Our Solar System is moving through interstellar space and scientists have long thought that the “bubble” around our Solar System – called the heliosphere – might have a tail, similar to how a comet has a tail or how other stars have astrospheres. But that has all been conjecture…. until now.
The IBEX spacecraft (Interstellar Boundary Explorer) has now seen the tail and has mapped out its structure. IBEX scientists were surprised to see the tail has twists and turns, with four separate “lobes,” making it appear somewhat like a four-leaf clover. This downwind region of the heliosphere is called the heliotail.
“Scientists have always presumed that the heliosphere had a tail,” said Eric Christian, IBEX mission scientist, speaking during a Google+ Hangout announcing the new findings. “But this is actually the first real data that we have to give us the shape of the tail.”
IBEX measures the neutral particles created by collisions at the solar system’s boundaries. This technique, called energetic neutral atom imaging, relies on the fact that the paths of neutral particles are not affected by the solar magnetic field. Instead, the particles travel in a straight line from collision to IBEX. Consequently, observing where the neutral particles came from describes what is going on in these distant regions.
“By collecting these energetic neutral atoms, IBEX provides maps of the original charged particles,” said David McComas, lead author on the team’s paper and principal investigator for IBEX at Southwest Research Institute. “The structures in the heliotail are invisible to our eyes, but we can use this trick to remotely image the outermost regions of our heliosphere.”
What they found was unexpected, McComas said.
“By very carefully assembling the statistical observations from the first three years of IBEX data we’ve been able to fill in what we couldn’t see before,” McComas said during the Hangout, “and what we found was that the heliotail was a much larger structure with a much more interesting configuration.
What they found was a tail that appears to have a combination of fast and slow moving particles. There are two lobes of slower particles on the sides, with faster particles above and below. The entire structure is twisted from the pushing and pulling of magnetic fields outside the solar system. McComas likened it to a how a beach ball might twist around if it was attached to a bungee cord.
The IBEX scientists speaking during the Hangout today said this new information will help us understand what the Voyager spacecraft may encounter as they reach the edge of our Solar System.
“IBEX and Voyager are incredibly complimentary missions,” said Christian. “I’ve often said that IBEX is like an MRI, where it can take an image to understand the big picture of what is going on, where the Voyagers are like biopsies, where we can see what is going on in the local area.”
This was the first time a NASA used a Google+ Hangout to broadcast a press briefing. You can watch the full Hangout below:
You can read David McComas’ blog post on the new findings here, and NASA’s press release here.
For years, scientists have thought a bow “shock” formed ahead of our solar system’s heliosphere as it moved through interstellar space – similar to the sonic boom made by a jet breaking the sound barrier. But new data from NASA’s Interstellar Boundary Explorer (IBEX) shows that our system and its heliosphere move through space too slowly to form a bow shock, and therefore does not exist. Instead there is a more gentle ‘wave.’
“While bow shocks certainly exist ahead of many other stars, we’re finding that our Sun’s interaction doesn’t reach the critical threshold to form a shock,” said Dr. David McComas, principal investigator of the IBEX mission, “so a wave is a more accurate depiction of what’s happening ahead of our heliosphere — much like the wave made by the bow of a boat as it glides through the water.”
From IBEX data, McComas and his team were able to make refinements in relative speed of our system, as well as finding more information about the local interstellar magnetic field strength. IBEX data have shown that the heliosphere actually moves through the local interstellar cloud at about 52,000 miles per hour, roughly 7,000 miles per hour slower than previously thought. That is slow enough to create more of a bow “wave” than a shock.
Another influence is the magnetic pressure in the interstellar medium. IBEX data, as well as earlier Voyager observations, show that the magnetic field is stronger in the interstellar medium requiring even faster speeds to produce a bow shock. Combined, both factors now point to the conclusion that a bow shock is highly unlikely.
The IBEX team combined its data with analytical calculations and modeling and simulations to determine the conditions necessary for creating a bow shock. Two independent global models — one from a group in Huntsville, Ala., and another from Moscow — correlated with the analytical findings.
