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Light of an alien “super-Earth”

Jonathan Nally — Tue, 08 May 2012 21:25:41 +0000

Artist's concept of the planet 55 Cancri e, a world that orbits its star so closely—about 25 times closer than Mercury is to our Sun—that it is tidally locked with one face forever blistering under the heat of its star.

NASA’S SPITZER SPACE TELESCOPE has detected light emanating from a “super-Earth” planet beyond our Solar System for the first time. While the planet is not habitable, the detection is a historic step toward the eventual search for signs of life on other planets.

While no current telescope is able to show us an image of the planet, Spitzer can detect the spectrum of light coming from it.

The planet, called 55 Cancri e, falls into a class of planets termed super Earths, which are more massive than our home world but lighter than giant planets like Neptune. Fifty-five Cancri e is about twice as big and eight times as massive as Earth. The planet orbits a bright star, called 55 Cancri, in a mere 18 hours.

Previously, Spitzer and other telescopes were able to study the planet by analysing how the light from 55 Cancri changed as the planet passed in front of the star. In the new study, Spitzer measured how much infrared light comes from the planet itself.

The results reveal the planet is likely dark and its sun-facing side is more than 1,700 degrees Celsius, hot enough to melt metal.

Distant water world

The new information is consistent with a prior theory that 55 Cancri e is a water world: a rocky core surrounded by a layer of water in a “supercritical” state where it is both liquid and gas, and topped by a blanket of steam.

“It could be very similar to Neptune, if you pulled Neptune in toward our Sun and watched its atmosphere boil away,” said Michael Gillon of Universite de Liege in Belgium, principal investigator of the research, which appears in the Astrophysical Journal. The lead author is Brice-Olivier Demory of the Massachusetts Institute of Technology in Cambridge.

Artist's impression of the Spitzer Space Telescope

The 55 Cancri system is relatively close to Earth at 41 light-years away. It has five known planets, with 55 Cancri e being the closest to the star and tidally locked, so one side always faces the star. Spitzer discovered the star-facing side is extremely hot, indicating the planet probably does not have a substantial atmosphere to carry the sun’s heat to the unlit side.

Direct measurements

In 2005, Spitzer became the first telescope to detect light from a planet beyond our Solar System. To the surprise of many, the observatory saw the infrared light of a “hot Jupiter,” a gaseous planet much larger than the solid 55 Cancri e.

Since then, other telescopes, including NASA’s Hubble and Kepler space telescopes, have performed similar feats with gas giants using the same method.

In this method, a telescope gazes at a star as a planet circles behind it. When the planet disappears from view, the light from the star system dips ever so slightly, but enough that astronomers can determine how much light came from the planet itself. This information reveals the temperature of a planet, and, in some cases, its atmospheric components. Most other current planet-hunting methods obtain indirect measurements of a planet by observing its effects on the star.

During Spitzer’s ongoing extended mission, steps were taken to enhance its unique ability to see exoplanets, including 55 Cancri e. Those steps, which included changing the cycling of a heater and using an instrument in a new way, led to improvements in how precisely the telescope points at targets.

NASA’s James Webb Space Telescope, scheduled to launch in 2018, likely will be able to learn even more about the planet’s composition. The telescope might be able to use a similar infrared method as Spitzer to search other potentially habitable planets for signs of molecules possibly related to life.

Adapted from information issued by NASA / JPL-Caltech.

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Billions of super-Earths “out there”

Jonathan Nally — Wed, 28 Mar 2012 10:00:45 +0000

Artist's impression of a planet circling the star Gliese 581. Astronomers estimate there could be tens of billions of "super-Earth" planets in our galaxy.

ROCKY PLANETS NOT MUCH BIGGER THAN EARTH are very common in the habitable zones around faint red stars, say astronomers.

The habitable zone is the distance from a star where it is neither too hot nor too cold for liquid water to exist on the surface of a rocky planet.

The international team used a “planet finder” instrument to estimate that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about 100 in the Sun’s immediate neighbourhood.

This is the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of the stars in the Milky Way.

This first direct estimate of the number of light planets circling red dwarf stars used observations made with the HARPS spectrograph on the 3.6-metre telescope at the European Southern Observatory’s La Silla Observatory in Chile.

