Voyager 1 Has Outdistanced the Solar Wind

Voyager 1 Mission


The venerable Voyager spacecraft are truly going where no one has gone before. Voyager 1 has now reached a distant point at the edge of our solar system where it is no longer detecting the solar wind. At a distance of about 17.3 billion km (10.8 billion miles) from the Sun, Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the sun has slowed to zero. Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars.

“The solar wind has turned the corner,” said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. “Voyager 1 is getting close to interstellar space.”

The event is a major milestone in Voyager 1’s passage through the heliosheath, the turbulent outer shell of the sun’s sphere of influence, and the spacecraft’s upcoming departure from our solar system.

Since its launch on Sept. 5, 1977, Voyager 1’s Low-Energy Charged Particle Instrument has been used to measure the solar wind’s velocity.

When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft’s speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 10.6 billion miles from the sun.

However, velocities can fluctuate, so the scientists watched four more monthly readings before they were convinced the solar wind’s outward speed actually had slowed to zero. Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 45,000 mph each year since August 2007, when the solar wind was speeding outward at about 130,000 mph. The outward speed has remained at zero since June.

“When I realized that we were getting solid zeroes, I was amazed,” said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again.”

Scientists believe Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles. Scientists are putting the data into their models of the heliosphere’s structure and should be able to better estimate when Voyager 1 will reach interstellar space. Researchers currently estimate Voyager 1 will cross that frontier in about four years.

Our sun gives off a stream of charged particles that form a bubble known as the heliosphere around our solar system. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the solar wind dramatically slows down and heats up in the heliosheath.

A sister spacecraft, Voyager 2, was launched in Aug. 20, 1977 and has reached a position 8.8 billion miles from the sun. Both spacecraft have been traveling along different trajectories and at different speeds. Voyager 1 is traveling faster, at a speed of about 38,000 mph, compared to Voyager 2’s velocity of 35,000 mph. In the next few years, scientists expect Voyager 2 to encounter the same kind of phenomenon as Voyager 1.

The results were presented at the American Geophysical Union meeting in San Francisco.

Source: NASA

Moon’s Mini-Magnetosphere

Many objects in the solar system have strong magnetic fields which deflect the charged particles of the solar wind, creating a bubble known as the magnetosphere. On Earth, this protects us from some of the more harmful solar rays and diverts them to create beautiful aurorae. Similar displays have been found to occur on the gas giants. However, many other objects in our solar system lack the ability to produce these effects, either because they don’t have a strong magnetic field (such as Venus), or an atmosphere with which the charged particles can interact (such as Mercury).

Although the moon lacks both of these, a new study has found that the moon may still produce localized “mini-magnetospheres”. The team responsible for this discovery is an international team composed of astronomers from Sweden, India, Switzerland, and Japan. It is based on observations from the Chandrayaan-1 spacecraft produced and launched by the Indian Space Research Organisation (ISRO).

Using this satellite, the team was mapping the density of backscattered hydrogen atoms that come from solar wind striking the surface and being reflected. Under normal conditions, 16-20% of incoming protons from the solar wind is reflected in this way.

For those excited above 150 electron volts, the team found a region near the Crisium antipode (the region directly opposite the Mare Crisium on the moon). This region was previously discovered to have magnetic anomalies in which the local magnetic field strength reached several hundred nanotesla. The new team found that the result of this was that incoming solar wind was deflected, creating a shielded region some 360 km in diameter surrounded by a “300-km-thick region of enhanced plasma flux that results from the solar wind flowing 23 around the mini-magnetosphere.” Although the flow bunches up, the team finds that the lack of a distinct boundary means that there is not likely to be a bow shock, which would be created as the buildup becomes sufficiently strong to directly interact with additional incoming particles.

Below energies of 100 eV, the phenomenon seems to disappear. The researchers suggest this points to a different formation mechanism. One possibility is that some solar flux breaks through the magnetic barrier and is reflected creating these energies. Another is that, instead of hydrogen nuclei (which composes the majority of the solar wind) this is the product of alpha particles (helium nuclei) or other heavier solar wind ions striking the surface.

