“Hot Jupiters” are lonely

63 Hot Jupiter Canridates. CREDIT: Fermilab Center for Particle Astrophysics

A group of scientist including UF astronomy professor Eric Ford has recently conducted a search for planets around stars already known to host “hot Jupiter” type planets, showing that these bodies are most likely to be alone in their systems.

“Hot Jupiters” are giant planets beyond our solar system, roughly the size of Jupiter orbiting very close to their parent stars and thus much hotter than the Earth or Jupiter (hence the name). They have very short orbital periods, completing a turn around their stars in less than 10 days. This study provides new insights into how they are formed.

The data used was gathered by NASA’s planet-hunter Kepler mission, which uses a 1-meter space telescope to stare constantly at a patch of the Milky Way, registering the small decreases in the light from stars caused when a planet crosses in front of it.

Scientists dug into Kepler’s data and selected a sample of 63 planetary systems containing previously detected hot Jupiter candidates. Then they looked for signals of additional planets either crossing in front of the host stars or gravitationally tugging on the hot Jupiter’s orbit. In all cases they found no evidence of additional planets. To allow comparisons, they used the same methods to study a sample of “warm Jupiter” candidates, equally big planets but located farther away from their parent stars and “hot Neptunes,” smaller but closer to the stars. They found compelling evidence that at least 10 percent of the warm Jupiters and one third of the hot Neptunes have other planetary companions nearby in the system. Thus, why are all the hot Jupiters so lonely?

Astronomers believe it results from the way the hot Jupiters are formed, now thought to be different from most other planets. Current models suggest that they are probably formed farther away from their host star, and then gravitational interactions with another body cause their orbits to become highly elongated. Each orbit the hot Jupiter passes very close to the host star and then travels far away. The star raises tides on the planet, repeatedly stretching it and causing its orbit to become smaller and more circular. This process would remove or destroy other low-mass planets that originally formed between the star and the giant planet.

“We looked for companion planets near hot Jupiters in order to learn a bit more about their formation,” Ford said. “The lack of nearby planets supports the theory that a close encounter with another body in the system caused the elongation of the orbit. When a giant planet repeatedly passes through the inner regions of a planetary system on an elongated orbit, it would wreak great havoc on any planets that had formed there. The other planets would either fall into the star, collide with the hot Jupiter or be kicked out of the system via a gravitational slingshot.”

In 1995 the first planet orbiting a sun-like star was discovered. It and most exoplanets found in the early days of the exoplanet search happened to be hot Jupiters.

“That was because they are easier to find than smaller planets or others more distant to their host star,” Ford said. “Now, we know that less than 1 percent of stars harbor hot Jupiters, so they are relatively rare. A special sequence of events like strong gravitational interactions between two giant planets followed by tidal circularization seems to be the most plausible scenario for the formation of hot Jupiters.”

The research was led by Jason Steffen from the Fermilab Center for Particle Astrophisics.

NASA’s Kepler Mission, operating since 2009, is revolutionizing the field of planetary science. For the first time it is enabling astronomers to conduct this kind of detailed population studies of planet candidates. By allowing astronomers to study systems other than our own, they are able to confront planet formation theories with observational data, giving important insights into the range of contemporary planetary system architectures and the possible existence of habitable planets within them.

Link to UF news http://news.ufl.edu/2012/05/07/hot-jupiters/

UF-led team use new observatory to characterize low-mass planets orbiting a nearby star

Published in University of Florida News on Thursday, April 9, 2012.

The narrow dust ring around Fomalhaut. Yellow at top is the ALMA image, and the blue at bottom is Hubble Space Telescope image. The star is at the location of the bright emission at the center of the ring.

CREDIT: A.C. Boley (University of Florida, Sagan Fellow), M.J. Payne, E.B. Ford, M. Shabran (UF), S. Corder (North American ALMA Science Center, NRAO), and W. Dent (ALMA, Chile), NRAO/AUI/NSF; NASA, ESA, P. Kalas, J. Graham, E. Chiang, E. Kite (UC, Berkeley), M. Clampin (NASA Goddard Space Flight Center), M. Fitzgerald (Lawrence Livermore National Laboratory), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory).

University of Florida astronomers have found compelling evidence for two low-mass planets orbiting the nearby star Fomalhaut, just 25 light years from Earth.

