NASA’s Cassini, Voyager Missions Suggest New Picture of Sun’s Interaction with Galaxy

New data from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions show that the heliosphere — the bubble of the sun’s magnetic influence that surrounds the inner solar system — may be much more compact and rounded than previously thought. The image on the left shows a compact model of the heliosphere, supported by this latest data, while the image on the right shows an alternate model with an extended tail. The main difference is the new model’s lack of a trailing, comet-like tail on one side of the heliosphere. This tail is shown in the old model in light blue. Credits: Dialynas, et al. (left); NASA (right). Hi-res image

Many other stars show tails that trail behind them like a comet’s tail, supporting the idea that our solar system has one too. However, new evidence from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions suggest that the trailing end of our solar system may not be stretched out in a long tail. From top left and going counter clockwise, the stars shown are LLOrionis, BZ Cam and Mira. Credits: NASA/HST/R.Casalegno/GALEX. Hi-res image

New data from NASA’s Cassini mission, combined with measurements from the two Voyager spacecraft and NASA’s Interstellar Boundary Explorer, or IBEX, suggests that our sun and planets are surrounded by a giant, rounded system of magnetic field from the sun — calling into question the alternate view of the solar magnetic fields trailing behind the sun in the shape of a long comet tail.

The sun releases a constant outflow of magnetic solar material — called the solar wind — that fills the inner solar system, reaching far past the orbit of Neptune. This solar wind creates a bubble, some 23 billion miles across, called the heliosphere. Our entire solar system, including the heliosphere, moves through interstellar space. The prevalent picture of the heliosphere was one of comet-shaped structure, with a rounded head and an extended tail. But new data covering an entire 11-year solar activity cycle show that may not be the case: the heliosphere may be rounded on both ends, making its shape almost spherical. A paper on these results was published in Nature Astronomy on April 24, 2017.

“Instead of a prolonged, comet-like tail, this rough bubble-shape of the heliosphere is due to the strong interstellar magnetic field — much stronger than what was anticipated in the past — combined with the fact that the ratio between particle pressure and magnetic pressure inside the heliosheath is high,” said Kostas Dialynas, a space scientist at the Academy of Athens in Greece and lead author on the study.

An instrument on Cassini, which has been exploring the Saturn system over a decade, has given scientists crucial new clues about the shape of the heliosphere’s trailing end, often called the heliotail. When charged particles from the inner solar system reach the boundary of the heliosphere, they sometimes undergo a series of charge exchanges with neutral gas atoms from the interstellar medium, dropping and regaining electrons as they travel through this vast boundary region. Some of these particles are pinged back in toward the inner solar system as fast-moving neutral atoms, which can be measured by Cassini.

“The Cassini instrument was designed to image the ions that are trapped in the magnetosphere of Saturn,” said Tom Krimigis, an instrument lead on NASA’s Voyager and Cassini missions based at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, and an author on the study. “We never thought that we would see what we’re seeing and be able to image the boundaries of the heliosphere.”

Because these particles move at a small fraction of the speed of light, their journeys from the sun to the edge of the heliosphere and back again take years. So when the number of particles coming from the sun changes — usually as a result of its 11-year activity cycle — it takes years before that’s reflected in the amount of neutral atoms shooting back into the solar system.

Cassini’s new measurements of these neutral atoms revealed something unexpected — the particles coming from the tail of the heliosphere reflect the changes in the solar cycle almost exactly as fast as those coming from the nose of the heliosphere.

“If the heliosphere’s ‘tail’ is stretched out like a comet, we’d expect that the patterns of the solar cycle would show up much later in the measured neutral atoms,” said Krimigis.

But because patterns from solar activity show just as quickly in tail particles as those from the nose, that implies the tail is about the same distance from us as the nose. This means that long, comet-like tail that scientists envisioned may not exist at all — instead, the heliosphere may be nearly round and symmetrical.

