 |
Mercury Venus The Moon Mars - Searching for Life on Mars -The Life Test Experiments - Searching for Life on Mars - The Martian Meteorites - Possible Habitats for Life on Mars - History of Mars Exploration - Is there Life on Mars? Jupiter Io Europa Ganymede Callisto Saturn Titan Uranus Neptune Triton Pluto The Other Outer Moons and Asteroids Comets Planets in Distant Star Systems Life in Deep Space |
This question has interested people for millennia. Now though, while we cannot confirm the presence of life on other planets in the Solar System, we do have a good idea of which places in the Solar System could support life and what that life may be like if it is there. Another question you may be asking is why are some places potential habitats for life while others are not? Let us take a journey through the Solar System and try and answer those questions by looking at all the major planets and moons. One thing is certain no advanced life or intelligent life, such as ourselves, exists off Earth in the Solar System. Current knowledge suggests that extraterrestrial Solar System life would most likely be microbial and single-celled in nature - similar to bacteria, nano-bacteria or archaea. They will almost certainly be some sort of extremophile. Off all the places in the Solar System that may support life, Mars and Jupiter's moon Europa may eventually confirm without doubt, that life exists or used to exist elsewhere than planet Earth. While Mars may reveal the expected microbes, Europa holds the exciting possibility that more developed life forms may exist there... But these two bodies are not the only targets we should be looking for life in the Solar System. Other places, such as Saturn's moon Titan, may be able to tell us about the chemistry of life, even if living organisms do not exist there. Callisto, another of Jupiter's moons, has recently been surveyed by theGalileo spacecraft. It too may hide secrets that life scientists will be interested to investigate further. |
Friday, 18 November 2011
IS THERE LIFE IN SOLAR SYSTEM
JUPITER'S MOON GIVES A HOPE OF ALIEN LIFE
Scientists have reported a large mass of water under the icy surface of Europa.
A BODY of water as big as North America's Great Lakes could lie beneath Europa, a shining enigmatic moon of Jupiter, astronomers have reported.
The theory is exciting because water is one of the key ingredients for life. Europa is the second-closest satellite of Jupiter, the biggest planet of the solar system.
Pictures of it sent back by the Galileo spacecraft during its 1995-2003 exploration point to a tortured surface of cracks and jumbled ice.
Seeking to understand how such weird topography evolved in a place with such dim sunlight, scientists believe that the answer lies in similar processes on Earth.
Beneath floating ice shelves and under glaciers that overlay volcanoes, interaction between ice and plumes of warm water gives rise to a phenomenon called chaos terrain, they say.
Their model suggests Europa's ice shell is about 10km thick and within it are giant pockets of water, lying at depths as shallow as 3km. Warm water from these sub-surface lakes well up in plumes, causing the ice to collapse. The ice turnover would be a plus for the prospects for life, as it would transfer energy and nutrients between the sub-glacial lake and the surface.
"One opinion in the scientific community has been, 'If the ice shell is thick, that's bad for biology - it might mean the surface isn't communicating with the underlying ocean'," said Britney Schmidt, a geophysicist at the University of Texas at Austin, who led the study.
"Now we see evidence that even though the ice shell is thick, it can mix vigorously.
"That could make Europa and its ocean more habitable."
The study, published in the British journal Nature, adds to a file of knowledge about ice moons of giant gassy planets.
LIFE EXIST ON EUROPA
Europa, Jupiter's icy moon, meets not one but two of the critical requirements for life, scientists say.
For decades, experts have known about the moon's vast underground ocean — a possible home for living organisms — and now a study shows that the ocean regularly receives influxes of the energy required for life via chaotic processes near the moon's surface.
Scientists discussed the implications of the new study, which appeared online Wednesday (Nov. 16) in the journal Nature, at an afternoon press briefing at NASA headquarters in Washington.
