Posted on by Fraser Cain

Titan is a World Both Familiar and Alien

On 14 January ESA’s Huygens probe made an historic first ever descent to the surface of Titan, 1.2 billion kilometres from Earth and the largest of Saturn’s moons. Huygens travelled to Titan as part of the joint ESA/NASA/ASI Cassini-Huygens mission. Starting at about 150 kilometres altitude, six multi-function instruments on board Huygens recorded data during the descent and on the surface. The first scientific assessments of Huygens’ data were presented during a press conference at ESA head office in Paris on 21 January.

“We now have the key to understanding what shapes Titan’s landscape,” said Dr Martin Tomasko, Principal Investigator for the Descent Imager-Spectral Radiometer (DISR), adding: “Geological evidence for precipitation, erosion, mechanical abrasion and other fluvial activity says that the physical processes shaping Titan are much the same as those shaping Earth.”

Spectacular images captured by the DISR reveal that Titan has extraordinarily Earth-like meteorology and geology. Images have shown a complex network of narrow drainage channels running from brighter highlands to lower, flatter, dark regions. These channels merge into river systems running into lakebeds featuring offshore ‘islands’ and ‘shoals’ remarkably similar to those on Earth.

Data provided in part by the Gas Chromatograph and Mass Spectrometer (GCMS) and Surface Science Package (SSP) support Dr Tomasko’s conclusions. Huygens’ data provide strong evidence for liquids flowing on Titan. However, the fluid involved is methane, a simple organic compound that can exist as a liquid or gas at Titan’s sub-170?C temperatures, rather than water as on Earth.

Titan’s rivers and lakes appear dry at the moment, but rain may have occurred not long ago.

Deceleration and penetration data provided by the SSP indicate that the material beneath the surface’s crust has the consistency of loose sand, possibly the result of methane rain falling on the surface over eons, or the wicking of liquids from below towards the surface.

Heat generated by Huygens warmed the soil beneath the probe and both the GCMS and SSP detected bursts of methane gas boiled out of surface material, reinforcing methane’s principal role in Titan’s geology and atmospheric meteorology — forming clouds and precipitation that erodes and abrades the surface.

In addition, DISR surface images show small rounded pebbles in a dry riverbed. Spectra measurements (colour) are consistent with a composition of dirty water ice rather than silicate rocks. However, these are rock-like solid at Titan’s temperatures.

Titan’s soil appears to consist at least in part of precipitated deposits of the organic haze that shrouds the planet. This dark material settles out of the atmosphere. When washed off high elevations by methane rain, it concentrates at the bottom of the drainage channels and riverbeds contributing to the dark areas seen in DISR images.

New, stunning evidence based on finding atmospheric argon 40 indicates that Titan has experienced volcanic activity generating not lava, as on Earth, but water ice and ammonia.

Thus, while many of Earth’s familiar geophysical processes occur on Titan, the chemistry involved is quite different. Instead of liquid water, Titan has liquid methane. Instead of silicate rocks, Titan has frozen water ice. Instead of dirt, Titan has hydrocarbon particles settling out of the atmosphere, and instead of lava, Titanian volcanoes spew very cold ice.

Titan is an extraordinary world having Earth-like geophysical processes operating on exotic materials in very alien conditions.

“We are really extremely excited about these results. The scientists have worked tirelessly for the whole week because the data they have received from Huygens are so thrilling. This is only the beginning, these data will live for many years to come and they will keep the scientists very very busy”, said Jean-Pierre Lebreton, ESA’s Huygens Project Scientist and Mission manager.

The Cassini-Huygens mission is a cooperation between NASA, ESA and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA’s Office of Space Science, Washington DC. JPL designed, developed and assembled the Cassini orbiter while ESA operated the Huygens atmospheric probe.

Original Source: ESA News Release

Posted on by Fraser Cain

Opportunity Finds an Iron Meteorite

NASA’s Mars Exploration Rover Opportunity has found an iron meteorite, the first meteorite of any type ever identified on another planet.

The pitted, basketball-size object is mostly made of iron and nickel according to readings from spectrometers on the rover. Only a small fraction of the meteorites fallen on Earth are similarly metal-rich. Others are rockier. As an example, the meteorite that blasted the famous Meteor Crater in Arizona is similar in composition.

“This is a huge surprise, though maybe it shouldn’t have been,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the science instruments on Opportunity and its twin, Spirit.

The meteorite, dubbed “Heat Shield Rock,” sits near debris of Opportunity’s heat shield on the surface of Meridiani Planum, a cratered flatland that has been Opportunity’s home since the robot landed on Mars nearly one year ago.

“I never thought we would get to use our instruments on a rock from someplace other than Mars,” Squyres said. “Think about where an iron meteorite comes from: a destroyed planet or planetesimal that was big enough to differentiate into a metallic core and a rocky mantle.”

Rover-team scientists are wondering whether some rocks that Opportunity has seen atop the ground surface are rocky meteorites. “Mars should be hit by a lot more rocky meteorites than iron meteorites,” Squyres said. “We’ve been seeing lots of cobbles out on the plains, and this raises the possibility that some of them may in fact be meteorites. We may be investigating some of those in coming weeks. The key is not what we’ll learn about meteorites — we have lots of meteorites on Earth — but what the meteorites can tell us about Meridiani Planum.”

