NASA Messenger: Mercury's magnetic field counteracted by Solar wind

The Messenger space probe - which took this image - has confirmed that the innermost planet has a magnetic field 150 times weaker than that of Earth. Researchers have now found an explanation for this. 

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury, the smallest of the eight planets with a diameter of 4900 kilometres and the closest to the Sun, looks more like the Moon than the Earth from the outside.

It is the only rocky planet that has a global magnetic field like Earth. But why is its magnetic field so much weaker than Earth’s?

Scientists at the Technische Universität Braunschweig and the Max Planck Institute for Solar System Research have now presented a new explanation: the solar wind counteracts Mercury’s internal dynamo and thus weakens its magnetic field.

Planetary magnetic fields are generated by flows in the hot, liquid iron cores of the planets.

Measurements made by Mariner 10 in 1974/75 showed that Mercury also has a magnetic field. According to the standard models, the dynamo effect in its metal core should generate similar field strengths to those on Earth.

Mercury’s magnetic field is 150 times weaker than that of our planet, however. This has recently been confirmed by the Nasa space probe Messenger.

How can the large discrepancy in the field strength be explained? This question has now been answered by a group headed by Karl-Heinz Glassmeier at the Technische Universität Braunschweig.

The solar wind – a constant stream of charged particles – plays a significant role. At an average distance from the Sun of only 58 million kilometres – around one third of the distance of the Earth – Mercury is much more exposed to these particles.

“We must keep in mind that Mercury stongly interacts with the surrounding solar wind,” says Daniel Heyner, lead author of the article published in Science and doctoral student at the International Max Planck Research School (IMPRS) in Katlenburg-Lindau.

This interaction drives strong electrical currents in the magnetosphere of the planet, whose magnetic fields counteract the internal dynamo effect.

The team’s new computer models show that a dynamo with this type of feedback is actually possible.

“These types of simulation of the dynamo process are the only possibility to sort of look into the iron core and to predict the strength and structure of the magnetic field,” says Johannes Wicht from the Max Planck Institute for Solar System Research, whose model made a significant contribution to the study.

The results show unambiguously that the feedback ultimately causes the weak magnetic field. “The dynamo process in Mercury’s interior is almost nipped in the bud by the interaction,” explains Glassmeier.

The researchers at the TU Braunschweig and the Max Planck Institute for Solar System Research are eagerly awaiting the next magnetic field measurements from the Messenger space probe and the observations of the two satellites of the European-Japanese mission BepiColombo.

The mission will carry an instrument developed by the TU Braunschweig. Starting in 2020 the researchers want to measure Mercury’s magnetic field with great precision.

The new data should allow the confirmation of this fascinating new idea of a dynamo weakened by the solar wind.


More information: Daniel Heyner, Johannes Wicht, Natalia Gómez-Pérez, Dieter Schmitt, Hans-Ulrich Auster, Karl-Heinz Glassmeier, Evidence from Numerical Experiments for a Feedback Dynamo Generating Mercury’s Magnetic Field, Science, 23 December 2011. DOI: 10.1126/science.120729

Space Debris: Metallic ball drops on Namibia

A large metallic ball fell out of the sky on a remote grassland in Namibia, prompting baffled authorities to contact NASA and the European space agency.

The hollow ball with a circumference of 1.1 metres (43 inches) was found near a village in the north of the country some 750 kilometres (480 miles) from the capital Windhoek, according to police forensics director Paul Ludik.

Locals had heard several small explosions a few days beforehand, he said.

With a diameter of 35 centimetres (14 inches), the ball has a rough surface and appears to consist of "two halves welded together".

It was made of a "metal alloy known to man" and weighed six kilogrammes (13 pounds), said Ludik.

It was found 18 metres from its landing spot, a hole 33 centimetres deep and 3.8 meters wide.

Several such balls have dropped in southern Africa, Australia and Latin America in the past twenty years, authorities found in an Internet search.

The sphere was discovered mid-November, but authorities first did tests before announcing the find.

Police deputy inspector general Vilho Hifindaka concluded the sphere did not pose any danger.

"It is not an explosive device, but rather hollow, but we had to investigate all this first," he said.

Shadow of the Milky Way: The Dark Rift

Thick dust clouds block our night-time view of the Milky Way, creating what is sometimes called the Dark Rift. 

