Posted on by Fraser Cain

Hubble’s View of a Giant Elliptical Galaxy

Like dust bunnies that lurk in corners and under beds, surprisingly complex loops and blobs of cosmic dust lie hidden in the giant elliptical galaxy NGC 1316. This image made from data obtained with the NASA Hubble Space Telescope reveals the dust lanes and star clusters of this giant galaxy that give evidence that it was formed from a past merger of two gas-rich galaxies.

The combination of Hubble’s superb spatial resolution and the sensitivity of the Advanced Camera for Surveys (ACS), installed onboard Hubble in 2002 and used for these images, enabled uniquely accurate measurements of a class of red star clusters in NGC 1316. Astronomers conclude that these star clusters constitute clear evidence of the occurrence of a major collision of two spiral galaxies that merged together a few billion years ago to shape NGC 1316 as it appears today.

NGC 1316 is on the outskirts of a nearby cluster of galaxies in the southern constellation of Fornax, at a distance of about 75 million light-years. It is one of the brightest ellipticals in the Fornax galaxy cluster. NGC 1316, also known as Fornax A, is one of the strongest and largest radio sources in the sky, with radio lobes extending over several degrees of sky (well off the Hubble image).

NGC 1316’s violent history is evident in various ways. Wide-field imagery from Cerro Tololo Interamerican Observatory in Chile shows a bewildering variety of ripples, loops and plumes immersed in the galaxy’s outer envelope. Amongst these so-called “tidal” features, the narrow ones are believed to be the stellar remains of other spiral galaxies that merged with NGC 1316 some time during the last few billion years. The inner regions of the galaxy shown in the Hubble image reveal a complicated system of dust lanes and patches. These are thought to be the remains of the interstellar medium associated with one or more of the spiral galaxies swallowed by NGC 1316.

The U.S. team of scientists, led by Dr. Paul Goudfrooij of the Space Telescope Science Institute in Baltimore, Maryland, used the ACS onboard Hubble to study star clusters in several nearby giant elliptical galaxies. Their study of NGC 1316 focused on globular clusters, which are compact stellar systems with hundreds of thousands to millions of stars formed at the same time.

The unprecedented sensitivity of the Hubble ACS data permitted the team to detect faint globular clusters previously impossible to reach. By counting the number of globular clusters detected as a function of their brightness they could, for the first time, see evidence of the gradual disruption of star clusters created during a past merger of gas-rich galaxies. They found that the relative number of low-mass clusters is significantly lower in the inner regions than in the outer regions, by an amount consistent with theoretical predictions.

These Hubble ACS images were taken in March 2003. The color composite is a combination of data taken in F435W (blue), F555W (yellow-green), and F814W (infrared) filters. The team’s results have improved our understanding of how elliptical galaxies and their star clusters may have formed during galaxy mergers and then evolve to resemble ‘normal’ elliptical galaxies after several billions of years.

Original Source: Hubble News Release

Posted on by Fraser Cain

Ultraviolet View of Mimas

Image credit: NASA/JPL/SSI
Saturn’s moon Mimas shines in reflected ultraviolet light from the Sun in this Cassini image. Ultraviolet images of Saturn’s moons often reveal the walls of their myriad craters in greater contrast than do images taken in visible light. This view, which shows the large impact crater Herschel, is no exception. Mimas is 397 kilometers (247 miles) across.

The image was taken with the Cassini spacecraft narrow-angle camera using a filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The image was acquired on Feb. 18, 2005, at a distance of approximately 938,000 kilometers (583,000 miles) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 99 degrees. The image scale is 6 kilometers (4 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. For additional images visit the Cassini imaging team homepage http://ciclops.org.

