Posted on by Jon Voisey

Searching for Exoplanet Oceans More Challenging Than First Thought

Earth Observation of sun-glinted ocean and clouds
Earth Observation of sun-glinted ocean and clouds. Credit: NASA

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As astronomers continue to discover more exoplanets, the focus has slowly shifted from what sizes such planets are, to what they’re made of. First attempts have been made at determining atmospheric composition but one of the most desirable finds wouldn’t be the gasses in the atmosphere, but the detection of liquid water which is a key ingredient for the formation of life as we know it. While this is a monumental challenge, various methods have been proposed, but a new study suggests that these methods may be overly optimistic.

One of the most promising methods was proposed in 2008 and considered the reflective properties of water oceans. In particular when the angle between a light source (a parent star) and an observer is small, the light is not reflected well and ends up being scattered into the ocean. However, if the angle is large, the light is reflected. This effect can be easily seen during sunset over the ocean when the angle is nearly 180° and the ocean waves are tipped with bright reflections and is known as specular reflection. This effect is illustrated in orbit around our own planet above and such effects were used on Saturn’s moon Titan to reveal the presence of lakes.

Translating this to exoplanets, this would imply that planets with oceans should reflect more light during their crescent phases than their gibbous phase. Thus, they proposed, we might detect oceans on extrasolar planets by the “glint” on their oceans. Even better, light reflecting off a smoother surface like water tends to be more polarized than it might be otherwise.

The first criticisms of this hypothesis came in 2010 when other astronomers pointed out that similar effects may be produced on planets with a thick cloud layer could mimic this glinting effect. Thus, the method would likely be invalid unless astronomers were able to accurately model the atmosphere to take its contribution into consideration.

The new paper brings additional challenges by further considering the way material would likely be distributed. Specifically, it is quite likely that planets in the habitable zones without oceans may have polar ice caps (like Mars) which are more reflective all around. Since the polar regions make up a larger percentage of the illuminated body in the crescent phase than during the gibbous, this would naturally lead to a relative diminishing in overall reflectivity and could give false positives for a glint.

This would be especially true for planets that are more oblique (are “tilted”). In this case, the poles receive more sunlight which makes the reflections from any ice caps even more pronounced and mask the effect further. The authors of the new study conclude that this as well as the other difficulties “severely limits the utility of specular reflection for detecting oceans on exoplanets.”

Posted on by Jason Major

Will This Be The Fate Of The Earth?

Artist's impression of PG0843+516, a white dwarf star surrounded by Earthlike planetary remains. (© Mark A. Garlick / space-art.co.uk / University of Warwick)

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Astronomers have found four nearby white dwarf stars surrounded by disks of material that could be the remains of rocky planets much like Earth — and one star in particular appears to be in the act of swallowing up what’s left of an Earthlike planet’s core.

The research, announced today by the Royal Astronomical Society, gives a chilling look at the eventual fate that may await our own planet.

Astronomers from the University of Warwick used Hubble to identify the composition of four white dwarfs’ atmospheres, found during a survey of over 80 such stars located within 100 light-years of the Sun. What they found was a majority of the material was composed of elements found in our own Solar System: oxygen, magnesium, silicon and iron. Together these elements make up 93% of our planet.

In addition, a curiously low ratio of carbon was identified, indicating that rocky planets were at one time in orbit around the stars.

Since white dwarfs are the leftover cores of stellar-mass stars that have burnt through all their fuel, the material in their atmosphere is likely the leftover bits of planets. Once held in safe, stable orbits, when their stars neared the ends of their lives they expanded, possibly engulfing the innermost planets and disrupting the orbits of others, triggering a runaway collision effect that eventually shattered them all, forming an orbiting cloud of debris.

This could very well be what happens to our Solar System in four or five billion years.

“What we are seeing today in these white dwarfs several hundred light years away could well be a snapshot of the very distant future of the Earth,” said Professor Boris Gänsicke of the Department of Physics at the University of Warwick, who led the study. “During the transformation of the Sun into a white dwarf, it will lose a large amount of mass, and all the planets will move further out. This may destabilise the orbits and lead to collisions between planetary bodies as happened in the unstable early days of our solar systems.”

