RSSArchive for October, 2010

Earth-sized Planets could be everywhere

Artist's impression of Earth-like planets

  • Galaxy could have more than 46 billion Earth-size planets
  • Small planets outnumber larger ones
  • Findings challenge theories of planet formation

Nearly one in four stars similar to the Sun may host planets as small as Earth, according to a new study funded by NASA and the University of California.

The study is the most extensive and sensitive planetary census of its kind. Astronomers used the W.M. Keck Observatory in Hawaii for five years to search 166 Sun-like stars near our Solar System for planets of various sizes, ranging from three to 1,000 times the mass of Earth.

All of the planets in the study orbit close to their stars. The results show more small planets than large ones, indicating small planets are more prevalent in our Milky Way galaxy.

“We studied planets of many masses—like counting boulders, rocks and pebbles in a canyon—and found more rocks than boulders, and more pebbles than rocks. Our ground-based technology can’t see the grains of sand, the Earth-size planets, but we can estimate their numbers,” said Andrew Howard of the University of California, Berkeley, lead author of the new study.

W.M. Keck Observatory

The W.M. Keck Observatory, atop Mauna Kea in Hawaii, was used to survey 166 Sun-like stars for planets of different sizes.

“Earth-size planets in our galaxy are like grains of sand sprinkled on a beach—they are everywhere.”

The study appears in the October 29 issue of the journal Science.

The research provides a tantalising clue that potentially habitable planets could also be common. These hypothesised Earth-size worlds would orbit farther away from their stars, where conditions could be favourable for life.

NASA’s Kepler spacecraft is also surveying Sun-like stars for planets and is expected to find the first true Earth-like planets in the next few years.

Small planets outnumber large ones

Howard and his planet-hunting team, which includes principal investigator Geoff Marcy, also of the University of California, Berkeley, looked for planets within 80-light-years of Earth, using the radial velocity, or “wobble,” technique.

They measured the numbers of planets falling into five groups, ranging from 1,000 times the mass of Earth, or about three times the mass of Jupiter, down to three times the mass of Earth.

The search was confined to planets orbiting close to their stars—within 0.25 astronomical units, or a quarter of the distance between our Sun and Earth.

A distinct trend jumped out of the data—smaller planets outnumber larger ones. Only 1.6 percent of stars were found to host giant planets orbiting close in. That includes the three highest-mass planet groups in the study, or planets comparable to Saturn and Jupiter.

About 6.5 percent of stars were found to have intermediate-mass planets, with 10 to 30 times the mass of Earth—planets the size of Neptune and Uranus. And 11.8 percent had the so-called “super-Earths,” weighing in at only three to 10 times the mass of Earth.

“During planet formation, small bodies similar to asteroids and comets stick together, eventually growing to Earth-size and beyond. Not all of the planets grow large enough to become giant planets like Saturn and Jupiter,” Howard said. “It’s natural for lots of these building blocks, the small planets, to be left over in this process.”

Diagram indicating numbers of different sized planets in the Galaxy

A new survey, funded by NASA and the University of California, reveals that small planets are more common than large ones.

Life in the hot zone

The astronomers extrapolated from these survey data to estimate that 23 percent of Sun-like stars in our galaxy host even smaller planets, the Earth-sized ones, orbiting in the hot zone close to a star.

“This is the statistical fruit of years of planet-hunting work,” said Marcy. “The data tell us that our galaxy, with its roughly 200 billion stars, has at least 46 billion Earth-size planets, and that’s not counting Earth-size planets that orbit farther away from their stars in the habitable zone.”

The findings challenge a key prediction of some theories of planet formation.

Models predict a planet “desert” in the hot-zone region close to stars, or a drop in the numbers of planets with masses less than 30 times that of Earth. This desert was thought to arise because most planets form in the cool, outer region of solar systems, and only the giant planets were thought to migrate in significant numbers into the hot inner region.

The new study finds a surplus of close-in, small planets where theories had predicted a scarcity.

“We are at the cusp of understanding the frequency of Earth-sized planets among planetary systems in the solar neighbourhood,” said Mario R. Perez, Keck program scientist at NASA Headquarters in Washington.

“This work is part of a key NASA science program and will stimulate new theories to explain the significance and impact of these findings.”

Adapted from information issued by NASA / JPL-Caltech / UC Berkeley / WMKO.

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Mission to Mars – a one-way trip?

Explorers on Mars

Artist's concept of explorers on Mars. Professors Dirk Schulze-Makuch and Paul Davies have suggested one-way colonisation missions to the Red Planet.