Original Source: NASA/JPL News Release

Posted on by Mark Mortimer

Book Review: Big Dish

The focal points in this book are the three largest communication antennas built by NASA, the backbone of the deep space network. Built roughly 120 degrees apart around the globe; Goldstone in California, Canberra in Australia, and Madrid in Spain, they spanned 64 metres in diameter originally though were later upgraded to 70 metres. Perhaps barely acknowledged by most space enthusiasts, they perform the critical service of linking us to our robot progeny in our reach off of Earth. Probes get sent commands to fire thrusters and in return send bits and bytes of video images of planets and moons. Robots get instructions to travel foreign terrains and provide visual treats of foreign lands. And perhaps most exciting, people on the moon interacted in (near) real time with Earth based operators. And lunar travel is the point in time when this book’s story begins.

Mudgway lays the groundwork to his story by outlining some of the significant political and space related issues. In the heydays of the 1960’s, a ready fiscal budget for space helped ensure the winning of the race and the build out of infrastructure like the antennae. Though the technology was still in its infancy a quick ramp up had to occur to meet the expectations of the space progam. On top of this groundwork he then builds a description of the existing state of technology and the requirements for the location and operation of the new antennae. What then follows in the book is an easy reading, chronologically arranged narrative of how the chosen people made it happen.

The narrative itself reads more like a fire side chat than like a specific technical treatise. The historical background and political circumstances embellish the reasoning for site selection. People’s names crop up, predominantly Bill Merrick the design and construction manager. Some of their more colourful actions and sayings enliven the text and remind the reader that people, not structures, were the central concern. Company names and their involvement get a slice of attention as well. So, as much as this book’s subject concerns the history of the antenna stations of the deep space network, the inclusion of people and extraneous events keeps the reading light and easy.

Nevertheless, the antenna stations are the main focus and there is a lot to learn within the book. Site selection had to meet limits on radio interference, ground stability and proximity of a workforce, even if Bogong moths were the initial main residents. Component fabrication and site build out gets a thorough description, from the laying of the continuous concrete ring 100 feet in diameter, 11 feet wide and 3 feet deep to using the quadripod support to install the feed system. In a pleasant manner, Mudgway effectively includes a sense of urgency by continually noting the need for the antenna to either support the manned space program or to be ready for a space probe doing a “once only” fly by of a distant planet.

Construction of the antenna encompasses a major portion of the book, though Mudgway also includes goodly portions on the operations and maintenance. We read how, just like a private residence, the antennae’s demands continually expanded to quickly exceed 100% availability. Then upgrades and procedure modifications allowed for better (faster and greater) abilities whose benefits were again quickly consumed by voracious researchers. Routine issues must have arisen, though none are included. Two major problems arose and are noted. One involves azimuthal motion. Oil allows a pad to travel across a steel runner. But if the runner gets uneven, contact occurs, and the antenna couldn’t turn until after signficiant repair work. In elevation, gears and bearings allowed the 4,000 ton dish to rotate in elevation, that is, until the bearings cracked. Again, things got very stressful and Mudgway does a wonderful job of describing the event, the people and the fix.

In a conversational, light tone, using generalist language, Mudgway gives an easy reading history of the antenna stations and the people involved. A reader can pick up some on the design and construction of the antenna and the people involved, however, don’t expect to learn much on the intricacies of microwave design or operation. Also, though chronological, the flow is uneven, at times like an old river that wanders and meanders without a clear focus, even though a destination does get reached.

The deep space network is the phone network that allows people to communicate with their mechanical offspring throughout our solar system. Douglas Mudgway in his book Big Dish, Building America’s Deep Space Connection to the Planets, gives a very smooth historical narrative of the people and events around the design, construction and upgrade of the three largest of the antennae.

Click here to read more reviews or order a copy online from Amazon.com.

Review by Mark Mortimer

Posted on by Fraser Cain

Is the Kuiper Belt Slowing the Pioneer Spacecraft?

Image credit: NASA
In ecology a pioneer is a “species establishing itself in a previously barren environment”. Among human beings, pioneers “settle in unknown or unclaimed territory”. Among astrophiles, Pioneer was our first effort to probe the solar system. But it appears that NASA’s twin pioneering efforts have now made less progress toward the stars than expected and the question is “Why?”.

