Life on earth could be decimated without warning by any of the countless cosmic clouds lurking perilously close to our solar system. According to Gary Zank of the Bartol Research Institute at the University of Delaware, a collision with even a tiny gas cluster could be enough to burst the delicate "breathing bubble" that makes current conditions on Earth so benign. 'We're surrounded by hot gas," explains Zank (sounds like a Science à GoGo editorial meeting - ed.). "As our sun moves through extremely 'empty' or low-density interstellar space, the solar wind produces a protective bubble - the heliosphere around our solar system, which allows life to flourish on Earth. Unfortunately, we could bump into a small cloud at any time, and we probably won't see it coming. Without the heliosphere, neutral hydrogen would interact with our atmosphere, possibly producing catastrophic climate changes, while our exposure to deadly cosmic radiation in the form of very high-energy cosmic rays would increase."
Zank's computer simulations, presented at the Spring meeting of the American Geophysical Union yesterday, are alarming indeed. Though the last five million years have seen "incredibly smooth sailing", Zank warns of cloudy skies ahead. Not only is the lethal Aquila Rift cloud region fast approaching (pushed by fierce galactic 'winds' and likely to reach us within the next 50,000 years), but some evidence suggests our immediate environment may be cheek-by-jowl with gas clusters known as the Local Fluff.
The solar system currently occupies a region of space containing between three and four particles per cubic inch. Even the wispiest of cosmic clouds are said to be at least a hundred times more dense. Existing instruments are too crude to detect these small but deadly knots of gas.
"We won't know that our heliosphere is collapsing until we see highly elevated levels of neutral hydrogen and cosmic rays, and a hydrogen wall in the vicinity of the outer planets," says Zank. Of course by that time, it will be too late.