  • One-way manned missions to Mars proposed
  • Would cut costs and make missions feasible
  • Martian colony could be springboard to other planets

For the chance to watch the sun rise over Olympus Mons, or maybe take a stroll across the vast plains of the Vastitas Borealis, would you sign on for a one-way flight to Mars?

It’s a question that gives pause to even Dirk Schulze-Makuch, a Washington State University associate professor, who, with colleague Paul Davies, a physicist and cosmologist from Arizona State University, argues for precisely such a one-way manned mission to Mars in an article published this month in the Journal of Cosmology.

In the article, “To Boldly Go: A One-Way Human Mission to Mars,” the authors write that while technically feasible, a manned mission to Mars and back is unlikely to lift off anytime soon – largely because it is a hugely expensive proposition, both in terms of financial resources and political will.

Explorers on Mars

One-way missions to Mars could help establish the first permanent off-Earth outpost.

And because the greatest portion of the expense is tied up in safely returning the crew and spacecraft to earth, they reason that a manned one-way mission would not only cut the costs by several fold, but also mark the beginning of long-term human colonisation of the planet.

Mars is by far the most promising for sustained colonisation and development, the authors conclude, because it is similar in many respects to Earth and, crucially, possesses a moderate surface gravity, an atmosphere, abundant water and carbon dioxide, together with a range of essential minerals.

It is the Earth’s second closest planetary neighbour (after Venus) and a trip to Mars takes about six months using the most favourable launch option and current chemical rocket technology.

Volunteers only

“We envision that Mars exploration would begin and proceed for a long time on the basis of outbound journeys only,” said Schulze-Makuch. “One approach could be to send four astronauts initially, two on each of two space craft, each with a lander and sufficient supplies, to stake a single outpost on Mars.”

“A one-way human mission to Mars would be the first step in establishing a permanent human presence on the planet.”

While acknowledging that the mission would necessarily be crewed by volunteers, Schulze-Makuch and Davies stress that they aren’t suggesting that astronauts simply be abandoned on the Red Planet for the sake of science. Unlike the Apollo moon missions, they propose a series of missions over time, sufficient to support long-term colonisation.

“It would really be little different from the first white settlers of the North American continent, who left Europe with little expectation of return,” Davies said of the proposed one-way Martian mission.

“Explorers such as Columbus, Frobisher, Scott and Amundsen, while not embarking on their voyages with the intention of staying at their destination, nevertheless took huge personal risks to explore new lands, in the knowledge that there was a significant likelihood that they would perish in the attempt.”

The authors propose the astronauts would be re-supplied on a periodic basis from Earth with basic necessities, but otherwise would be expected to become increasingly proficient at harvesting and utilising resources available on Mars.

Eventually they envision that outpost would reach self-sufficiency, and then it could serve as a hub for a greatly expanded colonisation program.

Explorers on Mars

Explorers would be expected to harvest and utilise resources available on Mars.

Springboard to the Solar System

The proposed project would begin with the selection of an appropriate site for the colony, preferentially associated with a cave or some other natural shelter, as well as other nearby resources, such as water, minerals and nutrients.

“Mars has natural and quite large lava caves, and some of them are located at a low elevation in close proximity to the former northern ocean, which means that they could harbour ice deposits inside similar to many ice-containing caves on Earth,” said Schulze-Makuch.

“Ice caves would go a long way to solving the needs of a settlement for water and oxygen. Mars has no ozone shield and no magnetospheric shielding, and ice caves would also provide shelter from ionising and ultraviolet radiation.”

The article suggests that, in addition to offering humanity a “lifeboat” in the event of a mega-catastrophe on Earth, a Mars colony would provide a platform for further scientific research.

Astrobiologists agree that there is a fair probability that Mars hosts, or once hosted, microbial life, perhaps deep beneath the surface and Davies and Schulze-Makuch suggest a scientific facility on Mars might therefore be a unique opportunity to study an alien life form and a second evolutionary record.

“Mars also conceals a wealth of geological and astronomical data that is almost impossible to access from Earth using robotic probes,” the authors write. “A permanent human presence on Mars would open the way to comparative planetology on a scale unimagined by any former generation…”

Explorers on Mars

Would the first explorers on Mars find evidence that life once existed on the Red Planet?

“A Mars base would offer a springboard for human/robotic exploration of the outer Solar System and the asteroid belt. And establishing a permanent multicultural and multinational human presence on another world would have major beneficial political and social implications for Earth, and serve as a strong unifying and uplifting theme for all humanity.”

