Universe Today

January 9, 2013December 23, 2015 by Jason Major

Clouds of Sand and Iron Swirl in a Failed Star’s Extreme Atmosphere

This artist's conception illustrates the brown dwarf named 2MASSJ22282889-431026. NASA's Hubble and Spitzer space telescopes observed the object to learn more about its turbulent atmosphere. Brown dwarfs are more massive and hotter than planets but lack the mass required to become sizzling stars. Their atmospheres can be similar to the giant planet Jupiter's. Spitzer and Hubble simultaneously observed the object as it rotated every 1.4 hours. The results suggest wind-driven, planet-size clouds. Image credit: — This artist's conception illustrates what a "hot jupiter" might look like.

Artist’s concept of brown dwarf 2MASSJ22282889-431026 (NASA/JPL-Caltech)

The complex weather patterns within the atmosphere of a rapidly-rotating brown dwarf have been mapped in the highest detail ever by researchers using the infrared abilities of NASA’s Spitzer and Hubble space telescopes… talk about solar wind!

Sometimes referred to as failed stars, brown dwarfs form from condensing gas and dust like regular stars but never manage to gather enough mass to ignite full-on hydrogen fusion in their cores. As a result they more resemble enormous Jupiter-like planets, radiating low levels of heat while possessing bands of wind-driven eddies in their upper atmospheric layers.

Although brown dwarfs are by their nature very dim, and thus difficult to observe in visible wavelengths of light, their heat can be detected by Hubble and the Spitzer Space Telescope — both of which can “see” just fine in near- and far-infrared, respectively.

Led by researchers from the University of Arizona, a team of astronomers used these orbiting observatories on July 7, 2011 to measure the light curves from a brown dwarf named 2MASSJ22282889-431026 (2M2228 for short.) What they found was that while 2M2228 exhibited periodic brightening in both near- and far-infrared over the course of its speedy 1.43-hour rotation, the amount and rate of brightening varied between the different wavelengths detected by the two telescopes.

“With Hubble and Spitzer, we were able to look at different atmospheric layers of a brown dwarf, similar to the way doctors use medical imaging techniques to study the different tissues in your body.”

– Daniel Apai, principal investigator, University of Arizona

This unexpected variance — or phase shift — most likely indicates different layers of cloud material and wind velocities surrounding 2M2228, swirling around the dwarf star in very much the same way as the stormy cloud bands seen on Jupiter or Saturn.

But while the clouds on Jupiter are made of gases like ammonia and methane, the clouds of 2M2228 are made of much more unusual stuff.

“Unlike the water clouds of Earth or the ammonia clouds of Jupiter, clouds on brown dwarfs are composed of hot grains of sand, liquid drops of iron, and other exotic compounds,” said Mark Marley, a research scientist at NASA’s Ames Research Center and co-author of the paper. “So this large atmospheric disturbance found by Spitzer and Hubble gives a new meaning to the concept of extreme weather.”

While it might seem strange to think about weather on a star, remember that brown dwarfs are much more gas planet-like than “real” stars. Although the temperatures of 1,100–1,600 ºF (600–700 ºC) found on 2M2228 might sound searingly hot, it’s downright chilly compared to even regular stars like our Sun, which has an average temperature of nearly 10,000 ºF (5,600 ºC). Different materials gather at varying layers of its atmosphere, depending on temperature and pressure, and can be penetrated by different wavelengths of infrared light — just like gas giant planets.

“What we see here is evidence for massive, organized cloud systems, perhaps akin to giant versions of the Great Red Spot on Jupiter,” said Adam Showman, a theorist at the University of Arizona involved in the research. “These out-of-sync light variations provide a fingerprint of how the brown dwarf’s weather systems stack up vertically. The data suggest regions on the brown dwarf where the weather is cloudy and rich in silicate vapor deep in the atmosphere coincide with balmier, drier conditions at higher altitudes — and vice versa.”

The team’s results were presented today, January 8, during the 221st meeting of the American Astronomical Society in Long Beach, CA.

Read more on the Spitzer site, and find the team’s paper in PDF form here.

Inset image: the anatomy of a brown dwarf’s atmosphere (NASA/JPL).