Three easy steps to planetary destruction. (© Mark A. Garlick / space-art.co.uk / University of Warwick)

One of the white dwarfs studied, labeled PG0843+516, may even be actively eating the remains of an once-Earthlike world’s core.

The researchers identified an abundance of heavier elements like iron, nickel and sulphur in the atmosphere surrounding PG0843+516. These elements are found in the cores of terrestrial planets, having sunk into their interiors during the early stages of planetary formation. Finding them out in the open attests to the destruction of a rocky world like ours.

Of course, being heavier elements, they will be the first to be accreted  by their star.

“It is entirely feasible that in PG0843+516 we see the accretion of such fragments made from the core material of what was once a terrestrial exoplanet,” Prof. Gänsicke said.

It’s an eerie look into a distant future, when Earth and the inner planets could become just some elements in a cloud.

Read the full story on the RAS site here.

 

Posted on by Nancy Atkinson

We Really Hope ET is Out There, But There’s Not Enough Scientific Evidence, Researchers Say

This artist's illustration gives an impression of how common planets are around the stars in the Milky Way. Credit: NASA, ESA, and M. Kornmesser (ESO)

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For many of us who grew up listening to Carl Sagan, watching robotic spacecraft travel to other worlds, and indulging in science fiction books and movies, it’s a given: one day we’ll find life somewhere else in the solar system or Universe. But are we being too optimistic? Two researchers say that our hopes and expectations of finding ET might be based more on optimism than scientific evidence, and the recent discoveries of exoplanets that might be similar to Earth are probably getting everyone’s hopes up too high.

Astrophysicist Edwin Turner from Princeton and researcher David Spiegel from the Institute for Advanced Study say the idea that life has or could arise in an another Earth-like environment has only a small amount of supporting evidence, most of it extrapolated from what is known about abiogenesis, or the emergence of life, on early Earth. Their research says the expectations of life cropping up on exoplanets are largely based on the assumption that it would or will happen if the same conditions as Earth exist elsewhere.

Using a Bayesian analysis — which weighs how much of a scientific conclusion stems from actual data and how much comes from the prior assumptions of the scientist — the duo concluded that current knowledge about life on other planets suggests Earth might be a cosmic aberration, where life took shape unusually fast and furious. If so, then the chances of the average terrestrial planet hosting life would be low.

“Fossil evidence suggests that life began very early in Earth’s history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn’t reveal much about the actual probability of life on other planets,” Turner said.

So, if a scientist starts out assuming that the chances of life existing on another planet is as large as on Earth, then their scientific results will be presented in a way that supports that likelihood, Turner said.

“Information about that probability comes largely from the assumptions scientists have going in, and some of the most optimistic conclusions have been based almost entirely on those assumptions,” he said.

Therefore, with all the exoplanets being found, and as our discoveries have become more and more enticingly Earth-like, these planets have our knowledge of life on Earth projected onto them, the researchers said.

How does an exoplanet researcher feel about this? Turner and Spiegel found a sympathetic soul in Joshua Winn from the Massachusetts Institute of Technology, who said that the two cast convincing doubt on a prominent basis for expecting extraterrestrial life.

“There is a commonly heard argument that life must be common or else it would not have arisen so quickly after the surface of the Earth cooled,” Winn said. “This argument seems persuasive on its face, but Spiegel and Turner have shown it doesn’t stand up to a rigorous statistical examination — with a sample of only one life-bearing planet, one cannot even get a ballpark estimate of the abundance of life in the universe.

It is true that science is about facts — not about what your gut feelings are. But there’s a strong argument that we need inspiration to do the best, most engaging science. Writer Andrew Zimmerman Jones blogged today at PBS about how many scientists were spurred to follow their careers by reading science fiction when they were young.

“The finest science fiction is inspired by the same thing that has inspired the greatest science discoveries throughout the ages: optimism for the future,” wrote Jones.

And perhaps that is what is mostly behind our hopes for finding ET: optimism for the future of the human race, that we really could one day travel to other worlds, and find new friends — “to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no one has gone before…”

Turner and Spiegel do say they are not making judgments, but just analyzing existing data that suggests the debate about the existence of life on other planets is framed largely by the prior assumptions of the participants.