Not discussed in the paper is just how valuable such features could be to future astronauts looking to create a base on the moon. While the field is relatively strong for local magnetic fields, it it still around two orders of magnitude weaker than that of Earth’s. Thus, it is unlikely that this effect would be sufficiently strong to protect a base, nor would it provide protection from the x-rays and other dangerous electromagnetic radiation that is provided by an atmosphere.

Instead, this finding poses more in the way of scientific curiosity and can help astronomers map local magnetic fields as well as investigate the solar wind if such mini-magnetospheres are located on other bodies. The authors suggest that similar features be searched for on Mercury and asteroids.

Astronomy Without A Telescope – A Universe Free Of Charge?


If there were equal amounts of matter and anti-matter in the universe, it would be easy to deduce that the universe has a net charge of zero, since a defining ‘opposite’ of matter and anti-matter is charge. So if a particle has charge, its anti-particle will have an equal but opposite charge. For example, protons have a positive charge – while anti-protons have a negative charge.

But it’s not apparent that there is a lot of anti-matter around as neither the cosmic microwave background, nor the more contemporary universe contain evidence of annihilation borders – where contact between regions of large scale matter and large scale anti-matter should produce bright outbursts of gamma rays.

So, since we do apparently live in a matter-dominated universe – the question of whether the universe has a net charge of zero is an open question.

It’s reasonable to assume that dark matter has either a net zero charge – or just no charge at all – simply because it is dark. Charged particles and larger objects like stars with dynamic mixtures of positive and negative charges, produce electromagnetic fields and electromagnetic radiation.

So, perhaps we can constrain the question of whether the universe has a net charge of zero to just asking whether the total sum of all non-dark matter has. We know that most cold, static matter – that is in an atomic, rather than a plasma, form – should have a net charge of zero, since atoms have equal numbers of positively charged protons and negatively charged electrons.

Stars composed of hot plasma might also be assumed to have a net charge of zero, since they are the product of accreted cold, atomic material which has been compressed and heated to create a plasma of dissociated nuclei (+ve) and electrons (-ve).

The principle of charge conservation (which is accredited to Benjamin Franklin) has it that the amount of charge in a system is always conserved, so that the amount flowing in will equal the amount flowing out.

Apollo 15's Lunar Surface Experiments Package (ALSEP). The Moon represents a good vantage point to measure the balance of incoming cosmic rays versus outgoing solar wind.

An experiment which has been suggested to enable measurement of the net charge of the universe, involves looking at the solar system as a charge-conserving system, where the amount flowing in is carried by charged particles in cosmic rays – while the amount flowing out is carried by charged particles in the Sun’s solar wind.

If we then look at a cool, solid object like the Moon, which has no magnetic field or atmosphere to deflect charged particles, it should be possible to estimate the net contribution of charge delivered by cosmic rays and by solar wind. And when the Moon is shadowed by the tail of the Earth’s magnetosphere, it should be possible to detect the flux attributable to just cosmic rays – which should represent the charge status of the wider universe.

Drawing on data collected from sources including Apollo surface experiments, the Solar and Heliospheric Observatory (SOHO), the WIND spacecraft and the Alpha Magnetic Spectrometer flown on a space shuttle (STS 91), the surprising finding is a net overbalance of positive charges arriving from deep space, implying that there is an overall charge imbalance in the cosmos.

Either that or a negative charge flux occurs at energy levels lower than the threshold of measurement that was achievable in this study. So perhaps this study is a bit inconclusive, but the question of whether the universe has a net charge of zero still remains an open question.

Further reading: Simon, M.J. and Ulbricht, J. (2010) Generating an electrical potential on the Moon by cosmic rays and solar wind?

What is the Aurora Australis?

Aurora australis (also known as the southern lights, and southern polar lights) is the southern hemisphere counterpart to the aurora borealis. In the sky, an aurora australis takes the shape of a curtain of light, or a sheet, or a diffuse glow; it most often is green, sometimes red, and occasionally other colors too.

