Don't worry about stocking up on sunscreen, but our solar system may be headed for a celestial version of global warming. A new analysis suggests that in about 100 years the sun could plunge into a hot cloud of interstellar gas. The change should have no impact on our planet, but it could boost the amount of deadly radiation in space, making missions more challenging for future astronauts.
The void beyond our atmosphere is anything but empty, with particles whizzing about in all directions. Energy from these particles can spike 14 billion or 15 billion kilometers away from the sun, the source of the stream of particles called the solar wind. That's what detectors aboard the Voyager 1 and Voyager 2 spacecraft discovered earlier this decade when they approached the termination shock, the place where the solar wind bumps into particles from interstellar space—a collision that creates a surge in radiation.
The Voyagers, whose cameras gave us some stunning close-up images of the four big outer planets and their moons in the 1980s, discovered a mystery about the termination shock: It is asymmetrical, with a flattened shape that suggests something is pushing on it unevenly. Determining the cause of that asymmetry has been part of the mission of the IBEX spacecraft, launched 2 years ago to collect, identify, and track particles flying in from the edges of the solar system.
Last year IBEX produced a mystery of its own, detecting what scientists are calling a ribbon of particles (see illustration) that congregates beyond the termination shock in interstellar space and runs between the current locations of the Voyagers. So far, no one has been able to explain the source of the feature. At first the IBEX team thought the ribbon stemmed from some type of interaction between the solar wind and the particles in the interstellar medium—also known as the local interstellar cloud (LIC).
Now an international group has come up with a different idea. In the June issue of The Astrophysical Journal Letters, the researchers propose that the ribbon could be generated by the collision of the LIC with something else outside the heliosphere: a million-degree remnant of an ancient supernova. So the ribbon could be the result of collisions between neutral hydrogen atoms whizzing in the LIC and high-energy protons zipping through the supernova cloud, which they've named the local bubble (LB).
If the analysis is correct, the sun and the rest of the solar system are headed straight for the LB. "The definitive source of the ribbon really isn't known yet," says co-author and IBEX principal investigator David McComas of the Southwest Research Institute in San Antonio, Texas. Nevertheless, he says, "understanding the IBEX results is critical for understanding the big picture of our solar system's past and future."
The ribbon "surprised everyone" on the IBEX team, says mission scientist Eric Christian of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Christian, who was not involved in this paper, says "understanding the data will tell us a lot about the part of the galaxy right outside the solar system."