The NASA Voyager 2 probe, launched in 1977, is just over 11 billion miles, or 17.7 billion kilometers, from Earth. At this distance, about 118 times that of Earth to the Sun, the spacecraft has detected an increase in cosmic rays that originate outside our solar system.
Once it leaves the heliosphere, it will become the second object created by man, after Voyager 1 six years ago, to penetrate interstellar space.
Since 2007, the probe has been traveling through the outermost layer of the heliosphere: the vast bubble that surrounds the Sun and the planets dominated by solar material and magnetic fields. Voyager scientists have been watching the spacecraft to reach the outer limit of the heliosphere, known as the heliopause.
Cosmic rays are fast-moving particles that originate outside the solar system. Some of these cosmic rays are blocked by the heliosphere, so mission planners expect Voyager 2 to measure an increase in the cosmic ray rate as it approaches and crosses the boundary of the heliosphere.
Since the end of August, the instrument of the Cosmic Ray Subsystem in Voyager 2 has measured around 5% increase in the rate of cosmic rays impacting the spacecraft compared to the beginning of the same month. The low energy charged particle instrument of the probe has detected a similar increase in cosmic rays of higher energy.
In May 2012, Voyager 1 experienced an increase in the cosmic ray rate similar to that which Voyager 2 is detecting. That was approximately three months before Voyager 1 crossed the heliopause and entered interstellar space.
However, members of the Voyager team point out that the increase in cosmic rays is not a definitive sign that the probe is about to cross the heliopause. Voyager 2 is in a different location than Voyager 1, and the possible differences in these locations mean that Voyager 2 may experience a different time-out than Voyager 1.
The fact that Voyager 2 can approach the heliopause six years after Voyager 1 is also relevant since the heliopause moves in and out during the 11-year activity cycle of the Sun. Solar activity refers to to emissions from the Sun, including solar flares and material eruptions called coronal mass ejections. During the solar cycle of 11 years, the Sun reaches a maximum and minimum activity level.
“We are seeing a change in the environment around Voyager 2, there is no doubt about it,” says Ed Stone, Voyager project scientist, based at Caltech in Pasadena (USA): “We are going to learn a lot in the coming months, but we do not yet know when we will reach the heliopause. what can I say with confidence? “
The Voyager spacecraft was built by NASA’s Jet Propulsion Laboratory in Pasadena, California, which continues to operate both. JPL is a division of Caltech. The Voyager missions are part of NASA’s Heliophysical System Observatory, administered by the Heliophysics Division of the Office of Scientific Missions in Washington.
Voyager 1 and 2 of the US Space Agency (NASA) have become two ancient inhabitants of heaven. When they were launched forty years ago, few thought they would continue to send information to Earth punctually, for so long. The first one is already in interstellar space and the second one is about to cross the border of the Solar System, becoming the objects created by man that have reached the furthest.
Voyager 2 was launched from Cape Canaveral in Florida (USA) on August 20, 1977, followed by her partner, who did it on September 5. The trajectory of the 1 was shorter and faster, which allowed him to take advantage and that is why he is in interstellar space flying at almost 17 kilometers per second. His slow sister moves to little more than 15, which is not little, it is still one of the fastest ships ever built.