Searching for Habitable Planets

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Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Fri Aug 27, 2010 2:31 pm


Someday it might be said that this was the beginning of the end of cosmic loneliness.

Presently perched on a Delta 2 rocket at Cape Canaveral is a one-ton spacecraft called Kepler. If all goes well, the rocket will lift off about 10:50 Friday evening on a journey that will eventually propel Kepler into orbit around the Sun. There the spacecraft’s mission will be to discover Earth-like planets in Earth-like places — that is to say, in the not-too-cold, not-too-hot, Goldilocks zones around stars where liquid water can exist.

The job, in short, is to find places where life as we know it is possible.

“It’s not E.T., but it’s E.T.’s home,” said William Borucki, an astronomer at NASA’s Ames Research Center at Moffett Field in California, who is the lead scientist on the project. Kepler, named after the German astronomer who in 1609 published laws of planetary motion that now bear his name, will look for tiny variations in starlight caused by planets passing in front of their stars. Dr. Borucki and his colleagues say that Kepler could find dozens of such planets — if they exist. The point is not to find any particular planet — hold off on the covered-wagon spaceships — but to find out just how rare planets like Earth are in the cosmos.

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Fri Aug 27, 2010 2:34 pm


Troy Cryder/NASA
COSMOS CENSUS TAKER The Kepler spacecraft is coated with solar panels

Jon Morse, director for astrophysics at NASA headquarters, calls Kepler the first planetary census taker.

Kepler’s strategy is, in effect, to search for the shadows of planets. The core of the spacecraft, which carries a 55-inch-diameter telescope, is a 95-million-pixel digital camera. For three and a half years, the telescope will stare at the same patch of sky about 10 degrees, or 20 full moons, wide, in the constellations Cygnus and Lyra. It will read out the brightnesses of 100,000 stars every half-hour, looking for the telltale blips when a planet crosses in front of its star, a phenomenon known as a transit.

To detect something as small as the Earth, the measurements need to be done with a precision available only in space, away from the atmospheric turbulence that makes stars twinkle, and far from Earth so that our home world does not intrude on the view of shadow worlds in that patch of sky. It will take three or more years — until the end of Barack Obama’s current term in office — before astronomers know whether Kepler has found any distant Earths.

If Kepler finds the planets, Dr. Borucki explained, life could be common in the universe. The results will point the way for future missions aimed at getting pictures of what Carl Sagan, the late Cornell astronomer and science popularizer, called “pale blue dots” out in the universe, and the search for life and perhaps intelligence.

But the results will be profound either way. If Kepler doesn’t come through, that means Earth is really rare and we might be the only extant life in the universe and our loneliness is just beginning. “It would mean there might not be ‘Star Trek,’ ” Dr. Borucki said during a recent news conference.

The need, indeed even the possibility, of a planetary census is a recent development in cosmic history. It was only in 1995 that the first planet was detected orbiting another Sun-like star, by Michel Mayor and his colleagues at Geneva Observatory. In the years since then there has been a torrent of discoveries, 340 and counting, that has bewildered astronomers and captured the popular imagination.

“What exists is an incredibly random, chaotic, wild range of planets,” said Debra Fischer of San Francisco State University, also a veteran planet hunter who is not a member of the Kepler team. So far none of them qualify as prime real estate for life, and few of them reside in systems that resemble our own solar system. Many of the first planets discovered were so-called hot Jupiters, gas giants zipping around their stars in a few days in tight, blisteringly hot orbits.

Most of the planets have been found by what is called the wobble method, in which the presence of a planet is deduced by observing the to-and-fro gravitational tug it gives its star as it orbits. The closer a planet is to its star, the bigger the tug and the easier it is to detect.

The smallest exoplanet discovered is about three times as massive as the Earth. It is known as MOA-2007-BLG-192-L b, but astronomers don’t know yet whether its home star is real star or a failed star called a brown dwarf.

Last summer Dr. Mayor announced that his team had found three so-called warm super-Earths — roughly four, seven and nine times the mass of the Earth — orbiting within frying distance of a star known as HD 40307 in the constellation Pictor. Indeed, Dr. Mayor proclaimed that according to their data, about a third of all Sun-like stars host such super-Earths or super-Neptunes in tight orbits.

