People probably suspect that lack of data is the worst frustration for scientists. In fact, having only one data source can be worse, since you do not know how typical this solitary example can be. But the worst situation is having two sources of data that do not completely agree, leaving you with the challenge of trying to determine what causes the differences.
This is where scientists working with NASA's Voyager probe data find after Voyager 2 reached interstellar space last year, making it the second spacecraft we built and made it there. Now, in a series of five reports, researchers have tried to compare or contrast the data from the two Voyagers and are trying to make sense of the contradictions, knowing that we have nothing built that will receive new data from that distance anytime soon.
At the end of the Solar System
The gravitational influence of the Sun extends to the edge of the Oort Cloud, three light-years from the Sun. But the Sun affects its environment in ways that go beyond ordinary gravity. It generates a huge magnetic field that extends far beyond the planets and emits a stream of charged particles that flow into the interstellar space. These effects are limited by the influence of our galaxy, which has its own magnetic field and an interstellar medium filled with its own charged particles.
At one point, distant from the Sun, these two influences collide: the influence of the Sun weakens, i.e. and the galaxy is taking over. There were a number of theoretical ideas about how this transition was made. But testing these ideas is obviously a real challenge, given that it requires sending hardware to the edge of the solar system.
Conveniently, more than 40 years ago we were going to send some there. It was an accident; The Voyager probe is built to study the outer planets, but they are given gravitational boosts that eventually send them to accelerate fast enough to cover three times the distance from Earth to the Sun each year. As early as 201
During this transition Voyager 1 observed a gradual increase in high-energy cosmic rays, but they were redirected by two spikes where high-energy cosmic rays suddenly rose. They correspond to two immersions in the intensity of the charged lower-energy particles from the Sun, suggesting that part of the interstellar medium is leaking into the solar system. In each of these cases, the solar influence is restored, with cosmic rays descending back to their gradual trend and the solar particles returning to their normal levels.
Then suddenly the solar particles dropped to almost zero until the cosmic rays reached a high level where they had remained since. All this indicates that Voyager has reached interstellar space.
Voyager 2 had already undergone the same transition process in interstellar space, but had slightly different experiences from its earlier brother. To begin with, as shown in the blue below, the appearance of high-energy cosmic rays is not altered by any of the sudden jumps observed by Voyager 1. Similarly, the levels of the solar particles remained stable throughout their approach to the edge of the Sun. system, and instead of falling off a cliff when the probe reached interstellar space, the solar particles continued to hit the Voyager 2 sensors for more than 50 days after the transition.
Another key difference is that Voyager 2 had a working tool for measuring the solar wind, which was non-functional on Voyager 1. The density of the solar wind is expected to be diluted with distance from the sun. However, Voyager 2 found that the wind increased in density as the probe approached the transition point and also became a little more energetic. These data suggest that the transition causes the solar wind to accumulate against the border. Voyager 1 may have experienced the same thing but failed to register it.
However, a number of features seen by the two spacecraft were similar in outline, if not in detail. Voyager 1 struck the boundary of about 122 astronomical units from the Sun (AU is the average distance from Earth to the Sun); Voyager 2 hit it at 119 AU. Both probes observe a transition zone, which is approximately eight AUs, although Voyager 1 sees an extended low-velocity particle zone in this region. In both cases, the magnetic field does not change directions, as the probes enter the interstellar space, which was unexpected, given that the solar and galactic magnetic fields are not oriented in the same way. (Voyager 2 also saw a much stronger magnetic field.)
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So what can explain all these differences? One potential contribution is solar cycles. Voyager 1 has crossed the border at a low point of solar activity, which may mean that the border is pushed inward. In contrast, Voyager 2 had to chase the edge of the sun at times when solar activity was higher.
These differences underline the more general explanation of why transient experiences are different: the boundary represents the intersection between two dynamic fluids, with all the complex interactions that it implies. To some extent it would be surprising if there were no differences.
But that doesn't mean we wouldn't want to know more. Unfortunately, the Voyagers contribution was probably made. The next structure that is expected to exist is the bow strike, but it will probably be over 100 AU further. "We will reach it, but without any power to send something back," Edward Stone told JPL at a press conference describing the studies. "We won't have enough power for any instrument for another five years or more.
" When the two Voyager launched, the Space Age was only 20 years old, "Stone continued." We did not know that things could last 40 years. there. "
The new horizons, the next farthest active mission, will disappear at a power of about 90 AU, so they won't be able to count when it reaches the limit that the Voyagers have set. A supporting perspective suggests that Voyager 2 will be the last a spacecraft that crosses this border for at least 25 years Although we are talking about building a specialized probe to cross a different part of the transition area, we will probably leave to analyze Voyager data for decades to come. years in defining planetary science.
Individual research articles can be found at this web site.