The numbers of exposed meteorites could be an indication of whether the plain is gradually eroding away or being built up.

NASA Chief Scientist Dr. Jim Garvin said, “Exploring meteorites is a vital part of NASA’s scientific agenda, and discovering whether there are storehouses of them on Mars opens new research possibilities, including further incentives for robotic and then human-based sample-return missions. Mars continues to provide unexpected science ‘gold,’ and our rovers have proven the value of mobile exploration with this latest finding.”

Initial observation of Heat Shield Rock from a distance with Opportunity’s miniature thermal emission spectrometer suggested a metallic composition and raised speculation last week that it was a meteorite. The rover drove close enough to use its Moessbauer and alpha particle X-ray spectrometers, confirming the meteorite identification over the weekend.

Opportunity and Spirit successfully completed their primary three-month missions on Mars in April 2004. NASA has extended their missions twice because the rovers have remained in good condition to continue exploring Mars longer than anticipated. They have found geological evidence of past wet environmental conditions that might have been hospitable to life.

Opportunity has driven a total of 2.10 kilometers (1.30 miles). Minor mottling from dust has appeared in images from the rover’s rear hazard-identification camera since Opportunity entered the area of its heat-shield debris, said Jim Erickson of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., rover project manager. The rover team plans to begin driving Opportunity south toward a circular feature called “Vostok” within about a week.

Spirit has driven a total of 4.05 kilometers (2.52 miles). It has been making slow progress uphill toward a ridge on “Husband Hill” inside Gusev Crater.

JPL, a division of the California Institute of Technology in Pasadena, has managed NASA’s Mars Exploration Rover project since it began in 2000. Images and additional information about the rovers and their discoveries are available on the Internet at http://www.nasa.gov/vision/universe/solarsystem/mer_main.html and at http://marsrovers.jpl.nasa.gov.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Brown Dwarfs are Heavier Than Previously Thought

Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time.

The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be.

This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young “brown dwarfs” and “free floating” extrasolar planets.

A winning combination
A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter.

This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or “failed stars”, are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior.

To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called “Kepler’s Third Law”). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time – one year – it takes our planet to make a tour around the Sun.

The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed in large telescopes.

Astronomers have however found ways to overcome this difficulty. For this, they rely on a combination of a well-considered observational strategy with state-of-the-art instruments.

High contrast camera
First, astronomers searching for very low mass objects look at young nearby stars because low-mass companion objects will be brightest while they are young, before they contract and cool off.

In this particular case, an international team of astronomers [1] led by Laird Close (Steward Observatory, University of Arizona), studied the star AB Doradus A (AB Dor A). This star is located about 48 light-years away and is “only” 50 million years old. Because the position in the sky of AB Dor A “wobbles”, due to the gravitational pull of a star-like object, it was believed since the early 1990s that AB Dor A must have a low-mass companion.

To photograph this companion and obtain a comprehensive set of data about it, Close and his colleagues used a novel instrument on the European Southern Observatory’s Very Large Telescope. This new high-contrast adaptive optics camera, the NACO Simultaneous Differential Imager, or NACO SDI [2], was specifically developed by Laird Close and Rainer Lenzen (Max-Planck-Institute for Astronomy in Heidelberg, Germany) for hunting extrasolar planets. The SDI camera enhances the ability of the VLT and its adaptive optics system to detect faint companions that would normally be lost in the glare of the primary star.

A world premiere
Turning this camera towards AB Dor A in February 2004, they were able for the first time to image a companion so faint – 120 times fainter than its star – and so near its star.

Says Markus Hartung (ESO), member of the team: “This world premiere was only possible because of the unique capabilities of the NACO SDI instrument on the VLT. In fact, the Hubble Space Telescope tried but failed to detect the companion, as it was too faint and too close to the glare of the primary star.”

The tiny distance between the star and the faint companion (0.156 arcsec) is the same as the width of a one Euro coin (2.3 cm) when seen 20 km away. The companion, called AB Dor C, was seen at a distance of 2.3 times the mean distance between the Earth and the Sun. It completes a cycle around its host star in 11.75 years on a rather eccentric orbit.

Using the companion’s exact location, along with the star’s known ‘wobble’, the astronomers could then accurately determine the companion’s mass. The object, more than 100 times fainter than its close primary star, has one tenth of the mass of its host star, i.e., it is 93 times more massive than Jupiter. It is thus slightly above the brown dwarf limit.

Using NACO on the VLT, the astronomers further observed AB Dor C at near infrared wavelengths to measure its temperature and luminosity.

“We were surprised to find that the companion was 400 degrees (Celsius) cooler and 2.5 times fainter than the most recent models predict for an object of this mass,” Close said.

“Theory predicts that this low-mass, cool object would be about 50 Jupiter masses. But theory is incorrect: this object is indeed between 88 to 98 Jupiter masses.”

These new findings therefore challenge current ideas about the brown dwarf population and the possible existence of widely publicized “free-floating” extrasolar planets.

Indeed, if young objects hitherto identified as brown dwarfs are twice as massive as was thought, many must rather be low-mass stars. And objects recently identified as “free-floating” planets are in turn likely to be low-mass brown dwarfs.

