Uranus's Moon Miranda: Bizarre Shape Explained

Uranus' icy moon Miranda is seen in this image from NASA's Voyager 2 probe on Jan. 24, 1986.

Credit: NASA/JPL-Caltech

The strange appearance of Uranus' moon Miranda may finally have an explanation.

Miranda resembles Frankenstein's monster, a bizarre jumble of parts that didn't quite merge properly.

Now, researchers suggest they may know why Miranda looks so odd: Constant squeezing and stretching from Uranus caused the moon's insides to heat up and churn.

Miranda is the innermost of Uranus' five major moons.

Though Miranda is only 293 miles (471 kilometers) wide, about one-seventh as large as Earth's moon, this ball of ice and rock possesses one of the oddest and most varied landscapes known among extraterrestrial bodies, including giant canyons up to 12 times deeper than the Grand Canyon.

"Miranda has a really bizarre, deformed surface," said study lead author Noah Hammond, a planetary scientist at Brown University in Rhode Island. "It's a really beautiful and exotic moon."

Miranda has three giant features known as coronae that are unique among known objects in the solar system.

They are shaped crudely, either like ovals or trapezoids, and each is least 120 miles (200 km) wide.

The coronae are separated from their more heavily cratered surroundings by belts of concentric ridges and troughs, making the coronae look like mismatched patches on a moth-eaten coat.

The three coronae, Arden, Elsinore and Inverness, are named after Scottish locations also mentioned in Shakespeare's plays.

This photo of Uranus' moon Miranda, taken by NASA's Voyager 2 probe in January 1986, shows an unusual "chevron" figure and regions of distinctly differing terrain on the mysterious satellite.

Credit: NASA/JPLView full size image

Researchers have long wondered how the coronae formed.

One possibility is that Miranda may have been disrupted by some catastrophic impact, after which its pieces chaotically reassembled.

The coronae formed as rocky material sank downward, triggering concentric wrinkles on Miranda's surface as it contracted, this idea goes.

Another possibility, one suggested by most scientists in the field, is that the coronae formed as buoyant domes of ice rose, causing Miranda's surface to crumple as matter was added to it.

However, it was not known where the heat to drive this ice upward might have come from. Since Miranda is relatively small, it would have cooled quickly after its creation, and it does not have the radioactive material that Earth possesses to help keep its innards hot.

Now, researchers show the gravitational pull of Uranus may have distorted Miranda enough to heat it up, leading its innards to churn much as Earth's does, thus explaining the coronae.

The gravity of Uranus pulls on Miranda, generating tidal forces, much as Earth's moondoes to Earth.

Tidal forces elsewhere in the solar system can be far greater than tidal effects on Earth, for instance, Jupiter's gravitational pull causes the solid rock surface of its third-largest moon Io to bulge up and down by as much as 300 feet (90 meters), generating enough heat to drive volcanic eruptions.

Miranda's orbit around Uranus was once eccentric, or oval-shaped, moving it closer to and farther from Uranus over time.

Three-dimensional computer simulations of Miranda's interior performed for the new study revealed the resulting tidal forces would repeatedly stretch and squeeze Miranda enough to generate substantial amounts of heat, about 5 gigawatts, or 2.5 times the peak power output of the huge Hoover Dam on the southwestern United States' Colorado River.

This heat would cause Miranda's icy mantle to churn with convection much like Earth's mantle of hot rock does. During convection, warm buoyant ice would have risen to Miranda's surface to contort it and create the coronae.

The research team's computer models accurately explained the locations of the coronae and the deformation patterns within the coronae, Hammond said.

"The features on Miranda may look really strange, but they formed in a way that is really similar to what happens on Earth, where convection in the interior drives surface deformation," Hammond told Space.com.

However, the scientists noted that for convection to drive Miranda's surface deformation, the moon's surface must be much weaker than predicted by laboratory experiments.

"The Earth has the same problem: For convection to deform Earth's surface, rocks have to behave weaker than expected," Hammond said.

"It'd be interesting to see what might explain the weakness seen in the surfaces of Miranda, Earth and elsewhere."

So far, scientists only know what Miranda's southern hemisphere looks like. NASA's Voyager 2 spacecraft photographed this part of the moon during its 1986 Uranus flyby but did not image Miranda's northern hemisphere.

"It'd be really interesting to think about what could be on the other side of Miranda," Hammond said. "Our study predicts there'd be one additional corona on Miranda's other side, and I would love to live long enough for a mission to go back to Uranus and test that hypothesis."

Hammond and his colleague Amy Barr detailed their findings online Sept. 15 in the journal Geology.

ESA GOCE and NASA GRACE detect Gravity Anomaly in Antarctic Ice Loss

Changes in Earth’s gravity field resulting from loss of ice from West Antarctica between November 2009 and June 2012 (mE = 10–12 s–2). 

 A combination of data from ESA’s GOCE mission and NASA’s Grace satellites shows the ‘vertical gravity gradient change’. 

Credit: ESA

Although not designed to map changes in Earth's gravity over time, ESA's extraordinary satellite has shown that the ice lost from West Antarctica over the last few years has left its signature.

Artist rendering of ESA's GOCE satellite in orbit. 

