New system would assess odds of life on other worlds

Earth-like? Habitable?

PULLMAN, Wash. – Within the next few years, the number of planets discovered in orbits around distant stars will likely reach several thousand or more. But even as our list of these newly discovered "exoplanets” grows ever-longer, the search for life beyond our solar system will likely focus much more narrowly on the relatively few of these new worlds which exhibit the most Earth-like of conditions.

For much of the scientific community, thesearch for alien life has long been dominated by the notion that our own planet serves as the best model of conditions best suited to the emergence of life on other worlds. And while there’s anundeniable logic to seeking life in the same sort of conditions in which you already know it to be successful, there are scientists like Dirk Schulze-Makuch, an astrobiologist with the Washington State University School of Earth and Environmental Sciences and Abel Mendez, a modeling expert from the University of Puerto Rico at Aricebo, who also see such a model as the product of a potentially limiting form of earthling-biased thinking.

To Schulze-Makuch and his nine fellow authors – an international working group representing, NASA, SETI,the German Aerospace Center, and four universities– the search for life on other worlds is really driven by two questions.

"The first question is whether Earth-like conditions can be found on other worlds, since we know empirically that those conditions could harbor life,” Schulze-Makuch said. "The second question is whether conditions exist on exoplanets that suggest the possibility of other forms of life, whether known to us or not.”

In a paper to be published in the December issue of the journal Astrobiology, Schulze-Makuch and his co-authors propose a new system for classifying exoplanets using two different indices – an Earth Similarity Index (ESI) for categorizing a planet’s more earth-like features and a Planetary Habitability Index (PHI) for describing a variety of chemical and physical parameters that are theoretically conducive to life in more extreme, less-earthlike conditions.

Similarity indices provide a powerful tool for categorizing and extracting patterns from large and complex data sets. They are relatively quick and easy to calculate and provide a simple quantitative measure of departure from a reference state, usually on a scale from zero to one. They are used in mathematics, computer imaging, chemistry and many other fields.

The two indices proposed by the group mark the first attempt by scientists to categorize the many exoplanets and exomoons that are expected to be discovered in the near future in accordance with their potential to harbor some form of life.

"As a practical matter, interest in exoplanets is going to focus initially on the search for terrestrial, Earth-like planets,” said Schulze-Makuch. "With that in mind, we propose an Earth Similarity Index which provides a quick screening tool with which to detect exoplanets most similar to Earth.”

But the authors believe that focusing exclusively on earth-based assumptions about habitability may well be too restrictive an approach for capturing the potential variety of life forms that, at least in principle, may also exist on other worlds.

"Habitability in a wider sense is not necessarily restricted to water as a solvent or to a planet circling a star,” the paper’s authors write. "For example, the hydrocarbon lakes on Titan could host a different form of life. Analog studies in hydrocarbon environments on Earth, in fact, clearly indicate that these environments are habitable in principle. Orphan planets wandering free of any central star could likewise conceivably feature conditions suitable for some form of life.”

The paper’s authors concede that attempting to rate the probability that life of some unknown form could exist on any given world is an intrinsically more speculative endeavor. But the alternative, they argue, is to risk overlookingpotentially habitable worlds by using overly restrictive assumptions.

"Our proposed PHI is informed by chemical and physical parameters that are conducive to life in general,” they write. "It relies on factors that, in principle, could be detected at the distance of exoplanets from Earth, given currently planned future (space) instrumentation.”

The paper, entitled A Two-Tiered Approach to Assessing the Habitability of Exoplanets, was written by Alfonso Davila, of SETI; Alberto Fairen, of NASA; Abel Mendez of the University of Puerto Rico at Aricebo; Philip von Paris, of the German Aerospace Center; David Catling, of the University of Washington; Louis N. Irwin, of the University of Texas-El Paso, and Marina Resendes de Sousa Antonia, Carol Turse, Grayson Boyer and Dirk Schulze-Makuch, all of Washington State University.