When NASA designs a mission assumptions are made about the craft’s operating environment. Initially, NASA had some deep concerns about sending the two Pioneer probes through the asteroid belt – after all, all those big ones could be joined by a lot of little ones!

Meanwhile NASA must plan a flight path to take the craft where it’s going. Based on route, mission payload, and other requirements, enough thrust must be provided to provide the needed lift. The big factor affecting thrust is gravity – the more you have, the more thrust you need.

One of the ingenious things about Pioneer 10 and 11 was NASA’s choice to equip the pair with two-way communications sensitive to doppler shifts. Based on frequency shifts NASA could determine craft speed relative to receiving stations on Earth. Using this data, NASA could adjust thrusters to fine tune probe trajectories toward their objectives. (Both craft flew by Jupiter while Pioneer 11 made a pass near Saturn.)

As long as the probes had fuel, mission controllers could adjust speeds and trajectories. But once out of fuel the pair could only make progress based on inertia and slingshot momentum provided by a Gas Giant.

It was during inertial flight that anomalies began to show up in the motions of the two craft. Doppler shifts showed an unexpected deceleration just outside the orbit of Uranus. At some 20 earth-sun distances (astronomical units – AUs) NASA began to see a “blue-shift” in probe transmissions. The pair continued “singing the blues” while surpassing Neptune’s orbit 10 AUs later. Today the probes have fallen short of their expected locations by a distance greater than the Earth to the Moon…

Speculation as to the cause of the blue shift abound. Pioneer 10 & 11 themselves have long been ruled out as the source. Most thinking cites an unexpected increase in gravitational pull toward the Sun. When transmitting signals back to the Earth, the craft’s electromagnetic beams “fall” further into the solar systems gravity well and that well is somehow “steeper” than once thought. Today the pair are not as far along in their outbound journey as anticipated.

The question is: “What is the source of the unexpected increase in gravity effecting the probes?”. One answer lies in “dark matter”. Strangely, another lies in “dark energy” – the opposing force to gravity in the Universe. A third is in the domain of “string theory” (two local “branes” – the equivalent of local n-dimensional “tectonic plates” – may intersect in our system). One theory relates to “back-gravitational pull” (from the opposite side of the Solar System opposite each probe). There is also the possibility that the pair are having “Solar Quadrupolar Moments” or are being slowed by unexpected material in the Kuiper Belt outside Uranus.

But when it comes to sorting out the perpetrators we can usually take Inspector Louie’s advice from the movie Casablanca: “Round up the usual suspects.”

Both probes are now more than 70 AU’s away from the Sun – but still within the solar system’s Kuiper Belt. Their deceleration pattern suggests that the source of the anomaly is widespread and constant. In a March 15, 2005 paper entitled “Pioneer anomaly: Gravitational pull due to the Kuiper belt”. Jose A. Diego and other investigators from the Institute of Astronomy of the National Autonomous University of Mexico write: “… there is no need to invoke all the dark forces of the Universe at the beginning, try first to explain this phenomenon with local, everyday physics and if this is not enough then use heavy machinery.”

And the everyday physics? Why the Kuiper Belt of course! But not exactly the same old Kuiper Belt. For Jose et al, the Kuiper Belt now begins some 10AU’s closer to the Sun – just outside the orbit of Uranus – and has a thickness of 1 AU. The team’s Kuiper Belt has gained mass to almost twice that of the Earth’s – a little less than ten times originally proposed. In addition that mass is biased toward the orbit of Uranus. The increase in mass arises from the fact that original estimates in total Kuiper Belt mass was based on small particulate sizes. By including ices of larger size – along with gases in its composition, the group believes enough mass can be accounted for to explain why the probes’ slowed down and carrier signals shifted.