“It could easily be that life came about on Earth one way, but came about on other planets in other ways, if it came about at all,” Turner said. “The best way to find out, of course, is to look. But I don’t think we’ll know by debating the process of how life came about on Earth.”

Read the team’s paper.

Sources: Princeton, PBS

Posted on by Jon Voisey

New Evidence For Fomalhaut Planets

Fomalhaut's exoplanet (NASA, ESA, P. Kalas (UC, Berkeley))

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The planetary system of the star Fomalhaut has been one of intense debate over the past few years. In 2008, it was announced that a large, Saturn mass planet shepherd a large dust ring and was spotted in visual images from Hubble. But in late 2011 infrared observations called the previous detections into question. Now joining the discussion is the recently completed Atacama Large Millimeter/sub-millimeter Array (ALMA). This radio observatory suggests that there may be more planets than previously detected.

ALMA sits in the high Atacama desert in northern Chile. This dry location is ideal for linking together the 66 radio dishes (although only 15 were used in the new observations) to give unprecedented resolution. With this new set of eyes, astronomers from the University of Florida and Bryant Space Science Center were able to study the fine details in the dust ring. These details were then compared to various models of how rings should function in different conditions.

The dust ring has several characteristics that any explanation would have to reproduce. The first was that the ring is slightly oval shaped. It must be exceptionally thin and have a sharp cutoff both on the interior and exterior edges. If the previously claimed planet, Fomalhaut b, were the only one present, it could not account for the outer edge of the disk being sharply truncated as well as the inner edge. Another possibility is that the ring is simply newly formed as the result of a collision between two planets and has not yet had time to dissipate giving it the sharp appearance. However, the authors note that planets at such a distance from the parent star shouldn’t have high enough relative velocities to crush them so finely.

Since neither of these explanations are sufficient, the team proposes that there are two planets that shepherd the ring: One interior and one exterior to it. Within our own solar system, we see similar effects in Uranus’ ε ring which is constrained by the moons Cordelia and Ophelia. Similarly, Saturn’s F ring is shepherded by Prometheus and Pandora. By varying the mass of hypothetical planets in the models, the authors could create a ring similar to that seen around Fomalhaut. However, the best fit was created by a pair of planets that were less than three times the mass of the Earth which would mean that the proposed mass for Fomalhaut b was significantly too high, further casting doubt on its existence. Additionally, the proposed orbit of Fomalhaut bwas 10 AU off from the orbit of the hypothetical interior shepherd planet.

Ultimately, these two planets are only hypothetical. Detecting them in a more direct fashion will prove challenging. The fact that their orbits wouldn’t be very close to line of sight as well as their distance from the star would make radial velocity detection impossible. Given the low proposed mass and the distance, they would reflect too little light to be able to be directly observed with current telescopes.

Posted on by Nancy Atkinson

Frantic Comet Massacre Taking Place at Fomalhaut

Herschel's far-infrared observations of Fomalhaut and its disk. Credit: ESA

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There may be some frantic activity going on in the narrow, dusty disk surrounding a nearby star named Fomalhaut. Scientists have been trying to understand the makeup of the disk, and new observations by the Herschel Space Observatory reveals the disk may come from cometary collisions. But in order to create the amount of dust and debris seen around Fomalhaut, there would have to be collisions destroying thousands of icy comets every day.

“I was really surprised,” said Bram Acke, who led a team on the Herschel observations. “To me this was an extremely large number.”

Fomalhaut is a young star, just a few hundred million years old, about 25.1 light years away and twice as massive as the Sun. It is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in our sky, visible in the southern sky in the northern hemisphere in fall and early winter evenings.

Fomalhaut’s toroidal dust belt was discovered in the 1980s by the IRAS satellite. It’s been viewed several times by the Hubble Space Telescope, but Herschel’s new images of the belt show it in much more detail at far-infrared wavelengths than ever before.

The narrow and asymmetrical properties of the disk are thought to be due to the gravity of a possible planet in orbit around the star, but the existence of the planet is still under study.

Hubble's view showing a possible exoplanet Fomalhaut b (NASA/HST)

Acke, from the University of Leuven in Belgium, and his team colleagues analyzed the Herschel observations and found the dust temperatures in the belt to be between –230 and –170 degrees C, and because Fomalhaut is slightly off-center and closer to the southern side of the belt, the southern side is warmer and brighter than the northern side.