Credit: ESA

More than doubling its planned life in orbit, GOCE spent four years measuring Earth's gravity in unprecedented detail.

Scientists are now armed with the most accurate gravity model ever produced.

This is leading to a much better understanding of many facets of our planet, from the boundary between Earth's crust and upper mantle to the density of the upper atmosphere.

The strength of gravity at Earth's surface varies subtly from place to place owing to factors such as the planet's rotation and the position of mountains and ocean trenches.

Changes in the mass of large ice sheets can also cause small local variations in gravity.

Recently, the high-resolution measurements from GOCE over Antarctica between November 2009 and June 2012 have been analysed by scientists from the German Geodetic Research Institute, Delft University of Technology in the Netherlands, the Jet Propulsion Lab in USA and the Technical University of Munich in Germany.

Remarkably, they found that the decrease in the mass of ice during this period was mirrored in GOCE's measurements, even though the mission was not designed to detect changes over time.

Using gravity data to assess changes in ice mass is not new.

The NASA, DLR (Germany) Grace satellite, which was designed to measure change, has been providing this information for over 10 years.

However, measurements from Grace are much coarser than those of GOCE, so they cannot be used to look at features such as Antarctica's smaller 'catchment basins'.

For scientific purposes, the Antarctic ice sheet is often divided into catchment basins so that comparative measurements can be taken to work out how the ice in each basin is changing and discharging ice to the oceans. Some basins are much bigger than others.

By combining GOCE's high-resolution measurements with information from Grace, scientists can now look at changes in ice mass in small glacial systems, offering even greater insight into the dynamics of Antarctica's different basins.



They have found that that the loss of ice from West Antarctica between 2009 and 2012 caused a dip in the gravity field over the region.

In addition, GOCE data could be used to help validate satellite altimetry measurements for an even clearer understanding of ice-sheet and sea-level change.

Using gravity data to assess changes in ice mass is not new. The NASA, DLR (Germany) Grace satellite, which was designed to measure change, has been providing this information for over 10 years.

However, measurements from Grace are much coarser than those of GOCE, so they cannot be used to look at features such as Antarctica's smaller 'catchment basins'.

For scientific purposes, the Antarctic ice sheet is often divided into catchment basins so that comparative measurements can be taken to work out how the ice in each basin is changing and discharging ice to the oceans. Some basins are much bigger than others.

By combining GOCE's high-resolution measurements with information from Grace, scientists can now look at changes in ice mass in small glacial systems, offering even greater insight into the dynamics of Antarctica's different basins.

They have found that that the loss of ice from West Antarctica between 2009 and 2012 caused a dip in the gravity field over the region.

In addition, GOCE data could be used to help validate satellite altimetry measurements for an even clearer understanding of ice-sheet and sea-level change.

Using 200 million measurements collected by ESA’s CryoSat mission between January 2011 and January 2014, researchers from the Alfred Wegener Institute in Germany have discovered that the Antarctic ice sheet is shrinking in volume by 125 cubic kilometres a year. 

The study, which was published in a paper published on 20 August 2014 in the European Geosciences Union’s Cryosphere journal, also showed that Greenland is losing about 375 cubic kilometres a year. 

Credit: ESA

ESA's CryoSat satellite, which carries a radar altimeter, has recently shown that since 2009 the rate at which ice is been lost from the West Antarctic Ice Sheet every year has increased by a factor of three.

And, between 2011 and 2014, Antarctica as a whole has been shrinking in volume by 125 cubic kilometres a year.

Johannes Bouman from the German Geodetic Research Institute said, "We are now working in an interdisciplinary team to extend the analysis of GOCE's data to all of Antarctica.

"This will help us gain further comparison with results from CryoSat for an even more reliable picture of actual changes in ice mass."

This new research into GOCE's gravity data revealing ice loss over time is being carried out through ESA's Earth Observation Support to Science Element.

Lunar explorers will walk at higher speeds

This is a composite image of the lunar nearside taken by the Lunar Reconnaissance Orbiter in June 2009, note the presence of dark areas of maria on this side of the moon. 

Credit: NASA

Anyone who has seen the movies of Neil Armstrong's first bounding steps on the moon couldn't fail to be intrigued by his unusual walking style, but, contrary to popular belief, the astronaut's peculiar walk was not the result of low gravity.

John De Witt

Wyle Science, Engineering and Technology scientist John De Witt explains that the early space suits were not designed for walking, so the astronauts adapted their movements to the restrictions of the suit.

Michael Gernhardt, the head of NASA's Extravehicular Activity Physiology, Systems and Performance Project, wants to learn more about how humans move in low gravity, including the speed at which we break from a walk into a run, to design a modern space suit that permits freer movement.

However, the only way to test the effects of true lunar gravity on our movements while based on earth is to hop aboard NASA's adapted DC-9 aircraft, which reduces the gravity on board by performing swooping parabolic flights, and get running.

EVA Physiology, Systems, & Performance (EPSP) Project 

Credit: NASA HACD

De Witt and his colleagues publish their discovery that astronauts will remain walking at higher speeds on the moon than had been previously thought in The Journal of Experimental Biology.

To make this discovery, De Witt and colleagues Brent Edwards, Melissa Scott-Pandorf and Jason Norcross recruited three astronauts and five other registered test subjects that could tolerate the discomfort of the aircraft's bucking flight to test their running.