The team goes on to say: “… it’s important to point out that the belt would also effect Neptune’s orbit…”. Effectively any increase in mass within the Kuiper Belt would cause Neptune to spiral in slightly closer to the Sun. The team estimates that the planet’s center of mass would shift 1.62 kilometers with each full revolution of 164.8 terran years.

“The radial density distribution of mass needed to explain the constant acceleration toward the Sun measured by the Pioneer space crafts can be explained by models of Solar System formation.” writes the team. To explain the greater concentration of mass around Uranus’ orbit they go on to describe “an inward transport of material” toward the orbit of Uranus over time.

Another potential source of unexpected slowing is drag on the craft caused by a steady stream of particles within the belt. In this scenario, the Kuiper Belt would also have more matter than originally thought but that material would be evenly distributed (to account for the constant loss seen in each probe’s momentum).

Whatever the ultimate source of the probe’s deceleration, there is no fear that – like its three earliest predecessors – the pair will reverse course and burn up in any atmosphere near us. These two Pioneers are still destined to “settle in unknown or unclaimed territory” as humankind’s first emissaries to the stars.

Written by Jeff Barbour

Posted on by Fraser Cain

Proton Launches Russian Communications Satellite

Image credit: ILS
The new Russian Express-AM2 communications satellite was successfully launched into orbit by Proton-K launch-vehicle with the DM accelerating propulsion system at 1.31 a.m. Moscow time (29/03/2005 22.31 GMT). The new Express-AM2 satellite will be placed into geostationary orbit at 80 E. In the beginning of July, upon completing in-orbit tests and the system performing check Express-AM2 will be put into operation as a part of RSCC in-orbit satellite constellation.

Express-AM2 is the fourth out of five new-generation Express-AM satellites to be produced and launched by the end of 2005 in the context of Russian Federal Space Program. The first three Express-AM satellites, i.e. Express-AM22 (53 E), Express-AM11 (96.5 E), and Express-AM1 (40 E) are being successfully operated on geostationary orbit. The fifth Express-AM satellite, Express-AM3 (140 E), is planned to be launched in June, 2005.

The Express-AM2 satellite (80E) was developed by Russian NPO PM in cooperation with Alcatel Space French company. Sberbank of the Russian Federation takes an active part in financing the Program for Renovation of Russian satellite constellation. The launch and operation of new Express-AM satellites, including Express-AM2, are insured by Ingosstrakh insurance company (Russia).

The spacecraft carries 16 C-band transponders (40 and 72 MHz bandwidth), 12 Ku-band transponders (54 MHz bandwidth) and 1 L-band transponder (0.5 MHz bandwidth) with improved performance characteristics. Its in-orbit operational life time is 12 years, station keeping accuracy is +0.05? north-south/west-east that allows to use cheap antenna sets without automatic tracking devices. Express-AM2 provides coverage across Russia, the western and eastern parts of China, Korea, Northern India, Bangladesh, Butan, Nepal, northern part of Indochina.

The new satellite is designed to carry out state missions (mobile presidential and governmental communications, federal broadcasting, deployment of special satellite communications networks) and to provide a multi service communications package (digital broadcasting/ distribution, telephony, videoconferencing, data, broadband Internet access). In addition, the new satellite will be used for VSAT networks, departmental and corporate networks, and to provide multimedia services (distance learning, telemedicine etc.).

“The new Express-AM2 satellite will be put into strategically important orbital point 80 East over West Siberian plain. It will enable RSCC to implement its strategy aimed at providing the users in Russia and CIS with modern and cost-effective communications and broadcasting services. Besides, such location of the spacecraft will consolidate the Russian position on satellite communication markets of Central and South-East Asia”- emphasized Acting Director General of RSCC Yuri Izmailov.

