Voyager 2 Has Left the (Interplanetary) Building

The NASA probe was launched in 1977 and has now joined its twin, Voyager 1, to begin a new chapter of interstellar discovery

Both Voyager 1 and 2 are sampling particles from the interstellar medium, becoming humanity’s furthest-flung missions into deep space [NASA/JPL-Caltech]

Carolyn Porco, planetary scientist and lead of the NASA Cassini mission imaging team, probably said it best:

Voyager 1 made us an interstellar species; 6 yrs later, Voyager 2 makes it look easy. While these are historic, soul-stirring achievements, I am most happy right now that Ed Stone, the best Project Scientist who ever lived, lived to see this moment. 

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It can be easy to lump today’s announcement about Voyager 2 entering interstellar space as “simply” another magnificent science achievement for NASA — but that would be too narrow; the Voyager spacecraft have become so much more. They represent humanity at our best; our will to explore, our need to push boundaries, our excitement for expanding the human experience far beyond terrestrial shores. They also act as a means to understand the sheer scale of our solar system. And what better way to measure that scale than with a human life. 

Ed Stone started working on the Voyager Program in 1972 as a project scientist. Now, at 82 years old, he’s still working on the Voyagers nearly half a century later as they continue to send back data from the frontier beyond our solar system. When we start measuring space missions in half-centuries, or missions that have lasted entire careers, it becomes clear how far we’ve come. Not only does NASA build really tough space robots that surpass expectations routinely, returning new discoveries and revelations about the universe that surrounds us, the Voyagers have become a monument to the essence of being human, something with which Stone would probably agree.

Although most of the instruments aboard the Voyagers are no longer functional, both missions are still returning data from the shores of the interstellar ocean and, on Nov. 5, mission controllers noticed that one of Voyager 2’s instruments, the Plasma Science Experiment (PSE), had detected a rapid change in its surrounding environment. Used to being immersed the comparatively warm and tenuous solar wind flowing past it, its plasma measurements detected a change. The spacecraft had passed into a region of space where the plasma was now denser and cooler. Three other particle experiments also detected a dramatic change; solar wind particle counts were down, but cosmic ray counts precipitously increased. Voyager 1’s PSE failed in 1980, so couldn’t measure this boundary when it entered interstellar space in 2012, so Voyager 2 is adding more detail about what we can expect happens when a spacecraft travels from the heliosphere, through the heliopause and into interstellar space. 


“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Stone in a NASA statement.

The heliosphere can be imagined as a vast magnetized bubble that is generated by the Sun. This bubble is inflated by the solar wind, a persistent stream of solar particles that ebb and flow with the Sun’s 11-year cycle. When the Sun is at its most active, the bubble expands; at its least active, it contracts. This dynamic solar sphere of influence affects the flux of high-energy cosmic rays entering the inner solar system, but the physics at this enigmatic boundary is poorly understood. With the help of the Voyagers, however, we’re getting an in-situ feel for the plasma environment at the boundary of where the Sun’s magnetism hits the interstellar medium.

To achieve this, however, we had to rely on two spacecraft that were launched before I was born, in 1977. Voyager 2 is now 11 billion miles away (Voyager 1 is further away, at nearly 14 billion miles) and it took the probe 41 years just to reach our interstellar doorstep. Neither Voyagers have “left” the solar system, not by a long shot. The gravitational boundary of the solar system is thought to lie some 100,000 AU (astronomical units, where one AU is the average distance from the Earth to the Sun), the outermost limit to the Oort Cloud — a region surrounding the solar system that contains countless billions of icy objects, some of which become the long-period comets that intermittently careen through the inner solar system. Voyager 2 is barely 120 AU from Earth, so as you can see, it has a long way to go (probably another 30,000 years) before it really leaves the solar system — despite what the BBC tells us.

So, tonight, as we ponder our existence on this tiny pale blue dot, look up and think of the two space robot pioneers that are still returning valuable data despite being in deep space for over four decades. I hope their legacy lives on well beyond the life of their radioactive generators, and that the next interstellar spacecraft (no pressure, New Horizons) lives as long, if not longer, than the Voyagers.

