Helios 1 & 2
December 1974 November 1981
by Hamish Lindsay
Honeysuckle Creek tracked the two Helios spacecraft throughout its Deep Space life, in fact our very last track was on Helios 1, which was launched on 10 December 1974, round about the time we joined the Deep Space Network. We spent countless hours tracking the two Helios spacecraft.
view of the solar system, not to any scale, and the Earths magnetosphere
and the Suns features are greatly simplified and magnified to show
Helios 1 was launched from Earth at the position marked A and its orbital path is shown in white. The Earth and Venus are shown when Helios reached its closest approach to the Sun the first time. Mercury at the same time is shown just below Helios.
There was a blackout period when Helios passed behind the Sun, shown between points B and C.
1. The Earths magnetosphere is shown streaming away from the Sun.
2. The Earths shock front. These two features are formed by the interaction between the Earths magnetic field and the solar wind passing by.
3. The Solar Wind originates from the hot Corona and travels at speeds of up to 1,800,000 kilometres per hour. It is not uniform as it is affected by magnetic clouds, interacting regions, and composition variations. If a slow moving stream of solar wind is overtaken by a faster moving stream the resulting interaction produces shock waves that can accelerate particles to extremely high speeds. It streams out like the water from a lawn sprinkler as the Sun spins on its axis every 27 Earth days.
4. Sunspots on the surface of the Sun. Sunspots have been known to exist since the invention of the telescope - Galileo is often quoted as one of the first to refer to them around 1610. Sunspots are thought to be the result of pent-up magnetic fields below the surface of the Sun breaking through making relatively cool areas when new hot gas is inhibited from reaching the surface. Sometimes larger than the Earth, they can be in groups, and last for weeks to months, depending upon their size. They do not appear randomly over the surface - they are concentrated above and below the solar equator. Spots that appear in the northern hemisphere are mirrored in the southern hemisphere, mostly in pairs, the leading spot carrying the opposite polarity to the trailing spot. Sunspots are linked to the Suns magnetic activity, their number rising and falling over 11 year cycles, called the Solar Cycle.
Sunspots under white light.
5. Long Filaments stretching out from the surface of the Sun. Filaments are long, thin regions of relatively cool gases stretching 100,000 kilometres out from the surface, held in place by magnetic fields above the chromosphere. They can last weeks, or months before dropping back to be absorbed back into the Suns surface.
A Filament photographed by the satellite TRACE.
6. The hot Corona is grouped into three types, the White Light Corona, Emission Line Corona, and X-Ray Corona. The Corona is the upper atmosphere of the Sun and can only be seen during total eclipses or with the use of special equipment as it is a million times darker than the Photosphere.
7. Coronal arches are fountains of hot gases stretching 480,000 kilometres above the surface. They heat up as they rise through the first 16,000 kilometres, flow along the magnetic lines and cool down as they stream back into the surface at more than 360,000 kilometres per hour. Millions of different sized arches make up the corona.
8. Streamers of magnetic loops extending between areas of opposite magnetic polarity. Streamers and loops are hot gases trapped in magnetic field lines up to 800,000 kilometres long. They emanate from constantly changing north and south poles scattered all over the surface. The magnetic fields are believed to originate from a region 220,000 kilometres below the surface which scientists believe is the source of all magnetism in the Sun.
9. The Coronal arches can continue into boundary regions in the interplanetary magnetic field.
10. The Interplanetary Magnetic Field, also called the IMF. Originating from the Sun the IMF spirals out (called the Parker Spiral) carried by the solar wind through the heliosphere to eventually reach Interstellar Space beyond the planet Pluto.
11. Alfven waves and shock waves (12) produced during flares on the Sun can cause kinks in the Suns magnetic field. Like the movement of a plucked guitar string, they travel down the Suns magnetic field, embedding in the solar wind to eventually cause auroras on Earth. They are named after Hannes Alfven who discovered them in 1942.
13. During flare eruptions, radio waves and X-ray waves occur when charged particles are accelerated to high energies.
14. The propagation of solar radiation takes place in the Coronas magnetic fields and in the spiral paths around the interplanetary magnetic field. Solar radiation is the electromagnetic radiation (light energy) transmitted into space in units of photons. Without this radiation life on Earth would not exist. It is over 9 KW/metre squared at Mercury, dropping to about 1.6 KW/metre squared at Earth to almost 0 at Saturn. Roughly half the radiation that reaches the Earths upper atmosphere reaches the surface.
15. Galactic cosmic radiation constantly penetrates into the interplanetary medium from outside the solar system.
16. The scattering of sunlight on small dust particles in space produces the Zodiacal Light. These dust particles are released into the interplanetary medium by comets and small asteroids. The smaller particles are blown away by the solar wind but the larger particles, 0.1 to 100 micrometre, spiral in to the Sun and form a flattened disc around it in the ecliptic plane, visible from the Earth under certain conditions.
17. Zodiacal Light may be regarded as a continuation of part of the Suns low-intensity Corona.