Physics Archives

August 18, 2008December 24, 2015 by Ian O'Neill

Ten Mysteries of the Solar System

Top 10 (unofficial) solar system mysteries (NASA)

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We’ve all wondered at some point or another what mysteries our Solar System holds. After all, the eight planets (plus Pluto and all those other dwarf planets) orbit within a very small volume of the heliosphere (the volume of space dominated by the influence of the Sun), what’s going on in the rest of the volume we call our home? As we push more robots into space, improve our observational capabilities and begin to experience space for ourselves, we learn more and more about the nature of where we come from and how the planets have evolved. But even with our advancing knowledge, we would be naive to think we have all the answers, so much still needs to be uncovered. So, from a personal point of view, what would I consider to be the greatest mysteries within our Solar System? Well, I’m going to tell you my top ten favourites of some more perplexing conundrums our Solar System has thrown at us. So, to get the ball rolling, I’ll start in the middle, with the Sun. (None of the following can be explained by dark matter, in case you were wondering… actually it might, but only a little…)

10. Solar Pole Temperature Mismatch

Why is the Sun’s South Pole cooler than the North Pole? For 17 years, the solar probe Ulysses has given us an unprecedented view of the Sun. After being launched on Space Shuttle Discovery way back in 1990, the intrepid explorer took an unorthodox trip through the Solar System. Using Jupiter for a gravitational slingshot, Ulysses was flung out of the ecliptic plane so it could pass over the Sun in a polar orbit (spacecraft and the planets normally orbit around the Sun’s equator). This is where the probe journeyed for nearly two decades, taking unprecedented in-situ observations of the solar wind and revealing the true nature of what happens at the poles of our star. Alas, Ulysses is dying of old age, and the mission effectively ended on July 1st (although some communication with the craft remains).

However, observing uncharted regions of the Sun can create baffling results. One such mystery result is that the South Pole of the Sun is cooler than the North Pole by 80,000 Kelvin. Scientists are confused by this discrepancy as the effect appears to be independent of the magnetic polarity of the Sun (which flips magnetic north to magnetic south every 11-years). Ulysses was able to gauge the solar temperature by sampling the ions in the solar wind at a distance of 300 million km above the North and South Poles. By measuring the ratio of oxygen ions (O⁶⁺/O⁷⁺), the plasma conditions at the base of the coronal hole could be measured.

This remains an open question and the only explanation solar physicists can currently come up with is the possibility that the solar structure in the polar regions differ in some way. It’s a shame Ulysses bit the dust, we could do with a polar orbiter to take more results (see Ulysses Spacecraft Dying of Natural Causes).

9. Mars Mysteries

Mars, just a normal planet. No mystery here... (NASA/Hubble)

Why are the Martian hemispheres so radically different? This is one mystery that had frustrated scientists for years. The northern hemisphere of Mars is predominantly featureless lowlands, whereas the southern hemisphere is stuffed with mountain ranges, creating vast highlands. Very early on in the study of Mars, the theory that the planet had been hit by something very large (thus creating the vast lowlands, or a huge impact basin) was thrown out. This was primarily because the lowlands didn’t feature the geography of an impact crater. For a start there is no crater “rim.” Plus the impact zone is not circular. All this pointed to some other explanation. But eagle-eyed researchers at Caltech have recently revisited the impactor theory and calculated that a huge rock between 1,600 to 2,700 km diameter can create the lowlands of the northern hemisphere (see Two Faces of Mars Explained).

Bonus mystery: Does the Mars Curse exist? According to many shows, websites and books there is something (almost paranormal) out in space eating (or tampering with) our robotic Mars explorers. If you look at the statistics, you would be forgiven for being a little shocked: Nearly two-thirds of all Mars missions have failed. Russian Mars-bound rockets have blown up, US satellites have died mid-flight, British landers have pock-marked the Red Planet’s landscape; no Mars mission is immune to the “Mars Triangle.” So is there a “Galactic Ghoul” out there messing with our ‘bots? Although this might be attractive to some of us superstitious folk, the vast majority of spacecraft lost due to The Mars Curse is mainly due to heavy losses during the pioneering missions to Mars. The recent loss rate is comparable to the losses sustained when exploring other planets in the Solar System. Although luck may have a small part to play, this mystery is more of a superstition than anything measurable (see The “Mars Curse”: Why Have So Many Missions Failed?).

8. The Tunguska Event

Artist impression of the Tunguska event (www.russianspy.org)

What caused the Tunguska impact? Forget Fox Mulder tripping through the Russian forests, this isn’t an X-Files episode. In 1908, the Solar System threw something at us… but we don’t know what. This has been an enduring mystery ever since eye witnesses described a bright flash (that could be seen hundreds of miles away) over the Podkamennaya Tunguska River in Russia. On investigation, a huge area had been decimated; some 80 million trees had been felled like match sticks and over 2,000 square kilometres had been flattened. But there was no crater. What had fallen from the sky?

This mystery is still an open case, although researchers are pinning their bets of some form of “airburst” when a comet or meteorite entered the atmosphere, exploding above the ground. A recent cosmic forensic study retraced the steps of a possible asteroid fragment in the hope of finding its origin and perhaps even finding the parent asteroid. They have their suspects, but the intriguing thing is, there is next-to-no meteorite evidence around the impact site. So far, there doesn’t appear to be much explanation for that, but I don’t think Mulder and Scully need be involved (see Tunguska Meteoroid’s Cousins Found?).

7. Uranus’ Tilt

Uranus. Does it on its side (NASA/Hubble)

Why does Uranus rotate on its side? Strange planet is Uranus. Whilst all the other planets in the Solar System more-or-less have their axis of rotation pointing “up” from the ecliptic plane, Uranus is lying on its side, with an axial tilt of 98 degrees. This means that for very long periods (42 years at a time) either its North or South Pole points directly at the Sun. The majority of the planets have a “prograde” rotation; all the planets rotate counter-clockwise when viewed from above the Solar System (i.e. above the North Pole of the Earth). However, Venus does the exact opposite, it has a retrograde rotation, leading to the theory that it was kicked off-axis early in its evolution due to a large impact. So did this happen to Uranus too? Was it hit by a massive body?