Super-Earths abound

The HARPS team has been searching 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.

“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone…,” says Xavier Bonfils (IPAG, Observatoire des Sciences de l’Univers de Grenoble, France), the leader of the team.

Diagram showing the habitable zone (green area) varies depending on the size and temperature of the star. Too close in (red area) and it's too hot; too far out (blue area) and it's too cold.

“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.”

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 stars Gliese 581 and Gliese 667 C respectively.

The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

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 in red dwarf systems.

They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.

On the other hand, more massive planets, similar to Jupiter and Saturn in our Solar System, are found to be rare in red dwarf systems. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1,000 times that of the Earth).

In the zone

As there are many red dwarf stars close to the Sun the new estimate means that there are probably about 100 super-Earth planets in the habitable zones around stars in the neighbourhood of the Sun at distances less than about 30 light-years.

“The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to [a red dwarf] star than the Earth is to the Sun,” says Stéphane Udry (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.”

One of the planets discovered in the HARPS survey of red dwarfs is Gliese 667 Cc. This is the second planet in this triple-star system and it seems to be situated close to the centre of the habitable zone.

This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone.

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.

Gliese 667 Cc 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,” concludes Xavier Delfosse, another member of the team.

Some of these planets are expected to pass in front of, or transit, their parent star as they orbit, and astronomers can use these transits to learn more about the planets’ atmospheres and look for signs of life.

Adapted from information issued by ESO / L. Calçada.

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Galaxy may swarm with ‘nomad’ planets

Jonathan Nally — Sun, 26 Feb 2012 11:18:28 +0000

A new study suggest there could be 100,000 times more free-floating planets in deep space than there are stars. (Artist's impression)

OUR GALAXY may be awash in homeless planets, wandering through space instead of orbiting a star.

In fact, there may be 100,000 times more “nomad planets” in the Milky Way than stars, according to a new study by researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and the SLAC National Accelerator Laboratory.

If observations confirm the estimate, this new class of celestial objects will affect current theories of planet formation and could change our understanding of the origin and abundance of life.

“If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist,” said Louis Strigari, leader of the team that reported the result in a paper submitted to the Monthly Notices of the Royal Astronomical Society.

Although nomad planets don’t bask in the warmth of a star, they may generate heat through internal radioactive decay and tectonic activity.

Universe is riddle with planets

Searches over the past two decades have identified more than 500 planets outside our Solar System, almost all of which orbit stars.

Last year, researchers detected about a dozen nomad planets, using a technique called gravitational microlensing, which looks for stars whose light is momentarily refocused by the gravity of passing planets.

This image is an artistic rendition of a nomad object wandering in interstellar space. The object is intentionally blurry to represent uncertainty about whether it has an atmosphere.

The research produced evidence that roughly two nomads exist for every typical, so-called main-sequence star in our galaxy. The new study estimates that nomads may be up to 50,000 times more common than that.

To arrive at what Strigari himself called “an astronomical number,” the KIPAC team took into account the known gravitational pull of the Milky Way galaxy, the amount of matter available to make such objects, and how that matter might divvy itself up into objects ranging from the size of Pluto to larger than Jupiter.

Not an easy task, considering no one is quite sure how these bodies form. According to Strigari, some were probably ejected from planetary systems, but research indicates that not all of them could have formed in that fashion.

“The universe is riddled with unseen planetary-mass objects that we are just now able to detect,” said Alan Boss of the Carnegie Institution for Science, who was not involved in the research.

Target for new telescopes

A good count, especially of the smaller objects, will have to wait for the next generation of big survey telescopes, especially the space-based Wide-Field Infrared Survey Telescope and the ground-based Large Synoptic Survey Telescope, both set to begin operation in the early 2020s.

The Large Synoptic Survey Telescope, set to begin operation in the early 2020s, will be able to discover numerous nomad planets.

A confirmation of the estimate could lend credence to another possibility mentioned in the paper—that as nomad planets roam their starry pastures, collisions could scatter their microbial flocks to seed life elsewhere.