The fact that, from Earth, the sun aligns with these clouds, or the galactic center, near the winter solstice is no cause for concern. Credit: A. Fujii

One of the most bizarre theories about 2012 has built up with very little attention to facts.

This idea holds that a cosmic alignment of the sun, Earth, the center of our galaxy - or perhaps the galaxy's thick dust clouds - on the winter solstice could for some unknown reason lead to destruction.

Such alignments can occur but these are a regular occurrence and can cause no harm (and, indeed, will not even be at its closest alignment during the 2012 solstice.)

The details are as follows: Viewed far from city lights, a glowing path called the Milky Way can be seen arching across the starry sky. This path is formed from the light of millions of stars we cannot see individually. It coincides with the mid plane of our galaxy, which is why our galaxy is also named the Milky Way.

Thick dust clouds also populate the galaxy. And while infrared telescopes can see them clearly, our eyes detect these dark clouds only as irregular patches where they dim or block the Milky Way's faint glow.

The most prominent dark lane stretches from the constellations Cygnus to Sagittarius and is often called the Great Rift, sometimes the Dark Rift.

Another impressive feature of our galaxy lies unseen in Sagittarius: the galactic center, about 28,000 light-years away, which hosts a black hole weighing some four million times the sun's mass.

The claim for 2012 links these two pieces of astronomical fact with a third - the position of the sun near the galactic center on Dec. 21, the winter solstice for the Northern Hemisphere - to produce something that makes no astronomical sense at all.

As Earth makes its way around the sun, the sun appears to move against the background stars, which is why the visible constellations slowly change with the seasons.

On Dec. 21, 2012, the sun will pass about 6.6 degrees north of the galactic center - that's a distance that looks to the eye to be about 13 times the full moon's apparent size - and it's actually closer a couple of days earlier.

There are different claims about why this bodes us ill, but they boil down to the coincidence of the solstice with the sun entering the Dark Rift somehow portending disaster or the mistaken notion that the sun and Earth becoming aligned with the black hole in the galactic center allows some kind of massive gravitational pull on Earth.

The first strike against this theory is that the solstice itself does not correlate to any movements of the stars or anything in the universe beyond Earth. It just happens to be the day that Earth's North Pole is tipped farthest from the sun.

Second, Earth is not within range of strong gravitational effects from the black hole at the center of the galaxy since gravitational effects decrease exponentially the farther away one gets.

Earth is 93 million miles from the sun and 165 quadrillion miles from the Milky Way's black hole. The sun and the moon (a smaller mass, but much closer) are by far the most dominant gravitational forces on Earth.

Throughout the course of the year, our distance from the Milky Way's black hole changes by about one part in 900 million - not nearly enough to cause a real change in gravity's pull. Moreover, we're actually nearest to the galactic center in the summer, not at the winter solstice.

Third, the sun appears to enter the part of the sky occupied by the Dark Rift every year at the same time, and its arrival there in Dec. 2012 portends precisely nothing.

Enjoy the solstice, by all means, and don't let the Dark Rift, alignments, solar flares, magnetic field reversals, potential impacts or alleged Maya end-of-the-world predictions get in the way.

LHC Discovers First New Particle - Chi_b (3P)

CERN physicists, analysing data from the Atlas experiment, have made their first new particle discovery at the Large Hadron Collider, known as Chi_b (3P), which will help scientists better understand the forces that hold matter together.

This is the first clear observation of a new particle since the LHC opened in 2009. The LHC is the largest facility exploring fundamental questions in "big physics" by colliding proton particles together.

Physicists said the Chi_b (3P), which like the Higgs boson, is a boson, portends a new way of combining a beauty quark and its antiquark so that they bind together. But whereas the Higgs is not made up of smaller particles, the Chi_b(3P) combines two very heavy objects via the same 'strong force' which holds the atomic nucleus together.

According to Professor Roger Jones, who works on the Atlas detector at the LHC, the Chi_b (3P) is a more excited state of Chi particles already seen in previous collision experiments. "The new particle is made up of a 'beauty quark' and a 'beauty anti-quark', which are then bound together," he said.

He noted that people have thought this more excited state should exist for years, but nobody has managed to see it until now.

"The Chi_b(3P) is a particle that was predicted by many theorists, but was not observed at previous experiments, such as in my previous work on the D-Zero experiment in Chicago," said Dr James Walder, a Lancaster research associate who worked on the analysis.

