About one year ago, the U.S. space agency NASA's Voyager 2 spacecraft left our solar system. Several reports recently releasedin Nature Astronomydescribe the spacecraft's main scientific findings.
NASA says Voyager 2's missionled to new discoveries about the border that divides our solar system from interstellar space. "Interstellar" means "between stars." But scientists define interstellar space as the place where the sun's continual flow of material and magnetic field stop affecting its surroundings.
Interstellar space is estimated to be about 18 billion kilometers from Earth.
What did the spacecraft find?
Project researchers say Voyager 2's scientific instruments discovered unexpected differences in the density of plasma, a collection of charged particles existing in the solar system.
This artist's concept shows NASA's Voyager spacecraft against a backdrop of stars.
NASA also says the new research reports confirmed that both Voyager 1 and Voyager 2 appear to be in a transitional area just beyond the heliosphere. The heliosphere is a protective bubble that protects our solar system. It is created by solar wind formed from charged particles. The border of the solar system - the place where solar wind ends and interstellar space begins - is called the heliopause.
The team reported that data from Voyager 2 suggests that the heliopause appears to be much thinner than expected.
Edward Stone is a physicist with the California Institute of Technology and a project leader for the Voyager program. Stone told reporters the findings represent "a very exciting time for us."
He said in a statement the Voyager 2 mission was providing details about how the sun interacts with the materials that fill most of the space between stars in the Milky Way galaxy.
Researchers said Voyager 2 also confirmed the existence of a "magnetic barrier" at the outer edge of the heliosphere that had been predicted by theory and observed by Voyager 1.
"Without this new data from Voyager 2, we wouldn't know if what we were seeing with Voyager 1 was characteristicof the entire heliosphere, or specificjust to the location and time when it crossed," Stone said.
Leonard Burlaga is a scientist at NASA's Goddard Space Flight Center and a lead researcher on one of the reports. He told the French news agency AFP there were some surprises. "Contraryto all expectations and predictions, the magnetic field direction did not change when Voyager 2 crossed the heliopause," he said.
The spacecraft also collected information on incoming cosmic rays - particles that hit Earth from anywhere beyond its atmosphere. The data showed that the rays grew stronger as the Voyager explorers neared the heliopause.
Origins of the Voyager spacecraft
Voyager 2 was one of two explorers launched by NASAback in the summer of 1977. The other was Voyager 1. Both spacecraft were first designed to carry out fly-by studies of Jupiter and Saturn.
Later, Voyager 2 completed the first-ever close observations of Uranus and Neptune. The fly-by trips involving the four planets became known as the Voyager "Grand Tour."
The two spacecraft then began a new mission to explore areas at the edge of the sun's influence.
The two Voyagers – first built to last only five years – have long outlasted their operational lifetimes. But after 42 years in action, both are expected to run out of power and go silent within five years.
However, that does not mean that they will disappear. Bill Kurth, a researcher at the University of Iowa and co-writer of one of the research reports, said he expects the space explorers to outlast Earth. "They are in their own orbits around the galaxy for five billion years or longer," he said. "And the probability of them running into anything is almost zero."
Words in This Story：
mission – n.an important task, usually involving travel
bubble – n.an enclosed or isolated space
transitional – adj.changing from one system or method to another
characteristic – adj.typical of someone or something
specific – adj.a particular thing and not something general
contrary – adj.opposite or very different