January 9, 2013December 23, 2015 by Nancy Atkinson

Astronomers Find a “Spine” Along Spiral Arms of the Milky Way

Researchers have identified the first "bone" of the Milky Way - a long tendril of dust and gas that appears dark in this infrared image from the Spitzer Space Telescope. Running horizontally along this image, the "bone" is more than 300 light-years long but only 1 or 2 light-years wide. It contains about 100,000 suns' worth of material. Credit: NASA/JPL/SSC

Astronomers have found what may be considered a piece of a galactic skeleton; a dark structure of gas and dust that might provide a backbone on which one of the spiral arms extend from the central bar of the Milky Way galaxy.

“This ‘bone’ is likely made from high density gas — the type that forms stars — and while the feature that we see is a sinuous distinction you get from dust, there is a huge amount of gas,” said Alyssa Goodman of the Harvard-Smithsonian Center for Astrophysics (CfA) at a press conference at the American Astronomical Society meeting in Long Beach, California today. “But we just don’t know yet what it is.”

A flipped image of IC342, in which a 'backbone' structure can be seen in the spiral arms. Credit: Jarret et al. 2012; WISE Enhanced Resolution Galaxy Atlas.

While this is the first time such a structure has been seen in our own galaxy, other spiral galaxies seemingly display internal “endoskeletons.” Observations, especially at infrared wavelengths of light, have found long skinny features jutting between galaxies’ spiral arms. These relatively straight structures are much less massive than the curving spiral arms.

Goodman said that since we view the Milky Way from the inside, its exact structure is difficult to determine, but it is thought to have a central bar and two major spiral arms that wrap around its disk.

A team of astronomers first spotted the galactic bone while studying a dust cloud nicknamed “Nessie,” since its shape is reminiscent of the Loch Ness monster. The central part of the “Nessie” bone was discovered in Spitzer Space Telescope data in 2010 by James Jackson (Boston University). With further analysis, Goodman’s team determined the dark cloud goes way beyond the original section that was first found, and is as much as eight times longer than Jackson’s original sighting.

Radio emissions from molecular gas show that the feature is not a chance projection of material on the sky, but instead a real feature. Not only is “Nessie” in the galactic plane, but also it extends much longer than anyone anticipated. This slender bone of the Milky Way is more than 300 light-years long but only 1 or 2 light-years wide. It contains about 100,000 suns’ worth of material, and now looks more like a cosmic snake.

“This bone is much more like a fibula – the long skinny bone in your leg – than it is like the tibia, or big thick leg bone,” Goodman said.

It lies along the plane of the Milky Way, and since our vantage point is just above the the plane, Goodman and her team are hopeful that the skeleton may be able to be mapped.

“It’s possible that the ‘Nessie’ bone lies within a spiral arm, or that it is part of a web connecting bolder spiral features. Our hope is that we and other astronomers will find more of these features, and use them to map the skeleton of the Milky Way in 3-D,” she said.

The team’s paper is not quite finished yet, but it is online on the new open source scientific collaboration site, Authorea.

For more information, visit http://milkywaybones.org.

Source: CfA, AAS

January 8, 2013December 23, 2015 by Nancy Atkinson

Chunks of Frozen Hydrocarbons May be Floating on Titan’s Lakes

This artist's concept envisions what hydrocarbon ice forming on a liquid hydrocarbon sea of Saturn's moon Titan might look like. Image credit: NASA/JPL-Caltech/USGS

The Cassini spacecraft has been getting some strange data from Saturn’s moon Titan, and scientists will soon test out whether there might be “icebergs” of sorts, blocks of hydrocarbon ice floating on the surface of the lakes and seas of liquid hydrocarbon.

“One of the most intriguing questions about these lakes and seas is whether they might host an exotic form of life,” said Jonathan Lunine, a paper co-author and Cassini interdisciplinary Titan scientist at Cornell University, Ithaca, N.Y. “And the formation of floating hydrocarbon ice will provide an opportunity for interesting chemistry along the boundary between liquid and solid, a boundary that may have been important in the origin of terrestrial life.”

Titan is the only other body besides Earth in our solar system with stable bodies of liquid on its surface. But it is too cold on Titan for water to be liquid, so hydrocarbons like ethane and methane fill lakebeds and seas there, and scientists have determined there is even a likely cycle of precipitation and evaporation that involves hydrocarbons.

Ethane and methane are organic molecules, which scientists think can be building blocks for the more complex chemistry from which life arose.