Original Source: RSCC News Release

Posted on by Mark Mortimer

DVD Review: Apollo 13 (10th Anniversary Edition)

Apollo13 launched in 1970. Because of an onboard malfunction no astronauts landed on the targeted moon and very nearly no astronauts returned safely to Earth. 1995 saw the original release of this film that so grippingly captured the tumultuous event. This year, Universal Pictures is offering an anniversary edition. The two DVD discs contain the drama, twice. One is in a 2.35:1 aspect ratio and the other, briefer version, is in IMAX.

The film centres on the astronauts. Three flew in the capsule while one, quarantined from a possible exposure to measles, remained behind. Suspense builds steadily even for viewers with prior knowledge of the crisis. Flight crew selection, training, and embarkation proceed apace with suitable backdrops of loving families and concerned mission controllers. The rather incredulous disinterest from the media during the launch and for the first tranquil day of flight particularly raises ire and expectation. Then comes the famous phrase, ‘Houston, we have a problem’, and the film soars. Continually shifting from the space craft to the control room to the families’ homes combines these people into one scene and one event. Problems arise, get dealt and solutions to the next ones sought. Knowing the final outcome in no way diminishes the gripping nature of the delivery. A sense of relief is quite palpable on seeing the astronauts being welcomed on the recovery ship after their return to Earth. The film superbly portrays the drama that unfolded during this crisis in space

In a surprising conundrum, this film is incredibly authentic even though no stock footage was used. Many of the participants who were involved with the event provided first hand recollections. The control room was rebuilt, to spec. The astronauts flew for several hundreds of cycles in the KC-135 (Vomit Comet) astronaut trainer getting footage of real weightlessness. Flight manuscripts got memorized and where appropriate were repeated word for word. Little seems to have been missed in the successful quest for accuracy, to the point where a landing capsule was built and dropped just for this movie. As a further note, astronauts viewing this film asked about the launch footage given some very unexpected and rewarding perspectives. Their answer gets discussed in the special features elsewhere within the DVD. As a reference both of the era and the event, this film greatly fills the need. Nevertheless, first and foremost this film is an entertaining drama of humans nearly failing in their out reach to space.

Joining the film are special features. Commentaries by the director and actors give insight into the push for authenticity. Perhaps most rewarding are the many appearances by James and Marilyn Lovell who have obviously put so much of their own memories into this production. A brief vignette recapping the last 45 years in space is a handy perspective for the uninitiated. These embellish the video package in a nice way but don’t necessarily add much to the film itself.

Apollo 13 was a memorable mission and “Apollo13” does great justice to it as a film. As there may not be many people who could appreciate the included IMAX version, there may not be much value in getting this version in addition to the original release. Some people even preferred the original. However, for those looking to add a copy of this film into their libraries and those who missed the original release, this is a great package. Solid directing, an experienced and involved cast and a resounding musical score keep this film entertaining. Faithful reproduction of surroundings and events of the era make this an accurate historical drama.

James Lovell’s view as an astronaut were that, “you’re there because you expect crisis”. Apollo 13 was a crisis and the film version, “Apollo 13” directed by Ron Howard allows us to relive this moment using both a detached analytical view and a very attached drama tical view. Some corollary can be shared between the event and the film, ‘though each participant was an exceptional individual it was team work that won the day’.

Click here to read more reviews or order a copy online from Amazon.com.

Review by Mark Mortimer

Posted on by Fraser Cain

Dying Stars Could Provide a Second Chance for Life

Scientists recently discovered a new frontier in the race to find life outside our solar system. Dying red giant stars may bring icy planets back from the dead. Once-frozen planets and moons may provide a new breeding ground for life as their stars enter the last, and brightest, phase of their lives. Previous ideas about the search for extra-solar life had excluded these regions.

An international team of astronomers estimates that the emergence of new life on a planet is possible within the red giant phase. “Our result indicates that searches for life-giving worlds outside our solar system should include planets around old stars,” said Dr. Bruno Lopez of the Observatoire de la Cote d’Azur, Nice, France. Lopez and his colleagues estimate that more than 150 red giant stars are close enough – within 100 light years – for upcoming or proposed missions to search for the signatures of life on distant worlds. A light year is the distance light travels in one year, almost six trillion miles!