“Few areas of science have excited as much popular and professional interest in recent times as the prevalence of life in the universe,” said co-author and KIPAC Director Roger Blandford.

“What is wonderful is that we can now start to address this question quantitatively by seeking more of these erstwhile planets and asteroids wandering through interstellar space, and then speculate about hitchhiking bugs.”

Adapted from information issued by Stanford University / LSST Corporation / Greg Stewart / SLAC National Accelerator Laboratory / ESO.

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Mini-Solar System has smallest planets found so far

Jonathan Nally — Wed, 11 Jan 2012 22:47:07 +0000

This artist's concept depicts an itsy bitsy planetary system -- so compact, in fact, that it's more like Jupiter and its moons than a star and its planets. Astronomers using data from NASA's Kepler mission and ground-based telescopes recently confirmed that the system, called KOI-961, hosts the three smallest exoplanets known so far to orbit a star other than our Sun.

ASTRONOMERS USING DATA from NASA’s Kepler mission have discovered the three smallest planets yet detected orbiting a star beyond our Sun. The planets orbit a single star, called KOI-961, and are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars.

All three planets are thought to be rocky like Earth but orbit close to their star, making them too hot to be in the habitable zone, which is the region where liquid water could exist.

Of the more than 700 planets confirmed to orbit other stars, called exoplanets, only a handful are known to be rocky.

“Astronomers are just beginning to confirm the thousands of planet candidates uncovered by Kepler so far,” said Doug Hudgins, Kepler programme scientist at NASA Headquarters in Washington. “Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us.”

Dramatic revision of planets sizes

Kepler searches for planets by continuously monitoring more than 150,000 stars, looking for telltale dips in their brightness caused by crossing, or transiting, planets. At least three transits are required to verify a dip as a planet.

Follow-up observations from ground-based telescopes also are needed to confirm the discoveries.

The latest discovery comes from a team led by astronomers at the California Institute of Technology in Pasadena. The team used data publicly released by the Kepler mission, along with follow-up observations from the Palomar Observatory, near San Diego, and the W.M. Keck Observatory atop Mauna Kea in Hawaii.

In many ways the KOI-961 planetary system is similar to Jupiter and the largest four of its many moons. (Artist's conception)

Their measurements dramatically revised the sizes of the planets from what was originally estimated, revealing their small nature.

The three planets are very close to their star, taking less than two days to orbit around it. The KOI-961 star, which is located about 130 light-years away, is a red dwarf with a diameter one-sixth that of our Sun, making it just 70 percent bigger than Jupiter.

Mini-Solar Systems could be everywhere

“This is the tiniest [planetary] system found so far,” said John Johnson, the principal investigator of the research from NASA’s Exoplanet Science Institute at the California Institute of Technology in Pasadena.

“It’s actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy.”

Red dwarfs are the most common kind of star in our Milky Way galaxy. The discovery of three rocky planets around one red dwarf suggests that the galaxy could be teeming with similar rocky planets.

“These types of systems could be ubiquitous in the universe,” said Phil Muirhead, lead author of the new study from Caltech. “This is a really exciting time for planet hunters.”

First Earth-sized planets

The discovery follows a string of recent milestones for the Kepler mission. In December 2011, scientists announced the mission’s first confirmed planet in the habitable zone of a Sun-like star: a planet 2.4 times the size of Earth called Kepler-22b.

Later in the month, the team announced the discovery of the first Earth-size planets orbiting a Sun-like star outside our Solar System, called Kepler-20e and Kepler-20f.

The smallest known exoplanets, or planets outside the Solar System, compared with Mars and Earth.

For the latest discovery, the team obtained the sizes of the three planets (called KOI-961.01, KOI-961.02 and KOI-961.03) with the help of a well-studied twin star to KOI-961, Barnard’s Star.

By better understanding the KOI-961 star, they could then determine how big the planets must be to have caused the observed dips in starlight.

In addition to the Kepler observations and ground-based telescope measurements, the team used modelling techniques to confirm the planet discoveries.

Prior to these confirmed planets, only six other planets had been confirmed using the Kepler public data.

Adapted from information issued by NASA / JPL-Caltech.