Source:
Dirk Schulze-Makuch,
WSU School of Earth & Environmental Science,
509-335-1180,
dirksm@wsu.edu

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Dark Matter Mystery Deepens

This artist's conception shows a dwarf galaxy seen from the surface of a hypothetical exoplanet. A new study finds that the dark matter in dwarf galaxies is distributed smoothly rather than being clumped at their centers. This contradicts simulations using the standard cosmological model known as lambda-CDM. Credit: David A. Aguilar (CfA)

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Cambridge, MA - Like all galaxies, our Milky Way is home to a strange substance called dark matter. Dark matter is invisible, betraying its presence only through its gravitational pull. Without dark matter holding them together, our galaxy's speedy stars would fly off in all directions. The nature of dark matter is a mystery -- a mystery that a new study has only deepened.

"After completing this study, we know less about dark matter than we did before," said lead author Matt Walker, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics.

The standard cosmological model describes a universe dominated by dark energy and dark matter. Most astronomers assume that dark matter consists of "cold" (i.e. slow-moving) exotic particles that clump together gravitationally. Over time these dark matter clumps grow and attract normal matter, forming the galaxies we see today.

Cosmologists use powerful computers to simulate this process. Their simulations show that dark matter should be densely packed in the centers of galaxies. Instead, new measurements of two dwarf galaxies show that they contain a smooth distribution of dark matter. This suggests that the standard cosmological model may be wrong.

"Our measurements contradict a basic prediction about the structure of cold dark matter in dwarf galaxies. Unless or until theorists can modify that prediction, cold dark matter is inconsistent with our observational data," Walker stated.

Dwarf galaxies are composed of up to 99 percent dark matter and only one percent normal matter like stars. This disparity makes dwarf galaxies ideal targets for astronomers seeking to understand dark matter.

Walker and his co-author Jorge Peñarrubia (University of Cambridge, UK) analyzed the dark matter distribution in two Milky Way neighbors: the Fornax and Sculptor dwarf galaxies. These galaxies hold one million to 10 million stars, compared to about 400 billion in our galaxy. The team measured the locations, speeds and basic chemical compositions of 1500 to 2500 stars.

"Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy," explained Peñarrubia. "That makes it much more challenging to determine the distribution of dark matter."

Their data showed that in both cases, the dark matter is distributed uniformly over a relatively large region, several hundred light-years across. This contradicts the prediction that the density of dark matter should increase sharply toward the centers of these galaxies.

"If a dwarf galaxy were a peach, the standard cosmological model says we should find a dark matter 'pit' at the center. Instead, the first two dwarf galaxies we studied are like pitless peaches," said Peñarrubia.

Some have suggested that interactions between normal and dark matter could spread out the dark matter, but current simulations don't indicate that this happens in dwarf galaxies. The new measurements imply that either normal matter affects dark matter more than expected, or dark matter isn't "cold." The team hopes to determine which is true by studying more dwarf galaxies, particularly galaxies with an even higher percentage of dark matter.

The paper discussing this research was accepted for publication in The Astrophysical Journal and is available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact: David A. Aguilar Director of Public Affairs Harvard-Smithsonian Center for Astrophysics 617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam Public Affairs Specialist Harvard-Smithsonian Center for Astrophysics 617-495-7463
cpulliam@cfa.harvard.edu

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Citizen Scientists, Kepler and Keck Uncover New Planets

Artists conception of Jupiter-like exoplanets orbiting close to their stars and detected by the Kepler telescope. It takes Keck telescopes to confirm the existence of these planets and extract more information about them. Credit: NASA

Astronomers at Yale University have announced the discovery of the first two potential exoplanets found by the online citizen scientist Planet Hunters program. Users of the Planet Hunters program analyze scientific data collected by NASA’s Kepler mission to assist astronomers in finding planets orbiting nearby stars. The most likely exoplanet candidates are then studied using the 10-meter telescopes of the W.M. Keck Observatory in Hawaii to confirm the planets’ existence.

Since the online citizen science project Planet Hunters launched last December, 40,000 web users from around the world have been helping professional astronomers analyze the light from 150,000 stars in the hopes of discovering Earth-like planets orbiting around them. A new study on the discovery is slated to be published (when?) in the Monthly Notices of the Royal Astronomical Society.

