Posted on by Fraser Cain

Wallpaper: Louros Valles

Image credit: ESA
These latest images show a system of sapping channels, called Louros Valles (named in 1982 after river in Greece), south of the Ius Chasma canyon which runs east to west.

These images were taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express during orbit 97 from an altitude of 269 kilometres. The images have a resolution of about 13 metres per pixel and are centred at 278.8? East and 8.3? South. The colour image has been created from the nadir and three colour channels. North is at the right.

The Ius Chasma belongs to the giant Valles Marineris canyon system on Mars. The Geryon Montes, visible at the right of this image, is a mountain range which divides the Ius Chasma into two parallel trenches. The dark deposits at the bottom of the Ius Chasma are possibly related to water and wind erosion.

‘Sapping’ is erosion by water that emerges from the ground as a spring or seeps from between layers of rock in a wall of a cliff, crater or other type of depression. The channel forms from water and debris running down the slope from the seepage area.

This is known from similar features on Earth, but on Mars it is thought that most of the water had probably either evaporated or frozen by the time it reached the bottom of the slope.

Original Source: ESA News Release

Posted on by Fraser Cain

Field Reversal Takes 7,000 Years

Image credit: NASA
The time it takes for Earth’s magnetic field to reverse polarity is approximately 7000 years, but the time it takes for the reversal to occur is shorter at low latitudes than at high latitudes, a geologist funded by the National Science Foundation (NSF) has concluded. Brad Clement of Florida International University published his findings in this week’s issue of the journal Nature. The results are a major step forward in scientists’ understanding of how Earth?s magnetic field works.

The magnetic field has exhibited a frequent but dramatic variation at irregular times in the geologic past: it has completely changed direction. A compass needle, if one existed then, would have pointed not to the north geographic pole, but instead to the opposite direction. Such polarity reversals provide important clues to the nature of the processes that generate the magnetic field, said Clement.

Since the time of Albert Einstein, researchers have tried to nail down a firm time-frame during which reversals of Earth’s magnetic field occur. Indeed, Einstein once wrote that one of the most important unsolved problems in physics centered around Earth’s magnetic field. Our planet’s magnetic field varies with time, indicating it is not a static or fixed feature. Instead, some active process works to maintain the field. That process is most likely a kind of dynamic action in which the flowing and convecting liquid iron in Earth’s outer core generates the magnetic field, geologists believe.

Figuring out what happens as the field reverses polarity is difficult because reversals are rapid events, at least on geologic time scales. Finding sediments or lavas that record the field in the act of reversing is a challenge. In the past several years, however, new polarity transition records have been acquired in sediment cores obtained through the international Ocean Drilling Program, funded by NSF. These records make it possible to determine the major features of reversals, Clement said.

“It is generally accepted that during a reversal, the geomagnetic field decreases to about 10 percent of its full polarity value,” said Clement. “After the field has weakened, the directions undergo a nearly 180 degree change, and then the field strengthens in the opposite polarity direction. A major uncertainty, however, has remained regarding how long this process takes. Although this is usually the first question people ask about reversals, scientists have been forced to answer with only a vague ‘a few thousand years.'”

The reason for this uncertainty? Each published polarity transition reported a slightly different duration, from just under 1,000 years to 28,000 years.

“Now, through the innovative use of deep-ocean sediment cores, Clement has demonstrated that magnetic field reversal events occur within certain time-frames, regardless of the polarity of the reversal,” said Carolyn Ruppel, program director in NSF’s division of ocean sciences. “Sediment cores originally drilled to meet disparate scientific objectives have led to a result of global significance, which underscores the value of collecting and maintaining cores and associated data.”

Clement examined the database of existing polarity transition records of the past four reversals. The overall average duration, he found, is 7,000 years. But the variation is not random, he said. Instead it alters with latitude. The directional change takes half as long at low-latitude sites as it does at mid- to high-latitude sites. “This dependence of duration on site latitude was surprising at first, but it?s exactly as would be predicted in geometric models of reversing fields,” Clement said.