Location, Location, Location
One of the secrets of Earth’s success in producing life is its location within the sphere of the Sun’s habitable zone. This sphere intersects the plane of the solar system to create a special donut-shaped boundary that outlines where water can exist as a liquid in our solar system, a necessity for the development of life. Get too far from the Sun – and it’s a lonely icebox. Too close – and the water evaporates into space, never to return again.

While the Earth currently sits well within this donut of life, our Sun is evolving and will one day grow to be a red giant star. Its habitable zone will expand with it, changing the locales where liquid water can splash and life may one day thrive.

In Light of the Sun, Mars May Be a Sound Investment
Lying just inside the outer limit of our Sun’s habitable zone, Mars remains a frozen world today because of its thin atmosphere. However, when the Sun becomes a red giant a few billion years from now, Mars may become the happening place to be. “Mars will be in the habitable zone for a couple billion years, so Martian life may get a second chance,” said Dr. William Danchi of NASA’s Goddard Space Flight Center, Greenbelt, Md.

In 2003, researchers monitored the amount of ice on Mars during its winter and spring seasons. In some regions, the water-ice content was more than 90% by volume. Scientists suspect that this water used to fill the planet’s now-dry lakes and seas. One day in the distant future, the frozen water on Mars may fill these dry basins again and bring forth new life in our solar system.

Red Giants Redefine the Search for Extra-Terrestrial Life
The same holds true for planets and moons as they orbit their own red giant suns. Billions of years ago, these stars were similar to our Sun. Imagine the events as they unfolded: A Sun-like star explodes into its red giant phase, growing tremendously in size and brightness. Warm rays from the star reach out to a once-frozen and dead moon. The solitary satellite’s icy top layer quickly melts into liquid water, which creeps across the surface and fills old dusty craters with warmer seas. The stage is set for the birth of new life in the moon’s now-vibrant oceans.

Currently, there are at least 150 red giant stars within 100 light years of Earth and many of them may have orbiting planets capable of supporting life. A new frontier has opened for planet-hunters around the world.

One such endeavor, NASA’s Kepler mission, hopes to discover smaller Earth-like planets outside our solar system. Looking for tiny dips in the brightness of a star when a planet crosses in front of it, researchers will observe about 100,000 stars in one small patch of sky for four years. Kepler is set for launch in 2007.

Original Source: NASA News Release

Posted on by Fraser Cain

How Galaxy Collisions Lead to Starbirth

Data from ISO, the infrared observatory of the European Space Agency (ESA), have provided the first direct evidence that shock waves generated by galaxy collisions excite the gas from which new stars will form. The result also provides important clues on how the birth of the first stars was triggered and speeded up in the early Universe.

By observing our galaxy and others, scientists have long concluded that the explosion of massive stars like supernovae generates shock waves and ?winds? that travel through and excite the surrounding gas clouds. This process triggers the collapse of nearby gas that eventually leads to the birth of new stars, like a domino effect.

The signature of this process is the radiation emitted by molecular hydrogen. When hydrogen molecules are ?excited? by the energy of a nearby explosion, they emit a distinctive type of radiation that can be detected in the infrared.

This type of radiation is also observed in places where galaxies have collided with one another and the formation of new stars goes at a very high rate. So far, however, there was no clear picture of what happens in the time between the collision of two galaxies and the birth of the first new stars.

The missing link has now been found by a team of German astronomers that have analysed ISO data of the galaxy pair nicknamed the ?Antennae? (NGC 4038/4039). These two galaxies, located 60 million light-years away in the constellation ?Corvus? (the Crow), are currently at an early stage of encounter. The scientists noticed that the overlapping region of the two colliding galaxies is very rich in molecular hydrogen, which is in an excited state.