But all this is prelude. Astronomers agree that these planets are oddballs according to any reasonable theory of planet formation. But as Alan Boss of the Carnegie Institution of Washington pointed out, they are easy to detect by the wobble method. The fact that they are there suggests that there are many more modest-size planets to be found in larger, more habitable orbits.

The Kepler mission is a tribute to the perseverance of Dr. Borucki, who began proposing it to NASA in the 1980s, before any exoplanets had been discovered, and kept campaigning for it. “He had the true faith,” Dr. Boss said.

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Fri Aug 27, 2010 2:36 pm

Many technical hurdles had be overcome before Kepler became practical. In particular it required very accurate and sensitive digital detectors, said James Fanson, of the Jet Propulsion Laboratory, Kepler’s project manager. As seen from outside the solar system, the Earth blocks only about 0.008 percent of the Sun’s light when it passes in front, or “transits.” Kepler has been built to detect changes in brightness as small as 0.002 percent, equivalent to a flea crawling across a car headlight.

By measuring the diminution of a star’s light during an exoplanet transit, astronomers in principle will be able to determine the size of the exoplanet. From the intervals between eclipses, astronomers will be able to determine its orbit.. By combining this with other data, from, say, wobble measurements, they will be able to zero in on important properties like mass and density.

However, natural variations in the star’s output, caused by something like starspots, could interfere with the data and obscure the signals from small planets. That is a problem, Dr. Fanson said, with the Corot satellite, which was launched by the European Space Agency at the end of 2006 and also carries a telescope and camera to look for small changes in starlight. To weed out the noisy stars, Kepler will keep track of 170,000 stars for the first year and then narrow its attention to a mere 100,000.

Corot, which stands for convection, rotation and planetary transits, is smaller than Kepler and is designed to investigate the structure of stars by detecting vibrations and tremors within them that cause them to periodically brighten and fade. Corot, which Dr. Borucki called “a complementary mission,” also looks at a given patch of stars for only a few months and so would miss the successive transits of an Earth-like planet, which, to be habitable, would have to take about a year to orbit a Sun-like star.

Not all 100,000 stars in the field of Kepler’s view would have their planetary systems oriented to provide eclipses from our particular point of view, of course. Dr. Borucki and his colleagues estimate that for an Earth-like star in its habitable zone, the stars would align to produce a blot out in half of 1 percent of cases, yielding a few dozen to a few hundred new Earths out there. For planets that are closer in, however, the odds rise to about 10 percent, so there are ample reasons to expect a bumper crop of new planets.

Dr. Borucki said the astronomers had set the goal of observing at least three such transits, to confirm the period and rule out interference from starspots, and then obtaining backup observations from other telescopes — of wobble measurements, say — before announcing they have found a planet.

“When we make a discovery we want it to be bulletproof,” Dr. Borucki said.

That means that the first planets to be discovered and announced will be the biggest planets with the shortest orbits, the so-called hot Jupiters. Four stars with such planets are in the search area and thus will be an early test of Kepler’s acuity.

“In the first six months, hot Jupiters are going to roll off the Kepler assembly line,” Dr. Fischer said, adding, “These are bizarre planets, we don’t understand how they form.”

The hardest and most exciting part of the mission, detecting bona fide Earths, will also take the longest. Such a planet should take about a year to circle a Sun-like star, producing only one blip a year in its starlight. So it would take more than three years to produce the requisite three blips and subsequent confirmation by ground-based telescopes before the epochal discovery is announced.

Dr. Borucki said, “We’re not going to be able to tell you very quickly.”

But they will eventually tell us.

Dr. Boss, a high-ranking member of the Kepler science team, said: “It really is going to count many Earths. About four years from now we will have a really good estimate of how many Earths there are.”

If the history of exoplanet astronomy is any guide, there are likely to be surprises that geologists had not imagined — water worlds, for example. And then, if all keeps going well, it will be time to confront the next series of questions: whether anywhere else in this galaxy the dust that once spewed from stars has come alive and conscious.

“In my 25 years of working with NASA this is the most exciting mission I’ve worked on, said Dr. Fanson, who will step down as project manager after the launching. “We are going to be able to answer for the first time a question that has been pondered since the time of the ancient Greeks. Are there other worlds like ours? The question has come down to us from 100 generations. We get to answer it. I find that tremendously exciting.”

