SPACE — Interstellar space is the area between the stars, but is far from empty. Interstellar space contains vast quantities of neutrinos, charged particles, atoms, molecules, dark matter, and photons ranging from the highest energy radiation to the slow light of the cosmic microwave background (CMB).
According to the National Radio Astronomy Observatory (NRAO), the average distance between stars in the Milky Way galaxy is about 5 light years. Scientists collectively call everything in this interstellar space the “interstellar medium,” or ISM for short.
The following are facts about interstellar space:
1. The composition of the ISM was analyzed by scientists at the Infrared Processing and Analysis Center (IPAC) at Caltech. The ISM consists mostly of hydrogen (~90%) and helium (~8%) atoms, which are the two most common atoms in the universe that were created in the Big Bang.
In addition, there are also other trace elements and molecules that contribute no more than 2% of the ISM. These elements, heavier than hydrogen and helium, all come from the death of stars and have been blown into space.
2. Where is interstellar space? The definition of the boundary of interstellar space is the region where the sun’s magnetic bubble weakens and ends. The magnetic bubble known as the heliosphere is filled with plasma (ionized gas). The heliosphere is blown by the solar wind which pulls magnetic field lines outward from the sun.
Plasma in the ISM exerts inward pressure on the edge of the heliosphere with its own magnetic field and charged particles, producing complex and varied structures at the boundary. The solar wind begins to weaken from between 600–700 kilometers per hour as it encounters interstellar space and slows to around 100 km/hour.
The point at which this occurs is called the Termination Shock. Regions in the heliosphere beyond Termination Shock where the solar wind continues to slow down is called a heliosheath. The outer boundary of the heliosphere is called the heliopause. That interstellar space is at the heliopause where the solar wind stops and gives way to interstellar space, about 18 billion km from the sun.
3. Only two active space probes have successfully crossed the heliopause and entered interstellar space. The two spacecraft are Voyager 1 and 2 which are missions from NASA.
4. Launched in 1977, Voyager 1 and 2 first visited the outer planets before continuing their journey deeper into space. In 2005, Voyager 1 made the pass termination shock at a distance of 94 astronomical units from the sun.
5. NASA announced that Voyager 2 had tracked in August 2007 at a distance of about 83 astronomical units. Voyager 1 and Voyager 2 have different directions.
The fact that the two cross termination shock towards the heliosheath at different distances from the sun suggests that the heliosphere is not symmetrical around the solar system. This shape is influenced by the balance between the outward strength of the solar wind and the ISM pressure on the heliosphere, especially in the direction of the sun’s movement through space.
6. On August 25, 2012, NASA announced that Voyager 1 had successfully crossed the heliopause, becoming the first space probe to leave the influence of the sun and enter interstellar space. This event occurred at a distance of 121 astronomical units from the sun, located on the comet’s ‘Scattered Disk’ near the edge of our solar system.
7. NASA also revealed that Voyager 2 crossed the heliopause and entered interstellar space on November 5 2018, at a distance of 121 astronomical units.
2024-02-19 07:44:00
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