Hubble Looks at Our Closest Cluster

Image credit: Hubble

The newest image from the Hubble Space Telescope reveals one of the nearest globular star clusters, NGC 6397, located only 8,200 light years away in the constellation Ara. The stars in this cluster are packed one million times more densely than our own galactic neighborhood; collisions between stars occur every few million years. Two colliding stars may merge to become a “blue straggler”; a bright, young hot star that looks very different from the rest of the stars in the cluster.

This Hubble Space Telescope view of the core of one of the nearest globular star clusters, called NGC 6397, resembles a treasure chest of glittering jewels. The cluster is located 8,200 light-years away in the constellation Ara.

Here, the stars are jam-packed together. The stellar density is about a million times greater than in our Sun’s stellar neighborhood. The stars are only a few light-weeks apart, while the nearest star to our Sun is over four light-years away.

The stars in NGC 6397 are in constant motion, like a swarm of angry bees. The ancient stars are so crowded together that a few of them inevitably collide with each other once in a while. Near misses are even more common. Even so, collisions only occur every few million years or so. That’s thousands of collisions in the 14-billion-year lifetime of the cluster.

These Hubble images were taken for a research program aimed at studying what is left behind when such collisions and near misses occur. When direct collisions occur, the two stars may merge to form a new star called a “blue straggler”; these hot, bright, young stars stand out among the old stars that make up the vast majority of stars in a globular cluster. Several such bright blue stars are visible near the center of the cluster in the Hubble Heritage image.

If two stars come close enough together without actually colliding, they may “capture” each other and become gravitationally bound. One type of binary that might form this way is a “cataclysmic variable”? a pairing of a normal, hydrogen-burning star and a burned-out star called a white dwarf. In a binary system, the white dwarf will pull material off the surface of the normal star. This material encircles the white dwarf in an “accretion disk,” and eventually falls onto it. The result of this accretion process is that cataclysmic variables are, as the name suggests, variable in brightness. The heat generated by the accreting material also generates unusual amounts of ultraviolet and blue light.

To search for cataclysmic variables, the program consisted of a series of 55 images of the cluster taken over a period of about 20 hours. Most of the images were taken in ultraviolet and blue filters; a few images were also taken at green and infrared wavelengths. By comparing the brightness of all the stars in all the images, the Hubble astronomers were able to identify several cataclysmic variable stars in the cluster. Comparison of their brightness in the different filters confirmed that they were emitting copious amounts of ultraviolet light. A few of these stars can be seen in the Hubble Heritage image as faint blue or violet stars.

One of the more intriguing results of this study was completely unexpected. Three faint blue stars can be seen near the center of the cluster ? in the Hubble Heritage image they appear turquoise. These three stars don’t vary in brightness at all, and were clearly not cataclysmic variables. These stars may be very-low-mass white dwarfs, formed in the cores of giant stars whose evolution is somehow interrupted before a full-fledged white dwarf has time to form.

Such an interruption might occur as the result of a stellar collision or an interaction with a binary companion. When a giant star interacts with another star, it can lose its outer layers prematurely, compared to its normal evolution, exposing its hot, blue core. The end result will be a white dwarf of a smaller mass than would have otherwise ensued. In any case, these unusual stars are yet more evidence that the center of a dense globular cluster is a perilous place to reside.

A large number of normal white dwarfs were also identified and studied. These stars appear throughout the cluster, since they form through normal stellar evolution processes and don’t involve any stellar interactions, which occur predominantly near the cluster center. Nearly 100 such burned-out stars were identified in these images, the brightest of which can be seen here as faint blue stars.

This Hubble image is a mosaic of two sets of images taken several years apart by the Wide Field Planetary Camera 2. Archival data from science teams led by Jonathan Grindlay (Harvard University) and Ivan King (University of California, Berkeley), taken in 1997 and 1999, were combined with Hubble Heritage data taken in 2001. Adrienne Cool (San Francisco State University), who was also on both archival science teams, worked with the Hubble Heritage team to acquire the new observations.

Original Source: Hubble News Release

Planning a Mars Party?

With Mars the closest it’s going to be in 60,000 years on August 27, I figure this’ll be a good time to get people interested in space and astronomy. Several astronomers have told me they’re planning to take their telescopes into parks, etc, and give people a chance to see the Red Planet with their own eyes.