'There is some unpleasantness,' recalls De Witt, adding, 'if you get sick you're done…. We wanted to be sure we had people that were used to flying.'

An astronaut performs a 10 km "Walk back" to test his ability to return to a habitat in the event of a rover vehicle failure on the Moon.

Credit: NASA HACD

Once the subjects were airborne, the team only had 20s during each roller-coaster cycle, when the gravity on-board fell to one-sixth of that on Earth, when they could test the runner's walking and running styles on a treadmill as the volunteers shifted over a range of speeds from 0.67 to 2m/s.

However, De Witt recalls that the experiments ran smoothly once the team had settled into a routine after the first few parabolas.

Back on the ground, De Witt and colleagues analysed the speed at which the walkers gently transitioned into a run.

'Running is defined as a period of time with both feet off the ground', explains De Witt, adding that the walk to run transition was expected to occur at 0.8m/s in lunar gravity, based on theoretical calculations.

However, when the team calculated the transition speed from their experiments, they were in for a surprise: 'The average was 1.4m/s', recalls De Witt.

A NEEMO crewmember wearing a mock-up of the EVA portable life support system (PLSS) walks up and down a ladder outside the underwater Aquarius habitat. 

The PLSS mock-up was placed in different configurations to test astronauts' ability to perform EVA tasks when their center of gravity is moved up, down, forward, and/or backward. 

Credit: NASA HACD

'This difference is, to me, the most interesting part of the experiment; to try to figure out why we got these numbers', says De Witt, who suggests that the acceleration forces generated by the counter-swinging arms and legs could account for the shift in transition speed.

'What I think ends up happening is that even though the atmosphere is lunar gravity, the effective gravity on our system is lunar gravity plus the forces generated by our swinging arms and legs', says De Witt.

He explains that this arm-and-leg swinging effect probably happens here on Earth too, but the forces generated by the swinging limbs are negligible relative to our gravity.

However, he suspects that they are more significant in weaker lunar gravity, saying, 'They contribute more to the gravity keeping you attached to the ground.'

De Witt also adds that the higher transition value is not without precedent. He explains that scientists on Earth have simulated lunar gravity by supporting five-sixths of a runner's weight in a sling, and the athletes also transitioned from a walk to a run at speeds of around 1.4m/s1.

'This tells researchers [that] what they have in the lab, which is a fraction of the cost of the airplane, is probably adequate at giving you the information you need', he says.

More information: De Witt, J. K. , Edwards, W. B. , Scott-Pandorf, M. M., Norcross, J. R. and Gernhardt, M. L. (2014). The preferred walk to run transition speed in actual lunar gravity. J. Exp. Biol. 217, 3200-3203. jeb.biologists.org/content/217/18/3200.abstract

Mysterious quasar sequence explained

A growing black hole, called a Quasar, can be seen at the center of a faraway galaxy in this artist's concept. 

Credit: NASA/JPL-Caltech

Quasars are supermassive black holes that live at the center of distant massive galaxies.

They shine as the most luminous beacons in the sky across the entire electromagnetic spectrum by rapidly accreting matter into their gravitationally inescapable centers.

Yue Shen

New work from Carnegie's Hubble Fellow Yue Shen and Luis Ho of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University solves a quasar mystery that astronomers have been puzzling over for 20 years.

Their work, published in the September 11 issue of Nature, shows that most observed quasar phenomena can be unified with two simple quantities: one that describes how efficiently the hole is being fed, and the other that reflects the viewing orientation of the astronomer.

Luis Ho

Quasars display a broad range of outward appearances when viewed by astronomers, reflecting the diversity in the conditions of the regions close to their centers, but despite this variety, quasars have a surprising amount of regularity in their quantifiable physical properties, which follow well-defined trends (referred to as the "main sequence" of quasars) discovered more than 20 years ago.

Shen and Ho solved a two-decade puzzle in quasar research: What unifies these properties into this main sequence?

Using the largest and most-homogeneous sample to date of over 20,000 quasars from the Sloan Digital Sky Survey (SDSS), combined with several novel statistical tests, Shen and Ho were able to demonstrate that one particular property related to the accretion of the hole, called the Eddington ratio, is the driving force behind the so-called main sequence.

The Eddington Ratio

The Eddington ratio describes the efficiency of matter fueling the black hole, the competition between the gravitational force pulling matter inward and the luminosity driving radiation outward.

This push and pull between gravity and luminosity has long been suspected to be the primary driver behind the so-called main sequence, and their work at long last confirms this hypothesis.

Of additional importance, they found that the orientation of an astronomer's line-of-sight when looking down into the black hole's inner region plays a significant role in the observation of the fast-moving gas innermost to the hole, which produces the broad emission lines in quasar spectra.

This changes scientists' understanding of the geometry of the line-emitting region closest to the black hole, a place called the broad-line region: the gas is distributed in a flattened, pancake-like configuration.

Going forward, this will help astronomers improve their measurements of black hole masses for quasars.

New work solves a quasar mystery that astronomers have been puzzling over for 20 years. 

It shows that most observed quasar phenomena can be unified with two simple quantities: one that describes how efficiently the hole is being fed, and the other that reflects the viewing orientation of the astronomer.