When a reporter departed from journalistic objectivity to venture a hope that other Earths are out there, Dr. Fanson happily joined in. “I hope the answer is yes,” he said. “I hope the universe is teeming with planets like Earth.”

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Fri Aug 27, 2010 2:41 pm

Kepler is designed to measure tiny brightness variations in stars that might indicate orbiting planets. NASA hopes to find Earth-like planets orbiting stars at a distance that would permit liquid water, potentially allowing them to support life. Kepler will be placed in an orbit around the Sun, surveying more than 100,000 stars for three years.


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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Fri Aug 27, 2010 2:54 pm


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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Fri Aug 27, 2010 2:55 pm


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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Tue Oct 05, 2010 1:57 am

วันที่ 05 ตุลาคม พ.ศ. 2553 ปีที่ 20 ฉบับที่ 7250 ข่าวสดรายวัน

ค้นพบดาวเคราะห์คล้ายโลกดวงใหม่ มีแรงดึงดูด-เย็นลบ12องศา



ภายหลังมีศาสตราจารย์นักคณิต ศาสตร์เคยออกมาพยากรณ์ว่า มนุษยชาติอาจได้ฟังข่าวดีเกี่ยวกับการค้นพบ "โลกใบใหม่" ที่มีสภาพคล้ายโลกภายในปี 2554 ดูเหมือนว่า ผลลัพธ์การค้นพบจะสอดคล้องไปในทางเดียวกับคำพยากรณ์

ล่าสุด นักดาราศาสตร์จากหอดูดาวดับเบิลยู. เอ็ม. เค็ก บนเกาะฮาวายของสหรัฐ เปิดเผยการค้นพบดาวเคราะห์ที่มีสภาพพื้นผิวดิน และบรรยากาศคล้ายโลก อยู่ห่างไปราว 190 ล้านล้านกิโลเมตร หรือราว 20 ปีแสง โคจรรอบดาวฤกษ์สีแดง ชื่อ "กลีส 581" ในระบบดาวฤกษ์กลีส กลางหมู่ดาวสิงโต หนึ่งในสมาชิกกาแล็กซีทางช้างเผือก ซึ่งระบบสุริยะของโลกเป็นสมาชิกอยู่เช่นกัน

ดาวเคราะห์ดังกล่าวถูกตั้งชื่อว่า "กลีส 581 จี" มีแรงดึง ดูดทำให้มนุษย์สามารถเดินบนผิวดาวได้เหมือนกับเดินเหินบนพื้นโลก และมีอุณหภูมิติดลบราว 12 องศาเซลเซียส ซึ่งมนุษย์สามารถมีชีวิตอยู่ได้ อย่างไรก็ตาม ยังไม่มีหลักฐานพิสูจน์ว่า มีน้ำอยู่บนดาวเคราะห์กลีส 581 จี หรือไม่

ดาวกลีส 581 จี ใช้เวลาแค่ 37 วันในการโคจรรอบดาวฤกษ์ ส่งผลให้ฤดูกาลเปลี่ยนแปลงรวดเร็ว ทั้งดาวเคราะหŒยังไม่หมุนรอบตัวเอง ทำให้มีด้านสว่างที่หันหน้าเข้าหาดาวฤกษ์กลีส 581 และด้านมืดก็มืดอยู่ตลอดเวลา โดยนักวิทยาศาสตร์คาดว่า พื้นที่ที่เหมาะสมที่สุดสำหรับมนุษย์หากจะไปตั้งรกรากบนดาวเคราะห์ดวงนี้น่าจะเป็นพื้นที่กึ่งกลางระหว่างด้านสว่างและมืด เรียกว่า "พื้นที่สีเทา" (เกรย์โซน)

ดร.สตีเว่น วอกต์ ผู้นำโครงการค้นหาดาวคล้ายโลก ระบุว่า การค้นพบนี้ใช้เวลาสำรวจนาน 11 ปี และดาวเคราะห์ที่ค้นพบมีสภาพคล้ายโลกมากที่สุดเท่าที่เคยมีการค้นพบมา มิหนำซ้ำยังอยู่ใกล้มากด้วย ตนสันนิษฐานว่า ดาวเคราะห์ที่มีสภาพแบบโลกนั้นไม่น่าจัดเป็นลักษณะหายากในจักรวาล เพราะถ้าหายากจริงคงไม่เจอบ่อยขึ้นเรื่อยๆ เช่นนี้

หน้า 28

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Tue Oct 19, 2010 10:57 pm

Almost 500 alien planets, and counting

By the end of this month, astronomers expect to have found 500 planets beyond our solar system. The current count is 494, including one that may be inhabitable by humans.