I think this is a great idea, so I figured I’ll start maintaining a list on Universe Today of all locations around the world that will have telescopes set up on the 27th.

Is your astronomy club planning a get together for Mars 2003? Let me know where you’re going to be and I’ll add you to the list. Then I’ll make it available as the event gets closer so people can find you and take a look through your telescopes. Even if you’re not part of a club, just take your telescope out to the park, and encourage the public to take a look. Sidewalk astronomy is one of the best ways that astronomers can share their hobby.

Send me an email at [email protected]


Fraser Cain
Universe Today

Astronomers Measure the Shape of a Supernova

Image credit: ESO

New data gathered by the European Southern Observatory’s Very Large Telescope (VLT) seems to indicate that supernovae might not be symmetrical when they explode – their brightness changes depending on how you look at them. This discovery is important, because astronomers use supernovae as an astronomical yardstick to measure distances to objects. If they’re brighter or dimmer depending on how you’re looking at them, it could cause errors in your distance calculations. But the new research indicates that they become more symmetrical over time, so astronomers just need to wait a little while before doing their calculations.

An international team of astronomers [2] has performed new and very detailed observations of a supernova in a distant galaxy with the ESO Very Large Telescope (VLT) at the Paranal Observatory (Chile). They show for the first time that a particular type of supernova, caused by the explosion of a “white dwarf”, a dense star with a mass around that of the Sun, is asymmetric during the initial phases of expansion.

The significance of this observation is much larger than may seem at a first glance. This particular kind of supernova, designated “Type Ia”, plays a very important role in the current attempts to map the Universe. It has for long been assumed that Type Ia supernovae all have the same intrinsic brightness, earning them a nickname as “standard candles”.

If so, differences in the observed brightness between individual supernovae of this type simply reflect their different distances. This, and the fact that the peak brightness of these supernovae rivals that of their parent galaxy, has allowed to measure distances of even very remote galaxies. Some apparent discrepancies that were recently found have led to the discovery of cosmic acceleration.

However, this first clearcut observation of explosion asymmetry in a Type Ia supernova means that the exact brightness of such an object will depend on the angle from which it is seen. Since this angle is unknown for any particular supernova, this obviously introduces an amount of uncertainty into this kind of basic distance measurements in the Universe which must be taken into account in the future.

Fortunately, the VLT data also show that if you wait a little – which in observational terms makes it possible to look deeper into the expanding fireball – then it becomes more spherical. Distance determinations of supernovae that are performed at this later stage will therefore be more accurate.

Supernova explosions and cosmic distances
During Type Ia supernova events, remnants of stars with an initial mass of up to a few times that of the Sun (so-called “white dwarf stars”) explode, leaving nothing behind but a rapidly expanding cloud of “stardust”.

Type Ia supernovae are apparently quite similar to one another. This provides them a very useful role as “standard candles” that can be used to measure cosmic distances. Their peak brightness rivals that of their parent galaxy, hence qualifying them as prime cosmic yardsticks.

Astronomers have exploited this fortunate circumstance to study the expansion history of our Universe. They recently arrived at the fundamental conclusion that the Universe is expanding at an accelerating rate, cf. ESO PR 21/98, December 1998 (see also the Supernova Acceleration Probe web page).

The explosion of a white dwarf star
In the most widely accepted models of Type Ia supernovae the pre-explosion white dwarf star orbits a solar-like companion star, completing a revolution every few hours. Due to the close interaction, the companion star continuously loses mass, part of which is picked up (in astronomical terminology: “accreted”) by the white dwarf.

A white dwarf represents the penultimate stage of a solar-type star. The nuclear reactor in its core has run out of fuel a long time ago and is now inactive. However, at some point the mounting weight of the accumulating material will have increased the pressure inside the white dwarf so much that the nuclear ashes in there will ignite and start burning into even heavier elements. This process very quickly becomes uncontrolled and the entire star is blown to pieces in a dramatic event. An extremely hot fireball is seen that often outshines the host galaxy.

The shape of the explosion
Although all supernovae of Type Ia have quite similar properties, it has never been clear until now how similar such an event would appear to observers who view it from different directions. All eggs look similar and indistinguishable from each other when viewed from the same angle, but the side view (oval) is obviously different from the end view (round).

And indeed, if Type Ia supernova explosions were asymmetric, they would shine with different brightness in different directions. Observations of different supernovae – seen under different angles – could therefore not be directly compared.

