Popcorn Supernovas

Like sediments in the Pacific Ocean, gas in the Local Bubble contains supernova-produced iron. "Iron atoms in the bubble have lost many of their electrons - knocked loose by collisions within the hot gas." CHIPS's spectrometer is able to detect spectral lines from iron atoms missing 8, 9, 10 and 11 electrons, respectively. By comparing the intensity of those four spectra lines, researchers can map the temperature and density of gas in the bubble.

"If we find a hot spot," says Hurwitz, "that might be the location of the most recent supernova." The spectra also tells researchers how fast the gas is cooling and thus how old different parts of the bubble might be. A fast-cooling knot of gas which is still hot must be pretty young, for example.

Exploring the internal geography of the bubble is important because what lies inside could affect our planet's future.

During the past few million years, wispy filaments of interstellar gas have drifted into the Local Bubble. Our solar system is immersed in one of those filaments - the "local fluff," a relatively cool (7000 K) cloud containing 0.1 atoms per cubic centimeter. By galactic standards, the local fluff is not very substantial. It has little effect on Earth because the solar wind and the Sun's magnetic field are able to hold the wispy cloud at bay.

more An artist's concept of the local fluff

There are, however, denser clouds out there. The Sco-Cen complex, for instance, is sending a stream of interstellar "cloudlets" in our direction. "Some of those cloudlets might be hundreds of times denser than the local fluff," says Priscilla Frisch, an astrophysicist at the University of Chicago who studies the local interstellar medium. "If we ran into one, it would compress the Sun's magnetic field and allow more cosmic rays to penetrate the inner solar system, with unknown effects on climate and life."

CHIPS is able to locate dense interstellar clouds by the shadows they cast. Cool clouds are partially opaque to the bubble's UV glow, so they appear as darker areas in CHIPS maps. Hurwitz notes that the mission's first sky maps are rather coarse, with a resolution of 5^o x 25^o. (The bowl of the Big Dipper, for comparison, is about 10 degrees wide.) Only the largest clouds would appear in those. Later, if the mission is extended beyond its first year, CHIPS will have time to produce sharper maps with 5^o x 6^o resolution.

Frisch has noted that Homo Sapiens arose only after the local interstellar medium was cleared out. Fewer clouds to run into would promote a stabler climate for our planet, she argues. So perhaps what Australopithecus saw was a good omen, after all....

CHIPS is helping us to find out.