Cassini has seen a vast network of these hydrocarbon seas cover Titan’s northern hemisphere, while a more sporadic set of lakes are in the southern hemisphere.

It has long been thought that lakes or seas dotted Titan, ever since Voyager 1 and 2 flew past the Saturn system in the early 1980’s. But with Titan’s thick atmosphere, direct evidence was not obtained until 1995 during observations from the Hubble Space Telescope. The Cassini mission has imaged and mapped many of these bodies of liquids on Titan.

The Cassini spacecraft has been getting mixed readings in the reflectivity of the surfaces of lakes on Titan. A smooth surface or liquids dotted with chunks of ice could be a possibility explanation for the readings.

Up to this point, Cassini scientists assumed that Titan lakes would not have floating ice, because solid methane is denser than liquid methane and would sink. But a new model considers the interaction between the lakes and the atmosphere, resulting in different mixtures of compositions, pockets of nitrogen gas, and changes in temperature. The result, scientists found, is that winter ice will float in Titan’s methane-and-ethane-rich lakes and seas if the temperature is below the freezing point of methane — minus 297 degrees Fahrenheit (90.4 kelvins). The scientists realized all the varieties of ice they considered would float if they were composed of at least 5 percent “air,” which is an average composition for young sea ice on Earth. (“Air” on Titan has significantly more nitrogen than Earth air and almost no oxygen.)

If the temperature drops by just a few degrees, the ice will sink because of the relative proportions of nitrogen gas in the liquid versus the solid. Temperatures close to the freezing point of methane could lead to both floating and sinking ice – that is, a hydrocarbon ice crust above the liquid and blocks of hydrocarbon ice on the bottom of the lake bed. Scientists haven’t entirely figured out what color the ice would be, though they suspect it would be colorless, as it is on Earth, perhaps tinted reddish-brown from Titan’s atmosphere.

“We now know it’s possible to get methane-and-ethane-rich ice freezing over on Titan in thin blocks that congeal together as it gets colder — similar to what we see with Arctic sea ice at the onset of winter,” said Jason Hofgartner, first author on the paper and a Natural Sciences and Engineering Research Council of Canada scholar at Cornell. “We’ll want to take these conditions into consideration if we ever decide to explore the Titan surface some day.”

Cassini’s radar instrument will be able to test this model by watching what happens to the reflectivity of the surface of these lakes and seas. A hydrocarbon lake warming in the early spring thaw, as the northern lakes of Titan have begun to do, may become more reflective as ice rises to the surface. This would provide a rougher surface quality that reflects more radio energy back to Cassini, making it look brighter. As the weather turns warmer and the ice melts, the lake surface will be pure liquid, and will appear to the Cassini radar to darken.

“Cassini’s extended stay in the Saturn system gives us an unprecedented opportunity to watch the effects of seasonal change at Titan,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We’ll have an opportunity to see if the theories are right.”

Source: NASA/JPL

January 8, 2013December 23, 2015 by Nancy Atkinson

Astronaut Captures Incredible Images of Australian Bush Fires

Lines of scorched earth and huge smoke plumes from wild fires in Australia were visible from the International Space Station on January 8, 2013. Credit: NASA/Chris Hadfield

Intense wild fires, or bush fires as they are called in Australia, are burning out of control across southeast Australia with authorities describing the condition as “catastrophic.” The huge fires were easily visible from the International Space Station on Tuesday and onboard, Canadian astronaut Chris Hadfield has been watching from above.

See more of his images below:

A long line of bush fires range in Australia, and are visible from space. Credit: NASA/Chris Hadfield

Officials say more than 130 fires, many uncontained, are burning in the heavily populated New South Wales state, where dry conditions are fueling the fires as temperatures reached 45 degrees and wind gusts reached more than 100 kilometers per hour.

Huge plumes of smoke from bush fires in Australia were visible from the International Space Station. Credit: NASA/Chris Hadfield.

In Tasmania, an island south of Australia, rescue officials are still trying to locate around 100 residents who have been missing after a fire tore through a village, destroying dozens of homes. You can see images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite that were taken on January 7, 2013 at the Earth Observatory website.

Follow Chris Hadfield on Twitter to see more images.