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First Earth-size planets orbiting a Sun-like star

Jonathan Nally — Wed, 21 Dec 2011 02:35:23 +0000

Comparison of newfound planets, Kepler-20e and Kepler-20f, with Venus and Earth from our Solar System. The two Kepler planets are the first Earth-size worlds found circling a Sun-like star elsewhere in our galaxy.

First Earth-size planets found orbiting another Sun-like star
The system is 1,000 light-years from Earth
Three other planets already known in this system

NASA’S KEPLER MISSION has discovered the first Earth-size planets orbiting a Sun-like star outside our Solar System. The planets, called Kepler-20e and Kepler-20f, are too close to their star to be in the so-called habitable zone where liquid water could exist on a planet’s surface, but they are the smallest exoplanets ever confirmed circling a star like our Sun.

The discovery marks the next important milestone in the search for planets like Earth.

The new planets are thought to be rocky. Kepler-20e is slightly smaller than Venus, measuring 0.87 times the radius of Earth. Kepler-20f is a bit larger than Earth, measuring 1.03 times its radius.

Both planets reside in a five-planet system called Kepler-20, approximately 1,000 light-years from Earth.

Kepler-20e orbits its parent star every 6.1 days and Kepler-20f every 19.6 days. These short orbital periods mean the planets circle close to their star, and are therefore very hot, inhospitable worlds.

Kepler-20f, at 800 degrees Fahrenheit, is similar to an average day on the planet Mercury. The surface temperature of Kepler-20e, at more than 760 degrees Celsius, would melt glass.

Earth-size planets now known to exist

“The primary goal of the Kepler mission is to find Earth-sized planets in the habitable zone,” said Francois Fressin of the Harvard-Smithsonian Centre for Astrophysics, and lead author of a new study published in the journal Nature.

“This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them.”

Artist's impression of Kepler-20e, which is about 0.87 times the radius of Earth.

The Kepler-20 system includes three other planets that are larger than Earth but smaller than Neptune. Kepler-20b, the closest planet, Kepler-20c, the third planet, and Kepler-20d, the fifth planet, orbit their star every 3.7, 10.9 and 77.6 days.

All five planets have orbits lying roughly within Mercury’s orbit in our Solar System. The host star belongs to the same G-type class as our Sun, although it is slightly smaller and cooler.

Odd planetary system

The system has an unexpected arrangement. In our Solar System, small, rocky worlds orbit close to the Sun and large, gaseous worlds orbit farther out. In comparison, the planets of Kepler-20 are organised in alternating size: large, small, large, small and large.

“The Kepler data are showing us some planetary systems have arrangements of planets very different from that seen in our Solar System,” said Jack Lissauer, planetary scientist and Kepler science team member at NASA’s Ames Research Centre.

“The analysis of Kepler data continue to reveal new insights about the diversity of planets and planetary systems within our galaxy.”

Scientists are not certain how the system evolved but they do not think the planets formed in their existing locations.

They theorise the planets formed farther from their star and then migrated inward, likely through interactions with the disc of material from which they originated.

This allowed the worlds to maintain their regular spacing despite alternating sizes.

Artist's impression of Kepler-20f, which is about 1.03 times as wide as Earth.

Cosmic game of hide and seek

The Kepler space telescope detects planets and planet candidates by measuring dips in the brightness of more than 150,000 stars to search for planets crossing in front, or transiting, their stars.

The Kepler science team requires at least three transits to verify a signal as a planet.

On December 5 the team announced the discovery of Kepler-22b in the habitable zone of its parent star. It is likely to be too large to have a rocky surface.

While Kepler-20e and Kepler-20f are Earth-size, they are too close to their parent star to have liquid water on the surface.

“In the cosmic game of hide and seek, finding planets with just the right size and just the right temperature seems only a matter of time,” said Natalie Batalha, Kepler deputy science team lead and professor of astronomy and physics at San Jose State University.

“We are on the edge of our seats knowing that Kepler’s most anticipated discoveries are still to come.”

Adapted from information issued by NASA/Ames/JPL-Caltech.