For Close and his colleagues, “this discovery will force astronomers to rethink what masses of the smallest objects produced in nature really are.”

More information
The work presented here appears as a Letter in the January 20 issue of Nature (“A dynamical calibration of the mass-luminosity relation at very low stellar masses and young ages” by L. Close et al.).

Notes
[1]: The team is composed of Laird M. Close, Eric Nielsen, Eric E. Mamajek and Beth Biller (Steward Observatory, University of Arizona, Tucson, USA), Rainer Lenzen and Wolfgang Brandner (Max-Planck Institut for Astronomie, Heidelberg, Germany), Jose C. Guirado (University of Valencia, Spain), and Markus Hartung and Chris Lidman (ESO-Chile).

[2]: The NACO SDI camera is a unique type of camera using adaptive optics, which removes the blurring effects of Earth’s atmosphere to produce extremely sharp images. SDI splits light from a single star into four identical images, then passes the resulting beams through four slightly different (methane-sensitive) filters. When the filtered light beams hit the camera’s detector array, astronomers can subtract the images so the bright star disappears, revealing a fainter, cooler object otherwise hidden in the star’s scattered light halo (“glare”). Unique images of Saturn’s satellite Titan obtained earlier with NACO SDI were published in ESO PR 09/04.

Original Source: ESO News Release

Posted on by Fraser Cain

Perspective View of Claritas Fossae

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, shows Claritas Fossae, a series of linear fractures located in the Tharsis region of Mars.

The HRSC obtained this image during orbit 563, with a resolution of approximately 62 metres per pixel. The image shows a region centred around latitude 25? South and longitude 253? East.

Claritas Fossae is located on the Tharsis rise, south of the three large volcanoes known as the Tharsis Montes, and extends roughly north to south for approximately 1800 kilometres. The linear fractures of Claritas Fossae have widths ranging from a few kilometres to 100 kilometres, and the region is about 150 kilometres wide in the north and 550 kilometres wide in the south.

These fractures are radial to the Tharsis rise, consistent with the idea that they are the result of enormous stresses associated with formation of the 8-10 kilometre high Tharsis rise. Faults running east to west are also visible in the colour image and may have a similar origin.

In the east of the colour image, a prominent linear feature with a dark shadow is visible. This is most likely a normal fault, the eastern edge of a 100 kilometre wide ?graben?. A graben is a block of Mars’s crust which has dropped down due to an extension, or pulling, of the crust. This graben is characterised by a smooth surface and the difference in height between the edge of the graben and the plains east of the normal fault is roughly 2.3 kilometres. Alternatively, this feature may have resulted from surface collapse due to magma withdrawal.

The smooth surfaces in the image suggest this terrain has been resurfaced by lava flows. The observation that the lava flows have covered some of these faults, particularly in the west and north-east of the image, suggests that Claritas Fossae is older than the surrounding terrain.

The outline of a crater with a diameter of 50 kilometres is visible in the centre of the image. The softened appearance of the crater, and especially the observation that fractures extend across the crater, suggest this crater pre-dates the formation of the fractures. South of this crater, a faint outline is visible with a diameter of 70 kilometres, which may be another ancient crater.

West of these two craters, there is a small region with an interesting morphology, shown in the close-up image. These features seem to be weakly influenced by the north-south fractures. While the cause of emplacement of this terrain is still unclear, collapse of the surface due to the removal of subsurface ice might be responsible for these features.

By supplying new image data for Clarita Fossae, the HRSC camera allows improved study of the complex geology and history of the area. The stereo and colour capability of the HRSC camera provides scientists with the opportunity to better understand the Red Planet?s morphology, the evolution of rocks and landforms, and helps to pave the way for future Mars missions.

Original Source: ESA News Release

Posted on by Mark Mortimer

Book Review: Rocket Science

Rocketry itself has a long history. Possibly its first instance saw gunpowder-driven, arrow-type rockets fired by the ancient Chinese. The modern history of rocketry, especially its science, gathered steam throughout the 1900s as advances in physics and the provisions of necessary materials made a thorough study possible. Within this book many of the relevant physical relationships show how to analyse rocket performance. These include the basics: the laws of thermodynamics, enthalpy and gravitational force, as well as the more particular: thrust, specific impulse and mass ratios. Whenever equations first arise, examples guide the reader (e.g. comparative specific impulses for turbojets, ramjets, scramjets and rockets). However, no derivations or messy calculus appear, so no one will be overcome by the mathematics often associated with rocketry.

The discussion of the necessary materials principally revolves around the fuel. This isn’t surprising, as fuel accounts for well above 90% of the mass of a typical rocket. The many possible fuel types have their pro’s and con’s listed, e.g. whether storable, cryogenic, hypergolic, expensive or toxic. The different containment shapes and methods get described, as do the metals used to contain and support the fuel. Esoteric fuels, such as nuclear fission or fusion, have their due but the authors acknowledge that these are not likely to be a fuel source in the near future.