Not knowing these angles, however, the astronomers would then infer incorrect distances and the precision of this fundamental method for gauging the structure of the Universe would be in question.

Polarimetry to the rescue
A simple calculation shows that even to the eagle eyes of the VLT Interferometer (VLTI), all supernovae at cosmological distances will appear as unresolved points of light; they are simply too far. But there is another way to determine the angle at which a particular supernova is viewed: polarimetry is the name of the trick!

Polarimetry works as follows: light is composed of electromagnetic waves (or photons) which oscillate in certain directions (planes). Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflecting off a pond.

When light scatters through the expanding debris of a supernova, it retains information about the orientation of the scattering layers. If the supernova is spherically symmetric, all orientations will be present equally and will average out, so there will be no net polarisation. If, however, the gas shell is not round, a slight net polarisation will be imprinted on the light.

“Even for quite noticable asymmetries, however, the polarisation is very small and barely exceeds the level of one percent”, says Dietrich Baade, ESO astronomer and a member of the team that performed the observations. “Measuring them requires an instrument that is very sensitive and very stable. ”

The measurement in faint and distant light sources of differences at a level of less than one percent is a considerable observational challenge. “However, the ESO Very Large Telescope (VLT) offers the precision, the light collecting power, as well as the specialized instrumentation required for such a demanding polarimetric observation”, explains Dietrich Baade. “But this project would not have been possible without the VLT being operated in service mode. It is indeed impossible to predict when a supernova will explode and we need to be ready all the time. Only service mode allows observations at short notice. Some years ago, it was a farsighted and courageous decision by ESO’s directorate to put so much emphasis on Service Mode. And it was the team of competent and devoted ESO astronomers on Paranal who made this concept a practical success”, he adds.

The astronomers [1] used the VLT multi-mode FORS1 instrument to observe SN 2001el, a Type Ia supernova that was discovered in September 2001 in the galaxy NGC 1448, cf. PR Photo 24a/03 at a distance of 60 million light-years.

Observations obtained about a week before this supernova reached maximum brightness around October 2 revealed polarisation at levels of 0.2-0.3% (PR Photo 24b/03). Near maximum light and up to two weeks thereafter, the polarisation was still measurable. Six weeks after maximum, the polarisation had dropped below detectability.

This is the first time ever that a normal Type Ia supernova has been found to exhibit such clear-cut evidence of asymmetry.
Looking deeper into the supernova

Immediately following the supernova explosion, most of the expelled matter moves at velocities around 10,000 km/sec. During this expansion, the outermost layers become progressively more transparent. With time one can thus look deeper and deeper into the supernova.

The polarisation measured in SN 2001el therefore provides evidence that the outermost parts of the supernova (which are first seen) are significantly asymmetric. Later, when the VLT observations “penetrate” deeper towards the heart of the supernova, the explosion geometry is increasingly more symmetric.

If modeled in terms of a flattened spheroidal shape, the measured polarisation in SN 2001el implies a minor-to-major axis ratio of around 0.9 before maximum brightness is reached and a spherically symmetric geometry from about one week after this maximum and onward.
Cosmological implications

One of the key parameters on which Type Ia distance estimates are based is the optical brightness at maximum. The measured asphericity at this moment would introduce an absolute brightness uncertainty (dispersion) of about 10% if no correction were made for the viewing angle (which is not known).

While Type Ia supernovae are by far the best standard candles for measuring cosmological distances, and hence for investigating the so-called dark energy, a small measurement uncertainty persists.

“The asymmetry we have measured in SN 2001el is large enough to explain a large part of this intrinsic uncertainty”, says Lifan Wang, the leader of the team. “If all Type Ia supernovae are like this, it would account for a lot of the dispersion in brightness measurements. They may be even more uniform than we thought.”

Reducing the dispersion in brightness measurements could of course also be attained by increasing significantly the number of supernovae we observe, but given that these measurements demand the largest and most expensive telescopes in the world, like the VLT, this is not the most efficient method.