Additional information on the bush fires from Voice of America

January 8, 2013December 23, 2015 by Nancy Atkinson

4 Cool Views of the Hot, Loopy, Spotty Sun

The Sun in H-Alpha on 01-07-2013, as seen with a Lunt Solar LS60Scope/LS50, and Hydrogen Alpha Solar filter. Credit: John Chumack

A few sunspots are now ‘peppering” the surface of our Sun — Spaceweather.com lists about 12 different sunspot groups today. Yesterday (January 7, 2013), astrophotographer John Chumack stepped outside over his lunch break and captured some cool-looking views of the Sun from his observatory in Ohio, using different filters.

See more below, plus the Solar Dynamics Observatory has a spectacular video of coronal loops on the Sun during January 5 through 7.

The video shows the 171 angstroms channel, which is especially good at showing coronal loops – the arcs extending off of the Sun where plasma moves along the magnetic field lines, said the SDO team. The brightest spots seen here are locations where the magnetic field near the surface is exceptionally strong. The characteristic temperature here is 1 million K (or 1.8 million F).

Many of these loops could fit several Earths inside of them.

Different views from different filters from John Chumack:

The Sun in H-Alpha, on 01-07-2013, using a Lunt Solar LS60Scope/LS50 Hydrogen Alpha Solar filter. Credit: John Chumack

The Sun on 1/07/13 as seen using a White Light Glass filter. Credit: John Chumack

See more of John’s work at his website, Galactic Images, or his Flickr page.

January 8, 2013April 26, 2016 by Nancy Atkinson

New Movie of a Neutron Star Looks Eerily Like the Phantom of the Opera

The Vela pulsar, a neutron star that was formed when a massive star collapsed. Credit: NASA

This incredible new movie of the Vela pulsar has the unnerving appearance of the Phantom of the Opera – wearing not only a mask, but also a steam-blowing hat like the Tin Man in “The Wizard of Oz.” What you are seeing here are observations from the Chandra X-ray Observatory, showing a fast moving jet of particles produced by a rapidly rotating neutron star. Scientists say these observations may provide new insight into the nature of some of the densest matter in the universe.

The Vela pulsar is about 1,000 light-years from Earth, about 19 km (12 miles) in diameter, and makes a complete rotation in 89 milliseconds. As the pulsar whips around, it spews out a jet of charged particles that race along the pulsar’s rotation axis at about 70 percent of the speed of light. The Chandra data used in the movie were obtained from June to September 2010, and it may suggest the pulsar may be slowly wobbling, or precessing, as it spins. The period of the precession, which is analogous to the slow wobble of a spinning top, is estimated to be about 120 days.

“We think the Vela pulsar is like a rotating garden sprinkler — except with the water blasting out at over half the speed of light,” said Martin Durant of the University of Toronto in Canada, who is the first author of the paper describing these results.

The eight images shown in the movie suggest that the pulsar may be slowly wobbling, or precessing, as it spins. If the evidence for precession of the Vela pulsar is confirmed, it would be the first time that a jet from a neutron star has been found to be wobbling, or precessing, in this way.

One possible cause of precession for a spinning neutron star is that it has become slightly distorted and is no longer a perfect sphere. This distortion might be caused by the combined action of the fast rotation and “glitches”, sudden increases of the pulsar’s rotational speed due to the interaction of the superfluid core of the neutron star with its crust.

A paper describing these results will be published in The Astrophysical Journal on January 10, 2013.

This is the second Chandra movie of the Vela pulsar. The first one, released in 2003, looks like a Halloween Jack-o-lanatern gone wrong:

This movie contains shorter, unevenly spaced observations so that the changes in the jet were less pronounced and the authors did not argue that precession was occurring. However, based on the same data, Avinash Deshpande of Arecibo Observatory in Puerto Rico and the Raman Research Institute in Bangalore, India, and the late Venkatraman Radhakrishnan, argued in a 2007 paper that the Vela pulsar might be precessing.

The Earth also precesses as it spins, with a period of about 26,000 years. In the future Polaris will no longer be the “north star” and other stars will take its place. The period of the Vela precession is much shorter and is estimated to be about 120 days.

Wide field Optical and X-ray image of the supernova remnant in the Vela Pulsar region. Credit: Anglo-Australian Observatory.

