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Mini-Solar System has smallest planets found so far

Artist's concept of the KOI-961 system

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.

Artist's conception comparing the KOI-961 system to the Jupiter system

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.

Chart comparing the smallest known exoplanets with Mars and Earth

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

Comparison of Kepler-20e and Kepler-20f with Venus and Earth

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

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

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

Artist's conception illustrates Kepler-22b

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

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.

Diagram comparing our Solar System to Kepler-22

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

Keck Observatory

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.

Artist's impression of an exoplanet

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.

Artist's impression of an exoplanet

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

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

Artist's concept of Kepler-16b

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.

Artist's concept of Kepler-16b

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

Artist's conception of exoplanet Kepler-19c

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

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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Alien world is blacker than coal

Artist's conception of exoplanet TrES-2b

Exoplanet TrES-2b (artist's conception) is darker than the blackest coal. This Jupiter-sized world reflects less than 1% of the light that falls on it, making it blacker than any planet or moon in our Solar System.

  • Exoplanet TrES-2b orbits a star 750 light-years from Earth
  • Reflects less than one percent of the starlight falling on it
  • The Jupiter-sized world puts out only a faint red glow

ASTRONOMERS HAVE DISCOVERED the darkest known exoplanet—a distant, Jupiter-sized gas giant known as TrES-2b. Their measurements show that TrES-2b reflects less than one percent of the starlight falling on it, making it blacker than coal or any planet or moon in our Solar System.

“TrES-2b is considerably less reflective than black acrylic paint, so it’s truly an alien world,” said astronomer David Kipping of the Harvard-Smithsonian Centre for Astrophysics (CfA), lead author on the paper reporting the research.

In our Solar System, Jupiter is swathed in bright clouds of ammonia that reflect more than a third of the sunlight reaching it. In contrast, TrES-2b (which was discovered in 2006 by the Trans-Atlantic Exoplanet Survey, or TrES) lacks reflective clouds due to its high temperature.

Pitch black planet … almost

TrES-2b orbits its star at a distance of only 4.8 million kilometres. The star’s intense light heats TrES-2b to a temperature of more than 1,000° Celsius—much too hot for ammonia clouds.

Instead, its exotic atmosphere contains light-absorbing chemicals like vaporised sodium and potassium, or gaseous titanium oxide. Yet none of these chemicals fully explain the extreme blackness of TrES-2b.

“It’s not clear what is responsible for making this planet so extraordinarily dark,” stated co-author David Spiegel of Princeton University. “However, it’s not completely pitch black. It’s so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove.”

Artist's impression of the Kepler spacecraft

Artist's impression of the Kepler spacecraft

One-sided world

Kipping and Spiegel determined the reflectivity of TrES-2b using data from NASA’s Kepler spacecraft. Kepler is designed to measure the brightnesses of distant stars with extreme precision.

The team monitored the brightness of the TrES-2 system as the planet orbited its star. They detected a subtle dimming and brightening due to the planet’s changing phase.

TrES-2b is believed to be tidally locked like our moon, so one side of the planet always faces the star. And like our moon, the planet shows changing phases as it orbits its star. This causes the total brightness of the star plus planet to vary slightly.

“By combining the impressive precision from Kepler with observations of over 50 orbits, we detected the smallest-ever change in brightness from an exoplanet—just 6 parts per million,” said Kipping. “In other words, Kepler was able to directly detect visible light coming from the planet itself.”

More where this one came from?

The extremely small fluctuations proved that TrES-2b is incredibly dark. A more reflective world would have shown larger brightness variations as its phase changed.

Kepler has located more than 1,200 planetary candidates in its field of view. Additional analysis will reveal whether any other unusually dark planets lurk in that data.

TrES-2b orbits the star GSC 03549-02811, which is located about 750 light-years from Earth. (One light-year is about 10 trillion kilometres.)

Adapted from information issued by CfA. Images courtesy David A. Aguilar (CfA) / NASA.

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Exoplanets have unearthly light shows

Artist's concept of a 'hot Jupiter' planet

Artist's concept of a 'hot Jupiter' planet with two moons and a Sun-like star. The planet is cloaked in brilliant aurorae—100-1000 times brighter than Earth's—triggered by stellar storms.

BEINGS LIVING ON ‘HOT JUPITER’ PLANETS could be treated to a dazzling nightly light show a thousand times better than Earth’s Northern and Southern Lights.

Earth’s aurorae provide a dazzling light show to people living in the polar regions, with shimmering curtains of green and red undulating across the sky like a living creature.