Original Source: NSF News Release

Posted on by Fraser Cain

Cassini Sees Merging Storms on Saturn

Image credit: NASA/JPL/Space Science Institute
Only a month and a half into its long approach to Saturn, the Cassini spacecraft captured two storms, each a swirling mass of clouds and gas, in the act of merging. With diameters close to 1000 kilometers (621 miles), both storms, which appear as spots in the southern hemisphere, were seen moving westward, relative to the rotation of Saturn’s interior, for about a month before they merged on Mar. 19-20, 2004.

Merging is one of the distinct features of storms in the giant planet atmospheres. On Earth, storms last for a week or so and usually fade away when they enter the mature phase and can no longer extract energy from their surroundings. On Saturn and the other giant planets, storms last for months, years, or even centuries, and instead of simply fading away, many storms on the giant planets end their lives by merging. How they form is still uncertain.

The series of eight images shown here was taken between Feb. 22 and Mar. 22, 2004; the image scale ranges from 381 kilometers (237 miles) to 300 kilometers (186 miles) per pixel. All images have been processed to enhance visibility. The top four frames, spanning 26 days, are portions of narrow angle camera images that were taken through a filter accepting light in the near-IR region of the spectrum centered at 619 nanometers, and show two spots approaching each other. Both storms are within half a degree of 36 degrees south latitude and sit in an anti-cyclonic shear zone, which means that the flow to the north is westward relative to the flow to the south. Consequently, the northern storm moves westward at a slightly greater rate than the southern one: 11 vs. 6 meters per second (25 and 13 miles per hour), respectively. The storms drift with these currents and engage in a counterclockwise dance before merging with each other.

The bottom four frames are from images taken on Mar. 19, 20, 21, and 22, respectively, in a region of the spectrum visible to the human eye and illustrate the storms’ evolution. Just after the merger, on Mar. 20, the new feature is elongated in the north-south direction, with bright clouds on either end. Two days later on Mar. 22, it has settled into a more circular shape and the bright clouds have spread around the circumference to form a halo. Whether the bright clouds are particles of a different composition or particles at a different altitude is uncertain.

The new storm is a few tenths of a degree farther south than either of its progenitors. There, its westward velocity is weaker and it is almost stationary relative to the planet’s rotation. Although these particular storms move slowly westward, storms at Saturn’s equator move eastward at speeds up to 450 meters per second (1000 mph), which is ~10 times the speed of the Earth’s jet streams and ~ three times greater than the equatorial winds on Jupiter. Saturn is the windiest planet in the solar system, which is another mystery of the ringed giant.

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 Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Hubble Peers Into the Heart of Galaxy NGC 300

Image credit: Hubble
What appear as individual grains of sand on a beach in this image obtained with NASA’s Hubble Space Telescope are actually myriads of stars embedded deep in the heart of the nearby galaxy NGC 300. The Hubble telescope’s exquisite resolution enables it to see the stars as individual points of light, despite the fact that the galaxy is millions of light-years away.

NGC 300 is a spiral galaxy similar to our own Milky Way. It is a member of a nearby collection of galaxies known as the Sculptor group, named for the southern constellation where the group can be found. The distance to NGC 300 is 6.5 million light-years, making it one of the Milky Way’s closer neighbors. At this distance, only the brightest stars can be picked out from ground-based images. With a resolution some 10 times better than ground-based telescopes, Hubble’s Advanced Camera for Surveys (ACS) resolves many more stars in this galaxy than can be detected from the ground.

A ground-based Digitized Sky Survey image of the full field of NGC 300 is shown in the top left frame. An outline of the Hubble Heritage ACS image is marked and shown in the image in the top right frame. A detailed blowup of this image (in the bottom frame) shows individual stars in the galaxy. A background spiral galaxy is visible in the lower right corner. The individual Hubble ACS exposures were taken in July and September 2002.

