Interstellar space is the space between stars, but not all space in space is interstellar space. If humans are ever to interstellar travel, they need to understand solar weather, interstellar weather, and heliopause.
In its most concise description, the edge of the heliopause is where our solar system ends, and interstellar space begins. The heliopause contains the climate of our solar system influenced by our Sun’s solar wind.
The edge of the heliopause is where our Sun’s solar wind is not strong enough to penetrate interstellar wind. The turbulent border is where our Sun’s solar winds and magnetic forces meet interstellar winds and repel each other with speeds of over 50,000 miles an hour(80,467 km/h). It would be the cosmic equivalent of Cape Agulhas and Cape Point in South Africa, where two oceans meet.
The heliopause edge can be considered a bit like two great ocean currents clashing, and it is not in a fixed location. The heliosphere boundary is indicated by clouds of interstellar gas surrounding our solar system. in 2015, NASA calculated that the heliosphere edge was over 12,161,300,000 miles (19,571,715,187 km) away from Earth.
When our Sun’s solar winds can no longer move forward and get forced back by interstellar winds, they move back towards and around our Sun, causing interesting astrophysical phenomena.
How was heliopause discovered?
As soon as we understood that our Sun was only one of the billions of stars, the boundary of our solar system became more relevant and monitoring the edge of the heliopause more critical. Justyna Sokol (scientist at SwRI) expects other stars to have their astrosphere just like our Sun has its heliosphere. The difference for our scientists is we can study our Sun’s heliosphere from the inside, which will begin to help them understand the rest of the universe.
Early probes such as Pioneer 10 and 11 launched in 1972 began providing evidence of the heliopause in data broadcast back to Earth in 2003.
In 2012, scientists got the most solid evidence for the heliopause when Voyager 1 detected a sudden drop in solar wind particles and a corresponding spike in galactic cosmic-ray particles, indicating that it had crossed the boundary into interstellar space. The evidence from Voyager 1 became more conclusive in 2018 when Voyager 2, on a different trajectory, detected a spike in galactic-ray particles and, simultaneously, a drop in solar wind particles, proving that the phenomenon wasn’t local to Voyager.
Astronomers and planners of interstellar travel will, in the future, use the location of the heliopause as a vital marker, much like the boundaries of a country map; they will use it like how sailors navigate oceans.
Right now, our heliosphere extends far beyond the orbit of Pluto. It protects the solar system from the interstellar (or galactic) wind, in the same sense that the Earth’s magnetic field protects it from the solar wind.
The heliosphere protects our planet
Without the heliosphere shield on cosmic rays, human missions would be limited in their duration. Without its protection, life on Earth would certainly be different or not evolve life at all. These are the views of Arik Posner, a heliophysicist at NASA Headquarters. He thinks it would even be difficult for humans to reach Mars without it.
Understanding the heliosphere and the heliopause interaction with cosmic rays is a challenge for scientists.
The medium part of the heliosphere is a part that scientists call the Termination Shock. Solarwinds heat up as they slow down to subsonic speeds and heat up because of the pressure from interstellar winds.
The particles are highly charged and become compressed together to form the heliosheath. The heliosheath is a region where the solar winds and the interstellar winds interact but where the influence of the solar winds is still more substantial than that of the interstellar winds. The heliosheath diminishes further away from the Sun when interstellar wind overpowers the solar wind.
A new frontier of space that needs explanations
The heliopause is mysterious to scientists because its extent is not fully known, and the clash of solar weather produces radio frequencies that otherwise couldn’t be explained.
How far the heliopause extends is not an easy question to answer, as only Voyager 1 and Voyager 2 have passed it. It’s not possible to measure the extent of the heliopause with just two probes. However, NASA has said it is making progress in mapping the heliopause due to NASA’s Interstellar Boundary Explorer (IBEX) mission (launched in 2008).
According to the data sent back by Voyager probes in 1993 (which relates to data gathered from the heliopause in May 1992), scientists believe the violent interaction between intense solar winds produces strong, low-frequency radio waves. These radio waves, in their view, are evidence of a definable boundary with interstellar space. They do not have any other explanation for what has caused the radio waves. They can only assume the heliopause is driving them, as they cannot observe any different structure causing them. Dr. Don Gurnett describes the radio emissions from the heliopause as “probably the most powerful radio source in our solar system,” Scientists have seen an increasing frequency of these radio emissions.
Feature image credit: Heliopause by NASA/Goddard Space Flight Center/CI Lab