Solar Astronomy Archives

April 29, 2009December 24, 2015 by Anne Minard

European, Chinese Satellites Watch Solar Storms Pummel Earth

Scientists have long understood that satellites are at risk from bombardment by solar storms. Now, they’ve gotten a closer look at how the storms are punishing Earth’s magnetosphere, leaving satellites exposed.

The movie above, and the solar flare video below, were released by the European Space Agency today, along with descriptions of two solar eruptions spotted using ESA’s four Cluster satellites and the two Chinese/ESA Double Star satellites.

High-energy (X-3) solar flare on 13 December 2006. Credit: ESA/NASA/SOHO

Under normal solar conditions, satellites orbit within the magnetosphere — the protective magnetic bubble carved out by Earth’s magnetic field. But when solar activity increases, the picture changes significantly: the magnetosphere gets compressed and particles get energized, exposing satellites to higher doses of radiation that can perturb signal reception.

Scientists have found that extreme solar activity drastically compresses the magnetosphere and modifies the composition of ions in the near-Earth environment. They are now challenged to model how these changes affect orbiting satellites, including the GPS system.

During two extreme solar explosions, or solar flares, on January 21, 2005 and December 13, 2006, the Cluster constellation and the two Double Star satellites were favorably positioned to observe the events on a large scale.

During both events, the velocity of positively charged particles in the solar wind was found to be higher than 900 km (559 miles) per second, more than twice their normal speed. In addition, the density of charged particles around Earth was recorded at five times higher than normal. The measurements taken in January 2005 also showed a drastic change in ion composition.

The second explosion in December 2006 released extremely powerful high-energy X-rays followed by a huge amount of mass from the solar atmosphere (called a coronal mass ejection). During the event, GPS signal reception on ground was lost.

Typical nose-like ion structures in near-Earth space were washed out as energetic particles were injected into the magnetosphere. These nose-like structures, that had formed earlier in the ‘ring current’ in the equatorial region near Earth, were detected simultaneously on opposite sides of Earth. Measurements of the ring current showed that its strength had increased.

These factors together caused the magnetosphere to be compressed. Data show that the ‘nose’ of the dayside magnetopause (the outer boundary of the magnetosphere), usually located about 60,000 km (40,000 miles) from Earth, was only 25,000 km (15,000 miles) away.

About five hours after the coronal mass ejection hit Earth’s magnetosphere, a Double Star satellite observed penetrating solar energetic particles on the night side. These particles are hazardous to astronauts as well as satellites.

“With these detailed observations, we’ll be able to plug in data and better estimate what happens to the inner magnetosphere and near-Earth space during such explosions on the Sun,” said Iannis Dandouras, principal investigator of the Cluster Ion Spectrometer and lead author on a paper about the findings.

“Looking at such a large-scale physical phenomena with a single satellite is akin to predicting the impact of a tsunami with a single buoy,” added Matt Taylor, ESA’s Project Scientist for Cluster and Double Star. “With Cluster and Double Star we have monitored both sides of Earth simultaneously, and obtained valuable in-situ data.”

The results appear in the February 2009) issue of Advances in Space Research. The abstract is available here.

Source: ESA

April 23, 2009December 24, 2015 by Nancy Atkinson

New Finding Shows Super-Huge Space Tornados Power the Auroras

Space tornadoes span a volume approximately the size of Earth or larger. Credit: Keiling, Glassmeier and Amm

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If you think tornadoes on Earth are scary, newly found “space tornadoes” sound downright horrifying. But they are likely the power source behind the beautiful Northern and Southern Lights. A new finding by a cluster of five space probes – the THEMIS, or Time History of Events and Macroscale Interactions during Substorms show that electrical funnels which span a volume as large as Earth produce electrical currents exceeding 100,000 amperes. THEMIS recorded the extent and power of these electrical funnels as the probes passed through them during their orbit of Earth. Ground measurements showed that the space tornadoes channel the electrical current into the ionosphere to spark bright and colorful auroras on Earth.