Like its northern sibling, the aurora australis is strongest in an oval centered on the south magnetic pole. This is because they are the result of collisions between energetic electrons (sometimes also protons) and atoms and molecules in the upper atmosphere … and the electrons get their high energies by being accelerated by solar wind magnetic fields and the Earth’s magnetic field (the motions are complicated, but essentially the electrons spiral around the Earth’s magnetic field lines and ‘touch down’ near to where those lines become vertical).

So by far the best place to see aurorae in the southern hemisphere is Antarctica! Oh, and at night too. When the solar cycle is near its maximum, aurora australis are sometimes visible in New Zealand (especially the South Island), southern Australia (especially Tasmania), and southern Chile and Argentina (sometimes in South Africa too).

About the colors: the physics is similar to what make a flame orange-yellow when salt is added to it (i.e. specific atomic transitions in sodium atoms); green and red come from atomic oxygen; nitrogen ions and molecules make some pinkish-reds and blue-violet; and so on.

How high are aurorae? Typically 100 to 300 km (this is where green is usually seen, with red at the top), but sometimes as high as 500 km, and as low as 80 km (this requires particularly energetic particles, to penetrate so deep; if you see purple, the aurora is likely to be this low).

There’s a good aurora FAQ at this University of Alaska Fairbanks’ Geophysical Institute site (though it, naturally, concentrates on the borealis!).

Aurorae on other planets? Well, as there are strong magnetic fields plus (not so strong) solar wind plus (really deep) atmosphere on Jupiter and Saturn, they have spectacular aurorae, in rings around their magnetic poles (which are closer to their rotation poles than Earth’s are). Aurorae have also been imaged on Venus, Mars, Uranus, Neptune, and even Io (atmosphere? solar wind? magnetic fields? sure, but very different than on planets).

Some Universe Today stories on aurorae: Aurora Australis at the South Pole, Aurora Reports from Around the World, Northern & Southern Aurorae Are Siblings, But Not Twins, Chandra Looks at the Earth’s Aurora, First Aurora Seen on Mars, and Saturn’s “Dualing” Aurorae.

What is the Aurora Borealis?

The aurora (plural aurorae) borealis has many other names: northern lights, northern polar lights, polar lights, and more. An aurora borealis is light seen in the sky, nearly always at night, in the northern hemisphere, commonly green but also red and (rarely) other colors; often in the shape of curtains, sheets, or a diffuse glow (when seen from the ground). Northern lights are most often seen at high latitudes – Alaska, Canada, northern Scandinavia, Greenland, Siberia, and Iceland – and during maxima in the solar cycle.

Aurora australis – southern lights – is the corresponding southern hemisphere phenomenon.

Seeing a bright auroral display may be on your list of ‘things to see before I die’! Yep, they are nature’s light show par excellence.

Aurora borealis occur in the Earth’s ionosphere, and result from collisions between energetic electrons (sometimes also protons, and even heavier charged particles) and atoms and molecules in the upper atmosphere. The ultimate origin of the energy which powers the aurora borealis is the Sun – via the solar wind – and the Earth’s magnetic field. Interactions between the solar wind (which carries its own tangled magnetic fields) and the Earth’s magnetic field may cause electrons (and other particles) to be trapped and accelerated; those particles which do not escape ‘downstream’ to the magnetic tail ‘touch down’ in the atmosphere, close to the north magnetic pole.

The different colors come from different atoms or ions; green and red from atomic oxygen, nitrogen ions and molecules make some pinkish-reds and blue-violet; purple is the appearance of combined colors from nitrogen ions and helium; neon produces the very rare orange. The ionosphere is home to most aurorae borealis, with 100-300 km being typical (this is where green is usually seen, with red at the top); however, some particularly energetic particles penetrate much deeper into the atmosphere, down to perhaps 80 km or lower (purple often comes from here).

Viewed from space, when the northern lights are intense they appear as a ring (an oval actually), the auroral zone, with the north magnetic pole near the center.

The University of Alaska Fairbanks’ Geophysical Institute has a good FAQ on the aurora borealis.