Some scientists believe that Uranus was the victim of a cosmic hit-and-run, but others believe there may be a more elegant way of describing the gas giant’s strange configuration. Early in the evolution of the Solar System, astrophysicists have run simulations that show the orbital configuration of Jupiter and Saturn may have crossed a 1:2 orbital resonance. During this period of planetary upset, the combined gravitational influence of Jupiter and Saturn transferred orbital momentum to the smaller gas giant Uranus, knocking it off-axis. More research needs to be carried out to see if it was more likely that an Earth-sized rock impacted Uranus or whether Jupiter and Saturn are to blame.

6. Titan’s Atmosphere

False colour image of Titan's atmosphere. Credit: NASA/JPL/Space Science Institute/ESA

Why does Titan have an atmosphere? Titan, one of Saturn’s moons, is the only moon in the Solar System with a significant atmosphere. It is the second biggest moon in the Solar System (second only to Jupiter’s moon Ganymede) and about 80% more massive than Earth’s Moon. Although small when compared with terrestrial standards, it is more Earth-like than we give it credit for. Mars and Venus are often cited as Earth’s siblings, but their atmospheres are 100 times thinner and 100 times thicker, respectively. Titan’s atmosphere on the other hand is only one and a half times thicker than Earth’s, plus it is mainly composed of nitrogen. Nitrogen dominates Earth’s atmosphere (at 80% composition) and it dominates Titans atmosphere (at 95% composition). But where did all this nitrogen come from? Like on Earth, it’s a mystery.

Titan is such an interesting moon and is fast becoming the prime target to search for life. Not only does it have a thick atmosphere, its surface is crammed full with hydrocarbons thought to be teeming with “tholins,” or prebiotic chemicals. Add to this the electrical activity in the Titan atmosphere and we have an incredible moon with a massive potential for life to evolve. But as to where its atmosphere came from… we just do not know.

5. Solar Coronal Heating

Coronal loops as imaged by TRACE at 171 Angstroms (1 million deg C) (NASA/TRACE)

Why is the solar atmosphere hotter than the solar surface? Now this is a question that has foxed solar physicists for over half a century. Early spectroscopic observations of the solar corona revealed something perplexing: The Sun’s atmosphere is hotter than the photosphere. In fact, it is so hot that it is comparable to the temperatures found in the core of the Sun. But how can this happen? If you switch on a light bulb, the air surrounding the glass bulb wont be hotter than the glass itself; as you get closer to a heat source, it gets warmer, not cooler. But this is exactly what the Sun is doing, the solar photosphere has a temperature of around 6000 Kelvin whereas the plasma only a few thousand kilometres above the photosphere is over 1 million Kelvin. As you can tell, all kinds of physics laws appear to be violated.

However, solar physicists are gradually closing in on what may be causing this mysterious coronal heating. As observational techniques improve and theoretical models become more sophisticated, the solar atmosphere can be studied more in-depth than ever before. It is now believed that the coronal heating mechanism may be a combination of magnetic effects in the solar atmosphere. There are two prime candidates for corona heating: nanoflares and wave heating. I for one have always been a huge advocate of wave heating theories (a large part of my research was devoted to simulating magnetohydrodynamic wave interactions along coronal loops), but there is strong evidence that nanoflares influence coronal heating too, possibly working in tandem with wave heating.

Although we are pretty certain that wave heating and/or nanoflares may be responsible, until we can insert a probe deep into the solar corona (which is currently being planned with the Solar Probe mission), taking in-situ measurements of the coronal environment, we won’t know for sure what heats the corona (see Warm Coronal Loops May Hold the Key to Hot Solar Atmosphere).

4. Comet Dust

Comets - where does their dust come from?

How did dust formed at intense temperatures appear in frozen comets? Comets are the icy, dusty nomads of the Solar System. Thought to have evolved in the outermost reaches of space, in the Kuiper Belt (around the orbit of Pluto) or in a mysterious region called the Oort Cloud, these bodies occasionally get knocked and fall under the weak gravitational pull of the Sun. As they fall toward the inner Solar System, the Sun’s heat will cause the ice to vaporize, creating a cometary tail known as the coma. Many comets fall straight into the Sun, but others are more lucky, completing a short-period (if they originated in the Kuiper Belt) or long-period (if they originated in the Oort Cloud) orbit of the Sun.

But something odd has been found in the dust collected by NASA’s 2004 Stardust mission to Comet Wild-2. Dust grains from this frozen body appeared to have been formed a high temperatures. Comet Wild-2 is believed to have originated from and evolved in the Kuiper Belt, so how could these tiny samples be formed in an environment with a temperature of over 1000 Kelvin?

The Solar System evolved from a nebula some 4.6 billion years ago and formed a large accretion disk as it cooled. The samples collected from Wild-2 could only have been formed in the central region of the accretion disk, near the young Sun, and something transported them into the far reaches of the Solar System, eventually ending up in the Kuiper Belt. But what mechanism could do this? We are not too sure (see Comet Dust is Very Similar to Asteroids).

3. The Kuiper Cliff

The bodies in the Kuiper Belt (Don Dixon)

Why does the Kuiper Belt suddenly end? The Kuiper Belt is a huge region of the Solar System forming a ring around the Sun just beyond the orbit of Neptune. It is much like the asteroid belt between Mars and Jupiter, the Kuiper Belt contains millions of small rocky and metallic bodies, but it’s 200-times more massive. It also contains a large quantity of water, methane and ammonia ices, the constituents of cometary nuclei originating from there (see #4 above). The Kuiper Belt is also known for its dwarf planet occupant, Pluto and (more recently) fellow Plutoid “Makemake”.

