Monday, 30 June 2014

"Energy from Sun Could Spawn Evolution of Life Forms on Titan" --NASA/Cassini Scientists

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"If there is sufficient energy pumped into Titan's atmosphere and surface from the sun, then it is possible that this would this would spawn evolution of life forms that take advantage of the energy source," said Howard Zebker, Professor of Geophysics and Electrical Engineering at Stanford University. "It would be very different life than on Earth, as it is minus 292 degrees Fahrenheit most of the time. Still, Titan remains one of the best places for life to evolve in the solar system."

Mysterious features spotted on Titan reveal the moon's seasonal changes. Bright spots in a large lake on Titan suggest that Saturn's largest moon supports processes similar to Earth's water cycle, says Zebker. At first glance, Titan has little in common with Earth. The largest moon of Saturn, temperatures on Titan's surface dip nearly 300 F below zero, its seas slosh with liquid methane, and its sky is a murky shade of creamsicle. And yet, fresh analysis of mysterious features spotted on the moon indicates that it experiences one of the same global processes that is important here on Earth.
In a study published in the latest issue of Nature Geoscience, scientists operating the Cassini satellite, including Zebker, present evidence that Titan has seasonal cycles analogous to Earth's, and that the moon's surface conditions change as the Titan year unfolds.

The Cassini satellite has been orbiting Saturn and its moons since 2004. Zebker, a professor of electrical engineering and of geophysics, is one of the lead scientists operating the spacecraft's radar instruments. Radar is critical for studying Titan in particular because the moon's atmosphere is typically too cloudy and thick for optical instruments to see through easily.

During five fly-bys of Titan's Ligeia Mare – a liquid methane sea larger than Lake Superior – the scientists noticed bright features that appeared and changed shape on the sea's surface. After ruling out a technical glitch or an exotic artifact of radar scattering, the group focused on three causes most likely for the phenomena.

"We are driven to use our imaginations and picture what could be happening on the sea to produce a transient feature," Zebker said.

One such explanation could involve low-density solids that usually sink below the surface – much like silt in a river delta – but then rise and clump together. Unlike ice on Earth, frozen methane is denser than its liquid phase, so it sinks instead of floats. "On Earth, ice floats and we get icebergs," Zebker said. "On Titan, icebergs would sink."

Seasonal temperature changes could account for the appearance and disappearance of these solids, as they might be released from the bottom and rise to the surface in warmer temperatures.

A second explanation involves bubbles. As summer temperatures warm the sea, bubbles trapped by the sunken frozen material could be released and float to the surface.

Finally, the bright features could be cresting waves, whipped up by summer winds.

"Waves are usually not visible on Titan, but in this case the onset of the summer season may create a more turbulent atmosphere," Zebker said. "On Earth we see this effect as the ocean warms and we start a new hurricane season."

All together, the observation and the possible explanations suggest that Titan's surface changes seasonally. They also support the idea that liquid methane might flow and evaporate in response to changing exposure to sunlight, in much the same way that water cycles through various systems on Earth.

Liquid methane lakes and seas have been observed on Titan's surface, and the atmosphere appears to carry methane and ethane similar to the way that Earth's atmosphere transports water vapor, Zebker said, and so scientists can expect Titan to have variations in liquid methane, ethane and other hydrocarbons driven by changes in temperature and sunlight.

As with any discovery that compares an alien world to Earth, the question of "Can it support life?" must be addressed. Although a dynamic process like the methane cycle and seasons go hand-in-hand with life on Earth, Zebker said that this discovery didn't significantly increase the chances that this moon of Saturn might support life.

Two-and-a-half billion years ago, the Earth's atmosphere was rich in hydrocarbons, similar to Saturn's moon, Titan. Before Earth's atmosphere ditched methane and began accumulating oxygen, though, our planet appears to have cycled back and forth every few million years between the two states years a hydrocarbon haze and clear skies. A sunlight-blocking haze most certainly affected the evolution of microbes that depend on light to photosynthesise and contributed to the delay before the final oxygenation of the atmosphere.