Lead author Britney Schmidt, a geophysicist at the University of Texas at Austin, explained that her team studied ice shelves and underground volcanoes on Earth in order to model the formation of odd features called "chaos terrains" that appear all over Europa. The researchers determined that it was heat rising from the moon's deep subterranean ocean and melting ice near the surface, creating briny lakes inside the moon's thick ice shell, that may have caused the collapse of these roughly circular structures above them.
These dynamic lakes, which melt and refreeze over the course of hundreds of thousands or millions of years, lie beneath as much as 50 percent of Europa's surface, the scientists said. [Jupiter Moon's Buried Lakes Evoke Antarctica]
Astrobiologist Tori Hoehler, a senior research scientist at NASA's Ames Research Center in Moffett Field, Calif., who was not involved in the new study, provided an outside perspective on its implications for life.
Europa's liquid water ocean "meets one of the critical requirements for life," Hoehler said, noting that its ocean chemistry is believed to be suitable for sustaining living things. "And what you're hearing about today from Britney bears on a second crucial requirement, and that is the requirement for energy."
The genesis of life on Earth is thought to have required some sort of injection of energy into the ocean — perhaps from a lightning strike. And during the 3.8 billion years since then, life's existence has depended on the continuous influx of energy from the sun.
Cut off from the sun, Europa's subterranean ocean would need some other energy source to sustain life. Hoehler said spacecraft observations show that there is a huge amount of stored energy in Europa's mineral-rich crust, but it is separated from the liquid ocean below by at least 6 miles (10 km) of ice. Like the two terminals of a battery, energy can flow from the surface material to the ocean only if the two are somehow connected, he said.
"What you're hearing about here today would be a way to take this surface material, transport it potentially down into the ocean and in essence tap Europa's battery. When you tap that battery, you move from a system which checks one of the requirements for life to a system that checks a second critical requirement for life, and I think this really impacts the way we consider habitability on Europa."
Europan life isn't a done deal just yet, though. Water and energy aren't the only ingredients on the checklist for life, and scientists aren't sure whether Europa has the others, such as the necessary organic chemicals.
Louise Prockter, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., said Europa's chaos regions "are going to be extremely important and possible future targets of exploration."
Aliens don't need a moon like ours
TALK about being over the moon. It seems planets don't need a big satellite like Earth's in order to support life, increasing the number on which life could exist.
In 1993, Jacques Laskar of the Paris Observatory in France and colleagues showed that the moon helps stabilise the tilt of Earth's rotation axis against perturbations by Jupiter's gravity. The researchers calculated that without the moon, Jupiter's influence would make the current tilt of some 23 degrees wander chaotically between 0 and 85 degrees. That could cause huge climate swings, making it hard for life to survive, especially large, land-based organisms like us.
The result was taken by many to imply that complex life is rare in the universe, since Earth's large moon is thought to have coalesced from the debris of a freak collision between a Mars-sized planet and Earth. Less than 10 per cent of Earth-sized planets are expected to experience such a trauma, making large moons a rarity.
But a study now suggests moonless planets have been dismissed unfairly. "There could be a lot more habitable worlds out there," says Jack Lissauer of NASA's Ames Research Center in Moffett Field, California, who led the research.
The 1993 study showed that the Earth would tilt wildly without the moon because two of its motions would end up in sync, allowing Jupiter to have an outsize influence. The Earth orbits the sun on an elliptical path, and the long axis of this path shifts position over time. The Earth also wobbles like a spinning top as it rotates. Without the moon's gravitational tugs, the rate of this wobbling would be slower, matching up in just the right way with the drifting of its elliptical orbit to magnify Jupiter's effects on Earth's spin axis, leading to big changes in tilt.
However, Laskar's study did not determine how fast these changes in tilt would occur. "The astrobiology community has taken it to mean there will be these really wild variations, and we wanted to test that," says Lissauer. He and his colleagues simulated a moonless Earth over 4 billion years, about the age of the Earth today. They found that our planet's tilt varied between only 10 and 50 degrees, a much smaller range than implied by the earlier study. There were also long stretches of up to 500 million years when the tilt was particularly stable, keeping between 17 and 32 degrees (Icarus, DOI: 10.1016/j.icarus.2011.10.013).