Those observations collected starlight scattering off the grains in the belt and showed it to be very faint at Hubble’s visible wavelengths, suggesting that the dust particles are relatively large. But that appears to be incompatible with the temperature of the belt as measured by Herschel in the far-infrared.

While observations with Hubble suggested the grains in the dust disk would be relatively large, the Herschel data show that the dust in the belt has the thermal properties of small solid particles, with sizes of only a few millionths of a meter across. HST observations suggested solid grains more than ten times larger.

To resolve the paradox, Acke and colleagues suggest that the dust grains must be large fluffy aggregates, similar to dust particles released from comets in our own Solar System. These would have both the correct thermal and scattering properties.

However, this leads to another problem.

The bright starlight from Fomalhaut should blow small dust particles out of the belt very rapidly, yet such grains appear to remain abundant there.

So, the only way to explain the contradiction is to resupply the belt through continuous collisions between larger objects in orbit around Fomalhaut, creating new dust.

This isn’t the first time that evidence of cometary collisions have been seen around another star. Last year, astronomers using the Spitzer Space Telescope detected activity resembling a ‘heavy bombardment’ type of event where icy bodies from the outer solar system are possibly pummeling rocky worlds closer to the star.

At Fomalhaut, however, to sustain the belt, the rate of collisions must be remarkable: each day, the equivalent of either two 10 km-sized comets or 2,000 1 km-sized comets must be completely crushed into small, fluffy dust particles.

In order to keep the collision rate so high, scientists say there must be between 260 billion and 83 trillion comets in the belt, depending on their size. This is not unfathomable, the team says, as our own Solar System has a similar number of comets in its Oort Cloud, which formed from objects scattered from a disc surrounding the Sun when it was as young as Fomalhaut.

“These beautiful Herschel images have provided the crucial information needed to model the nature of the dust belt around Fomalhaut,” said Göran Pilbratt, ESA Herschel Project Scientist.

Source: ESA

Posted on by Nancy Atkinson

How Would Humans Respond to First Contact from an Alien World?

Artist concept of an exoplanet. Credit: David A. Hardy.

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According to Star Trek lore, it is only 51 years until humans encounter their first contact with an alien species. In the movie “Star Trek: First Contact,” on April 5, 2063, Vulcans pay a visit to an Earth recovering from a war-torn period (see the movie clip below.) But will such a planet-wide, history-changing event ever really take place? If you are logical, like Spock and his Vulcan species, science points towards the inevitability of first contact. This is according to journalist Marc Kaufman, who is a science writer for the Washington Post and author of the book “First Contact: Scientific Breakthroughs in the Hunt for life Beyond Earth.” He writes that from humanity’s point of view, first contact would be a “harbinger of a new frontier in a dramatically changed cosmos.”

What are some of the arguments for and against the likelihood of first contact ever taking place and what would the implications be?

“One argument against first contact is from those who say there is no other life in the Universe,” said Kaufman, speaking to Universe Today via phone, “and with that is the Fermi paradox, which says that if there is so much life out there, why hasn’t it visited us yet? That was first posited back in the 1950’s and with everything we’ve learned since then, it seems rather presumptuous and Earth-centric to say that because no one has come to Earth, there is no life out there.”

Kaufman argues the Universe is so vast, the number of exoplanets is so huge – with the number of exoplanets in habitable zones now gaining in numbers almost daily – and we now understand that all the makings for the building blocks of life are out in space, so it defies logic to argue there is no other life out there.

Another argument against first contact states there might be microbial life elsewhere in the Universe, but it is not intelligent. “This is where the Fermi paradox comes in even more,” Kaufman said. “It certainly is true — as far as we know — that no intelligent life has made contact with Earth. But when you look at the amount of time we’ve been a technologically advanced society, it has only been a few hundred years. In the vastness of time, that is a pitifully small amount of time – truly nothing.”

In the immensity of cosmological time, Kaufman said, it is quite possible that microbial life emerged and evolved a billion years ago on another world and we missed coinciding with it, as civilizations could have come and gone.