This graph shows the distribution of about 20,000 luminous Sloan Digital Sky Survey (SDSS) quasars in the two-dimensional space of broad line width versus FeII strength, colour-coded by the strength of the narrow [OIII] line emission.

The strong horizontal trend is the main sequence of quasars driven by the efficiency of the black hole accretion, while the vertical spread of broad line width is largely due to our viewing angle to the inner region of the quasar. 

Credit: Yue Shen

"Our findings have profound implications for quasar research. This simple unification scheme presents a pathway to better understand how supermassive black holes accrete matter and interplay with their environments," Shen said.

"And better black hole mass measurements will benefit a variety of applications in understanding the cosmic growth of supermassive black holes and their place in galaxy formation," Ho added.

More information: The diversity of quasars unified by accretion and orientation, Nature, dx.doi.org/10.1038/nature13712

ESA GOCE: Lifetime of gravity measurements heralds new beginning

ESA's GOCE mission has delivered the most accurate model of the 'geoid' ever produced, which will be used to further our understanding of how Earth works. 

The colours in the image represent deviations in height (-100 m to +100 m) from an ideal geoid. 

The blue shades represent low values and the reds/yellows represent high values. 

A precise model of Earth's geoid is crucial for deriving accurate measurements of ocean circulation, sea-level change and terrestrial ice dynamics. 

The geoid is also used as a reference surface from which to map the topographical features on the planet. 

In addition, a better understanding of variations in the gravity field will lead to a deeper understanding of Earth's interior, such as the physics and dynamics associated with volcanic activity and earthquakes. 

Image courtesy ESA/HPF/DLR.

Although ESA's GOCE satellite is no more, all of the measurements it gathered during its life skirting the fringes our atmosphere, including the very last as it drifted slowly back to Earth, have been drawn together to offer new opportunities for science.

Carrying the first 3D gravity sensor in space, this state-of-the-art satellite measured Earth's gravity with unprecedented accuracy.

GOCE's four years in orbit resulted in a series of four gravity models, each more accurate than the last.

These models have been used to generate corresponding 'geoids' - the surface of a global ocean moulded by gravity alone.

Shaped by differences in gravity, the geoid is a crucial reference for understanding ocean circulation, sea-level change and ice dynamics.

From a mission that just keeps giving, a fifth model has now been produced. It incorporates data collected throughout the satellite's 42-month operational life.

The previous geoid, released in March 2013, was based on 27 months of measurements.

The satellite was designed to orbit at an extremely low altitude of 255 km to gain the best possible gravity measurements.

At the end of 2012, low fuel consumption allowed operators to extend its life and start to lower the satellite a further 31 km for even more accurate measurements.

This was at the very limit of its capability but maximised the return for science.

After more than doubling its planned life in orbit, the satellite ran out of fuel and drifted back into the atmosphere in November 2013.

The fifth gravity model and geoid, which ESA has recently made available, includes these final precious measurements, right up until the satellite finally stopped working and ironically succumbed to the force it was designed to measure.

Although the satellite is no longer in orbit, scientists now have the best possible information to hand about Earth's gravity, effectively a new beginning for the mission.

GOCE has already shed new light on different aspects of Earth and surpassed its original scope in a number of ways.

It is being used to understand how oceans carry huge quantities of heat around the planet and to develop a global height reference system.

It has provided information about atmospheric density and winds, mapped the boundary between Earth's crust and upper mantle, and used to understand what is going on in these layers far below our feet.

GOCE's achievements also include mapping a scar in Earth's gravity caused by the 2011 Japanese earthquake.

Changes in Earth’s gravity field resulting from the earthquake that hit Japan on 11 March 2011 (mE=10-12s-2). 

A combination of data from ESA’s GOCE mission and the NASA–German Grace satellite, shows the ‘vertical gravity gradient change’. The 'beachball' marks the epicentre.

Credit: ESA

The ultimate geoid model and gravity data will be used for years to come for a deeper understanding of Earth.

ESA's GOCE Mission Manager, Rune Floberghagen, said, "We are very happy with the results of the final, super-low altitude phase of our mission.

"In fact, efforts made by the mission team and by scientists to secure flight operations at these extreme altitudes and to process the data have resulted in a doubling of the information content and a very significant increase in spatial resolution.

"Indeed, our new 'Release 5 solutions' go well beyond the ambitious objectives we had when the GOCE project started.

"Scientists worldwide now have a satellite-based gravity field model at hand that will remain the de facto standard for many years to come."

Mysterious signal detected in galaxy 240 million light years away

Astronomers have detected a mysterious signal 240 million light years away from Earth. The unidentified signal is a 'spike of intensity at a very specific wavelength of x-ray light', but scientists don't yet know what the origin is.

Picked up in the Perseus Cluster, one of the biggest objects in the universe, the discovery is said to be the best evidence of dark matter yet.

Astronomers believe dark matter constitutes 85 per cent of the matter in the universe, but doesn't emit or absorb light like normal matter such as protons or electrons, which are known to make up the familiar elements seen in planets, stars, and galaxies.