“This is the first time that the public has used data from a NASA space mission to detect possible planets orbiting other stars,” said Yale astronomer and exoplanet expert Debra Fischer, who helped launch the citizen science project.

The candidate planets orbit their host stars with periods ranging from 10 to 50 days—much shorter than the 365 days it takes the Earth to orbit the Sun—and have radii that range in size from two-and-a-half to eight times Earth’s radius. Despite those differences, one of the two candidates could be a rocky, Earth-mass planet (as opposed to a giant gas planet like Jupiter), although they aren’t in the so-called “habitable zone” where liquid water, and therefore life as we know it, could exist.

Next, the professional astronomy team – a collaboration between astronomers at Yale, the University of Oxford and the Adler Planetarium in Chicago
—used the Keck Observatory in Hawaii to analyze the spectra of the host stars. The spectra reveal whether the stars are wobbling, and by how much and at what speed – all of which reveal clues to the planets orbiting them.

The Kepler team had already announced they had identified 1,200 exoplanet candidates and that they would follow up on the highest potential ones, but they had discarded the two found by Planet Hunters users for various technical reasons that led them to believe they weren’t promising candidates.

“These two candidates might have gone undetected without Planet Hunters and its citizen scientists,” said Meg Schwamb, a Yale researcher and Planet Hunters co-founder. “Obviously Planet Hunters doesn’t replace the analysis being done by the Kepler team. But it has proven itself to be a valuable tool in the search for other worlds.”

Users found the two candidates in the first month of Planet Hunters operations using data the Kepler mission made publicly available. The Planet Hunters group sent the top 10 candidates found by the citizen scientists to the Kepler team, who analyzed the data and determined that two of the 10 met their criteria for being classified as planet candidates. The two candidates were flagged as potential planets by several dozen different Planet Hunters users, as the same data are analyzed by more than one user.

“Scientists on the Kepler team obtained the data, but the public helped finance the project with their tax dollars,” Fischer said. “It’s only right that this data has been pushed back into the public domain, not just as scientifically digested results but in a form where the public can actively participate in the hunt. The space program is a national treasure—a monument to America’s curiosity about the Universe. It is such an exciting time to be alive and to see these incredible discoveries being made.”

Planet Hunters users are now sifting through the next 90 days of Kepler data in the hopes of adding to the count. “This is what we found after just a preliminary glance through the first round of Kepler data,” Fischer said. “There’s no doubt that, with each new round of data, there will be more discoveries to come.”

# # #

Learn more about Planet Hunters:
http://www.planethunters.org

Watch a video of Planet Hunters co-founders Debra Fischer and Kevin Schawinski explaining the project:
http://www.youtube.com/user/YaleUniversity#p/search/0/18NCx-iBHBQ

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which removes much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Adapted from a press release by Yale University

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Fifty New Exoplanets Discovered by HARPS

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Artists’s impression of one of more than 50 new exoplanets found by HARPS: the rocky super-Earth HD 85512 b

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Artists’s impression of one of more than 50 new exoplanets found by HARPS: the rocky super-Earth HD 85512 b

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Artists’s impression of one of more than 50 new exoplanets found by HARPS:
the rocky super-Earth HD 85512 b

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Artists’s impression of one of more than 50 new exoplanets found by HARPS: the rocky super-Earth HD 85512 b

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Close-up view of the star HD 85512

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The habitable zone around some stars with planets

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Wide-field view of the sky around the star HD 85512

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ESOcast 35: Fifty New Exoplanets

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Animation of artist’s impression of the super-Earth planet HD 85512 b

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Animation of artist’s impression of the super-Earth planet HD 85512 b

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Zooming in on HD 85521 b

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Video News Release 34: Fifty New Exoplanets

Richest haul of planets so far includes 16 new super-Earths

Astronomers using ESO’s world-leading exoplanet hunter HARPS have today 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 HARPS planets found so far, the team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.

The HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile is the world’s most successful planet finder [1]. The HARPS team, led by Michel Mayor (University of Geneva, Switzerland), today announced the discovery of more than 50 new exoplanets orbiting nearby stars, including sixteen super-Earths [2]. This is the largest number of such planets ever announced at one time [3]. The new findings are being presented at a conference on Extreme Solar Systems where 350 exoplanet experts are meeting in Wyoming, USA.