Expressions of interest

Although they believe the strategy of colonising Mars with one-way missions brings the goal of colonising another planet technologically and financially within our reach, Schulze-Makuch and Davies acknowledge that such a project would require not only major international co-operation, but a return to the exploration spirit and risk-taking ethos of the great period of the Earth’s exploration.

They write that when they raise the idea of a one-way Mars colonisation mission among their scientific colleagues, a number express an interest in making the trip.

“Informal surveys conducted after lectures and conference presentations on our proposal, have repeatedly shown that many people are willing to volunteer for a one-way mission, both for reasons of scientific curiosity and in a spirit of adventure and human destiny,” they write.

And yes, Schulze-Makuch offered that he too would be prepared to “boldly go” on a one-way mission to the Red Planet. But he hedges just a bit, holding out the single caveat that he would want the launch to wait until his young children have all grown into adults.

Adapted from information issued by WSU / ASU / NASA / Pat Rawlings (SAIC).

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A dying star’s farewell show

Planetary nebula NGC 6210

Planetary nebula NGC 6210 in the constellation Hercules. A planetary nebula is a complex cloud of gas given off during the dying stages of a Sun-like star's life.

The NASA/ESA Hubble Space Telescope has taken a striking high-resolution image of the curious planetary nebula NGC 6210.

Located about 6,500 light-years away, in the constellation of Hercules, NGC 6210 was discovered in 1825 by the German astronomer Friedrich Georg Wilhelm Struve. Although through a small telescope it appears only as a tiny disc, it is fairly bright as planetary nebulae go.

Despite their name, planetary nebulae have nothing to do with planets. They got their name because, through early telescopes, they looked more like planets than stars.

In fact, a planetary nebula is a complex cloud of gas produced in the dying stages of certain stars’ lives.

In this instance, NGC 6210 is the last gasp of a star slightly less massive than our Sun. Multiple shells of gas ejected by the dying star are superimposed on one another in different orientations, giving NGC 6210 its odd shape.

See a full-size, high-resolution wallpaper image here (new window).

This sharp image shows the inner region of this planetary nebula in unprecedented detail, where the central star is surrounded by a thin, bluish bubble that has a delicate filamentary structure. This bubble is superposed onto an asymmetric, reddish gas complex where holes, filaments and pillars are clearly visible.

A star’s life ends when the fuel available to its thermonuclear engine runs out. The estimated lifetime for a Sun-like star is some ten billion years. When the star is about to expire, it becomes unstable and ejects its outer layers, forming a planetary nebula and leaving behind a tiny, but very hot, remnant, known as white dwarf.

This compact object, visible at the centre of the image, cools down and fades very slowly. Stellar evolution theory predicts that our Sun will experience the same fate as NGC 6210 in about five billion years.

Adapted from information issued by ESA / Hubble / NASA.

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How to weigh a star using a moon

Artist’s concept of an exoplanet and its moon transiting a star

Artist’s concept of an exoplanet and its moon transiting (passing in front of) a sun-like star. Such a system could be used to directly weigh the star.

How do astronomers weigh a star that’s trillions of kilometres away and much too big to fit on a bathroom scale? In most cases they can’t, although they can get a best estimate using computer models of stellar formation.

New work by astrophysicist David Kipping says that in special cases, we can weigh a star directly. If the star has a planet, and that planet has a moon, and both of them cross in front of their star, then we can measure their sizes and orbits to learn about the star.

“I often get asked how astronomers weigh stars. We’ve just added a new technique to our toolbox for that purpose,” said Kipping, a pre-doctoral fellow at the Harvard-Smithsonian Centre for Astrophysics.

Astronomers have found more than 90 planets that cross in front of, or transit, their stars. By measuring the amount of starlight that’s blocked, they can calculate how big the planet is relative to the star.

But they can’t know exactly how big the planet is unless they know the actual size of the star. Computer models give a very good estimate but in science, real measurements are best.

Kipping realised that if a transiting planet has a moon big enough for us to detect (by also blocking starlight), then the planet-moon-star system could be measured in a way that lets us calculate exactly how large and massive all three bodies are.

“Basically, we measure the orbits of the planet around the star and the moon around the planet. Then through Kepler’s Laws of Motion, it’s possible to calculate the mass of the star,” explained Kipping.

The process isn’t easy and requires several steps. By measuring how the star’s light dims when planet and moon transit, astronomers learn three key numbers: 1) the orbital periods of the moon and planet, 2) the size of their orbits relative to the star, and 3) the size of planet and moon relative to the star.

