July 2, 2013
It has been almost 36 years since the launch of Voyager 1 and Voyager 2 spacecrafts, one of the most exciting space missions in the history of mankind. Even today, these almost forgotten probes keep writing our history as Voyager 1 is about to become the first man-made object to leave our solar system and make us an interstellar species.
Voyager probes leaving the solar system.
In August and September 1977, NASA has launched two spacecrafts, Voyager 1 and Voyager 2, with the mission of taking a close look at outer planets in our solar system. Voyager 1 encountered Jupiter in 1979 and Saturn in 1980, sending us a batch of pictures like we've never seen before. After the Voyager 2 passed Neptune in 1989, the mission changed its name from Voyager Outer Planets Mission to Voyager Interstellar Mission. Today, scientists are analyzing data sent from Voyager 1 and debate whether it has left our system or not.
Where is the border of the solar system? The solar system does not end with the orbit of Neptune nor it is defined by Kuiper belt or Oort cloud. Kuiper belt is an outer region of solar system, consisting of small, icy objects, some 30 to 50 Astronomical units from the Sun, while hypothesized Oort cloud lies even farther away, at 50000 AU. The border of our system is defined by the heliosphere. The heliosphere is an area around the Sun in which charged particles that emanate from the Sun are carried outwards by the solar wind. At the end of this area, the pressure of the solar wind and the interstellar medium balance and charged particles come to a stop. At this point, the lines of solar magnetism change their orientation to match those of interstellar space.
Although there were signs that Voyager 1 already left the solar system, with the American Geophysical Union even announcing it earlier this year, the Voyager team denies those claims. "The Voyager team is aware of reports today that NASA’s Voyager 1 has left the solar system. It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space," said Ed Stone, Voyager's project manager.
Analyzing data from 2012, scientists have determined that the Voyager 1 is in the zone named heliosphere depletion region, where there is considerably more cosmic rays and less particles from the Sun than in the heliosphere. It has left and entered the heliosphere depletion region for at least five times in 2012, indicating it is at the verge of leaving the solar system.
Although the Sun's magnetic field is losing its influence and being overtaken by the interstellar magnetism, magnetic lines still haven't change their direction which is why the Voyager team insists that the probe is still in our system. "The magnetic field suddenly doubled, becoming extraordinarily smooth. But since there was no significant change in the magnetic field direction, we’re still observing the field lines originating at the Sun," said Leonard Burlaga of NASA's Goddard Space Flight Center in Greenbelt, Maryland, USA.
When it will truly leave the solar, we don't know. It is amazing that at about 124 AU, the Voyager 1 is still at our doorstep. A distance of 18.5 billion kilometers in nothing if we keep in mind that the nearest star is about 2200 times farther away. Yet, we don't know much about objects that lie beyond Kuiper belt and data that Voyager 1 and Voyager 2 send us are very valuable to us.