A rounded heliosphere could come from a combination of factors. Data from Voyager 1 show that the interstellar magnetic field beyond the heliosphere is stronger than scientists previously thought, meaning it could interact with the solar wind at the edges of the heliosphere and compact the heliosphere’s tail.

The structure of the heliosphere plays a big role in how particles from interstellar space — called cosmic rays — reach the inner solar system, where Earth and the other planets are.

“This data that Voyager 1 and 2, Cassini and IBEX provide to the scientific community is a windfall for studying the far reaches of the solar wind,” said Arik Posner, Voyager and IBEX program scientist at NASA Headquarters in Washington, D.C., who was not involved with this study. “As we continue to gather data from the edges of the heliosphere, this data will help us better understand the interstellar boundary that helps shield the Earth environment from harmful cosmic rays.”

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By Sarah Frazier
NASA’s Goddard Space Flight Center, Greenbelt, Md. 
Editor: Rob Garner   S

Source: NASA/Sun

NASA Awards Radiation Challenge Winners, Launches Next Round to Seek Ideas for Protecting Humans on the Journey to Mars

This illustration depicts our heliosphere, showing the approximate locations of Voyager 1 and Voyager 2 spacecraft. Galactic cosmic rays originate outside the heliosphere and stream in uniformly from all directions. Image Credit: NASA

NASA awarded $12,000 to five winners of a challenge to mitigate radiation exposure on deep space missions and launched a new follow-on challenge to identify innovative ways of protecting crews on the journey to Mars.

The follow-on challenge offers an award of up to $30,000 for design ideas to protect the crew on long-duration space missions. Anyone can participate in the challenge, which will be open Wednesday, April 29 through Monday, June 29, 2015.

"We are very impressed with the enthusiasm and sheer number of people from the public who showed interest in solving this very difficult problem for human space exploration,” said Steve Rader, deputy manager of the Center of Excellence for Collaborative Innovation. "We look forward to seeing what people will come up with in this next challenge to find the optimal configuration for these different protection approaches.”

Galactic cosmic rays (GCRs), high-energy radiation that originates outside the solar system are a major issue facing future space travelers venturing beyond low-Earth orbit. These charged particles permeate the universe and exposure to them is inevitable during space exploration. Because missions to Mars will require crews to remain beyond the protection of Earth’s magnetic field and atmosphere for approximately 500 days and potentially more than 1,000 days, learning how to protect human explorers from the effect of exposure to GCRs is a high priority.

While the five winners selected in the first challenge did not identify a solution that ultimately solves the problem of GCR risk to human crews, the first place idea did provide a novel approach to using and configuring known methods of protection to save substantial launch mass and lower launch costs over multiple missions. The other winning submissions all provided solid proposed configurations on known approaches and were supported with sound engineering and mathematics.

NASA received 136 submissions. The five selected winners are:

• 1st place ($5,000): George Hitt, assistant professor of Physics and Nuclear Engineering at Khalifa University, United Arab Emirates, for his novel idea on reusing a shield that could be placed in a Mars Transfer Orbit.
• 2nd Place ($3,000): Ian Gallon, retired researcher in electro-magnetics of Bridport, England, for his mathematical details on what it would take for an active radiation mitigation system to function well.
• 3rd Place ($2,000): Olivier Loido, freelance engineer of Toulouse, France, for his concepts for a launch configuration and deploying an array of magnets.
• 4th Place ($1,000 each): Markus Novak, recent graduate from Ohio State University of Dublin, Ohio, for his creation of safe areas through particle trajectory simulations, and Mikhail Petrichenkov of Russia for his concept of operations making use of NASA Storm Shelter work.

NASA’s goal is to identify key solutions that will reduce crew members’ total radiation dose from exposure to GCRs on long duration deep space missions by at least a factor of four.

In a continued effort to achieve that goal, the agency has developed a second challenge that asks the public for ideas on optimal configurations of active and passive solutions to provide crew members maximum protection. Active protection uses magnetic or electrostatic fields to deflect the harmful radiation, while passive protection uses material layering to shield the crew from the GCRs.

