In a news
conference yesterday, NASA announced that its Voyager 2 probe exited the
heliosphere - the protective bubble composed of particles from the
solar wind created by our Sun. This marks the second time in history in
which a human-made object has left the near solar system.
Comparing
data gathered using different instruments on the spacecraft, scientists
realized that the probe crossed the boundary on November 5. Although
Voyager 1 made this crossing six years ago, Voyager 2 will be able to
provide unique observations through its still-functioning array of
instruments unlike its predecessor.
Scientists realized that
the spacecraft left the solar system when Voyager 2's Plasma Science
Experiment (PLS) observed a steep decline in the speed of the solar wind
particles on Nov. 5. Since that time, this instrument has detected
virtually no solar wind flow in its environment around Voyager.
"Working
on Voyager makes me feel like an explorer, because everything we're seeing is
new," said John Richardson, principal investigator for the PLS instrument and a
principal research scientist at the Massachusetts Institute of Technology in
Cambridge. "Even though Voyager 1 crossed the heliopause in 2012, it did so at
a different place and a different time, and without the PLS data. So we're
still seeing things that no one has seen before."
Although
both probes have crossed the heliosphere, these two spacecraft have not
left the solar system entirely. The boundary of the solar system is
considered to be beyond the outer edge of the Oort Cloud. The distance
of this collection of small objects under the gravity of the Sun is
currently known, but it is estimated that it may begin 1,000
astronomical units (AU) from the Sun and extend to over 100,000 AU.
Image Credit: NASA/JPL-Caltech
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