Original Source: Hubble News Release

Posted on by Mark Mortimer

Book Review: Practical Astronomy

The first half of the book is a reference source for how to observe. With good sense, it gives credit to the unaided eye and it extols the benefits of quickly and easily orienting yourself amongst the limitless dots and streaks in the black canopy of night. Visual aids are described. Telescope types; refractor, reflector and catadioptric, are compared. Ancillary equipment from red lights, to telescope drives to planispheres are also discussed. There are star charts (white dot on blue background) for the complete sky, that is both northern and southern hemispheres. These charts show stars up to magnitude 5 as well as the constellations and their boundaries. This half of the book also includes a section on how to locate the constellations and many of the most significant stars using the altazimuthal system, celestial coordinates, and/or from starting from other, easy to find sights such as Orion.

The second half of the book categorizes the sources of light from near Earth outwards. It starts with meteors, satellites and auroras, then to the Moon, the Sun, and through each of the planets. The final section looks at star clusters, binary stars and nebulae. There is even a brief discussion of galaxies and some exciting amateur prints of them. Rather than solely stating where to find each object, this half discusses characteristics of interest (e.g. the cusps of Venus), noteworthy events (e.g. occultations) and effects in time (e.g. variable stars). Throughout this half the author emphasizes the benefits of recording observations, such as by sketching. This is both for self-satisfaction and as a means of proving observations of an original event.

I like this book as it explains all the necessary fundamentals for sky watching. Without costing more than the price of this text, a person can occupy themselves for a long time in getting acquainted with the sights and events that occur while most everyone else is safely tucked into bed. Sometimes I did find the text a little difficult to follow especially with some of the explanations. Yet there are many prints and drawings that provide a lot of clarity. Also, there are enough inline references throughout the text to aid in following any particular topic.

In all, Practical Astronomy is a great reference for getting a person started onto the road of understanding the night sky and enjoying a pastime that keeps many night owls happily occupied.

Buy this book and others from Amazon.com

Review by Mark Mortimer

Posted on by Fraser Cain

Aura Satellite Delivered to Launch Facility

Image credit: NASA/JPL
NASA’s Aura spacecraft, the latest in the Earth Observing System series, has arrived at Vandenberg Air Force Base, Calif., to begin launch preparations.

Aura was transported from Northrop Grumman’s Space Park manufacturing facility in Redondo Beach, Calif. The spacecraft will undergo final tests and integration with a Boeing Delta II rocket for a scheduled launch in June.

Aura’s four state-of-the-art instruments, including two built and managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., will study the atmosphere’s chemistry and dynamics. The spacecraft will provide data to help scientists better understand Earth’s ozone, air quality and climate change. JPL’s Tropospheric Emission Spectrometer is an infrared sensor designed to study Earth’s troposphere-the lowest region of the atmosphere-and to look at ozone. JPL’s Microwave Limb Sounder is an instrument intended to improve our understanding of ozone in Earth’s stratosphere, vital in protecting us from solar ultraviolet radiation.

“The entire Aura team is very excited to see all our efforts come to fruition and is looking forward to a successful launch,” said Rick Pickering, Aura project manager at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Aura fulfills part of NASA’s commitment to study Earth as a global system and represents a key agency contribution to the U.S. Global Change Research Program. This mission will continue the global data collection underway by NASA’s other Earth Observing System satellites: Terra, which monitors land; and Aqua, which observes Earth’s water cycle.

The Aura spacecraft is part of NASA’s Earth Science Enterprise, a long-term research effort to determine how human-induced and natural changes affect the global environment.

For more information about Aura on the Internet, visit http://aura.gsfc.nasa.gov . For more information about the Tropospheric Emission Spectrometer on the Internet, visit http://tes.jpl.nasa.gov/ . For more information about the Microwave Limb Sounder on the Internet, visit http://mls.jpl.nasa.gov/ .

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Outer Planets Could Warm Up as Sun Dies

Image credit: NASA
We are doomed. One day the Earth will be a burnt cinder orbiting a swollen red star.

This is the ultimate fate of any planet living close to a main sequence star like our sun. Main sequence stars run on hydrogen, and when this fuel runs out, they switch over to helium and become a red giant. While the sun’s transition into a red giant is sad news for Earth, the icy planets in the most distant regions of our solar system will bask in the sun’s warmth for the first time.