These challenges are managed by the Center of Excellence for Collaborative Innovation (CoECI). CoECI is a multi-center organization established at the request of the White House Office of Science and Technology Policy to advance NASA’s open innovation efforts and extend that expertise to other federal agencies.

CoECI is directly supported by the Human Health and Performance Directorate at NASA’s Johnson Space Center in Houston. The challenges are hosted on the NASA Innovation Pavilion through its contract with InnoCentive, Inc.

To participate in the challenge beginning April 29, visit: https://www.innocentive.com/pavilion/NASA

For additional information about the galactic cosmic ray challenges, visit: http://go.nasa.gov/1Es4AgJ

Stephanie Schierholz
Headquarters, Washington
202-358-1100
stephanie.schierholz@nasa.gov

'Pale Blue Dot' Images Turn 25

These six narrow-angle color images were made from the first ever "portrait" of the solar system taken by Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. Image credit: NASA/JPL-Caltech.  › Full image and caption

 

The cameras of Voyager 1 on Feb. 14, 1990, pointed back toward the sun and took a series of pictures of the sun and the planets, making the first ever "portrait" of our solar system as seen from the outside. Image credit: NASA/JPL-Caltech.  › Full image and caption

 

This narrow-angle color image of the Earth, dubbed "Pale Blue Dot," is a part of the first ever "portrait" of the solar system taken by Voyager 1. Image credit: NASA/JPL-Caltech. › Full image and caption

Valentine's Day is special for NASA's Voyager mission. It was on Feb. 14, 1990, that the Voyager 1 spacecraft looked back at our solar system and snapped the first-ever pictures of the planets from its perch at that time beyond Neptune.

This "family portrait" captures Neptune, Uranus, Saturn, Jupiter, Earth and Venus from Voyager 1's unique vantage point. A few key members did not make it in: Mars had little sunlight, Mercury was too close to the sun, and dwarf planet Pluto turned out too dim. 

Taking these images was not part of the original plan, but the late Carl Sagan, a member of the Voyager imaging team at the time, had the idea of pointing the spacecraft back toward its home for a last look. The title of his 1994 book, "Pale Blue Dot," refers to the image of Earth in this series.

"Twenty-five years ago, Voyager 1 looked back toward Earth and saw a 'pale blue dot,' " an image that continues to inspire wonderment about the spot we call home," said Ed Stone, project scientist for the Voyager mission, based at the California Institute of Technology, Pasadena. 

The image of Earth contains scattered light that resembles a beam of sunlight, which is an artifact of the camera itself that makes the tiny Earth appear even more dramatic. Voyager 1 was 40 astronomical units from the sun at this moment. One astronomical unit is 93 million miles, or 150 million kilometers.

These family portrait images are the last that Voyager 1, which launched in 1977, returned to Earth. Mission specialists subsequently turned the camera off so that the computer controlling it could be repurposed. The spacecraft is still operating, but no longer has the capability to take images. 

"After taking these images in 1990, we began our interstellar mission. We had no idea how long the spacecraft would last," Stone said.

Today, Voyager 1, at a distance of 130 astronomical units, is the farthest human-made object from Earth, and it still regularly communicates with our planet. In August 2012, the spacecraft entered interstellar space - the space between the stars -- and has been delivering data about this uncharted territory ever since. Its twin, Voyager 2, also launched in 1977, is also journeying toward interstellar space. 

Voyager 1 is more than three times farther from Earth than it was on Valentine's Day 25 years ago. Today, Earth would appear about 10 times dimmer from Voyager's vantage point.

Sagan wrote in his "Pale Blue Dot" book: "That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. ... There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world."

A video clip of Ann Druyan, Carl Sagan's co-author and widow, discussing the pale blue dot image, is available at:  http://www.jpl.nasa.gov/video/details.php?id=1363

NASA's Jet Propulsion Laboratory, Pasadena, California, built and operates the twin Voyager spacecraft. The Voyagers Interstellar Mission is a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's Science Mission Directorate in Washington.