Much larger changes might still occur on timescales longer than 4 billion years, the team admits. But in that case they might be irrelevant for life anyway, they say, because sun-like stars burn out after 10 billion years.
Large moons are not required for a stable tilt and climate, agrees Darren Williams of Pennsylvania State University in Erie. In some circumstances, he adds, large moons can even be detrimental, depending on the arrangement of planets in a given system. "Every system is going to be different."
Jason Barnes of the University of Idaho in Moscow, who co-authored the latest study, is now leading simulations to look at how planet tilts behave in a wider variety of circumstances, including planets arranged in different ways to our solar system.
Why cold, dead moon stayed magnetic
HOW did the moon remain magnetic tens of millions of years after its molten core stopped sloshing?
Early in its life, the moon probably had a core hot enough to churn violently, with the movement of this electrically charged fluid creating a magnetic field. But as the core cooled, the convection should have eased enough to kill the field. So it was a puzzle when Apollo moon rocks suggested the moon still had a magnetic field 4.2 billion years ago, millions of years after the powerful mixing ended. Now two groups have come up with explanations for what could have kept the core stirred up.
The moon is thought to have formed closer to the Earth than it is now and spun faster, slowing down and moving away over time throughtidal interactions with Earth. Christina Dwyer at the University of California, Santa Cruz, and colleagues say previous models did not take into account this faster spin, which would have agitated the molten core like water in a washing machine. This could have enabled the magnetic field to last until 2.7 billion years ago (Nature,DOI: 10.1038/nature10564).
Michael Le Bars at the Non-Equilibrium Phenomena Research Institute in Marseille, France, says large meteorite impacts that occurred until about 3.9 billion years ago also could have set the lunar core sloshing for periods of 10,000 years at a time (Nature,DOI: 10.1038/nature10565).
The models might also explain how some asteroids came to be magnetised, says Ben Weiss at the Massachusetts Institute of Technology.
Strange domes on Europa formed on thin ice
Jupiter's icy moon Europa is pockmarked by curious domes and depressions. How they formed has been a mystery, but now it seems they are areas where liquid water once appeared close to the surface.
Europa is thought to harbour a saltwater ocean, sandwiched between a 20-kilometre-thick layer of surface ice and a rocky core below. For clues as to what might be happening there, Britney Schmidt of the University of Texas, Austin, and colleagues looked at studies of subglacial volcanoes and ice shelves on Earth. They concluded that ice rising from the bottom of Europa's surface layer created its 300-metre-high "chaos terrains".
As Europa orbits Jupiter, it flexes as a result of slight variations in the gravitational tug of the giant planet. The energy that goes into this bending is converted into heat that warms the bottom of the surface ice, pushing plumes of it upwards. This changes the pressure in the ice above, creating pockets of liquid water. The water breaks up the overlying ice and refreezes over tens of thousands of years, creating jumbled domes.
A large dark spot on Europa called Thera Macula (shown right) could result from warm ice rising beneath it, says Schmidt. "We are probably witnessing active chaos formation."
Could this liquid water close to the surface support life? Not unless it was already in the icy crust, says team member Paul Schenk of the Lunar and Planetary Institute in Houston, Texas. "Because these water pockets are short-lived – [it takes] 10,000 to 100,000 years before they refreeze – it seems doubtful anything could grow unless it were already embedded within the ice," he says.
But if there is any life in Europa's oceans, the process might bring it up into the icy crust, making the domes intriguing targets for future landers, he says.
Journal reference: Nature, DOI: 10.1038/nature10608
Third wheel' stars get cast out at high speeds
Love triangles are rarely sustainable – even in space. New simulations show that single stars that try to come between a tight stellar pair are kicked into space at breakneck speeds, explaining the origin of "runaway" stars that have puzzled astronomers for half a century.
Most stars in the Milky Way plod around the galaxy at a relatively sedate pace of 5 kilometres per second. But some rocket along at more than 30 kilometres per second, faster than the Earth orbits the sun.