Their paper was published today in the journal Science.
How does this new finding change our understanding of our heliosphere?
“It’s too early to say exactly what this new data means for our heliosphere,” McComas said. “Decades of research have explored scenarios that included a bow shock. That research now has to be redone using the latest data. Already, we know there are likely implications for how galactic cosmic rays propagate around and enter the solar system, which is relevant for human space travel.”
If we could board the starship Enterprise-D and were able to look through Giordi LaForge’s visor we might be able to see the interstellar medium – the ‘stuff’ between the stars — as wispy clouds of oxygen, hydrogen, helium and neon. Instead, since we are back in the 21st century, we have the Interstellar Boundary Explorer (IBEX) spacecraft, which has now made the first–ever direct observations of neutral hydrogen and oxygen atoms drifting into our solar system from the region outside our heliosphere. Surprisingly, this material is more ‘alien’ than scientists were expecting, as the matter in the galactic wind doesn’t contain the same exact material as what our solar system is made of.
The most important finding is there is less oxygen ‘out there.’ For every 20 neon atoms in the galactic wind, there are 74 oxygen atoms. In our own solar system, however, for every 20 neon atoms there are 111 oxygen atoms. That translates to more oxygen in any given region of the solar system than in the local interstellar space.
“Our solar system is different than the space right outside it and that suggests two possibilities,” said David McComas the principal investigator for IBEX. “Either the solar system evolved in a separate, more oxygen-rich part of the galaxy than where we currently reside or a great deal of critical, life-giving oxygen lies trapped in interstellar dust grains or ices, unable to move freely throughout space.”
Either way, the scientists said, this affects scientific models of how our solar system – and life – formed. And more than just helping to determine the distribution of elements in the interstellar medium, these new measurements provide clues about how and where our solar system formed, the forces that physically shape our solar system, and even the history of other stars in the Milky Way.
“This alien interstellar material is really the stuff that stars and planets and people are made of — and it’s very important to be measuring it directly,” McComas said during a press briefing on Tuesday.
If Spock were a member of this mission, he would probably raise an eyebrow and say, “Fascinating.”*
Interstellar clouds hold the elements of exploded supernovae, which are dispersed throughout the galaxy. As the interstellar wind blows these charged and neutral particles through the Milky Way, the spacecraft can measure samples that make it into our solar system. IBEX scans the entire sky once a year, and every February, its instruments point in the correct direction to intercept incoming neutral atoms. IBEX counted those atoms in 2009 and 2010 and has now captured the best and most complete glimpse of the material that lies so far outside our own system.
In addition to sampling the raw “star stuff,” the findings are important because the interstellar gas surrounding us can affect the strength of the Sun’s heliosphere – the area of influence by the Sun, and like a shielding bubble, protects us from dangerous galactic cosmic rays, the majority of which would come into the inner solar system if not for this bubble.
IBEX also discovered that the interstellar wind is approximately 7,000 miles per hour slower than previously thought. This indicates that our solar system is still in what’s referred to as the “local interstellar cloud.” However, the scientists noted that we will transition into a different region at any time within a few thousand years (very short on astronomical time scales) where conditions will change and affect the heliosphere’s protective capability. And no one knows if that change will be for the better or worse.
As our solar system travels around the Milky Way through the vast sweep of cosmic time, the ever-changing nature of the heliosphere has likely had implications on the evolution of life on Earth as varying levels of radiation spurred genetic mutations and, perhaps, wholesale extinctions.
“This is all very exciting, and it has important implications as the Sun moves through space and in and out of interstellar clouds , the flux of galactic cosmic rays varies,” said Priscilla Frisch, senior scientist, Department of Astronomy and Astrophysics at the University of Chicago, and part of the IBEX mission. “And that is recorded in the geo-isotopic records. Someday maybe we can link the Sun’s motion through interstellar clouds with geological records on Earth, and trace the geological history of Earth.”