Thus, if the brightness measured a week or two after maximum was used instead, the sphericity would then have been restored and there would be no systematic errors from the unknown viewing angle. By this slight change in observational procedure, Type Ia supernovae could become even more reliable cosmic yardsticks.
Theoretical implications

The present detection of polarised spectral features strongly suggests that, to understand the underlying physics, the theoretical modelling of Type Ia supernovae events will have to be done in all three dimensions with more accuracy than is presently done. In fact, the available, highly complex hydrodynamic calculations have so far not been able to reproduce the structures exposed by SN 2001el.
More information

The results presented in this press release have been been described in a research paper in “Astrophysical Journal” (“Spectropolarimetry of SN 2001el in NGC 1448: Asphericity of a Normal Type Ia Supernova” by Lifan Wang and co-authors, Volume 591, p. 1110).

[1]: This is a coordinated ESO/Lawrence Berkeley National Laboratory/Univ. of Texas Press Release. The LBNL press release is available here.

[2]: The team consists of Lifan Wang, Dietrich Baade, Peter H?flich, Alexei Khokhlov, J. Craig Wheeler, Daniel Kasen, Peter E. Nugent, Saul Perlmutter, Claes Fransson, and Peter Lundqvist.

Original Source: ESO News Release

Perseid Meteor Shower Next Week

Image credit: ESA

The annual Perseid meteor shower is due to make its appearance in mid-August this summer. The shower began on July 23 and will end on August 22, but the bulk of shooting stars will appear on August 13, when upwards of one meteor per minute is visible in the night sky. Unfortunately, the full Moon will brighten the sky and make some of the fainter meteors harder to see. To get the best view of the Perseids, get away from the city lights to a place which is as flat as possible to give you a wide view of the sky.

A fantastic, free light show occurred in the morning of Wednesday, 13 August 2003, in the form of the Perseid meteor shower!

This impressive set of shooting stars appears in the skies every year from around 23 July to 22 August, with its peak on 13 August. First recorded as long ago as 36 AD, the Perseids are also known as ‘the tears of St. Lawrence’ after the Roman martyr.

Typically, you can see this phenomenon with the naked eye, with a shooting star appearing every minute until about 03.00 CET on Wednesday morning. You may also see meteors a few days before or after this time.

However, this year the Moon will be full near the Perseid’s maximum, which will reduce observed rates by a factor of three or so. It will not be until around 2007 when the Moon’s phase is more favourable than that of last year.

Meteor showers occur when the Earth passes through the trail of debris often left behind by a comet. By studying meteor showers, scientists can learn more about cometary debris, but ESA is going a step further with its Rosetta comet-chasing mission which will examine a comet at close range.

Comets are considered to be the primitive building blocks of the Solar System, and the Rosetta mission could help us to understand if life on Earth began with the help of ‘comet seeding’.

The meteors we see are actually tiny bits of comet debris, most of which are only as big as a grain of sand, so they do not pose a threat to us. However, they do provide a spectacular light show as they vaporise on entering the Earth’s atmosphere. This particular shower is named after the Perseus constellation because the shooting stars can appear to start there, but the material was actually shed by the Comet Swift-Tuttle.

To get the best view of the light show, get as far away from city lights as you can since these affect your ability to see the meteor shower.

Make sure that you are comfortable – gazing at the sky for hours can cause neck strain. Find a reclining garden chair or lay out a blanket on the ground. The meteors can appear in any part of the sky, so make sure that you have as wide a view of it as possible.

However, if poor weather prevents you seeing this spectacular show, or you simply cannot stay awake that long, do not give up. You have a chance to view another set of shooting stars in November 2003 when the Leonid meteor shower comes our way. In the third week of November, the Leonids will appear – though 2002 was supposed to be their last big show for the next 30 years.

The Leonids are the leftovers from Comet 55P/Tempel-Tuttle, and ESA scientists regularly conduct intense observation campaigns of these to understand more about comets and cometary debris.

Original Source: ESA News Release

Asteroid Juno Has a Chunk Out of It

Image credit: Harvard

New images taken by the 100-inch Hooker telescope at Mount Wilson Observatory show Asteroid Juno with a huge chunk taken out of it. Harvard astronomer Sallie Baliunas used the adaptive optics system on the Hooker telescope, which compensates for distortions in the atmosphere, to take photos of the 241 km asteroid with incredible clarity. The photos show that Juno is misshapen and has a 100 km crater from an impact with another asteroid in the past.