Cosmic Ambassador? Mazlan Othman, head of the UN's Office for Outer Space Affairs,
in a speech on Oct. 5, asks: Who should represent humanity if aliens do come to this planet?

Less than 20 years after first finding a planet beyond our solar system, astronomers are poised to hit a big milestone — the discovery of alien world No. 500.

As of Tuesday, the confirmed tally stands at 494 extrasolar planets, with more than 70 discovered so far in 2010 alone. At that rate, No. 500 could be announced before October is out — just a month or so after another watershed moment, the discovery of the first potentially habitable alien planet.

"Where we are, I'd expect that by the end of October, we'll be at 500 if things keep going the way they're going," said Jon Jenkins of the SETI (Search for Extraterrestrial Intelligence) Institute. Jenkins is the analysis lead for NASA's planet-hunting Kepler mission.

And the 1,000th world could be discovered surprisingly soon, as the space-based Kepler mission has already offered up hundreds of planet candidates that await further observation and confirmation.

Alien worlds piling up

Most of these extrasolar planets, or exoplanets, have been found using two different strategies.

Astronomers can scrutinize the movements of faraway stars, watching for the telltale gravitational tug of orbiting planets. Or they look for tiny dips in a star's brightness — evidence that a planet is transiting, or passing in front of, the star from our perspective.

Astronomers first definitively found an alien world in 1992, when researchers led by Alex Wolszczan of Penn State detected two planets orbiting a rotating neutron star, or pulsar, about 1,000 light-years from Earth. Confirmation of a planet circling a "normal" main-sequence star did not come until 1995.

Since then, however, the alien planet finds have been rolling in, accelerating in recent years as planet hunters honed their techniques and instruments became more powerful. [Gallery: Strangest Alien Planets]

That trend will likely continue, Jenkins said, as data keeps pouring in from Kepler — which was launched in March 2009 to search for Earth-like alien planets — and other telescopes.

The Kepler mission, for example, has confirmed and announced seven new alien worlds to date. But Kepler, which hunts by looking for transiting planets, has already identified more than 700 "candidates" — stars that may harbor alien planets.

Researchers are following up on these promising leads, trying to rule out any false alarms. They're checking out the candidates with ground-based instruments as well as orbiting assets like the Hubble Space Telescope and the Spitzer Space Telescope.

When such work is done, the number of known alien worlds could increase by several hundred — and it could happen soon.

"One could reasonably expect many of these to be vetted within the next year or so," Jenkins told SPACE.com.

The number of confirmed exoplanets could rise even more dramatically if some of the candidates host multiple planets.

Recent discoveries suggest this is not an unreasonable expectation. Five planets are known to orbit the star HD 10180, for example, and at least six — including the potentially habitable planet Gliese 581g — circle the star Gliese 581 just over 20 light-years from Earth.

"We have a sense now that our solar system isn't such a weirdo," Jenkins said. "It may be that multi-planet systems are quite common."

Reaching other milestones

Other important milestones could follow closely on the heels of exoplanet 500, not all of them numerical. One big moment that should happen relatively soon, Jenkins said, is the discovery of a potentially habitable alien world that's transiting its star, a setup that would allow for more detailed observations.

The rocky, roughly Earth-sized Gliese 581g apparently does not transit its star as seen from our point of view, and as a result astronomers will have trouble searching for signs of life on that alien world, at least for a while.

When a planet transits its parent star, starlight passes through its atmosphere (if the planet has one). Astronomers can scrutinize this light for compelling evidence of life in the planet's air, such as significant quantities of both methane and oxygen. As one example, a gas giant planet called HD 209458b has been found to contain oxygen, carbon and water.

So the discovery of a transiting Earth-like world in its parent star's habitable zone — that range of distances that supports the existence of liquid water — would occasion some celebration in planet-hunting circles, as well as a frenzy of follow-up research. And it could be just around the corner.

"I wouldn't be surprised if that happened next year," Jenkins said.

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Tue Oct 19, 2010 11:09 pm

Gliese 581g, a new planet like Earth: Could humans live there?

