WASHINGTON (Reuters) - The solar system may not be a nice round shape, but rather a bit squashed and oblong, according to data from the Voyager 2 spacecraft exploring the solar system’s outer limits, scientists said on Wednesday.

Earth's solar system is seen in a 2004 illustration distributed by NASA's Jet Propulsion Laboratory. REUTERS/NASA Jet Propulsion Laboratory/Handout

Launched in 1977, the Voyager 1 and Voyager 2 unmanned probes are now studying the edges of the heliosphere, the huge magnetic “bubble” around our solar system created by the solar wind as it runs up against the thin gas in interstellar space.

The solar wind is made up of electrically charged particles blown into space in all directions by the sun. The boundary between the heliosphere and the rest of interstellar space is known as the “termination shock.”

Voyager 2 in August 2007 crossed this boundary 7.8 billion miles from the sun.

Voyager 1 had crossed the boundary in December 2004 about 10 billion miles away from Voyager 1 and almost a billion miles farther from the sun.

Scientists think this indicates that the bubble carved into interstellar space by the heliosphere, which extends well past the distant orbit of Pluto, is not perfectly round, and the solar system is shaped a bit like an oblong.

“Imagine a balloon is being blown up by the solar wind. You might imagine that if you took a balloon, which is mainly spherical, and pushed it against the wall, it would be blunted on one side,” said Edward Stone of the California Institute of Technology, one of the scientists involved in the research.

That’s what has happened with the heliosphere, he said.

The findings were published in the journal Nature.

The Voyager spacecraft were launched in 1977 with a mission to fly by and observe the giant planets Jupiter and Saturn. The two spacecraft then continued their mission into the outer solar system. They are flying through remote, cold and dark conditions, powered by long-life nuclear batteries in the absence of solar energy.