5 mins read 02 Nov 2019

Voyager 2 leaves the Solar System: Australia's role

Humanity’s second object leaves the Solar System and Australian radio telescopes helped scientists record the data from this historic moment.

Illustration showing the location of the two Voyager spacecraft as they leave the heliopause beyond Pluto. Credit: NASA/JPL

The Canberra Deep Space Network (DSN) tracking station and Parkes radio telescope have helped NASA scientists communicate with the Voyager 2 spacecraft as it left the boundaries of our solar system in 2018, and became the second object in history to enter interstellar space.

At a distance of about 18 billion kilometres from Earth, Voyager 2 entered the region of space between the stars, where the boundary of the Sun’s heliopause and noted two changes across its instruments. The first, the rate of heliospheric particles detected by instruments plummeted indicating the Sun’s plasma influence drops off in this region; and the second the rate of cosmic rays (particles accelerated by exploding stars in the galaxy) increased dramatically and stayed high.

The heliosphere is a bubble around the sun created by the outward flow of the solar wind from the sun and the opposing inward flow of the interstellar wind. That heliosphere is the region influenced by the dynamic properties of the sun that are carried in the solar wind--such as magnetic fields, energetic particles, and solar wind plasma. The heliopause marks the end of the heliosphere and the beginning of interstellar space.

Five new research papers published in the science journal, Nature detail the findings from Voyager 2's operating science instruments: a magnetic field sensor, two instruments to detect energetic particles in different energy ranges and two instruments for studying plasma (a gas composed of charged particles). The dramatic changes indicating Voyager 2’s historic crossing into interstellar space occurred on 5 November 2018.

The new papers also now confirm that Voyager 2 is not yet in undisturbed interstellar space: Like its twin, Voyager 1, Voyager 2 appears to be in a perturbed transitional region just beyond the heliosphere.

Australia’s Deep Space Tracking Role

The Canberra Deep Space Network. Credit: NASA/JPL

To keep track and communicate NASA utilises an international array of giant radio antennas known as the Deep Space Network that supports interplanetary spacecraft missions, plus a few that orbit Earth. The DSN consists of three facilities spaced equidistant from each other – approximately 120 degrees apart in longitude – around the world. These sites are at Goldstone, near Barstow, California; near Madrid, Spain; and near Canberra, Australia. The strategic placement of these sites permits constant communication with spacecraft as our planet rotates.

Canberra DSN is managed and operated by the CSIRO, which currently includes five antennas operating at the Canberra station: one 70-metre (DSS 43) and four 34-metre radio dishes that receive data from, and transmit commands to, spacecraft on deep space missions.

Canberra DSN currently also supports signal acquisition and communication with Martian missions (such as the Insight and Curiosity rovers), New Horizons spacecraft – which has also left the outer reaches of the planets after visiting Pluto and space-based solar observatories.

The Parkes radio telescope, also operated by the CSIRO, is located in the central NSW town of Parks and is a single 64m diameter steerable-dish that is able to receive signals from deep space objects or spacecraft. Unlike DSS 43, the Parkes telescope cannot broadcast signals.

Both the Canberra DSN and the Parkes radio telescope also played an important role in the Apollo moon-landing programs.

Voyager Spacecraft

The two Voyager spacecraft left Earth to explore the larger planets of our solar system in 1977, and have since been travelling out into interstellar space during their 42-year missions. Both spacecraft have performed and lasted well past their expected lifetimes and continue to return data back to Earth, through the Deep Space Network.

Voyager 1 launched on 5 September 1977, visiting Jupiter and Saturn in 1979-1980, whilst Voyager 2, over the period of 1979-1989, visited both the gas giants Jupiter and Saturn and the ice giants Uranus and Neptune To date, Voyager 2 remains the only spacecraft to have visited the ice giants, providing scientists with a large portion of knowledge about these outer bodies.

The two Voyager spacecraft have now confirmed that the plasma in local interstellar space is significantly denser than the plasma inside the heliosphere, as scientists expected. Voyager 2 has now also measured the temperature of the plasma in nearby interstellar space and confirmed it is colder than the plasma inside the heliosphere.

Both Voyager spacecraft carry a greeting to any form of life, should that be encountered. The message is carried by a phonograph record - -a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth. The contents of the record were selected for NASA by a committee chaired by Carl Sagan of Cornell University. Dr. Sagan and his associates assembled 115 images and a variety of natural sounds. To this, they added musical selections from different cultures and eras and spoken greetings from Earth-people in fifty-five languages.