Conference to learn about sun's bubble in stuff between the stars

The first report on data from NASA's Interstellar Boundary Explorer (IBEX) satellite, which is measuring the size and shape of the sun's 'bubble' in space, is scheduled to be presented this weekend at a conference in Hawai'i.

Although it should take about a year to map the full sky, details from the satellite's first data will be reported at 'Voyagers in the Heliosheath,' a conference organised by The University of Alabama in Huntsville's Centre for Space Plasma and Aeronomic Research. The conference is scheduled for 9-14 January on the island of Kauai, HI.

For more than a dozen years, Dr Gary Zank and his small team of scientists now at UAHuntsville have developed models that try to explain what is happening at the boundary between the outer edges of the solar wind and the thin soup of particles and magnetic fields that flow around the edge of the Milky Way galaxy - the sun's bubble in the stuff between the stars.

'For the first time, we will be able to map the bubble in which we live,' said Zank, the Pei-Ling Chan eminent scholar in physics at UAHuntsville. 'This is the first really detailed way to probing the material and the magnetic fields right outside where we live.'

'Right' outside is a relative thing: The nearest edge of the solar system's bubble, or heliosphere, is about one hundred times as far from the sun as Earth or about 9.3 billion miles away - approximately two and a half times farther out than the non-planet Pluto.

A hot solar particle blown into space by the solar wind will take just over two years to travel that distance. During that time it might cool from one million degrees Celsius to only 20,000 C when it runs into the termination shock at about 400 kilometres per second (on the order of 864,000 mph).

Starting about 1995 when they were at the University of California at Riverside, Zank and his colleagues have developed detailed models of what probably happens when warm solar plasma - in astronomy 20,000 C is 'warm' - runs into the ambient atoms, ions and molecules that orbit the galaxy.

By forecasting what this collision zone should look like from Earth, these models helped scientists and engineers design the sensors and instruments aboard IBEX. The satellite was launched in October and in mid-November entered a highly elliptic (oblong) orbit that takes the satellite five-sixths of the distance to the Moon.

The UAHuntsville models will also help scientists analyse data collected by the IBEX sensors. Those sensors detect energetic neutral atoms formed in the collision zone when energetic charged particles 'steal' an electron from another particle.

Because they are now electrically neutral these energised atoms are no longer affected by solar magnetic fields, so they travel in straight lines. Some of them will wind up in IBEX sensors, which count oxygen, hydrogen and neon atoms, measure the energy they carry and calculate the direction from which they travelled to Earth.

Throw in a little calculus and the IBEX team can now create full-sky maps of the heliosphere.

'The sky maps will provide a global structure of the heliosphere,' Zank said. 'It will also tell us the direction that the local interstellar field flows. It will tell us how hot that region is and how big it is.'

The models say the sun's bubble should be tear shaped, like the wave around a tree limb dipped into a flowing river.

While they are mapping the bubble, scientists also hope to solve a mystery found in data from NASA's STEREO satellites. Although designed as solar observatories, those satellites also detected an intense 'column' of energetic neutral atoms that does not seem to line up with any expected or known source.

'The STEREO data is a real puzzle,' Zank said. 'If STEREO is seeing energetic neutrals, then there are ten times too many of them. So that's one thing we will be trying to study and understand.'