First spacecraft to map edge of Solar System ready

for launch
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: October 15, 2008

The Interstellar Boundary Explorer (IBEX) is go for launch on 19 October and will be the first NASA spacecraft to image and map the dynamic interactions occurring at the edge of the Solar System.

The solar wind blows out a giant ‘bubble’ in our Solar System, known as the heliosphere (see diagram). At some distance, the solar wind begins to slow down – this marks the location of the termination shock. Eventually the solar wind is stopped completely by stellar winds from other stars in the interstellar medium – this marks the theoretical boundary known as the heliopause.

IBEX will chart the interactions between the edge of the solar wind contained within the heliosheath, and the interstellar medium. Image: NASA.

IBEX will conduct extremely high-altitude orbits above Earth to investigate and capture images of processes taking place at the farthest reaches of the Solar System, and the data returned from the mission will complement the lessons learnt from the Voyager spacecraft. Voyager 1 crossed the termination shock boundary on 16 December 2004 at a distance of 94 astronomical units. Voyager 2 crossed the termination shock just last year, at a distance 1.6 billion kilometres closer than Voyager 1, revealing that the heliosphere is squashed at that location due to the influence of the interstellar magnetic field.

Before the spacecraft crossed the boundary they recorded increases in the intensity of the lowest energy energetic particles they could observe. The instruments also measured an abrupt increase in the magnetic field strength as well as increased levels of compressive turbulence, evidence which all pointed to the spacecraft having crossed the termination shock. Furthermore, an instrument on Voyager 2 measured the abrupt slowdown of the solar wind that defines the termination shock, an instrument that had failed on Voyager 1 earlier in the mission.

Voyager 2 is thought to have crossed the boundary five times because of the dynamic nature of the termination shock, the location of which is constantly changing in response to the Sun's activity, such as coronal mass ejections that temporarily push the boundary outwards. Both spacecraft are now travelling through a region of slower solar wind within the heliosheath towards interstellar space.

While the Voyager measurements have provided new insight into the structure of the Solar System’s outer limits, the measurements were all in situ for one specific location and at one time only. IBEX will offer global maps of the interstellar interaction, and will provide valuable context for the data returned by the long lived Voyager spacecraft.

The two-year mission has a launch window of just eight minutes, between 1:44pm and 1:52pm EDT on Sunday. Live coverage of the IBEX launch will be hosted on the NASA home page.

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