Researchers suggest intensity coming from the Perseus Cluster could be a signature from the decay of a 'sterile neutrino,' which are a hypothetical type of neutrino thought to interact with normal matter via gravity but while holding exciting potential, the results must be confirmed with additional data to rule out other explanations and to see whether it is plausible that dark matter has been observed.

Chandra Sagittarius A*: Black holes at centre of galaxies are wormholes

Credit: X-ray: NASA /UMass /D.Wang et al., IR: NASA/STScI

Zilong Li and Cosimo Bambi with Fudan University in Shanghai have come up with a very novel idea, those black holes that are believed to exist at the center of a lot of galaxies, may instead by wormholes.

They've written a paper, uploaded to the preprint server arXiv, describing their idea and how what they've imagined could be proved right (or wrong) by a new instrument soon to be added to an observatory in Chile.

Sagittarius A*: NASA's Chandra Finds Milky Way's Black Hole may be Grazing on Asteroids

Back in 1974, space scientists discovered Sagittarius A* (SgrA ∗), a bright source of radio waves emanating from what appeared to be near the center of the Milky Way galaxy.

Subsequent study of the object led scientists to believe that it was (and is) a black hole, the behaviour of stars nearby, for example, suggested it was something massive and extremely dense.

What we're able to see when we look at SgrA ∗ are plasma gasses near the event horizon, not the object itself as light cannot escape.

That should be true for wormholes too, of course, which have also been theorized to exist by the Theory of General Relativity. Einstein even noted the possibility of their existence.

GRAVITY overview. The beam combiner instrument (bottom right) is located in the VLTI laboratory. 

The infrared wavefront-sensors (bottom left) are mounted to each of the four UTs. 

The laser metrology is launched from the beam-combiner and is detected at each UT/AT (top middle).

Unfortunately, no one has ever come close to proving the existence of wormholes, which are believed to be channels between different parts of the universe, or even between two universes in multi-universe theories.

In their paper, Li and Bambi suggest that there is compelling evidence suggesting that many of the objects we believe to be black holes at the center of galaxies, may in fact be wormholes.

Plasma gases orbiting a black hole versus a wormhole should look different to us, the pair suggest, because wormholes should be a lot smaller.

Plus, the presence of wormholes would help explain how it is that even new galaxies have what are now believed to be black holes, such large black holes would presumably take a long time to become so large, so how can they exist in a new galaxy?

They can't Li and Bambi conclude, instead those objects are actually wormholes, which theory suggests could spring up in an instant, and would have, following the Big Bang.

Making the two's speculation more exciting is the soon to be installed piece of equipment known as GRAVITY, it will be added to the European Space Observatory (ESO) in Chile, giving researchers there an unprecedented view of SgrA ∗ (and other black holes).

In just a couple of years, it should be possible to prove whether Li and Bambi's idea is correct or not, the photon capture sphere of the wormhole should be much smaller than that for a black hole, they note, if that's the case with SgrA ∗, space scientists will have to do some serious rethinking of wormholes and how they might fit in to current theories describing the universe.

More information: Distinguishing black holes and wormholes with orbiting hot spots, arXiv:1405.1883

ESA SWARM: Trio Heading for new heights - Video

The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. 

The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds. 

Credit: ESA/ATG medialab

Some tricky manoeuvres are now under way to steer ESA's trio of Swarm satellites into their respective orbits so that they can start delivering the best-ever survey of our magnetic field.
Since the Swarm constellation was launched last November, engineers have been busy putting the satellites through their paces to make sure that the craft and instruments are working correctly.

This commissioning phase is an essential part of the mission before it starts providing data to further our understanding of the complex and constantly changing magnetic field.

Essential to life, the magnetic field protects us from cosmic radiation and charged particles that bombard Earth in solar winds.

Since the intensity of solar activity is currently lower than anticipated, the original plan of where to place the satellites at the beginning of science operations has been reviewed recently by the scientific community and experts in ESA.

Low solar activity means the satellites experience lower atmospheric drag, as clearly demonstrated by ESA's GOCE mission.

Swarm is tasked with measuring and untangling the different magnetic signals that stem from Earth's core, mantle, crust, oceans, ionosphere and magnetosphere.

Launched together, the three identical Swarm satellites were released into adjacent orbits at an altitude of 490 km.

The satellites may be identical, but to optimise sampling in space and time their orbits are different – a key aspect of the mission.

The data acquired from different locations can be used to distinguish between the changes in the magnetic field caused by the Sun's activity and those signals that originate from inside Earth.

The result for Swarm is a slightly different orbit configuration that will save satellite fuel at the beginning of the mission and offer a better return for science at a later stage.

Two satellites are now being lowered to an altitude of about 462 km and an inclination of 87.35°. They will orbit almost side by side, about 150 km apart as they pass over the equator. Over the life of the mission they will both descend to about 300 km.

The third satellite is being placed in a higher orbit of 510 km and at a different inclination of 87.75°, slightly closer to the pole.

Swarm is ESA’s first Earth observation constellation of satellites. 

The trio of identical satellites are designed to identify and measure precisely the different magnetic signals that make up Earth's magnetic field. 

The electrical field instrument, positioned at the front of each satellite, measures plasma density, drift and acceleration in high resolution to characterise the electric field around Earth. 

