Spacecraft Detects Mysterious “Ribbon” at Edge of Solar System

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Since it launched a year ago, the Interstellar Boundary Explorer (IBEX) has been monitoring heliosphere and how our Sun interacts with and the local interstellar medium — the gas and dust trapped in the vacuum of space. The first results from the mission, combined with data from the Cassini mission, are showing the heliosphere to be different from what researchers have previously thought. Data show an unexpected bright band or ribbon of surprisingly high-energy emissions. “We knew there would be energetic neutral atoms coming in from the very edge of the heliosphere, and our theories said there would be small variations in their emissions,” said David McComas, IBEX Principal Investigator at a press conference on Thursday. “But instead we are seeing two-to-three hundred percent variations, and this is not entirely understood. Whatever we thought about this before is definitely not right.”

The energies IBEX has observed range from 0.2 to 6.0 kiloelectron volts, and the scientists said its flux is two to three times greater than the ENA activity throughout the rest of the heliosphere. McComas and his colleagues said that no existing model can explain all the dominant features of this “ribbon.” Instead, they suggest that these new findings will prompt a change in our understanding of the heliosphere and the processes that shape it.

This image illustrates one possible explanation for the bright ribbon of emission seen in the IBEX map. The galactic magnetic field shapes the heliosphere as it drapes over it. The ribbon appears to trace the area where the magnetic field is most parallel to the surface of the heliosphere (the heliopause).  Credit:  Southwest Research institute
This image illustrates one possible explanation for the bright ribbon of emission seen in the IBEX map. The galactic magnetic field shapes the heliosphere as it drapes over it. The ribbon appears to trace the area where the magnetic field is most parallel to the surface of the heliosphere (the heliopause). Credit: Southwest Research institute

McComas suggested that the energetic neutral atom (ENA) ribbon could be caused by interactions between the heliosphere and the local interstellar magnetic field. “The local interstellar magnetic field is oriented in such a way that it correlates with the ribbon. If you ‘paint’ the ribbon on the boundary of the heliosphere, the magnetic field is like big bungie cords that pushing in along the sides and at southern part of the heliosphere. Somehow the magnetic field seems to be playing a dominant roll in these interactions, but we don’t know it could produced these higher fluxes. We have to figure out what physics were are missing.”

The solar wind streaks away from the sun in all directions at over a millions kilometers per hour. It creates a bubble in space around our solar system.

For the first ten billion kilometers of its radius, the solar wind travels at over a million kilometers per hour. It slows as it begins to collide with the interstellar medium, and the point where the solar wind slows down is the termination shock; the point where the interstellar medium and solar wind pressures balance is called the heliopause; the point where the interstellar medium, traveling in the opposite direction, slows down as it collides with the heliosphere is the bow shock.

The heliosphere. Credit: NASA
The heliosphere. Credit: NASA

The Voyager spacecraft have explored this region, but didn’t detect the ribbon. Team member Eric Christian said the ribbon wound in between the location of Voyager 1 and 2, and they couldn’t detect it in their immediate areas. Voyager 1 spacecraft encountered the helioshock in 2004 when it reached the region where the charged particles streaming off the sun hit the neutral gas from interstellar space. Voyager 2 followed into the solar system’s edge in 2007. While these spacecraft made the first explorations of this region, IBEX is now revealing a a more complete picture, filling in where the Voyagers couldn’t. Christian compared Voyager 1 and 2 to be like weather stations while IBEX is first weather satellite to provide more complete coverage.

McComas said his first reaction when the data started coming in was that of terror because he thought something must be wrong with the spacecraft. But as more data kept coming back each week, the team realized that they were wrong, and the spacecraft was right.

“Our next steps will be to go through all the detailed observations and rack them up against the various models and go find what it is that we are missing, what we’ve been leaving out,” he said.

For more information and visuals, see this NASA webpage.

What is Interplanetary Space?

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The region of space within our Solar System is called interplanetary space, also known as interplanetary medium. Most people are so fascinated by the planets, Sun, and other celestial objects that they do not pay any attention to space. After all, there is nothing in outer space right? A common misconception is that outer space is a perfect vacuum, but there are actually particles in space including dust, cosmic rays, and burning plasma spread by solar winds. Particles in interplanetary space have a very low density, approximately 5 particles per cubic centimeter around Earth and the density decreases further from the Sun. The density of these particles is also affected by other factors including magnetic fields. The temperature of interplanetary medium is about 99,727°C.

Interplanetary space extends to the edge of the Solar System where it hits interstellar space and forms the heliosphere, which is a kind of magnetic bubble around our Solar System. The boundary between interplanetary space and interstellar space is known as the heliopause and is believed to be approximately 110 to 160 astronomical units (AU) from the Sun. The solar winds that blow from the Sun, and are part of the material in interplanetary space, flow all the way to the edge of the Solar System where they hit interstellar space. The magnetic particles in these solar winds interact with interstellar space and form the protective sphere.

The way that interplanetary space interacts with the planets depends on the nature of the planets’ magnetic fields. The Moon has no magnetic field, so the solar winds can bombard the satellite. Astronomers study rocks from Earth’s Moon to learn more about the effects of solar winds. So many particles have hit the Moon that it emits faint radiation. Some planets, including Earth, have their own magnetospheres where the planets’ magnetic fields override the Sun’s.  The Earth’s magnetic field deflects dangerous cosmic rays that would otherwise damage or kill life on Earth. Material leaking from the solar winds is responsible for auroras in our atmosphere. The most famous aurora is the Aurora Borealis, which appears in the sky and is only visible in the Northern Hemisphere.

Interplanetary medium also causes a number of phenomena including the zodiacal light, which appear as a faint broad band of light only seen before sunrise or after sunset. This light, brightest near the horizon, occurs when light bounces off dust particles in the interstellar medium near Earth. In addition to interplanetary space, there is also interstellar space, which is the space in a galaxy in between stars.

Universe Today has a number of articles on space including the heliosphere and zodiacal light.

Check out these articles from NASA on the heliosphere and sunspots leaking plasma into interplanetary space.

Astronomy Cast has an episode on the heliosphere and interstellar medium.

References:
NASA: Heliosphere
NASA Voyager: Interstellar Mission
What’s It Like Where Voyager Is?