To compete their overview of rocketry, the authors first identify some of the key players in the pre-World War II time frame. Then they show how the German’s successes with the V-1, V-2 and Rheinbote during World War II led directly to the acquisition and enhancement of this technology by the USA and the USSR. Next, however, the authors pointedly show how these two countries diverged in their pursuits. The USSR stayed with a few capable techniques and from there developed a workhorse capability that today is providing the sole support for the International Space Station. The USA, on the other hand, has pursued many technologies and techniques; almost regularly spending billions of dollars to get to a demonstration phase only to drop further development. With this in mind, a final brief but insightful expos? on the future of rocket development shortlists the needs required to further people’s adventure into space.

As an overview, this book brings together a lot of information into a short, concise, yet expansive text. Facts and figures support many observations and opinions. Quotes and quips from bygone movers and shakers (e.g. Von Braun) add spice and warmth to these numbers. Many tables and figures show the progress (or lack thereof) within the industry. Photographs, both colour and black and white, show many of the rocket systems in use today. Most of NASA’s dreams and hopes (e.g. the NERVA, the nuclear rocket engine) have schematics and/or photographs as well, to round out the information provided.

Perhaps what isn’t expected is the information on satellite production and usage, solar sail utility, sex in space and politics. That is, this book includes more about the rocket or space industry than just the science of rockets. Some of the diversions, however, are worthwhile. For example, the authors include business details like the ‘cost per mile’ or ‘cost per person’. All in all though, this breadth of information makes for a handy reference to a general practitioner or an excellent introduction to a young student with a burgeoning interest in space.

Rockets just might be the pinnacle technical achievement of humankind. With artful combinations of liquids within a shaped chamber or from the pull of materials from a cylinder’s wall, a rocket counters the force of gravity to send people and material off our world. Alfred J. Zaehringer and Steve Whitfield in their book ‘Rocket Science‘ provide the facts, figures and photos to guide any interested person in some of the wizardry of rockets. Rocket science can appear daunting but with this book, anyone can easily delve into the magic.

To get your own copy, visit Countdown Creations.

Review by Mark Mortimer

Posted on by Fraser Cain

ESA and Russia Get Closer

Image credit: ESA
Today in Moscow, ESA Director General, Jean-Jacques Dordain and the Head of the Russian Federal Space Agency, Anatoly Perminov signed an agreement for long-term cooperation and partnership in the development, implementation and use of launchers.

This agreement, which comes within the general framework of the Agreement between ESA and the Russian Federation for Cooperation and Partnership in the Exploration and Use of Outer Space for Peaceful Purposes, will strengthen cooperation between ESA and Russia, ESA?s first partner in the long-term cooperation on access to space.

ESA-Russian partnership is based on two main pillars: the exploitation of the Russian Soyuz launcher from Europe?s Spaceport in French Guiana and cooperation, without exchange of funds, on research and development in preparation for future launchers.

The Soyuz at Europe?s Spaceport programme covers the construction of the Soyuz launch facilities in French Guiana and the adaptations that Soyuz will need to enable it to be launched from French Guiana. A number of ESA Member States have signed up for this optional ESA programme and their contributions will be supplemented by a loan to Arianespace from the European Investment Bank, guaranteed by the French Government as a temporary measure pending the creation by the European Commission of a guarantee reserve mechanism. Complementary funding from the European Union is also envisaged.

Work to prepare the Spaceport for Soyuz is already underway in French Guiana as the first launch from Europe?s Spaceport is scheduled to take place in 2007.

Today?s agreement will also allow work to begin on the second pillar: preparation activities for the development of future space transport systems. Europe and the Russian Federation will collaborate in developing the technology needed for future launchers. Russian and European engineers will work together to develop reusable liquid engines, reusable liquid stages and experimental vehicles.

ESA?s aim is to have a new generation launcher ready by 2020.

Original Source: ESA News Release

Posted on by Fraser Cain

Giant Iceberg on Collision Course

Some anticipated the ‘collision of the century’: the vast, drifting B15-A iceberg was apparently on collision course with the floating pier of ice known as the Drygalski ice tongue. Whatever actually happens from here, Envisat’s radar vision will pierce through Antarctic clouds to give researchers a ringside seat.

A collision was predicted to have already occurred by now by some authorities, but B-15A’s drift appears to have slowed markedly in recent days, explains Mark Drinkwater of ESA’s Ice/Oceans Unit: “The iceberg may have run aground just before colliding. This supports the hypothesis that the seabed around the Drygalski ice tongue is shallow, and surrounded by deposits of glacial material that may have helped preserve it from past collisions, despite its apparent fragility.

“What may be needed to release it from its present stalled location is for the surface currents to turn it into the wind, combined with help from a mixture of wind, tides and bottom melting to float it off its perch.”

To follow events for yourself, visit ESA’s Earthwatching site, where the latest images from Envisat’s Advanced Synthetic Aperture Radar (ASAR) instrument are being posted online daily.

Opposing ice objects
The largest floating object on Earth, the bottle-shaped B-15A iceberg is around 120 kilometres long with an area exceeding 2500 square kilometres, making it about as large as the entire country of Luxembourg.

B15-A is the largest remaining segment of the even larger B-15 iceberg that calved from the Ross Ice Shelf in March 2000. Equivalent in size to Jamaica, B-15 had an initial area of 11 655 square kilometres but subsequently broke up into smaller pieces.