Twice as massive as the sun and 20 times brighter, Fomalhaut is surrounded by a ring of dust and debris, making it a favorite system for astronomers to study and a natural laboratory for testing planet formation theories.

In 2008, images of Fomalhaut taken by the Hubble Space Telescope led to the discovery of “Fomalhaut b,” the first extrasolar planet to be directly detected in visible light. At the time, astronomers believed it to be a giant planet, akin to Jupiter or Saturn, but later infrared images failed to detect the planet, meaning that it had to be smaller than Saturn.

UF astronomers, along with scientists from the new Atacama Large Millimeter Array in Chile, known as ALMA, and the National Radio Astronomy Observatory, used ALMA’s superior resolution and sensitivity to study the system in unprecedented detail. Their results indicate that there are not one, but two planets, with masses between that of Mars and a few times larger than Earth, working together to shape the ring of dust.

The new study reveals that the ring is sharply truncated in the inner and outer edges and is only about 16 astronomical units, or AU, wide, or about 16 times the distance between the Earth and the sun. That may seem large, but the center of the ring is about 140 AU, making the ring relatively very narrow. It also finds that the ring is vertically thin, about one-seventh as tall as it is wide. Those properties give important clues to explain the planetary system of Fomalhaut.

The results are described in a paper to appear this month in the Astrophysical Journal Letters.

“Combining ALMA observations of the ring’s shape with computer models, we can place very tight limits on the mass and orbit of any planet near the ring.” said Aaron Boley, a Sagan Postdoctoral Fellow at UF and leader of the study. “The masses of the planets must be small so they do not destroy the ring, but their masses cannot be too low or they would not shape the ring.”

Although Fomalhaut is a much hotter star than the sun, the planets are so far from their host star that they are among the coldest planets known around a normal star. They are thought to be low-mass bodies, but astronomers do not have enough data to tell whether they have a significant amount of hydrogen gas or are mostly rock and ice.

“ALMA observations show that Fomalhaut’s ring is even more narrow and thinner than previously known,” said Matthew Payne, an astronomer at the University of Florida who contributed to the study. “Fomalhaut b alone only explains the ring's sharp inner edge. Our analysis suggests that two planets, one interior and one exterior, are shepherding the ring, analogous to how Uranus’ moons Cordelia and Ophelia confine Uranus’ brightest ring.”

Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope A. Fujii/Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble). Music: John Dyson (from the album Moonwind).

The Atacama Large Millimeter/submillimeter Array, located in the Atacama desert of northern Chile at an altitude of 16,400 feet is the largest astronomical project in existence. Still under construction, ALMA began scientific operations in September.

“ALMA may still be under construction, but it has already proved to be the world’s most powerful telescope for observing the universe at millimeter and submillimeter wavelengths of light.” said Stuartt Corder, an astronomer at the National Radio Astronomy Observatory and co-author of the study.

“Once ALMA is completed, we will be able to study systems like Fomalhaut with even greater detail, and see through the veil of dust that hides the early stages of planet formation,” said co-author Bill Dent, an astronomer at ALMA.

This research was supported by the NASA Sagan Fellowship Program, the National Radio Astronomy Student Observing Support Program and the University of Florida's College of Liberal Arts and Sciences. The Joint ALMA Observatory is a partnership of the European Organization for Astronomical Research in the Southern Hemisphere, the National Astronomical Observatory of Japan (on behalf of the National Institutes of Natural Sciences and Academia Sinica), and the NRAO (managed by Associated Universities, Inc. on behalf of the NSF and the National Research Council of Canada) in cooperation with the Republic of Chile.

Reflections on Kepler's 3rd birthday



Artist's rendition of Kepler spacecraft. Credit: NASA/Kepler mission/Wendy Stenzel

Three years ago, I witnessed the launch of NASA's Kepler mission. As the first space mission designed from the ground-up to study exoplanets, it was a major juncture in the search for other worlds and all of astronomy. Yet, the launch was really one more opportunity to practice patience. As a part of the Kepler Science Team, I waited to learn of the spacecraft's health, then the pointing and focus, then the data quality, then enough data to begin to do science, then the first planet candidates, then the progress of our colleagues in improved data analysis techniques. Now, we wait for Kepler to observe long enough to find Earth-size planets in the habitable zones of solar-like stars.

