NASA’s Voyager I is now in interstellar space, making it the first and farthest human-made space probe. New measurements of solar tsunami waves drew the scientists to formulate the conclusion.
“Normally, interstellar space is like a quiet lake,” said Ed Stone of the California Institute of Technology in Pasadena, California, the mission's project scientist since 1972 in a statement released on NASA’s website.
“But when our sun has a burst, it sends a shock wave outward that reaches Voyager about a year later. The wave causes the plasma surrounding the spacecraft to sing.”
Scientists studied these waves and came to the conclusion, in the fall of 2013, that Voyager had departed the sun's bubble and entered a new frontier.
“All is not quiet around Voyager,” said Don Gurnett of the University of Iowa, Iowa City, the principal investigator of the plasma wave instrument on the craft. “We're excited to analyze these new data. So far, we can say that it confirms we are in interstellar space.”
The tsunami is caused by emissions called coronal mass ejections (CME) - shock waves prompted by enormous and violent eruptions on the sun.
The bursts emit massive quantities of matter and electromagnetic radiation, and are associated with solar flares and prominence eruptions.
Voyager I’s cosmic ray instrument has picked up CME waves released from the sun, while another instrument can measure oscillations of surrounding space ‘plasma’ electrons.
One CME occurred in March 2012 and its shock waves reached Voyager I in April last year. Further research ensued, and scientists discovered another event from late 2012 which had previously been ignored.
Combining the separate sets of data with knowledge of the craft’s cruising speed meant that the researchers deduced Voyager I entered interstellar space in August 2012.
Details of a third CME shock wave, originally observed in March, were announced on Monday.
While the mission has not left the solar system (the outskirts of which are marked by a final ‘halo’ of comets around the sun), it has broken through the heliosphere which is the vast ‘wind-blown’ space surrounding the sun.
The area is occupied by space ‘plasma’, which, while dense, is approximately 40 times ‘lighter’ than the plasma outside the heliosphere. Voyager signals indicate that the craft is in an area occupied by thicker ‘plasma’.
“The tsunami wave rings the plasma like a bell,” Stone said. It oscillates more quickly than the ‘lighter’ plasma and resonates with a different frequency when struck by shock waves.
Voyager I was launched in order to study Jupiter and Saturn. It is approximately 11 billion miles from Earth and over 5 billion miles past Pluto.