Since then B-15A has found its way to McMurdo Sound, where its presence has blocked ocean currents and led to a build-up of sea ice. This has led to turn to resupply difficulties for the United States and New Zealand scientific stations in the vicinity and the starvation of numerous local penguins unable to forage the local sea.

ESA’s Envisat has been tracking the progress of B-15A for more than two years. An animated flyover based on past Envisat imagery begins by depicting the region as it was in January 2004, as seen by the optical Medium Resolution Imaging Spectrometer (MERIS) instrument (View the full animation – Windows Media Player, 3Mb).

The animation then moves four months back in time to illustrate the break-up of the original, larger B-15A (the current B-15A having inherited its name), split asunder by storms and currents while run aground on Ross Island, as observed by repeated ASAR observations. The animation ends with a combined MERIS/ASAR panorama across Victoria Land, including a view of the the Erebus ice tongue, similar to B-15A’s potential ‘victim’, the Drygalski ice tongue.

As the animation shows, ASAR is extremely useful for tracking changes in polar ice. ASAR can peer through the thickest polar clouds and work through local day and night. And because it measures surface texture, the instrument is also extremely sensitive to different types of ice ? so the radar image clearly delineates the older, rougher surface of ice tongues from surrounding sea ice, while optical sensors simply show a continuity of snow-covered ice.

“An ice tongue is ‘pure’ glacial ice, while the surrounding ice is fast ice, which is a form of saline sea ice,” Drinkwater says. “To the radar there is extreme backscatter contrast between the relatively pure freshwater ice tongue ? which originated on land as snow ? and the surrounding sea ice, due to their very different physical and chemical properties.”

The Drygalski ice tongue is located at the opposite end of McMurdo Sound from the US and New Zealand bases. Large and (considered) permanent enough to be depicted on standard atlas maps of the Antarctic continent, the long narrow tongue stretches 70 kilometres out to sea as an extension of the land-based David Glacier, which flows through coastal mountains of Victoria Land.

Measurements show the Drygalski ice tongue has been growing seaward at a rate of between 50 and 900 metres a year. Ice tongues are known to rapidly change their size and shape and waves and storms weaken their ends and sides, breaking off pieces to float as icebergs.

First discovered by British explorer Robert Falcon Scott in 1902, the Drygalski ice tongue is around 20 km wide. Its floating glacial ice is between 50 and 200 metres thick. The tongue’s history has been traced back at least as far as 4000 years. One source has been radiocarbon dating of guano from penguin rookeries in the vicinity ? the ice tongue has a body of open water on its north side that its presence blocks from freezing, sustaining the penguin population.

ESA’s Envisat environmental satellite
“The Drygalski ice tongue has been remarkably resilient over at least the last century,” Drinkwater concludes. “In spite of its apparent vulnerability, shallower bathymetry of the area ? enhanced by deposition of glacial sediments ? may play an important role in diverting the larger icebergs with more significant draught around this floating promontory.

“This may rule out its potential catastrophic removal from collision with a large drifting berg in the short term. That leaves the elements of temperature variations, wave and tidal flexure, or bending, to weaken and periodically whittle pieces off the end of the ice promontory.”

The 400-kilometre swath, 150-metre resolution images shown here of B-15A and the Drygalski ice tongue are from ASAR working in Wide Swath Mode (WSM). Envisat also monitors Antarctica in Global Monitoring Mode (GMM), with the same swath but a resolution of one kilometre, enabling rapid mosaicking of the whole of Antarctica to monitor changes in sea ice extent, ice shelves and iceberg movement.

Often prevailing currents transport icebergs far from their initial calving areas way across Antarctica, as with B-15D, another descendant of B-15, which has travelled a quarter way counterclockwise (westerly) around the continent at an average velocity of 10 km a day.

ASAR GMM images are routinely provided to a variety of users including the US National Oceanic and Atmospheric Administration (NOAA) National Ice Center, responsible for tracking icebergs worldwide.

ASAR imagery is also being used operationally to track icebergs in the Arctic by the Northern View and ICEMON consortia, providing ice monitoring services as part of the Global Monitoring for Environment and Security (GMES) initiative, jointly backed by ESA and the European Union. The two consortia are considering plans to extend their services to the Antarctic.

This year also sees the launch of ESA’s CryoSat, a dedicated ice-watching mission designed to precisely map changes in the thickness of polar ice sheets and floating sea ice.

CryoSat should answer the question of whether the kind of icesheet calving that gave rise to B-15 and its descendants are becoming more common, as well as improving our understanding of the relationship between

Original Source: ESA News Release

Posted on by Fraser Cain

How Far Can You See?

Image credit: Jason Ware
Amateur astronomy isn’t for everyone. But unlike other interests, it could be! After all, there’s plenty of sky to go around. And to enjoy the sky doesn’t take much. To start, just the power of human sight and the ability to “keep looking up”.

Appreciating the night sky and its numerous denizens is akin to enjoying any great work of art. Anyone captive to a painting by Van Gogh, statue by Roden, sonata by Beethoven, play by Shakespeare, or poem by Tennyson, can certainly appreciate a constellation wrought by nature’s sculpting hand. So like such great works of art, a fine appreciation of the night sky can be cultivated. Yet unlike such works, there is something far more primordial and immediately evocative about the heavens – a thing that defies any need for profound study or inculturation by others.

