StarDate: Distant Borders

FROM THE UNIVERSITY OF TEXAS McDONALD OBSERVATORY, AS HEARD ON KCBS RADIO WEEKDAYS @ 9:52 A.M., 7:35 P.M. & 2:52 A.M

STARDATE 5/19/14:  Our solar system has a lot of borders. One is the orbit of Neptune, which marks the edge of the realm of the planets. Another is the Oort Cloud, a shell of icy leftovers from the birth of the planets that marks the edge of the Sun's gravitational grip. And yet another is the heliopause, which marks the edge of the Sun's magnetic influence.

Voyager 1 crossed that boundary a couple of years ago — 11 billion miles from the Sun.

The Sun generates a strong magnetic field, forming a "bubble" in space. The bubble is filled with particles of the solar wind — electrically charged particles from the Sun itself.

Voyager had been flirting with the edge of this bubble for years. In 2004, it saw a sharp jump in the level of cosmic rays, which are screened out by the Sun's magnetic field. Later, it saw a sharp drop in the number of particles from the Sun. And just last year, it detected radio waves coming from the space around it. Those waves were generated as a burst of particles from the Sun ran into the particles in interstellar space. They confirmed that Voyager had left the realm of the Sun's magnetic dominance.

It's not completely away from the Sun's influence, though. Instead, it's in a transition zone — one that's clearly more outside than inside the Sun's magnetic influence.

We'll talk about another solar system boundary tomorrow.

Script by Damond Benningfield Copyright ©2014 The University of Texas McDonald Observatory