One year ago, on November 5, 2018, NASA Voyager 2 became just the second spacecraft in history to leave the heliosphere – the protective bubble of particles and magnetic fields created by our Sun. At about 11 billion miles (18 billion kilometers) from Earth – well beyond Pluto's orbit – Voyager 2 has entered the interstellar space or the area between the stars. Today, five new scientific papers in the journal by Nature Astronomy describe what scientists have observed during and after the historic crossing of Voyager 2.
Each document describes the results of one of the five scientific instruments of Voyager 2: a magnetic field sensor, two instruments for detecting energy particles in different energy ranges, and two instruments for plasma study (gas composed of charged particles). Taken together, the discoveries help paint a picture of this cosmic coastline where the environment created by our sun ends and the vast ocean of interstellar space begins.
The heliosphere of the sun is like a ship sailing through interstellar space. Both the heliosphere and the interstellar space are filled with plasma, a gas that has some of its atoms devoid of their electrons. The plasma inside the heliosphere is hot and scarce, while the plasma in the interstellar space is colder and denser. The space between stars also contains cosmic rays or particles accelerated by exploding stars. Voyager 1 has discovered that the heliosphere protects Earth and other planets from more than 70% of this radiation.
When Voyager 2 emerged from the heliosphere last year, scientists announced that its two energy particle detectors saw drastic changes: The speed of heliospheric particles detected by the instruments collapsed, while the velocity of cosmic rays (which usually have higher energy rays) heliospheric particles) increased dramatically and remained high. The changes confirmed that the probe had entered a new area of space.
Before Voyager 1 reached the edge of the heliosphere in 2012, scientists did not know exactly how far this boundary was from the Sun. The two probes emerged from the heliosphere in different places, and also at different times in a continuously repeating, approximately 11-year solar cycle, during which the Sun undergoes a period of high and low activity. Scientists have expected that the edge of the heliosphere, called heliopause, can move when the sun's activity changes, such as expanding the lungs and contracting the breath. This was in line with the fact that the two probes encountered heliopause at different distances from the Sun.
New documents confirm that Voyager 2 is not yet in pristine interstellar space: Like your twin, Voyager 1, Voyager 2 appear to be in a confused transitional region just beyond the heliosphere.
"Voyager probes show us how our Sun interacts with things that fill most of the space between stars in the Milky Way galaxy," says Ed Stone, a Voyager scientist and professor of physics at Caltech. "Without this new Voyager 2 data, we wouldn't know if what we see with Voyager 1 is specific to the entire heliosphere or is specific to the location and time it passes."
Pushing Through Plasma
The two Voyager spacecraft have confirmed that the plasma in the local interstellar space is much more dense than the plasma inside the heliosphere, as scientists expected. Voyager 2 also measured the plasma temperature in the near interstellar space and confirmed that it was colder than the plasma inside the heliosphere.
In 2012, Voyager 1 observed slightly higher than expected plasma density outside the heliosphere, i. indicating that the plasma is compressing slightly. Voyager 2 noticed that the plasma outside the heliosphere was slightly warmer than expected, which may also indicate that it was compressing. (The plasma outside is still colder than the plasma inside.) Voyager 2 also observes a slight increase in plasma density just before exiting the heliosphere, indicating that the plasma is compressing around the inner edge of the bladder. But scientists still do not fully understand what causes compression on both sides.
If the heliosphere is like a ship sailing through interstellar space, the hull appears to be somehow permeable, One of the Voyager particle tools showed that a helipad particle shell sneaks across the border and into interstellar space. Voyager 1 emerged near the very front of the heliosphere, relative to the motion of the bubble through space. Voyager 2, on the other hand, is located closer to the flank and this region looks more porous than the region in which Voyager 1. is located.
Mystery Magnetic Field
the magnetic field of Voyager 2 confirms the surprising result of Voyager 1: The magnetic field in the area just beyond the heliopause is parallel to the magnetic field inside the heliosphere. With Voyager 1, scientists had only one sample of these magnetic fields and could not say for certain whether the apparent alignment was characteristic of the entire outer region or a mere coincidence. Observations on the Voyager 2 magnetometer confirm the Voyager 1's finding and show that the two fields align according to Stone.
Voyager probes launched in 1977, both flying from Jupiter and Saturn. Voyager 2 changed Saturn's course to fly from Uranus and Neptune, playing the only close-up aircraft on these planets in history. Voyager probes completed their grand tour of the planets and began their Interstellar Heliopause Mission in 1989. Voyager 1, the faster of the two probes, is currently over 13.6 billion miles (22 billion kilometers) from the Sun while Voyager 2 is 11.3 billion miles (18.2 billion kilometers) from the sun. It takes about 16.5 hours to travel from Voyager 2 to Earth. In comparison, light traveling from the sun takes about eight minutes to reach Earth.
Voyager 2 reaches interstellar space: Scientists detect jump in plasma density
Dense density near and beyond the heliopause of the Voyager Plasma Wave 1 and 2 Plasma Instruments, Nature Astronomy (2019). Doi: 10.1038 / s41550-019-0929-2, https://nature.com/articles/s41550-019-0918-5
Cosmic ray measurements from Voyager 2 as it passed into interstellar space, Natural Astronomy (2019). DOI: 10.1038 / s41550-019-0928-3, https://nature.com/articles/s41550-019-0928-3 records19659005 imagesVoyager 2 plasma observations of heliopause and interstellar environment, Nature Astronomy (2019 ). DOI: 10.1038 / s41550-019-0929-2, https://nature.com/articles/s41550-019-0929-2 records19659005SenseMagnetic field and particle measurements made by Voyager 2 at and near heliopause, Nature Astronomy (2019). DOI: 10.1038 / s41550-019-0929-2, https://nature.com/articles/s41550-019-0920-y records19659005SenseEnergetic measurements of Voyager 2 particles during heliopause and beyond, Nature Astronomy (2019). Doi: 10.1038 / s41550-019-0929-2, https://nature.com/articles/s41550-019-0927-4
Voyager 2 illuminates the boundary of interstellar space (2019, November 5)
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