Massive Black Holes Caught in Death Spiral

BY DENNIS OVERBYE



The apocalypse is still on, apparently-at least in a galaxy about 3.5 billion light-years from here.

Last winter, astronomers at the California Institute of Technology reported that two supermassive black holes appeared to be spiraling toward a cataclysmic collision that could bring an end to that galaxy.

The evidence was a rhythmic flickering from the galaxy’s nucleus, a quasar known as PG1302-102, which Matthew Graham and his colleagues interpreted as the fatal mating dance of a pair of black holes with a total mass of more than a billion suns. Their merger, the astronomers calculated, could release as much energy as 100 million supernova explosions, mostly in the form of violent ripples in space-time known as gravitational waves that would blow the stars out of that hapless galaxy like leaves off a roof.

The supermassive black holes are all that remains of galaxies once all protons decay, but even these giants are not immortal. (Photo credit: Wikipedia)

Now a new analysis of the system by Daniel D’ Orazio of Columbia University in New York and his colleagues has added weight to that conclusion. Mr. D’ Orazio, a graduate student, and Zoltan Haiman and David Schiminovich propose that most of the light from the quasar is coming from a vast disk of gas surrounding the smaller of the two black holes.

As the black holes and their attendant disks swing around each other at high speeds, the light from the disk that is coming toward us receives a boost from relativistic effects-a so-called Doppler boost-the way a siren grows louder and more high-pitched as it approaches, giving rise to a periodic increase in brightness every five years.

The Columbia astronomers ‘model predicts that the variation would be two or three times greater in ultraviolet light than in visible light. And that is exactly what they found when they compared archival data from the Hubble Space Telescope and NASA’s Galex space telescope to the visible-light data previously analyzed by Dr. Graham’s group.

“What’s big is that the Doppler boost is inevitable,” Dr. Haiman said in an email. Given reasonable assumptions about the masses of the black holes, their model predicts the right ultraviolet data.

“This is rare in ‘messy’ astronomy,” he said, “to have an indisputable clean effect, which explains the data.”

Follow-up observations of ultraviolet and visible light emissions in the coming years could help clinch the case, the authors said. Their paper was published last month in the journal Nature.

Their model suggests that the black holes are orbiting each other at a distance of some 320 billion kilometers, less than tenth of a lightyear, a cosmic whisker. At that distance, the black holes would be rapidly losing energy by radiating gravitational waves and could spiral together into the final bang in as little as 100,000 years, Dr. Haiman said, depending on their relative masses.

An artist's conception of a supermassive black hole and accretion disk. (Photo credit: Wikipedia)

“Basically, the more massive the holes, the faster gravitational waves drive them together, and we do require them to be as massive as allowed to be ,” he said in an email. For their model to hold up, the larger of the black holes has to be a billion solar masses or more.

(Because the galaxy is so far away, the cataclysm might well have already happened more than three billion years ago, but the news still won’t reach us for another 100,000 years or so. So it is still in the future, as far as earthlings-whoever they will be by then-are concerned.)

E.Sterl Phinney, a Caltech astronomer and expert on supermassive black holes, agreed that Dr.Haiman’s model explained the quasar variations. “So Occam’s razor makes it attractive,” he said, referring to the long-held principle that physicists should adopt the simplest theory that fits the facts. But it was surprising, he said, to find two supermassive black holes that have gotten so close.

Black holes, predicted by Albert Einstein’s general theory of relativity, are objects so dense that not even light can escape from them. Every galaxy of note seems to have a supermassive black hole, weighing millions or billions of times as much as the sun, burping sparks of half-eaten stars and gas.

“A scientific theory is only as good as the tests which it has passed,” Mr. D’ Orazio said.

Einstein’s theory has passed all of the observational and experimental tests thrown at it so far. But some of its predictions can be tested only in the most extreme gravitational environments, namely black holes.



Taken from TODAY Saturday Edition, The New York Times International Weekly, October 3, 2015

Planet Mercury Is Shown To Be More Than a Little Bore

English: Artist's rendering of the MESSENGER spacecraft orbiting Mercury (Photo credit: Wikipedia)

By KENNETH CHANG


NASA’s Messenger spacecraft, in orbit around Mercury for the past four years, came to an abrupt end on April 30 when it crashed into the surface.