As a member of the transiting timing variations working group, I'm also anxiously waiting for enough data to measure the masses of small planets, so we can map the transition between "super-Earth's" and "mini-Neptunes". These new classes of planets for which there is no analog in our solar system are actually quite common for other stars. Why doesn't our own solar system have any super-Earths (or mini-Neptunes)? How did Earth resist Icarus's urge to fly too close too the Sun for life, like most of the thousands of planets being discovered by Kepler? Is there something special about our solar system? Continued observations and analysis of the Kepler data provide best chance to address questions like these.

At the launch, several mission's founders were already a tight nit team. Over the last three years, I and my small research group at UF have become part of the Kepler family. I can't guess how many emails, telecons, heated debates we've had. Those have pushed us to work many late nights to search for planets, to vet planet candidates, to optimize the next quarter's target list, to provide some analysis in time for another team member's paper, to explain why NASA should keep the mission alive beyond 2012, and to convey results and the sense of wonder to the public. It's been an exhausting, but exhilarating ride. I hope we can hang on for a few more years.

Prof. Ford during the Kepler launch, 2009. Credit: NASA/Kepler Mission.

Kepler has opened our eyes to the power of time-domain astronomy, providing nearly-continuous, long-term and ultra-high precision photometry. The only analogy I can offer is to how much we learned about the universe when previous NASA missions made it possible to see the sky in wavelengths previously inaccessible due to Earth's atmosphere hanging over telescopes on the ground. Far above Earth's atmosphere, Kepler's data quality is so much better than anything before it that most astronomers are just beginning to appreciate the possibilities for studying planets and stars in ways never before possible. Kepler has already returned a treasure trove of data, one that will be mined by astronomers for many years if not decades into the future.

Kepler was always intended to be a stepping stone towards future missions that could study the atmospheres and surfaces of potentially Earth-like planets. I hope that humans will muster another great observatory optimized for exoplanet science, so we can realize those goals during my career, or at least my lifetime. If not, at least we have the Kepler Mission.

Professor Eric B. Ford.

Kepler Mission facebook page

UF astronomers contribute to NASA’s planet discoveries

Published on University of Florida News on Thursday, January 26, 2012.

GAINESVILLE, Fla. — NASA announced today the discovery of 11 new “solar systems” hosting at least 26 planets found with data from NASA’s Kepler Mission.

Kepler's Planetary Systems, Jan. 2012 Multiple planet systems discovered by NASA's Kepler mission. Newly found planets are shown here in green. The eight planets of the solar system are shown in blue. Credit: NASA Ames/Jason Steffen, Fermilab Center for Particle Astrophysics

The discovery nearly doubles the number of verified Kepler planets so far. It also triples the number of stars known to have more than one planet that transits – or passes in front of — its host star. Such systems are particularly valuable for the clues they provide about how planets form.

Eric B. Ford, associate professor of the astronomy department at the University of Florida, is part of the Kepler Mission science team. Ford’s research group at UF, including graduate student Robert Morehead and postdoctoral associate Althea Moorhead, has contributed to several previous Kepler discoveries. Ford is lead author of the paper describing Kepler-23 and Kepler-24, two of the 11 systems announced today.

In this research, Ford and his team not only describe the two new planetary systems but also develop a new technique that, in Ford’s words “dramatically accelerates planet discovery and will enable astronomers to confirm planets transiting fainter and more distant stars.”

The Kepler Mission uses a 1-meter space telescope to stare constantly at a patch of the Milky Way, registering the small decreases in the light from stars caused when a planet crosses in front of it. With this tool, astronomers are able to constantly monitor more than 160,000 stars at a time.

Until now, confirming that small decreases in a star’s brightness was caused by a planet required additional observations and time-consuming analysis. The new technique takes advantage of the gravitational effects that different planets in a system have on each other’s orbits. By precisely timing the deviations from the expected orbital times caused by this effect, the team was able to detect the gravitational tug exerted by the planets on each other, and confirm 10 of the newly announced planetary systems.

Five of the new planetary systems contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Another five systems contain a pair of planets where the outer planet circles the star twice for every three times the inner planet orbits its star.

“These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher,” said Jason Steffen, the Brinson Postdoctoral Fellow at Fermilab Center for Astroparticle Physics and lead author of a paper confirming four of the systems.

The new planets orbit close to their host stars, their size ranging from 1.7 times the radius of Earth to about the size of Jupiter. Fifteen of them are smaller than Neptune and further observations will be required to determine which of them are rocky like Earth and which have thick gaseous atmospheres like Neptune. The confirmed planets orbit their host star once every 6 to 143 days, so all of them are closer to their host star than Venus is to the sun.

