How Did That Dent Get There?

Second digression of the day, but this time relate to astrophysics, is the news that the two Voyager spacecraft, launched in 1977 mind you, have both now passed through the heliopause. This is the somewhat fluid boundary between the edge of our solar system as defined by the meeting of the solar wind with the interstellar medium in our neighborhood of the Milky Way.

Think of it like this...

The sun generates energy in the form of radiation that blasts out into space in all directions (like an expanding sphere or bubble with the sun, and with it the solar system, at its center). But our solar system is surrounded by other stars and gas and dust in our galaxy. So the outward expansion of the bubble created by our sun burning is balanced at somepoint by the pressure from not only all the other bubbles around stars in our neighborhood, but also from the existence of gas and dust between the stars in our galaxy (the aforementioned interstellar medium). The balancing point between these two forces is termed the heliopause, helio for sun and pause as in break.

The scientific result of this event is that the two Voyager spacecraft left our solar system, crossing the heliopause at two different points of the bubble. They have since reported back to us and it turns out that our bubble is dented! Have a read if you want to know more:

Scientists find the dent in our solar system
http://www.msnbc.msn.com/id/22186054/

(photo credit: Opher et al. 2006, 2006AIPC..858...45O)