But some 2.4 billion years ago, photosynthesising microbes generated enough oxygen for it create the "great oxygenation event." But the reason for that lag, says bio-geochemist Aubrey Zerkle of Newcastle University, UK, "is one of the great mysteries of Earth's history."
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Will Earth Appear Habitable to Alien Astronomers? --NASA: "Ocean Glint May be a Clue"

“The LCROSS spacecraft observed the Earth and made statements about ozone in Earth’s atmosphere and also liquid water,” said lead researcher Tyler Robinson, a postdoctoral researcher at the NASA Ames Research Center in Mountain View, Calif. “We also used it to validate a tool to simulate how a distant Earth would appear.”
A paper on the research, “Detection of Ocean Glint and Ozone Absorption Using LCROSS Earth Observations,” is available now on the pre-publishing site Arxiv and has been accepted in the Astrophysical Journal.

LCROSS, which was smashed into the Moon as planned in 2009, had a primary mission to look for the signature of lunar water. About a decade before, NASA’s Lunar Prospector mission found hints of hydrogen in craters at the Moon’s poles. The divots are permanently shadowed from the heat of the Sun.

LCROSS was to follow up on those observations, and it repaid the investment in spades. It tracked what happened after its spent Centaur rocket stage crashed into the crater Cabeus near the Moon’s south pole, and found signs of hydrogen in spectroscopic measurements spanning infrared and ultraviolet light.

When LCROSS crashed into the moon itself, observations with NASA’s Lunar Reconnaissance Orbiter and others revealed about 100 kilograms of water in the crater it punched in the regolith, which was about 20 meters (66 feet) across.

The spacecraft was indeed successful in finding (and helping other spacecraft find) water on the Moon. But could it also find water on our ocean-rich Earth at a distance? Scientists became curious about the prospect, especially after seeing that our oceans make a mirror-like reflection, called “glint,” when a distant Earth appears as a crescent from the perspective of the Moon.

The image at the top of the page shows the first flash of sunlight reflected off a lake on Saturn's moon Titan. The glint off a mirror-like surface is known as a specular reflection. It confirmed the presence of liquid in the moon's northern hemisphere, where lakes are more numerous and larger than those in the southern hemisphere.

LCROSS did three observation sessions of Earth in 2009. Interestingly, the spacecraft was not originally tasked to look at Earth as an exoplanet. Instead, scientists were evaluating how accurately the spacecraft was pointing after launch, said co-author and NASA astrophysicist Kimberly Ennico-Smith. The data was later repurposed for the exoplanet modeling used in this research.

“You never know what else another pair of eyes looking at data can bring you,” she wrote in an e-mail. “That’s why having and maintaining archives is so important.”

For example, finding hydroxyl — a type of water — on the Moon came from combining sets from India’s Chandryaan-1 lunar spacecraft, and NASA’s Cassini spacecraft on its way to Saturn. Both missions were using the Moon to calibrate their instruments; ocean examinations were not the main objective.

Looking at the repurposed data yielded a surprise. Not only did LCROSS see a glint, but it was a lot different than what researchers expected.

“The glint detection I found to be surprising for a couple of reasons,” Robinson said. “The spacecraft observation of glint was in disagreement with some previous observations that were done from the ground.”

Specifically, some researchers had tried to make predictions of the Earth’s glint based on gazing at the Moon. When looking at the Moon outside of full phase, it’s possible to see the Earth’s light shining faintly off of it in a phenomenon called “Earthshine.”

By comparing Earthshine data from a crescent-phase Earth with data from other phases, it’s possible to get measurements of how significant glint is in observations of Earth’s crescent sliver. These measurements predicted a much stronger glint than what Robinson’s team saw using the LCROSS data.

What also surprised researchers was how different the glint appeared in different wavelengths of light. At some wavelengths, glint dominated Earth’s appearance, while at other wavelengths, the glint effect was more muted, as it was masked by certain atmospheric phenomenon.

“Also, the Earth at crescent phase, thanks to the ocean, can be twice as bright. If it’s something you look for in exoplanets, it can be a significant effect,” added Robinson.

If over the course of several orbits, a planet is observed as more reflective at crescent phases and less reflective at other phases, then can it be assumed that ocean glint is the cause? Robinson cautions that the answer is not that simple.

“There could be other explanations,” he said. “Clouds have a tendency to reflect better at crescent phases than at other phases, and recent work has shown that, under some circumstances, the ice-covered polar regions can mimic certain glint effects.”

But there could be other indications of habitability and life as well. One thing they noticed from a distance was ozone, which was not as much of a surprise to scientists but still a useful tool for observations. Ozone especially showed up in ultraviolet light, and it could be a “bio-indicator,” or sign of life, on distant planets, Robinson said.

