The Kepler mission launched in 2009, and this week it has grabbed some impressive headlines. Meanwhile, Voyager 1 and 2 launched more than 30 years prior to Kepler, and they continue to make news. This week, several sessions are devoted to the aging spacecraft at the annual American Geophysical Union (AGU) meeting, and last week, a paper in Science covered some of its newest discoveries.
The two Voyagers are almost in interstellar space, at the edge of our Solar System. In a sense, they are the Star Trek Enterprise of satellites, “boldy going where no one has gone before.” Voyager 1 lies about 11 billion miles from the Sun; Voyager 2, a bit behind at 9 billion miles from the Sun. At these distances, on the boundary of the Sun’s influence, the two spacecraft provide amazing new discoveries.
The press conference at AGU on Monday described the kind of twilight zone Voyager 1 currently inhabits. The spacecraft has sped outside the heliosphere, a “bubble” of gas blow into space by our Sun. But Voyager 1 has not yet reached interstellar space. It’s detecting small amounts of both solar wind and interstellar wind and appears to be in a “stagnation region,” described in a press release as “a kind of cosmic purgatory.”
(More on the interstellar winds: supernovae explosions cause these winds and they tend to come from a direction near the center of our Milky Way galaxy.)
The two spacecraft travel one billion miles every three years, and researchers are unsure when they will reach interstellar space. Ed Stone, the Voyager Project Scientist from Caltech, estimates it could take anywhere from a few months to a few years. We can only hope that at least one of the spacecraft reaches interstellar space before they are both powered off. Power for all instruments exists through 2020, with both spacecrafts shut down by 2025.
The press conference participants (and many in the audience) gushed about the productivity of the two middle-aged spacecraft.
Lyman-alpha emissions are produced when ultraviolet light hits neutral hydrogen atoms, splitting them into protons and electrons. When the two recombine, they can form an atom in an excited state that emits ultraviolet light at a characteristic wavelength, known as the Lyman-alpha band.
Because this high energy occurs in star-forming regions, scientists believe that these detections suggest the birth of stars in both our galaxy and beyond. The Lyman-alpha emissions from sources other than our Sun are virtually undetectable from within the solar system, so these detections come as exciting news for astronomers.