The Sun warms the Earth, making it habitable for humans and animals. But that’s not the only thing it does, and it affects a much wider area of space. The heliosphere, the area of space affected by the Sun, is a hundred times larger than the distance from the Sun to the Earth.
The Sun is a star that constantly emits a steady stream of plasma, high-energy ionized gas, called the solar wind. In addition to the constant solar wind, the Sun also occasionally releases bursts of plasma called coronal mass ejections and bursts of light and energy called flares, which can contribute to the aurora.
Plasma from the Sun expands in space along with the Sun’s magnetic field. Together, they form the heliosphere (the plasma, neutral particles, and dust that fill the space between stars and associated astrospheres) in the surrounding local interstellar medium. Heliophysicists like me want to understand the heliosphere and how it interacts with the interstellar medium.
The eight known planets in the solar system, the asteroid belt between Mars and Jupiter, and the Kuiper Belt, a belt of celestial bodies beyond Neptune that includes the planetoid Pluto, all lie within the heliosphere. The heliosphere is so large that objects orbiting the Kuiper Belt are closer to the Sun than to the nearest boundary of the heliosphere.
heliosphere protection
When distant stars explode, they blast large amounts of radiation into interstellar space in the form of high-energy particles known as cosmic rays. These cosmic rays can be dangerous to living organisms and damage electronic devices and spacecraft.
Earth’s atmosphere protects life on the planet from the effects of cosmic radiation, but even before that the heliosphere itself acts as a cosmic shield against most interstellar radiation.
In addition to cosmic radiation, neutral particles and dust are constantly flowing into the heliosphere from the local interstellar medium. These particles can affect the space around Earth and even change the way the solar wind reaches Earth.
Supernovae and the interstellar medium may also have influenced the origins of life and the evolution of humans on Earth. Some researchers speculate that millions of years ago the heliosphere came into contact with a cold, dense cloud of particles in the interstellar medium, causing the heliosphere to contract, exposing Earth to the local interstellar medium.
an unknown shape
But scientists don’t really know what the shape of the heliosphere is. The shapes of the patterns range from spherical to comet-like to croissant-shaped. These estimates range in size from hundreds to thousands of times the distance from the Sun to the Earth.
However, scientists defined the direction in which the Sun moves as the “nose” direction, and the opposite direction as the “tail” direction. The nose direction should have the shortest distance to the heliopause (the boundary between the heliosphere and the local interstellar medium).
Neither probe has been able to take a good look at the heliosphere from outside or properly sample the local interstellar medium. Doing so could give scientists more information about the shape of the heliosphere and its interaction with the local interstellar medium and the space environment beyond the heliosphere.
Crossing the heliopause with Voyager
In 1977, NASA launched the Voyager mission: Two spacecraft flew past Jupiter, Saturn, Uranus, and Neptune in the outer solar system. After observing these gas giants, scientists determined that the probes separately crossed the heliopause and into interstellar space in 2012 and 2018, respectively.
Although Voyager 1 and 2 are the only probes with the potential to cross the heliopause, they are well beyond their intended mission lifetime. As their devices slowly fail or lose power, they can no longer retrieve the necessary data.
This spacecraft was designed to study planets, not the interstellar medium. This means scientists don’t have the right tools to take all the measurements of the interstellar medium, or heliosphere, that they need.
This is where a potential interstellar probe mission could come into play. A probe designed to fly beyond the heliopause would help scientists understand the heliosphere by observing it from the outside.
An interstellar probe
Because the heliosphere is so large, it would take decades for a probe to reach the limit, even using gravitational support from a large planet like Jupiter.
The Voyager spacecraft will no longer be able to provide data from interstellar space long before an interstellar probe exits the heliosphere. And once the probe is launched, it will take about 50 years or more to reach the interstellar medium, depending on the orbit. This also means that the longer NASA waits to launch a probe, the less likely scientists will be able to operate in the outer heliosphere or local interstellar medium.
NASA is considering developing an interstellar probe. This probe will take measurements of plasma and magnetic fields in the interstellar medium and image the heliosphere from the outside. To prepare, NASA asked more than 1,000 scientists for input on a mission concept.
The initial report recommended that the probe proceed in an orbit approximately 45 degrees off the nose of the heliosphere. This orbit will follow part of Voyager’s path as it reaches some new regions of space. In this way, scientists can examine new regions and revisit some partially known regions of space.
This path would give the probe only a partially angled view of the heliosphere and would not be able to see the heliotail, the region about which scientists know the least.
In the Heliotail, scientists speculate that the plasma that forms the heliosphere mixes with the plasma that forms the interstellar medium. This occurs through a process called magnetic reconnection, which allows charged particles to flow from the local interstellar medium into the heliosphere. Just like neutral particles entering the nose, these particles affect the space environment within the heliosphere.
But in this case the particles have a charge and can interact with solar and planetary magnetic fields. While these interactions occur at the boundaries of the heliosphere, far from Earth, they affect the structure of the heliosphere’s interior.
In a new study published in the journal Frontiers in Astronomy and Space Sciences, my colleagues and I evaluated six potential launch directions, from nose to tail. We found that an orbit that crosses the side of the heliosphere towards the tail, rather than exiting close to the nose direction, will give the best perspective on the shape of the heliosphere.
An orbit in this direction would offer scientists a unique opportunity to study a completely new region of space within the heliosphere. As the probe emerges from the heliosphere into interstellar space, it will obtain an outside view of the heliosphere, giving scientists a more detailed idea of its shape; especially in the controversial tail area.
In the end, no matter which direction an interstellar probe sets off, the science it returns will be priceless and literally astronomical.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by: Sarah A. Spitzer, university of michigan.
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Sarah A. Spitzer works as a research assistant in the Department of Climate and Space Sciences and Engineering at the University of Michigan. She receives funding from the University of Michigan and grants from organizations such as NASA. Affiliated with the University of Michigan and the Interstellar Research Team.