Read more about today’s news in my article for


C.A.T. Scans of the Solar Wind

Guest article by Dr. Mario M. Bisi (Research Focus)

A cut in the ecliptic plane through a 3D reconstruction on 08 November 2004 at 0000 UT using white-light data from SMEI. The view is from directly North of the ecliptic; the Sun is at the centre marked by a +, the Earth is on the right marked with a ⊕ along with its orbit as a black near-circular line around the Sun (the Earth orbits anti-clockwise around the Sun from this point of view). The darker the colour, the greater the density of material in the ecliptic.  (©Dr. Mario M. Bisi)
A cut in the ecliptic plane through a 3D reconstruction on 08 November 2004 at 0000 UT using white-light data from SMEI. The view is from directly North of the ecliptic; the Sun is at the centre marked by a +, the Earth is on the right marked with a ⊕ along with its orbit as a black near-circular line around the Sun (the Earth orbits anti-clockwise around the Sun from this point of view). The darker the colour, the greater the density of material in the ecliptic. (©Dr. Mario M. Bisi)

The Computer Assisted Tomography (C.A.T.) technique has been used for many years now and is well known for use on people where certain health conditions need more thorough, detailed, and deeper scans into the human body and the need for three-dimensional (3D) reconstructed imaging. However, similar such scans can also be used on the solar wind to discover the shapes and sizes of structures near Earth and throughout the inner heliosphere in three dimensions. These scans have been carried out for some time, pioneered in the most part by those at the Center for Astrophysics and Space Sciences (CASS), University of California, San Diego (UCSD) in La Jolla, CA, U.S.A. in close-collaboration with the Solar-Terrestrial Environment Laboratory (STELab), Nagoya University, Toyokawa, Japan…
Continue reading “C.A.T. Scans of the Solar Wind”

IBEX Will Spread its Wings Today

Probably one of the coolest missions designed to study the termination shock (the region of space where the solar wind and interstellar medium interact) located a little under 100 AU from the Sun, will be launched today (Sunday). The Interstellar Boundary Explorer (IBEX) will be carried into space on board a Pegasus rocket installed under a L-1011 carrier aircraft from the Reagan Test Site at Kwajalein Atoll in the South Pacific (about 2500 miles from Hawaii in the direction of Australia). Out of interest, the aircraft will take off from the same region that SpaceX use to send their Falcon 1 rocket (and first ever commercial orbital vehicle) into space…

IBEX inside the Pegasus launch vehicle before transport from Vandenberg Air Force Base on October 11th (NASA)

The termination shock is a mysterious region of space as yet to be explored. Although Voyager 1 and 2 passed through this point, it is of critical importance to astrophysicists to measure the temporal and spatial changes at the boundary between the Solar System and the rest of interstellar space, as my previous Universe Today article explains:

In 2004, Voyager 1 hit it and in 2006, Voyager 2 hit it. The first probe flew through the termination shock at around 94 AU (8 billion miles away); the second measured it at only 76 AU (7 billion miles). This result alone suggests that the termination shock may be irregularly shaped and/or variable depending on solar activity. Before the Voyager missions, the termination shock was theorized, but there was little observational evidence until the two veteran probes traversed the region. The termination shock is of paramount importance to understanding the nature of the outer reaches of the solar system as, counter-intuitively, the Sun’s activity increases, the region beyond the termination shock (the heliosheath) becomes more efficient at blocking deadly cosmic rays. During solar minimum, it becomes less efficient at blocking cosmic rays. – Excerpt from IBEX Mission Will View the Final Frontier of the Solar System

So how will IBEX aid astrophysicists? It will count energetic neutral atoms (or ENAs for short) originating from the turbulent interaction region of the termination shock and build up a distribution of where the ENAs come from.

The Pegasus launch system in action (Univ. of Colarado/NASA)
The Pegasus launch system in action (Univ. of Colarado/NASA)

Scientists have known for a long time that neutral atoms appear to be generated at the termination shock. The solar wind carries energetic charged particles (or ions, mainly protons) into the far reaches of the heliosphere which eventually encounter interstellar neutral atoms. It is important to keep in mind at this point that any interstellar ions trying to get into the heliosphere are swept aside as the Solar System carries on its merry way through the galaxy; the heliospheric magnetic field deflects them. Therefore, only neutral interstellar particles are allowed in.

As the solar wind protons interact with the interstellar medium at the termination shock, they collide with the interstellar neutral atoms. When this happens, a mechanism known as charge exchange occurs. Electrons are ripped from these neutral interstellar atoms, creating very energetic neutral hydrogen atoms (i.e. 1× solar wind proton + 1× interstellar neutral atom electron). These ENAs are then blasted away from the point of charge exchange in a straight line (as energetic neutral atoms are not deflected by magnetic fields).

IBEX will be ideally placed to detect these ENAs whilst it orbits Earth so a better idea about termination shock dynamics can be gained. So, IBEX is set for launch on Sunday at 1:48 pm EDT during an eight minute launch window on board an aircraft-launched Pegasus rocket. I can’t wait for the results it will return, IBEX will, quite literally, paint a picture of how our Solar System interacts with the interstellar medium…

For more information on IBEX:

Original source: NASA