The Kuiper Belt is already a pretty unexplored region of the Solar System as it is (we wait impatiently for NASA’s New Horizons Pluto mission to arrive there in 2015), but it has already thrown up something of a puzzle. The population of Kuiper Belt Objects (KBOs) suddenly drops off at a distance of 50 AU from the Sun. This is rather odd as theoretical models predict an increase in number of KBOs beyond this point. The drop-off is so dramatic that this feature has been dubbed the “Kuiper Cliff.”

We currently have no explanation for the Kuiper Cliff, but there are some theories. One idea is that there are indeed a lot of KBOs beyond 50 AU, it’s just that they haven’t accreted to form larger objects for some reason (and therefore cannot be observed). Another more controversial idea is that KBOs beyond the Kuiper Cliff have been swept away by a planetary body, possibly the size of Earth or Mars. Many astronomers argue against this citing a lack of observational evidence of something that big orbiting outside the Kuiper Belt. This planetary theory however has been very useful for the doomsayers out there, providing flimsy “evidence” for the existence of Nibiru, or “Planet X.” If there is a planet out there, it certainly is not “incoming mail” and it certainly is not arriving on our doorstep in 2012.

So, in short, we have no clue why the Kuiper Cliff exists…

2. The Pioneer Anomaly

Artist impression of the Pioneer 10 probe (NASA)

Why are the Pioneer probes drifting off-course? Now this is a perplexing issue for astrophysicists, and probably the most difficult question to answer in Solar System observations. Pioneer 10 and 11 were launched back in 1972 and 1973 to explore the outer reaches of the Solar System. Along their way, NASA scientists noticed that both probes were experiencing something rather strange; they were experiencing an unexpected Sun-ward acceleration, pushing them off-course. Although this deviation wasn’t huge by astronomical standards (386,000 km off course after 10 billion km of travel), it was a deviation all the same and astrophysicists are at a loss to explain what is going on.

One main theory suspects that non-uniform infrared radiation around the probes’ bodywork (from the radioactive isotope of plutonium in its Radioisotope Thermoelectric Generators) may be emitting photons preferentially on one side, giving a small push toward the Sun. Other theories are a little more exotic. Perhaps Einstein’s general relativity needs to be modified for long treks into deep space? Or perhaps dark matter has a part to play, having a slowing effect on the Pioneer spacecraft?

So far, only 30% of the deviation can be pinned on the non-uniform heat distribution theory and scientists are at a loss to find an obvious answer (see The Pioneer Anomaly: A Deviation from Einstein Gravity?).

1. The Oort Cloud

Artist's impression of the Oort Cloud. (NASA/JPL)

How do we know the Oort Cloud even exists? As far as Solar System mysteries go, the Pioneer anomaly is a tough act to follow, but the Oort cloud (in my view) is the biggest mystery of all. Why? We have never seen it, it is a hypothetical region of space.

At least with the Kuiper Belt, we can observe the large KBOs and we know where it is, but the Oort Cloud is too far away (if it really is out there). Firstly, the Oort Cloud is predicted to be over 50,000 AU from the Sun (that’s nearly a light year away), making it about 25% of the way toward our nearest stellar neighbour, Proxima Centauri. The Oort Cloud is therefore a very long way away. The outer reaches of the Oort Cloud is pretty much the edge of the Solar System, and at this distance, the billions of Oort Cloud objects are very loosely gravitationally bound to the Sun. They can therefore be dramatically influenced by the passage of other nearby stars. It is thought that Oort Cloud disruption can lead to icy bodies falling inward periodically, creating long-period comets (such as Halley’s comet).

In fact, this is the only reason why astronomers believe the Oort Cloud exists, it is the source of long-period icy comets which have highly eccentric orbits emanating regions out of the ecliptic plane. This also suggests that the cloud surrounds the Solar System and is not confined to a belt around the ecliptic.

So, the Oort Cloud appears to be out there, but we cannot directly observe it. In my books, that is the biggest mystery in the outermost region of our Solar System…

August 7, 2008December 24, 2015 by Ian O'Neill

Could Jupiter and Saturn Contain Liquid Metal Helium?

Rendering of a blue liquid metal... could this be what metallic helium looks like? Source: http://tinyurl.com/6lffol (waxellis)

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The interiors of the two gas giants, Jupiter and Saturn, are pretty extreme places. With atmospheric pressures of around 70 million Earth atmospheres, the phases of material become a bit difficult to understand. Usually when we think of a liquid metal, we have thoughts about liquid mercury at room temperature (or the reassembling liquid metal T-1000 played by Robert Patrick in the film Terminator 2), rarely do we consider two of the most abundant elements in the Universe to be a liquid metal in certain conditions. And yet, this is what a team of physicists from UC Berkley are claiming; helium and hydrogen can mix together, forced by the massive pressures near the cores of Jupiter and Saturn, forming a liquid metal alloy, possibly changing our perception of what lies beneath those Jovian storms…

Usually planetary physicists and chemists focus most of their attention on the characteristics of the most abundant element in the Universe: hydrogen. Indeed, over 90% of both Jupiter and Saturn is hydrogen too. But within these gas giant’s atmospheres is not the simple hydrogen atom, it is the surprisingly complex diatomic hydrogen gas (i.e. molecular hydrogen, H₂). So, to understand the dynamics and nature of the insides of the most massive planets in our Solar System, researchers from UC Berkley and London are looking into a far simpler element; the second most abundant gas in the Universe: helium.

Raymond Jeanloz, a professor at UC Berkeley, and his team have uncovered an interesting characteristic of helium at the extreme pressures that can be exerted near the cores of Jupiter and Saturn. Helium will form a metallic liquid alloy when mixed with hydrogen. This state of matter was thought to be rare, but these new findings suggest liquid metal helium alloys may be more common than we previously thought.

