It looks as if our trusty ol' solar system is poised to enter a "dense" cloud of interstellar gas, an event that would change our atmosphere in unpredictable ways. But not to worry -- it's not going to happen for several tens of thousands of years.
Within about 50,000 years, the solar system could enter a much denser portion of the interstellar medium. How would that affect our atmosphere? Yellow arrow: sun's movement through space. White arrows: movement of gas cloud. Courtesy of Priscilla Frisch, the University of Chicago.
Could the denser gas in "outer space" affect the atmosphere, and conditions on our planet? That's something that Priscilla Frisch, an astronomer at University of Chicago, wonders about. She notes that for the past 5 to 10 million years, Earth has occupied a region that's "virtually empty."
When she says "virtually," she's serious: The interstellar medium now has about 0.1 hydrogen atom per cubic centimeter (and that's 1,000 times as dense as the last cloud). Astronomers don't bother comparing the density of the medium to that of liquid water, which weighs one gram per cubic centimeter (cc). Instead, they count the number of hydrogen atoms per cc. (For comparison, there are 700 billion billion hydrogen atoms in a cc of pure hydrogen gas at the pressure at Earth's surface).
Frisch suggests that the vacuum-like interstellar medium may have promoted a stable atmosphere. "If the sun was being buffeted by a dense interstellar medium, it would probably affect our climate, although we don't know exactly how."
Collision course
Looking for planets in areas where the interstellar medium is thin, says Frisch, may be "a first step to finding other solar systems with stable planetary climates and atmospheres."
Both our solar system and the interstellar medium are moving through space, although not in the same direction. Within roughly 50,000 years, Earth may enter a cloud that's 1 million times denser, Frisch says. This thick cloud of gas is left over from star explosions called supernovas (defined).
Caution: detour ahead
We couldn't resist showing you this cool new picture of an exploding star that's not a supernova. The massive star Eta carinae blew up about 150 years ago, forming this two-lobed structure that's expanding at about 1.5 million miles per hour. The star survived the explosion and can be seen at the center, where it's radiating five million times as much power as our sun. Between the lobes is a flat disk of ejected material.
Photo from the Hubble Space Telescope, courtesy of Jon Morse (University of Colorado) and NASA.
Getting back on track
The two streams of particles and energy balance at a place called the heliopause (defined). Today, the heliopause is about 100 astronomical units (defined) from the sun. In other words, twice the distance of Pluto from the sun.
Since the position of the heliopause depends on the balance between the strength of the flow of interstellar medium and the strength of the solar wind, if the interstellar medium gets much denser, it could shrink the heliopause significantly.
If the heliopause shrinks to inside Earth's orbit, our planet would be exposed directly to the interstellar medium, possibly causing an increase in cosmic rays at the top of the atmosphere, a decrease in ultraviolet radiation, and other changes that could affect the atmosphere, weather and life in unpredictable ways.
Forget gas clouds and planets. Is anyone searching for space cadets?
Right now, we get almost no exposure to the interstellar medium, thanks to the solar wind (defined). This spray of hot, charged particles emanating from the sun's corona pushes against the interstellar medium.