In particular, the radiation from molecular hydrogen is evenly strong in the northern and southern areas of the overlap region. Much to the team?s surprise, however, there are too few supernova explosions or regions of intense star formation there to explain the observed molecular hydrogen emission. So, the excitation of the molecular hydrogen must be the signature of that observationally rare pre-star birth phase in which hydrogen is excited by the mechanical energy produced in the collision and transported by shock waves. In other words, these results provide the first direct evidence of the missing link between gas collision and the birth of the first stars. The team estimates that when the gas will collapse to form new stars, during the next million years, the Antennae galaxy will become at least two times brighter in the infrared.

The astronomers believe that star formation induced by shocks may have played a role in the evolution of proto-galaxies in the first thousand million years of life of our Universe. Shock waves produced through the collision of proto-galaxies may have triggered the condensation process and speeded-up the birth of the very first stars. These objects, made up of only hydrogen and helium, would otherwise have taken much longer to form, since light elements such as hydrogen and helium take a long time to cool down and condense into a proto-star. Shock waves from the first cloud collisions may have been the helping hand.

Original Source: ESA News Release

Posted on by Fraser Cain

Medusa Fossae Region on Mars

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, shows part of the Medusa Fossae formation and adjacent areas at the highland-lowland boundary on Mars.

The HRSC obtained this image during orbit 917 with a resolution of approximately 13 metres per pixel. The scene shows an area located at about 5? South and 213? East.

The Medusa Fossae formation is an extensive unit of enigmatic origin found near the Martian ?highland-lowland dichotomy boundary? between the Tharsis and Elysium centres of volcanic activity. This dichotomy boundary is a narrow region separating the cratered highlands, located mostly in the southern hemisphere of Mars, from the northern hemisphere’s lowland plains.

The cratered highlands stand two to five kilometres higher than the lowland plains, so the boundary is a relatively steep slope. The processes that created and modified the dichotomy boundary remain among the major unanswered issues in Mars science.

The boundary between the old volcanic plateau region and part of the widespread deposits of the Medusa Fossae formation, called Amazonis Sulci, is shown in this image. In general, the formation appears as a smooth and gently undulating surface, but is partially wind-sculpted into ridges and grooves, as shown in the mosaic of nadir images.

It is commonly agreed that the materials forming Medusa Fossae were deposited by pyroclastic flows or similar volcanic ash falls. The plateau walls of the volcanic massif are partly covered by lava flows and crossed in places by valleys which were most likely carved by fluvial activity.

The remains of water-bearing inner channels are visible in the centre of the valleys and at the bottom of the massif. Superposition of the lobe-fronted pyroclastic flows indicates that the water erosion ended before their deposition. Later, a ?bolide? impacted near the massif and the ejecta blanket was spread as a flow over parts of the plateau, implying water or ice was present in the subsurface at the time of impact.

A bolide is any extraterrestrial body in the 1-10 kilometre size range, which impacts on a planetary surface, explodes on impact and creates a large crater. This is a generic term, used when we do not know the precise nature of the impacting body, whether it is a rocky or metallic asteroid, or an icy comet, for example.

Original Source: ESA News Release

Posted on by Fraser Cain

New Milky Way Dwarf Satellite Galaxy Discovered

Large spiral galaxies such as our own Milky Way are like huge sprawling continents in space. Like any continent, such galaxies should have many smaller islands lying off the coast. Current models of galaxy formation suggest that galactic continents should have more neighboring islands than actually seen with telescopes. Now one more island has been added to the Milky Way’s contingent and this one is small enough to map well against predictions. Other dwarfs – like the one recently discovered in Ursa Major – are likely to follow.

Located 300 thousand plus light-years away in the direction of the Big Dipper, the recently discovered Ursa Major (UMa) dwarf galaxy has roughly one-tenth the surface brightness of the next smallest Milky Way dwarf (located in Sextans). Like the Sextans dwarf, the UMa dwarf is spherical in shape (galaxy type dSph) and is in some ways similar to globular clusters which are also found in association with large spiral galaxies.