That event brought to a close a mission that has painted an unexpected portrait of Mercury, once thought a boring round rock not much different from Earth’s moon. Mercury, the smallest planet in our solar system, is only slightly larger than the moon, although it has more drastic temperature swings – 427 degrees Celsius during the day, minus 184 degrees at night.

“It’s really been exciting to see a planet unfold, a planet that is one of our neighbors,” said Sean C. Solomon, the principal investigator for the mission. “Almost every aspect of Mercury has had its share of surprises.”

Messenger – a shortening of Mercury Surface, Space Environment, Geo-chemistry and Ranging – discovered that Mercury shrank slightly as it cooled over billions of years; mapped ancient lava flows; found enigmatic shallow depressions that are some of the youngest and brightest features on the surface; and confirmed the presence of ice in perpetually dark crates near the poles.

The water ice, perhaps a billion tons, was not a complete surprise. Radio telescope observations from Earth had hinted at something reflective, and the shadowed craters are extremely cold. Beyond confirming the suspected, Messenger also made a new discovery: The ice was covered by an unexplained dark layer.

“We have a reasoned hypothesis,” Dr. Solomon said. The material could be carbon-rich compounds, similar to substances found in certain meteorites and in comets. “It’s tarlike in its consistency,” he said. “It’s as dark as tar.”

The biggest scientific finding of the mission, Dr. Solomon said, was that Mercury was rich in “volatiles,” elements like chlorine, sulfur, potassium and sodium that easily evaporate at moderate temperatures. Mercury is small and dense, full of iron, and the thinking about how it formed was that it must have been heated to temperatures that should have boiled off the volatiles. Yet the volatiles are still there.

Scientists now have to come up with new ideas to explain how Mercury formed. When NASA launched Messenger in 2004, knowledge of Mercury was sparse. The only close-ups had come in three flybys by NASA’s Mariner 10 in the 1970’s

For more than six years, Messenger took a circuitous route through the inner solar system, making flybys of Earth, Venus and Mercury, to slow itself down enough to enter orbit around Mercury. On March 18, 2011, finally arrived.

The orbital portion of the mission was to last one year, then was extended twice.

Even the craft’s destruction could provide insights by digging up what lies beneath the surface- but it will be some time before anyone will see what that is. NASA does not have any follow-up Mercury missions set, but an ambitious European and Japanese collaboration called BepiColombo is scheduled to launch in 2017. It is to arrive at Mercury in 2024.

That mission consists of two orbiters, one focusing on the planet, the other on the surrounding space environment, in greater and finer detail than Messenger.

Johannes Benkhoff, the project scientist for BepiColombo at the European Space Agency, described Messenger as “really a fantastic mission.”

“It’s perfect that we have BepiColombo to follow on” Messenger’s findings, Dr. Benkhoff said. “They have provided a lot of new results, unexpected results.”

BepiColombo is named after Giuseppe Colombo, an Italian scientist nicknamed Bepi who came up with the orbital trajectories that enabled NASA’s Mariner10 flybys.

Dr. Solomon is looking forward to the next trip to Mercury I still want to learn more about, “he said.


Taken from TODAY Saturday Edition, The New York Times International Weekly, May 9, 2015

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Imaginings of the Cosmos Through the Ages

English: Artist's conception of the spiral structure of the Milky Way with two major stellar arms and a central bar. "Using infrared images from NASA's Spitzer Space Telescope, scientists have discovered that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to possess four major arms." (Photo credit: Wikipedia)

Exterior of the Chora Church in Istanbul, today a museum. It is famous for it Byzantine mosaics. (Photo credit: Wikipedia)

Nicolaus Copernicus Monument in Kraków, by Professor Cyprian Godebski. Esperanto: Monumento pri Koperniko ĉe la Malnova Universitato de Krakovo. Polski: Pomnik Mikołaja Kopernika w Krakowie. (Photo credit: Wikipedia)

MICHAEL BENSON


Four elegantly cloaked gentlemen in idiosyncratic caps peer through what seems to be a porthole at distant Earth – a planet as spiky with spires as to look machine-made.