For more information about Voyager, visit: http://voyager.jpl.nasa.gov

Media Contact

Elizabeth Landau
NASA's Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
Elizabeth.Landau@jpl.nasa.gov

 

 

  Source: JPL-Caltech/News

NASA's Voyager Hits New Region at Solar System Edge

Artist concept of Voyager 1 encountering a stagnation region
Full image and caption

PASADENA, Calif. -- NASA's Voyager 1 spacecraft has entered a new region between our solar system and interstellar space. Data obtained from Voyager over the last year reveal this new region to be a kind of cosmic purgatory. In it, the wind of charged particles streaming out from our sun has calmed, our solar system's magnetic field is piled up, and higher-energy particles from inside our solar system appear to be leaking out into interstellar space.

"Voyager tells us now that we're in a stagnation region in the outermost layer of the bubble around our solar system," said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. "Voyager is showing that what is outside is pushing back. We shouldn't have long to wait to find out what the space between stars is really like."

Although Voyager 1 is about 11 billion miles (18 billion kilometers) from the sun, it is not yet in interstellar space. In the latest data, the direction of the magnetic field lines has not changed, indicating Voyager is still within the heliosphere, the bubble of charged particles the sun blows around itself. The data do not reveal exactly when Voyager 1 will make it past the edge of the solar atmosphere into interstellar space, but suggest it will be in a few months to a few years.

The latest findings, described today at the American Geophysical Union's fall meeting in San Francisco, come from Voyager's Low Energy Charged Particle instrument, Cosmic Ray Subsystem and Magnetometer.

Scientists previously reported the outward speed of the solar wind had diminished to zero in April 2010, marking the start of the new region. Mission managers rolled the spacecraft several times this spring and summer to help scientists discern whether the solar wind was blowing strongly in another direction. It was not. Voyager 1 is plying the celestial seas in a region similar to Earth's doldrums, where there is very little wind.

During this past year, Voyager's magnetometer also detected a doubling in the intensity of the magnetic field in the stagnation region. Like cars piling up at a clogged freeway off-ramp, the increased intensity of the magnetic field shows that inward pressure from interstellar space is compacting it.

Voyager has been measuring energetic particles that originate from inside and outside our solar system. Until mid-2010, the intensity of particles originating from inside our solar system had been holding steady. But during the past year, the intensity of these energetic particles has been declining, as though they are leaking out into interstellar space. The particles are now half as abundant as they were during the previous five years.

At the same time, Voyager has detected a 100-fold increase in the intensity of high-energy electrons from elsewhere in the galaxy diffusing into our solar system from outside, which is another indication of the approaching boundary.

"We've been using the flow of energetic charged particles at Voyager 1 as a kind of wind sock to estimate the solar wind velocity," said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "We've found that the wind speeds are low in this region and gust erratically. For the first time, the wind even blows back at us. We are evidently traveling in completely new territory. Scientists had suggested previously that there might be a stagnation layer, but we weren't sure it existed until now."

Launched in 1977, Voyager 1 and 2 are in good health. Voyager 2 is 9 billion miles (15 billion kilometers) away from the sun.

The Voyager spacecraft were built by NASA's Jet Propulsion Laboratory in Pasadena, Calif., which continues to operate both. JPL is a division of the California Institute of Technology. The Voyager missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate in Washington. For more information about the Voyager spacecraft, visit: http://www.nasa.gov/voyager .

For more information about NASA media events at the American Geophysical Union meeting, visit: http://www.nasa.gov/agu .

Jia-Rui C. Cook/Alan Buis 818-354-0850/818-653-8339
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov/alan.d.buis@jpl.nasa.gov

Steve Cole 202-358-0918
NASA Headquarters, Washington
stephen.e.cole@nasa.gov