“This is a breakthrough in terms of our understanding of materials, and that’s important because in order to understand the long-term evolution of planets, we need to know more about their properties deep down. The finding is also interesting from the point of view of understanding why materials are the way they are, and what determines their stability and their physical and chemical properties.” – Raymond Jeanloz.

Jupiter for example exerts an enormous pressure on the gases in its atmosphere. Due to it’s large mass, one can expect pressures up to 70 million Earth atmospheres (no, that isn’t enough to kick-start fusion…), creating core temperatures of between 10,000 to 20,000 K (that’s 2-4 times hotter than the Sun’s photosphere!). So helium was chosen as the element to study under these extreme conditions, a gas that makes up 5-10% of the Universe’s observable matter.

Using quantum mechanics to calculate the behaviour of helium under different extreme pressures and temperatures, the researchers found that helium will turn into a liquid metal at very high pressure. Usually, helium is thought of as a colourless and transparent gas. In Earth-atmosphere conditions this is true. However, it turns into an entirely different creature at 70 million Earth atmospheres. Rather than being an insulating gas, it turns into a conducting liquid metal substance, more like mercury, “only less reflective,” Jeanloz added.

This result comes as a surprise as it has always been thought that massive pressures make it more difficult for elements like hydrogen and helium to become metal-like. This is because the high temperatures in locations like Jupiter’s core cause increased vibrations in atoms, thus deflecting the paths of electrons trying to flow in the material. If there is no electron flow, the material becomes an insulator and cannot be called a “metal.”

However, these new findings suggest that atomic vibrations under these kinds of pressures actually have the counter-intuitive effect of creating new paths for the electrons to flow. Suddenly the liquid helium becomes conductive, meaning it is a metal.

In another twist, it is thought that the helium liquid metal could easily mix with hydrogen. Planetary physics tells us that this isn’t possible, hydrogen and helium separate like oil and water inside the gas giant bodies. But Jeanloz’s team has found that the two elements could actually mix, creating a liquid metal alloy. If this is to be the case, some serious re-thinking of planetary evolution needs to be done.

Both Jupiter and Saturn release more energy than the Sun provides meaning both planets are generating their own energy. The accepted mechanism for this is condensing helium droplets that fall from the planets’ upper atmospheres and to the core, releasing gravitational potential as the helium falls as “rain.” However, if this research is proven to be the case, the gas giant interior is likely to be a lot more homogenous than previously thought meaning there can be no helium droplets.

So the next task for Jeanloz and his team is to find an alternate power source generating heat in the cores of Jupiter and Saturn (so don’t go re-writing the textbooks quite yet…)

Source: UC Berkeley

August 7, 2008December 24, 2015 by Ian O'Neill

Get Ready for September 10th: CERN Announces LHC Switch-On

A series of problems forced LHC shutdown (CERN/LHC)

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It’s official, the Large Hadron Collider (LHC) will begin operations in a little over a month. On September 10th, the most sophisticated particle accelerator will go online, injecting the first circulation of accelerated particles. Actual experiments involving collisions will occur once scientists are satisfied the LHC is fully optimized and calibration is complete. The LHC has been undergoing “cool-down” for some time, ensuring the LHC’s eight sectors are approaching the 1.9K (-271Â°C) operational temperature (that is 1.9 degrees above absolute zero). All going well, on September 10th, the first beam will be accelerated to an energy of 450 GeV (0.45 TeV), the preliminary step on the path to attaining particle energies of 5 TeV, a record breaking target… awesome.

Earlier today, CERN announced that the LHC will be ready by September 10th to attempt to circulate a beam of particles. This news comes as the “cool-down” phase of LHC commissioning reaches a successful conclusion, cooling all eight sectors to 1.9 degrees above absolute zero. To manage temperatures this extreme has been a long and painstaking task, referred to as a “marathon” by the project leader:

“We’re finishing a marathon with a sprint. It’s been a long haul, and we’re all eager to get the LHC research programme underway.” – LHC project leader Lyn Evans.

Now scientists and engineers must synchronize the LHC with the Super Proton Synchrotron (SPS) accelerator, which is the last component in the LHC’s particle injector chain. For the system to work, the LHC and SPS must be synchronized to within a fraction of a nanosecond. This task is expected to begin on August 9th (Saturday). These calibration tasks are expected to continue through August and into the beginning of September, preparing the LHC for its first particle injection on the 10th.

The LHC will accelerate particles to relativistic velocities, accessing energies previously unimaginable. Once the LHC reaches its optimum design specification (possibly by 2010), it will generate beams seven-times more energetic and 30-times more intense than any other particle accelerator on the planet. The accelerator ring lies below the Swiss countryside with a circumference of 27 km (17 miles).

Source: CERN

July 27, 2008December 24, 2015 by Ian O'Neill

IBEX Mission Will View the Final Frontier of the Solar System

The heliopause is the frontier between the Solar System and the interstellar medium. Credit: NASA/JPL

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Space is far from empty. The Solar System can be viewed as a “bubble” of solar matter – filled with particles emitted by the Sun as the solar wind – extending well beyond the orbit of Pluto. The solar wind velocity is supersonic for most of this distance (exceeding a million miles per hour), but the point at which it begins to interact with the interstellar medium (ISM), the solar wind drops to subsonic velocities, creating a region of compression known as the termination shock. After 26 years of flight, the Voyager 1 deep space probe entered this bizarre, turbulent region of space, where solar particles build up and magnetic fields become twisted. Now a new mission has been designed to watch this region of space from afar to begin to understand the boundary of our solar system, where violent turbulence rules and high-energy atoms are generated…

In 2004, Voyager 1 hit it and in 2006, Voyager 2 hit it. The first probe flew through the termination shock at around 94 AU (8 billion miles away); the second measured it at only 76 AU (7 billion miles). This result alone suggests that the termination shock may be irregularly shaped and/or variable depending on solar activity. Before the Voyager missions, the termination shock was theorized, but there was little observational evidence until the two veteran probes traversed the region. The termination shock is of paramount importance to understanding the nature of the outer reaches of the solar system as, counter-intuitively, the Sun’s activity increases, the region beyond the termination shock (the heliosheath) becomes more efficient at blocking deadly cosmic rays. During solar minimum, it becomes less efficient at blocking cosmic rays.

