Voyager 1 Has Left the Solar System

Voyager 1 appears to have at long last left our solar system and entered interstellar space, says a University of Maryland-led team of researchers. (Credit: NASA)

Voyager 1 appears to have at long last left our solar system and entered interstellar space, says a University of Maryland-led team of researchers.

Carrying Earthly greetings on a gold plated phonograph record and still-operational scientific instruments -- including the Low Energy Charged Particle detector designed, built and overseen, in part, by UMD's Space Physics Group -- NASA's Voyager 1 has traveled farther from Earth than any other human-made object. And now, these researchers say, it has begun the first exploration of our galaxy beyond the Sun's influence.

"It's a somewhat controversial view, but we think Voyager has finally left the Solar System, and is truly beginning its travels through the Milky Way," says UMD research scientist Marc Swisdak, lead author of a new paper published online this week in The Astrophysical Journal Letters. Swisdak and fellow plasma physicists James F. Drake, also of the University of Maryland, and Merav Opher of Boston University have constructed a model of the outer edge of the Solar System that fits recent observations, both expected and unexpected.

Their model indicates Voyager 1 actually entered interstellar space a little more than a year ago, a finding directly counter to recent papers by NASA and other scientists suggesting the spacecraft was still in a fuzzily-defined transition zone between the Sun's sphere of influence and the rest of the galaxy.

why the controversy?

At issue is what the boundary-crossing should look like to Earth-bound observers 11 billion miles (18 billion kilometers) away. The Sun's envelope, known as the heliosphere, is relatively well-understood as the region of space dominated by the magnetic field and charged particles emanating from our star. The heliopause transition zone is both of unknown structure and location. According to conventional wisdom, we'll know we've passed through this mysterious boundary when we stop seeing solar particles and start seeing galactic particles, and we also detect a change in the prevailing direction of the local magnetic field.

NASA scientists recently reported that last summer, after eight years of travel through the outermost layer of the heliosphere, Voyager 1 recorded "multiple crossings of a boundary unlike anything previously observed." Successive dips in, and subsequent recovery of, solar particle counts caught researchers' attention. The dips in solar particle counts corresponded with abrupt increases in galactic electrons and protons. Within a month, solar particle counts disappeared, and only galactic particle counts remained. Yet Voyager 1 observed no change in the direction of the magnetic field.

To explain this unexpected observation, many scientists theorize that Voyager 1 has entered a "heliosheath depletion region," but that the probe is still within the confines of the heliosphere. Swisdak and colleagues, who are not part of the Voyager 1 mission science teams, say there is another explanation.

In previous work, Swisdak and Drake have focused on magnetic reconnection, or the breaking and reconfiguring of close and oppositely-directed magnetic field lines. It's the phenomenon suspected to lurk at the heart of solar flares, coronal mass ejections and many of the sun's other dramatic, high-energy events. The UMD researchers argue that magnetic reconnection is also key to understanding NASA's surprising data.

Though often depicted as a bubble encasing the heliosphere and its contents, the heliopause is not a surface neatly separating "outside" and "inside." In fact, Swisdak, Drake and Opher assert that the heliopause is both porous to certain particles and layered with complex magnetic structure. Here, magnetic reconnection produces a complex set of nested magnetic "islands," self-contained loops which spontaneously arise in a magnetic field due to a fundamental instability. Interstellar plasma can penetrate into the heliosphere along reconnected field lines, and galactic cosmic rays and solar particles mix vigorously.

Most interestingly, drops in solar particle counts and surges in galactic particle counts can occur across "slopes" in the magnetic field, which emanate from reconnection sites, while the magnetic field direction itself remains unchanged. This model explains observed phenomena from last summer, and Swisdak and his colleagues suggest that Voyager 1 actually crossed the heliopause on July 27, 2012.