The tenor of the scene – the brilliant sun above, a pale crescent moon below the terrestrial sphere – suggests that these are the great astronomers of history, engaged in discussions about the design of the universe. They’re positioned, however, on a weedy slope, which raises a question: Where are they, exactly?

The picture comes from a 15th-century French translation of the 1240 work “De Proprietatibus Rerum” (“On the Properties of Things”), by one Bartholomeus Anglicus, among the earliest forerunners of the modern encyclopedia.

The image, by an anonymous artist, was revelatory: at once enigmatic and precise, a 600-year-old proto-science-fiction rendering of the cosmos. It is one of about 300 in my new book, “Cosmigraphics: Picturing Space Through Time,” a survey of many in about 4,000 years of attempts to represent the universe in graphic form, whether in manuscripts, paintings, prints or books, all the way up to 21st-century supercomputer simulations of galaxy groups in flux and sunspots in bloom.

In “Laniakea Supercluster,” for example, the astronomer R. Brent Tully uses a supercomputer to visualize gravitational flow lines knitting together an echoing expanse of space-time more than 500 million light-years in diameter. In this, the image was the discovery.

Perhaps the most extraordinary set of pictures depicting space-time’s origins dates from 1573. Discovered in the mid-20th century in an obscure notebook in the National Library of Spain, it was painted by the Portuguese artist and philosopher Francisco de Holanda, a student and lifelong friend of Michelangelo.

In one image, a set of elongated triangles represents the holy trinity, with the Greek letters alpha and omega on top and “Fiat Lux” (“let there be light “) just below. Swathed in flames, they extend down to a kind of clay vessel. The images are startlingly modern.

On another page, the Creator, belted by stars, has assumed a material form, centered on a single planet. It has become the multiple nested crystalline spheres that for more than 15 centuries were thought to carry the planets, the sun and moon on their courses, with Earth at their nucleus. This cosmological design was first proposed by Aristotle, and later modified and expanded by Ptolemy in the second century A.D.

Finally, de Holanda depicts a geometry of turning forms set in motion by God’s luminescent command. A giant sun pinions tiny Earth in a shadow-casting ray. This work contains a remarkable insight: Although the sun nominally rotates around Earth, in fact it dominates the picture, suggesting that the artist has grasped that it is the true center of our planetary system.

The image is one of several medieval and Renaissance depictions of cosmic design that seem to exhibit a kind of precognitive intuition of what Nicolaus Copernicus proposed in 1543 – the revolutionary notion of a heliocentric planetary system. (While de Holanda painted 30 years after Copernicus’s death, heliocentrism didn’t become accepted for at least another century, and it’s unlikely the artist meant to advocate it, if he even knew of it.)

We have had a gradually dawning, forever incomplete situational awareness about the cosmos and our place within it, rising across millenniums.

Among the narrative threads are the 18th-century visual meditations on the possible design of the Milky Way – including the work of the English astronomer Thomas Wright, who in 1750 reasoned his way to the flattened-disk form of our galaxy. Wright also conceived of another revolutionary concept: a multigalaxy cosmos.

We now have our contemporary understanding of space-time, in which whirling star-spirals glint all the way to the fading edge of the visible. But while the center doesn’t hold in this vision, neither does anarchy: We’re left with a spongiform universe of galaxy clusters foaming along weblike filaments of dark matter. It all looks rather like a visualization of the Internet.

So where will it all end? Maybe a 14th-century vision of weightlessness provides a clue: A fresco on the ceiling of the Chora Church in Istanbul depicts a human figure (evidently wearing a supernatural kind of space helmet). It has become known as “The Angel of the Lord Rolling Up the Scroll of Heaven at the End of Time.”


Taken from TODAY Saturday Edition, November 1, 2014

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An asteroid did it!

It's definitive: An asteroid wiped out the dinosaurs


AFP - Friday, March 5




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Artist's rendition released by NASA shows an asteroid belt in orbit around a star. A huge asteroid that smashed into Earth with the force of a billion atomic bombs wiped out the dinosaur, scientists said Thursday, hoping to lay to rest a long-running debate over a mass extinction 65 million years ago.
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WASHINGTON (AFP) - – Dinosaurs were wiped out by a huge asteroid that smashed into Earth 65 million years ago with the force of a billion atomic bombs, scientists said Thursday, hoping to lay an age-old debate to rest once and for all.