The sun has been slowly but steadily growing brighter and hotter over the course of its lifetime. When the sun becomes a red giant in about 4 billion years, our familiar yellow sun will turn a vivid red, as it mainly emits the lower frequency energy of infrared and visible red light. It will grow thousands of times brighter and yet have a cooler surface temperature, and its atmosphere will expand, slowly engulfing Mercury, Venus and possibly even the Earth.

While the sun’s atmosphere is predicted to reach Earth’s orbit of 1 AU, red giants tend to lose a lot of mass, and this wave of expelled gases could push Earth just out of range. But whether the Earth is consumed or merely singed, all life on Earth will have passed into oblivion.

Yet the conditions that make life possible could appear elsewhere in the solar system, according to a paper published in the journal Astrobiology by S. Alan Stern, Director of the Southwest Research Institute’s Department of Space Studies in Boulder, Colorado. He says that planets located 10 to 50 AU will be in the red giant sun’s habitable zone. The habitable zone of a solar system is the region where water can remain in a liquid state.

The habitable zone will shift gradually through the 10 to 50 AU region as the sun grows brighter and brighter, evolving through its red giant phase. Saturn, Uranus, Neptune and Pluto all lie within 10 to 50 AU, as do their icy moons and the Kuiper Belt Objects. But not all these worlds will have an equal chance at life.

The prospects for habitability on the gaseous planets Saturn, Neptune and Uranus may not be affected all that much by the red giant transition. Astronomers have discovered gaseous planets orbiting very close to their parent star in other solar systems, and these “hot Jupiters” seem to hold onto their gaseous atmospheres despite their proximity to the intense radiation. Life as we know it is not likely to appear on gaseous planets.

Stern thinks Neptune’s moon Triton, Pluto and its moon Charon, and the Kuiper Belt Objects will have the best chances for life. These bodies are rich in organic chemicals, and the heat of the red giant sun will melt their icy surfaces into oceans.

“When the sun is a red giant, the ice worlds of our solar system will melt and become ocean oases for tens to several hundreds of millions of years,” says Stern. “Our solar system will then harbor not one world with surface oceans, as it does now, but hundreds, for all of the icy moons of the giant planets, and the icy dwarf planets of the Kuiper Belt will also bear oceans then. Because temperature on Pluto will not be very different then, than Miami Beach’s temperature now, I like to call these worlds ‘warm Plutos,’ in analogy to the plethora of hot Jupiters found orbiting sun-like stars in recent years.”

The influence of the sun is not the whole story, however – the characteristics of a planetary body go a long way toward determining habitability. Such characteristics include a planet’s internal activity, the reflectivity, or “albedo” of a planet, and the thickness and composition of the atmosphere. Even if a planet has all the elements that favor habitability, life will not necessarily appear.

“We don’t know what is needed to start life,” says Don Brownlee, an astronomer with the University of Washington in Seattle and co-author of the book, “The Life and Death of Planet Earth.” Brownlee says that if warm wet interiors and organic materials are all that’s needed, then Pluto, Triton, and the Kuiper Belt Objects could harbor life.

“As a word of caution, however, the interiors of asteroids that produced the carbonaceous chondrite meteorites were warm and wet for perhaps millions of years in the early history of the solar system,” says Brownlee. “These bodies are extremely rich in both water and organic materials, and yet there is no compelling evidence that any asteroidal meteorite ever had living things in it.”

A planetary body’s orbit also will affect its chances for life. Pluto, for instance, doesn’t have a nice, regular orbit like the Earth. The orbit of Pluto is comparatively eccentric, varying in distance from the sun. From January 1979 through February 1999, Pluto was closer to the sun than Neptune, and in a hundred years, it’ll be almost twice as far out as Neptune. This type of orbit will cause Pluto to undergo extreme heating alternating with extreme cooling.

Triton’s orbit, too, is peculiar. Triton is the only large moon to orbit backwards, or “retrograde.” Triton may have this unusual orbit because it formed as a Kuiper Belt Object and then was captured by Neptune’s gravity. It’s an unstable alliance, since the retrograde orbit creates tidal interactions with Neptune. Scientists predict that someday Triton will either crash into Neptune, or break up into tiny pieces and form a ring around the planet.