Plugging those numbers into Kepler’s Third Law yields the density of the star and planet. Since density is mass divided by volume, the relative densities and relative sizes gives the relative masses. Finally, scientists measure the star’s wobble due to the planet’s gravitational tug, known as the radial velocity. Combining the measured velocity with the relative masses, they can calculate the mass of the star directly.

“If there was no moon, this whole exercise would be impossible,” stated Kipping. “No moon means we can’t work out the density of the planet, so the whole thing grinds to a halt.”

Kipping hasn’t put his method into practice yet, since no star is known to have both a planet and moon that transit. However, NASA’s Kepler spacecraft should discover several such systems.

“When they’re found, we’ll be ready to weigh them,” said Kipping.

Adapted from information issued by CfA / David A. Aguilar.

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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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Hubble sees a mini-Milky Way

Galaxy NGC 3982

Hubble Space Telescope image of galaxy NGC 3892. It is 30,000 light-years wide and 68 million light-years from Earth.

Though the universe is chock full of spiral-shaped galaxies, no two look exactly the same.

This face-on spiral galaxy, called NGC 3982, is striking for its rich tapestry of star birth, along with its winding arms. It’s like a smaller version of our Milky Way.

The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars.

The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the centre.

NGC 3982 is located about 68 million light-years away in the direction of the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy.

See the full-size, high-resolution image here (new window).

This colour image is composed of exposures taken by the Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between March 2000 and August 2009.

The rich colour range comes from the fact that the galaxy was photographed in visible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms.

Adapted from information issued by NASA / ESA / HHT (STScI/AURA) / A. Riess (STScI).

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Encounter with a comet

Artist's concept of Deep Impact encounter

Artist's concept of the Deep Impact spacecraft's previous encounter, with Comet Tempel 1 (not to scale). Deep Impact, renamed the EPOXI mission, will encounter another comet, Hartley 2, on November 4.

  • EPOXI spacecraft to visit Comet Hartley 2
  • Close fly-by set for November 4
  • Only fifth mission to rendezvous with a comet

NASA’s Deep Impact/EPOXI spacecraft is hurtling toward Comet Hartley 2 for a breathtaking 700-kilometre flyby on November 4. Mission scientists say all systems are go for a close encounter with one of the smallest yet most active comets they’ve seen.

“There are billions of comets in the Solar System, but this will be only the fifth time a spacecraft has flown close enough to one to snap pictures of its nucleus,” says Lori Feaga of the EPOXI science team. “This one should put on quite a show!

Cometary orbits tend to be highly elongated; they travel far from the Sun and then swing much closer. At encounter time, Hartley 2 will be nearing the Sun and warming up after its cold, deep space sojourn. The ices in its nucleus will be vaporising furiously—spitting out dust and spouting gaseous geysers or jets.

“Hartley 2’s nucleus is small, less than a mile in diameter,” says Feaga. “But its surface offgasses at a higher rate than [cometary] nuclei we’ve seen before. We expect more jets and outbursts from this one.”

EPOXI will swoop down into the comet’s bright coma—the sparkling cloud of debris, illuminated by the Sun—shrouding the nucleus. The spacecraft’s cameras, taking high-resolution (7 metres per pixel at closest approach) pictures all the while, will reveal this new world in all its fizzy glory.

Comet Hartley 2

Comet Hartley 2, photographed on October 13 by Nick Howes using the 2-metre Faulkes North Telescope in Hawaii.

“We hope to see features of the comet’s scarred face: craters, fractures, vents,” says Sebastien Besse of the science team. “We may even be able to tell which features are spewing jets!”

The spacecraft’s instruments are already trained on their speeding target.

“We’re still pretty far out, so we don’t yet see a nucleus,” explains Besse. “But our daily observations with the spectrometer and cameras are already helping us identify the species and amounts of gases in the coma and learn how they evolve over time as we approach.”

Solar System leftovers

The aim of the mission is to gather details about what the nucleus is made of and compare it to other comets. Because comets spend much of their time far from the sun, the cold preserves their composition—and that composition tells a great story.

“Comets are left-overs from the ‘construction’ of our Solar System,” explains Besse. “When the planets formed out of the ‘stuff’ in the solar nebula spinning around the sun, comets weren’t drawn in.”

Researchers study these pristine specimens of the primal solar system to learn something about how it formed, and how it birthed a life-bearing planet like Earth.

EPOXI mission logo

The EPOXI mission logo.

“These flybys help us figure out what happened 4.5 billion years ago,” says Feaga. “So far we’ve only seen four nuclei. We need to study more comets to learn how they differ and how they are the same. This visit will help, especially since Hartley 2 is in many ways unlike the others we’ve seen.”

