Heliophysics Big Idea 2.2

What should learners know about this topic at each level?

Introductory: Interstellar space is literally the space between the stars. It contains gas and dust at very low density called the interstellar medium. It can also be thought of as the region between our Sun’s heliosphere and the heliospheres of other stars, which are called astrospheres.

Intermediate: Our heliosphere is a vast bubble of plasma – a gas of charged particles – that spews out of the Sun. This outflow is known as the solar wind. The bubble surrounds the Sun and stretches beyond the planets. Both Voyager spacecraft had to travel more than 11 billion miles (17 billion kilometers) from the Sun in order to cross the edge of the heliosphere. This bubble is moving through interstellar space as the Sun orbits the center of the Milky Way galaxy. As our heliosphere plows through space, it creates a bow wave, like the wave formed by the bow of a ship.

Advanced: The interstellar medium near our sun is actually a low-density void created by a supernova explosion several million years ago. The medium is an ionized hydrogen gas at a density of about 100000 ions per cubic meter. There are also interstellar clouds with slightly higher densities filling this void. Our sun is currently passing through one of these clouds known as te Local Fluff in the general direction of the bright star Vega. Our heliosphere takes on a comet like appearance as it plows through this Local Fluff gas.

What should learners know about this topic at each level?

Introductory: Every magnet produces an invisible volume of influence around itself in space. When things made of metal or other magnets come close to this region of space, they feel a pull or a push from the magnet. Scientists call these invisible influences fields. You can make magnetic fields visible to the eye by using iron chips sprinkled on a piece of paper with a magnet underneath. Did you know that the Earth, as well as some other planets, has a magnetic field? There are even magnetic fields on the Sun!

Intermediate: Magnetic fields are regions around a magnetic material or a moving electric charge within which the force of magnetism acts. Some materials such as iron are strongly attracted by magnets while other materials such as copper are not attracted. Our sun is composed of an electrically-conducting plasma in which portions of the plasma are in rapid movement. Like electrical currents flowing in a wire, the solar plasma creates magnetic fields.

Advanced: Gravity always points in the direction of the matter producing it. On Earth’s surface, this direction is towards the center of Earth. Magnetism depends on your location with respect to where the currents are located, and so the magnetic field has two poles called a North and South polarity. Depending on where you are located, the strength and direction of the field will vary. Magnetic fields store energy. To release it in a process called magnetic reconnection, opposing magnetic polarities have to be pushed into contact and compressed. This causes the magnetic field strength to increase, which causes currents to flow that then dissipate the magnetic energy as thermal and kinetic energy. If the magnetic fields are pushed together in a vacuum, however, no energy will be released since no intermediary plasma is present to form the necessary currents.

What should learners know about this topic at each level?

Introductory: Plasma is the most common, easily observable, state of matter in the universe. All stars, including our Sun, are made of plasma.

Intermediate: Plasma is a gas consisting of electrically charged particles, a state of matter distinct from solids, liquids and gases. Though rare on Earth, plasma makes up over 99% of the observable (i.e., not dark) matter in the universe, including every star, including our Sun, and much of the material between them. On Earth, plasma is found in fluorescent lights, torches used for metalworking, and lightning strikes. Plasma forms when the atoms in a gas become ionized, meaning electrons separate from the atom and move around independently. This makes plasmas electrically charged and they can interact with external electric and magnetic fields. They can also create their own electric and magnetic fields. Plasmas also undergo an explosive process called magnetic reconnection. Magnetic reconnection is a rapid transfer of magnetic energy into motion that powers solar flares and coronal mass ejections.

Advanced: Plasma processes accelerate and transport particles throughout the Sun and the solar system. The existence of charged particles causes plasma to generate, and be affected by, magnetic fields. This can cause extremely complex dynamics. Under certain circumstances, plasmas cannot cross magnetic field lines, though they can slide along them like beads on an elastic string. As a result, a strong plasma can bend weak magnetic fields, and strong magnetic fields can hold back weak plasmas.

What should learners know about this topic at each level?

Introductory: The solar wind is a gusty stream of material that flows from the Sun in all directions, all the time, carrying the Sun’s magnetic field out into space.

Intermediate: While it is much less dense than wind on Earth, solar wind is much faster, typically blowing at speeds of one to two million miles per hour. The solar wind is made of charged particles — electrons and ionized atoms — that interact with each other and the Sun’s magnetic field. The extent of the solar wind creates the heliosphere, the Sun’s region of influence within interstellar space.

Advanced: The origin of the solar wind seems to be in the corona of the sun where magnetic fields are ‘reconnecting’ and depositing energy into the coronal plasma. This plasma becomes hot enough to escape the gravitational influence of the Sun and flow out into interplanetary space.

What should learners know about this topic at each level?

Introductory: Space weather refers to conditions in space produced by the Sun’s activity. Prediction of space weather helps to protect human in space, technology, communications, and power systems on Earth. Solar flares are the most powerful explosions in the solar system. The energetic particles accelerated by flares travel nearly at the speed of light, and can travel the 93 million miles between the Sun and Earth in less than 20 minutes.

Intermediate: A geomagnetic storm is a major disturbance of Earth’s magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind and coronal mass ejections into the space environment surrounding Earth. Space weather is the interaction of matter and energy from the Sun with magnetic fields such as Earth’s. Radio blackouts occur when the strong, sudden burst of x-rays from a solar flare hits Earth’s atmosphere, disturbing high and low frequency waves in the ionosphere. The loss of low frequency radio communication causes GPS measurements to be off by feet to miles, and can also affect the applications that govern satellite positioning.

Advanced: Variable features of the Sun due to strong, dynamic magnetic fields include sunspots, solar flares, prominences, and coronal mass ejections (CMEs). These processes occur on a variety of time scales, from minutes to years. Solar flares are energetic bursts of light and particles triggered by the release of magnetic energy on the Sun. Geomagnetic storms result from variations in the solar wind that produces major changes in the currents, plasmas, and fields in Earth’s magnetosphere. The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several to many hours) periods of high-speed solar wind, and most importantly, a southward directed solar wind magnetic field (opposite the direction of Earth’s field) at the dayside of the magnetosphere. This condition is effective for transferring energy from the solar wind into Earth’s magnetosphere.