“The timescale for the tidal decay of Triton’s orbit is uncertain, so it could be around, or it might have already crashed by the time the sun goes red giant,” says Stern. “If Triton is around, it’ll probably end up looking like the same kind of organic-rich ocean world as Pluto.”

The sun will burn as a red giant for about 250 million years, but is that enough time for life to get a foothold? During most of the red giant lifetime, the sun will be only 30 times brighter than its current state. Toward the end of the red giant phase the sun will grow more than 1,000 times brighter, and occasionally release pulses of energy reaching 6,000 times current brightness. But this period of intense brightness will last for a few million years, or tens of millions of years at most.

The brevity of the red giant’s brightest phases suggests to Brownlee that Pluto doesn’t hold much promise for life. Because of Pluto’s average orbit of 40 AU, the sun would have to be 1,600 times brighter for Pluto to get the same solar radiation we currently get on Earth.

“The sun will reach this brightness, but only for a very brief period of time – only a million years or so,” says Brownlee. “The surface and atmosphere of Pluto will be ‘improved’ from our point of view, but it won’t be a nice place for any significant period of time”.

After the red giant phase, the sun will become fainter, and will shrink to the size of the Earth, becoming a white dwarf. The distant planets that basked in the light of the red giant will become frozen ice worlds once again.

So if life is to appear in a red giant system, it will need a quick start. Life on Earth is thought to have originated 3.8 billion years ago, some 800 million years after our planet was born. But that is probably because the planets in the inner solar system experienced 800 million years of heavy asteroid bombardment. Even if life had gotten started immediately, the early rain of asteroids would’ve wiped the Earth clean of that life.

Brownlee says a new era of bombardment could begin for the outer planets, because the red giant sun could disturb the vast number of comets in the Kuiper Belt.

“When the red giant sun is 1,000 times brighter, it loses almost half of its mass to space,” says Brownlee. “This causes orbiting bodies to move outward. Gas loss and other effects might destabilize the Kuiper Belt and create another period of interesting bombardment.”

But Stern says that planets made habitable by a red giant sun won’t be bombarded as often as the early Earth was, because the ancient asteroid belt had much more material than the Kuiper Belt has today.

In addition, the outer planets won’t experience the same ultraviolet (UV) levels that Earth has had to endure, since red giants have very low UV radiation. The higher intensity UV of a main sequence star can be damaging to the delicate proteins and RNA strands needed for life’s origin. Life on Earth could only originate underwater, in depths protected from this light intensity. Life on Earth is therefore inextricably linked to liquid water. But who knows what sort of life might originate on planets that have no need for UV shielding?

Stern thinks we should look for evidence of life on Pluto-like worlds orbiting around red giants today. We currently know of 100 million solar-type stars in the Milky Way galaxy that burn as red giants, and Stern says that all of these systems could have habitable planets within 10 to 50 AU. “It would be a good test of the time required to create life on warm, water-rich worlds,” he says.

“The idea of organic-rich distant bodies getting baked by a red giant star is an intriguing one, and could provide very interesting if short-lived habitats for life,” adds Brownlee. “But I am glad that our sun has a good margin of time left.”

What’s Next
While much of what we know about the outer solar system is based on distant measurements made from Earth-based telescopes, on January 2, 2004, scientists caught a close-up glimpse of a Kuiper Belt Object. The Stardust spacecraft passed within 136 kilometers of comet Wild2, an enormous snowball that spent most of its 4.6 billion-year lifetime orbiting in the Kuiper Belt. Wild2 now orbits mostly inside the orbit of Jupiter. Brownlee, who is the Principle Investigator for the Stardust mission, says that the Stardust images show fantastic surface details of a body shaped both by its ancient and recent history. Stardust images show gas and dust jets shooting off the comet, as Wild2 rapidly disintegrates in the strong solar heat of the inner solar system.

To learn more about the outer solar system, we’ll need to send a spacecraft out there to investigate. In 2001, NASA selected the New Horizons mission for just such a purpose.