The supernova that formed the Vela pulsar exploded over 10,000 years ago. This optical image from the Anglo-Australian Observatory’s UK Schmidt telescope shows the enormous apparent size of the supernova remnant formed by the explosion. The full size of the remnant is about eight degrees across, or about 16 times the angular size of the Moon. The square near the center shows the Chandra image with a larger field-of-view than used for the movie, with the Vela pulsar in the middle.

Source: NASA

January 8, 2013December 23, 2015 by Nancy Atkinson

Curiosity Tidies Up a Bit on Mars

This image from the Mars Hand Lens Imager (MAHLI) on NASA's Mars rover Curiosity shows the patch of rock cleaned by the first use of the rover's Dust Removal Tool (DRT). Image Credit: NASA/JPL-Caltech/MSSS

It’s a bit dusty on Mars, and so the Curiosity rover has now cleaned up a little spot. For the first time ever, the newest Mars rover has used its Dust Removal Tool.

“The underlying rock and the windblown dust on top of it are made of different material,” the @Mars_Curiosity Twitter feed explained. “Analysis to come.”

It will be interesting to find out what the dark circular features are in the rock. The target areas that was cleaned is named “Ekwir_1,” and it is on a rock in the “Yellowknife Bay” area of Mars’ Gale Crater. The rover team is also evaluating rocks in that area as potential targets for first use of the rover’s hammering drill in coming weeks.

The Dust Removal Tool is a motorized, wire-bristle brush designed to prepare selected rock surfaces for enhanced inspection by the rover’s science instruments. It is built into the turret at the end of the rover’s arm, visible in the image below.

Camera and brushes on Curiosity's Arm as Seen by Camera on Mast. Image credit: NASA/JPL-Caltech/MSSS

The science team said that choosing an appropriate target was crucial for the first-time use of the Dust Removal Tool.

“We wanted to be sure we had an optimal target for the first use,” said Diana Trujillo of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., the mission’s activity lead for the Dust Removal Tool. “We need to place the instrument within less than half an inch of the target without putting the hardware at risk. We needed a flat target, one that wasn’t rough, one that was covered with dust. The results certainly look good.”

The Dust Removal Tool was built by Honeybee Robotics, which also built the Rock Abrasion Tool for the Spirit and Opportunity rovers.

Larger images and more info about the brushed area on Ekwir are online here and here.

Source: JPL

January 7, 2013December 23, 2015 by Nancy Atkinson

Exciting Potential for Habitable ExoMoons

Artistic rendition of a sunset view from the perspective of an imagined Earth-like moon orbiting the giant planet, PH2 b. Image Credit: H. Giguere, M. Giguere/Yale University

Imagine moons like Europa or Enceladus that are orbiting distant gas giant exoplanets located in the habitable zone of their star. What would be the potential for life on those moons? Hopefully one day we’ll find out, as that could be the scenario at an exoplanet that has been found by the Planet Hunter citizen science project. This is the second confirmed planet found by Planet Hunters, and the newest planet, PH2 b, is a Jupiter-size world in the habitable zone of a Sun-like star.

“There’s an obsession with finding Earth-like planets but what we are discovering, with planets such as PH2 b, is far stranger,” said Chris Lintott of Oxford University and Zooniverse. “Jupiter has several large water-rich moons – imagine dragging that system into the comfortably warm region where the Earth is. If such a planet had Earth size moons, we”d see not Europa and Callisto but worlds with rivers,lakes and all sorts of habitats – a surprising scenario that might just be common.”

Astronomers with Planet Hunters estimate the surface temperature PH2 b is 46 degrees Celsius. That’s a “just right” temperature for there to be liquid water, but it is extremely unlikely that life exists on PH2 b because it is a gas planet, and might be similar to Jupiter, so there is no solid surface or liquid environment for life to thrive. But if this planet is anything like the gas giant planets in our solar sytem, there could be a plethora of moons orbiting them.

“We can speculate that PH2 b might have a rocky moon that would be suitable for life, said lead author of the paper that has been published in arXiv, Dr Ji Wang, from Yale University. I can’t wait for the day when astronomers report detecting signs of life on other worlds instead of just locating potentially habitable environments. That could happen any day now.”

Additionally, the Zooniverse’s Planet Hunters team announced today that their citizen science volunteers have discovered 31 long-period planet candidates, with 15 of these new planet candidates orbiting in the habitable zones of other stars.

