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Boiling over in zero-g

HERE ON EARTH, boiling is used for tasks ranging from cooking and heating to power generation. In space, boiling may be used for power generation and other applications.

But because boiling works differently in a zero-gravity environment, it is difficult to design hardware that will not overheat or cause other problems.

University of Maryland Professor Jungho Kim of the A. James Clark School’s Department of Mechanical Engineering, is working with John McQuillen, project scientist at NASA’s Glenn Research Centre in Ohio, to study how boiling is altered in zero-gravity.

Their experiment, the Microheater Array Boiling Experiment (MABE), launched on the space shuttle Discovery on February 24, 2011, bound for a long-term operation aboard the International Space Station (ISS).

The experiment has already been tested on NASA’s ‘Vomit Comet’ (‘weightlessness aircraft’) and the European Space Agency’s Parabolic Flight Campaign in France.

The results could help engineers design space hardware that uses boiling for multiple applications.

“In space, boiling may be required to generate vapour to power turbines in some advanced concepts for power generation, for temperature control aboard spacecraft, and for water purification,” says Kim.

The video at the top of the page shows the experimenters testing the equipment aboard the NASA’s ‘Vomit Comet’…an aircraft that flies parabolic trajectories to simulate short periods of weightlessness. The video below is a close-up of one of the experiments:

How it works

When a liquid is boiled on Earth, vapour, which is less dense than liquid, is removed from heated surfaces through the action of buoyancy. In zero-gravity, the buoyancy force becomes negligible and vapour can blanket the heated surfaces rather than moving away, potentially leading the surfaces to a state known as critical heat flux.

Critical heat flux occurs when a heater or plate becomes too hot, restricting the flow of liquid to the surface and causing the plate to overheat and potentially burn out.

Since liquids boil differently in space, an understanding of how these fluids behave can improve the reliability and expand the applications of space exploration hardware.

The experiment that will take place on the ISS will use two arrays of platinum microheaters bonded to a quartz plate. The arrays measure 7mm and 2.7mm across. The heaters are warmed when electricity is applied, and spaces between the heater lines will allow the boiling process to be seen through the transparent quartz. Boiling of a refrigerant-like fluid (FC-72) will be filmed at high speed and the video sent back to Earth along with the heater data in real-time for analysis.

More Information: Video about zero-G flight experiments

Adapted from information issued by the University of Maryland.

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Water world found in deep space?

Artist’s impression of super-Earth GJ 1214b

This artist’s impression shows the super-Earth exoplanet orbiting the nearby star GJ 1214. The planet, GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes.

  • Atmosphere of “super-Earth” GJ 1214b analysed
  • Planet air is either full of steam or clouds and hazes
  • First “super-Earth” to have it’s atmosphere studied

THE ATMOSPHERE of a “super-Earth” exoplanet has been analysed for the first time by an international team of astronomers using the European Southern Observatory’s (ESO) Very Large Telescope.

Exoplanet are ones that orbit stars beyond our Solar System. Over 500 have been detected so far. A “super-Earth” is one that is not much bigger than our own planet.

This particular planet, discovered in 2009 and known as GJ 1214b, was studied as it passed in front of its parent star and some of the starlight passed through the planet’s atmosphere.

The research team, led by Jacob Bean (Harvard–Smithsonian Centre for Astrophysics) say the atmosphere is either mostly water in the form of steam or is dominated by thick clouds or hazes.

“This is the first super-Earth to have its atmosphere analysed. We’ve reached a real milestone on the road toward characterising these worlds,” said Bean.

GJ 1214b has a radius of about 2.6 times that of the Earth and is about 6.5 times as massive, putting it squarely into the super-Earth class. Its orbits a star located about 40 light-years from Earth.

The star is faint, but it is also small, which means that the size of the planet is large compared to the star’s disc, making it relatively easy to study.

Although the planet is too far away for astronomers to take pictures of it, they can

The planet passes across the face of the star once every 38 hours as it orbits at a distance of only two million kilometres—about 70 times closer than the Earth orbits the Sun.

Initial discovery

GJ 1214b was discovered as a “transiting object” by the MEarth project, which focuses on about 2,000 low-mass stars in the hope of finding exoplanets. MEarth uses an armada of eight small telescopes each with a diameter of 40cm, located on top of Mount Hopkins, Arizona, USA.

Artist's impression of an exoplanet transit

As a planet passes in front of its star, part of the starlight passes through the planet's atmosphere. Astronomers can tell what's in the atmosphere by analysing that light. (Artist's impression)

MEarth looks for stars that change brightness as a planet crosses in front of, or transits, its star. During such a mini-eclipse, the planet blocks a small portion of the star’s light, making it dimmer.

NASA’s Kepler space telescope also uses transits, to look for Earth-sized planets orbiting Sun-like stars.