Credit: ESA/ATG medialab

Ralf Bock

The mission's System Engineer, Ralf Bock, said, "We are taking the satellites to their new heights through careful thrust and aim to achieve the constellation for science operations around mid-April."

Karim Bouridah, the System Manager, added, "We are also continuing to fine-tune the satellite sensors, such as the new electric field instrument."

Each satellite carries a novel instrument to measures the velocity, direction and temperature of incoming ions.

This information will be used to calculate the electric field near the satellite, an important counterpart to the magnetic field for studying processes in the upper atmosphere.

In fact, Swarm is the first mission to make these global, multipoint measurements.

Johnathan Burchill from the University of Calgary explains, "Spanning more than an orbit, the images in this movie demonstrate the capability of the instrument to operate under a wide range of plasma conditions."

Newly discovered celestial object defies categories

This is an image of the ROXs 42B system obtained with the Keck telescope. 

The star is located in the center of the masked region. 

ROXs 42Bb orbits at about 150 astronomical units (AU). 

(1 AU=the distance from Earth to the Sun.) 

The other object ("c") is a likely unrelated background star. 

Credit: Thayne Currie

An object discovered by astrophysicists at the University of Toronto (U of T) nearly 500 light years away from the Sun may challenge traditional understandings about how planets and stars form.

The object is located near and likely orbiting a very young star about 440 light years away from the Sun, and is leading astrophysicists to believe that there is not an easy-to-define line between what is and is not a planet.

Thayne Currie

"We have very detailed measurements of this object spanning seven years, even a spectrum revealing its gravity, temperature, and molecular composition. Still, we can't yet determine whether it is a planet or a failed star – what we call a 'brown dwarf'. Depending on what measurement you consider, the answer could be either," said Thayne Currie, a post-doctoral fellow in U of T's Department of Astronomy & Astrophysics and lead author of a report on the discovery published this week in Astrophysical Journal Letters.

Named ROXs 42Bb for it's proximity to the star ROXs 42B, the object is approximately nine times the mass of Jupiter, below the limit most astronomers use to separate planets from brown dwarfs, which are more massive.

However, it is located 30 times further away from the star than Jupiter is from the Sun.

"This situation is a little bit different than deciding if Pluto is a planet. For Pluto, it is whether an object of such low mass amongst a group of similar objects is a planet," said Currie.

"Here, it is whether an object so massive yet so far from its host star is a planet. If so, how did it form?"

Most astronomers believe that gas giant planets like Jupiter and Saturn formed by core accretion, whereby the planets form from a solid core that then accretes a massive gaseous envelope.

Core accretion operates most efficiently closer to the parent star due to the length of time required to first form the core.

An alternate theory proposed for forming gas giant planets is disk instability – a process by which a fragment of a disk gas surrounding a young star directly collapses under its own gravity into a planet. This mechanism works best farther away from the parent star.

More information: The discovery is reported in a study titled "Direct imaging and spectroscopy of a candidate companion below/near the deuterium-burning limit in the young binary star system, ROXs 42B" which can also be viewed on arXiv.org at arxiv.org/abs/1310.4825.

Currie will present these and other findings at the annual meeting of the American Astronomical Society in Washington, DC this week.

Comet ISON drawn in by Sun's gravity and burns up - Video

The comet has most likely disintegrated under the high heat and gravitational stress of the Sun on Nov. 28, 2013. 

It is not visible in Solar Dynamics Observatory (SDO) footage and NASA scientists confirmed that they do not see it. 

 Credit: NASA / SDO / SOHO

NASA Grail: Twin Probes to Crash into Moon Next Week

Artist's concept of NASA's Grail mission. Grail's twin spacecraft are flying in tandem orbits around the moon to measure its gravity field in unprecedented detail. 

CREDIT: NASA/JPL

NASA's twin Grail spacecraft will crash into the lunar surface intentionally next week, bringing their gravity-mapping mission to a spectacular end.

The probes, known as Ebb and Flow, will be commanded to slam into the moon on Dec. 17, NASA officials said.

The agency will host a press conference to discuss the impact and the events leading up to it.

The $496 million Grail mission (Gravity Recovery and Interior Laboratory) launched in September 2011 to map the moon's gravity field in unprecedented detail.

Ebb and Flow arrived in orbit around the moon about one year ago — on New Year's Eve and New Year's Day, respectively.

The washing-machine-size spacecraft were originally tasked with 90-day science missions, which ran from March to May. but NASA extended Grail, allowing the two probes to gather a trove of additional data.

Ebb and Flow have been flying in formation around the moon, detecting the tiny changes in the distance between them caused by lunar mountains, craters and subsurface mass concentrations.

Scientists used these ultra-precise measurements to construct an incredibly accurate map of the lunar gravity field.

This map, unveiled last week at the fall meeting of the American Geophysical Union (AGU) in San Francisco, reveals that the moon's crust is almost completely pulverized.

The surprising find suggests that the moon and other rocky bodies in the inner solar system were pounded by long-ago impacts far more violently than previously believed, researchers said.

The new map was based on data gathered during Grail's original science mission; scientists expect to upgrade it based on measurements the spacecraft made during their extended mission, which brought them even closer to the lunar surface — an average altitude of 14 miles (23 km) as opposed to 34 miles (55 km).