The team said that with 19 similar planets already discovered in habitable zones, where the temperature is neither too hot nor too cold for liquid water, the new finds suggest that there may be a “traffic jam” of all kinds of strange worlds in regions that could potentially support life.

Although most of these planets are large, like Neptune or Jupiter, these discoveries increase the sample size of long-period planet candidates by more than 30% and almost double the number of known gas giant planet candidates in the habitable zone, Wang said. “In the future, we may find moons around these planet candidates (just like Pandora around Polyphemus in the movie Avatar) that allows life to survive and evolve under a habitable temperature.”

They also have a “watch list” for 9 further planet candidates which have only 2 transits observed.

To study the PH2 b system, the astronomy team from Planet Hunters used the HIRES spectrograph and NIRC2 adaptive optics system on the Keck telescopes in Hawaii to obtain both high resolution spectrum and high spatial-resolution images.

“The observations help us to rule out possible scenarios for false positive detections and give us a measured confidence level of more than 99.9% that PH2 b is a bona-fide planet rather than just an illusion,” Wang wrote on the Planet Hunter’s blog.

More than 40 volunteers were listed as co-authors on the paper, acknowledging the contributions of hundreds of volunteers to the effort. Among them is Roy Jackson, a 71-year-old retired police officer who lives in Birtley, near Gateshead. He said:
“It is difficult to put into words, the pleasure, wonderment and perhaps even pride that I have in some small way been able to assist in the discovery of a planet. But I would like to say that the discovery makes the time spent on the search well worth the effort.”

Mark Hadley, an electronics engineer from Faversham, another of the Planet Hunters credited on the paper, said: “Now, when people ask me what I achieved last year I can say I have helped discover a possible new planet around a distant star! How cool is that?”

“These are planet candidates that slipped through the net, being missed by professional astronomers and rescued by volunteers in front of their web browsers,” said Lintott. It’s remarkable to think that absolutely anyone can discover a planet.”

Sources: Yale University, Planet Hunters blog.

January 7, 2013December 23, 2015 by Jason Major

Kepler Finds Hundreds of New Exoplanet Candidates

Artist’s depiction of the Kepler 10 system, which contains planets 2.2 and 1.4 times the size of Earth. (NASA/Ames/JPL-Caltech)

Kepler mission scientists announced today the discovery of literally hundreds of new exoplanet candidates — 461, to be exact — orbiting distant stars within a relatively small cross-section of our galaxy, bringing the total number of potential planets awaiting confirmation to 2,740. What’s more, at least 4 of these new candidates appear to be fairly Earth-sized worlds located within their stars’ habitable zone, the orbital “sweet spot” where surface water could exist as a liquid.

Impressive results, considering that NASA’s planet-hunting spacecraft was launched a little under 4 years ago (and watching 150,000 stars to spot the shadows of planets is no easy task!)

“… the ways by which men arrive at knowledge of the celestial things are hardly less wonderful than the nature of these things themselves.”

— Johannes Kepler

Since the last official announcement of Kepler candidates in Feb. 2012 the number of smaller Earth- and super-Earth-sized worlds observed has risen considerably, as well as the identification of multi-planet systems that are organized more-or-less along a flat plane… just like ours.

“There is no better way to kickoff the start of the Kepler extended mission,” said Kepler scientist Christopher Burke, “than to discover more possible outposts on the frontier of potentially life bearing worlds.”

From the NASA press release:

Since the last Kepler catalog was released in February 2012, the number of candidates discovered in the Kepler data has increased by 20 percent and now totals 2,740 potential planets orbiting 2,036 stars. The most dramatic increases are seen in the number of Earth-size and super Earth-size candidates discovered, which grew by 43 and 21 percent respectively.

The new data increases the number of stars discovered to have more than one planet candidate from 365 to 467. Today, 43 percent of Kepler’s planet candidates are observed to have neighbor planets.

The most dramatic increases are seen in the number of Earth-size and super Earth-size candidates discovered, which grew by 43 and 21 percent respectively. (NASA)

Although some of the new candidates announced today are large Neptune-sized planets, more than half are Earth- to super-Earth sized worlds less than twice the radius of our own planet.

In order for Kepler candidates to be “officially” called exoplanets, they must be observed 3 times on a regular orbit — that is, their signature dimming of the light from their home star must occur as predicted once their presence and then orbital period is calculated. Only then is an exoplanet confirmed.