Artist impression of Voyager 1, the first probe to traverse the heliosheath (NASA)

In an effort to map the location and characteristics of the termination shock and heliosheath beyond, NASA scientists are preparing the Interstellar Boundary Explorer (IBEX) for launch in October. IBEX is part of NASA’s Small Explorer program (SMEX), where inexpensive, small probes are used to efficiently observe particular cosmic phenomena. IBEX will be orbiting beyond the influence of the Earth’s magnetic field (the magnetosphere) at a 200,000 mile distance from the Earth. This is because the phenomenon IBEX will be observing can be generated by our own magnetic field. So what will IBEX be measuring? To understand the interaction between solar wind ions and the interstellar medium, IBEX will use two sensors to detect energetic neutral atoms (ENAs) being blasted from the outermost reaches of the solar system.

How are ENAs generated and how are they a measurement of the interaction between the heliosphere and the ISM? Out there in the ISM exists neutral atoms and ions. As the solar system passes through interstellar space, the strong magnetic field generated around the heliosphere deflects the charged ions, pushing them out of the way. However, slow-moving neutral atoms are not affected by the magnetic field and penetrate deep into the heliosheath. When this happens, these neutral atoms from the ISM interact with energetic protons (which do have charge) rapidly spiralling along the magnetic field embedded in the solar wind. When this interaction occurs (known as charge exchange), an electron is stripped from the ISM atom and attracted to the energetic solar wind proton, thus making it neutral. When this exchange occurs, an energetic hydrogen atom (electron and proton) is ejected. An ENA is born.

Now, this is where the clever bit comes in. As mentioned before, neutral atoms do not “feel” magnetic fields, so when ENAs are created they are ejected in a straight line. Some of these atoms will be directed toward the Earth. IBEX will then measure these ENAs and work out where they came from. As they will have travelled directly to IBEX, the location of the termination shock may be deduced. Over a period of time, IBEX will be able to build up a picture of the locations of these atomic interactions and relate them the characteristics of the boundary of our Solar System.

But the best thing is, we won’t need to send a probe into deep space and wait for decades before it traverses the boundary layer, we will be able to make these measurements from Earth orbit. Such an exciting mission. Roll on the Pegasus rocket launch October 5th, 2008!

Source: Physorg.com

July 10, 2008December 24, 2015 by Ian O'Neill

Particle Physicists Discover Lowest Energy “Bottomonium” Particle

During particle collisions, hadrons split into quarks and bosons (University of Oregon)

Particle physicists working with the BaBar detector at Stanford Linear Accelerator Center have discovered a new particle in the bottomonium family of “quarkonium” particles. Technically it isn’t a “new particle” it is a previously unobserved state of particle, but when we are talking about subatomic particles, their energy states become a big deal (and their names get very cool). We are in the realms of the vanishingly small and the discovery of the lowest energy bottomonium particle may not seem very significant. But in the world of quantum chromodynamics, this completes the long quest to find experimental evidence for this elusive meson and may help explain why there is more matter than anti-matter in the Universe…

Quarkonia are types of mesons containing two quarks: one quark and its anti-quark (they are therefore “colourless”). They belong to one of two families: “bottomonium” or “charmonium”. As the names suggest, bottomonium contains a bottom quark and anti-bottom quark; charmonium contains a charm quark and anti-charm quark. Groups of three quarks (interacting via the strong force) are baryons (i.e. protons and neutrons) whereas groups of two quarks are mesons. Mesons are all thought to be made from a quark-antiquark pair and are therefore of huge importance when studying why there is more matter than anti-matter in the Universe.

This is where the BaBar detector at the Stanford Linear Accelerator Center (SLAC), CA, comes in. The BaBar international collaboration investigates the behaviour of particles and anti-particles during the production of the bottomonium meson (bottom-antibottom quark pairs) in the aim of explaining why there is an absence of anti-particles in everyday life.

For each particle of matter there exists an equivalent particle with opposite quantum characteristics, called an anti-particle. Particle and anti-particle pairs can be created by large accumulations of energy and, conversely, when a particle meets an anti-particle they annihilate with intense blasts of energy. At the time of the big-bang, the large accumulation of energy must have created an equal amount of particles and anti-particles. But in everyday life we do not encounter anti-particles. The question, therefore, is “What has happened to the anti-particles?” – From the BaBar/SLAC collaboration pages.

All matter has a “ground state”, or the lowest energy the system is trying to attain. As particles for instance try to reach this ground state, they lose energy, often in the form of electromagnetic radiation. Once reached, the ground state determines the baseline at which measurements can be made for higher energy states of those particles. And this is what the BaBar team has done, they have been able to isolate the lowest possible energy state for the bottomonium particle (which is far from easy). So what have they named the ground state of bottomonium? Quite simply: Î·b, pronounced “eta-sub-b“.

The bottomonium particle was generated during a collision between an electron and positron. The energy generated by this collision created a bottom quark and an anti-bottom quark bound together. At this point, the bottomonium particle was of too high an energy, but it very quickly decayed, emitting a gamma ray leaving the Î·b behind. However, Î·b’s are highly unstable and will quickly decay into other particles, plus they are very rare and difficult to detect. This particular decay event only occurs once in every two or three thousand higher energy bottomonium decays, so many collisions had to be measured and a huge amount of data had to be gathered by the BaBar detector before a precise measurement of the Î·b ground state could be gained.