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Kepler finds planet in the habitable zone

Jonathan Nally — Mon, 05 Dec 2011 21:37:21 +0000

This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a Sun-like star. It is the first planet that NASA's Kepler mission has confirmed to orbit in a star's habitable zone—the region around a star where liquid water, a requirement for life on Earth, could persist. The planet is 2.4 times the size of Earth.

“Super Earth” found in its star’s “habitable zone”
Located 600 light-years away from our planet
Scientists studying 2,326 planet candidates

NASA’S KEPLER MISSION has confirmed its first planet in the “habitable zone,” the region around a star where liquid water could exist on a planet’s surface.

Kepler also has discovered more than 1,000 new planet candidates, nearly doubling its previously known count.

Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star. Candidates require follow-up observations to verify they are actual planets.

The newly confirmed planet, Kepler-22b, is the smallest yet found to orbit in the middle of the habitable zone of a star similar to our Sun. The planet is about 2.4 times the radius of Earth.

Scientists don’t yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets.

Clear confirmation

Previous research hinted at the existence of near-Earth-size planets in habitable zones, but clear confirmation proved elusive.

Two other small planets orbiting stars smaller and cooler than our Sun recently were confirmed on the very edges of the habitable zone, with orbits more closely resembling those of Venus and Mars.

“This is a major milestone on the road to finding Earth’s twin,” said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington.

Artist's impression of the Kepler space telescope

“Kepler’s results continue to demonstrate the importance of NASA’s science missions, which aim to answer some of the biggest questions about our place in the universe.”

Kepler discovers planets and planet candidates by measuring dips in the brightness of more than 150,000 stars to search for planets that cross in front, or “transit,” the stars. Kepler requires at least three transits to verify a signal as a planet.

Follow-up with ground-based telescopes

“Fortune smiled upon us with the detection of this planet,” said William Borucki, Kepler principal investigator at NASA Ames Research Centre, who led the team that discovered Kepler-22b.

“The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season.”

The Kepler science team uses ground-based telescopes and NASA’s Spitzer Space Telescope to review observations on planet candidates the spacecraft finds.

The star field that Kepler observes in the constellations Cygnus and Lyra can only be seen from ground-based observatories in the Northern Hemisphere’s spring through early autumn.

The data from these other observations help determine which candidates can be validated as planets.

Over 1,000 new planet candidates

Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a Sun-like star resembles that of our world. The planet’s host star belongs to the same class as our Sun, called G-type, although it is slightly smaller and cooler.

Of the 54 habitable zone planet candidates reported in February 2011, Kepler-22b is the first to be confirmed.

The Kepler team is hosting its inaugural science conference at Ames this week, announcing 1,094 new planet candidate discoveries.

This diagram compares our own Solar System to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth.

Since the last catalogue was released in February, the number of planet candidates identified by Kepler has increased by 89 percent and now totals 2,326.

Of these, 207 are approximately Earth-size, 680 are super Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter.

The findings, based on observations conducted May 2009 to September 2010, show a dramatic increase in the numbers of smaller-size planet candidates.

Abundant Earths out there?

Kepler observed many large planets in small orbits early in its mission, which were reflected in the February data release.

Having had more time to observe three transits of planets with longer orbital periods, the new data suggest that planets one to four times the size of Earth may be abundant in the galaxy.

The number of Earth-size, and super Earth-size candidates, has increased by more than 200 and 140 percent since February, respectively.

There are 48 planet candidates in their star’s habitable zone.

While this is a decrease from the 54 reported in February, the Kepler team has applied a stricter definition of what constitutes a habitable zone in the new catalogue, to account for the warming effect of atmospheres, which would move the zone away from the star, out to longer orbital periods.

“The tremendous growth in the number of Earth-size candidates tells us that we’re honing in on the planets Kepler was designed to detect: those that are not only Earth-size, but also are potentially habitable,” said Natalie Batalha, Kepler deputy science team lead at San Jose State University.

“The more data we collect, the keener our eye for finding the smallest planets out at longer orbital periods.”

Adapted from information issued by NASA/Ames/JPL-Caltech.

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18 new giant planets found

Jonathan Nally — Sat, 03 Dec 2011 08:10:25 +0000

The 18 new planets were detected using the Keck Observatory in Hawaii.