"It's also interesting for what it tells us about the forces that hold the quark and the anti-quark together - the strong nuclear force. And that's the same force that holds, for instance, the atomic nucleus together with its protons and the neutrons," Jones said.

The physicist explained that LHC discoveries are an important part of this quest because they add to the wider background knowledge.

"The better we understand the strong force, the more we understand a large part of the data that we see, which is quite often the background to the more exciting things we are looking for, like the Higgs," Jones noted.

"While people are rightly interested in the Higgs boson, which we believe gives particles their mass and may have started to reveal itself, a lot of the mass of everyday objects comes from the strong interaction we are investigating using the chi b," he concluded.

Hubble and Spitzer Telescopes discover star factory

A star factory from the dawn of time has been discovered that is churning out new suns at the rate of 100 a year.

It has taken 12.9 billion years for light from the blob-shaped galaxy GN-108036 to reach the Earth. When the light began its journey, the universe was only 750 million years old.

Data from the Spitzer and Hubble space telescopes revealed a star production rate within GN-108036 equivalent to around 100 suns per year.

In contrast, our own Milky Way galaxy which is five time larger and 100 times more massive produces 30 times fewer stars.

"The discovery is surprising because previous surveys had not found galaxies this bright so early in the history of the universe," said Dr Mark Dickinson from the National Optical Astronomy Observatory in Tucson, Arizona, US.

"It may be a special, rare object that we just happened to catch during an extreme burst of star formation."

Its great distance was carefully measured from the "redshift" stretching of light to longer red wavelengths by the expansion of the universe.

Objects with larger redshifts are more distant and seen further back in time.

Astronomers first identified the remote galaxy after scanning a large patch of sky with the Subaru Telescope on Mauna Kea, Hawaii.

Only a handful of galaxies have confirmed redshifts greater than seven. GN-108036 has a redshift of 7.2.

Jupiter's heart is dissolving

Even the mighty can lose heart. New calculations suggest that Jupiter's rocky core is dissolving like an antacid tablet plopped in water.

The work could help explain why its core appears smaller and its atmosphere richer in heavy elements than predicted.

Giant planets like Jupiter and Saturn are thought to have begun their lives as solid bodies of rock and ice. 

When they grew to about 10 times the mass of Earth, their gravity pulled in gas from their birth nebula, giving them thick atmospheres made mainly of hydrogen.

Curiously, some studies have suggested that Jupiter's core may weigh less than 10 Earths, while the core of its smaller sibling Saturn packs a bigger punch at 15 to 30 Earths. Last year, researchers led by Shu Lin Li of Peking University in China offered a grisly explanation – a rocky planet bigger than Earth slammed into Jupiter long ago, vaporising most of the giant planet's core.

That scenario could also explain another mystery – why Jupiter's atmosphere contains a higher fraction of heavy elements than the sun, whose composition is thought to mirror that of the nebula that gave birth to the solar system's planets.

Now Hugh Wilson and Burkhard Militzer of the University of California, Berkeley, suggest a competing – though no less macabre – explanation: Jupiter's core has gradually been dissolving since its formation 4.5 billion years ago.

Read More at Jupiter's heart is dissolving

NASA Cassini: Saturn's Moons Titan and Dione

Image credit: NASA/JPL-Caltech/Space Science Institute

Saturn's third-largest moon Dione can be seen through the haze of its largest moon, Titan, in this view of the two posing before the planet and its rings from NASA's Cassini spacecraft.

The north polar hood can be seen on Titan appearing as a detached layer at the top of the moon here.

See PIA08137 and PIA09739 to learn more about Titan's atmosphere and the north polar hood.

See PIA10560 and PIA07638 to learn more about and see a closer view of the wisps on Dione's trailing hemisphere, which appear as bright streaks here.

This view looks toward the anti-Saturn side of Titan (3200 miles, 5150 kilometers across) and Dione (698 miles, 1123 kilometers across). North is up on the moons. This view looks toward the northern, sunlit side of the rings from just above the ring plane.

Images taken using red, green and blue spectral filters were combined to create this natural colour view.

The images were obtained with the Cassini spacecraft narrow-angle camera on May 21, 2011 at a distance of approximately 1.4 million miles (2.3 million kilometers) from Titan 2 million miles (3.2 million kilometers) from Dione. Image scale is 9 miles (14 kilometers) per pixel on Titan and 12 miles (19 kilometers) on Dione.

For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org