Astronomers have, for the first time, determined the shape of the heliosphere, the boundary marking the end of the solar wind for our star, in a discovery that could help better understand the environment of the solar system.
“Physical models have theorized these limits for years. But this is the first time we’ve actually been able to measure and map them in 3D,” said astronomer Dan Reisenfeld of Los Alamos National Laboratory.
The sun is constantly pushing a stream of charged particles – supersonic winds of ionized plasma – into space. Eventually, the solar wind loses its power over the distance, so that it is no longer sufficient to drive the pressure of interstellar space. The point at which this occurs is called the heliosphere.
Interstellar space does not contain a great deal of material, but there is enough, because it has a low density of atoms, and cosmic winds blow between the stars.
(Los Alamos National Laboratory)
Reisenfeld and his team used data from NASA’s Earth-orbiting Interstellar Boundary Explorer (IBEX) satellite, an observatory that measures particles falling from the heliosphere, the very outer region of the heliosphere. And some of these particles are what scientists call active neutral atoms, or ENAs. It is generated by collisions between particles from the solar wind and particles from the interstellar wind, and its signal strength depends on the strength of the solar wind at the time of the collision.
“The solar wind signal sent by the Sun varies in strength and forms a unique pattern. IBEX will see the same pattern in the returning ENA signal, two to six years later, depending on the energy of the ENA and the direction that IBEX is looking at through the heliosphere. That time difference is How did we find the distance to the ENA source region in a specific direction.”
The team used data from an entire solar cycle, from 2009 to 2019. The map created in this way is a bit rough, but it does reveal interesting things about the heliosphere.
We now know, for example, that it has a slightly comet-like shape, with a tail of at least 350 AU (the current limit of the IBEX range).
The IBEX mission will continue until at least 2025. The Interstellar Mapping and Acceleration Probe is scheduled to begin in 2025, when IBEX is discontinued.
The team hopes that the two missions will provide more data to help improve the shape of the heliosphere.
The search was published in strophysical Journal Supplement Series.
Source: Science Alert