“But all the makings are there and unless we want to say that Earth was made through divine creation or only through an unbelievable set of circumstances this is the only place in the Universe where life began, it just seems hugely, hugely implausible,” Kaufman said.

So, Kaufman says, the best, most logical argument is that life exists beyond Earth and in some instances includes what we would consider intelligence.

“If you have microbial life and billions of planets in habitable zones, the logic says that some of them will advance like we did,” Kaufman said. “There’s no reason to say that evolution is exclusive to Earth. It feels very 14th or 15th century-Earth-centric to say that we are the only place where there is intelligent life.”

Our continued scientific understanding, and in particular, the recent ongoing finding of so many exoplanets, has been a real revolution in our understanding of the cosmos, Kaufman said, and it is a huge boost to the logic of finding life elsewhere.

“It was hypothesized for decades, if not centuries that other planets were out there,” he said. “Now that we are finding planets almost every day, from a scientific perspective, it shows us that if the science is pointing in a certain direction, you just need to have the technology and the knowledge catch up to that hypothesis.”

Kaufman says that like the surge in finding exoplanets, astrobiology is likely the next area of science where breakthroughs will happen.

“Scientists almost unanimously believe there is other life out there, but we just don’t have the technology to find it yet,” he said. “Even with the recent potential cuts in NASA’s budget for planetary missions, and even if NASA is not able to send up as many missions, there is a broad movement going on in college campuses and institutes – from working on synthetic life, to studies in cosmology, and astrochemistry — all of those things are moving forward because there is a real sense that something is within reach. This area of science is just going to blossom.”

So if tomorrow (or on April 5, 2063) a spaceship shows up, how would we respond?

“On one level, I’d hope there would be a huge amount of wonder and awe and a recognition of the vastness of the Universe. But I also imagine there would be a lot of defensiveness, as well,” said Kaufman, referring to some, like Stephen Hawking, who say we shouldn’t send messages out into space — because if a more technically advanced civilization comes to Earth, the outcome for the less advanced (us) would likely be bad.

But Kaufman has hope that Earthlings would welcome a visit.

“Look at the continuing fascination of Roswell or UFOs,” he said. “Throughout history, humans have looked to the skies and thought that we’ve experienced something ‘out there’ – be it angels or gods or spaceships. There is, I believe, a deep human craving that we aren’t alone, and that would be a significant part of our response.”

For more information see Kaufman’s book, and website,”Habitable Zones”

Posted on by Nancy Atkinson

Kepler Mission Extended to 2016

Artist concept of Kepler in space. Credit: NASA/JPL

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With NASA’s tight budget, there were concerns that some of the agency’s most successful astrophysics missions might not be able to continue. Anxieties were rampant about one mission in particular, the very fruitful exoplanet-hunting Kepler mission, as several years of observations are required in order for Kepler to confirm a repeated orbit as a planet transits its star. But today, after a long awaited Senior Review of nine astrophysics missions, surprisingly all have received funding to continue at least through 2014, with several mission extensions, including Kepler.

“Ad Astra… Kepler mission extended through FY16! We are grateful & ecstatic!” the @NASAKepler Twitter account posted today.

Additionally, missions such as Hubble, Fermi and Swift will receive continued funding. The only mission that took a hit was the Spitzer infrared telescope, which – as of now — will be closed out in 2015, which is sooner than requested.

The Senior Review of missions takes place every two years, with the goal assisting NASA to optimize the scientific productivity of its operating missions during their extended phase. In the Review, missions are ranked as which are most successful; previous Senior Reviews led to the removal of funding for the weakest 10-20% of extended missions, some of which had partial instrument failures or significantly reduced capabilities.

But this year’s review found all the astrophysics mission to be successful.

“These nine missions comprise an extremely strong ensemble to enter the Senior Review process and we find that all are making very significant scientific contributions,” the Review committee wrote in their report.

Here’s a rundown of the missions and how their funding was affected by the Senior Review:

• The Hubble Space Telescope will continue at the currently funded levels.

• Chandra will also continue at current levels, but its Guest Observer budget will actually be increased to account for decreases in Fiscal Year 2011.

• Fermi operations are extended through FY16, with a 10 percent per year reduction starting in FY14.

• Swift and Kepler mission operations are extended through FY16, including funding for data analysis.