Gliese 581g would be the first Earth-like planet found orbiting in a star's habitable zone. The new plant is located in a region where temperatures could sustain life and liquid water on its surface.



Astronomers have found a planet that is in the Goldilocks zone – just right for life.
Not too hot, not too cold. And it's relatively close - about 120 trillion miles away.
Artist rendering by Lynette Cook.

An Earth-size planet has been spotted orbiting a nearby star at a distance that would make it not too hot and not too cold — comfortable enough for life to exist, researchers announced Wednesday, Sept. 29.

If confirmed, the exoplanet, named Gliese 581g, would be the first Earth-like world found residing in a star's habitable zone — a region where a planet's temperature could sustain liquid water on its surface.

And the planet's discoverers are optimistic about the prospects for finding life there.

"Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent," said Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz, during a press briefing today. "I have almost no doubt about it."

IN PICTURES: Planets

His colleague, Paul Butler of the Carnegie Institution of Washington, in Washington, D.C., wasn't willing to put a number on the odds of life, though he admitted he's optimistic.

"It's both an incremental and monumental discovery," Sara Seager, an astrophysicist at the Massachusetts Institute of Technology, told SPACE.com. It's incremental because the method used to find Gliese 581g already has found several planets, including super-Earths, outside their stars' habitable zone, along with non-Earth-like planets within the habitable zone.

"It really is monumental if you accept this as the first Earth-like planet ever found in the star's habitable zone," said Seager, who was not directly involved in the discovery.

(Gliese 581g: If there's life there, how will we know?)

Vogt, Butler and their colleagues will detail the planet finding in the Astrophysical Journal.

The newfound planet joins more than 400 other alien worlds known to date. Most are huge gas giants, though several are just a few times the mass of Earth.

Stellar tugs

Gliese 581g is one of two new worlds the team discovered orbiting the red dwarf star Gliese 581, bumping that nearby star's family of planets to six. The other newfound planet, Gliese 581f, is outside the habitable zone, researchers said.

The star is located 20 light-years from Earth in the constellation Libra. One light-year is about 6 trillion miles (10 trillion km).

Red dwarf stars are about 50 times dimmer than our sun. Since these stars are so much cooler, their planets can orbit much closer to them and still remain in the habitable zone.

Estimates suggest Gliese 581g is 0.15 astronomical units from its star, close enough to its star to be able to complete an orbit in just under 37 days. One astronomical unit is the average distance between the Earth and sun, which is approximately 93 million miles (150 million km).

The Gliese 581 planet system now vaguely resembles our own, with six worlds orbiting their star in nearly circular paths.

With support from the National Science Foundation and NASA, the scientists — members of the Lick-Carnegie Exoplanet Survey — collected 11 years of radial velocity data on the star. This method looks at a star's tiny movements due to the gravitational tug from orbiting bodies.

The subtle tugs let researchers estimate the planet's mass and orbital period, how long it takes to circle its star.

Gliese 581g has a mass three to four times Earth's, the researchers estimated. From the mass and estimated size, they said the world is probably a rocky planet with enough gravity to hold onto an atmosphere.

The planet is tidally locked to its star, so that one side basks in perpetual daylight, while the other side remains in darkness. This locked configuration helps to stabilize the planet's surface climate, Vogt said.

"Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude," Vogt said, suggesting that life forms that like it hot would just scoot toward the light side of that line while forms with polar-bear-like preferences would move toward the dark side.

Between blazing heat on the star-facing side and freezing cold on the dark side, the average surface temperature may range from 24 degrees below zero to 10 degrees Fahrenheit (minus 31 to minus 12 degrees Celsius), the researchers said.

Are you sure?

Supposedly habitable worlds have been found and later discredited, so what makes this one such a breakthrough?

There's still a chance that further observations will dismiss this planet, also. But over the years, the radial velocity method has become more precise, the researchers point out in their journal article.

In addition, the researchers didn't make some of the unrealistic assumptions made in the past, Seager said.

For instance, another planet orbiting Gliese 581 (the planet Gliese 581c) also had been considered to have temperatures suitable for life, but in making those calculations, the researchers had come up with an "unrealistic" estimate for the amount of energy the planet reflected, Seager pointed out. That type of estimate wasn't made for this discovery.