While it is true that some ingenious devices (such as the quadrant) were developed early on in the history of astronomy, it wasn’t until the time of Galileo (the early 17th century) that astronomers began probing the universe in detail. Before that time, the human eye placed such constraints on what could be seen that all we knew of the heavens was limited to two large bright bodies (Sun and Moon), numerous faint lights (the fixed stars and infrequent novae), and an intermediate group (the planets and occasional comets). Using instruments such as the quadrant (for position), and waterclock (for time), it became possible to predict the movements of all such bodies. And it was prediction – not understanding – that drove observation using the human eye alone.

Ultimately it was the telescope that made discovery – rather than measurement – the driving force behind the science of astronomy. For without the telescope, the Universe would be a far smaller place and populated by far, far fewer things. Consider that at 2.3 million light-years, the most distant celestial object visible unaided – the Great Galaxy of Andromeda – could never have been so-named at all. In fact, it might not have even received its older name: The Great Nebula in Andromeda. First noted in the 10th century text “Book of Fixed Stars”, sharp-eyed Abd-al-Rahman Al Sufi described the Great Galaxy as “a little cloud”. And that – without the telescope – is all we would ever have seen of this:

Because of the telescope, we now know far more about Sun, Moon, planets, comets, and stars than simply where they might be found in the sky. We understand that our Sun is a nearby star and that our Earth, the planets, and those “harbingers of doom” – the comets – are all part of a solar system. We have detected other such stellar systems beyond our own. We know we live in a galaxy that – from a distance of two million light-years – would appear much like M31 -1. We have determined that several billion years hence, our galaxy and M31 will embrace spiral arms. And we recognize that the Universe is extraordinary in its vastness, diversity, beauty, and harmony of inter-connectedness.

We know all this because we possess the telescope – and similar instruments – that can sound the depths of the cosmos across numerous octaves of spectral vibrancy.

But it all begins with the human eye…

The working of the human eye is based on three of the four main properties of light. Light may be refracted, reflected, diffracted, or absorbed. Light enters the eye as parallel beams from the distance. Because it is limited in aperture, the eye is only able to collect a very small proportion of the rays coming from any one thing. That collecting area – roughly 38 square millimeters (fully dilated and dark-adapted), allows the eye to normally see stars down to about magnitude 6. Ancient astronomers – free of the effects of modern sources of atmospheric illumination (light pollution) – were able to catalogue about 6000 individual stars (with a sprinkling of other objects). The faintest of these were classed of the “sixth magnitude”, and brightest of the “first”.

But the eye is also limited by the principle of diffraction. This principle prevents us from seeing exceedingly fine details. Because the eye is limited in aperture, parallel beams of light begin to “spread out” or propagate after entering the iris. Such diffusion means that – despite the use of refraction to focus – photons can only come so close together. For this reason, there is an ultimate limit to how much detail may be seen by any aperture – and that includes the eye itself.

The eye, of course, exploits the principle of refraction to organize beams of light. Photons enter the cornea, bend, and pass to the lens behind it. (The cornea does the bulk of the focusing and leaves about a third up to the lens.) The lens itself adjusts ray angles to bring things – near or far – to focus. It does this by changing radius of curvature. In this way, parallel rays from a distance or diverging rays from nearby may project an image on the retina where tiny neurons convert light-energy into signals for interpretation by the brain. And it is the brain – primarily the occipital lobes at the back of the head – that does the “image processing” needed to give coherence to that steady stream of neural signals arriving from the eye.

To detect light, the retina employs the principle of absorption. Photons cause sensory neurons to depolarize. Depolarization projects chemo-electrical signals from axons to dendrites deeper in the brain. Retinal neurons may be rod-shaped or conical. Rods detect light of any color and are more sensitive to light than cones. Cones detect specific colors only and are found in greater concentration along the main axis of the eye. Meanwhile rods dominate off-axis. The averted eye can see stars roughly two and half-times fainter than those held direct.

Beyond aversion, neural signals passing from the retina (via the optical chiasm) are first processed by the superior collicus. The collicus gives us our visual “flinch” response – but more importantly – it does less filtering of the visual field than the occipital lobes. Because of this, the collicus can detect even fainter sources of light – but only when in apparent motion. Thus the discerning observer can detect faint stars – and faintly glowing objects – some 4 times fainter than those seen through ordinary “straight-on” viewing. (This is done by sweeping the eye across the night sky – or across the field of view of the telescope.)

In addition to aversion and eye movement, the eyes increase sensitivity by adapting to low light conditions. This is done in two ways: First, fine muscles retract the iris (located between cornea and lens) to admit as much light as possible. Second, within roughly 30 minutes of exposure to darkness, “visual purple” (rhodopsin) on retinal rods takes on a transmissive rosey-red color. This change increases the sensitivity of rods to the point where even a single photon of visible light may be detected.