According to Beth Willman of New York University – principal investigator of a team of 15 astronomers studying data returned by the Sloan Digital Sky Survey (SDSS), “Ursa Major appears to be old and metal poor, like all of the other known Milky Way dwarf spheroidal companions. However, it may be 10 times fainter than the faintest known Milky Way satellite. We are in the process of obtaining more detailed observations that will provide a more detailed picture of UMa’s properties, which we will then compare with the other known satellites.

Beth goes on to explain, “UMa was detected as part of a systematic survey for Milky Way companions. It was detected as a slight statistical fluctuation in the number of red stars in that region of the sky.”

All galaxies and globular clusters include a wide range of stellar types in their makeup. These range from young, massive, short-lived, intensely bright blue-giants, through longer-lived, modestly massive, mostly middle-aged fainter yellow stars such as our Sun, to old, moderately bright, but hugely swollen red-giants similar to Scorpio’s Antares and Orion’s Betelguese. When it comes to finding nearby dwarf galaxies – such as the UMa dwarf – it is this last group of stars that are of especial interest. Red-giants are bright enough to be detected, identified spectroscopically, and counted using automated sky-surveying telescopes such as the SDSS in New Mexico – even from small satellite galaxies located several hundreds of thousands of light years away.

Once data from SDSS is available, teams such as Beth’s can analyze it for high-concentrations of red-giants in small regions of the sky. Their presence can indicate an unsupected dwarf galaxy or a globular cluster. Spectrographic information is used by teams such as Beth’s to filter out fainter – but far closer – red stars within the Milky Way itself. Finally a more detailed view of the study can be made using higher sensitivity instruments at other observatories.

Once data showed that a UMa dwarf galaxy might exist, the 2.5 meter wide-field camera of the Isaac Newton Telescope in the Canary Islands helped determine its general appearance. Images from the Newton Telescope plus data from SDSS was combined to verify the nature of the study as a spheroidal galaxy and not simply a rogue globular cluster – such as the Intergalactic Wanderer (NGC 2419) in Lynx located at a similar distance in space.

Although smaller dwarf galaxies have absolute magnitudes similar to the brightest globular clusters, one important difference between large globulars and small dwarfs lies in their size. The UMa dwarf is roughly ten times as large as the largest globulars known. And much of its mass is likely to be non-stellar “dark matter” – while nearly all the mass in a globular cluster is packed into stars. Since it’s large, but not very luminous, the team has tagged UMa as a dwarf galaxy.

From a cosmological perspective, satellite galaxies such as the Ursa Major dSph play an important role in explaining the formation of large, intermediate, and smaller scale structure throughout the Universe. On the largest scales, spiral galaxies (such as our Milky Way and the Great Galaxy of Andromeda) are known to dwell in extended groups of galaxies called groups and clusters. Our own group (the Local Group) is small in mass and extent while its two largest members, though large by spiral galaxy standards, are quite modest in comparison to the largest galaxies known to astronomers (the giant ellipticals). The very largest scales of galactic formation in the Universe include thousands of large galaxies while our own local group has but several dozen members. On the very smallest scales, the Milky Way and its retinue, which include the two irregular Magellanic Clouds plus now ten dwarf sphericals, make up a single gravitationally bound contingent. Because of this, astronomers have an opportunity to explore the smallest possible building blocks of extragalactic structure.

In their paper entitled “A new Milky Way Dwarf Galaxy In Ursa Major” Beth and her team go on to say, “UMa was detected very close to our detection limits. Numerous other dwarfs with properties similar to or fainter than the Ursa Major dSph may thus exist around the Milky Way… it is reasonable to expect that 8-9 additional dwarfs brighter than our detection limits still remain undiscovered over the entire sky. If true, that number would preclude (galactic formation) models that do not predict the presence of many ultra-faint dwarfs.”

Written by Jeff Barbour