Solar System "Force Field" Shrinks Fast

As charged particles flow out from the sun, they eventually bump up against interstellar medium—the relatively empty areas between stars. These interactions "inflate" a protective bubble that shields Earth and the entire solar system from potentially harmful cosmic rays (solar system pictures).

Now IBEX has surprised astronomers by showing that this force field-like structure, the heliosphere, is an unexpectedly dynamic, unpredictable boundary.

"If we've learned anything from IBEX so far, it is that the models that we're using for interaction of the solar wind with the galaxy were just dead wrong," David McComas, principal investigator for the IBEX program, said during a NASA press conference Thursday.

Heliosphere Changes Fast

For starters, it's been assumed that the heliosphere's expansion and contraction follows the sun's roughly 11-year activity cycle, during which the flow rate of charged particles, or solar wind, fluctuates.

But when scientists compared IBEX maps of the heliosphere taken just six months apart, the researchers found that it had shrunk to a much greater extent than expected. (See "Sun's Power Hits New Low, May Endanger Earth?")

This quick shrinkage could be a concern for astronauts, said McComas, of the Southwest research Institute in San Antonio, Texas. That's because, as the heliosphere shrinks, it lets in more cosmic radiation, which can compromise the body's immune system.

(Related: "Solar System Is 'Bullet Shaped.'")

Among IBEX's other new surprises: a long, mysterious ribbon of uncharged particles found last year that has apparently lost its brightest, most energetic region since its 2009 discovery.

"What we're seeing is the knot pull apart as it spreads across a region of the ribbon," McComas said in a press statement.

"To this day the science team can't agree on exactly what causes the knot or the ribbon, but by comparing different sky maps, we find the surprising result that the region is changing over relatively short time periods. Now we have to figure out why."

Our Solar System May Have Millions of "Twins"

While that might not sound like much, the find suggests that several hundred million star systems look a lot like the one we call home, the study authors say.

The research is based on surveys of stars with gas giant planets—similar to Jupiter and Saturn—that orbit far from their stars.

As in our solar system, vast distances stretch between these stars and their gas giants. This creates ample room for rocky planets to thrive in the stars' habitable zones, the regions where liquid water can exist.

And that boosts the likelihood that other Earths, and maybe even other forms of life, abound in the Milky Way.

"For the first ten years of planet hunting, we were feeling a bit worried—other systems looked so different from our own solar system," noted Debra Fischer, an astronomer at San Francisco State University who was not involved in the research.

"[These] results are reassuring us that there are solar systems akin to our own. This is real data that strengthens the hypothesis that there are many habitable worlds like our Earth."

Cosmic Magnifying Glass

Astronomers think that gas giants generally form farther from their stars, while rocky worlds like Earth form closer in.

But in some star systems it's thought that gas giants migrate inward, knocking any smaller planets out of their orbits or destroying the rocky worlds outright.

Meanwhile, star systems like ours have gas giants in stable outer orbits.

"In these systems there is room for terrestrial planets to prosper and not get knocked out of their orbits," said study co-author Andy Gould, an astronomer at Ohio State University. 

What's more, studies of Jupiter suggest that outer gas giants can act as gravitational shields, protecting inner rocky worlds—and any life-forms on them—from frequent asteroid impacts.

To find such star systems, nearly a hundred scientists joined forces as part of the Microlensing Follow-Up Network, or MicroFUN, to scour the galaxy using a technique called gravitational microlensing.

In this method, when one star passes in front of another, as seen from Earth, the nearer star's gravity acts like a lens, bending and magnifying the more distant star's light.

If the nearer star has orbiting planets, keen-eyed observers can spot the subtle clues of their presence in the magnified light.

If all the stars in the Milky Way hosted solar system twins, astronomers should have found at least six such systems them by now, according to a statistical analysis of four years' worth of microlensing data.

But so far, only one other system like ours has been spotted: In 2006 astronomers found a star with its own versions of Jupiter and Saturn.

That means just 15 percent of the galaxy's stars must have solar systems like ours, Gould and colleagues announced this week at the 215th meeting of the American Astronomical Society in Washington, D.C.

Solar system surrounded by bright ribbon

A bright ribbon of hydrogen atoms marks the edge of the solar system, where the Sun's wind meets emissions from the rest of the galaxy, US researchers report.

The results come from the Interstellar Boundary Explorer spacecraft (IBEX), the latest in NASA's series of low-cost, rapidly developed space missions.

Launched last October it has already has produced stunning results, say scientists.

They used telescopes aboard the orbiting or IBEX to look toward the heliopause, which is the boundary where solar wind meets galactic wind at the edge of the solar system beyond Pluto.

Researchers combined images from IBEX with data from the Cassini spacecraft, near Saturn. They say the results, which appear in the latest issue of Science, are changing their ideas about what this border area looks like.

"The IBEX results are truly remarkable, with emissions not resembling any of the current theories or models of this never-before-seen region," David McComas of the Southwest Research Institute in San Antonio, who led the research.

"We expected to see small, gradual spatial variations at the interstellar boundary, some ten billion miles (16 billion km) away.

"IBEX is showing us a very narrow ribbon that is two to three times brighter than anything else in the sky."

Big picture

Scientists have long been keen to gain greater understanding of the heliosphere, described by NASA as a 'giant bubble' that protects the solar system from high-energy cosmic rays.

They are particularly eager to learn more about the invisible boundary of our solar system and dust and gas that fills the area between the stars, referred to as interstellar medium.

The interstellar medium is created in part by the interaction between the solar wind -- charged particles continuously traveling at supersonic speeds away from the Sun in all directions.

The two Voyager spacecraft, the robotic space probes sent to the outer solar system and beyond, have in the past provided data about more localised parts of the interstellar boundary region, but NASA officials say IBEX is helping fill in the "big picture" of what the space boundary looks like.