The definitive verdict came from an international panel of experts who reviewed 20 years' worth of evidence about what caused the Cretaceous-Tertiary (KT) extinction that wiped out more than half the species on the planet.


They determined it was a massive asteroid, measuring around 15 kilometers (nine miles) wide, which smashed into what is today Chicxulub in Mexico.


The event marked a pivotal point in history because it cleared the way for mammals to become the dominant species on Earth.


"The asteroid is believed to have hit Earth with a force one billion times more powerful than the atomic bomb at Hiroshima," the researchers said in a report published in the journal Science.


"It would have blasted material at high velocity into the atmosphere, triggering a chain of events that caused a global winter, wiping out much of life on Earth in a matter of days."


The panel of 41 scientists hope their findings will lay to rest once and for all the debate about what caused the KT extinction.


Some scientists have argued that dinosaurs and species including bird-like pterosaurs and large sea reptiles were wiped out by a series of volcanic eruptions in what is now India that lasted some 1.5 million years.


The eruptions spewed enough basalt lava across the Deccan Traps in west-central India to fill the Black Sea twice and were thought to have caused a cooling of the atmosphere and acid rain on a global scale.


But the evidence gathered for the study published in Science showed that marine and land ecosystems were destroyed rapidly in the KT extinction, leading the scientists to rule out volcanic activity as the culprit, because its effects would have whittled away at dinosaurs and other species over time.


"Despite evidence for relatively active volcanism in the Deccan Traps at the time, marine and land ecosystems showed only minor changes within the 500,000 years before the time of the KT extinction," the scientists said.


"Computer models and observational data suggest that the release of gases such as sulphur into the atmosphere after each volcanic eruption... would have had a short-lived effect on the planet and would not cause enough damage to create a rapid mass extinction of land and marine species."


The Chicxulub asteroid, on the other hand, could very well have made short shrift of dinosaurs, pterosaurs and other species, the scientists said.


The impact of the large asteroid would have "triggered large-scale fires, earthquakes measuring more than 10 on the Richter scale, and continental landslides which created tsunamis," said Joanna Morgan, a lecturer in geophysics at Imperial College, London and co-author of the study.


The asteroid hit Earth 20 times faster than a speeding bullet and exploded into a deadly mix of hot rock and gas which would have "grilled any living creature in the immediate vicinity that couldn't find shelter," said Gareth Collins, a research fellow at Imperial College.


"The final nail in the coffin for the dinosaurs happened when blasted material was ejected at high velocity into the atmosphere," shrouding the planet in darkness and causing a global winter that killed off species that "couldn't adapt to this hellish environment," added Morgan.


Another clue that the KT extinction was caused by a huge asteroid and not volcanic activity was evidence in geological records of "shocked" quartz in rock layers at KT boundary levels around the world.


Quartz is "shocked" when it is hit very quickly by a massive force -- such as a 15-kilometer-wide asteroid traveling 20 times faster than a bullet.


The KT extinction marked the end of the 160-million-year reign of the dinosaurs and allowed mammals, and eventually humans, to become the dominant species on earth.




From Yahoo.SG News; source article is found here.
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Dinosaurs' long-lost relatives: FOUND

Scientists find early dinosaur cousin
AFP - Friday, March 5



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A recent image released by Chicago's Field Museum shows an artist's impression of the Asilisaurus kongwe, a close dinosaur relative. Scientists have uncovered the bones of a dinosaur-like creature that roamed Earth at least 10 million years earlier than the oldest known dinosaur, according to a study published in Nature.
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PARIS (AFP) - – Scientists have uncovered the bones of a dinosaur-like creature that roamed Earth at least 10 million years earlier than the oldest known dinosaur, according to a study published Thursday.


Discovered in Tanzania, Asilisaurus kongwe would have been waist-high to a human, ate plants, and lived some 240 million years ago, said the study, published in Nature.


The discovery means that dinosaurs probably appeared much earlier than previously thought, the researchers said.


It also points to a rich variety of fauna during the crucial period before dinosaurs began their 165-million domination of the planet.


