News in Science

Slower Sun leaves no shock wave

No shocker Our solar system's journey through space is slower and heading in a different direction to what was previously thought, according to new data.

The findings reported in the journal Science, also indicate the Sun appears to have a weaker interaction with the gas and dust that surrounds our solar system, known as the interstellar medium.

The new observations are based on fresh data from NASA's Interstellar Boundary Explorer (IBEX) spacecraft.

Launched in 2008, IBEX is designed to map the boundary of the heliosphere, a bubble created by the Sun's magnetic field and solar wind which contains the solar system.

The boundary where the heliosphere interacts with the interstellar medium, marks the edge of the solar system.

IBEX principal investigator, Dr David McComas from the South West Research Institute in Texas, and colleagues calculated the speed of the heliosphere with respect to the interstellar medium as 23.2 kilometres per second - significantly less than the previous estimate of 26.3 kilometres per second.

They also determined that the heliosphere's interstellar interaction is weaker and more magnetically dominated than previously thought.

McComas and colleagues say this explains the lack of a bow shock, where the interstellar medium abruptly slows before hitting the heliosphere.

It may also have implications for how much radiation - in the form of galactic cosmic rays - enters our solar system.

New eyes a 'big leap forward'

Before IBEX, essentially all outer heliospheric calculations and modelling were based on observations supplied by the joint NASA/ESA Ulysses spacecraft.

Ulysses was launched by the Space Shuttle Discovery in 1990 to study the Sun from an orbit above its poles.

McComas and colleagues say earlier speed and direction measurements by Ulysses will now need to be revised.

They say the IBEX observations are also more consistent with newer and independent astronomical measurements.

Professor John Dickey, head of the school of mathematics and physics at the University of Tasmania says the new IBEX data refines the original figures.

"We've done astronomical measurement of what we think is the Sun's motion around the galactic centre and its motion relative to nearby stars," says Dickey.

"But it's a bit harder to measure the gas which is mostly individual atoms between stars, things like hydrogen, helium and some heavier elements like carbon and oxygen."

"That's why IBEX is such a big leap forward. It can detect individual atoms entering the heliosphere from the interstellar medium."

Dickey says the paper shows "quite a different interstellar interaction than previously thought".

"The discovery that the magnetic field around the local interstellar medium is strong enough to suppress the formation of a bow shock ahead of the heliosphere is unexpected."