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Voyager 1 Reaches Interstellar Space
letxa2000 writes "CNN is reporting that Voyager 1, now some 8.4 billion miles (90 AUs) from the sun, has left the solar system and entered interstellar space by reaching the heliopause. However, whether the probe has reached the heliopause or is just coming close is the subject of two papers to be published in Thursday's Nature Magazine. The probe supposedly has enough nuclear fuel to last until 2020. Will it be able to find anything interesting outside the solar system in the next 17 years?"
Heliopause
From Wikipedia, the free encyclopedia.
The heliopause is the boundary where our Sun's solar wind is stopped by the interstellar medium.
The solar wind blows a "bubble" in the interstellar medium (the rareified hydrogen and helium gas that permeates the galaxy). The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause, and is often considered to be the outer "border" of the solar system.
The distance to the heliopause is not precisely known. It is probably much smaller on the side of the solar system facing the orbital motion through the galaxy. It may also vary depending on the current velocity of the solar wind and the local density of the interstellar medium. It is known to lie far outside the orbit of Pluto. The current mission of the Voyager 1 and 2 spacecraft is to find and study the heliopause.
An alternative definition is that the heliopause is the magnetopause between the solar system's magnetosphere and the galaxy's plasma currents.
Voyager uses a radioisotope thermoelectric generator for its power. This means that radioactive decay of its fuel creates heat, which is used to create power. That fuel's going to decay no matter what, so you either use the power or lose it.
I worked at JPL for the power group, so I can actually say something about this. All of the deep-space probes run on radiothermal generators. What this is basically a radioactive source surrounded by thermoelectric generators and alpha particle absorbers. Thus, both the thermal gradient established between the radioactive material and space (via heat pipes and radiators) and the alpha particles emitted by the radioactive material are able to generate power. There are two limitations on the lifetime of these generators - the lifetime of the radioactive isotope, and the durability of the thermoelectrics and alpha particle absorbers. I don't know too much about the particle absorbers, but I worked with the thermoelectrics, and there are durability runs of several years. However, Voyager is far older then any test we could ever do. My feeling in this is that barring high-heat conditions, the thermoelectrics should be able to last nearly indefinitely.
For many years I was a co-investigator on Voyager (actually, technically, I suppose that I still am; I have never been notified that the status ever changed). Anyway, the best guess when I was an active participant, throughout the 80s and half of the 90s, was more-or-less the year 2010. That was predicted to be the year at which the always-decreasing power output from the transmitter, the ever-increasing distance and the more-or-less constant sensitivity of the DSN (Deep Space Network) system combined to reduce the received signal to the point where it the bit rate at which information could be extracted was too low to be useful.
The general supposition was that funding would be eliminated before that date.