• Planck will support one year extended operations of the Low Frequency Instrument (LFI).

• Spitzer’s operations are extended through FY14 with closeout in FY15.

• U.S. science support of Suzaku is extended to March 2015.

• Funding for U.S. support of XMM-Newton is extended through March 2015.

NASA says that all FY15-FY16 decisions are for planning purposes and they will be revisited in the 2014 Senior Review.

Read more in the full report (pdf).

Posted on by Jason Major

“Tidal Venuses” May Have Been Wrung Out To Dry

Extreme heating from tidal stresses may render a "Tidal Venus" planet inhabitable

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Earth-sized exoplanets within a distant star’s habitable zone could still be very much uninhabitable, depending on potential tidal stresses — either past or present — that could have “squeezed out” all the water, leaving behind a bone-dry ball of rock.

New research by an international team of scientists suggests that even a moderately eccentric orbit within a star’s habitable zone could exert tidal stress on an Earth-sized planet, enough that the increased surface heating due to friction would boil off any liquid water via extreme greenhouse effect.

Such planets are dubbed “Tidal Venuses”, due to their resemblance to our own super-heated planetary neighbor. This evolutionary possibility could be a factor in determining the actual habitability of an exoplanet, regardless of how much solar heating (insolation) it receives from its star.

The research, led by Dr. Rory Barnes of the University of Washington in Seattle, states that even an exoplanet currently in a circular, stable orbit could have formed with a much more eccentric orbit, thus subjecting it to tidal forces. Any liquid water present after formation would then have been slowly but steadily evaporated and the necessary hydrogen atoms lost to space.

The risk of such a “desiccating greenhouse” effect would be much greater on exoplanets orbiting lower-luminosity stars, since any potential habitable zone would be closer in to the star and thus prone to stronger tidal forces.

And as far as such an effect working to create habitable zones further out in orbit than otherwise permissible by stellar radiation alone… well, that wouldn’t necessarily be the case.

Even if an exoplanetary version of, say, Europa, could be heated through tidal forces to maintain liquid water on or below its surface, a rocky world the size of Earth (or larger) would still likely end up being rather inhospitable.

“One couldn’t do it for an Earthlike planet — the tidal heating of the interior would likely make the surface covered by super-volcanoes,” Dr. Barnes told Universe Today.

So even though the right-sized exoplanets may be found in the so-called “Goldilocks zone” of their star, they may still not be “just right” for life as we know it.

The team’s full paper can be found here.

Posted on by Nancy Atkinson

Astronomers Discover Ancient Planetary System

Artist’s impression of HIP 11952 and its two Jupiter-like planets. Image credit: Timotheos Samartzidis

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From a press release from the Max Planck Institute for Astronomy:

A group of European astronomers has discovered an ancient planetary system that is likely to be a survivor from one of the earliest cosmic eras, 13 billion years ago. The system consists of the star HIP 11952 and two planets, which have orbital periods of 290 and 7 days, respectively. Whereas planets usually form within clouds that include heavier chemical elements, the star HIP 11952 contains very little other than hydrogen and helium. The system promises to shed light on planet formation in the early universe – under conditions quite different from those of later planetary systems, such as our own.

It is widely accepted that planets are formed in disks of gas and dust that swirl around young stars. But look into the details, and many open questions remain – including the question of what it actually takes to make a planet. With a sample of, by now, more than 750 confirmed planets orbiting stars other than the Sun, astronomers have some idea of the diversity among planetary systems. But also, certain trends have emerged: Statistically, a star that contains more “metals” – in astronomical parlance, the term includes all chemical elements other than hydrogen and helium – is more likely to have planets.

This suggests a key question: Originally, the universe contained almost no chemical elements other than hydrogen and helium. Almost all heavier elements have been produced, over time inside stars, and then flung into space as massive stars end their lives in giant explosions (supernovae). So what about planet formation under conditions like those of the very early universe, say: 13 billion years ago? If metal-rich stars are more likely to form planets, are there, conversely, stars with a metal content so low that they cannot form planets at all? And if the answer is yes, then when, throughout cosmic history, should we expect the very first planets to form?