Stern, who is the Principal Investigator for the New Horizons mission, reports that the spacecraft assembly is scheduled to begin this summer. The spacecraft is due to launch in January 2006, and arrive at Pluto the summer of 2015.

The New Horizons mission will allow scientists to study the geology of Pluto and Charon, map their surfaces, and take their temperatures. Pluto’s atmosphere also will be studied in detail. In addition, the spacecraft will visit the icy bodies in the Kuiper Belt in order to make similar measurements.

Original Source: Astrobiology Magazine

Posted on by Fraser Cain

Genesis Prepares to Return to Earth

Image credit: NASA/JPL
Since October 2001 NASA’s Genesis spacecraft has exposed specially designed collector arrays of sapphire, silicon, gold and diamond to the Sun’s solar wind.

That collection of pristine particles of the Sun came to an end last week, when NASA’s Genesis team at the Jet Propulsion Laboratory in Pasadena, Calif., ordered the spacecraft’s collectors deactivated and stowed. The closeout process was completed when Genesis closed and sealed the spacecraft’s sample-return capsule.

“This is a momentous step,” said Genesis project manager Don Sweetnam. “We have concluded the solar-wind collection phase of the mission. Now we are focusing on returning to Earth, this September, NASA’s first samples from space since Apollo 17 back in December 1972.”

NASA’s Genesis mission was launched in August 2001 from the Cape Canaveral Air Force Station, Fla. Three months and about one million miles later, the spacecraft began to amass solar wind particles on hexagonal wafer-shaped collectors made of pure silicon, gold, sapphire and diamond.

“The material our collector arrays are made of may sound exotic, but what is really unique about Genesis is what we collected on them,” said mission principal investigator Don Burnett. “With Genesis we’ve had almost 27 months far beyond the Moon’s orbit collecting atoms from the Sun. With data from this mission, we should be able to say what the sun is composed of at a level of precision for planetary science purposes that has never been seen before.”

To get Genesis’ precious cargo into the sterilized-gloved hands of Burnett and solar scientists around the world is an exotic endeavor in itself.

Later this month, Genesis will execute the first in a series of trajectory maneuvers that will place the spacecraft on a route toward Earth. On Sept. 8, 2004, the spacecraft will dispatch a sample-return capsule containing its solar booty. The capsule will re-enter Earth’s atmosphere for a planned landing at the U.S. Air Force Utah Test and Training Range at about 9:15 a.m. EDT.

To preserve the delicate particles of the Sun in their prisons of gold, sapphire and diamond, specially trained helicopter pilots will snag the return capsule from mid-air using giant hooks. The flight crews for the two helicopters assigned for the capture and return of Genesis are former military aviators, Hollywood stunt pilots and an active-duty Air Force test pilot.

For information about NASA and agency missions on the Internet, visit http://www.nasa.gov . For information about Genesis on the Internet, visit http://genesismission.jpl.nasa.gov/ . For information about the capture-and-return process on the Internet, visit http://www.genesismission.org/mission/recgallery.html.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Milky Way is a Dangerous, Turbulent Place

Image credit: ESO
Home is the place we know best. But not so in the Milky Way – the galaxy in which we live. Our knowledge of our nearest stellar neighbours has long been seriously incomplete and – worse – skewed by prejudice concerning their behaviour. Stars were generally selected for observation because they were thought to be “interesting” in some sense, not because they were typical. This has resulted in a biased view of the evolution of our Galaxy.

The Milky Way started out just after the Big Bang as one or more diffuse blobs of gas of almost pure hydrogen and helium. With time, it assembled into the flattened spiral galaxy which we inhabit today. Meanwhile, generation after generation of stars were formed, including our Sun some 4,700 million years ago.

But how did all this really happen? Was it a rapid process? Was it violent or calm? When were all the heavier elements formed? How did the Milky Way change its composition and shape with time? Answers to these and many other questions are ‘hot’ topics for the astronomers who study the birth and evolution of the Milky Way and other galaxies.

Now the rich results of a 15 year-long marathon survey by a Danish-Swiss-Swedish research team [2] are providing some of the answers.

