The New Horizons spacecraft has been making a lot of discoveries on its mission to explore space beyond our solar system but its most recent might also be it’s most significant. Now at a distance of four billion miles away from Earth, approximately, the spacecraft appears to have encountered with scientists believe is the furthest reaches of our yellow sun’s energy: a wall of hydrogen.
Finally reaches the distance the Voyager mission reached three decades ago, New Horizons will now be able to provide what the previous mission could not. NASA scientists wrote, in the journal Geophysical Research Letters, “Long-term observations made with the Alice instrument on the New Horizons spacecraft confirm measurements made 30 years earlier with the Voyager spacecraft. Both sets of data are best explained if the observed ultraviolet light is not only a result of the scattering of sunlight by hydrogen atoms within the solar system but includes a substantial contribution from a distant source…the signature of a ‘wall’ of hydrogen, formed near where the interstellar observations from New Horizons are planned about twice each year.”
According to study author Randy Gladstone, of the Southwest Research Institute, “We assume there’s something extra out there, some extra source of brightness. If we get a chance with New Horizons we can maybe image it.”
Now, light from the sun carries charged particles away from the core and these cause hydrogen particles floating in the space between the planets to release their own ultraviolet light. Of course, it is inevitable that the sun’s energy will eventually wane and this will create a boundary where this interstellar hydrogen will begin to pile up against the outward pressure coming from the energy of the solar wind.
The tricky thing, of course, is that the boundary of our solar system is not, exactly, something easy for us to define. For example, if we could manage to conceptualize where the influence of this solar wind ends, there is still a—theoretical—Oort cloud, which is basically an icy sphere of orbital comets that circle our Sun about one third the distance to our next stellar neighbor.