"This new evidence suggests they were really only one of several large and distinct groups of animals that exploded in diversity in the Triassic, including silesaurs, pterosaurs, and several groups of crocodilian relatives," said Sterling Nesbitt, a researcher at the University of Texas in Austin.


Pterosaurs were flying reptiles.


The newly-found creature is a silesaur, which Nesbitt described as a "sister" taxon to the one that gave rise to dinosaurs.


Their evolutionary relationship would be roughly analogous to that between humans and chimps, whose genomes overlap by 99 percent, he said.


Silesaurs and dinosaurs lived side-by-side throughout much of the Triassic Period, between 250 and 200 million years ago.


Fossil bones from at least 14 Asilisaurus specimens were recovered from a site in southern Tanzania. Scientists were able to reconstruct a nearly complete skeleton, with only small portions of the head and hand missing.


The animal stood half-a-meter to a meter (1.5 to 2.0 feet) tall at the hips, and were one-to-three meters (three-to-five feet) long.


They weighed between 10 and 30 kilogrammes (22 and 66 pounds), and walked on all four legs.


The shape of the teeth and a beak-like lower jaw suggest that the animals could eat meat or plants.


Scientists speculated that the animals were originally carnivores but evolved into omnivores to enhance their chances of survival.


While they did not persist as long as dinosaurs, silesaurs had a good run, lasting some 45 million years.


The first specimen from the silesaur group was discovered only in 2003, but since then eight other specimens have been dug up from Triassic rock around the globe.


"This goes to show that there are whole groups of animals out there that we've never even found evidence of that were very abundant during the Triassic," Nesbitt said.


The names Asilisaurus kongwe comes from "asili," which means "founder" in Swahili, "sauros, the Greek for "lizard", and "kongwe," Swahili for "ancient."




From Yahoo.SG News; source article is found here.
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Chile quake may have moved Earth's axis

Chile quake moved Earth's axis, shortened days: scientist

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AFP - Wednesday, March 3

A gap in a road caused by Saturday's earthquake and the ensuing tsunami in Pulluhue, 320 km south of Santiago. The powerful earthquake that shook Chile on Saturday probably shifted the Earth's axis and made days slightly shorter, a NASA scientist said.

WASHINGTON (AFP) - – The powerful earthquake that shook Chile on Saturday probably shifted the Earth's axis and made days slightly shorter, a NASA scientist said.

Richard Gross, a research scientist at NASA's Jet Propulsion Laboratory in California, calculated that the planet's axis would have shifted by eight centimeters (three inches) during the 8.8 magnitude quake, NASA said in a statement.

Earth days are 24 hours long because that's the amount of time it takes the planet to make one full rotation on its axis, so shifting the axis would affect rotation.

If, indeed, the planet's axis did shift by eight centimeters during the Chilean quake, days would have shortened by 1.26 microseconds, Gross calculated.

A microsecond is one-millionth of a second, so no need to adjust watches just yet.

The Chilean quake shifted the Earth's axis by even more than the 9.1-magnitude temblor off Indonesia that set off the deadly tsunami in Asia in 2004, Gross worked out.

That's partly because the faultline responsible for the earthquake in Chile "dips into Earth at a slightly steeper angle than does the fault responsible for the 2004 Sumatran earthquake" and is more effective at moving Earth's mass vertically and shifting the planet's axis.

The 2004 quake in Asia caused the Earth to move by around seven centimeters and chopped an estimated 6.8 microseconds off the length of a day, NASA said.

From Yahoo.SG News; original article is found here

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Dwarf Dinosaurs

Image via Wikipedia

'JURASSIC PARKETTE' WAS RULED BY DWARF DINOSAURS

------------------------------------------------

LONDON - A prehistoric "lost world" ruled by miniature dinosaurs has been discovered by palaeontologists. The creatures lived on an island - a kind of pigmy Jurassic Park - and were up to eight times smaller than some of their mainland cousins.