“This very significant observation was made possible by the tremendous luminosity of the PEP-II accelerator and the great precision of the BaBar detector, which was so well calibrated over the BaBar experiment’s 8-plus years of operation. These results were highly sought after for over 30 years and will have an important impact on our understanding of the strong interactions.” – Hassan Jawahery, BaBar Spokesperson, University of Maryland.

If you want to find out more, you can check out the BaBar team’s publication (with the longest list of co-authors I’ve ever seen!) or the SLAC press release.

Source: SLAC

July 9, 2008December 24, 2015 by Ian O'Neill

Large Hadron Collider Could Generate Dark Matter

One of the biggest questions that occupy particle physicists and cosmologists alike is: what is dark matter? We know that a tiny fraction of the mass of the universe is the visible stuff we can see, but 23% of the Universe is made from stuff that we cannot see. The remaining mass is held in something called dark energy. But going back to the dark matter question, cosmologists believe their observations indicate the presence of darkmatter, and particle physicists believe the bulk of this matter could be held in quantum particles. This trail leads to the Large Hadron Collider (LHC) where the very small meets the very big, hopefully explaining what particles could be generated after harnessing the huge energies possible with the LHC…

The excitement is growing for the grand switch-on of the LHC later this summer. We’ve been following all the news releases, research possibilities and some of the more “out there” theories as to what the LHC is likely to discover, but my favourite bits of LHC news include the possibility of peering into other dimensions, creating wormholes, generating “unparticles” and micro-black holes. These articles are pretty extreme possibilities for the LHC, I suspect the daily running of the huge particle accelerator will be a little more mundane (although “mundane” in accelerator physics will still be pretty damn exciting!).

David Toback, professor at Texas A&M University in College Station, is very optimistic as to what discoveries the LHC will uncover. Toback and his team have written a model that uses data from the LHC to predict the quantity of dark matter left over after the Big Bang. After all, the collisions inside the LHC will momentarily recreate some of the conditions at the time of the birth of our Universe. If the Universe created dark matter over 14 billion years ago, then perhaps the LHC can do the same.

Should Toback’s team be correct in that the LHC can create dark matter, there will be valuable implications for both particle physics and cosmology. What’s more, quantum physicists will be a step closer to proving the validity of the supersymmetry model.

“If our results are correct we now know much better where to look for this dark matter particle at the LHC. We’ve used precision data from astronomy to calculate what it would look like at the LHC, and how quickly we should be able to discover and measure it. If we get the same answer, that would give us enormous confidence that the supersymmetry model is correct. If nature shows this, it would be remarkable.” – David Toback

So the hunt is on for dark matter production in the LHC… but what will we be looking for? After all dark matter is predicted to be non-interacting and, well, dark. The supersymmetry model predicts a possible dark matter particle called the neutralino. It is supposed to be a heavy, stable particle and should there be a way of detecting it, there could be the opportunity for Toback’s group to probe the nature of the neutralino not only in the detection chamber of the LHC, but the nature of the neutralino in the Universe.

“If this works out, we could do real, honest to goodness cosmology at the LHC. And we’d be able to use cosmology to make particle physics predictions.” – Toback

Source: Physorg.com

June 30, 2008December 24, 2015 by Ian O'Neill

Forget Neutron Stars, Quark Stars Might be the Densest Bodies in the Universe

The difference between a neutron star and a quark star (Chandra)

So neutron stars may not be the densest exotic objects in the cosmos after all. Recent observations of ultra-luminous supernovae suggest that these explosions may create an even more exotic remnant. Neutron stars can form after a star ends its life; measuring only 16 km across, these small but massive objects (one and a half times the mass of the Sun) may become too big for the structure of neutrons to hold it together. What happens if the structures of the neutrons inside a neutron star collapse? Quark stars (a.k.a. “Strange” stars) may be the result, smaller and denser than neutron stars, possibly explaining some abnormally bright supernovae observed recently…

Three very luminous supernovae have been observed and Canadian researchers are hot on the trail as to what may have caused them. These huge explosions occur at the point when a massive star dies, leaving a neutron star or black hole in their wake. Neutron stars are composed of neutron-degenerate matter and will often be observed as rapidly spinning pulsars emitting radio waves and X-rays. If the star was massive enough, a black hole might be formed after the detonation, but is there a phase between the mass of a neutron star and a black hole?

It appears there might be a smaller, more massive star on the block, a star composed not of hadrons (i.e. neutrons), but of the stuff that makes up hadrons: quarks. They are thought to be one step up the star-mass ladder, the point at which the mass of the supernova remnant is slightly too big to be a neutron star, but too small to form a black hole. They are composed of ultra-dense quark matter, and as neutrons break down it is thought some of their “up” and “down” quarks are converted into “strange” quarks, forming a state known as “strange matter.” It is for this reason that these compact objects are also known as strange stars.

Quark stars may be hypothetical objects, but the evidence is stacking up for their existence. For example, supernovae SN2005gj, SN2006gy and SN2005ap are all approximately 100 times brighter than the “standard model” for supernova explosions, leading the Canadian team to model what would happen if a heavy neutron star were to become unstable, crushing the neutrons into a soup of strange matter. Although these supernovae may have formed neutron stars, they became unstable and collapsed again, releasing vast amounts of energy from the hadron bonds creating a “Quark-Nova”, converting the oversized neutron star into a quark star.

If quark stars are behind these ultra-luminous supernovae, they may be viewed as super-sized hadrons, not held together by the nuclear strong force, but by gravity. Now there’s a thought!