EPOXI will provide not only a birds-eye view of a new world but also the best extended view of a comet in history.

“This spacecraft is built for close encounters. Its instruments and our planned observations are optimised for this kind of mission. When, as Deep Impact, it flew by Tempel 1, it turned its instruments away from the nucleus to protect them from debris blasted up by the impactor. This time we won’t turn away.”

The EPOXI team will be waiting at NASA’s Jet Propulsion Laboratory.

“We’ll start diving into the data as soon as we receive it,” says Feaga. “We’ll work round the clock, on our toes the whole time, waiting for the next thing to come down.”

Sounds like it could be intense.

“It’s already intense,” says Besse. “We’re getting more and more data, but at encounter we’ll be flooded!”

And that will be only the beginning.

Adapted from information issued by Dauna Coulter / Dr Tony Phillips / Science@NASA / Pat Rawlings / JPL / UMD.

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Unicorn cloud reveals its inner self

Monoceros R2

Infrared image of the nearby star formation region Monoceros R2, located 2,700 light-years away in the constellation Monoceros (the Unicorn).

  • Infrared images can look through dust clouds
  • VISTA telescope designed for infrared sky surveys
  • Image penetrates into the heart of region called Monoceros R2

A new infrared image from the European Southern Observatory’s (ESO) VISTA survey telescope reveals a scene of glowing tendrils of gas, dark dust clouds and young stars within the constellation Monoceros (the Unicorn).

Known as Monoceros R2, this star-forming region is embedded within a huge dark cloud rich in molecules and dust and hiding an active stellar “nursery”.

VISTA telescope

The enclosure of the VISTA survey telescope at the ESO Paranal Observatory in northern Chile.

At “normal”, visible light wavelengths (see comparison images below), a grouping of massive hot stars can be seen amidst a beautiful collection of “reflection nebulae”, where bluish starlight is scattered from parts of the foggy outer layers of a cloud of molecular gas.

Most of the newborn massive stars in the nursery remain hidden at visible light wavelengths, as the thick dust clouds strongly absorb and block the stars’ ultraviolet and visible light from reaching us.

But spectacular detail pops out at VISTA’s infrared wavelengths. See the full-size, high-resolution version here (0.7MB, new window)

Taken from ESO’s Paranal Observatory in northern Chile, the VISTA image shows how the dark curtain of cosmic dust is penetrated to reveal in detail the folds, loops and filaments sculpted from the dusty interstellar matter by the intense particle winds and radiation emitted by hot young stars.

“When I first saw this image I just said, ‘Wow!’” says Jim Emerson, of Queen Mary, University of London and leader of the VISTA consortium. “I was amazed to see all the dust streamers so clearly around the Monoceros R2 cluster, as well as the jets from highly embedded young stellar objects.”

Stars form in a process that typically lasts few million years and which takes place inside large clouds of interstellar gas and dust, hundreds of light-years across.

Interstellar dust blocks visible light wavelengths but lets infrared and radio wavelengths through… so observations at the latter wavelengths are crucial in the understanding of the earliest stages of the stellar evolution.

Visible light wavelength image of Monoceros R2

A visible light wavelength image of Monoceros R2. Compare this to the infrared image at the top of the page. At infrared wavelengths, the thick, rich dust clouds that cover much of the image become nearly transparent and a whole host of young stars and associated outflows become apparent.

Home to newborn stars

Since dust is largely transparent at infrared wavelengths, many young stars that cannot be seen in visible-light images become apparent in Monoceros R2. The most massive of these stars are less than 10 million years old.

At the centre of the image lies Monoceros R2 dense core, no more than two light-years in extent, which is packed with very massive young stars, as well as a cluster of bright infrared sources, which are typically newborn massive stars still surrounded by dusty clouds.

The rightmost of the bright clouds in the centre is called NGC 2170, the brightest reflection nebula in this region. In visible light, the nebulae appear as bright, light blue islands in a dark ocean, while infrared reveals their interiors where hundreds of massive stars are coming into existence.

NGC 2170—faintly visible through a small telescope—was discovered from England in 1784 by astronomer William Herschel.

Although Monoceros R2 appears close in the sky to the more familiar Orion Nebula it is actually almost twice as far from Earth, at a distance of about 2,700 light-years. The width of VISTA’s field of view is equivalent to about 80 light-years at this distance.

With its 4.1-metre primary mirror, VISTA is the largest survey telescope in the world and is equipped with the largest infrared camera on any telescope, with 67 million pixels. It is dedicated to sky surveys.