18 new planets found orbiting “retired” stars
50 per cent increase in this class of planets
Competing ideas for how giant planets form

DISCOVERIES OF NEW PLANETS just keep coming and coming. Take, for instance, the 18 recently found by a team of astronomers led by scientists at the California Institute of Technology (Caltech).

“It’s the largest single announcement of planets in orbit around stars more massive than the Sun, aside from the discoveries made by the Kepler [space telescope] mission,” says John Johnson, assistant professor of astronomy at Caltech.

Using the Keck Observatory in Hawaii—with follow-up observations using the McDonald and Fairborn Observatories in Texas and Arizona, respectively—the researchers surveyed about 300 stars.

They focused on “retired” A-type stars that are more than 1.5 times more massive than the Sun. These stars are just past the main stage of their life—hence, “retired”—and are now puffing up into what’s called sub-giant stars.

The astronomers searched for stars of this type that wobble, which could be caused by the gravitational tug of an orbiting planet.

By searching the stars’ spectra for Doppler shifts—the lengthening and contracting of wavelengths due to motion away from and toward the observer—the team detected 18 planets with masses similar to Jupiter’s.

This marks a 50 percent increase in the number of known planets orbiting massive stars.

There are competing ideas about how giant planets form.

Competing planet formation concepts

The researchers say the findings also lend further support to the idea that planets grow from seed particles that accumulate gas and dust in a cloud surrounding a newborn star.

In this concept, tiny particles start to clump together, eventually snowballing into a planet. If this is correct, the characteristics of the resulting planetary system—such as the number and size of the planets, or their orbital shapes—will depend on the mass of the star.

In another theory, planets form when large amounts of gas and dust in the cloud spontaneously collapse into big, dense clumps that then become planets. But in this picture, it turns out that the mass of the host star doesn’t affect the kinds of planets that are produced.

So far, as the number of discovered planets has grown, astronomers are finding that stellar mass does seem to be important in determining the prevalence of giant planets. The newly discovered planets further support this pattern—and are therefore consistent with the first theory, the one stating that planets are born from seed particles.

Nature vs nurture?

There’s another interesting twist, Johnson adds: “Not only do we find Jupiter-like planets more frequently around massive stars, but we find them in wider orbits.” If you took a sample of 18 planets around Sun-like stars, he explains, half of them would orbit close to their stars. But in the cases of the new planets, all are farther away.

Something stops giant planets from spiralling into their host stars.

In systems with Sun-like stars, gas giants like Jupiter acquire close orbits when they migrate toward their stars. According to theories of planet formation, gas giants could only have formed far from their stars, where it’s cold enough for their constituent gases and ices to exist.

So for gas giants to orbit nearer to their stars, gravitational interactions have to have taken place to pull the planets in. Then, some other mechanism—perhaps the star’s magnetic field—has to kick in to stop them from spiralling into a fiery death.

The question, Johnson says, is why this doesn’t seem to happen with so-called “hot Jupiters” orbiting massive stars, and whether that dearth is due to nature or nurture.

In the nature explanation, Jupiter-like planets that orbit massive stars just wouldn’t ever migrate inward. In the nurture interpretation, the planets would move in, but there would be nothing to prevent them from plunging into their stars. Or perhaps the stars evolve and swell up, consuming their planets.

Adapted from information issued by Caltech. Images courtesy Rick Peterson / W.M. Keck Observatory / Gbacon / STScI / AVL.

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Over 50 new planets discovered

Jonathan Nally — Mon, 19 Sep 2011 03:42:21 +0000

ASTRONOMERS HAVE ANNOUNCED a rich haul of more than 50 new exoplanets, including 16 super-Earths, one of which orbits at the edge of the habitable zone of its star. By studying the properties of all the planets found so far by this project, the team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.

The discoveries were made using the HARPS spectrograph on the 3.6-metre telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile.

The new exoplanets orbit nearby stars, and include sixteen super-Earths. This is the largest number of such planets ever announced at one time.

Planets with a mass between one and ten times that of the Earth are called super-Earths. There are no such planets in our Solar System, but they appear to be very common around other stars. Discoveries of such planets in the habitable zones around their stars are very exciting because—if the planet were rocky and had water, like Earth—they could potentially be an abode of life.

