Image Credit: NASA/A predecessor to IMAP, IBEX is studying how our heliosphereThe bubble-like region surrounding the solar system inflated by the solar wind, shielding the solar system from interstellar radiation. interacts with interstellar space. IBEX created the first maps showing the interactions at that border, and how they change over timeA measure of the flow of events../Adler Planetarium
Billions of miles into space, an invisible boundary is formed around our solar system by the interaction between the continual flow of energetic particlesCharged particles (electrons, protons, and ions) that are moving very fast (high energy). If the particles originate at the Sun, they are known as Solar Energetic particles (SEPs). from the Sun, the solar windA stream of charged particles, mostly protons and electrons, that escapes into the Sun's outer atmosphere at high speeds and streams out into the solar system in all directions., and the material found between the stars - the interstellar medium (ISM). The solar wind streams outward from the Sun into space and carves out a protective bubble around our entire solar system in the ISM. We call this protective bubble-region the heliosphere. It provides a shield against the harsh radiationUsually refers to electromagnetic waves, such as light, radio, infrared, X-rays, ultraviolet; also sometimes used to refer to atomic particles of high energy, such as electrons (beta-radiation), helium nuclei (alpha-radiation), and so on. present in the galaxyA huge collection of millions to trillions of stars and their planetary systems held together by gravity, and the gas, plasma, and dust that are also gravitationally held to the galaxy. The galaxy our solar system is found in is called the Milky Way., creating and maintaining a habitable solar system for us. Understanding the physics of this boundary and its dynamic changes over time can help us comprehend how our solar system can support life as we know it as well as informing us in the search for life beyond the solar system.
The heliosphere is a definable, measurable region in space with a distinct geography of its own. The inner heliosphere is created as the solar wind blows through our solar system in all directions. It slows as it approaches the interstellar medium and begins to interact with it in a region called the termination shockThe boundary marking one of the outer limits of the Sun's influence. At the termination shock, solar wind particles slow down as they begin to press into the particles forming the interstellar medium. The solar wind particles then continue to travel outward at a slower rate of speed. This is similar to cars speeding along a highway which then slow down as they encounter many more cars involved in a traffic jam. The jammed cars continue to move outward, although much more slowly., forming an inner edge of the solar boundary. The outermost edge, or heliopauseThe outermost boundary of the heliopause formed where the Sun's solar wind and the interstellar medium, and their associated magnetic fields, meet., is formed where the solar wind no longer reaches into the ISM. The inner edge of this boundary is located approximately an average of 9 billion miles (14 billion km) away from Earth, or around 100 times the distance between the Earth and the Sun. However, this distance from the Sun is not uniform and the average distance varies with the activity level of the Sun (the solar cycleThe approximately 11-year quasi-periodic variation in frequency or number of sunspots, coronal mass ejections, solar flares, and other solar activity caused by internal restructuring of the solar magnetic field that results in a flipping of the solar magnetic poles every solar maximum.). The solar wind is also not evenly distributed, and coronal massA measure of an object's resistance to change in its motion (inertial mass); a measure of the strength of gravitational force an object can produce (gravitational mass). ejections (solar storms) are directional, and these create a rippled effect in the boundary encompassing our solar system. Parts of the outer edge of the solar system boundary, the heliopause, are 11 billion miles (18 billion kilometers) from Earth, while in other directions the heliopause is much further. Fundamental scientific questions await answers about the essential physical processes occurring in this area and its influence on our solar system’s evolving space environment.
The IMAP Mission
Image Credit: NASA/Princeton/Patrick McPike
NASA's Interstellar Mapping and Acceleration Probe (IMAP)'s groundbreaking mission takes up these questions by studying the heliosphere boundary from afar. IMAP orbits the Sun at a location 1 million miles closer towards the Sun than the Earth, called Lagrange Point 1 (L1). As it travels this orbital path, IMAP is free from any magnetic interferenceAny spacecraft generates a magnetic field, and that magnetic field changes with time. This field combines with (interferes with) the interplanetary magnetic field that a magnetometer is trying to observe. Luckily the spacecraft magnetic field gets smaller as you get farther from the main spacecraft. Putting a magnetometer out on a boom reduces the interference and so the magnetometer can get a more accurate measurement of the interplanetary magnetic field. from the planets. IMAP spins, once every 15 seconds, allowing the comprehensive suite of 10 sensor instruments to scan every part of the heliosphere. IMAP collects and maps near real-time measurements of the solar wind’s high-energy particles and magnetic fields in interplanetary spaceThe area of space found surrounding and between planets of a star system., as well as collect, count, measure and map energetic neutral atoms returning from the interactive region of the heliopause towards the Sun. The unprecedented new data is utilized to create a comprehensive map of the Sun's influence, an instrumental piece in resolving the fundamental physical processes that control our solar system’s evolving space environment and advance the understanding of:
The compositionThe specific components or “ingredients” that make up a substance or type of matter. and propertiesA characteristic of a substance that can be observed or measured without changing the identity of the substance. of the local interstellar medium.
How magnetic fields interact from the Sun through the local interstellar medium.
How the solar wind and interstellar medium interact through the boundaries of our heliosphere.
How particles are accelerated to high energies throughout the solar system.
Mission Heritage: Building on the Past
The IMAP mission’s scientific goals and objectives build upon a heritage of findings from past missions that have expanded our knowledge of the heliosphere and its dynamics.
Starting in the late 1970s and 1980s, NASA's Voyager spacecraft expanded our knowledge of the outer Solar System. Voyager 1 launched September 5, 1977, and Voyager 2 launched August 20, 1977. After making designated planetary observations, both spacecraft continued outward into space in different directions. Voyager were only supposed to last a few years, but they have continued to operate for almost 50 years, well past their designed lifetimes.
Voyager 1 reached the termination shock on December 16, 2004, at a distance of 8.4 billion miles (14.1 billion kilometers) from the Sun. Voyager 2 reached the termination shock on August 30, 2007, at a distance of 7.8 billion miles (12.6 billion kilometers) from the Sun. This discrepancy in distances and dates is due to the facts that Voyager 1 is traveling faster than Voyager 2 and that the distance of the termination shock from the Sun varies.
Today, the Voyager spacecraft have left the solar system’s boundary region, but they can only sample the conditions at their specific locations – not the entire global heliosphere shielding our solar neighborhood. Since 2009, NASA's Interstellar Boundary Explorer (IBEX) mission has imaged the entire sky, giving us a complete global view of the boundary. The data from Voyager has been combined with IBEX’s data, allowing scientists to create a more complete model of the boundary of our Solar System. With IBEX, critical questions have been raised for IMAP to answer about the nature, properties, and dynamic conditions of our heliosphere and local interstellar medium. This also includes determining the physical origin of the concentrations of energetic neutral atoms (ENA’s) forming “the Ribbon” that IBEX has revealed to wrap across the nose of the heliosphere.
Building off Voyager’s and IBEX’s successful measurements, IMAP provides unparalleled new observations that allow us to connect the Sun’s activity to the observed dynamics in our solar system’s boundaries.