"We're looking at this one as basically the tip of the iceberg, and we're expecting more to be found," Seager said.

One way to make this a reality, according to study researchers, would be "to build dedicated 6- to 8-meter-class Automated Planet Finder telescopes, one in each hemisphere," they wrote.

The telescopes — or "light buckets" as Seager referred to them — would be dedicated to spying on the nearby stars thought to potentially host Earth-like planets in their habitable zones. The result would be inexpensive and probably would reveal many other nearby potentially habitable planets, the researchers wrote.

Beyond the roughly 100 nearest stars to Earth, there are billions upon billions of stars in the Milky Way, and with that in mind, the researchers suggest tens of billions of potentially habitable planets may exist, waiting to be found.

Planets like Gliese 581g that are tidally locked and orbit the habitable zone of red dwarfs have a high probability of harboring life, the researchers suggest.

Earth once supported harsh conditions, the researchers point out. And since red dwarfs are relatively "immortal" living hundreds of billions of years (many times the current age of the universe), combined with the fact that conditions stay so stable on a tidally locked planet, there's a good chance that if life were to get a toe-hold it would be able to adapt to those conditions and possibly take off, Butler said.

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Tue Oct 19, 2010 11:12 pm



An artists rendering image shows an exoplanet 6 times the Earth circulate around its low-mass host star at a distance equal to 1/20th of the Earth-Sun distance. European astronomers announced they had found 32 new planets orbiting stars outside our solar system on Monday. They believe their find means that 40 percent or more of Sun-like stars have such planets. The host star in this image is a companion to two other low-mass stars, seen in the distance.

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Tue Oct 19, 2010 11:16 pm

Mars may have been habitable underground, new research suggests

Evidence from an ancient meteor strike on Mars indicates the presence of liquid water at some point in the Red Planet's ancient past.



A picture released by the European Space Agency on October 8 shows Melas Chasma,
a rift that sinks some five and a half miles below the surrounding Martian plains.
New research indicates that Mars may have been habitable underground.

An ancient meteor strike on Mars has revealed the first direct evidence of how warm liquid water may have shaped a habitable underground environment.

Images taken by NASA's Mars Reconnaissance Orbiter have revealed the first carbonate rocks found inside Leighton Crater at a level that was once buried 4 miles (6 km) below the red planet's surface.

Carbonates hold carbon dioxide and can form readily in the presence of water, but have previously been found only in a few scattered locations on Mars.



Mars Spirit rover: What a long-range trip it's been

This first-time discovery of carbonates in an underground location points to a warmer epoch in the ancient Martian past with more atmospheric carbon dioxide, as well as ancient seas. The carbonates also turned up alongside silicate minerals and clays that suggest the presence of hydrothermal systems — similar to the deep sea vents on Earth.

"This discovery doesn't really hint at life, but it does reveal a very strong candidate for a habitable environment, perhaps the best discovered so far," said Paul Niles, a planetary geologist with the NASA Johnson Space Center in Houston.

The ancient rocks may date back as far as 3.5 or 4 billion years, according to Joseph Michalski, a planetary geologist at the Planetary Science Institute in Arizona. That means they don't necessarily reflect the Martian underground as it exists today, but they do point to processes which could make the Mars subsurface a habitable place.

Researchers have long looked to the underground environment in hopes of finding Martian life, because cold, dry conditions coupled with ultraviolet radiation on the surface of Mars makes existence up above unlikely.

"The subsurface environment provides a warm, stable environment that should be conducive for life to evolve given our limited understanding of that process," Niles said in an e-mail.

The research is detailed in the Oct. 10 issue of the journal Nature Geosciences.

The methane mystery

The findings may also prove a huge step toward solving the mystery of methane gas on Mars today. Such gas could originate from either methane-burping microbes or non-organic geological processes, but so far no signs of life have turned up as the culprit.

A recent study showed that methane disappears from Mars within less than a year — another sign that something must be constantly creating the methane on the red planet.

But now researchers may have a geological, rather than biological, answer.

Hydrothermal processes with warm liquid water can chemically interact with rocks in a way that produces methane, and the recent Leighton Crater study has laid out strong evidence of hydrothermal systems having at least existed on Mars.

A triumph of the geological explanation does not automatically rule out the chances for life, said Michalski, who coauthored the recent study with Niles. That's because hydrothermal systems would make the underground Martian environment an even more attractive-looking place for life to hide out.