However, Earth-sized planets transiting Sun-like stars dim the starlight by only one part in ten thousand. The higher precision required to detect the drop means that such worlds can only be found from space.

In contrast, a super-Earth such as GJ 1214b—orbiting a smaller, dimmer star—yields a greater proportional decrease in brightness and a stronger signal that is detectable from telescopes on the ground.

To confirm the planetary nature of GJ 1214b and to gauge its mass (using the so-called Doppler method), the astronomers needed the full precision of the HARPS spectrograph, attached to ESO’s 3.6-metre telescope at La Silla in Chile.

An atmosphere analysed

To study the atmosphere, the team observed the light coming from the star as the planet passed in front of it. During these “transits”, some of the starlight passes through the planet’s atmosphere and, depending on the chemical composition and weather on the planet, specific wavelengths of light are absorbed.

The following video shows an artist’s impression of the GJ 1214 system:

The team then compared these precise new measurements with what they would expect to see for several possible atmospheric compositions.

Before the new observations, astronomers had suggested three possible atmospheres for GJ 1214b.

The first was the intriguing possibility that the planet was shrouded by water, which, given the close proximity to the star, would be in the form of steam.

The second possibility was that this is a rocky world with an atmosphere consisting mostly of hydrogen, but with high clouds or hazes obscuring the view.

The third option was that this exoplanet was like a mini-Neptune, with a small rocky core and a deep hydrogen-rich atmosphere.

The new measurements do not show the telltale signs of hydrogen and hence rule out the third option. So the atmosphere is either rich in steam, or it is blanketed by clouds or hazes—similar to those seen in the atmospheres of Venus and Titan in our Solar System—which hide the signature of hydrogen.

“Although we can’t yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,” says Bean.

“Follow-up observations in longer wavelength infrared light are now needed to determine which of these atmospheres exists on GJ 1214b.”

Adapted from information issued by ESO / L. Calçada.

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Moon’s buried treasure uncovered

  • LCROSS and LRO missions crashed into lunar south pole
  • Detected water ice plus a suite of other useful chemicals
  • Could be a good place for future lunar base

Nearly a year after announcing the discovery of water molecules on the Moon, scientists Thursday revealed new data uncovered by NASA’s Lunar CRater Observation and Sensing Satellite, or LCROSS, and Lunar Reconnaissance Orbiter, or LRO.

The missions found evidence that the lunar soil within shadowy craters is rich in useful materials, and the Moon is chemically active and has a water cycle. Scientists also confirmed the water was in the form of mostly pure ice crystals in some places.

The results are featured in six papers published in the October 22 issue of Science.

“NASA has convincingly confirmed the presence of water ice and characterised its patchy distribution in permanently shadowed regions of the Moon,” said Michael Wargo, chief lunar scientist at NASA Headquarters in Washington. “This major undertaking is the one of many steps NASA has taken to better understand our Solar System, its resources, and its origin, evolution, and future.”

The twin impacts of LCROSS and a companion rocket stage in the Moon’s Cabeus crater on October 9, 2009, lifted a plume of material that might not have seen direct sunlight for billions of years.

Artist's impression of LCROSS about to impact the Moon

Artist's impression of LCROSS studying the plume of lunar soil flung up by the impact of the spent Centaur rocket booster.

As the plume travelled nearly 15 kilometres above the rim of Cabeus, instruments aboard LCROSS and LRO made observations of the crater and debris and vapour clouds. After the impacts, grains of mostly pure water ice were lofted into the sunlight in the vacuum of space.

“Seeing mostly pure water ice grains in the plume means water ice was somehow delivered to the Moon in the past, or chemical processes have been causing ice to accumulate in large quantities,” said Anthony Colaprete, LCROSS project scientist and principal investigator at NASA’s Ames Research Centre.

“Also, the diversity and abundance of certain materials called volatiles in the plume, suggest a variety of sources, like comets and asteroids, and an active water cycle within the lunar shadows.”

Volatiles are chemical compounds that freeze and are trapped in the cold lunar craters and vaporise when warmed by the Sun. The suite of LCROSS and LRO instruments determined that as much as 20 percent of the material kicked up by the LCROSS impact was volatiles, including methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide.

Silver lining

The instruments also discovered relatively large amounts of light metals such as sodium, mercury and possibly even silver. Scientists believe the water and mix of volatiles that LCROSS and LRO detected could be the remnants of a comet impact.

According to scientists, these volatile chemical by-products are also evidence of a cycle through which water ice reacts with lunar soil grains.

LRO’s Diviner instrument gathered data on water concentration and temperature measurements, and LRO’s Lunar Exploration Neutron Detector mapped the distribution of hydrogen. This combined data led the science team to conclude the water is not uniformly distributed within the shadowed cold traps, but rather is in pockets, which may also lie outside the shadowed regions.

