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Defining ‘how big is the Solar System’ is the fodder of an ongoing debate among scientists. As humans, we like definitive answers and sure quantitative numbers to bandy about when we talk about anything. That is just impossible with the solar system. The main restrictions lie within our inability to ‘see’ the distances necessary to find the answers that we seek. According to NASA and other leading authorities on the subject, there are multiple theories. In the spirit of free knowledge, here are a few of the dominant theories on ‘how big is the Solar System’.
One of the more widely held theories is that the Solar System exists to the edge of the Sun’s gravitational influence. That is believed to be about 125,000AU or two light years. Earth is 1 AU from the Sun to give you an idea of the distances being considered. Beyond that all objects are more strongly influenced by other stars. The problems with this theory is that science is unable to detect objects at that distance and can not determine beyond a reasonable doubt how they are influenced or by what.
Another dominant theory is that the Solar System extends to the edge of the heliosphere. The heliosphere is the region where the solar wind interacts with the interstellar medium and is slowed down. The heliopause is where interstellar medium stops the solar wind from our Sun and the solar winds of other stars holds sway. This is thought to happen at about 95 AU, but, again, this is only a theory since o spacecraft has encountered this barrier. Voyager 1 is currently on a trajectory that will take it out of our Solar System. By 2014 Voyager 1 should hit the heliopause. Hopefully, its instruments will still be functioning and able to return data as this happens.
NASA’s twin STEREO spacecraft been able to map the region where the hot solar wind meets up with the cold interstellar medium. Not visually, but through neutral, or uncharged, atoms. These atoms help to explain some findings by Voyager 2 as it passed beyond the Solar System in 2007. Scientist hope to use this data to produce a map of the helioshpere.
Although, it is impossible to visualize ‘how big is the Solar System’ with current optical technology, science is making strides by using neutral atoms. The two Voyager spacecraft are also contributing a great deal of information to be analyzed. The NASA probe IBEX is weighing in on the fray as well. With all of the information coming in, a more definitive answer should be on the way.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.