But new research shows that aurorae on ‘hot Jupiter’ planets closely orbiting distant stars could be 100-1000 times brighter than Earthly aurorae. They also would ripple from equator to poles (due to the planet’s proximity to any stellar eruptions), treating the entire planet to an otherworldly spectacle.

“I’d love to get a reservation on a tour to see these aurorae!” said lead author Ofer Cohen, a SHINE-NSF postdoctoral fellow at the Harvard-Smithsonian Centre for Astrophysics (CfA).

Gigantic stellar blasts

Earth’s aurorae are created when energetic particles from the Sun slam into our planet’s magnetic field. The field guides the particles toward the poles, where they smash into Earth’s atmosphere, causing air molecules to glow like a neon sign.

The same process can occur on planets orbiting distant stars, known as exoplanets.

Aurora Australis seen from the International Space Station

The Southern Lights or Aurora Australis seen from the International Space Station on July 14, 2011.

Particularly strong aurorae result when Earth is hit by a coronal mass ejection or CME—a gigantic blast that sends billions of tonnes of solar plasma (electrically charged, hot gas) into the Solar System.

A CME can disrupt Earth’s magnetosphere—the bubble of space protected by Earth’s magnetic field—causing a geomagnetic storm. In 1989, a CME hit Earth with such force that the resulting geomagnetic storm blacked out huge regions of Quebec.

Planets in the firing line

Cohen and his colleagues used computer models to study what would happen if a gas giant planet in a close orbit, just a few million kilometres from its star, were hit by a stellar eruption.

He wanted to learn the effect on the exoplanet’s atmosphere and surrounding magnetosphere.

The alien gas giant would be subjected to extreme forces. In our Solar System, a CME spreads out as it travels through space, so it’s more diffuse once it reaches us.

Aurora planet animation

In this animation, stunning aurorae (pink/purple) ripple around a 'hot Jupiter' planet.

A ‘hot Jupiter’ would feel a stronger and more focused blast, like the difference between being 100 kilometres from an erupting volcano or one kilometre away.

“The impact to the exoplanet would be completely different than what we see in our Solar System, and much more violent,” said co-author Vinay Kashyap of CfA.

Yet despite the extreme forces involved, the exoplanet’s magnetic field would shield its atmosphere from erosion.

Too close for comfort

This work has important implications for the habitability of rocky worlds orbiting distant stars. Since red dwarf stars are the most common stars in our galaxy, astronomers have suggested focusing on them in the search for Earth-like worlds.

However since a red dwarf is cooler than our Sun, a rocky planet would have to orbit very close to the star to be warm enough for water to exist as a liquid. There, it would be subjected to the sort of violent stellar eruptions Cohen and his colleagues studied.

Their future work will examine whether rocky worlds could shield themselves from such eruptions.

Adapted from information issued by the Harvard-Smithsonian Centre for Astrophysics. Images courtesy David A. Aguilar (CfA). Animation produced by Hyperspective Studios.

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Aussie scope to be upgraded

Artist's impression of an exoplanet

The University of Western Australia's 1-metre robotic Zadko Telescope will search for new planets, exploding stars and space junk.

THE UNIVERSITY OF WESTERN AUSTRALIA’S (UWA) Gingin-based Zadko Telescope will get a clearer view thanks to an agreement signed between UWA and the WA Department of Environment and Conservation (DEC) that enhances the partnership between these two organisations.

The 1-metre robotic Zadko Telescope is currently housed in an inadequate dome that is not up to the rigours of robotic operation.

Zadko Telescope

Zadko Telescope

Under the collaboration between DEC and UWA, DEC will contribute $100,000 towards the construction of a new building where the telescope will reach its full potential.

DEC astronomer Ralph Martin of Perth Observatory said: “Part of the collaboration with UWA includes searching for undiscovered planets orbiting distant stars.”

Zadko Telescope Director, UWA Associate Professor David Coward, said the new Zadko Observatory building would significantly enhance the research capabilities of DEC and UWA.

“The upgrade will also strengthen our collaboration with TAROT (Fast Action Telescopes for Transient Objects), the French international network of robotic telescopes,” Professor Coward said. “Our international team will be on the hunt for new planets and exploding stars.”

“The new Zadko Observatory building will also allow our collaboration to scan the sky for space junk that threatens the satellites on which we depend for almost every aspect of daily life from telecommunications, weather reports, security and navigation, to information about mineral deposits.”

Adapted from information issued by UWA.

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