Space tornadoes are rotating plasmas of hot, ionized gas flowing at speeds of more than a million miles per hour, far faster than the 200 m.p.h. winds of terrestrial tornadoes, according to Andreas Keiling, a research space physicist at the University of California, Berkeley’s Space Sciences Laboratory.

Keiling works on THEMIS, which was built and is now operated by UC Berkeley. The five space probes were launched by NASA in February 2007 to solve a decades-long mystery about the origin of magnetic storms that power the Northern and Southern Lights.

Electric currents in the funnels power auroras. Credit: Keiling, Glassmeier, and Amm

Both terrestrial and space tornadoes consist of funnel-shaped structures. Space tornadoes, however, generate huge amounts of electrical currents inside the funnel. These currents flow along twisted magnetic field lines from space into the ionosphere where they power several processes, most notably bright auroras such as the Northern Lights, Keiling said.

While these intense currents do not cause any direct harm to humans, on the ground they can damage man-made structures, such as power transformers.

The THEMIS spacecraft observed these tornadoes, or “flow vortices,” at a distance of about 40,000 miles from Earth. Simultaneous measurements by THEMIS ground observatories confirmed the tornadoes’ connection to the ionosphere.

Keiling’s colleagues include Karl-Heinz Glassmeier of the Institute for Geophysics and Extraterrestrial Physics (IGEP, TU) in Braunschweig, Germany, and Olaf Amm of the Finnish Meteorological Institute.

The findings were presented today at the general assembly of the European Geosciences Union (EGU) in Vienna, Austria.

Source: EGU

April 20, 2009December 24, 2015 by Nancy Atkinson

Solar Sigmoids Explained

This figure shows the time evolution and final eruption of the sigmoid. Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)

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S-shaped structures called ‘Sigmoids’ have been found in the outer atmosphere of the Sun — the corona. Sigmoids are thought to be a crucial part of explosive events like solar flares. Now a group of astronomers have developed the first model to reproduce and explain the nature of the different stages of a sigmoid’s life. Recently, the X-Ray Telescope (XRT) on board the Hinode space mission was used to obtain the first images of the formation and eruption phase of a sigmoid at high resolution. These observations revealed sigmoids have very complex structures.

Professor Alan Hood and Dr. Vasilis Archontis, both from the Mathematical Institute at St. Andrews University, Scotland, presented their team’s findings today at the European Week of Astronomy and Space Science conference at the University of Hertfordshire.
Over the years a series of theoretical and numerical models have been proposed to explain the nature of sigmoids but until now there was no explanation on how such complex structures form, erupt and fade away. The new model describes how sigmoids consist of many thin and twisted layers (or ribbons) of strong electric current. When these layers interact it leads to the formation of the observed powerful flares and the eruption of strong magnetic fields which carry highly energetic particles into interplanetary space. The team also found that as the sigmoids die out, they produce a ‘flare’ eruption.

Dr. Archontis sees the connection between the two astronomers’ model and work on predicting solar flares. He remarks, “Sigmoids work as ‘mangers’ or ‘cocoons’ for solar eruptions. There is a high probability that they will result in powerful eruptions and other explosive events. Our model helps scientists understand how this happens.”

Prof. Hood adds that these events have real significance for life on Earth, “Sigmoids are among the most interesting features for scientists trying to forecast the solar eruptions – events that can disrupt telecommunications, damage satellites and affect the way navigation systems are operated’.

Explanation of image: This figure shows the time evolution and final eruption of the sigmoid. It consists of three columns (time is running from top to bottom). Columns 1 and 2 show results from numerical experiments. The yellow isosurfaces are surfaces of electric current (left panels). Column 2 (middle panels) shows temperature. Column 3 shows ‘temperature’ (intensity) as it is recorded by the observations (Hinode mission). Notice that the agreement on the shape of the sigmoid, internal structure and thermal distribution along the sigmoid, between numerical experiments and observations is very good and fairly balanced. Notice, that even the ‘flaring’ episode (flashing) at the middle of the sigmoid at the down-right snapshot from observations is reproduced exceptionally well by our numerical experiments (down-middle). Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)

Source: RAS

April 14, 2009December 24, 2015 by Nancy Atkinson

The Anatomy of a Solar Explosion in 3-D

STEREO-A viewing a coronal mass ejection leaving the sun between December 12-13, 2008. Credit: NASA

Wouldn’t it be great if solar physicists could predict sun storms just like meteorologist predict hurricanes? Well, now perhaps they can. NASA’s twin STEREO observatories have made the first 3-D measurements of solar explosions, known as coronal mass ejections (CMEs), allowing scientists to see their size and shape, and image them as they travel approximately 93 million miles from the sun to Earth. With STEREO, scientists can now capture images of solar storms and make real-time measurements of their magnetic fields, much the same way that satellites allow forecasters to see the development of a hurricane. Eruptions from the sun’s outer atmosphere, or corona, can wreak havoc on satellites (and astronauts) in orbit or induce large currents in power grids on Earth, which can cause power disruptions or black outs.

“We can now see a CME from the time it leaves the solar surface until it reaches Earth, and we can reconstruct the event in 3D directly from the images,” said Angelos Vourlidas, a solar physicist at the Naval Research Laboratory, Washington, and project scientist for the Sun Earth Connection Coronal and Heliospheric Investigation aboard STEREO. In the video above, see some of the 3-D imagery, and hear Vourlidas talk about about the new findings.

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CMEs spew billions of tons of plasma into space at thousands of miles per hour and carry some of the sun’s magnetic field with it. These solar storm clouds create a shock wave and a large, moving disturbance in the solar system. The shock can accelerate some of the particles in space to high energies, a form of “solar cosmic rays” that can be hazardous to spacecraft and astronauts. The CME material, which arrives days later, can disrupt Earth’s magnetic field, or magnetosphere, and upper atmosphere.

STEREO consists of two nearly identical observatories that make simultaneous observations of CMEs from two different vantage points. One observatory ‘leads’ Earth in its orbit around the sun, while the other observatory ‘trails’ the planet. STEREO’s two vantage points provide a unique view of the anatomy of a solar storm as it evolves and travels toward Earth. Once the CME arrives at the orbit of Earth, sensors on the satellites take in situ measurements of the solar storm cloud, providing a “ground truth” between what was seen at a distance and what is real inside the CME.

The combination is providing solar physicists with the most complete understanding to date of the inner workings of these storms. It also represents a big step toward predicting when and how the impact will be felt at Earth. The separation angle between the satellites affords researchers to track a CME in three dimensions, something they have done several times in the past few years as they have learned to use this new space weather tool.

Visualization of a coronal mass ejection event on December 12-13, 2008 as seen simultaneously by the two STEREO spacecraft. The images on the right were taken by STEREO-A, while the images on the left were taken by STEREO-B. The images were taken by the COR2 telescopes on STEREO’s SECCHI instrument suite. Credit: NASA

“The in situ measurements from STEREO and other near-Earth spacecraft link the physical properties of the escaping CME to the remote images,” said Antoinette “Toni” Galvin, a solar physicist at the University of New Hampshire, and the principal investigator on STEREO’s Plasma and Suprathermal Ion Composition (PLASTIC) instrument. “This helps us to understand how the internal structure of the CME was formed and to better predict its impact on Earth.”

Until now, CMEs could be imaged near the sun but the next measurements had to wait until the CME cloud arrived at Earth three to seven days later. STEREO’s real-time images and measurements give scientists a slew of information—speed, direction, and velocity—of a CME days sooner than with previous methods. As a result, more time is available for power companies and satellite operators to prepare for potentially damaging solar storms.

Much like a hurricane’s destructive force depends on its direction, size, and speed, the seriousness of a CME’s effects depends on its size and speed, as well as whether it makes a direct or oblique hit across Earth’s orbit.

CMEs disturb the space dominated by Earth’s magnetic field. Disruptions to the magnetosphere can trigger the brightly colored, dancing lights known as auroras, or Northern and Southern Lights. While these displays are harmless, they indicate that Earth’s upper atmosphere and ionosphere are in turmoil.

Sun storms can interfere with communications between ground stations and satellites, airplane pilots, and astronauts. Radio noise from a storm can also disrupt cell phone service. Disturbances in the ionosphere caused by CMEs can distort the accuracy of Global Positioning System (GPS) navigation and, in extreme cases, induce stray electrical currents in long cables and power transformers on the ground.

The twin STEREO spacecraft were launched October 25, 2006, into Earth’s orbit around the sun.

Sources: NASA, APL

April 2, 2009December 24, 2015 by Nancy Atkinson

Where Are All the Sunspots?

The Michelson Doppler Imager on SOHO captured this white light continuum image of the spotless sun on March 31, 2009. Credit: SOHO, NASA/ESA.

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There’s not a lot happening on the sun these days, at least in the sunspot department. “We’re experiencing a very deep solar minimum,” says solar physicist Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, Md. In 2008, no sunspots were observed on 266 of the year’s 366 days (73 percent). Sunspot counts for 2009 have dropped even lower, percentage-wise. As of March 31st, there were no sunspots on 78 of the year’s 90 days (87 percent). Those who keep an eye on the sun say this is the quietest sun in almost a century. So, what does this all mean?

Sunspots are planet-sized islands of magnetism on the surface of the sun, and they are sources of solar flares, coronal mass ejections, and intense UV radiation. The sun has a natural cycle of about 11 years of high and low sunspot activity. This was discovered by German astronomer Heinrich Schwabe in the mid-1800s. Plotting sunspot counts, Schwabe saw that peaks of solar activity were always followed by valleys of relative calm—a clockwork pattern that has held true for more than 200 years.

The current solar minimum is part of that pattern. In fact, it’s right on time. But is it supposed to be this quiet?

The sunspot cycle from 1995 to the present. The jagged curve traces actual sunspot counts. Smooth curves are fits to the data and one forecaster's predictions of future activity. Credit: David Hathaway, NASA/MSFC

Measurements by the Ulysses spacecraft reveal a 20 percent drop in solar wind pressure since the mid-1990s—the lowest point since such measurements began in the 1960s. The solar wind helps keep galactic cosmic rays out of the inner solar system. With the solar wind flagging, more cosmic rays penetrate the solar system, resulting in increased health hazards for astronauts. Weaker solar wind also means fewer geomagnetic storms and auroras on Earth.

Careful measurements by several NASA spacecraft have also shown that the sun’s brightness has dimmed by 0.02 percent at visible wavelengths and a whopping 6 percent at extreme UV wavelengths since the solar minimum of 1996. Radio telescopes are recording the dimmest “radio sun” since 1955.

All these lows have sparked a debate about whether the ongoing minimum is extreme or just an overdue correction following a string of unusually intense solar maxima.

“Since the Space Age began in the 1950s, solar activity has been generally high,” said forecaster David Hathaway of NASA’s Marshall Space Flight Center. “Five of the ten most intense solar cycles on record have occurred in the last 50 years. We’re just not used to this kind of deep calm.”

Deep calm was fairly common a hundred years ago. The solar minima of 1901 and 1913, for instance, were even longer than what we’re experiencing now. To match those minima in depth and longevity, the current minimum will have to last at least another year.

In a way, the calm is exciting, says Pesnell. “For the first time in history, we’re getting to observe a deep solar minimum.” A fleet of spacecraft — including the Solar and Heliospheric Observatory (SOHO), the twin probes of the Solar Terrestrial Relations Observatory (STEREO), and several other satellites — are all studying the sun and its effects on Earth. Using technology that didn’t exist 100 years ago, scientists are measuring solar winds, cosmic rays, irradiance and magnetic fields and finding that solar minimum is much more interesting than anyone expected.

Modern technology cannot, however, predict what comes next. Competing models by dozens of solar physicists disagree, sometimes sharply, on when this solar minimum will end and how big the next solar maximum will be. The great uncertainty stems from one simple fact: No one fully understands the underlying physics of the sunspot cycle.

And the only thing scientists can do it to keep watching. Pesnell believes sunspot counts should pick up again soon, “possibly by the end of the year,” to be followed by a solar maximum of below-average intensity in 2012 or 2013.

Source: NASA

February 21, 2009December 24, 2015 by Ian O'Neill

Sounds Painful: Are Deadly Asteroids Stuck in Earth’s Lagrangian Points?

Did the asteroid that hit the Earth, creating the Moon, originate from one of Earth's Lagrangian points? (ESA)

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Two solar telescopes launched to study coronal mass ejections and the solar wind have been sent to do an entirely different task. Currently, the Solar Terrestrial Relations Observatory (STEREO) probes are flying in opposite directions; one directly in front of Earth’s orbit and the other directly behind. This unique observatory is intended to view the solar-terrestrial environment in unprecedented detail, allowing us to see the Sun from two vantage points.

This might sound like an exciting mission; after all, how many space-based observatories have such a unique perspective on the Solar System from 1 AU? However, both STEREO probes are currently moving further away from the Earth (in opposite directions), approaching a gravitational no-man’s land. STEREO is about to enter the Earth-Sun Lagrangian points L₄ and L₅ to hunt for some sinister lumps of rock…

The Lagrangian points of a two-body system, such as the Earth and the Sun.

Lagrangian points in planetary systems are islands of gravitational stability. They are volumes of space where the gravity of two massive bodies cancel out. The first two Lagrangian points in the Earth-Sun system are fairly obvious. The L₁ point is located directly between the Earth and Sun, about 1.5 million km from the surface of the Earth, the point at which the gravitational pull of the Sun and Earth cancel each other out.

The L₂ point is located at approximately the same distance, but on the opposite side of the Earth. In this case, the Earth is constantly eclipsing the Sun. The L₃ point is on the opposite side of the Sun from the Earth, at approximately 1AU. Now this is where it starts to get a little strange. The L₄ and L₅ points are located 60° in front and 60° behind the Earth’s orbit. The 4th and 5th Lagrangian points are also the most gravitationally stable regions, primordial debris lurks, trapped in the Lagrangian prisons. Although the L₁ point is often considered to be the most stable of the Lagrangian points (as it’s directly locked between the gravity of the Sun and Earth), even space observatories (such as SOHO and ACE) have to carry out complex orbits to remain in place. Otherwise the delicate balance will be lost and they will drop away from L₁.

L₄ and L₅ are in fact the most stable locations, balanced by a complex cage of competing gravitational components from the Earth and the Sun. It is thought that these two regions have trapped lumps of rock and dust all the way through the evolution of the Solar System, making them a very interesting place to send a space mission. And the two solar probes of STEREO are currently racing toward L₄ and L₅, about to explore the gravitational dead zone, whether they like it or not.

It is a known fact that other planets in the Solar System possess these islands of gravitational calm, and asteroids have been observed sitting in stable locations in front and behind of Jupiter’s orbit for example (called “Trojans” and “Greeks”). Does Earth have a swarm of asteroids sitting in its L₄ and L₅ points? Scientists believe this is a certainty. However, no asteroids have ever been observed.

Although millions of kilometres across, L₄ and L₅ can only be observed at dawn and dusk. Any possibility of spotting a large asteroid diminishes rapidly as they are obscured by the Sun. So, the STEREO space telescopes are going to take the dive into L₄ and L₅ to see, first hand, what lies in wait.

Artist impression of the STEREO probes going their separate ways (NASA)

Early on in the STEREO mission, scientists discussed the possibility of stopping the spacecraft inside the two islands of calm to provide an advanced warning of incoming charged particles from coronal mass ejections during solar maximum. However, slowing the craft down would have cost the mission too much fuel, so the decision was made to let the solar telescopes pass straight through. It will take a few months to complete the journey through the huge Solar System badlands, but it will serve a valuable purpose, STEREO has become NASA’s makeshift asteroid hunting mission.

Although STEREO wasn’t designed for this work, the mission already has a team of volunteer near-Earth asteroid hunters at the ready and their optics are more than capable of looking out for large lumps of rock invisible from Earth.

“The close-up investigation of L4 and L5 is completely new. That makes it something we should be driving,” says Richard Harrison of the Rutherford Appleton Laboratory in Oxfordshire, UK and a member of the STEREO project. “Wouldn’t it be spectacular if we actually backed past an asteroid? Saw it come creeping into view around the camera.” Now that would be a huge discovery.

This isn’t simply out of academic curiosity however. The Earth’s Moon is thought to have been formed after a huge cosmic impact with a small planetary body. The problem comes when trying to explain where the offending planetary body could have come from; too far away and it will have had too much energy. Rather than punching into the side of the Earth it would have shattered our planet. So the body must have formed a lot closer to our planet.

Did this body evolve in either the L₄ and L₅ points? If it did, and then somehow got kicked out of the gravitational island, perhaps careering toward the Earth, causing the cataclysmic impact that seeded the formation of the Moon.

It is exciting to think that STEREO may make some ground-breaking discoveries not Sun related. I just hope they don’t bump in to any chunks of rock, it could be pretty crowded out there…

Source: New Scientist

December 15, 2008December 24, 2015 by Ian O'Neill

The Neutral Hydrogen Gun: A New Solar Flare Phenomenon

The X9-class solar flare of Dec. 5, 2006, observed by the Solar X-Ray Imager aboard NOAAs GOES-13 satellite (NASA)

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In 2006, one of the largest solar flares observed for 30 years erupted, saturating X-ray cameras on board observatories orbiting Earth. The December 5th event was a powerful X-ray flare, registering “X9” on the scale of powerful “X-class” flares. Even though flares weighing in at X20+ have been observed, the X9 is a rare event all the same. However, this 2006 flare is fast becoming known not only for its energetic characteristics. Shortly after the flare, solar astronomers expected to see a flood of interplanetary ions being ejected by the Sun. However, they detected something else; not only a particle they weren’t expecting, but a particle that shouldn’t be there…

When a blast the size of a hundred million nuclear bombs detonates, you wouldn’t expect anything to be intact at ground-zero, would you? In the case of solar flares, a huge amount of magnetic energy is unleashed through a process known as reconnection, quickly accelerating and heating solar plasma. Depending on the conditions, different solar flare energies are possible, but in the case of the Dec. 5th 2006 flare, solar plasma was rapidly and violently accelerated, unleashing X-ray radiation. At the flare site, within the knotted and twisted magnetic flux, plasma temperatures can soar to 10-20 million Kelvin (occasionally, for the biggest flares, 100 million Kelvin). In these conditions, nothing stays intact. Any atoms in the local area become stripped of their electrons, leaving an energetic soup of ionized particles (like protons and helium nuclei) and electrons.

So you can imagine the surprise of a group of solar physicists using data from the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft orbiting the Sun (one ahead of the Earth’s orbit, and one behind), when they detected a jet of pure neutral hydrogen atoms emanating from the flare.

“We’ve detected a stream of perfectly intact hydrogen atoms shooting out of an X-class solar flare,” says Richard Mewaldt of Caltech,. “What a surprise! These atoms could be telling us something new about what happens inside flares.”

“No other elements were present, not even helium (the sun’s second most abundant atomic species). Pure hydrogen streamed past the spacecraft for a full 90 minutes.”

STEREO particle counts after the flare (NASA)

Measurements of radio emissions indicated that a shock wave had been generated low in the solar atmosphere during the flare, revealing the interaction of incoming solar ions. Physicists waited for an hour for the incoming ions (the time calculated for ions to travel from the Sun to the STEREO spacecraft), but instead the stream of neutral atoms arrived. The stream of hydrogen lasted for 90 minutes, and then it went quiet for 30 minutes only for the expected ions to flood the sensors as predicted.

At first glance, the impossible had been achieved; a solar flare had somehow manufactured, then sorted the neutral hydrogen from the soup of plasma and shot it into space. But this produced a very perplexing puzzle: neutral hydrogen, lots of it, has been detected as a result of a solar flare, and yet these atoms cannot exist in the extreme environment surrounding the flare site. What gives?

Actually, these hydrogen atoms were not generated inside the flare, they formed after the flare as the products from the explosion spiralled into interplanetary space.

