Our solar system's natural defenses are down and a vigorous cosmic dust storm is blowing through, according to a new study. The forecast calls for a prolonged and increasing blizzard of small interstellar bits.

While no serious consequences are expected, the extra dust could slightly alter our night sky and might pose an increased risk to spacecraft, which are vulnerable to high-speed impacts from the tiny particles.

The whole scenario is also a vivid reminder that there is no such thing as empty space.

The number of incoming particles recently tripled and the pace is expected to grow over the next decade. Terrestrial weather and climate will not likely be affected, but more shooting stars could grace the night sky, said the study's leader, Markus Landgraf of the European Space Agency (ESA).

The fresh influx is related to a periodic weakening of the Sun's magnetic field.

The discovery was made using data from ESA's Ulysses spacecraft, which orbits the Sun on a noncircular path between Earth and Jupiter and his been monitoring the situation since 1992. The probe detects small particles and, based on direction, mass and speed, figures out which ones came from outside the solar system.

Threefold increase

The number of interstellar dust grains increased from four per day, per meter in 1997 to 12 per day in 2000, Landgraf said. The results were announced earlier this month. He expects the rate to stay constant until 2005, and then increase by another factor of 3 prior to 2013.

The potential effects are not well known, according to Landgraf and his colleagues at the Max-Planck-Institute.

"Generally interstellar dust is not considered a problem, as it does not penetrate typical spacecraft structures," Landgraf explained in an e-mail interview. "However, due to the high impact velocity, sensitive high-voltage instruments can suffer a short circuit after an exceptionally big impact. Also, sensitive optical instruments have to worry about the erosion of polished surfaces."

Most interstellar grains are just one-hundredth the diameter of a human hair. But they move fast, roughly 58,160 mph (26 kilometers per second) relative to the Sun.

Secondary effects

Any notable effects on Earth will likely involve secondary processes. When interstellar dust hits comets and asteroids, it's like shooting a tiny bullet at a rock, and more dust is kicked up, and the follow-on dust tends to be bigger.

More interstellar dust means more dust generated in-house.

"This has a number of potential effects," Landgraf said, cautioning that they haven't been observed yet, however.

One possibility is an increased number of sporadic meteors, those not associated with known showers like the summer Perseids or the November Leonids. Meteors are created when something vaporizes in Earth's atmosphere. Space rocks as big as peas and baseballs crash through now and then, but most shooting stars are made of mere dust.

It's also possible, Landgraf said, that the eerie Zodiacal Light -- a "false dawn" caused by sunlight reflecting off space dust -- will be enhanced.

And in general, more material might rain down to Earth from space every year.

Astronomers armed with huge telescopes will be interested to see if increased secondary dust brightens the Kuiper Belt, a region of frozen rocks and dust beyond Neptune. "With the brighter dust, especially infrared space telescopes will have a harder time to see faint objects behind the dust," Landgraf said.

Among other tasks, infrared telescopes on the ground and in space are used to study dust around other stars.

More to come

The solar system is always plowing through interstellar material. The Sun's giant magnetic field thwarts much of the dust from entering the solar system. But the magnetic field weakens periodically, on a cycle that lasts roughly 22-years. The cycle is related to an 11-year cycle of sunspot activity.

This is the first of the related dust storms that has been seriously monitored by a spacecraft.

Some day, the influx could get worse. The solar system is plowing toward the fringes of a galactic cloud known as the G-cloud.

"The time of the entry into the G-cloud is unknown, but is expected to occur any time in the next 10,000 years," Landgraf said. "There will be a constant increase [in dust rates], because the G-cloud is more dense than the local interstellar cloud that is now surrounding our Sun."

The study will be published in the Journal of Geophysical Research.