Source: NSF

June 21, 2008December 24, 2015 by Ian O'Neill

Newsflash: The LHC Won’t Punch a Hole in the Earth After All…

Particle Collider — Today, CERN announced that the LHCb experiment had revealed the existence of two new baryon subatomic particles. Credit: CERN/LHC/GridPP

Its official: We’re not going to be blown up, smothered in stranglets, sucked into a black hole or turned into ooze by the Large Hadron Collider (LHC). To put any concerns to rest, CERN (the European Organization for Nuclear Research) has concluded in another approved safety report that the LHC is harmless and will not hurt us, our planet or the Universe. This new investigation builds on previous findings that the LHC is safe, reiterating what scientists have been telling us for years. Besides, the LHC isn’t doing anything that nature isn’t already doing every second…

I actually thought the LHC safety reports were done and dusted (the original report was actually completed in 2003), but it seems, to be thorough, CERN wanted to re-confirm their previous conclusions that the LHC was safe and ready for use later this year.

The LHC is understandably under intense scrutiny and will be subject to a range of audits from safety to environmental impact. This new report commissioned to investigate whether any of the theoretical particles created in the LHC collision chamber could pose a threat, not only to the cows and sheep in the Swiss countryside, but to the Earth and the Cosmos. Strengthened with experimental and observational research, the new report prepared by a team of physicists at CERN, UC Santa Barbara and the Institute for Nuclear Research of the Russian Academy of Sciences, has covered all the factors from previous safety investigations, and again concluded that the LHC is… safe.

As with any high-energy experiment, scientists and governments are under increased pressure to ensure every step is being taken to safeguard against any catastrophic accident. The LHC, soon to be the world’s most powerful particle accelerator, has seen more criticism than most physics experiments. For one, it is expensive (Â£2.4 billion or $4.7 billion), so collaborating governments and institutions want to know where their money is going, but second, CERN wants to avoid public misconceptions about what harm the LHC could do. This is epitomised in a recent lawsuit a Hawaiian man filed against CERN, citing the new accelerator might generate a black hole (that the Earth would get sucked into) or create a chain reaction, unleashing exotic “stranglets” on the planet. This is an extreme case of a misconception about what the LHC is capable of, so it seems essential that in-depth studies into LHC safety must be carried out continuously.

Listed is the safety reports perceived LHC threats (with likelihood of occurrence in parentheses):

Microscopic black holes (not very likely): Although it would be pretty cool if micro-black holes were generated, the report concludes that this event will be unlikely, although theoretically possible. If a micro-black hole was produced by an LHC collision, it is very likely that it would evaporate very quickly (via Hawking Radiation), making it difficult for any observation attempt. If a micro-black hole was produced but it didn’t evaporate (which isn’t possible, in theory), depending on its charge, it would behave differently. Charged, the micro-black hole could interact with matter and get stopped as it tries to pass through the Earth. Un-charged, the micro-black hole will pass straight through the Earth and into space (as it will be weakly interacting) or simply hang around inside our planet. We know collisions between cosmic rays and the Earth’s atmosphere happen naturally, often at higher energies than the LHC. Therefore, if micro-black holes are possible, the only option would be that they evaporate very quickly.. Besides, even if they were stable, they cannot suck in any matter and grow because they will have minimal gravitational influence over matter. Boring really…
Strangelets (practically impossible): This hypothetical “strange matter” (containing up, down and strange quarks) could theoretically change ordinary matter into strange matter in a thousand-millionth of a second. This possibility was raised in 2000 before the opening of the Relativistic Heavy Ion Collider (RHIC) in the US. This collider uses heavier particles than most of the LHC tests and therefore more likely to produce stranglets. In fact some of its experiments are set up to detect this strange matter. No stranglets have been found in eight years; not only that, but the chain reaction theorized (turning the world into a clump of strangeness) has no experimental foundation. Stranglets do not exist, and the LHC will not produce them.
Vacuum bubbles (practically impossible): Perhaps the Universe is not in its most stable configuration. Perturbations generated by the LHC could push it into a more stable state (a vacuum bubble), destroying the Universe as we know it. Not very likely. Again, collisions of higher energies happen throughout the cosmos, let alone in our own atmosphere, we’re still here, our Universe is still here (or is it?).
Magnetic monopoles (practically impossible): Hypothetical particles with a single magnetic pole, either north or south. If they could exist, they might mess around with protons possibly causing them to spontaneously decay. There is no reason to suspect they can exist, and even if they did, they could not be produced by the LHC as they are too heavy. Again, cosmic rays come to the rescue; as the high energy natural particle hit the atmosphere, their collisional energy is higher than the LHC. No magnetic monopoles, not end of the world.

Is that all there is? Surely there are more new and inventive ways to destroy the planet? Oh well…

So, it looks like we are in the clear for the grand switch on of the LHC! And now, you can have a ring-side seat, watching all the operations at the LHC via the array of webcams CERN has up and running:

Source: CERN

June 7, 2008April 26, 2016 by Ian O'Neill

Can a Wormhole Generate its Own Magnetic Field?

Artist impression of what it could look like when entering a wormhole (http://en.wikipedia.org/wiki/Image:FY221c15.png)

Wormholes are a strange consequence of Einstein’s theory of general relativity. These “shortcuts” through the fabric of space and time may link two different locations in the universe; they may even connect two different universes together. This also leads to the possibility that wormholes can allow travel between two points in time. These strange entities have provided science fiction stories with material for many years, but there is credible physics behind wormholes. Now it seems that in theory slowly-rotating wormholes may be able to generate their own magnetic field. Could this be used to detect the presence of wormholes in our observable Universe?

In a previous Universe Today article, I found some interesting research about the possibility of observing a wormhole using sensitive radio telescopes. What’s more, an observer may be able to see the light from another part of the Universe that has travelled along the wormhole and then emitted through the wormhole’s mouth. An observer could expect to see a bubble-like sphere floating in space, with emitted light intensifying around the rim.