The new discoveries will be published in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society. Searching for exoplanets using real Kepler data is open to everyone by visiting planethunters.org. For more information about the Kepler mission visit: http://www.nasa.gov/kepler.

NASA‘s Kepler mission and UF astronomer find two new planets orbiting double suns

Published on UF News, January 11th 2012.

Using data from NASA’s Kepler mission, a team that includes a University of Florida astronomer has discovered two new planets orbiting double star systems, something that had never been seen until last September.

The newly confirmed planets, called Kepler-34b and Kepler-35b, will be announced in Wednesday’s online edition of the journal Nature, said Eric B. Ford, UF associate professor of astronomy. William F. Welsh, associate professor at San Diego State University, is the lead author on the paper.

An artist's rendition of the Kepler-35 planetary system, in which a Saturn-size planet orbits a pair of stars.
Image credit: Lynette Cook / extrasolar.spaceart.org

Kepler-34b and Kepler-35b both orbit a “binary star.” They are actually a pair of gravitationally bound stars that orbit each other. While the existence of such bodies, called “circumbinary planets,” had long been predicted, they remained just a theory until the team discovered Kepler-16b in September 2011. They dubbed Kepler-16b “Tatooine” because of its resemblance to the two-sun world depicted in the “Star Wars” film series.

“We have long believed these kinds of planets to be possible, but they have been very difficult to detect for various technical reasons,” Ford said. “With the discoveries of Kepler-16b, 34b and 35b, the Kepler mission has shown that the galaxy abounds with millions of planets orbiting two stars.”

The planets were discovered by measuring the star light decrease as the planets pass in front of, or transit, either of the two stars. Kepler also measures the star light decrease when one of the stars passes in front of the other. The mutual gravitational tugs of the stars and planets cause the times of the transits to deviate from a regular schedule, allowing astronomers to confirm the planet and measure its mass.

Both planets are low-density gas giants, comparable in size to Jupiter, but much less massive. Compared to Jupiter, Kepler-34 is about 24 percent smaller in size, but has 78 percent less mass. It can complete a full orbit in 288 terrestrial days. Kepler-35 is about 26 percent smaller, has 88 percent less mass, and completes its orbit around the stars much faster – just 131 days.

The astronomers believe the planets are made primarily of hydrogen and too hot to sustain life.

“Circumbinary planets can have much more complex climates, since the distance between the planet and each star change significantly during each orbital period, the length of an alien planet’s year,” Ford said. “For Kepler-35b, the amount of incoming star light changes by over 50 percent within a single Earth year. For Kepler-34b, each Earth-year brings ‘summers’ with 2.3 times as much star light as winters. Over the course of a year, the change in the amount of sunlight heating the Earth varies by only 6 percent.”

NASA’s Kepler mission, which began in March 2009, uses a 1-meter space telescope trained on one small portion of the Milky Way for several years. Astronomers analyze data from the telescope for periodic dimming that indicates a planet crossing in front of its host star. The mission’s goal is to find the frequency of Earth-size planets in the habitable zone of their host stars – where a planet might have liquid water on its surface.

Most Sun-like stars in the galaxy are not alone, like the Earth’s sun, but have a “dance partner,” forming a binary system or binary star. Kepler has already identified about 2,165 eclipsing binaries, of the more than 160,000 stars being observed.

NASA originally planned to stop receiving data from the Kepler spacecraft in November 2012.

“Astronomers are practically begging NASA to extend the Kepler mission until 2016, so it can characterize the masses and orbits of Earth-size planets in the habitable zone. Kepler is revolutionizing so many fields, not just planetary science,” Ford said. “It would be a shame not to maximize the scientific return of this great observatory. Hopefully common sense will prevail and the mission will continue.”

The public can contribute to searching for planets using real Kepler data by visiting planethunters.org, which works with the latest versión of Internet Explorer, Chrome and Firefox. For additional information, downloadable slides, and full resolution versions of artwork after the embargo lifts, please see http://sdsu.edu/kepler. For more information about the Kepler mission, visit: http://www.nasa.gov/kepler.

Follow this link to see the original UF press release.

Discovery by UF-led team refutes previous theory about galaxies

The world’s largest optical telescope has allowed University of Florida astronomers to see new details about deep space galaxies, finding new clues to explain the evolution of galaxies like our own.