Additionally, while the new findings provide a greater understanding of our heliosphere, it will also aid scientists in exploring analogous structures called “astrospheres,” surrounding other stars throughout the galaxy.
“We know at least two cases of another star with a planetary system and an astrosphere around it, and these are the true analogs to our own solar system,” said Seth Redfield, assistant professor, Astronomy Department, Wesleyan University, in Middletown, Connecticut, also speaking at the press briefing. “The discovery of other planets coupled with our understanding of the impact these galactic cosmic rays could potentially have on planets and the emergence and evolution of life. These are connections that we haven’t explored fully, and with these new findings from IBEX, are now coming together to a very interesting topic to explore.”
IBEX is a small spacecraft, roughly the size of a card table, and is one of NASA’s low-cost missions. It is in Earth orbit, but can observe the edges of the solar system with detectors that “look” outward and collect particles called energetic neutral atoms. With data from IBEX, scientists are creating the first map of the boundary of our solar system.
These latest findings from IBEX were presented in a series of science papers appearing in the Astrophysics Journal on January 31, 2012.
“This set of papers provide many of the first direct measurements of the interstellar medium around us,” says McComas. “We’ve been trying to understand our galaxy for a long time, and with all of these observations together, we are taking a major step forward in knowing what the local part of the galaxy is like.”
A year ago, researchers from the IBEX mission – NASA’s Interstellar Boundary Explorer – announced the discovery of an unexpected bright band or ribbon of surprisingly high energy emissions at the boundary between our solar system and interstellar space. Now, after a year of observations, scientists have seen vast changes, including an unusual knot in the ribbon which appears to have ‘untied.’ Changes in the ribbon — a ‘disturbance in the force,’ so to speak, along with a shrunken heliosphere, may be allowing galactic cosmic rays to leak into our solar system. Continue reading “Mysterious Ribbon at Edge of Solar System is Changing”
Though the Cassini mission has focused intently on scientific exploration of Saturn and its moons, data taken by the spacecraft has significantly changed the way astronomers think about the shape of our Solar System. As the Sun and planets travel through space, the bubble in which they reside has been thought to resemble a comet, with a long tail and blunt nose. Recent data from Cassini combined with that of other instruments, shows that the local intertstellar magnetic field shapes the heliosphere differently.
The Solar System resides in a bubble in the interstellar medium – called the “heliosphere” – which is created by the solar wind. The shape carved out of the interstellar dust by the solar wind has been thought for the past 50 years to resemble a comet, with a long tail and blunted nose shape, caused by the motion of the Solar System through the dust.
The shape of the heliosphere was previously thought to have been carved out solely by the interaction of the solar wind particles with the interstellar medium, the resulting “drag” creating a wispy tail. The new data suggests, however, that the interstellar magnetic field slips around the heliosphere and the outer shell, called the heliosheath, leaving the spherical shape of the heliosphere intact. Below is an image representing what the heliosphere was thought to look like before the new data.
The new data also provide a much clearer indication of how thick the heliosheath is, between 40 and 50 astronomical units. This means that NASA’s Voyager spacecraft, Voyager 1 and Voyager 2, which are both traveling through the heliosheath now, will cross into interstellar space before the year 2020. Previous estimates had put that date as far back as 2030.
MIMI was originally designed to take measurements of Saturn’s magnetosphere and surrounding energetic charged particle environment. Since Cassini is far away from the Sun, though, it also places the spacecraft in a unique position to measure the energetic neutral atoms coming from the boundaries of the heliosphere. Energetic neutral atoms form when cold, neutral gas comes into contact with electrically-charged particles in a plasma cloud. The positively-charged ions in plasma can’t reclaim their own electrons, so they steal those of the cold gas atoms. The resulting particles are then neutrally charged, and able to escape the pull of magnetic fields and travel into space.