One of the newly discovered planets, HD 85512 b, is estimated to be only 3.6 times the mass of the Earth and is located at the edge of its star’s habitable zone — a narrow zone around a star in which water may be present in liquid form if conditions are right.

Adapted from information issued by ESO / M. Kornmesser.

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“Star Wars” planet discovered

Jonathan Nally — Thu, 15 Sep 2011 21:52:12 +0000

This artist's concept shows Kepler-16b (black circle), dubbed the most "Tatooine-like" planet yet found in our galaxy because it orbits two stars (a big yellow one, and a small red one). Tatooine is the name of Luke Skywalker's home world in the science fiction movie Star Wars. In this case, the planet it not thought to be habitable. It is a cold world, with a gaseous surface.

THE EXISTENCE OF A WORLD with a double sunset, as portrayed in the film Star Wars more than 30 years ago, is now scientific fact. NASA’s Kepler mission has made the first unambiguous detection of a Saturn-sized ‘circumbinary’ planet—a planet orbiting two stars—200 light-years from Earth.

Unlike Star Wars’ Tatooine, the planet is cold, gaseous and not thought to harbour life, but its discovery demonstrates the diversity of planets in our galaxy.

Previous research has hinted at the existence of circumbinary planets, but clear confirmation proved elusive. Kepler detected such a planet, known as Kepler-16b, by observing transits, where the brightness of a parent star dims from the planet crossing in front of it.

“This discovery confirms a new class of planetary systems that could harbour life,” Kepler principal investigator William Borucki said. “Given that most stars in our galaxy are part of a binary system, this means the opportunities for life are much broader than if planets form only around single stars.”

“This milestone discovery confirms a theory that scientists have had for decades but could not prove until now.”

Hunting in the ‘habitable zone’

A research team led by Laurance Doyle of the SETI Institute in Mountain View, California, used data from the Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets.

Kepler is the first NASA mission capable of finding Earth-size planets in or near the “habitable zone,” the region in a planetary system where liquid water can exist on the surface of the orbiting planet.

This artist's concept illustrates Kepler-16b, the first planet known to definitively orbit two stars—what's called a circumbinary planet. The planet, which can be seen in the foreground, was discovered by NASA's Kepler mission.

Scientists detected the new planet in the Kepler-16 system, a pair of orbiting stars that eclipse each other from our vantage point on Earth.

When the smaller star partially blocks the larger star, a primary eclipse occurs, and a secondary eclipse occurs when the smaller star is occulted, or completely blocked, by the larger star.

Astronomers further observed that the brightness of the system dipped even when the stars were not eclipsing one another, hinting at the presence of a third body.

Two stars for the price of one

The additional dimming in brightness events, called the tertiary and quaternary eclipses, reappeared at irregular intervals of time, indicating the stars were in different positions in their orbit each time the third body passed.

This showed the third body was circling, not just one, but both stars, in a wide circumbinary orbit.

The gravitational tug on the stars, measured by changes in their eclipse times, was a good indicator of the mass of the third body. Only a very slight gravitational pull was detected, one that only could be caused by a small mass.

“Most of what we know about the sizes of stars comes from such eclipsing binary systems, and most of what we know about the size of planets comes from transits,” said Doyle, who also is the lead author and a Kepler participating scientist.

“Kepler-16 combines the best of both worlds, with stellar eclipses and planetary transits in one system.”

Here’s a short animation that shows the planet’s strange orbit:

More than we can imagine

This discovery confirms that Kepler-16b is an inhospitable, cold world about the size of Saturn and thought to be made up of about half rock and half gas.

The parent stars are smaller than our Sun. One is 69 percent the mass of the Sun and the other only 20 percent.

Kepler-16b orbits around both stars every 229 days, similar to Venus’ 225-day orbit, but lies outside the system’s habitable zone, where liquid water could exist on the surface, because the stars are cooler than our Sun.

“Working in film, we often are tasked with creating something never before seen,” said visual effects supervisor John Knoll of Industrial Light & Magic, a division of Lucasfilm Ltd., in San Francisco. “However, more often than not, scientific discoveries prove to be more spectacular than anything we dare imagine.”