Before these new observations, it was believed that galaxies in the young universe were much denser and compact than they are now, undergoing at some point a mysterious transformation growing in size and mass. Astronomers around the world struggled to find an explanation.

Now, a UF-led team has used the Gran Telescopio Canarias, or GTC, to point out the solution to the mystery: The data gathered by lesser telescopes was not accurate enough, which led to misinterpretation.

The GTC in Spain’s Canary Islands has a primary mirror of 10.4 meters, or 27.6 feet, which allowed the team led by UF graduate student Jesus Martinez and professor Rafael Guzman, to observe four of these dense galaxies with a level of detail unachieved so far. They found that the four were six times less massive, on average, than previously believed, as described in the September issue of The Astrophysical Journal Letters.

It takes time for light to travel through the universe. Considering the great distances the light must travel to get to Earth, looking through larger telescopes means not only being able to see farther in distance, but also back in time — in this case 9 billion years ago.

Martinez and teammates from Spanish research centers Instituto de Astrofisica de Canarias and Universidad Complutense de Madrid, concluded that what had been thought of as super-dense galaxies actually were not so dense and had not undergone dramatic transformation — a discovery that shows how scientists must always question previously accepted principles.

Cutting-edge scientific tools such as the GTC help bolster this kind of healthy scepticism.

UF is a 5 percent partner in the $180 million GTC, which was inaugurated in 2009

Martinez’s work has been partially funded by a UF alumni fellowship and the government of Spain’s Consolider-Ingenio 2010 program.

Javier Barbuzano.

Astronomers plan second look at mega star birthing grounds

via University of Florida News

Astronomers this summer will take a close look at a rare cosmic cradle for the universe’s largest stars, baby bruisers that grow up to have 50 times the sun’s mass.

The international team of astronomers headed by University of Florida scientist Peter Barnes used an Australian radio telescope to find the cloud of gas and dust 8,000 light years away in the Southern sky constellation Carina. The cloud is in the early stages of collapsing in on itself, offering astronomers an unusual vista on the first contractions of behemoth star birth.

“We understand some of it, but we really don’t have a clear picture of what’s important,” Barnes said. “This should help us learn a lot more about the process.”

Although our sun has far less mass than the incipient stars in the gas cloud, studying their formation could help astronomers understand how our solar system formed, Barnes said. That is because many stars the size of our sun are thought to have formed in clusters that dispersed into space over millions of years. It’s possible, Barnes said, that our sun traces its origin to such a cluster, and in fact chemical anomalies on meteorites suggest that’s the case.

The latest findings, which appeared in the monthly journal Notices of the Royal Astronomical Society, have spurred the team to plan a closer look with another Australian telescope in August. The team will also use the Gemini South telescope, equipped with a mid-infrared camera designed and built at UF, to observe the cloud from the telescope’s location in Chile.

Stars at least 10 times the mass of our sun are rare, comprising only about 4 percent of those in the universe. Most are also at least 1,000 light years away and hard to study. It’s exceptionally rare for astronomers to encounter clouds of gas and dust early in the process of collapsing into large stars because the stars tend to destroy their natal origins.

“They’re rather nasty tykes,” Barnes said. “They make a big mess.”

The astronomers discovered the gas cloud as part of a survey of 300 large gas clouds using the Australia Telescope National Facility’s 22-meter Mopra radio telescope in southeastern Australia. The telescope’s world-class spectrometer allows astronomers to identify and image carbon monoxide and other molecules in large gas clouds. Even with that technology, the mega star birthing cloud was the only one of its kind among the 300 surveyed.

The cloud is also unusual in its rapid pace of collapse and the amount of dust and gas, an amount so large it eclipsed the large stars that had already coalesced inside the cloud. “It is a few light years across, and it has maybe 20,000 times the sun’s mass worth of gas and dust, and most of that is participating in the collapse,” Barnes said.

The Formation of Stars

University of Florida professor Jonathan Tan gave recently a science symposium at the Space Telescope Science Institute on the formation of stars. For an up to date description of the field and professor Tan's past, present, and future research, follow this link.

Stars to Galaxies Conference

The Stars to Galaxies conference was held in Gainesville, FL from the 7th to the 10th of April. The conference, which was chaired by University of Florida professor Jonathan Tan, was a complete success. Scientific posters and talks are now available online for the scientific community.