This is a drawing of the heliosphere.
Click on image for full size


"Helios" is the ancient Greek word for the "sun". The Heliosphere is the entire region of space influenced by the sun. That would include the regions of space which contain the IMF.

The magnetic field of the sun (the IMF) is enormous and is carried throughout space by the solar wind.

The solar wind and the IMF push back the Interstellar magnetic field and plasma of interstellar space. They create a bubble or cavity, within which the sun and planets reside. The boundary between space dominated by the sun and interstellar space is called the heliopause. No one knows just how far away the heliopause, or "edge" of the heliosphere is, but it could be as far away as 100 AU.

The Voyager 1 and Voyager 2 spacecraft have passed the orbit of Pluto. So, they are now exploring the environment of space. Scientists have received signals from both spacecraft that imply that the spacecraft are coming near the heliopause. For the spacecraft to pass beyond the heliosphere, they will first have to pass through a termination shock. They will then enter interstellar space where no spacecraft has ever gone before. It is thought that the Voyager probes will reach the termination shock in 2001-2002 and that they will be completely clear of the heliosphere by ~2008.

Last modified September 26, 2000 by Jennifer Bergman.

You might also be interested in:


IMF stands for Interplanetary Magnetic Field. It is another name for the Sun's magnetic field. The Sun's magnetic field is enormous and is carried by the solar wind. The solar wind and magnetic field are...more

Voyager Update - Where No Spacecraft Has Ever Gone Before!

The Voyager program celebrated its 20th anniversary in 1997. Now Voyager is celebrating another milestone! The Voyager 1 and Voyager 2 spacecraft have passed the orbit of Pluto and they are now exploring...more

ACE Mission Page

The ACE (Advanced Compostion Explorer) was launched aboard a Delta II rocket in August 1997. This unique NASA mission will run a minimum of 2 years (with an expected lifetime of over 5 years). This mission...more

COSPIN Instrument Page

COSPIN is one of the instruments onboard the Ulysses spacecraft. COSPIN stands for the COsmic and Solar Particle INvestigation. The COSPIN instrument is actually made up of 5 different sensors: the Dual...more

VHM/FGM Instrument Page

Until recently, spacecraft have only been able to measure a limited, two-dimensional section of the heliosphere. This is because spacecraft were confined to stay within the plane of the ecliptic (the plane...more

SWOOPS Instrument Page

SWOOPS stands for "Solar Wind Observations Over the Poles of the Sun". This Solar Wind Plasma Experiment onboard Ulysses is basically making a map of the interplanetary plasma within the heliosphere (i.e.,...more

The Sun and the Solar Atmosphere

What are the "parts" of the Sun? The photosphere, the visible "surface" of the Sun, defines the outermost boundary of the "inside" of the Sun. The three main regions of the...more

Space Weather Mysteries & Unanswered Questions

The study of space weather is a relatively young science. As such it has many unanswered questions and unsolved mysteries. Although some of our data relevant to space weather, such as sunspot counts, go...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA