RSSArchive for March, 2012

VIDEO: When worlds (seem to) collide

LAST YEAR, EUROPE’S MARS EXPRESS spacecraft—in orbit around Mars—underwent a special manoeuvre to observe a conjunction between Jupiter and the larger of Mars’ two moons, Phobos. A conjunction is when two unrelated astronomical bodies appear to line up in the sky.

This sequence of images shows Phobos moving from right to left through the camera’s field of view and then disappearing from the field of view. At the moment when Mars Express, Phobos and Jupiter were in a line, Phobos was 11,389 km from the spacecraft, while Jupiter was more than 529,000,000 km away.

Because Jupiter was nearly 50,000 times as far away as Phobos, the largest planet in the Solar System (140,000 km in diameter) appears much smaller than the Martian moon.

While Mars Express and Phobos were both moving through space, the spacecraft’s camera was fixed on Jupiter. The sequence includes a total of 104 individual images that were taken over a span of 68 seconds.

Adapted from information issued by ESA / DLR / FU Berlin (G. Neukum).

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What’s up? Night sky for April 2012

Star trails over an observatory

The southern sky is full of wonderful treats for the stargazer. (This star trail photo by Iztok Boncina was made by keeping the camera shutter open.)

Except where indicated, all of the phenomena described here can be seen with the unaided eye. And unless otherwise specified, dates and times are for the Australian Eastern Standard Time zone, and sky directions are from the point of view of an observer in the Southern Hemisphere. (If you’re in the Northern Hemisphere, please see the video at the bottom of the page for What’s Up in your night sky.)

April 3

The Moon, now just over three-quarters full, will be about 11 Moon widths above and to the left of the bright blue star, Regulus, the brightest star of the constellation Leo. A little further below is what looks like a red star, but is actually the planet Mars. The colours of Regulus and Mars make a nice contrast. About 77.5 light years from Earth, Regulus is not one star but four, grouped into two pairs. Multiple star systems are very common throughout the Milky Way galaxy.

April 4

The Moon is still in the vicinity of Mars tonight, being above and to the right of the planet. Incidentally, when I use a term such as “vicinity”, it is not to be taken as suggesting the two bodies are physically near each other out there in space. Rather, they are simply within similar lines-of-sight from our vantage point on Earth.

April 4 sky view

April 4, 8:00pm. The Moon, Mars and the star Regulus will make an attractive triangle in the northern part of the sky. Note the colour difference between blue Regulus and ruddy Mars.

April 7

Full Moon occurs today at 5:19am Sydney time (19:19 Universal Time on April 6). In a similar fashion to its “encounters” with Regulus and Mars a few days earlier, tonight the Moon will be about six Moon widths to the right of another bright star, Spica, and about 10 Moon widths above the planet Saturn. Spica is the brightest star of the constellation Virgo; it is a blue giant star about 260 light years from Earth. This is a great time to see Saturn (see April 16), so it’s a good idea to use the nearby Moon to identify it.

April 8

Today the Moon will be at the closest point in its orbit, called perigee. The distance between the two bodies today will be 358,311 kilometres.

April 10

This evening, take a look about 12 Moon widths below the Moon and you’ll see a reddish looking star that looks a bit like Mars. It’s the star Antares, and its name actually “rival of Mars”. Antares is the brightest star of the constellation Scorpius, and is a red supergiant star about 883 times bigger than our Sun!


Saturn, as it appears through a backyard telescope. Image by Steve Massey.

April 13

It is Last Quarter Moon tonight at 8:50pm Sydney time (10:10 Universal Time).

April 16

Today the planet Saturn reaches what astronomers call “opposition”. This means that, from an Earthly perspective, it is the opposite direction to the Sun—so if you could look down on the Solar System from above you’d see the Sun, Earth and Saturn (in that order) in a straight line … although Saturn, of course, is much further from us than the Sun. The period around opposition is a considered a great time to view a planet, as it rises in the east around the same time as the Sun sets in the west, and is therefore nice and high in the sky by late evening.

April 19

If you’re an early riser, out to east this morning before sunrise you’ll see the very thin crescent Moon. Above and to its right is a bright looking star. Well that’s not a star; it’s the planet Mercury, the closest planet to the Sun.

April 19 sky view

April 19, 6:30am. The thin crescent Moon and the planet Mercury will be visible together in the eastern sky before sunrise.

April 21

New Moon occurs today at 5:18pm Sydney time (07:18 Universal Time).

April 23

Today the Moon will again reach the farthest point in its orbit, apogee, at a distance from Earth of 406,421 kilometres.

April 24

Today the Moon makes another apparent close approach to a star, this time Aldebaran, the brightest star of the constellation Taurus. The pair will be low in the western sky after sunset. Like Antares, Aldebaran too is a red star, but not a supergiant—it is only about 44 times the size of our Sun. It’s about 65 light years from Earth.

April 25

There’ll be a lovely astronomical pairing in this evening’s sky, with the Moon very close to Venus. The Moon is the second-brightest object in our night sky, and Venus is the third-brightest.

April 25 sky view

April 25, about 7:15pm. The thin crescent Moon and Venus will be close together in the western sky.

April 29

It is First Quarter Moon today at 7:58pm Sydney time (09:58 Universal Time). First Quarter is a good time to look at the Moon through a telescope, as the sunlight angle means the craters and mountains are throwing nice shadows, making it easier to get that 3D effect.

There’s more great night sky viewing information at Melbourne Planetarium’s Skynotes site.

If you’re in the Northern Hemisphere, here’s a Jet Propulsion Laboratory video that details what you can see this month:

If you have any questions or comments on the night sky, we’d be happy to answer them. Please use the Feedback Form below. Happy stargazing!

Images courtesy IAU and Iztok Boncina / ESO.

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Rocket volley to study the atmosphere

NASA SUCCESSFULLY LAUNCHED five suborbital sounding rockets March 27 from its Wallops Flight Facility in Virginia as part of a study of the upper level jet stream.

The first rocket was launched at 4:58am US EDT and each subsequent rocket was launched at 80 second intervals. Each rocket released a chemical tracer that created milky, white clouds at the edge of space.

The goal of the Anomalous Transport Rocket Experiment (ATREX) was to improve understanding of the process that drives fast-moving winds high in the thermosphere.

Tracking the way the clouds move can help scientists understand the movement of the winds some 110 kilometres up in the sky, which in turn will help create better models of the electromagnetic regions of space that can damage man-made satellites and disrupt communications systems.

Winds up high

Fiery trails from four of the five sounding rockets are clearly visible in the time-lapse photograph (bottom of this page) of the launch. The other image (below) shows two of the clouds left in the wake of the experiment; the rockets released trimethyl aluminium, a substance that burns spontaneously in the presence of oxygen.

The harmless by-products of this glowing reaction were visible to the naked eye as far south as Wilmington, North Carolina; west to Charlestown, West Virginia; and north to Buffalo, New York. Both photographs were taken near the launch site at NASA’s Wallops Flight Facility in Virginia.

Throughout the experiment, researchers used specialised cameras in North Carolina, Virginia, and New Jersey—as well as temperature and pressure instruments on two of the rockets—to monitor the clouds.

By measuring how quickly the clouds move away from each other and integrating that information into atmospheric models, they hope to improve their understanding of the 320 to 480 kilometre winds in the thermosphere.

ATREX experiment clouds

Each ATREX rocket released a chemical that reacts with oxygen, forming milky white clouds in the upper atmosphere.

First noticed by scientists in the 1960s, the winds are thought to be part of a high-altitude jet stream that’s distinct from the one lower in the troposphere, where commercial aircraft fly. Observing the turbulence produced by these winds should make it possible to determine what’s driving them.

An improved understanding of the upper jet stream will make it easier to model the electromagnetic regions of space that can damage satellites and disrupt communications systems. The experiment will also help explain how the effects of atmospheric disturbances in one part of the globe can be transported to other parts of the globe in a mere day or two.

The launches are part of a broader sounding rocket programmeat NASA that conducts approximately 20 flights a year from launch sites around the world.

The trails of the five ATREX sounding rockets captured in a time-lapse photo.

The trails of the five ATREX sounding rockets captured in a time-lapse photo.

Photographs courtesy NASA’s Wallops Flight Facility. Text adapted from information issued by Karen Fox and Adam Voiland, NASA Earth Observatory.

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Billions of super-Earths “out there”

Artist's impression of a planet circling a red dwarf star

Artist's impression of a planet circling the star Gliese 581. Astronomers estimate there could be tens of billions of "super-Earth" planets in our galaxy.

ROCKY PLANETS NOT MUCH BIGGER THAN EARTH are very common in the habitable zones around faint red stars, say astronomers.

The habitable zone is the distance from a star where it is neither too hot nor too cold for liquid water to exist on the surface of a rocky planet.

The international team used a “planet finder” instrument to estimate that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about 100 in the Sun’s immediate neighbourhood.

This is the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of the stars in the Milky Way.

This first direct estimate of the number of light planets circling red dwarf stars used observations made with the HARPS spectrograph on the 3.6-metre telescope at the European Southern Observatory’s La Silla Observatory in Chile.

Super-Earths abound

The HARPS team has been searching for exoplanets orbiting the most common kind of star in the Milky Way—red dwarf stars (also known as M dwarfs. These stars are faint and cool compared to the Sun, but very common and long-lived, and therefore account for 80% of all the stars in the Milky Way.

“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone…,” says Xavier Bonfils (IPAG, Observatoire des Sciences de l’Univers de Grenoble, France), the leader of the team.

Diagram showing the habitable zone for small, medium and large stars.

Diagram showing the habitable zone (green area) varies depending on the size and temperature of the star. Too close in (red area) and it's too hot; too far out (blue area) and it's too cold.

“Because red dwarfs are so common—there are about 160 billion of them in the Milky Way—this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

The HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period. A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of stars Gliese 581 and Gliese 667 C respectively.

The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are in red dwarf systems.

They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.

On the other hand, more massive planets, similar to Jupiter and Saturn in our Solar System, are found to be rare in red dwarf systems. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1,000 times that of the Earth).

In the zone

As there are many red dwarf stars close to the Sun the new estimate means that there are probably about 100 super-Earth planets in the habitable zones around stars in the neighbourhood of the Sun at distances less than about 30 light-years.

“The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to [a red dwarf] star than the Earth is to the Sun,” says Stéphane Udry (Geneva Observatory and member of the team).

“But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely.”

One of the planets discovered in the HARPS survey of red dwarfs is Gliese 667 Cc. This is the second planet in this triple-star system and it seems to be situated close to the centre of the habitable zone.

Artist’s impression of a sunset seen from the super-Earth Gliese 667 Cc

This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone.

Although this planet is more than four times heavier than the Earth it is the closest twin to Earth found so far, and almost certainly has the right conditions for the existence of liquid water on its surface.

Gliese 667 Cc is the second super-Earth planet inside the habitable zone of a red dwarf discovered during this HARPS survey, after Gliese 581d was announced in 2007 and confirmed in 2009.

“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments,” concludes Xavier Delfosse, another member of the team.

Some of these planets are expected to pass in front of, or transit, their parent star as they orbit, and astronomers can use these transits to learn more about the planets’ atmospheres and look for signs of life.

Adapted from information issued by ESO / L. Calçada.

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Earth’s other moons

EARTH USUALLY HAS MORE THAN ONE MOON, according to a team of astronomers from the University of Helsinki, the Paris Observatory and the University of Hawaii at Manoa.

Our 3,400-kilometre-diameter Moon, so beloved by poets, artists and romantics, has been orbiting Earth for over 4 billion years. Its much smaller cousins, dubbed “minimoons,” are thought to be only metres across and to usually orbit our planet for less than a year before resuming their previous lives as asteroids orbiting the Sun.

Mikael Granvik (formerly at UH Manoa and now at Helsinki), Jeremie Vaubaillon (Paris Observatory) and Robert Jedicke (UH Manoa) calculated the probability that at any given time Earth has more than one moon. They used a supercomputer to simulate the passage of 10 million asteroids past Earth. They then tracked the trajectories of the 18,000 objects that were captured by Earth’s gravity.

They concluded that at any given time there should be at least one asteroid with a diameter of at least one metre orbiting Earth. Of course, there may also be many smaller objects orbiting Earth, too.

Captured by Earth’s gravity

According to the simulation, most asteroids that are captured by Earth’s gravity would not orbit Earth in neat circles. Instead, they would follow complicated, twisting paths. This is because a minimoon would not be tightly held by Earth’s gravity, so it would be tugged into a crazy pathby the combined gravity of Earth, the Moon and the Sun.

Path of a simulated minimoon

The path of a simulated minimoon that is temporarily captured by Earth. The object approaches Earth from the right and finally escapes capture along the red path to the upper right. The size of Earth and the Moon are not to scale but the size of the minimoon’s path is to scale in the Earth-Moon system. Inset: Radar image of near-Earth asteroid 1999. This 3.5-km-wide asteroid is more than 1,000 times larger than the biggest minimoons, but it shows the irregular shape and expected of minimoons.

A minimoon would remain captured by Earth until one of those tugs breaks the pull of Earth’s gravity, and the Sun once again takes control of the object’s trajectory. While the typical minimoon would orbit Earth for about nine months, some of them could orbit our planet for decades.

“This was one of the largest and longest computations I’ve ever done,” said Vaubaillon. “If you were to try to do this on your home computer, it would take about six years.”

In 2006, the University of Arizona’s Catalina Sky Survey discovered a minimoon about the size of a car. Known by the unimaginative designation 2006 RH120, it orbited Earth for less than a year after its discovery, then resumed orbiting the Sun.

“Minimoons are scientifically extremely interesting,” said Jedicke. “A minimoon could someday be brought back to Earth, giving us a low-cost way to examine a sample of material that has not changed much since the beginning of our Solar System over 4.6 billion years ago.”

The team used the Jade supercomputer at the National Computer Centre for Higher Education (Centre Informatique National de l’Enseignement Supérieur, or CINES) at Montpelier, France.

The team’s paper, “The population of natural Earth satellites,” appears in the March issue of the journal Icarus.

Adapted from information issued by the University of Hawaii at Manoa. 1999 JM8 image made with NASA’s Goldstone Solar System Radar in California and the Arecibo Observatory in Puerto Rico by a team of astronomers led by Dr. Lance Benner of NASA’s Jet Propulsion Laboratory in Pasadena, California

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Space foil helps build safer cars

Hermes spaceplane

Europe’s Hermes spaceplane was intended to provide independent European manned access to space. Designed to take three astronauts to orbits of up to 800 km altitude on missions of 30–90 days, the spaceplane would have been launched using the Ariane 5 rocket.

A SPECIAL FOIL SENSOR developed to measure the pressure on a spaceplane’s wings during re-entry into Earth’s atmosphere is now helping to build safer cars.

This ‘space’ foil has been transformed into a new super-thin and accurate sensor used by VW to measure every deformation suffered by cars during crash tests.

It all started in the early 1990s, when German engineer Paul Mirow was working on Europe’s Hermes spaceplane at Technical University Berlin. Hermes was planned as a reusable manned vehicle launched on Ariane 5.

To map the pressure distribution on the wings as Hermes returned through the atmosphere, a new sensor was needed because regular instruments were too bulky and added unrealistic drag. So Paul’s team turned to a special ‘piezoelectric’ foil to do the job.

Piezoelectric materials on a tooth

Piezoelectric materials were painted on a tooth to measure the forces exerted by a toothbrush.

Piezoelectric materials have a special property that converts physical effects like vibration and pressure into minute electric pulses. “It takes movement, forces or vibration, and turns it into an electrical signal,” Paul notes.

Super-thin sensor

In foil form, piezoelectric materials can serve as extremely lightweight sensors, able to cover an entire surface without distorting the results by adding drag.

“The piezoelectric foil is very thin, about 30 microns – a third of the thickness of a human hair,” explains Paul.

While other types of sensors create obstacles, with these piezoelectric foils, “You can just glue it to the surface, without creating any disturbances in the structure.”

The tests of Hermes’ wing in a hypersonic wind tunnel went well, and in 1995 Paul and his partners decided to adapt their piezoelectric foil for terrestrial applications.

One was even created for a dental company: “We painted a tooth with piezoelectric paint so they could measure the forces created by the toothbrush on the molar.”

Piezoelectric sensor

To map the pressure distribution on Hermes' wings as the spaceplane returned through the atmosphere, a new sensor was developed based on super-thin piezoelectric materials. They have a special property that converts physical effects like vibration and pressure into minute electric pulses.

Making cars safer

One of the most exciting applications was developed for VW to use in their crash tests.

At the yearly Hannover Fair, the German car company saw Paul’s products at the stand organised by ESA’s Technology Transfer Programme Office and its German partner, technology broker MST Aerospace.

VW hoped that the space sensors would solve a problem encountered in crash tests: sensors on cars are often destroyed at impact, making it difficult to collect highly accurate data throughout the crash process.

Contained in a highly flexible polymer film, the piezoelectric sensor is simply applied to the car’s surfaces. It moves with the metal as the car crashes, rather than being destroyed by the impact.

“The VW people asked, ‘is it possible to use this in crash tests?’” recalls Paul. “We said, ‘let’s try.’”

“We wanted to know at which moment which parts of the car are deformed,” explained Jens Weinrich, an engineer at VW.

“In a crash situation, it’s always a problem that you never know exactly what will happen.”

Crash test

The foil sensor is now used by German Volkswagen to measure their crash tests.

Paul’s firm developed a sensor in which each strip of foil contains 50 piezoelectric sensors, each about a square centimetre.

This makes it possible to measure exactly what is happening, and when, in exactly which places on the car. How fast is the metal bending? Is it bending 20º in one direction, or 60º in the other? And where precisely did it bend?

At the end of each strip, an equally thin, flexible printed circuit board with a 50-channel amplifier records the electrical impulses created by the mechanical deformations.

“We wanted not just qualitative, but also quantitative results,” said Mr Weinrich. “We wanted to know where it folded, and how much it folded.”

Following the development of the piezoelectric foil sensors, VW has now used them in a number of crash tests.

Adapted from information issued by ESA. Images courtesy ESA / D. Ducros / Mirow Systemtechnik GmbH / Volkswagen Media Service.

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Unknown objects at the limits

NASA’s FERMI GAMMA-RAY TELESCOPE is finding hundreds of new objects at the very edge of the electromagnetic spectrum. Many of them have one thing in common—astronomers have no idea what they are. This short video from NASA explains what it’s all about.

Adapted from information issued by NASA.

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New Australian satellite to launch

Artist's impression of the Jabiru-1 satellite

Artist's impression of the Jabiru-1 satellite, due to launch in 2014 aboard an Ariane 5 rocket.

IT WAS ANNOUNCED TODAY that Australian communications company NewSat has chosen Arianespace to launch its first satellite, Jabiru-1, in 2014.

Jean-Yves Le Gall, Chairman and CEO of Arianespace, and Adrian Ballintine, founder and Chief Executive Officer of NewSat Limited (NewSat), today signed the launch services contract for the Jabiru-1 satellite at Satellite 2012 in Washington, DC.

Jabiru-1 will be boosted into geostationary transfer orbit by an Ariane 5 launch vehicle from the Guiana Space Centre, Europe’s Spaceport in French Guiana, during the fourth quarter of 2014.

Geostationary transfer orbit is a “halfway” orbit, from which a satellite’s own rocket  motor then boosts it into its final orbit.

Jabiru-1 is currently being built by Lockheed Martin Commercial Space Systems using an A2100 platform. Weighing 5,900 kg at launch, it will be fitted with 50 Ka-band transponders configured in a variety of multi-spot, steerable and regional beams.

Launch of an Ariane 5 rocket

Launch of an Ariane 5 rocket

Jabiru-1’s high-powered capacity will provide flexible communication solutions to enterprise and government customers across Asia, the Middle East and eastern Africa. It offers a design life of 15 years.

Jean-Yves Le Gall, Chairman and CEO of Arianespace, said: “We are delighted to have been chosen by NewSat to launch their first satellite. Arianespace is particularly proud of this opportunity to serve a new Australian operator. For us, this latest contract provides further recognition of the outstanding quality and competitiveness of our launch services.”

The announcement comes only months after Arianespace also won the competition to launch Optus’ next satellite, Optus 10.

“Jabiru-1 is very important for us and we are very pleased to entrust Arianespace with its launch, since Arianespace sets the world standard in this market,” said Adrian Ballintine. “It is extremely important for us at NewSat to know that our first satellite will be launched by Arianespace and by Ariane 5, both synonymous with reliability and excellence.”

Arianespace is the world’s leading launch service & solutions company, providing innovation to its customers since 1980. As of 1st March 2012, Arianespace had performed 204 Ariane launches (298 payloads), 26 Soyuz launches (24 at Baikonur, Kazakhstan, and two at the Guiana Space Centre) and the first launch of Vega. It has a backlog of 23 Ariane 5, 15 Soyuz and two Vega launches, equal to more than three years of business.

More information:



Adapted from information issued by Arianespace.

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New images of an icy world

Cassini image of Rhea

NASA's Cassini spacecraft took this raw, unprocessed image of Saturn's moon Rhea on March 10, 2012. The camera was pointing toward Rhea from a distance of approximately 41,873 kilometres.

THESE RAW, UNPROCESSED IMAGES of Saturn’s second largest moon, Rhea, were taken on March 10, 2012, by NASA’s Cassini spacecraft. This was a relatively distant flyby with a close-approach distance of 42,000 kilometres, well suited for global geologic mapping.

At 1,530 kilometres diameter, Rhea is the ninth-largest moon in the Solar System.

During the flyby, Cassini captured these views of the moon’s cratered surface, creating a 30-frame mosaic of Rhea’s leading hemisphere and the side of the moon that faces away from Saturn.

The observations included the large Mamaldi (480 kilometres across) and Tirawa (360 kilometres across) impact basins and the 47-kilometre-wide “ray crater”Inktomi, one of the youngest surface features on Rhea.

Cassini image of Rhea

This second raw, unprocessed Cassini image of Rhea was taken from a distance of approximately 42,258 kilometres, and shows the moon's icy, cratered surface. The streaks on the right are an artefact of the imaging.

Cassini image of Rhea

Shadows help to give a 3D effect to Rhea's craters in this raw, unprocessed Cassini shot taken from a distance of approximately 42,096 kilometres.

Cassini image of Rhea

This raw, unprocessed shot was taken from much further away, approximately 115,060 kilometres, and shows Rhea's "terminator"—the dividing line between day and night.

Cassini has been investigating Saturn and its moons since 2004. This included dropping a probe called Huygens onto the surface of Saturn’s largest moon, Titan, in 2005. Launched in 1997, Cassini-Huygens mission is a co-operative project of NASA, the European Space Agency and the Italian Space Agency.

See all of Cassini’s raw images at NASA’s Saturn page.

Adapted from information issued by NASA / JPL-Caltech / SSI.

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Solar storm reaches Earth

Illustration of space weather

Artist's illustration of events on the Sun changing the conditions in Near-Earth space

THIS WEEK SAW A HUGE solar disturbance that sent a storm of energy on a collision course with our planet.

The Sun erupted with one of the largest solar flares of this solar cycle on March 6. The flare was categorised as an X5.4, making it the second largest flare—after an X6.9 on August 9, 2011—since the Sun’s activity moved into a period of relatively low activity called solar minimum in early 2007. The current increase in the number of X-class flares is part of the Sun’s normal 11-year solar cycle, during which activity ramps up to solar maximum, which is expected to peak in late 2013.

About an hour later, the same region let loose an X1.3 class flare. An X1 is 5 times smaller than an X5 flare.

Space weather starts at the Sun. It begins with an eruption such as a huge burst of light and radiation called a solar flare or a gigantic cloud of solar material called a coronal mass ejection (CME). But the effects of those eruptions are felt at Earth, or at least near-Earth space. Scientists monitor several kinds of “space weather” events—geomagnetic storms, solar radiation storms, and radio blackouts—all caused by these immense explosions on the Sun.

Geomagnetic storms

One of the most common forms of space weather, a geomagnetic storm refers to any time Earth’s magnetic environment, the magnetosphere, undergoes sudden and repeated change. This is a time when magnetic fields continually re-align and energy dances quickly from one area to another.

Geomagnetic storms occur when certain types of CMEs connect up with the outside of the magnetosphere for an extended period of time. The solar material in a CME travels with its own set of magnetic fields. If the fields point northward, they align with the magnetosphere’s own fields and the energy and particles simply slide around Earth, causing little change. But if the magnetic fields point southward, in the opposite direction of Earth’s fields, the effects can be dramatic. The Sun’s magnetic fields peel back the outermost layers of Earth’s fields changing the whole shape of the magnetosphere. This is the initial phase of a geomagnetic storm.

The next phase, the main phase, can last hours to days, as charged particles sweeping into the magnetosphere accumulate more energy and more speed. These particles penetrate closer and closer to the planet. During this phase viewers on Earth may see bright aurora at lower latitudes than usual. The increase—and lower altitude—of radiation can also damage satellites travelling around Earth.

The final stage of a geomagnetic storm lasts a few days as the magnetosphere returns to its original state.

The movie below shows the March 6, 2012 X5.4 flare, captured by the Solar Dynamics Observatory (SDO) spacecraft. One of the most dramatic features is the way the entire surface of the Sun seems to ripple with the force of the eruption. This movement comes from something called EIT waves—because they were first discovered with the Extreme ultraviolet Imaging Telescope (EIT) on the Solar Heliospheric Observatory (SOHO).

Since SDO captures images every 12 seconds, it has been able to map the full evolution of these waves and confirm that they can travel across the full breadth of the Sun. The waves move at over a million miles per hour, zipping from one side of the Sun to the other in about an hour. The movie shows two distinct waves. The first seems to spread in all directions; the second is narrower, moving toward the southeast. Such waves are associated with, and perhaps trigger, fast coronal mass ejections, so it is likely that each one is connected to one of the two CMEs that erupted on March 6.

Geomagnetic storms do not always require a CME. Mild storms can also be caused by something called a co-rotating interaction region (CIR). These intense magnetic regions form when high-speed solar winds overtake slower ones, thus creating complicated patterns of fluctuating magnetic fields. These, too, can interact with the edges of Earth’s magnetosphere and create weak to moderate geomagnetic storms.

Geomagnetic storms are measured by ground-based instruments that observe how much the horizontal component of Earth’s magnetic field varies. Based on this measurement, the storms are categorized from G1 (minor) to G5 (extreme). In the most extreme cases transformers in power grids may be damaged, spacecraft operation and satellite tracking can be hindered, high frequency radio propagation and satellite navigation systems can be blocked, and auroras may appear much further south than normal.

Solar radiation storms

A solar radiation storm, which is also sometimes called a solar energetic particle (SEP) event, is much what it sounds like: an intense inflow of radiation from the Sun. Both CMEs and solar flares can carry such radiation, made up of protons and other charged particles. The radiation is blocked by the magnetosphere and atmosphere, so cannot reach humans on Earth. Such a storm could, however, harm humans travelling from Earth to the Moon or Mars, though it has little to no effect on airplane passengers or astronauts within Earth’s magnetosphere. Solar radiation storms can also disturb the regions through which high frequency radio communications travel. Therefore, during a solar radiation storm, airplanes travelling routes near the poles—which cannot use GPS, but rely exclusively on radio communications—may be re-routed.

Photo of an aurora

Aurorae occur primarily near Earth's poles. They are the most common and the only visual result of space weather. This aurora image associated with solar flares and CMEs on February 23-24, 2012 was taken over Muonio, Finland before sunrise on February 27, 2012.

Solar radiation storms are rated on a scale from S1 (minor) to S5 (extreme), determined by how many very energetic, fast solar particles move through a given space in the atmosphere. At their most extreme, solar radiation storms can cause complete high frequency radio blackouts, damage to electronics, memory and imaging systems on satellites, and radiation poisoning to astronauts outside of Earth’s magnetosphere.

Radio blackouts

Radio blackouts occur when the strong, sudden burst of X-rays from a solar flare hits Earth’s atmosphere, jamming both high and low frequency radio signals. The X-rays disturb a layer of Earth’s atmosphere known as the ionosphere, through which radio waves travel. The constant changes in the ionosphere change the paths of the radio waves as they move, thus degrading the information they carry. This affects both high and low frequency radio waves alike. The loss of low frequency radio communication causes GPS measurements to be off by feet to miles, and can also affect the applications that govern satellite positioning.

Radio blackouts are rated on a scale from R1 (minor) to R5 (extreme). The strongest radio blackouts can result in no radio communication and faulty GPS for hours at a time.

More information: Space Weather Frequently Asked Questions

Adapted from information issued by NASA. Images courtesy NASA and Thomas Kast. Video courtesy NASA / GSFC / SDO.

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