Now a group of astronomers, including researchers from the Max-Planck-Institute for Astronomy in Heidelberg, Germany, has discovered a planetary system that could help provide answers to those questions. As part of a survey targeting especially metal-poor stars, they identified two giant planets around a star known by its catalogue number as HIP 11952, a star in the constellation Cetus (“the whale” or “the sea monster”) at a distance of about 375 light-years from Earth. By themselves, these planets, HIP 11952b and HIP 11952c, are not unusual. What is unusual is the fact that they orbit such an extremely metal-poor and, in particular, such a very old star!

For classical models of planet formation, which favor metal-rich stars when it comes to forming planets, planets around such a star should be extremely rare. Veronica Roccatagliata (University Observatory Munich), the principal investigator of the planet survey around metal-poor stars that led to the discovery, explains: “In 2010 we found the first example of such a metal-poor system, HIP 13044. Back then, we thought it might be a unique case; now, it seems as if there might be more planets around metal-poor stars than expected.”

HIP 13044 became famous as the “exoplanet from another galaxy” – the star is very likely part of a so-called stellar stream, the remnant of another galaxy swallowed by our own billions of years ago.

Compared to other exoplanetary systems, HIP 11952 is not only one that is extremely metal-poor, but, at an estimated age of 12.8 billion years, also one of the oldest systems known so far. “This is an archaeological find in our own backyard,” adds Johny Setiawan of the Max Planck Institute for Astronomy, who led the study of HIP 11952: “These planets probably formed when our Galaxy itself was still a baby.”

“We would like to discover and study more planetary systems of this kind. That would allow us to refine our theories of planet formation. The discovery of the planets of HIP 11952 shows that planets have been forming throughout the life of our Universe”, adds Anna Pasquali from the Center for Astronomy at Heidelberg University (ZAH), a co-author of the paper.

Posted on by Nancy Atkinson

Billions of Habitable Worlds Likely in the Milky Way

Artist’s impression of sunset on the super-Earth world Gliese 667 Cc. Credit: ESO

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Could there be ‘tens of billions’ of habitable worlds in our own galaxy? That’s the results from a new study that searched for rocky planets in the habitable zones around red dwarf stars. An international team of astronomers using ESO’s HARPS spectrograph now estimates that there are tens of billions of such planets in the Milky Way galaxy, with probably about one hundred in the Sun’s immediate neighborhood, less than 30 light years away.

“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet,” said Xavier Bonfils, from IPAG, Observatoire des Sciences de l’Univers de Grenoble, France, and the leader of the team. “Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

This is the first direct estimate of the number of smaller, rocky planets around red dwarf stars. Add this to another recent finding which suggested that every star in our night sky has at least one planet circling it — which didn’t include red dwarf stars – and our galaxy could be teeming with worlds.

This team used the HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile to search for exoplanets orbiting the most common kind of star in the Milky Way — red dwarf stars (also known as M dwarfs). These stars are faint and cool compared to the Sun, but very common and long-lived, and therefore account for 80% of all the stars in the Milky Way.

The Milky Way over the ESO 3.6-metre Telescope, a photo submitted via Your ESO Pictures Flickr Group. Credit: ESO/A. Santerne

The HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period. A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of Gliese 581 and Gliese 667 C respectively.

By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are around red dwarfs. They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.

Bonfils and his team also found that rocky planets were far more common than massive gas giants like Jupiter and Saturn. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1000 times that of the Earth).

However, the rocky worlds orbiting red dwarfs wouldn’t necessarily be a good place to spend your first exo-vacation – or for harboring life.

“The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun,” said Stéphane Udry from the Geneva Observatory and member of the team. “But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely.”

New Exoplanet Discovered

A new exoplanet was discovered in this HARPS survey of red dwarfs: Gliese 667 Cc. This is the second planet in this triple star system and seems to be situated close to the center of the habitable zone. Although this planet is more than four times heavier than the Earth it is the closest twin to Earth found so far and almost certainly has the right conditions for the existence of liquid water on its surface. This is the second super-Earth planet inside the habitable zone of a red dwarf discovered during this HARPS survey, after Gliese 581d was announced in 2007 and confirmed in 2009.

“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments,” said Xavier Delfosse, another member of the team. “Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet’s atmosphere and searching for signs of life.”

Research papers: Bonfils et al. and Delfosse et al.

Source: ESO