Aside from limitations imposed by diffraction, there is a second natural limit to how much detail can be seen by the eye. For neurons can be made only so small and placed only so close together. Meanwhile at about 25mm’s in focal length, the eye can only see “1x”. Add this to the fact that the greatest opening achieved by the eye (the entrance pupil) is 7mms and human eyes become the effective equivalent of a pair of “1x7mm” binoculars.

All these factors limit the eye – even under the best observing conditions (like the vacuum of space) – to seeing stars (using direct vision) of the eighth magnitude (1500 times fainter than the brightest stars) and resolving close pairs to about 2 arc-minutes of angular separation (1/15th the apparent size of the Moon).

Observational astronomy begins with the eyes. But new instrumentation evolved because some eyes have difficulty focusing light. Because of human near- and far- sightedness, the first spectacle lenses were ground. And it was only a matter of experimentation before someone combined one of each type lens together to form the first telescope or “instrument of long seeing”.

Today’s astronomers are able to augment the human eye’s capacity to the point where we can almost peer back to the beginning of time itself. This is done through the use of chemical and solid-state principles embodied in photography and charge-coupled devices (CCDs). Such tools are able to accumulate photons in a way the eye can not. As a result of these “visual aids”, we have discovered things once unimagined about the universe. Many of these discoveries were unknown to us – even as recently as the beginning of the era of the Great Observatories (the early twentieth century). Today’s astronomy has expanded the range of cosmic vision across numerous bands of the electromagnetic spectrum – from radio to X-rays. But we do far more than simply find stuff and measure positions. We seek to grasp more than light – but comprehension as well…

Today’s amateur astronomers – such as the author – use hand- and mass-produced telescopes from all parts of the world to peer billions of light-years into the depths of the Universe.-2 This type long-seeing is possible because the eye and telescope can work together to collect “more and finer light” from on high.

How far can you see?

-1According to NASA the Milky Way galaxy would appear very much like 15.3 MLY distant barred spiral M83 found in the constellation Hydra (as seen at right). A human being in space would just be able to hold the bright central portion of this 8.3 magnitude galaxy as a “fuzzy star” using averted vision. M83 can easily be found using low power binoculars from Earth.

-2 Bearing a variable visual magnitude of 12.8, 2 billion-light year distant quasar 3C273 can just be held direct by the human eye when augmented by a six-inch / 150mm aperture telescope at 150x through night time skies of 5.5 unaided limiting magnitude and 7/10p seeing stability. A pair of 10x50mm binoculars would reveal 3C273 as a faint star from Earth orbit.

Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff got a start in astronomy and space science at the age of seven. Currently he devotes considerable time maintaining the website Astro.Geekjoy.

Posted on by Fraser Cain

Red Dwarfs Destroy Their Dusty Disks

Astronomers announced Jan. 10 that they have a lead in the case of the missing disks. The report was presented by UCLA graduate student and Ph.D. candidate Peter Plavchan; his adviser, Michael Jura; and Sarah Lipscy, now at Ball Aerospace, to the American Astronomical Society meeting in San Diego. This lead may account for the missing evidence of red dwarfs forming planetary systems.

The evidence
Red dwarfs (or M Dwarfs) are stars like our Sun in many respects but smaller, less massive and fainter. Approximately 70 percent of all the stars in our galaxy are red dwarfs.

“We would like to understand whether these stars form planets, as the other stars in our galaxy do,” said Plavchan, who leads this research investigation.

Approximately half of all newborn stars are known to possess the materials to make planets. When stars are born, the leftover materials form what astronomers refer to as a primordial disk surrounding the star. From this primordial disk, composed of gas and small grains of solid material astronomers call “dust,” planets can start to grow. As these “planetesimals” grow by accreting nearby material in the primordial disk, they also collide with one another. These collisions are frequent and violent, producing more dust forming a new disk of debris after the star is about 5?10 million years old. In our own solar system, we see evidence everywhere of these violent collisions that took place more than 4 billion years ago ? such as the craters on the moon.

The debris disk of “dust” left over from these ancient collisions in our own solar system has long since dissipated. Astronomers, however, have discovered many young stars in the local part of our galaxy where these debris disks still can be seen. These stars are caught in the act of forming planets and are of great interest to astronomers who want to understand how this process works. Curiously though, only two of these stars with debris disks were found to be red dwarfs: AU Microscopium (AU Mic) and GJ 182, located 32.4 light-years and approximately 85 light-years from Earth, respectively.

Despite red dwarfs holding a solid majority among the different kinds of stars in our galaxy, only two have been found with evidence of debris disks. If half of all red dwarfs started with the material to form planets, what happened to the rest of them? Where did the material and dust surrounding these stars go? Factors such as the ages, smaller sizes and faintness of red dwarfs do not fully account for these missing disks.

The investigation
In December 2002 and April 2003, Plavchan, Jura and Lipscy observed a sample of nine nearby red dwarfs with the Long Wavelength Spectrometer, an infrared camera on the 10-meter telescope at the Keck Observatory on Mauna Kea, Hawaii. These nine stars all are located within 100 light-years of Earth and were thought potentially to possess debris disks. None, however, showed any evidence for the presence of warm dust produced by the collisions of forming planets.

Backed by the previous research investigations that also came up empty-handed, the researchers considered what makes red dwarfs different from other bigger, brighter stars that have been found with debris disks.