To date Kepler has confirmed 105 exoplanets.

The longer the mission continues, the better the chance that Kepler will be able to confirm smaller Earth-sized worlds in longer-period orbits.

“The analysis of increasingly longer time periods of Kepler data uncovers smaller planets in longer period orbits — orbital periods similar to Earth’s,” said Steve Howell, Kepler mission scientist. “It is no longer a question of will we find a true Earth analogue, but a question of when.”

Scientists analyzed more than 13,000 transit-like signals called ‘threshold crossing events’ to eliminate known spacecraft instrumentation and astrophysical false positives, phenomena that masquerade as planetary candidates, to identify the potential new planets. Watch the video below to see how Kepler observes the light-curve of transit events.

Read more on the NASA press release, and learn more about the Kepler mission here.

January 7, 2013December 23, 2015 by Nancy Atkinson

Nearly All Sun-Like Stars Have Planetary Systems

A new analysis examined the frequencies of planets of different sizes based on findings from NASA's Kepler spacecraft, correcting for both incompleteness and false positives. The results show that one in six stars has an Earth-sized planet in a tight orbit. Credit: F. Fressin (CfA)

The latest analysis of data from the Kepler planet-hunting spacecraft reveals that almost all stars have planets, and about 17 percent of stars have an Earth-sized planet in an orbit closer than Mercury. Since the Milky Way has about 100 billion stars, there are at least 17 billion Earth-sized worlds out there, according to Francois Fressin of the Harvard-Smithsonian Center for Astrophysics (CfA), who presented new findings today in a press conference at the American Astronomical Society meeting in Long Beach, California. Moreover, he said, almost all Sun-like stars have planetary systems.

The holy grail of planet-hunting is finding a twin of Earth – a planet of about the same size and in the habitable zone around similar star. The odds of finding such a planet is becoming more likely Fressin said, as the latest analysis shows that small planets are equally common around small and large stars.

While the list of Kepler planetary candidates contains majority of the knowledge we have about exoplanets, Fressin said the catalog is not yet complete, and the catalog is not pure. “There are false positives from events such as eclipsing binaries and other astrophysical configurations that can mimic planet signals,” Fressin said.

By doing a simulation of the Kepler survey and focusing on the false positives, they can only account for 9.5% of the huge number of Kepler candidates. The rest are bona-fide planets.

This artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft. Credit: C. Pulliam & D. Aguilar (CfA)

Altogether, the researchers found that 50 percent of stars have a planet of Earth-size or larger in a close orbit. By adding larger planets, which have been detected in wider orbits up to the orbital distance of the Earth, this number reaches 70 percent.

Extrapolating from Kepler’s currently ongoing observations and results from other detection techniques, it looks like practically all Sun-like stars have planets.

The team then grouped planets into five different sizes. They found that 17 percent of stars have a planet 0.8 – 1.25 times the size of Earth in an orbit of 85 days or less. About one-fourth of stars have a super-Earth (1.25 – 2 times the size of Earth) in an orbit of 150 days or less. (Larger planets can be detected at greater distances more easily.) The same fraction of stars has a mini-Neptune (2 – 4 times Earth) in orbits up to 250 days long.

Larger planets are much less common. Only about 3 percent of stars have a large Neptune (4 – 6 times Earth), and only 5 percent of stars have a gas giant (6 – 22 times Earth) in an orbit of 400 days or less.

The researchers also asked whether certain sizes of planets are more or less common around certain types of stars. They found that for every planet size except gas giants, the type of star doesn’t matter. Neptunes are found just as frequently around red dwarfs as they are around sun-like stars. The same is true for smaller worlds. This contradicts previous findings.

“Earths and super-Earths aren’t picky. We’re finding them in all kinds of neighborhoods,” says co-author Guillermo Torres of the CfA.

Planets closer to their stars are easier to find because they transit more frequently. As more data are gathered, planets in larger orbits will come to light. In particular, Kepler’s extended mission should allow it to spot Earth-sized planets at greater distances, including Earth-like orbits in the habitable zone.

Kepler detects planetary candidates using the transit method, watching for a planet to cross its star and create a mini-eclipse that dims the star slightly.

Sources: Harvard Smithsonian CfA, AAS Press Conference