By mapping the southern sky systematically, VISTA will gather some 300 gigabytes per night, providing a huge amount of information on those regions that will be studied in greater detail by the Very Large Telescope (VLT), the Atacama Large Millimetre/submillimetre Array (ALMA) and, in the future, by the European Extremely Large Telescope (E-ELT).

Adapted from information issued by ESO / J. Emerson / VISTA / Cambridge Astronomical Survey Unit.

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Aussie student finds ‘living dinosaurs’ in space

Galaxies

Australian astronomers have found "living dinosaur" galaxies in the nearby universe. These types of galaxies had been thought to exist only earlier in the universe.

Using Australian telescopes, Swinburne University astronomy student Andy Green has found ‘living dinosaurs’ in space: galaxies in today’s Universe that were thought to have existed only in the distant past.

The report of his finding—Green’s first scientific paper—appears on the cover of the 7 October issue of the scientific journal, Nature.

“We didn’t think these galaxies existed. We’ve found they do, but they are extremely rare,” said Professor Karl Glazebrook, Green’s thesis supervisor and team leader.

The Swinburne researchers have likened the galaxies to the ‘living dinosaurs’ or Wollemi Pines of space—galaxies you just wouldn’t expect to find in today’s world.

“Their existence has changed our ideas about how star formation is fuelled and understanding star formation is important. Just look at the Big Bang, which is how we all got here,” Glazebrook said.

The galaxies in question look like discs, reminiscent of our own galaxy, but unlike the Milky Way they are physically turbulent and are forming many young stars.

“Such galaxies were thought to exist only in the distant past, ten billion years ago, when the Universe was less than half its present age,” Glazebrook said. “Stars form from gas, and astronomers had proposed that the extremely fast star formation in those ancient galaxies was fuelled by a special mechanism that could exist only in the early Universe—cold streams of gas continually falling in.”

Simulation of a star-forming galaxy

A simulation of a star-forming galaxy. Cold gas (red) flows into a spiral galaxy, feeding the process that forms stars.

But finding the same kind of galaxy in today’s Universe means that that mechanism can’t be the only way such rapid star formation is fuelled.

Instead it seems that when young stars form, they create turbulence in their surrounding gas. The more stars are forming in a galaxy, the more turbulence it has. “Turbulence affects how fast stars form, so we’re seeing stars regulating their own formation,” Green said.

“We still don’t know where the gas to make these stars comes from though,” he said. Understanding star formation is one of the most basic, unsolved problems of astronomy.

Another significant aspect of the paper is that it was authored by a PhD student. As Glazebrook pointed out, being first author of a Nature paper as a student is as rare as the galaxies they’ve discovered. This is an achievement not lost on the young scientist. “Nature is one of the most prestigious journals in science. It was a pleasant surprise for our work to receive this kind of accolade,” Green said.

Anglo-Australian Telescope

The 3.9-metre Anglo-Australian Telescope was one of the telescopes used in the study.

Australian observatories

The study was based on selected galaxies from the Sloan Digital Sky Survey, a kind of census of modern galaxies. “We studied extreme galaxies to compare them with the ancient Universe,” Green said. He observed them using the Anglo-Australian Telescope (AAT) and the Australian National University’s 2.3-metre telescope, both located at Siding Spring Observatory in New South Wales.

Professor Matthew Colless, Director of the Australian Astronomical Observatory, which operates the AAT, said that the study highlighted the value of the instruments found at Australia’s telescopes. “They are ideal for studying in detail the nearby counterparts of galaxies seen in the distant Universe by the eight and 10 metre telescopes,” he said.

For the next stage of his research, Green plans to use one of these 10 metre telescopes—in fact the largest optical telescope in the world at the Keck Observatory—to take an even closer look at the rare galaxies he has discovered. Green admitted: “Really, we need a bigger telescope, the Giant Magellan Telescope, to understand star formation. But, until it’s constructed, Keck is the best tool available.”

Green’s access to the Keck will be possible thanks to Swinburne’s agreement with Caltech, which gives the Swinburne astronomers access to the Keck Observatory in Hawaii for up to 20 nights per year.

Adapted from information issued by Swinburne University / Rob Crain / James Geach / Virgo Consortium / Andy Green / Swinburne Astronomy Productions. AAT photo by Barnaby Norris.

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Life on Titan: up in the air?