Magnetic fields plus solar wind … so you’d expect aurorae on Jupiter and Saturn, right? And auroral displays around the magnetic poles of these planets are now well documented. Aurorae have also been imaged on Venus, Mars, Uranus, Neptune, and even Io.

Some Universe Today stories on aurorae – borealis, australis, … and extra-terrestrial: What are the Northern Lights?, Aurora Reports from Around the World, Behind the Power and Beauty of the Northern Lights, Northern & Southern Aurorae Are Siblings, But Not Twins, Two Rockets Fly Through Auroral Arc, Chandra Looks at the Earth’s Aurora, First Aurora Seen on Mars, and Saturn’s “Dualing” Aurorae.

NASA IBEX Spacecraft Detects Neutral Hydrogen Bouncing Off Moon


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.

Source: Southwest Research Institute

Branson Wants to Fly Space Tourists into the Northern Lights


For his next big plan for the private space industry, Richard Branson is thinking up new ways to excite affluent space tourists: flying them into the biggest lightshow on Earth, the Aurora Borealis. Although the New Mexico Virgin Galactic Spaceport isn’t scheduled for completion until 2010, the British entrepreneur is already planning his next project intended for cruises into the spectacular space phenomenon from an Arctic launchpad.

Located in the far north of Sweden (in the Lapland province), the small town of Kiruna has a long history of space observation and rocket launches. The Arctic location provides the town with unrivalled views of the Aurora Borealis as it erupts overhead. The Auroral lightshow is generated by atmospheric reactions to impacting solar wind particles as they channel along the Earth’s magnetic field and down into the thickening atmospheric gases.

Once a view exclusive only to sounding rockets, this awe inspiring sight may in the future be seen from the inside, and above, by fee-paying space tourists as they are launched into space from a new spaceport, on the site of an existing base called Esrange. Although launching humans into an active aurora holds little scientific interest (if it did, it would have probably been done by now), it does pose some prudent health and safety questions. As Dr Olle Norberg, Esrange’s director, confidently states: “Is there a build-up of charge on the spacecraft? What is the radiation dose that you would receive? Those studies came out saying it is safe to do this.” Phew, that’s a relief.

The chance to actually be inside this magnificent display of light will be an incredible selling point for Virgin Galactic and their SpaceShipTwo flights. As if going into space were not enough, you can see and fly through the atmosphere at it’s most magnificent too.

Source: The Guardian Unlimited

SoHO Celebrates its 12th Birthday


On December 2nd, 1995 a large joint ESA and NASA mission was launched to gain an insight to the dynamics of the Sun and its relationship with the space between the planets. 12 years on, the Solar and Heliospheric Observatory (SoHO) continues to witness some of the largest explosions ever seen in the solar system, observes beautiful magnetic coronal arcs reach out into space and tracks comets as they fall to a fiery death. In the line of duty, SoHO even suffered a near-fatal shutdown (in 1998). As far as astronomy goes, this is a tough assignment.

By the end of 1996, SoHO had arrived at the First Lagrange Point between the Earth and the Sun (a gravitationally stable position balanced by the masses of the Sun and Earth, about 1.5 million km away) and orbits this silent outpost to this day. It began to transmit data at “solar minimum”, a period of time at the beginning of the Solar Cycle, where sunspots are few and solar activity is low, and continues toward the upcoming solar minimum after the exciting firworks of the last “solar maximum”. This gives physicists another chance to observe the majority of a Solar Cycle with a single observatory (the previous long-lasting mission was the Japanese Yohkoh satellite from 1991-2001).

On board this ambitious observatory, 11 instruments constantly gaze at the Sun, observing everything from solar oscillations (“Sun Quakes�), coronal loops, flares, CMEs and the solar wind; just about everything the Sun does. SoHO has become an indispensable mission for helping us to understand how the Sun influences the environment around our planet and how this generates the potentially dangerous “Space Weather�.

The SoHO mission site confidently states that SoHO will remain in operation far into the next Solar Cycle. I hope this is the case as the new Hinode and STEREO probes will be good company for this historic mission.

Source: NASA News Release