“We have to consider how the dust in these young red dwarfs gets removed and where it goes,” said Jura, Plavchan’s thesis adviser.

In other young, more massive stars ? A-, F- and G-types ? the dust primarily is removed by Poynting-Robertson drag, radiative blowout and collisions.

“These first two processes are simply ineffective for red dwarfs, so something else must be going on to explain the disappearance of the debris disks,” Plavchan said.

Under Poynting-Robertson drag, a consequence of special relativity, the dust slowly spirals in towards the star until it heats up and sublimates.

The new lead in the case
Plavchan, Jura and Lipscy have discovered that there is another process similar to Poynting-Robertson drag that potentially can solve the case of the missing red dwarf debris disks: stellar wind drag.

Stars like our Sun and red dwarfs possess a stellar wind ? protons and other particles that are driven by the magnetic fields in the outer layers of a star to speeds in excess of a few hundred miles per second and expelled out into space. In our own solar system, the solar wind is responsible for shaping comets’ tails and producing the Aurorae Borealis on Earth.

This stellar wind also can produce a drag on dust grains surrounding a star. Astronomers have long known about this drag force, but it is less important than Poynting-Robertson drag for our own Sun. Red dwarfs, however, experience stronger magnetic storms and consequently have stronger stellar winds. Furthermore, X-ray data show that the red dwarf winds are even stronger when the stars are very young and planets are forming.

“Stellar wind drag can ‘erase’ the evidence of forming planets around red dwarfs by removing the dust that is produced in the collisions that are taking place. Without stellar wind drag, the debris disk would still be there and we would be able to see it with current technology,” Plavchan said.

This research potentially solves the case of the missing disks, but more work is needed. Astronomers know little about the strength of stellar winds around young stars and red dwarfs. While further observations of red dwarfs by the Spitzer Infrared Telescope Facility have supported this research, this case will not be closed until we can directly measure the strength of stellar winds around young red dwarfs.

This research has been submitted to The Astrophysical Journal for publication and is supported by funding from NASA.

Original Source: UCLA News Release

Posted on by Fraser Cain

Huygens Landed in Mud

Although Huygens landed on Titan’s surface on 14 January, activity at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, continues at a furious pace. Scientists are still working to refine the exact location of the probe’s landing site, seen above.

While Huygens rests frozen at -180 degrees Celsius on Titan’s landscape, a symbolic finale to the engineering and flight phase of this historic mission, scientists have taken little time off to eat or sleep.

They have been processing, examining and analysing data, and sometimes even dreaming about it when they sleep. There’s enough data to keep Huygens scientists busy for months and even years to come.

Recreating Huygens’ descent profile
One of the most interesting early results is the descent profile. Some 30 scientists in the Descent Trajectory Working Group are working to recreate the trajectory of the probe as it parachuted down to Titan’s surface.

The descent profile provides the important link between measurements made by instruments on the Huygens probe and the Cassini orbiter. It is also needed to understand where the probe landed on Titan. Having a profile of a probe entering an atmosphere on a Solar System body is important for future space missions.

After Huygens’ main parachute unfurled in the upper atmosphere, the probe slowed to a little over 50 metres per second, or about the speed you might drive on a motorway.

In the lower atmosphere, the probe decelerated to approximately 5.4 metres per second, and drifted sideways at about 1.5 metres per second, a leisurely walking pace.

“The ride was bumpier than we thought it would be,” said Martin Tomasko, Principal Investigator for the Descent Imager/Spectral Radiometer (DISR), the instrument that provided Huygens’ stunning images among other data.

The probe rocked more than expected in the upper atmosphere. During its descent through high-altitude haze, it tilted at least 10 to 20 degrees. Below the haze layer, the probe was more stable, tilting less than 3 degrees.

Tomasko and others are still investigating the reason for the bumpy ride and are focusing on a suspected change in wind profile at about 25 kilometres altitude.

The bumpy ride was not the only surprise during the descent.

Landing with a splat
Scientists had theorised that the probe would drop out of the haze at between 70 and 50 kilometres. In fact, Huygens began to emerge from the haze only at 30 kilometres above the surface.

When the probe landed, it was not with a thud, or a splash, but a ‘splat’. It landed in Titanian ‘mud’.

“I think the biggest surprise is that we survived landing and that we lasted so long,” said DISR team member Charles See. “There wasn’t even a glitch at impact. That landing was a lot friendlier than we anticipated.”

DISR’s downward-looking High Resolution Imager camera lens apparently accumulated some material, which suggests the probe may have settled into the surface. “Either that, or we steamed hydrocarbons off the surface and they collected onto the lens,” said See.

“The probe’s parachute disappeared from sight on landing, so the probe probably isn’t pointing east, or we would have seen the parachute,” said DISR team member Mike Bushroe.

When the mission was designed, it was decided that the DISR’s 20-Watt landing lamp should turn on 700 metres above the surface and illuminate the landing site for as long as 15 minutes after touchdown.

“In fact, not only did the landing lamp turn on at exactly 700 metres, but also it was still shining more than an hour later, when Cassini moved beyond Titan’s horizon for its ongoing exploratory tour of the giant moon and the Saturnian system,” said Tomasko.

Original Source: ESA News Release