One of the island-dwelling dinosaurs, named Magyarosaurus, was a little bigger than a horse, but was related to some of the largest creatures to ever walk the Earth - gigantic titanosaurs such as Argentinosaurus, which reached up to 100 feet (30.5 metres) long and weighed around 80 tonnes. Another of the dinosaurs was found to be a primitive dwarfed species similar to large duck-billed herbivores like Iguanodon, which could grow to be up to 10 feet long and weighed more than three tonnes.

Fossils from the dwarf dinosaurs were found in modern day Romania, in an area known as Hateg, which was an island 65 million years ago.

Professor Michael Benton, from the University of Bristol, who carried out the research with scientists at the Universities of Bucharest and Bonn, said the dinosaurs seemed to have evolved into smaller bodies after becoming marooned there. THE DAILY TELEGRAPH

From TODAY, Monday, 22-Feb-2010

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Galactic smash-up

Image by earthhopper via Flickr

Australian amateur tells of 'one in a million' Jupiter spot

SYDNEY - An Australian amateur stargazer who spotted a "one in a million" impact on Jupiter told of his astonishment yesterday as he chanced upon the Earth-sized dent in its gassy atmosphere.

Mr Anthony Wesley, 44, who has had a life-long passion for the stars, was photographing the planet near midnight on Sunday when he noticed a black mark that had not been there two nights earlier.

The computer programmer, who watches the sky with his 37cm telescope in the backyard of his farm outside Canberra said he first thought it was a shadow cast by one of the planet's 63 moons.

A photo of Jupiter as taken from Canberra on Monday by amateur astronomer Anthony Wesley.

For the next two hours, Mr Wesley frantically photographed the mark, then started emailing astronomers, "to get the professional astronomers in and let them take over".

After Nasa experts spent six hours examining the spot with an infra-red telescope in Hawaii, the verdict came in - Jupiter had been hit, possibly a stray comet or a block of ice which left an Earth-sized dent in its gaseous atmosphere.

Mr Franck Marchis, an astronomer at the Seti Institute said humans should be thankful for Jupiter.

"We should thank our giant planet for suffering for us," he said.

"Its strong gravitational field is acting like a shield protecting us from comets coming from the outer part of the solar system." Agencies

From TODAY, World – Thursday, 23-Jul-2009

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Saturn moon may harbour life-giving ocean: study

AFP - Thursday, June 25

PARIS (AFP) - - Huge geysers on Saturn's moon Enceladus may be fed by a salty sea below its surface, boosting the odds of extraterrestrial life in our own Solar System, according to a study released Wednesday.

This 2006 NASA Cassini space probe mosaic image shows Saturn's moon Enceladus. Huge geysers on Saturn's moon Enceladus may be fed by a salty sea below its surface, boosting the odds of extraterrestrial life in our own Solar System, according to a study released Wednesday.

Researchers in Europe detected salt particles in the volcanic vapour-and-ice jets that shoot hundreds of kilometres (miles) into space, the strongest evidence to date of a liquid ocean under the moon's icy crust.

Scientists already knew that tiny Enceladus, only 500 kilometers across, had two of the three essential ingredients for the emergence of life.

One is an energy source, produced in this case by "tidal warming" driven by the shifting gravitational tug of its parent planet during the moon's lopsided orbit, and perhaps by other forces too.

The Cassini spacecraft circling Saturn since 2004 has also found a potentially life-sustaining mix of organic chemicals in Enceladus' plumes, ejected from a quartet of 120-kilometer (75-mile) long fractures -- known as "tiger stripes" -- aligned on the moon's south pole.

That left the third critical ingredient: liquid water.

Since their discovery in 2005, the giant geysers have fueled intense speculation on the presence of a subterranean ocean, and the new discovery goes a long way toward resolving one of the most hotly debated topics in planetary science.

A team led by Frank Postberg of the University of Heidelberg studied data from Cassini's Cosmic Dust Analyzer, and tested their findings in laboratory experiments.

Their results, published in the British journal Nature, show that ice grains in the Enceladus plumes contain substantial quantities of sodium salts, and that the moon's hidden sea -- if there is one -- could be as salty as Earth's oceans.

"The abundance of various salt components in the particles ... exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core," the researchers conclude.

"Individual plume sources stay active for years, implying outflow from a large reservoir."

Sodium is a good telltale tracer of possible liquid water for two reasons, according to John Spencer of the Southwest Research Institute in Boulder, Colorado.