Cambridge, MA -If someone sneaks a bite of your chocolate chip cookie, they leave behind evidence of their pilferage in the form of a crescent of missing cookie. The same is true in our solar system, where an impact can take a bite out of a planet or moon, leaving behind evidence in the form of a crater. By combining modern technology with a historical telescope, astronomers have discovered that the asteroide Juno has a bite out of it. The first direct images of the surface of Juno show that it is scarred by a fresh impact crater.

Juno, the third asteroid ever discovered, was first spotted by astronomers early in the 19th century. It orbits the Sun with thousands of other bits of space rock in the main asteroid belt between Mars and Jupiter. One of the largest asteroids, at a size of 150 miles across, Juno essentially is a leftover building block of the solar system.

Astronomer Sallie Baliunas (Harvard-Smithsonian Center for Astrophysics) and colleagues photographed Juno when it was located relatively nearby in astronomical terms, about 10 percent further from the Earth than the Earth is from the Sun. Even at that distance, Juno appeared very tiny in the sky, subtending only 330 milli-arcseconds – the equivalent of a dime seen at a distance of 7 miles. Imaging Juno at the high resolution needed to resolve surface details thus presented a challenge.

To solve the problem, the scientists used an adaptive optics system connected to the 100-inch Hooker telescope at Mount Wilson Observatory. Adaptive optics enables astronomers to compensate for the distortion created by air currents in our planet’s atmosphere, yielding images as sharp and clear as those taken in space.

Their surface maps showed that Juno, like other asteroids, is misshapen rather than round, and that it has “sharp” edges. Even better, as Juno tumbled through space during the night of observing, a “bite” came into view – an area that appeared dark as seen at near-infrared wavelengths. The astronomers concluded that the asteroid had recently (in astronomical terms) collided with another object, resulting in a 60-mile-wide crater, or possibly a smaller crater that is surrounded by a 60-mile blanket of ejecta debris.

“I look at an asteroid as a garden – a garden not of flowers and leaves, but one of rubble and dust churned up by constant impacts. This process of gardening pulverizes the asteroid’s surface into a fine-grained regolith,” said Baliunas. “The recent, large impact on Juno gives us an opportunity to see through the regolith and study excavated material from beneath the surface – a rare look into the material out of which the early Earth was formed.”

The blast that knocked a bite out of Juno may also have provided researchers with a convenient way of studying that asteroid up close without ever leaving our planet. Some meteorites found on the Earth are actually pieces of large asteroids like Juno. Those pieces were broken off and launched into space by an impact, and then fell on our planet. The newly-found impact crater on Juno may have sent samples of that asteroid to the Earth.

This remarkable result demonstrates how technology can be used to renew historical observatories, giving them a new lease on life. The Hooker telescope, now nearing the end of its first century of observing, can use adaptive optics systems to obtain views of the cosmos as clear as though the telescope were in space. Hence, the telescope that Edwin Hubble and his assistant used to discover evidence of the expanding universe continues to make groundbreaking discoveries today.

These results were published in the May 2003 issue of the astronomy journal Icarus.

Original Source: CfA News Release

Canada’s Space Telescope Begins Operations

Image credit: CSA

After one month in space, Canada’s Microvariability & Oscillations of STars (MOST) space telescope began operations for the first time last week. A team of engineers and scientists from Dynacon, and the Universities of Toronto and BC issued the command that opens the door, allowing starlight into the sensitive observatory. MOST will measure the oscillation in the light intensity coming from various stars to help determine their composition and age.

After a perfect launch and orbit insertion one month ago, Canada’s first space telescope – called MOST (Microvariability & Oscillations of STars) – opened its eye to the cosmos for the first time last week. Astronomers traditionally call this milestone for a telescope “first light.”

A joint team of engineers and scientists from Dynacon Inc. and the Universities of Toronto and British Columbia issued the command to open the door on the MOST satellite to allow starlight to strike its sensitive electronic detectors. A star image obtained immediately after this operation confirmed that the optics and electronics are performing well.

MOST Mission Scientist and UBC astronomer Dr. Jaymie Matthews was elated at this successful operation: “One of my worst nightmares was having our superb instrument blind behind a stuck door. This is just another in a series of successful milestones which are a testament to the skills of all the Canadian hardware and software engineers on the MOST team.”

The Canadian Space Agency’s MOST space mission is designed to detect tiny vibrations in starlight and reflected light from planets outside the Solar System. These signals will enable Canadian astronomers to be the first to probe both the hidden deep interiors of stars and the outer atmospheres of mysterious extrasolar planets.