Read the full NASA Voyager statement here:  NASA Voyager Statement about Competing Models to Explain Recent Spacecraft Data

Voyager Interstellar Mission :

In the 36th year after their 1977 launches, the twin Voyager 1 and 2 spacecraft continue exploring where nothing from Earth has flown before. Their primary mission was the exploration of Jupiter and Saturn. After making a string of discoveries there -- such as active volcanoes on Jupiter's moon Io and intricacies of Saturn's rings -- the mission was extended. Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. The current mission for both spacecraft, the Voyager Interstellar Mission, is to explore the outermost edge of the Sun's domain and beyond. Both Voyagers are capable of returning scientific data from a full range of instruments, with adequate electrical power and attitude control propellant to keep operating until 2020. Voyager 2 is expected to enter interstellar space a few years after its twin. The Voyager spacecraft were built and continue to be operated by NASA's Jet Propulsion Laboratory, in Pasadena, Calif.

University of Maryland scientists lead the Deep Impact spacecraft science team and are part of the science teams of many of the other spacecraft exploring our Solar System, including both Voyagers and Cassini.

Source : University of Maryland.

By Science and Universe

: University of Maryland.By Science and Universe

A cometary graveyard

<<Image : These illustration show the asteroid belt in the present day and in the early Solar System, located between the Sun (at centre) and four terrestrial planets (near the Sun) and Jupiter (at bottom left). The top image shows the conventional model for the asteroid belt; largely composed of rocky material. The middle image shows the proposed model, with a small number of active comets and a dormant cometary population. The lower diagram shows how the asteroid belt might have looked in the early Solar System, with vigorous cometary activity. Credit: Ignacio Ferrin / University of Antioquia

A team of astronomers from the University of Anitoquia, Medellin, Colombia, have discovered a graveyard of comets. The researchers, led by Antioquia astronomer Prof. Ignacio Ferrin, describe how some of these objects, inactive for millions of years, have returned to life leading them to name the group the 'Lazarus comets'. The team publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Comets are amongst the smallest objects in the Solar System, typically a few km across and composed of a mixture of rock and ices. If they come close to the Sun, then some of the ices turn to gas, before being swept back by the light of the Sun and the solar wind to form a characteristic tail of gas and dust.

Most observed comets have highly elliptical orbits, meaning that they only rarely approach the Sun. Some of these so-called long period comets take thousands of years to complete each orbit around our nearest star. There is also a population of about 500 short period comets, created when long period comets pass near Jupiter and are deflected in orbits that last anything between 3 and 200 years. Although uncommon events, comets also collide with the Earth from time to time and may have helped bring water to our planet.

The new work looked at a third and distinct region of the Solar System, the main belt of asteroids between the orbits of Mars and Jupiter. This volume of space contains more than 1 million objects ranging in size from 1 m to 800 km. The traditional explanation for asteroids is that they are the building blocks of a planet that never formed, as the movement of the pieces was disrupted by the strong gravitational field of Jupiter.

In the last decade 12 active comets have been discovered in the asteroid main belt region. This was something of a surprise and the Medellin team set out to investigate their origin. The team, made up of Prof. Ferrin and his colleagues Profs. Jorge Zuluaga and Pablo Cuartas, now think they have an explanation.

"We found a graveyard of comets", exclaims Professor Ferrín. He adds: "Imagine all these asteroids going around the Sun for aeons, with no hint of activity. We have found that some of these are not dead rocks after all, but are dormant comets that may yet come back to life if the energy that they receive from the Sun increases by a few per cent."

Surprisingly, this can happy fairly easily, as the orbits of many objects in the asteroid belt are nudged by the gravity of Jupiter. The shape of their orbits can then change, leading to a decrease in the minimum distance between the object and the Sun (perihelion) and a slight increase in average temperature.

According to this interpretation, millions of years ago the main belt was populated by thousands of active comets. This population aged and the activity subsided. What we see today is the residual activity of that glorious past. Twelve of those rocks are true comets that were rejuvenated after their minimum distance from the Sun was reduced a little. The little extra energy they received from the Sun was then sufficient to revive them from the graveyard.

Prof. Ferrin describes the 12 active comets. "These objects are the 'Lazarus comets', returning to life after being dormant for thousands or even millions of years. Potentially any one of the many thousands of their quiet neighbours could do the same thing."

Article Source : Royal Astronomical Society (RAS).

By Science & Universe