In 1961, Adriaan Blaauw of Leiden University in the Netherlands suggested that the runaways were shoved to punishing speeds when a companion star exploded as a supernova, a picture that was bolstered by the discovery of just such a pair in 1997.
But last year, two high-speed stars were spotted fleeing a cluster of stars called R136, a dense group of infant stars thought to be less than 2 million years old.
"That was odd," says Simon Portegies Zwart of Leiden University. Because such stars don't explode until they're at least 3 million years old, the exiles from R136 could not have been kicked out by detonating partners.
Portegies Zwart had another idea: instead of having just one violent companion, the runaways were the unfortunate victims of a love triangle.
Tighter pair
Massive stars in clusters sometimes come close enough to a pair of stars to be caught in their orbit. But the trio is gravitationally unstable – someone has to go. The intruder typically doesn't have enough energy to unbind the binary, so it's the one to get the boot. The energy it receives in the process only ties the couple together more tightly.
To test this idea, Michiko Fujii, also at Leiden, and Portegies Zwart ran about 60 simulations of star clusters. They found that each cluster developed a binary "bully" that ejected about 21 stars from the cluster before leaving the cluster itself.
That can easily account for most of the runaway stars observed in the Milky Way. "Right now I would say the majority, maybe even the vast majority, of runaways are produced by dynamical ejection," Portegies Zwart says.
New results show neutrinos still faster than light
One of the most staggering results in physics – that neutrinos may go faster than light – has not gone away with two further weeks of observations. The researchers behind the jaw-dropping finding are now confident enough in the result that they are submitting it to a peer-reviewed journal.
"The measurement seems robust," says Luca Stanco of the National Institute of Nuclear Physics in Padua, Italy. "We have received many criticisms, and most of them have been washed out."
Stanco is a member of the OPERA collaboration, which shocked the world in September with the announcement that the ghostly subatomic particles had arrived at the Gran Sasso mine in Italy about 60 nanoseconds faster than light speed from the CERN particle accelerator near Geneva, Switzerland, 730 kilometres away.
Tighter bunches
Theorists have been struggling to reconcile the September result with the laws of physics. Einstein's theory of special relativity posits that nothing can travel faster than light, and many physicists believe the result could disappear in a puff of particles.
The result also unsettled those within the OPERA collaboration. Stanco was one of 15 team members who did not sign the original preprint of the paperbecause they thought the results were too preliminary.
One of the main concerns was that it was difficult to link individual neutrino hits at Gran Sasso to the particles that left CERN. To double check, the team ran a second set of measurements with tighter bunches of particles from 21 October to 6 November.
In that time, they observed 20 new neutrino hits – a piddling number compared with the 16,000 hits in the original experiment. But Stanco says the tighter particle bunches made those hits easier to track and time: "So they are very powerful, these 20 events."
More checks
The team also rechecked their statistical analysis, confirming that the error on their measurements was indeed 10 nanoseconds. Some team members, including Stanco, had worried that the true error was larger. What they found was "absolutely compatible" with the original announcement, he says.
That was enough for Stanco to put his name to the paper, although he says six or seven team members are still holding out. The team was planning to submit the paper to a European physics journal on Thursday.
They are still running other tests, including measuring the length of a fibre-optic cable that carries information from the underground lab at Gran Sasso to a data-collection centre on the surface. The team is also trying to do the same test using another detector at the lab called RPC. That test will take another several months.
Even though he agreed to sign the paper, Stanco says: "I'm not so happy. From a theoretical point of view, it is not so appealing. I still feel that another experiment should make the measurement before I will say that I believe this result."
Astrophile: Supercritical water world does somersaults
Astrophile is our weekly column covering curious cosmic objects, from within the solar system to the furthest reaches of the multiverse
Object type: Extrasolar planet
Composition by mass: 70 per cent rock, 30 per cent supercritical water
Orbital angle: Constantly changing
Composition by mass: 70 per cent rock, 30 per cent supercritical water
Orbital angle: Constantly changing
Imagine that you are floating thousands of kilometres below the surface of a vast ocean that is neither liquid nor gas, but somewhere in between. Above you, the constellations very slowly shift and change as your watery world and its host star turn somersaults in space.