“We believe they began their journey to Earth in pieces, as protons and electrons,” said Mewaldt. “Before they escaped the sun’s atmosphere, however, some of the protons recaptured an electron, forming intact hydrogen atoms. The atoms left the sun in a fast, straight shot before they could be broken apart again.”

The reason why these neutral atoms appeared at STEREO faster than the ion cloud is because the neutral hydrogen did not get influenced (slowed down) by the Sun’s magnetic field; the atoms shot out, in a straight line, rather than being deflected by magnetic flux. And how did they form? Physicists believe the protons “recaptured” the free electrons in the space between the flare and detector through the well known mechanisms radiative recombination and charge exchange.

Now, solar physicists want to replicate these findings to see whether these hydrogen jets are a common feature of solar flares… but they might have to wait a while, the Sun is still enjoying its quiet spell...

Source: NASA

October 23, 2008December 24, 2015 by Ian O'Neill

Asteroseismology: Observing Stars Vibrate with CoRoT

Modes of solar oscillation plotted over our Sun. Could the same things be done with other stars? (NASA/TRACE/NCAR)

[/caption]Observing a stars brightness pulsate may reveal its internal structure say researchers using the Convection Rotation and Planetary Transits (CoRoT) observatory. The highly sensitive orbital telescope can detect tiny variations in a distant star’s brightness, leading astronomers into a new field of stellar seismology called “asteroseismology.”

Seismology is more commonly used by scientists on Earth to see how waves travel through the terrestrial crust, thereby revealing the structure of the material below us. Even solar physicists use the method of helioseismology to understand the interior of our Sun by observing its wobble. Now, by observing the slight changes in stellar brightness, it is possible to remotely probe deep into the inner workings of a distant star…

CoRoT is a joint French Space Agency (CNES) and European Space Agency (ESA) mission to detect slight variations in the brightness of stars launched in 2006. As extrasolar planets pass in front of (or “transit”) a star, the brightness will decrease. The highly sensitive 27 cm-diameter telescope and spectroscopic instrumentation has the ability of detecting extrasolar rocky planets a few times the size of Earth and new gas giants (a.k.a. Hot Jupiters).

Another mission objective for the 630 kg satellite is to detect luminosity variations associated with acoustic pulsations passing through the body of the star. A similar method known as helioseismology uses the Solar and Heliospheric Observatory (SOHO) to detect the propagation of pressure waves through the Sun so a better idea of solar internal dynamics and structure can be gained.

CoRoT has been watching three stars, 20-40% more massive than the Sun, vibrate in reaction to the convective processes on the stellar surfaces. Some areas will expand and cool, whilst others with contract and heat up. This creates an oscillation, and a pulsation in brightness, providing information about the inner structure of these distant stars. The three stars brightened and dimmed 1.5 times more dramatically than solar helioseismology observations. However, this is still 25% weaker than expected from theory, so it would seem stellar physics still has a long way to go.

“This really marks the start of a completely new era of space-based asteroseismology,” said Joergen Christensen-Dalsgaard of the University of Aarhus in Denmark. “It shows that CoRoT can do what it set out to do.”

Asteroseismology can also be used to gauge the precise age of a star. Usually, the age of a star is determined by looking at a star cluster where it is assumed the majority of the stars are of a similar age. However, as a star ages, different elements undergo nuclear fusion at different times. This alters the star’s interior structure and therefore alters the vibrational characteristics of the star. This can be detected by CoRoT, hopefully aiding astronomers when deducing the precise ago of a particular star.

“In principle, you can look at one star all on its own and determine how old it is,” adds Michael Montgomery of the University of Texas.

Source: New Scientist

October 6, 2008December 24, 2015 by Astronomy Cast

Podcast: The Life of the Sun

The surface of the Sun. Image credit: NASA

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We’ve talked about the Sun before, but this time we’re going to look at the entire life cycle of the Sun, and all the stages it’s going to go through: solar nebula, protostar, main sequence, red giant, white dwarf, and more. Want to know what the future holds for the Sun, get ready for the grim details.

Click here to download the episode.

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

The Life of the Sun – Transcript and show notes.

