meteorology and managing weather satellites.

Researchers use several methods to understand these cosmic processes. Some use in situ measurements to take direct readings. They do this using sounding rockets and various spacecraft. Other scientists use remote sensing to study plasmas from a distance. They might use radar methods like Incoherent scatter. They also use GPS scintillation to gather data. Many experts also perform theoretical studies. They use models like magnetohydrodynamics, which is a type of fluid theory. They may also use kinetic theory to understand particle movements. These different approaches help map the invisible forces of space.

Space physics is closely linked to several other scientific fields. Plasma physics studies the most fundamental physics of these materials. It also looks at laboratory plasmas and fusion plasmas. Atmospheric physics and atmospheric chemistry investigate the upper layers of Earth's atmosphere. There is also astrophysical plasmas, which involves natural plasmas found beyond our Solar System. These connections allow scientists to see how small particles affect large systems. Understanding these links helps us predict how the Sun affects Earth.

Humans have observed space phenomena for thousands of years. Chinese sources describe aurora-like features from 2000 B.C.E. In the sixth century B.C.E., the Greek writer Xenophanes observed them too. He described them as moving accumulations of burning clouds. Around the eleventh century, Chinese sources invented the compass. This was an early sign of a global geomagnetic field. In the 16th century, William Gilbert wrote De Magnete. He explained that the Earth acts like a great magnet. This discovery helped explain why compass needles point north.

Many researchers helped build our modern understanding of magnetism. George Graham studied magnetic declination near London. He discovered irregular fluctuations called magnetic storms. Alexander Von Humboldt later gave these storms their name. Gauss and William Weber made very precise magnetic measurements. Their work suggested that external forces influence the Earth. They noticed these forces came from the Sun and sunspots. In 1747, Anders Celsius and Olof Peter Hiorter linked aurorae to magnetic disturbances. In 1860, Elias Loomis found aurorae occur in an oval around the magnetic pole.

New theories emerged as scientists studied particle movement. In the late 1870s, Henri Becquerel suggested sunspots release fast protons. He believed the Earth's magnetic field guides these to the poles. In the early 1900s, Kristian Birkeland built a terrella. This was a laboratory device that simulated Earth's magnetic field in a vacuum. He used a cathode ray tube to simulate the solar wind. This helped create a theory about how the solar wind interacts with Earth. These early experiments laid the groundwork for modern space science.

Modern space physics began with direct measurements in the 1950s. A team led by Van Allen launched rockets to 110 km. The Sputnik 2 and Explorer 1 satellites detected radiation belts. These are now known as the Van Allen belts. Explorer 10 later studied the boundary of Earth's magnetic field. Since then, many spacecraft have explored deeper into space. The WIND spacecraft and the Advanced Composition Explorer (ACE) study the solar wind. The Ulysses and IBEX missions look at different parts of space. The Parker Solar Probe and SOHO also study the Sun directly.