That's what you would see if you could swim on the planet 55 Cancri e, the most watery world discovered to date. New observations suggest that the planet is probably covered in so-called supercritical water
, a kind of water that blurs the line between liquid and gas.
, a kind of water that blurs the line between liquid and gas.Not only that, but as the planet and its four planetary siblings orbit their host star, the whole system rotates in space due to tugs from a partner star, as if Saturn and its rings were turning on a spit.
Planet in hot water
55 Cancri, a sun-like star 41 light years from Earth in the constellation Cancer, is one of only a handful of stars that hosts five planets or more. Its innermost planet, 55 Cancri e, was detected in 2004, given away by the wobbles it induced in its host star.
Those first observations suggested the planet orbited the star once every 2.8 days. But last year, a pair of astronomers realised that gaps in the observations had skewed the statistics. The planet's year was actually only17 hours, 41 minutes long, meaning the planet's distance from its host star is 1/20th that of Mercury from the sun.
At that distance, the temperature at the planet's surface is a scorching 2700 °C. But to astronomers' delight, the short year also means they can watch the planet cross in front of its star, or transit, in less than one Earth day. That makes 55 Cancri e the first known planet to transit in front of a naked-eye star.
Wettest world
More importantly, watching a transit lets astronomers determine the planet's size, giving a clue to its density and composition.
This spring, two independent groups using the space telescopes MOST(Microvariability and Oscillations of Stars) and Spitzer did just that.
Diana Valencia of the Massachusetts Institute of Technology and colleagues have now combined the results, finding that the planet is 2.17 times as wide as Earth. Combined with its mass of 8.57 Earths, that size suggests the planet has a dense rocky core, surrounded by a 3000-kilometre-thick envelope of nearly pure water.
The team calculates that it is probably 30 per cent water by mass, making 55 Cancri e the most watery world yet discovered. "It's really the most water-dominated planet, by mass," Valencia says.
It also places 55 Cancri e in a totally new class of planets, right in the middle of two previously known types. Other planets with similar masses, known as super-Earths, are thought to be either smaller and rockier, or bigger and puffier, like miniature Neptunes.
"We have two families, and 55 Cancri e is kind of in between," Valencia says. "It is the first one that is right at the edge."
Slick fluid
Because of the extreme temperatures and pressures, the water is probably in the supercritical phase, where gas and liquid are indistinguishable. As easily as the water we are familiar with flows, it is still 10 times as viscous as supercritical water. Other materials can dissolve in supercritical water, so in theory 55 Cancri e's oceans could be salty.
The density of the supercritical water would vary from the rocky core to the edge of space, with no clear boundary between sea and sky. At a certain distance from the centre there would be a level where humans would be buoyant, Valencia says. Assuming we could breathe and withstand the temperatures, we would float.
The star also has a small companion, a red dwarf star that lies about 1000 times as far away as Earth's distance from the sun. This red dwarf pulls on the 55 Cancri system, and because all five planets in the system – and their host star – are such a tight-knit family, they behave like ice skaters holding hands, so that the companion star's tugs cause them all to do somersaults in space.
"The crazy thing is, over the course of hundreds of millions of years, your orientation relative to the other stars in the galaxy would totally change," saysNathan Kaib of Queen's University in Kingston, Ontario, who led the research team that found the head-over-heels motion. "You'd get flipped upside-down, but it's a very subtle effect. The only thing you're going to notice is that your view of the night sky gets flipped on its head."
That might be bad news for any seafaring creatures living in 55 Cancri e's supercritical oceans and using the stars to navigate. "You couldn't use them reliably for any trips that took millions of years," Kaib jokes.
Reference: arxiv.org/abs/1110.4783; arxiv.org/abs/1110.5911, to be published in a forthcoming issue of The Astrophysical Journal Letters
Subscribe to:
Posts (Atom)