“With MOST, we will finally be able to determine the dynamic composition of stars,” said Steve Torchinsky, scientist with the CSA’s Space Astronomy Program. “Furthermore, since MOST is able to see the light reflected from planets and to record minuscule variations in luminosity, this will provide us with data we never had access to before, since no other telescope – not even Hubble – is capable of collecting this type of information.”

Despite such lofty goals, the MOST satellite has been dubbed the “Humble Space Telescope” because it’s just the mass and size of a suitcase. Its price tag is modest too: only about $10 million. To accomplish science that’s normally the domain of observatories 50 times larger and tens to hundreds of times more expensive, the MOST project has adopted a new approach to space science, as part of the Canadian Space Agency’s Small Payloads initiative.

Packed in the MOST space suitcase are new stabilising technologies from the Canadian aerospace firm Dynacon Inc., innovative microsatellite designs by the SpaceFlight Lab of the University of Toronto Institute for Aerospace Studies (UTIAS), and unique optics and electronics developed at the Department of Physics & Astronomy of the University of British Columbia (UBC).

MOST was launched from the Plesetsk Cosmodrome in northern Russia on 30 June 2003, entering orbit perfectly. It now circles the Earth every 100 minutes, pole over pole, at an altitude of 820 km. Since orbital insertion, the MOST team has been carefully activating and testing the satellite systems. The satellite was oriented so the telescope opening – still covered by a door to protect it from harmful direct sunlight – was pointed safely away from the Sun. Last Tuesday, MOST team leaders all agreed it was safe to open the door, built by Routes AstroEngineering Ltd. in Ottawa, Ontario.

At the moment, the MOST satellite is in its coarse pointing mode, looking towards the constellation Capricorn. The next step in the mission will be to activate the fine pointing system and redirect the telescope to a pre-selected target star for calibration. Routine scientific operations could begin within a few weeks, and the first public announcement of scientific results is anticipated in the fall.

Original Source: CSA News Release

Cosmonaut Planning Space Marriage

Russian cosmonaut Yuri Malenchenko is going ahead with his plans to marry his fianc? from space on August 10, despite protests from the Russian Aerospace Agency. Malenchenko will be represented at the wedding by a lawyer, and he’ll call in from the station during a special time when the astronauts are allowed to call their families. Astronaut Ed Lu quietly arranged to have his tailcoat and ring sent up on a recent Progress cargo ship.

NASA Picks the Next Mars Lander

Image credit: NASA/JPL

NASA announced on Monday that it has selected the University of Arizona’s “Phoenix” mission to launch to Mars in 2007 as part of its new, low-cost Scout mission. NASA has granted the university $325 million to build the spacecraft, which will land on the planet’s northern pole, which is rich in water ice. The mission will have two goals: to study the geologic history of water, and to search for evidence of a habitable zone that may exist in the ice-soil boundary.

In May 2008, the progeny of two promising U.S. missions to Mars will deploy a lander to the water-ice-rich northern polar region, dig with a robotic arm into arctic terrain for clues on the history of water, and search for environments suitable for microbes.

NASA today announced that it has selected the University of Arizona “Phoenix” mission for launch in 2007 as what is hoped will be the first in a new line of smaller competed “Scout” missions in the agency’s Mars Exploration Program.

Dr. Peter H. Smith of the University of Arizona Lunar and Planetary Laboratory heads the Phoenix mission, named for the mythological bird that is repeatedly reborn of ashes. The $325 million NASA award is more than six times larger than any other single research grant in University of Arizona history.

“The selection of Phoenix completes almost two years of intense competition with other institutions,” Smith said. “I am overjoyed that we can now begin the real work that will lead to a successful mission to Mars.”

Phoenix is a partnership of universities, NASA centers, and the aerospace industry. The science instruments and operations will be a University of Arizona responsibility. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., will manage the project and provide mission design. Lockheed Martin Space Systems, Denver, will build and test the spacecraft. Canadian partners will provide the meteorological instrumentation, including an innovative laser-based sensor.

Phoenix has the scientific capability “to change our thinking about the origins of life on other worlds,” Smith said. “Even though the northern plains are thought to be too cold now for water to exist as a liquid, periodic variations in the martian orbit allow a warmer climate to develop every 50,000 years. During these periods the ice can melt, dormant organisms could come back to life, (if there are indeed any), and evolution can proceed. Our mission will verify whether the northern plains are indeed a last viable habitat on Mars.”