Location of Cabeus crater

False-colour image showing the location of the impact point in Cabeus crater.

The proportion of volatiles to water in the lunar soil indicates a process called “cold grain chemistry” is taking place. Scientists also theorise this process could take as long as hundreds of thousands of years and may occur on other frigid, airless bodies, such as asteroids; the moons of Jupiter and Saturn, including Europa and Enceladus; Mars’ moons; interstellar dust grains floating around other stars and the polar regions of Mercury.

“The observations by the suite of LRO and LCROSS instruments demonstrate the Moon has a complex environment that experiences intriguing chemical processes,” said Richard Vondrak, LRO project scientist at NASA’s Goddard Space Flight Centre. “This knowledge can open doors to new areas of research and exploration.”

By understanding the processes and environments that determine where water ice will be, how water was delivered to the Moon and its active water cycle, future mission planners might be better able to determine which locations will have easily-accessible water.

The existence of mostly pure water ice could mean future human explorers won’t have to retrieve the water out of the soil in order to use it for valuable life support resources. In addition, an abundant presence of hydrogen gas, ammonia and methane could be exploited to produce fuel.

LCROSS launched with LRO aboard an Atlas V rocket from Cape Canaveral on June 18, 2009, and used the Centaur upper stage rocket to create the debris plume. The research was funded by NASA’s Exploration Systems Missions Directorate at the agency’s headquarters. LCROSS was managed by Ames and built by Northrop Grumman. LRO was built and is managed by Goddard.

Adapted from information issued by NASA.

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Was Venus once habitable?

Artist’s concept of lightning on Venus

If Venus had more water in its distant past, could it have been a habitable planet like Earth?

  • Venus might once had have more water
  • Water split by sunlight; hydrogen/oxygen escaped to space
  • If it was wetter, could it have had life?

The Venus Express spacecraft is helping planetary scientists investigate whether Venus once had oceans. If it did, it may even have begun its existence as a habitable planet similar to Earth.

These days, Earth and Venus seem completely different. Earth is a lush, clement world teeming with life, whilst Venus is hellish, its surface roasting at temperatures of a furnace.

Venus in the ultraviolet

Sunlight breaks up water molecules in Venus' clouds, letting hydrogen and oxygen atoms to escape into space.

But underneath it all the two planets share a number of striking similarities. They are nearly identical in size and now, thanks to the European Space Agency’s (ESA) Venus Express orbiter, planetary scientists are seeing other similarities too.

“The basic composition of Venus and Earth is very similar,” says Håkan Svedhem, ESA Venus Express Project Scientist.

One difference stands out—the planet has very little water. Were the contents of Earth’s oceans to be spread evenly across Venus, they would create a layer 3km deep. If you were to condense the current amount of water vapour in Venus’ atmosphere onto its surface, it would create a global puddle just 3cm deep.

Water lost into space

Yet there is another similarity here. Billions of years ago, Venus probably had much more water. Venus Express has confirmed that the planet has lost a large quantity of water into space.

This happens because ultraviolet radiation from the Sun streams into Venus’ atmosphere and breaks the water molecules into their atoms—two of hydrogen and one of oxygen. These then escape to space.

Venus Express has measured the rate of this escape and confirmed that roughly twice as much hydrogen is escaping as oxygen. It’s therefore thought that water is the source of these escaping atoms.

It has also shown that a heavy form of hydrogen, called deuterium, is enriched in the upper echelons of Venus’s atmosphere, because the heavier hydrogen finds it harder to escape the planet’s grip.

Artist's impression of the Venus Express spacecraft

The Venus Express spacecraft is helping scientists study the water history of Venus.

“Everything points to there being large amounts of water on Venus in the past,” says Colin Wilson, Oxford University, UK. But that doesn’t necessarily mean there were oceans on the planet’s surface.

No oceans, but life anyway?

Eric Chassefière, Université Paris-Sud, France, has developed a computer model that suggests the water was largely atmospheric and existed only during the very earliest times, when the surface of the planet was completely molten.

As the water molecules were broken into atoms by sunlight and escaped into space, the subsequent drop in temperature probably triggered the solidification of the surface. In other words, no oceans.

Although it is difficult to test this hypothesis, it does raise a key question. If Venus ever did possess surface water, could planet have had an early habitable period?

Even if true, Chassefière’s model does not preclude the chance that colliding comets might have brought additional water to Venus after its surface solidified, and these could have created bodies of standing water in which life may have been able to form.

Adapted from information issued by ESA / MPS / DLR / IDA / J. Whatmore.

Search for life might need rethink

Image from orbit showing an ocean-covered part of Earth.

One percent of Earth's water does not contain any life, even after 4 billion years of evolution.

  • Some Earth water is “uninhabited”
  • Spread all around the globe
  • Implications for life on Mars

NASA’s “follow the water” strategy to find life on other planets might need rethinking, according to Australian National University (ANU) research describing the amount of water on Earth that doesn’t support life.