In a publication last month, Mubasher Jamil and Muneer Ahmad Rashid from the National University of Sciences and Technology in Pakistan investigates the properties of a slowly rotating wormhole and the effect this would have on a surrounding volume of space. Their calculations assume a cloud of charged particles (i.e. electrons) are gravitationally attracted to the entity, and as the wormhole rotates, it drags the cloud of electrons with it. This approach had already been carried out when considering the effects of a slowly rotating compact star on surrounding stellar plasma.

This gravitational effect is known as “frame-dragging”. As the wormhole is predicted to have a gravitational influence on the space surrounding it, Einstein’s general relativity predicts that space-time will be warped. The best way to visualize this is to imagine a heavy ball on an elastic sheet; the ball causes the sheet to stretch downward, in a cone-shape. If the ball is spun on the sheet, friction between the ball and elastic will cause the sheet to distort in another way, it will begin to twist out of shape. If you apply this idea to space-time (the elastic sheet), and you have a slowly rotating wormhole (the ball), distortions in space-time will have a dragging effect on the surrounding particles, causing them to spin with the wormhole.

This is where Jamil and Rashid’s paper steps in. If you have a rotating mass of charged particles, a magnetic field may be generated (as a consequence of Maxwell’s equations). Therefore, in theory, a slowly-rotating wormhole could have its own magnetic field as a consequence of the electromagnetic field set up by the motion of charged particles.

So could a wormhole be detected by instrumentation? That depends on the magnitude of the warping of space-time a rotating wormhole has on local space; the smaller the wormhole, the smaller the density of rotating charged particles. As theorized natural wormholes are expected to be microscopic, I doubt there will be a large magnetic field generated. And besides, you’d have to be very close to the mouth of a wormhole to stand the chance of measuring its magnetic field. The possibility of detecting a wormhole may remain in the realms of science-fiction for a while yet…

Source: arXiv preprint server

June 2, 2008December 24, 2015 by Ian O'Neill

How do you Model the Earth’s Magnetic Field? Build your own Baby Planet…

The model Earth, can a magnetic field be modelled in the lab? (Flora Lichtman, NPR)

The Earth’s magnetic field is quite a mystery. How is it generated? How does it remain so stable? We have known of the Earth’s magnetic field for hundreds of years and the humble compass has been telling us the direction of magnetic North Pole since the 12th Century. Animals use it for navigation and we have grown dependent on its existence for the same reason. What’s more, the magnetosphere gives us a powerful shield against the worst solar storm. Yet we still have little idea about the mechanisms generating this field deep in the core of the Earth. In the hope of gaining a special insight to the large-scale, planetary magnetic field, a geophysicist from the University of Maryland has built his very own baby Earth in his laboratory, and it will be spinning (liquid metal included) by the end of the year…

This story reminds me of a classic experiment carried out by Norwegian Kristian Birkeland at the turn of the 19th Century. In an attempt to understand the dynamic Aurora Borealis (Northern Lights), Birkeland experimentally proved that electrical currents could flow along magnetic field lines (a.k.a. Birkeland, or “field-aligned” currents, pictured left). This can be observed in nature as charged particles from the solar wind interact with the Earth’s magnetosphere and are then guided down to the Earth’s magnetic poles. As the particles flow into the upper polar atmosphere, they collide with atmospheric gases, generating a colourful light display called aurorae. However, this early experiment simulated a magnetic field; it did not model how the Earth generates it in the first place.

Now, in a laboratory in the University of Maryland, geophysicist Dan Lathrop is pursuing this mystery by building his very own scale version of the Earth (pictured top). The model is set up on apparatus that will spin the 10-foot diameter ball to an equatorial speed of 80 miles per hour. To simulate the Earth’s molten outer core, Lathrop will fill the sphere with molten metal. The whole thing will weigh in at 26 tonnes.

This is Lathrop’s third attempt at generating a scale model of the Earth’s magnetic field. The last two attempts were much smaller, so this large experiment had to be constructed by a company more used to engineering heavy-duty industrial equipment.

It is believed that the Earth’s molten outer core, starting 2,000 miles below the Earth’s crust, generates the global magnetic field. This “dynamo effect” is somehow created through the interaction of turbulent liquid iron flow (which is highly conductive) with the spin of the planet. In Lathrop’s model, he will be using another conductive liquid metal, sodium. Molten iron is too hot to maintain in this environment, sodium exists at a liquid phase at far lower temperatures (it has a melting point close to that of the boiling point of water, nearly 100°C), but there are some serious hazards associated with using sodium as an iron analog. It is highly flammable in air and is highly reactive with water, so precautions will have to be taken (for one, the sprinkler system has been disabled, water in the case of a sodium fuelled fire will only make things worse!). This whole experiment, although risky, is required as there is no direct way to measure the conditions in the outer core of the Earth.

“The conditions of the core are more hostile than the surface of the sun. It’s as hot as the surface of the sun but under extremely high pressures. So there’s no way to probe it, no imaginable technique to directly probe the core.” – Dan Lathrop

Spinning this heavy sphere should cause sustained turbulence in the flow of the liquid sodium and it is hoped a magnetic field can be generated. There are many puzzles this experiment hopes to solve, such as the mechanics behind magnetic polar shift. Throughout the Earth’s history there is evidence that the magnetic poles have switched polarity, prolonged spinning of the model may cause periodic magnetic pole reversal. Testing the conditions in the conductive liquid metal may shed some light on what influences this global pattern of polar shift.

This kind of experiment has been done before, but scientists have directed the flow of liquid metal through the use of pipes, but this model will allow the metal to naturally organize itself, creating its own turbulent flow. Whether or not this test generates a magnetic field it is unknown, but it should aid our understanding about how magnetism is generated inside the planets.

See the video at National Public Radio »

Source: National Public Radio