1,001 nights at the telescopes
The team spent more than 1,000 observing nights over 15 years at the Danish 1.5-m telescope of the European Southern Observatory at La Silla (Chile) and at the Swiss 1-m telescope of the Observatoire de Haute-Provence (France). Additional observations were made at the Harvard-Smithsonian Center for Astrophysics in the USA. A total of more than 14,000 solar-like stars (so-called F- and G-type stars) were observed at an average of four times each – a total of no less than 63,000 individual spectroscopic observations!

This now complete census of neighbourhood stars provides distances, ages, chemical analysis, space velocities and orbits in the general rotation of the Milky Way. It also identifies those stars (about 1/3 of them all) which the astronomers found to be double or multiple.

This very complete data set for the stars in the solar neighbourhood will provide food for thought by astronomers for years to come.

A dream come true
These observations provide the long-sought missing pieces of the puzzle to get a clear overview of the solar neighbourhood. They effectively mark the conclusion of a project started more than twenty years ago..

In fact, this work marks the fulfilment of an old dream by Danish astronomer Bengt Str?mgren (1908-1987), who pioneered the study of the history of the Milky Way through systematic studies of its stars. Already in the 1950’s he designed a special system of colour measurements to determine the chemical composition and ages of many stars very efficiently. And the Danish 50-cm and 1.5-m telescopes at the ESO La Silla Observatory (Chile) were constructed to make such projects possible.

Another Danish astronomer, Erik Heyn Olsen made the first step in the 1980’s by measuring the flux (light intensity) in several wavebands (in the “Str?mgren photometric system”) of 30,000 A, F and G stars over the whole sky to a fixed brightness limit. Next, ESA’s Hipparcos satellite determined precise distances and velocities in the plane of the sky for these and many other stars.

The missing link was the motions along the line of sight (the so-called radial velocities). They were then measured by the present team from the Doppler shift of spectral lines of the stars (the same technique that is used to detect planets around other stars), using the specialized CORAVEL instrument.

Stellar orbits in the Milky Way
With the velocity information completed, the astronomers can now compute how the stars have wandered around in the Galaxy in the past, and where they will go in the future, cf. PR Video Clip 04/04.

Birgitta Nordstr?m, leader of the team, explains: “For the first time we have a complete set of observed stars that is a fair representation of the stellar population in the Milky Way disc in general. It is large enough for a proper statistical analysis and also has complete velocity and binary star information. We have just started the analysis of this dataset ourselves, but we know that our colleagues worldwide will rush to join in the interpretation of this treasure trove of information.”

The team’s initial analysis indicates that objects like molecular clouds, spiral arms, black holes, or maybe a central bar in the Galaxy, have stirred up the motion of the stars throughout the entire history of the Milky Way disc.

This in turn reveals that the evolution of the Milky Way was far more complex and chaotic than traditional, simplified models have long so far assumed. Supernova explosions, galaxy collisions, and infall of huge gas clouds have made the Milky Way a very lively place indeed!

Original Source: ESO News Release

Posted on by Fraser Cain

Asteroid Search Looks South

Image credit: UA
The hunt for space rocks on a collision course with Earth has so far been pretty much limited to the Northern Hemisphere.

But last week astronomers took the search for Earth-threatening asteroids to southern skies.

Astronomers using a refurbished telescope at the Australian National University’s Siding Spring Observatory discovered their first two near-Earth asteroids (NEAs) on March 29. NEAs are asteroids that pass near the Earth and may pose a threat of collision.

Siding Spring Survey (SSS) astronomer Gordon Garradd detected a roughly 100-meter (about 300-foot) diameter asteroid and 300-meter (about 1,000-foot) diameter asteroid in images he obtained with the 0.5-meter (20-inch) Uppsala Schmidt telescope.

SSS partner Robert H. McNaught confirmed both discoveries in images he took with the Siding Spring 1-meter (40-inch) that same night.