“Ozone is a key potential indicator of life, and it appears most strongly in ultraviolet observations of Earth,” he said. “So, future telescopes could look to the ultraviolet as a place to more easily detect biosignature gases.”

Such a telescope, however, will be a couple of decades down the line. While NASA’s James Webb Space Telescope will be an able planet-hunter, it will take the resolution of something like the cancelled NASA Terrestrial Planet Finder project to make better progress in searching these worlds, he said. There were a few different ideas for what it would look like, but one design had intended to combine four, 3.5-meter telescopes in space to look at parameters such as temperature and atmosphere, among others.

Another important aspect of the observations performed by LCROSS is that they become the basis for new telescope designs. NASA’s work allows researchers to gather data on which designs would best pick out certain features of planets, such as the reflectivity or ozone that LCROSS observed.

“It’s using current tools to predict and understand what future telescopes might one day see. By studying Earth now, you can ensure that we don’t accidentally engineer the telescope of the future and find out we didn’t build it strong enough,” Robinson said.
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Thursday, 26 June 2014

Long-Sought Gravity Waves Detected from Three Orbiting Supermassive Black Holes --The Elusive 'Ripples' in Spacetime


The discovery of three closely orbiting supermassive black holes in a galaxy more than four billion light years away could help astronomers in the search for gravitational waves: the 'ripples in spacetime' predicted by Einstein. At this point, very little is actually known about black hole systems that are so close to one another that they emit detectable gravitational waves.

"This discovery not only suggests that close-pair black hole systems emitting at radio wavelengths are much more common than previously expected, but also predicts that radio telescopes such as MeerKAT and the African VLBI Network (AVN, a network of antennas across the continent) will directly assist in the detection and understanding of the gravitational wave signal," said Matt Jarvis of Oxford University's Department of Physics. Further in the future the SKA will allow them to find and study these systems in exquisite detail, and allow them to gain a much better understanding of how black holes shape galaxies over the history of the Universe.
An international team, including Oxford University scientists, led by Dr Roger Deane from the University of Cape Town, examined six systems thought to contain two supermassive black holes. The team found that one of these contained three supermassive black holes – the tightest trio of black holes detected at such a large distance – with two of them orbiting each other rather like binary stars. The finding suggests that these closely-packed supermassive black holes are far more common than previously thought.

'What remains extraordinary to me is that these black holes, which are at the very extreme of Einstein's Theory of General Relativity, are orbiting one another at 300 times the speed of sound on Earth," said Roger Deane from the University of Cape Town. "Not only that, but using the combined signals from radio telescopes on four continents we are able to observe this exotic system one third of the way across the Universe. It gives me great excitement as this is just scratching the surface of a long list of discoveries that will be made possible with the Square Kilometre Array (SKA).'

'General Relativity predicts that merging black holes are sources of gravitational waves and in this work we have managed to spot three black holes packed about as tightly together as they could be before spiralling into each other and merging," said Oxford's Jarvis. "The idea that we might be able to find more of these potential sources of gravitational waves is very encouraging as knowing where such signals should originate will help us try to detect these 'ripples' in spacetime as they warp the Universe.'

The team used a technique called Very Long Baseline Interferometry (VLBI) to discover the inner two black holes of the triple system. This technique combines the signals from large radio antennas separated by up to 10,000 kilometres to see detail 50 times finer than that possible with the Hubble Space Telescope. The discovery was made with the European VLBI Network, an array of European, Chinese, Russian and South African antennas, as well as the 305 metre Arecibo Observatory in Puerto Rico. Future radio telescopes such as the SKA will be able to measure the gravitational waves from such black hole systems as their orbits decrease.

While the VLBI technique was essential to discover the inner two black, the team has also shown that the binary black hole presence can be revealed by much larger scale features. The orbital motion of the black hole is imprinted onto its large jets, twisting them into a helical or corkscrew-like shape. So even though black holes may be so close together that our telescopes can't tell them apart, their twisted jets may provide easy-to-find pointers to them, much like using a flare to mark your location at sea. This may provide sensitive future telescopes like MeerKAT and the SKA a way to find binary black holes with much greater efficiency.

The image at the top of the page shows galaxy NGC 4258 (M106) has been know to have a mysterious extra set of arms. Shown here in vivid red, the extra appendages are now known to be caused by a high energy jet emanating from the supermassive black hole in the galaxy's center. The jet creates a shock wave that excites material in the galaxy's halo, seen here in the ionized light emitted by hydrogen atoms.
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