In an effort to find the limits of terrestrial life, ANU PhD student Eriita Jones and Dr Charles Lineweaver from the ANU Planetary Science Institute have mapped out the ‘uninhabited’ water on Earth.

The researchers say that life on Earth is constrained to live in a thin shell that amounts to less than 1 per cent of the volume of the planet. Yet roughly 3.5 per cent of the volume of the Earth can have liquid water in it.

“Our initial goal was to locate regions on Mars where the temperatures and pressures are suitable for life, but we soon realized that since we know a lot more about the Earth we should look here first,” Ms Jones said.

“Our initial expectation was that we would find all liquid water on Earth to be inhabited. We were surprised to find that this wasn’t the case.”

Some water doesn’t support life

The researchers compared the extent of liquid water environments on Earth with the environments inhabited by terrestrial life in order to locate ‘uninhabited’ water.

Mars from space

NASA is "following the water" on Mars to look for life.

Although all terrestrial life requires liquid water during some phase of its life cycle, the researchers found not just any water will do. Some water is too hot or too cold or too salty or too poor in nutrients to support life.

“We compiled global temperature and pressure limits to get a comprehensive view of the environmental limits of terrestrial life,” Ms Jones said. “We mapped out all possible environments on Earth where there is water and all the environments in which life is known to exist.”

“We found that roughly 1 per cent of the water on Earth is ‘uninhabited’, but that 1 per cent is incredibly spread out in the crust and upper mantle. This means that 88 per cent of the volume of the Earth where there is some liquid water is uninhabited.”

Dr Lineweaver said: “Even after roughly four billion years of evolution, life on Earth has not been able to figure out how to live in some water on this planet.”

“The fundamental limits that we have identified may be more than just limits on terrestrial life – they may apply to any terrestrial-like life in the universe.”

The researchers’ paper To What Extent Does Terrestrial Life “Follow the Water”? is being published this week in the journal Astrobiology.

Adapted from information issued by ANU.

Earth was wet in its youth

Earth seen from space

Extreme greenhouse concentrations weren't needed to keep Earth's oceans from freezing billions of years ago.

Four billion years ago, our then stripling Sun radiated only 70 to 75 percent as much energy as it does today. Other things on Earth being equal, with so little energy reaching the planet’s surface, all water on the planet should been have frozen.

But ancient rocks hold ample evidence that the early Earth was awash in liquid water – a planetary ocean of it. So something must have compensated for the reduced solar output and kept Earth’s water wet.

To explain this apparent paradox, a popular theory holds there must have been higher concentrations of greenhouse gases in the atmosphere, most likely carbon dioxide, which would have helped retain a greater proportion of the solar energy that arrived.

But a team of scientists including researchers from Stanford have analysed the mineral content of 3.8-billion-year-old marine rocks from Greenland and concluded otherwise.

Swirls of cloud over the ocean

Swirls of cloud over the ocean

“There is no geologic evidence in these rocks for really high concentrations of a greenhouse gas like carbon dioxide,” said Dennis Bird, professor of geological and environmental sciences.

Instead, the team proposes that the vast global ocean of early Earth absorbed a greater percentage of the incoming solar energy than today’s oceans, enough to ward off a frozen planet.

Earth was a water world

Because the first landmasses that formed on Earth were small – mere islands in the planetary sea – a far greater proportion of the surface was covered with water than today.

The crux of the theory is that because oceans are darker than continents, particularly before plants and soils covered landmasses, seas absorb more sunlight.

“It’s the same phenomenon you will experience if you drive to Wal-Mart on a hot day and step out of your car onto the asphalt,” Bird said. “It’s really hot walking across the blacktop until you get onto the white concrete sidewalk.”

Another key component of the theory is in the clouds. “Not all clouds are the same,” Bird said.

Clouds reflect sunlight back into space to a degree, cooling Earth, but how effective they are depends on the number of tiny particles available to serve as nuclei around which the water droplets can condense. An abundance of nuclei means more droplets of a smaller size, which makes for a denser cloud and a greater reflectivity, or albedo, on the part of the cloud.

The edge of Earth's atmosphere

The edge of Earth's atmosphere

Most nuclei today are generated by plants or algae and promote the formation of numerous small droplets. But plants and algae didn’t flourish until much later in Earth’s history, so their contribution of potential nuclei to the early atmosphere circa 4 billion years ago would have been minimal. The few nuclei that might have been available would likely have come from erosion of rock on the small, rare landmasses of the day and would have caused larger droplets that were essentially transparent to the solar energy that came in to Earth, according to Bird.

“We put together some models that demonstrate, with the slow continental growth and with a limited amount of clouds, you could keep water above freezing throughout geologic history,” Bird said.

Adapted from information issued by Stanford University.