The 100-meter asteroid, designated 2004 FH29, makes a complete orbit around the sun every 2.13 years. It missed Earth by 3 million kilometers (1.9 million miles), or 8 times the Earth-to-moon distance, yesterday, traveling at 10 km per second (22,000 mph) relative to Earth.

The 300-meter asteroid, designated 2004 FJ29, orbits the sun about every 46 weeks. It came within 20 million kilometers (12 million miles), or within 52 lunar distances of Earth, last Tuesday, March 30, traveling at 18 km per second (40,000 mph) relative to Earth.

Neither object poses a direct threat of colliding with Earth.

Had the asteroids not missed, damage from their impacts would have depended on what kind of rock they’re made of. The 100-meter object likely would mostly burn up in Earth’s atmosphere in an airblast equivalent to 10 megatons of TNT, comparable to the 1908 explosion above the Tunguska River valley in Siberia, McNaught said. The 300-meter rocky asteroid likely would reach Earth’s surface, dumping the equivalent of 1,400 megatons of TNT energy into Earth’s atmosphere, he added. That’s comparable to 200 Tunguskas, or 24 times the largest thermonuclear bomb explosion, a 58 megaton Soviet bomb exploded in 1961.

The new survey is a joint collaboration between the University of Arizona Lunar and Planetary Laboratory and ANU’s Research School of Astronomy and Astrophysics. It is funded by NASA’s Near-Earth Object Observation Program, a 10-year effort to discover and track at least 90 percent of the one kilometer (six-tenths of a mile) or larger NEOs with the potential to become impact hazards.

When astronomers detect what they suspect is an NEA, they immediately must take additional images to confirm their discovery, McNaught said. Surveys often have to suspend their NEA searches and spend observing time confirming NEAs, or they risk losing them altogether because follow-up observations were made too late, he added.

The SSS plan is to use the 1-meter (40-inch) telescope for part of the month to quickly confirm suspect asteroids detected with the Uppsala, freeing the smaller telescope to continue it searches.

“Our confirmation strategy worked beautifully on our first try,” McNaught said.

The Uppsala Schmidt telescope was built in the 1950s for Uppsala Observatory in Sweden. It was sited at Stromlo as the Uppsala Southern Station to make wide field photographs of the southern sky. Increasing light pollution from Canberra led to its relocation to Siding Spring, near Coonabarabran in New South Wales, in 1982. Despite its high quality optics, the telescope drifted into disuse because it used photographic film rather than modern electronic detectors and had to be operated manually.

In 1999, McNaught and Stephen M. Larson of UA?s Lunar and Planetary Laboratory joined in an effort to refurbish and upgrade the Uppsala telescope. Larson had similarly just overhauled a manually operated, photographic wide-field Schmidt telescope in the Santa Catalina Mountains north of Tucson for his Catalina Sky Survey (CSS), part of the NASA-funded program to spot and track asteroids headed toward Earth.

The SSS builds on telescope control, detector technology and software developed for the CSS in Tucson. During the upgrade, the Uppsala was completely reconditioned, and fitted with computer control, a large format (16 megapixel) solid state detector array, and extensive support computers and software that detects objects moving against background stars.

Larson said his reaction to the SSS milestone was “one of relief, since it took several years to make the telescope and facility modifications. Now the real work begins.”

Larson and Catalina Sky Survey team member Ed Beshore worked on commissioning the Uppsala telescope during the past few months. Commissioning a telescope is like commissioning a ship: You have to get all the parts working and working together, and adjust things so they perform as expected.

“We actually achieved ‘first light’ last summer, with good images from the start,” Larson said.

McNaught and Garradd will operate SSS about 20 nights each month. They suspend operations when the week around full moon brightens the sky, making faint object detection difficult.

The Catalina telescope, which Larson and his team upgraded again in May 2000, features new optics that give it a 69 centimeter (27-inch) aperture and a new, more sensitive camera. In addition to Larson and Beshore, Eric Christensen, Rik Hill, David McLean, and Serena Howard operate CSS.

Both CSS and SSS telescopes can detect objects as faint as 20th magnitude, close to sky background level generated by scattered city light and auroral glow that brightens Earth?s upper atmosphere.

Original Source: UA News Release