Ebb and Flow are now running low on fuel as expected, NASA officials said, so the end is near for the probes. Mission managers will ensure that they go out in style on Dec. 17.

The Whirlpool Galaxy: M51

This image of the Whirlpool by Martin Pugh took the top accolade of Astronomy Photographer of the Year.

We can clearly see the galaxy's spiral arms, as well as its smaller companion galaxy being torn apart by M51's gravity.

(Image: Martin Pugh)

ESA Venus: The Venus Environment will kill in less than 10 seconds

Credit: ESA Artist Impression

Is there anyone who hasn’t admired the lovely beacon of Venus hanging bright in a cerulean sky? So bright in fact, it is regularly reported as UFO, or even more ludicrously, a mystery planet denied by orthodox astronomers.

I’ve written about Venus elsewhere, but let’s talk about the conditions there.

Under the gleaming sulphurous clouds, the planet has a surprisingly flat landscape with occasional ranges of gently rolling hills.

There are two major highlands, almost continents, but 80% of Venus is covered in these level lava plains.

The dense soupy atmosphere (96% carbon dioxide, 4% nitrogen) gives the landscape an oppressive and murky look.

This extreme atmosphere makes Venus deadly. The atmosphere exerts 90 times as much force per square centimetre as Earth’s atmosphere does on us, meanwhile this atmosphere has trapped millennia’s worth of solar heat.

Venus is hot. At 450 degrees Celsius, it is not quite a blast furnace but it’s nearly there.

Kilauea: Tiny Gravity Changes Show Magma's Underground Movements

Kilauea's current eruption is still going strong after 29 years.

CREDIT: USGS/HVO.

The secret movements of magma deep inside a volcano can be detected by tracking the subtle changes in gravity they cause.

Surprising readings from a Hawaiian volcano have researchers hoping to better understand volcanic activity through gravity monitoring.

Continuous gravity measurements of active volcanoes are relatively rare, with most results coming from Mount Etna in Italy.

"One problem is the expense," researcher Michael Poland, a geophysicist at the U.S. Geological Survey's Hawaiian Volcano Observatory, explained.

"Gravity measurements have always been a really expensive endeavor. The big users are oil and mining companies."

Now scientists have monitored the gravity at Kīlauea, a popular tourist destination on Hawaii's Big Island, and discovered a regular cycle of fluctuations that suggest magma is churning a kilometer (0.6 miles) below the surface.

The way magma churns in underground chambers below volcanic vents is key to understanding how persistent volcanoes are, and whether or not they might catastrophically erupt in the future.

However, what goes on deep under the Earth's surface is difficult to monitor.

One way to peer underground is by looking at Earth's gravity, the researchers said. Anything that has mass has a gravity field that pulls objects toward it.

The strength of this field depends on the amount of mass. Since the Earth's mass is not spread out evenly, this means the strength of the planet's gravitational pull is stronger in some places and weaker in others.

As such, the flow of magma from one place to another can be detected from above.

Most active volcano

"Kīlauea is the world's most active volcano," Poland said. "It's erupted almost continuously since 1983. It's a natural 'lab volcano' ―a great place to try and study something like gravity measurements."

The researchers installed two continuous gravity meters at the summit of the volcano in 2010. One was about 1.2 miles (2 kilometers) northwest of the eruptive vent at the summit and recorded measurements every10 seconds, while the other was placed about 500 feet (150 meters) east and recorded data every second.

They detected gravity fluctuations that came in a cycle about 150 seconds long.

"There was no expectation for that kind of result," Poland reported. "That gravity oscillation came out of nowhere. It points to the idea that there's probably a lot of things going on in volcanoes, glaciers, wherever you look, but we haven't developed the tools to detect these sorts of things."

NASA GRAIL: Lunar twins Ebb and Flow have extended mission to map gravity

NASA’s twin GRAIL spacecraft, named Ebb and Flow, have successfully completed their primary mission of mapping lunar gravity. 

They have now entered an extended mission in order to obtain gravity maps of even higher resolution than before.

The two spacecraft entered this phase of the mission at 16:28 UT on 30 August when they moved to a lower orbit.

The orbital altitude of the extended mission will see the craft at an average of only 23 kilometres (14 miles) above the Moon’s surface, compared to the average orbital height of 55 kilometres (34 miles) during the primary mission.

At this lower altitude Ebb and Flow will be within 8 kilometres (5 miles) of some of the Moon's higher surface features.

The data collected during the primary mission of GRAIL - which stands for Gravity Recovery And Interior Laboratory - is being analysed and "holds the promise of producing a gravity field map of extraordinary quality and resolution" according to Maria Zuber, principal investigator for GRAIL.

"Mapping at a substantially lower altitude during the extended mission, and getting an even more intimate glimpse of our nearest celestial neighbour, provides the unique opportunity to globally map the shallow crust of a planetary body beyond Earth."

The extended mission will run from 30 August until 3 December, and it will map the gravitational fields of small lunar features, such as craters and mountains.

This unprecedented resolution will help scientists to comprehend the formation and evolution of the Moon.

"Ebb and Flow, and our mission operations team, are both doing great, which is certainly notable considering all the milestones and challenges they have experienced," said David Lehman, GRAIL project manager.