September 25, 2008December 24, 2015 by Ian O'Neill

Solar System’s Protective Shield is Weakening; Solar Wind Velocity at Record Low

The three Ulysses spacecraft orbits of the Sun. Figure shows radial solar wind velocity and images of the Sun at varying degrees of activity (McComas et al. GRL, 2008)

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Solar wind output is at its lowest since accurate records began 50 years ago. This finding comes from the seasoned ESA/NASA solar probe Ulysses, which completed nearly three polar orbits of the Sun from 1993 to 2008 (it is still functioning today, but at a reduced capacity). Although a weakening of the solar wind may not sound very important, the effects of this reduction will have serious implications, diminishing the natural defences of the heliopause (our Solar System’s invisible barrier) which protects us from high energy cosmic rays blasting through intergalactic space…

Ulysses has orbited the Sun four times longer than was originally planned. This tough solar satellite was launched in 1990 on board Space Shuttle Discovery, and in 1992, the probe used Jupiter to slingshot it out of the Solar System’s ecliptic to begin taking in situ measurements of solar wind speed and density at all latitudes from pole-to-pole. This is an unprecedented mission that continues to function today. However, Ulysses’ plutonium fuel in its radioisotope thermoelectric generator (RTG) is dwindling to the point where this landmark mission will die from old age over the coming months.

And yet, the geriatric spaceship still reveals characteristics about our Sun that we could never hope to observe confined to the ecliptic plane. So, in (possibly) one of Ulysses’ biggest discoveries to date, scientists have uncovered the strange phenomenon that the solar wind output has decreased to an all-time low (since accurate records began half a century ago), as the Ulysses Principal Investigator explains:

“The Sun’s 1.5 million km-per-hour solar wind inflates a protective bubble around the Solar System and can influence how things work here on Earth and even out at the boundary of our Solar System, where it meets the galaxy. Ulysses data indicate the solar wind’s global pressure is the lowest we have seen since the beginning of the space age.” – Dave McComas, Principal Investigator for the Ulysses solar wind instrument and senior Executive Director at the Southwest Research Institute in San Antonio, Texas.

This “protective bubble” is also known as the heliosphere, a huge volume of space in which all the planets, asteroids and comets are deep inside. It is the total extent of the Sun’s influence, pushing out into interstellar space, the limit of which is known as the heliopause. The heliopause is formed through a balance between the outward pressure of the solar wind and the inward pressure of the interstellar medium, should one of these pressures fluctuate, the heliopause will expand or contract. Should the solar wind pressure decrease, the heliopause will shrink under the greater interstellar medium pressures. This is exactly what Ulysses has detected: a reduction in solar wind pressure.

So what does this mean to us? The heliopause blocks and deflects the majority of damaging high energy interstellar particles (a.k.a. cosmic rays). Should the solar wind weaken, the heliopause will become a less-effective shield, letting more cosmic rays into the Solar System.

“Galactic cosmic rays carry with them radiation from other parts of our galaxy. With the solar wind at an all-time low, there is an excellent chance that the heliosphere will diminish in size and strength. If that occurs, more galactic cosmic rays will make it into the inner part of our Solar System.” – Ed Smith, NASA’s Ulysses Project Scientist from the Jet Propulsion Laboratory, California.

The effects of this happening will be far-reaching and could severely impact the future of manned exploration of the Solar System.

Solar physicists made this discovery when analysing Ulysses data from the probe’s third scan of the solar wind and interplanetary magnetic field (IMF) from the Sun’s north to south poles. On comparison with previous scans, it was found that the solar wind pressure and the radial component of the magnetic field embedded in the solar wind had decreased by 20%. The magnetic field strength surrounding Ulysses had dropped by a huge 36%.

So what could this be attributed to? Physicists simply do not know. Perhaps it might be related to the extended solar minimum in recent months, as Smith appears to suggest. “The sun cycles between periods of great activity and lesser activity,” Smith said. “Right now, we are in a period of minimal activity that has stretched on longer than anyone anticipated.”

Compelling results from a compelling solar mission…

Source: ESA