“There is no doubt these discoveries influence and inspire storytellers,” added Knoll. “Their very existence serves as cause to dream bigger and open our minds to new possibilities beyond what we think we know.’”

Adapted from information issued by NASA. Images courtesy NASA / JPL-Caltech / T. Pyle, and NASA / JPL-Caltech / R. Hurt.

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Unseen planet uncovered

Jonathan Nally — Wed, 14 Sep 2011 00:30:00 +0000

The "invisible" world Kepler-19c, seen in the foreground of this artist's conception, was discovered solely through its gravitational influence on the companion world Kepler-19b—seen as a dot crossing the star's face. Kepler-19b is slightly more than twice the diameter of Earth, and is probably a "mini-Neptune." Nothing is known about Kepler-19c, other than that it exists.

USUALLY, RUNNING FIVE MINUTES LATE is a bad thing since you might lose your dinner reservation or miss out on tickets to the latest show. But when a planet runs five minutes late, astronomers get excited because it suggests that another world is nearby.

NASA’s Kepler spacecraft has spotted a planet that alternately runs late and early in its orbit because the gravity of a second, “invisible” world is tugging on it. This is the first definite detection of a previously unknown planet using this method. No other technique could have found the unseen companion.

“This invisible planet makes itself known by its influence on the planet we can see,” said astronomer Sarah Ballard of the Harvard-Smithsonian Centre for Astrophysics (CfA). Ballard is lead author on the study, which has been accepted for publication in The Astrophysical Journal.

“It’s like having someone play a prank on you by ringing your doorbell and running away. You know someone was there, even if you don’t see them when you get outside,” she added.

Found in transit

Both the seen and unseen worlds orbit the Sun-like star Kepler-19, which is 650 light-years from Earth.

Kepler locates planets by looking for a star that dims slightly as a planet transits the star—that is, passing across the star’s face from our point of view.

Transits give one crucial piece of information—the planet’s physical size. The greater the dip in light, the larger the planet relative to its star.

However, the planet and star must line up exactlyfor us to see a transit.

Artist's impression of the Kepler spacecraft

In this case, the known planet, called Kepler-19b, transits its star every 9 days and 7 hours. It orbits the star at a distance of 13.5 million kilometres, where it is heated to a temperature of about 480 degrees Celsius.

Kepler-19b has a diameter of 29,000 kilometres, making it slightly more than twice the size of Earth. It may resemble a “mini-Neptune,” however its mass and composition remain unknown.

Given away by gravity

If Kepler-19b were alone, each transit would follow the next like clockwork. Instead, the transits come up to five minutes early or five minutes late.

Such transit timing variations show that another world’s gravity—dubbed Kepler-19c—is pulling on Kepler-19b, alternately speeding it up or slowing it down.

Historically, the planet Neptune was discovered similarly. Astronomers tracking Uranus noticed that its orbit didn’t match predictions. They realised that a more distant planet might be nudging Uranus and calculated the expected location of the unseen world. Telescopes soon spotted Neptune near its predicted position.

Multiple p

“This method holds great promise for finding planets that can’t be found otherwise,” stated Harvard astronomer and co-author David Charbonneau.

Very little known

So far, astronomers don’t know anything about the invisible world Kepler-19c, other than that it exists. It weighs too little to gravitationally tug the star enough for them to measure its mass.

And Kepler hasn’t detected it transiting the star, suggesting that its orbit is tilted relative to Kepler-19b.

“Kepler-19c has multiple personalities consistent with our data. For instance, it could be a rocky planet on a circular 5-day orbit, or a gas-giant planet on an oblong 100-day orbit,” said co-author Daniel Fabrycky of the University of California, Santa Cruz (UCSC).

The Kepler spacecraft will continue to monitor Kepler-19 throughout its mission. Those additional data will help nail down the orbit of Kepler-19c.

Future ground-based instruments will attempt to measure the mass of Kepler-19c. Only then will we have a clue to the nature of this invisible world.

Adapted from information issued by the Harvard-Smithsonian Centre for Astrophysics. Graphics by David A. Aguilar (CfA) and NASA.

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