It is highly soluble, "so any Enceladan water that has prolonged contact with the moon's silicate core should be rich is sodium salts, like Earth's oceans," he noted in a commentary for Nature.

Sodium also scatters sunlight efficiently in the orange-yellow range of the spectrum, and is thus easy to detect even in minute quantities.

In a second study, also in Nature, a team led by Nicholas Schneider of Colorado University likewise looked for salts in Enceladus' plumes, this time using spectrographs on Earth-bound telescopes.

That it failed to detect any would seem to challenge Postberg's findings, but the Earth-based observations -- combined with the Cassini data -- may in fact give us additional clues as to how they may be true, said Spencer.

It tells us, for example, that the plumes could not have been formed by boiling salty water spewing directly out of Enceladus' tiger stripes, otherwise the sodium would be so abundant as to be observable from Earth.

Instead, the plumes could come from salty water distilling into fresh water vapours, but not through evaporation as happens over Earth's oceans, but rather in pressurised chambers under the moon's surface.

Cassini is scheduled to make four additional up-close fly-bys of Enceladus before mid-2010, and another dozen in the next five years if its mission is extended, so lingering doubts on the moon's hidden seas may soon be put to rest.

From Yahoo! News; see the source article here.

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Earth-Venus smash-up possible in 3.5 billion years: study

AFP - Thursday, June 11

This undated handout illustration provided by Nature Publishing group shows what a collision between Earth and Venus might look like. A force known as orbital chaos may cause our Solar System to go haywire, leading to possible collision between Earth and Venus or Mars, according to a study.

PARIS (AFP) - A force known as orbital chaos may cause our Solar System to go haywire, leading to possible collision between Earth and Venus or Mars, according to a study released Wednesday.

The good news is that the likelihood of such a smash-up is small, around one-in-2500.

And even if the planets did careen into one another, it would not happen before another 3.5 billion years.

Indeed, there is a 99 percent chance that the Sun's posse of planets will continue to circle in an orderly pattern throughout the expected life span of our life-giving star, another five billion years, the study found.

After that, the Sun will likely expand into a red giant, engulfing Earth and its other inner planets -- Mercury, Venus and Mars -- in the process.

Astronomers have long been able to calculate the movement of planets with great accuracy hundreds, even thousands of years in advance. This is how eclipses have been predicted.

But peering further into the future of celestial mechanics with exactitude is still beyond our reach, said Jacques Laskar, a researcher at the Observatoire de Paris and lead author of the study.

"The most precise long-term solutions for the orbital motion of the Solar System are not valid over more than a few tens of millions of years," he said in an interview.

Using powerful computers, Laskar and colleague Mickael Gastineau generated numerical simulations of orbital instability over the next five billion years.

Unlike previous models, they took into account Albert Einstein's theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in dramatically different orbital paths.

The researchers looked at 2,501 possible scenarios, 25 of which ended with a severely disrupted Solar System.

"There is one scenario in which Mars passes very close to Earth," 794 kilometres (493 miles) to be exact, said Laskar.

"When you come that close, it is almost the same as a collision because the planets gets torn apart."

Life on Earth, if there still were any, would almost certainly cease to exist.

To get a more fine-grained view of how this might unfold, Laskar and Gastineau ran an additional two hundred computer models, slightly changing the path of Mars each time.

All but five of them ended in a two-way collision involving the Sun, Earth, Mercury, Venus or Mars. A quarter of them saw Earth smashed to pieces.

The key to all the scenarios of extreme orbital chaos was the rock closest to the Sun, found the study, published in the British journal Nature.

"Mercury is the trigger, and would be be the first planet to be destabilised because it has the smallest mass," explained Laskar.

At some point Mercury's orbit would get into resonance with that of Jupiter, throwing the smaller orb even more out of kilter, he said.

Once this happens, the so-called "angular momentum" from the much larger Jupiter would wreak havoc on the other inner planets' orbits too.

"The simulations indicate that Mercury, in spite of its diminutive size, poses the greatest risk to our present order," noted University of California scientists Gregory Laughlin in a commentary, also published in Nature.

From Yahoo! News; see the source article here.

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