We now have a 3 dimensional map of 1 of the boundaries of the solar-system .
For the 1st time, astronomers are able to determine the form or shape of the heliosphere, the boundary that marks end of influence of our star solar radiation . This discovery could help us better understand the environment of the solar-system , and the way it interacts with interstellar space .
“Physics models have theorized this boundary for years,” said astronomer Dan Reisenfeld of Los Alamos National Laboratory. “But this is often the 1st time we’ve actually been ready to measure it and make a 3-dimensional map of it.”
Actually, we’ve had encounters with edge of heliosphere, a boundary referred to as the heliopause. Both Voyager probes, launched over 40 years ago, have encountered it and traveled past into interstellar space.
The heliopause may be a fascinating place. The Sun is consistently gusting a stream of charged particles – a supersonic wind of ionized plasma – out into space. Eventually, the solar-wind loses strength over distance, in order that it’s not sufficient to push against the pressure of the interstellar region . The purpose at which that happens is that the heliopause.
Interstellar space doesn’t have an excellent deal of material’ in it, but there’s enough that it does have a low-density of atoms, and a cosmic wind blowing between stars .
The shape of the boundary between the 2 has been a matter of some debate. Is it a rounded bubble? A comet-shaped structure, with a tail streaming behind solar-system because it moves round the Milky Way galaxy? Or something a bit more sort of a strange croissant?
We can’t exactly just nip over and take a survey – Voyagers 1 & 2 of were 121 & 119 astronomical units from the Sun respectively once they encountered the heliopause, and had taken decades to urge there.
But that does not mean we cannot take a glance . Reisenfeld and his team used data from NASA’s Earth-orbiting Interstellar Boundary Explorer (IBEX) satellite, an observatory that measures particles flung from the heliosheath, the very outer region of the heliosphere.
Some of those particles are what scientists call energetic neutral atoms, or ENAs. These are generated by collisions between particles from the solar-wind’ & particles from the interstellar wind, and therefore the strength of their signal depends on the strength of the solar-wind at the time of the collision – a bit like the wind on Earth, the solar-wind doesn’t always blow at an equivalent intensity.
Decoding this signal to map the heliopause may be a bit just like the way a bat uses sonar to map its physical surroundings. The strength of the signal and therefore the delay between sending and receiving can reveal shape & distance of obstacles.
“The solar radiation ‘signal‘ sent out by the Sun varies in strength, forming a specific pattern,” explained Reisenfeld.
“IBEX will see that very same pattern within the returning ENA signal, 2-6 years later, depending on ENA energy and therefore the direction IBEX is rummaging through the heliosphere. this time’ difference is how we found distance to ENA-source region in particular direction.”
The team used data from a full solar cycle, from 2009-2019. The map thus generated remains a small little approx., but it’s already revealing interesting things about the heliopause.
We now know, for instance , that the shape of it (animated above) appears to be a bit like comet, with a tail that’s a minimum of 350 astronomical units long (that’s the present limit of IBEX’s reach), although the length of the tail is impossible to measure . It might be short & stumpy. On the opposite hand, the minimum radial distance to the ‘nose’ of the heliopause seems to be around 110-120 astronomical units, according to the Voyager crossings.
At high latitudes, the heliopause extends to 150-175 astronomical units. This shows that shape is more bullet-like, not in the least according to the weird croissant model.
The IBEX mission still going, and can continue until a minimum of 2025. The Interstellar Mapping and Acceleration Probe is thanks to commence in 2025, learning where IBEX leaves off.
The team hopes that both these missions will provide more data to assist refine the heliopause’s shape.
The research has been published in The Astrophysical Journal Supplement Series.