Titan, Epimetheus and Saturn's rings

Saturn's moon Titan looms large behind the planet's rings. (A smaller moon, Epimetheus, is in the foreground.) Chemical reactions in Titan's upper atmosphere could form molecules that are the precursor of life.

  • Titan’s atmosphere simulated in the lab
  • Chemical reactions produce amino acids
  • Key ingredients for life as we know it

While simulating possible chemical processes that could occur in the hazy atmosphere of Titan, Saturn’s largest moon, a University of Arizona-led planetary research team found amino acids and nucleotide bases in the mix—the most important ingredients of life on Earth.

“Our team is the first to be able to do this in an atmosphere without liquid water. Our results show that it is possible to make very complex molecules in the outer parts of an atmosphere,” said Sarah Hörst, a graduate student in the University of Arizona’s (UA) Lunar and Planetary Lab, who led the international research effort together with her adviser, planetary science professor Roger Yelle.

The molecules discovered include the five nucleotide bases used by life on Earth to build the genetic materials DNA and RNA: cytosine, adenine, thymine, guanine and uracil, and the two smallest amino acids, glycine and alanine. Amino acids are the building blocks of proteins.

Reaction chamber

A window into Titan’s atmosphere: Energised by microwaves, the gas mix inside the reaction chamber lights up like a pink neon sign. Thousands of complex organic molecules accumulated on the bottom of the chamber during this experiment.

The results suggest not only that Titan’s atmosphere could be a reservoir of pre-biotic molecules that serve as the springboard to life, but they offer a new perspective on the emergence of terrestrial life as well: Instead of coalescing in a primordial soup, the first ingredients of life on our planet may have rained down from a primordial haze high in the atmosphere.

Oddball of the Solar System

Titan has fascinated—and puzzled—scientists for a long time.

“It’s is the only moon in our Solar System that has a substantial atmosphere,” Hörst said. “Its atmosphere stretches out much further into space than Earth’s. The moon is smaller so it has less gravity pulling it back down.”

Titan’s atmosphere is much denser, too—on the surface, atmospheric pressure equals that at the bottom of a 5-metre-deep pool on Earth.

“At the same time, Titan’s atmosphere is more similar to ours than any other atmosphere in the Solar System,” Hörst said. “In fact, Titan has been called ‘Earth frozen in time’ because some believe this is what Earth could have looked like early in time.”

Saturn's moon Titan

Saturn's moon Titan has a thick, hazy atmosphere.

When the Voyager I spacecraft flew by Titan in the 1970s, the pictures transmitted back to Earth showed a blurry, orange ball.

“For a long time, that was all we knew about Titan,” Hörst said. “All it saw were the outer reaches of the atmosphere, not the moon’s body itself. We knew it has a an atmosphere and that it contains methane and other small organic molecules, but that was it.”

In the meantime, scientists learned that Titan’s haze consists of aerosols, just like the smog that cloaks many metropolitan areas on Earth. Aerosols, tiny particles about a quarter millionth of an inch across, resemble little snowballs when viewed with a high-powered electron microscope.

The exact nature of Titan’s aerosols remains a mystery. What makes them so interesting to planetary scientists is that they consist of organic molecules—potential ingredients for life.

“We want to know what kinds of chemistry can happen in the atmosphere and how far it can go.” Hörst said. “Are we talking small molecules that can go on to becoming more interesting things? Could proteins form in that atmosphere?”

What it takes to make life’s molecules

For that to happen, though, energy is needed to break apart the simple atmospheric molecules—nitrogen, methane and carbon monoxide—and rearrange the fragments into more complex compounds such as pre-biotic molecules.

“There is no way this could happen on Titan’s surface,” Hörst said. “The haze is so thick that the moon is shrouded in a perpetual dusky twilight. Plus, at -124 degrees Celsius, the water ice that we think covers the moon’s surface is as hard as granite.”

However, the atmosphere’s upper reaches are exposed to a constant bombardment of ultraviolet radiation and charged particles coming from the sun and deflected by Saturn’s magnetic field, which could spark the necessary chemical reactions.

Smog-like particles

Tiny particles are thought to create the smog-like haze that enshrouds Saturn's moon Titan.

To study Titan’s atmosphere, scientists have to rely on data collected by the spacecraft Cassini, which has been exploring the Saturn system since 2004 and flies by Titan every few weeks on average.

“With Voyager, we only got to look,” says Hörst. “With Cassini, we get to touch the moon a little bit.”

During fly-by manoeuvres, Cassini has gobbled up some of the molecules in the outermost stretches of Titan’s atmosphere and analysed them with its on-board mass spectrometer. Unfortunately, the instrument was not designed to unravel the identity of larger molecules—precisely the kind that were found floating in great numbers in Titan’s mysterious haze.