"That is what's cool about Martian methane; it either formed organically or in an environment that's conducive to habitability," Michalski told SPACE.com.

Scratching the surface

Finding out more about the Martian underground has been difficult because of a volcanic upper crust that hides what lies beneath. The Leighton Crater itself sits just southwest of a giant dormant Martian volcano named Syrtis Major, between the northern lowlands and the southern highlands.

If researchers can find other craters that provide more windows into the underground scene, they could confirm a sneaking suspicion about carbonates being spread across a large region of Mars. Such minerals could prove invaluable for their record of water's history that dates back to the warmer, carbon dioxide-rich period of ancient Mars.

"The difficulty with Mars is we only see the surface layer for a long time [because of a lack of plate tectonics]," Michalski explained. "The best way to look at the deeper part of the crust is to look at impact craters several kilometers down."

Future robotic missions beyond the Mars Science Laboratory, NASA's SUV-sized rover slated to launch in 2011, could also target areas similar to the Leighton Crater so that they can study the chemical makeup of the rocks in detail.

Meanwhile, the Mars Reconnaissance Orbiter's instruments — the Compact Reconnaissance Imaging Spectrometer for Mars and High Resolution Imaging Science Experiment — continue to pay off for researchers more than five years since the probe launched.

"These missions are part of a big group effort," Michalski said. "Even though there are just two authors on the paper, we never want to give impression that we're working alone."


แก้ไขล่าสุดโดย sunny เมื่อ Tue Oct 19, 2010 11:39 pm, ทั้งหมด 1 ครั้ง

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Tue Oct 19, 2010 11:20 pm

How Titan might be making DNA building blocks

Saturn's moon Titan has many of the components for life – but no liquid water. A new study shows how the moon's atmosphere might be producing the molecules that make up DNA anyway.



Chemical reactions in the orange atmospheric haze that surrounds Titan could be
creating the molecules that make up DNA, according to a new study.

The orange hydrocarbon haze that shrouds Saturn's frosty moon Titan could be creating the molecules that make up DNA without the help of water – an ingredient widely thought to be necessary for the molecules' formation.

What's more, it could be doing this with help from an unexpected source: another moon of Saturn some 610,000 miles away.

Just because Titan's atmosphere is creating these molecules doesn't mean that the molecules are combining to form life, caution the researchers from the US and France who conducted the experiments. But the results could prompt astrobiologists to consider a wider range of extrasolar planets as potential hosts for at least simple forms of organic life, the team of scientists from the US and France suggests.

Moreover, the results could offer greater insight into how life on Earth formed.

Although Titan is far colder than the early Earth would have been, the makeup of its atmosphere is thought to be comparable to that of Earth's billions of years ago. The new findings suggest that on the early Earth, the planet's upper atmosphere – not just the so-called primordial soup on the surface – may have been the sources for these "prebiotic" molecules, amino acids and the so-called nucleotide bases that make up DNA.

"We're really starting to get a sense for what kind of chemistry an atmosphere is capable of" performing, says Sarah Hörst, a graduate student in planetary science at the University of Arizona, who led the research effort.

Titan's mystery molecules

The inspiration for the experiments came from NASA's Cassini spacecraft, which has detected large molecules at altitudes of some 600 miles above Titan's surface. But the molecules are so far unidentified because of limitations to the craft's instruments.

Lab instruments back on Earth, however, have no such limitations, so the team decided to replicate Titan's atmosphere in a large chamber at the temperatures present in the moon's upper atmosphere. To play the role of the sun's ultraviolet light hitting Titan's atmosphere, they used radio energy at a power level comparable to a modestly bright light bulb.

The UV light is important because it breaks up molecules such as molecular nitrogen or carbon monoxide in Titan's atmosphere, leaving the individual atoms to choose up different partners, forming new molecules.

The experiment yielded tiny aerosol particles. The team ran the particles through a sensitive mass spectrometer, which showed the chemical formulas for the molecules that made up the aerosols.

Ms. Hörst then ran the formulas past a roster of molecules biologically important for life on Earth. She got 18 hits, including the four nucleotides whose combinations form an organism's genetic information encoded in DNA.

In the end, she says, it appears to be less important that water is present to form these molecules than it is for some form of oxygen to be present in the mix of ingredients.