Energetic neutral atoms form in the magnetic fields around planets, but are also emitted by the interaction between the solar wind and the interstellar medium. Tom Krimigis, principal investigator of the Magnetospheric Imaging Instrument (MIMI) at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Md and his team weren’t sure if the instruments on Cassini would originally be able to detect sources of energetic neutral atoms from as far out as the heliosphere, but after their four-year study of Saturn, they looked into the data from the instrument to see if any particles had strayed in from sources outside the gas planet. To their surprise, there was enough data to complete a map of the intensity of the atoms, and discovered a belt of hot, high pressure particles where the interstellar wind flows by our heliosheath bubble.
The data from Cassini complements that taken by IBEX and the two Voyager spacecraft. The combined information from IBEX, Cassini and the Voyager missions enabled scientists to complete the picture of our little corner of space. To see a short animation of the heliosphere as mapped by Cassini, go here. The results of the combined imaging were published in Science on November 13th, 2009.
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.
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 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.
NASA’s Interstellar Boundary Explorer (IBEX) spacecraft has made the first observations of fast hydrogen atoms coming from the moon, following decades of speculation and searching for their existence. Launched last October, the IBEX has a mission to image and map the dynamic interactions caused by the hot solar wind slamming into the cold expanse of space. But as the IBEX team commissioned the spacecraft, they discovered the stream of neutral hydrogen atoms which are caused by the solar wind scattering off the moon’s surface.
The detector which made the discovery, called IBEX-Hi, was designed and built by the Southwest Research Institute and Los Alamos National Labs to measure particles moving at speeds of 0.5 million to 2.5 million miles an hour.
“Just after we got IBEX-Hi turned on, the moon happened to pass right through its field of view, and there they were,” says Dr. David J. McComas, IBEX principal investigator and assistant vice president of the SwRI Space Science and Engineering Division, where the IBEX-Hi particle detector was primarily built. “The instrument lit up with a clear signal of the neutral atoms being detected as they backscattered from the moon.”
The solar wind, the supersonic stream of charged particles that flows out from the sun, moves out into space in every direction at speeds of about a million mph. The Earth’s strong magnetic field shields our planet from the solar wind. The moon, with its relatively weak magnetic field, has no such protection, causing the solar wind to slam onto the moon’s sunward side.
From its vantage point in high earth orbit, IBEX sees about half of the moon — one quarter of it is dark and faces the nightside (away from the sun), while the other quarter faces the dayside (toward the sun). Solar wind particles impact only the dayside, where most of them are embedded in the lunar surface, while some scatter off in different directions. The scattered ones mostly become neutral atoms in this reflection process by picking up electrons from the lunar surface.
The IBEX team estimates that only about 10 percent of the solar wind ions reflect off the sunward side of the moon as neutral atoms, while the remaining 90 percent are embedded in the lunar surface. Characteristics of the lunar surface, such as dust, craters and rocks, play a role in determining the percentage of particles that become embedded and the percentage of neutral particles, as well as their direction of travel, that scatter.
McComas says the results also shed light on the “recycling” process undertaken by particles throughout the solar system and beyond. The solar wind and other charged particles impact dust and larger objects as they travel through space, where they backscatter and are reprocessed as neutral atoms. These atoms can travel long distances before they are stripped of their electrons and become ions and the complicated process begins again.
The combined scattering and neutralization processes now observed at the moon have implications for interactions with objects across the solar system, such as asteroids, Kuiper Belt objects and other moons. The plasma-surface interactions occurring within protostellar nebula, the region of space that forms around planets and stars — as well as exoplanets, planets around other stars — also can be inferred.
IBEX’s primary mission is to observe and map the complex interactions occurring at the edge of the solar system, where the million miles per hour solar wind runs into the interstellar material from the rest of the galaxy. The spacecraft carries the most sensitive neutral atom detectors ever flown in space, enabling researchers to not only measure particle energy, but also to make precise images of where they are coming from.
And the spacecraft is just getting started. Towards the end of the summer, the team will release the spacecraft’s first all-sky map showing the energetic processes occurring at the edge of the solar system. The team will not comment until the image is complete, but McComas hints, “It doesn’t look like any of the models.”
The research was published recently in the journal Geophysical Research Letters.