“Cassini can’t get very close to the surface because the atmosphere gets in the way and causes drag on the spacecraft,” Hörst said. “The deepest it went was 900 kilometres (560 miles) from the surface. It can’t go any closer than that.”

To find answers, Hörst and her co-workers had to recreate Titan’s atmosphere here on Earth. More precisely, in a lab in Paris, France.

“Fundamentally, we cannot reproduce Titan’s atmosphere in the lab, but our hope was that by doing these simulations, we can start to understand the chemistry that leads to aerosol formation,” Hörst said. “We can then use what we learn in the lab and apply it to what we already know about Titan.”

Like a spy in a movie

Hörst and her collaborators mixed the gases found in Titan’s atmosphere in a stainless-steel reaction chamber and subjected the mixture to microwaves causing a gas discharge—the same process that makes neon signs glow—to simulate the energy hitting the outer fringes of the moon’s atmosphere.

The electrical discharge caused some of the gaseous raw materials to bond together into solid matter, similar to the way UV sunlight creates haze on Titan. The synthesis chamber, constructed by a collaborating group in Paris, is unique because it uses electrical fields to keep the aerosols in a levitated state.

“The aerosols form while they’re floating there,” Hörst explains. “As soon as they grow heavy enough, they fall onto the bottom of the reaction vessel and we scrape them out.”

“And then,” she added, “the samples went on an adventure.”

To analyse the aerosols, Hörst had to use a high-resolution mass spectrometer in a lab in Grenoble, about a three-hour ride from Paris on the TGV, France’s high-speed train.

“I always joke that I felt like [I was in ] a spy in a movie because I would take our samples, put them into little vials, seal them all up and then I’d get on the TGV, and every 5 minutes I’d open the briefcase, ‘Are they still there? Are they still there?’ Those samples were really, really precious.”

Analysing the reaction products with a mass spectrometer, the researchers identified about 5,000 different molecular formulas.

Sarah Hörst

“When I came back and looked at the screen, I thought: That can’t be right,” said graduate student Sarah Hörst.

“We really have no idea how many molecules are in these samples other than it’s a lot,” Hörst said. “Assuming there are at least three or four structural variations of each, we are talking up to 20,000 molecules that could be in there. So in some way, we are not surprised that we made the nucleotide bases and the amino acids.”

“The mass spectrometer tells us what atoms the aerosols are made of, but it doesn’t tell us the structure of those molecules,” Hörst said. “What we really wanted to find out was, what are all the formulas in this mass spectrum?”

“On a whim, we said, ‘Hey, it would be really easy to write a list of the molecular formulas of all the amino acids and nucleotide bases used by life on Earth and have the computer go through them.’”

“I was sitting in front of my computer one day—I had just written up the list—and I put the file in, hit ‘Enter’ and went to go do something,” she said. “When I came back and looked at the screen, it was printing a list of all the things it had found and I sat there and stared at it for a while. I thought: That can’t be right.”

“I ran upstairs to find Roger, my adviser, and he wasn’t there,” Hörst said with a laugh. “I went back to my office, and then upstairs again to find him and he wasn’t there. It was very stressful.”

“We never started out saying, ‘we want to make these things,’ it was more like ‘hey, let’s see if they’re there.’ You have all those little pieces flying around in the plasma, and so we would expect them to form all sorts of things.”

In addition to the nucleotides, the elements of the genetic code of all life on Earth, Hörst identified more than half of the molecular formulas for the 22 amino acids that life uses to make proteins.

Titan: A window into Earth’s past?

In some way, Hörst said, the discovery of Earth’s life molecules in an alien atmosphere experiment is ironic.

Here is why: The chemistry occurring on Titan might be similar to that occurring on the young Earth that produced biological material and eventually led to the evolution of life. These processes no longer occur in the Earth’s atmosphere because of the large abundance of oxygen cutting short the chemical cycles before large molecules have a chance to form. On the other hand, some oxygen is needed to create biological molecules. Titan’s atmosphere appears to provide just enough oxygen to supply the raw material for biological molecules, but not enough to quench their formation.

“There are a lot of reasons why life on Titan would probably be based on completely different chemistry than life on Earth,” Hörst added, “one of them being that there is liquid water on Earth. The interesting part for us is that we now know you can make pretty much anything you want in an atmosphere. Who knows this kind of chemistry isn’t happening on planets outside our Solar System?”

Adapted from information issued by UA / S. Hörst / NASA.

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