The lander for Phoenix was built and was being tested to fly as part of the 2001 Mars Surveyor Program, but the program was canceled after the Mars Polar Lander was lost upon landing near Mars’ south pole in December 1999. Since then, the 2001 lander has been stored in a clean room at Lockheed Martin in Denver, managed by NASA’s new Mars Exploration Program as a flight asset.

Renamed Phoenix, it will carry improved versions of University of Arizona panoramic cameras and volatiles-analysis instrument from the ill-fated Mars Polar Lander, as well as experiments that had been built for the 2001 Mars Surveyor Program, including a JPL trench-digging robot arm and a chemistry-microscopy instrument. The science payload also includes a descent imager and a suite of meteorological instruments.

The mission has two goals. One is to study the geologic history of water, the key to unlocking the story of past climate change. Two is to search for evidence of a habitable zone that may exist in the ice-soil boundary, the “biological paydirt.”

The Phoenix robotic arm will scoop up martian soil samples and deliver them for heating into tiny ovens of the volatiles-analysis instrument so team members can measure how much water vapor and carbon dioxide gas are given off, how much water ice the samples contain, and what minerals are present that may have formed during a wetter, warmer past climate. The instrument, called thermal evolved gas analyzer, will also measure any organic volatiles.

Using another instrument, researchers will examine soil particles as small as 16 microns across. They will measure electrical and thermal conductivity of soil particles using a probe on the robotic arm scoop. One of the most interesting experiments is the wet chemistry laboratory, Smith said.

“We plan to scoop up some soil, put it in a cell, add water, shake it up, and measure the impurities dissolved in the water that have leached out from the soil. This is important, because if the soil ever gets wet, we’ll know if microbes could survive. We’ll know if the wet soil is super acidic or alkaline and salty, or full of oxidants that can destroy life. We’ll test the environment that microbes might have had to live and grow in,” Smith said.

Information is available online about NASA’s Mars exploration at and about Phoenix at .

Original Source: NASA News Release

Three Gorges Dam Seen From Above

Image credit: ESA

China’s Three Gorges Dam was recently photographed from above by the European Space Agency’s CHRIS instrument on the Proba satellite. Since the sluice gates were closed in June, the water levels have risen 135 metres, and the dam will begin generating its first commercial electricity in August. More than 600,000 people were forced to abandon their homes, and the same number again will have to leave before the waters reach their planned 175 metre depth.

Water churns through diversion holes in the world?s largest dam – China?s Three Gorges project on the Yangtze River, imaged here by ESA?s Proba satellite this week. Seen to the left, the waters behind the dam have risen to a level of 135 metres since the sluice gates were first closed in early June, and in August Three Gorges is due to generate its first commercial hydroelectricity.

The Three Gorges project is set to create a new 600-km-long body of water on the face of the 21st century Earth: the thick concrete dam walls stand 190 metres tall and already they hold back an estimated 10 billion cubic metres of water. More than 600,000 people have had to abandon their homes to the rising reservoir, and as many again will have to relocate before the waters reach their final planned level of 175 metres.

Water flows through dam diversion holes
It can be clearly seen in the image how the river has burst its banks and is inundating the land upriver of the dam. The waters of the world?s third-longest river appear brown in colour because they are heavy with sediment.

Many environmentalists have campaigned against the ?20 billion-plus Three Gorges project due to the drowning of multiple cultural heritage sites, the fear that reservoir will collect industrial pollution and sewage that cannot now be washed to the sea, and the risk posed to downstream populations if the dam should ever break. But the Chinese government says the project will tame the flood-prone Yangtze River and generate much-needed electricity for economic development.

This 18-metre resolution image was acquired by the CHRIS sensor onboard Proba on 30 July 2003.

About Proba
Proba (Project for On Board Autonomy) is a micro-satellite the size of a small box, launched by ESA in October 2001 and operated from ESA’s Redu Ground Station (Belgium). Orbiting 600 km above the Earth?s surface, Proba was designed to be a one-year technology demonstration mission but has since had its lifetime extended as an Earth Observation mission. It now routinely provides scientists with detailed environmental images thanks to CHRIS – a Compact High Resolution Imaging Spectrometer developed by UK-based Sira Electro-Optics Ltd – the main payload on the 100 kg spacecraft.

