NASA Voyager 2 Could Be Nearing Interstellar Space
NASA's Voyager 2 probe, currently on a journey toward interstellar space, has detected an increase in cosmic rays that originate outside our solar system.
NASA's
Voyager 2 probe, currently on a journey toward interstellar space, has detected
an increase in cosmic rays that originate outside our solar system. Launched in
1977, Voyager 2 is a little less than 11 billion miles (about 17.7 billion
kilometers) from Earth, or more than 118 times the distance from Earth to the Sun.Since 2007
the probe has been traveling through the outermost layer of the heliosphere -- the
vast bubble around the Sun and the planets dominated by solar material and
magnetic fields. Voyager scientists have been watching for the spacecraft to
reach the outer boundary of the heliosphere, known as the heliopause. Once
Voyager 2 exits the heliosphere, it will become the second human-made object, after
Voyager 1, to enter interstellar space.Since late
August, theCosmic Ray Subsysteminstrument on Voyager 2 has measured about a 5 percent increase in the rate of
cosmic rays hitting the spacecraft compared to early August. The probe's Low-Energy
Charged Particle instrument has detected a similar increase in higher-energy
cosmic rays.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
that Voyager 2 will measure an increase in the rate of cosmic rays as it approaches
and crosses the boundary of the heliosphere.In May 2012,
Voyager 1 experienced an increase in the rate of cosmic rays similar to what
Voyager 2 is now detecting. That was about three months before Voyager 1 crossed
the heliopause and entered interstellar space.However,
Voyager team members note 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
in the heliosheath -- the outer region of the heliosphere -- than Voyager 1 had
been, and possible differences in these locations means Voyager 2 may experience
a different exit timeline than Voyager 1.The fact that
Voyager 2 may be approaching the heliopause six years after Voyager 1 is also
relevant, because the heliopause moves inward and outward during the Sun's
11-year activity cycle. Solar activity refers to emissions from the Sun, including
solar flares and eruptions of material called coronal mass ejections. During
the 11-year solar cycle, the Sun reaches both a maximum and a minimum level of activity."We're
seeing a change in the environment around Voyager 2, there's no doubt about
that," said Voyager Project Scientist Ed Stone, based at Caltech in
Pasadena. "We're going to learn a lot in the coming months, but we still
don't know when we'll reach the heliopause. We're not there yet -- that's one
thing I can say with confidence."The Voyager spacecraft
were 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 a part of the NASA Heliophysics System Observatory, managed by the
Heliophysics Division of the Science Mission Directorate in Washington.For more information about
the Voyager spacecraft, visit:https://www.nasa.gov/voyagerhttps://voyager.jpl.nasa.gov