Energetic events in the galaxy, like a supernova, can accelerate particles near to the speed of light. These particles rocket out in all directions into space including the solar system. These particles can create havoc if they make it to the Earth. This is prevented because of the Earth’s magnetic field & atmosphere and thereby makes Earth habitable. But what about Space travellers & astronauts? How are they safe in outer space? The answer is heliosphere. Our solar system which consists of the Sun and its planets are encased in a bubble-like structure called the heliosphere. They act as a protective shield.
What is heliosphere?
A thin stream of electrically charged gas continuously blows outward from the sun called the Solar wind. The solar wind goes out in all directions & travels at an average speed of 300-700 km per second. The strength of the solar wind dies down as it spreads over long distances in space. As it approaches the strength of the interstellar wind coming from the rest of the Milky Way, its motion slows down abruptly. This point is called the termination shock. The interstellar wind begins to be felt at this point.
The extent to which the solar winds travels defines the final frontier of the influence of the Sun and is called the Heliosphere. This region is filled with the solar magnetic field and the protons & electrons of the solar wind. It acts as a giant shield, which protects the planets from the harmful effects of interstellar wind & galactic cosmic radiations.
The Heliosheath is the outer region of the heliosphere and acts as a transitional region beyond the termination shock. The wind becomes denser and hotter at this point. Here the solar wind piles up and presses outward against the wind approaching from interstellar space. At some point, the solar wind and the interstellar wind balance out with each other and it marks the boundary of heliosphere called the Heliopause.
The Sun travels in the galactic medium just like a ship in the ocean. Like the ocean water being pushed aside by the bow of a great ship, the Sun with its solar wind does the same in the Galactic medium. This is called the Bow Shock and it marks the final extension to the solar winds. The outside heliosphere is the interstellar medium which consists of ionized gas and magnetic field that fills the space between stellar systems in our galaxy.
The only way to determine how far away these bow shocks are and to thereby calculate the full size of the solar system is to go this far and report back the distance travelled. This is exactly what the two Voyager space crafts (Voyager 1& Voyager 2) have done. They directly measured this region, leaving us with just two points of data to determine Heliosphere’s actual shape.
SHAPE OF OUR SHIELD
The shape of the heliosphere is a long-debated topic. Traditionally, Scientists have thought of the heliosphere as a comet shape, with a round leading edge, called the nose, and a long tail trailing behind. According to the latest research developments, the shape of the heliosphere is deflated croissant.
The heliosphere’s shape is difficult to measure from within the Solar System. Therefore we study the interstellar boundary by capturing and observing the particles flying towards the Earth. These particles include those that were already present in the Solar System, along with galactic cosmic rays, which were deflected back towards the Earth when they travelled out towards the heliosphere. These particles are called as Energetic neutral atoms. Since they were created by the interaction with interstellar medium, they act as a useful substitute for studying the Solar system’s shape. To further make sense of this complex data, scientists use computer models to turn this data into a prediction of the heliosphere’s characteristics.
Furthermore, the New Horizons mission has provided measurements of pick-up ions. They are particles that are ionized in space & move along with the Solar wind. The pick-up ions are much hotter than the solar wind particles. The research was done by separating these 2 components of the solar wind & modelling them to obtain the 3D shape. The solar magnetic field acted as a dominant force in shaping heliosphere. A deflated croissant shape, with 2 jets curling away from the central bulging part of the heliosphere was observed.
Heliosphere absorbs about three-quarters of galactic cosmic rays which can create havoc if they make their way into the solar system. The effect of these rays can harm both electronics and human cells. Thus heliosphere acts as the main defence mechanism against galactic cosmic rays. Therefore understanding the shape & how it influences the rate of harmful rays pelting the solar system is a key consideration topic in space exploration.
Reference: https://www.nasa.gov
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