Proba boasts an ?intelligent? payload, has the ability to observe the same spot on Earth from a number of different angles and can record images of an 18.6 km square area to a resolution of 18 m. More than 60 scientific teams across Europe are making use of Proba data. A follow-on mission, Proba-2, is due to be deployed by ESA around 2005.

Original Source: ESA News Release

Searching For Life on Non-Earthlike Planets

Image credit: NASA

A team of astronomers from Ohio State University believe that we should be seeking life on a wider range of planets than previously speculated. They calculated that NASA’s upcoming Space Interferometry Mission (SIM) should be able to detect habitable planets near stars which are much larger than the Sun. This opens up a whole new range of planets to look at. SIM was originally supposed to launch in 2009, but NASA is considering whether to use these funds to maintain Hubble past 2010 instead.

The search for life on other planets could soon extend to solar systems that are very different from our own, according to a new study by an Ohio State University astronomer and his colleagues.

In fact, finding a terrestrial planet in such a solar system would offer unique scientific opportunities to test evolution, said Andrew Gould, professor of astronomy here.

In a recent issue of Astrophysical Journal Letters, he and his coauthors calculated that NASA?s upcoming Space Interferometry Mission (SIM) would be able to detect habitable planets near stars significantly more massive than the sun.

Scientists have typically thought that the search for life should focus on finding planets like Earth that orbit stars like the sun, but this new finding shows that ?the field is wide open,? Gould said.

?Here?s a type of solar system that we never thought to look at,? he added, ?but now we?ll have the tools to do it.?

Gould is on the science team that is helping to plan the SIM mission, and he is working to define the capabilities of the satellite.

The satellite was set to launch in 2009, but its fate is now uncertain. NASA is considering whether to divert funds to maintain the Hubble Space Telescope beyond its scheduled retirement in 2010, Gould explained, and he has been asked to address the issue for an assembly of astronomers in Washington D.C. on Thursday, July 31.

SIM would help astronomers find habitable planets, Gould said. The key is detecting planets that circle a star at just the right distance to maintain a supply of liquid water. The range of most promising orbits depends on the type of the star, and is called the ?habitable zone.?

The earth resides directly in the habitable zone for our solar system, some 93 million miles from the sun. The nearest planets, Venus and Mars, barely lie within the edges of the habitable zone.

Hotter, more massive stars have always been considered less likely to harbor life, though not because they would be too hot. Planets could still enjoy temperate climates, just at orbits farther away from the star.

The problem is one of time, not temperature, Gould said.
Hotter stars tend to ?burn out? faster — perhaps too fast for life to develop there.

Our sun is approximately 4.5 billion years old; in contrast, one of the stars examined in the study is 1.5 times more massive than the sun, and would probably only generate life-sustaining energy for about two billion years.

Given the billions of years required for evolution of life on earth, scientists could question whether life would stand a chance in a shorter-lived solar system.

?We have no idea how evolution would proceed on any planet other than our own,? Gould said. ?If we find a planet around a shorter-lived star, we may be able to test what would happen to evolution under those circumstances.?

SIM will use Interferometry — a technique that involves the interference of light waves — to very accurately measure the position of stars in the sky. The satellite would notice, for instance, if a point of light on the surface of the moon moved the width of a dime.

In the case of distant stars, SIM will pick up on the tiny wobble in the position of a star caused by the gravity of its orbiting planets.

That?s what will make SIM ideal for studying hotter, massive stars, Gould said. Planets that orbit far from a star — as the habitable planets around a hot star would have to do — create a larger wobble.

He and study coauthors Eric B. Ford of Princeton University and Debra A. Fischer of the University of California, Berkeley, determined that SIM is sensitive enough for the task.

Previously, Gould and Ohio State professor Darren DePoy and graduate student Joshua Pepper determined that another future NASA mission could be used to find habitable planets around very small stars, which are much more plentiful in the galaxy than stars like our sun.

That mission, the Kepler Mission, will detect planetary transits — events where planets pass in front of a star and block the star?s light from reaching earth. Transits of planets orbiting close to a star are easier to detect, and because these small stars are very dim, the habitable zone would also be very close to the star.

?The point is that the various methods for planet detection complement each other, and can be used to find habitable planets around a wide variety of stars,? Gould said.

NASA funded this research.

Original Source: OSU News Release