"The twins have endured the lunar eclipse of June 4, 2012, and 26 rocket burns since arriving in lunar orbit at the beginning of the year.

Down here in our control room, with all the planning and mission operations we have been doing, it feels as though we've been riding right along with them. Of course, they have the better view."

It was not guaranteed that the GRAIL twins would survive the lunar eclipse in June.

The spacecraft are mainly powered by solar panels, and there were fears that the batteries on board would not be able to power the craft for the duration of the eclipse.

Fortunately, the NASA spacecraft proved their resilience, enabling the extended phase of the mission to go ahead.

Leland Melvin, NASA Associate Administrator for Education, left, Maria Zuber, GRAIL Prinicipal Investigator at the Massachusetts Institute of Technology, and James Green, Director of the Planetary Science Division in the Science Mission Directorate at NASA Headquarters, right, applaud students from Emily Dickinson Elementary School in Bozeman, Mont. during a news conference, Tuesday, Jan. 17, 2012, at NASA Headquarters in Washington. 

Nine hundred classrooms and more than 11,000 students from 45 states, as well as Puerto Rico and the District of Columbia, participated in a contest that began in October 2011 to name the twin lunar probes.

Photo Credit: NASA/Paul E. Alers

 The GRAIL twins map the lunar gravity by measuring the varying distance between two craft using radio signals. The distance between Ebb and Flow will change depending on the amount of mass

below them, allowing the craft a glimpse into the lunar interior.

The GRAIL spacecraft were launched on 10 September 2011, arrived at the Moon over the New Year and began their primary science mission on 7 March 2012.

Milky Way: Dark Matter Mysteriouly Missing

This artist’s impression shows the Milky Way galaxy. The blue halo of material surrounding the galaxy indicates the expected distribution of the mysterious dark matter, which was first introduced by astronomers to explain the rotation properties of the galaxy and is now also an essential ingredient in current theories of the formation and evolution of galaxies.

CREDIT: ESO/L. Calçada

Dark matter is mysteriously missing from the sun's neighborhood, according to a new study that could provide ammunition for skeptics who argue that the invisible substance is just an illusion.

"There will be people claiming dark matter doesn't exist because of this result," predicted study leader Christian Moni-Bidin, an astronomer at Chile's University of Concepción.

"These observations alone do not prove that dark matter does not exist. Still, it is not where we expected it and where we needed it."
 

Even though dark matter particles can't be detected with current instruments, astronomers think the substance must make up about a quarter of the universe, based on the gravitational effect it has on visible matter such as galaxies and galaxy clusters.

Since its discovery in the 1930s, the material has become crucial for galaxy-formation theories, which say that dark matter functions as a kind of invisible scaffold around which normal matter gravitationally coalesces to form stars and larger objects.

Current models of how galaxies form and rotate suggest that the Milky Way is embedded in a cloud, or halo, of dark matter. Astronomers can't tell precisely what shape this halo takes, but they expected to find significant amounts of dark matter in the region around the sun. 

Sun's Motion Reveals No Dark Matter?
In the new study, Moni-Bidin and his colleagues used the European Southern Observatory's La Silla and Las Campanas telescopes in Chile to map the three-dimensional motions of more than 400 red giant stars up to 13,000 light-years from the sun.

Stars in the sky may appear static, but they're constantly in motion as they get minutely pushed and pulled by the gravitational effects of neighboring objects, including other stars, gas clouds, or clumps of dark matter.

The team compared their measurements of stellar motion with what they predicted the motions would be if the stars' movements were affected by visible matter alone.

To their surprise, the two sets of measurements matched. In other words, dark matter was not necessary to explain the motions of the sun and its close neighbors.

"These observations point to the fact that in this volume [of space], there is no dark matter," Moni-Bidin said.

Dark-Matter Study Has Achilles Heel
However, the new results are being met with some skepticism, because they rely on ten simplifying assumptions, said Avi Loeb, chair of the astronomy department at Harvard University, who was not involved in the study.

For example, the analysis assumes that the average speed at which the stars in question orbit the center of the Milky Way is the same no matter the stars' distances from the galactic center. Knowing this speed is important for creating a complete picture of the factors that influence a star's motion.

But "this assumption by itself requires dark matter, unless gravity is modified," Loeb said in an email.

One reason scientists think dark matter exists is because stars in the outer parts of galaxies have been seen to orbit the center as fast as stars in the inner parts. The laws of gravity dictate that such fast-moving stars near the edges of galaxies should fly off into space. Instead, the theory goes, the added mass of dark matter holds them in place.

An alternative idea is that gravity itself behaves differently at different distances from the galactic core. However, "if gravity is modified, then it is unclear which equations one should use in the [new study's] modeling," Loeb said.

"Extraordinary claims require extraordinary evidence," he added, "and these ten assumptions are the Achilles heel of the claim that dark matter is absent in the solar neighborhood."

For his part, study author Moni-Bidin thinks it's too early for astronomers to give up on dark matter, because the substance is still too important for widely held theories about how the universe works.

"We are far from being able to live without [dark matter]," he said. "At the moment we need it to explain too many observations where alternative theories fail."

The new dark-matter research will be detailed in an upcoming issue of the Astrophysical Journal.