Enceladus's helping hand

On Earth, oxygen early in the planet's pre-life history would come in the form of carbon dioxide and carbon monoxide from volcanic activity, as well as from water released by volcanism and through meteor and comet impacts.

On Titan, the oxygen appears to be coming from Enceladus, an intriguing moon of Saturn in its own right because of icy geysers spewing into space from near its south pole. Some researchers think the geysers hint at a subsurface sea – or at least sizable deposits of slush – and a potential habitat for life.

Last year, researchers showed how water molecules ejected as part of Enceladus's geysers can be carried great distances through the Saturn system. Some of those oxygen-bearing molecules make their way to Titan's neighborhood.

If Titan's atmosphere indeed is forming nucleotides, amino acids, and perhaps other large biomolecules, and if this atmospheric chemistry factory is present on planets around other stars, that does not mean conditions there are right for combining these molecules in ways that lead to critters big or small, Hörst cautions.

On other planets and under other conditions, atmospheres "may not make these molecules," she says, "but they still might make other molecules" that life on Earth could could use.

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Re: Searching for Habitable Planets

ตั้งหัวข้อ  sunny on Sun Oct 24, 2010 1:11 am

Silver found on Moon
By Steve Connor, Science Editor

An ambitious attempt to discover the contents of a lunar crater by crash landing a spent rocket has revealed a "treasure chest" of elements on the Moon.



Nasa last night said that its mission last year to fire a rocket into the dark shadows of the Cabeus crater near the lunar South Pole produced a plume of debris containing an astonishing array of volatile substances, including silver and enough water to fill a paddling pool.

An analysis of the chemical constituents of the plume, published in the journal Science, shows that 155kg (342lbs) of water ice were blown out of the crater when the Lunar Crater Observation and Sensing Satellite (LCROSS) hurled its spent rocket section into centre of Cabeus, which is in permanent shadow.

Nasa scientists said that the deliberate crash landing into the lunar crater had revealed that the make-up of the Moon's soil and subsurface is more complex than they had previously believed. The soil also contains carbon monoxide, carbon dioxide, sodium, mercury and trace amounts of silver.

"This place looks like it's a treasure chest of elements, of compounds that have been released all over the Moon, and they've been put in this bucket in the permanent shadows," said Peter Schultz of Brown University, Rhode Island, one of the scientific investigators on the LCROSS mission.

It is believed that many of these compounds have been deposited on the lunar surface by comets and meteorites which have crashed into the Moon over many millions of years. The permanent shade of the lunar craters at the poles has prevented these substances from evaporating back into space, Professor Schultz said.

"There's a balance between delivery and removal. This suggests the delivery is winning. We're collecting material, not simply getting rid of it," he added.

The researchers estimated that about 6 per cent of the crater's contents could be water ice left behind by passing comets. If other craters at the lunar polar also contained similar amounts of water then there could be enough of this vital substance to sustain a permanently manned lunar base.

Until last year, many lunar scientists had thought that there would only be trace amounts of water on the lunar surface, but the LCROSS mission demonstrated for the first time that there were significantly bigger quantities that could prove useful for future manned missions to the Moon.

It appears that many of the chemical elements and compounds deposited on the Moon by passing comets, asteroids and meteorites eventually migrate to the polar regions, where the deeper, shaded craters provide permanent protection against the burning heat of the Sun, the scientists said.

Nasa estimates that there are 12,500sq km of permanently shaded terrain on the Moon and if the top one metre of this area were to hold just 1 per cent by mass of water, this would still produce thousands of litres of water.

Apollo astronauts collected evidence showing that there were trace amounts of silver and gold on the side of the Moon that always faces the Earth.

The LCROSS mission produced an impact hole between 70 and 100ft wide and tossed up lunar soil from 6ft below the surface to a height of half a mile, high enough for it to be illuminated by sunlight so that spectroscopic instruments on board another spacecraft could analyse its constituent materials.

Mission facts

70-100 The diameter, in feet, of the crater left when the Nasa rocket hit the surface of the moon.

6 The depth, in feet, of the lunar material thrown up by the impact.

800 The height, in metres, of the plume of debris that rose from the crash site.

4 The number of minutes after the collision in which the scientists were able to study the ejecta.

2 The weight, in tons, of the material dislodged by the rocket.

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