“The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better — the new results show that the pace of discovery is accelerating,” says Mayor.

In the eight years since it started surveying stars like the Sun using the radial velocity technique HARPS has been used to discover more than 150 new planets. About two thirds of all the known exoplanets with masses less than that of Neptune [4] were discovered by HARPS. These exceptional results are the fruit of several hundred nights of HARPS observations [5].

Working with HARPS observations of 376 Sun-like stars, astronomers have now also much improved the estimate of how likely it is that a star like the Sun is host to low-mass planets (as opposed to gaseous giants). They find that about 40% of such stars have at least one planet less massive than Saturn. The majority of exoplanets of Neptune mass or less appear to be in systems with multiple planets.

With upgrades to both hardware and software systems in progress, HARPS is being pushed to the next level of stability and sensitivity to search for rocky planets that could support life. Ten nearby stars similar to the Sun were selected for a new survey. These stars had already been observed by HARPS and are known to be suitable for extremely precise radial velocity measurements. After two years of work, the team of astronomers has discovered five new planets with masses less than five times that of Earth.

“These planets will be among the best targets for future space telescopes to look for signs of life in the planet’s atmosphere by looking for chemical signatures such as evidence of oxygen,” explains Francesco Pepe (Geneva Observatory, Switzerland), the lead author of one of the recent papers.

One of the recently announced newly discovered planets, HD 85512 b, is estimated to be only 3.6 times the mass of the Earth [6] and is located at the edge of the habitable zone — a narrow zone around a star in which water may be present in liquid form if conditions are right [7].

“This is the lowest-mass confirmed planet discovered by the radial velocity method that potentially lies in the habitable zone of its star, and the second low-mass planet discovered by HARPS inside the habitable zone,” adds Lisa Kaltenegger (Max Planck Institute for Astronomy, Heidelberg, Germany and Harvard Smithsonian Center for Astrophysics, Boston, USA), who is an expert on the habitability of exoplanets.

The increasing precision of the new HARPS survey now allows the detection of planets under two Earth masses. HARPS is now so sensitive that it can detect radial velocity amplitudes of significantly less than 4 km/hour [8] — less than walking speed.

"The detection of HD 85512 b is far from the limit of HARPS and demonstrates the possibility of discovering other super-Earths in the habitable zones around stars similar to the Sun," adds Mayor.

These results make astronomers confident that they are close to discovering other small rocky habitable planets around stars similar to our Sun. New instruments are planned to further this search. These include a copy of HARPS to be installed on the Telescopio Nazionale Galileo in the Canary Islands, to survey stars in the northern sky, as well as a new and more powerful planet-finder, called ESPRESSO, to be installed on ESO’s Very Large Telescope in 2016 [9]. Looking further into the future also the CODEX instrument on the European Extremely Large Telescope (E-ELT) will push this technique to a higher level.

"In the coming ten to twenty years we should have the first list of potentially habitable planets in the Sun's neighbourhood. Making such a list is essential before future experiments can search for possible spectroscopic signatures of life in the exoplanet atmospheres," concludes Michel Mayor, who discovered the first-ever exoplanet around a normal star in 1995.

Notes

[1] HARPS measures the radial velocity of a star with extraordinary precision. A planet in orbit around a star causes the star to regularly move towards and away from a distant observer on Earth. Due to the Doppler effect, this radial velocity change induces a shift of the star’s spectrum towards longer wavelengths as it moves away (called a redshift) and a blueshift (towards shorter wavelengths) as it approaches. This tiny shift of the star’s spectrum can be measured with a high-precision spectrograph such as HARPS and used to infer the presence of a planet.

[2] 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.

[3] Currently the number of exoplanets stands at close to 600. In addition to exoplanets found using radial velocity techniques, more than 1200 exoplanet candidates have been found by NASA’s Kepler mission using an alternative method — searching for the slight drop in the brightness of a star as a planet passes in front of it (transits) and blocks some of the light. The majority of planets discovered by this transit method are very distant from us. But, in contrast, the planets found by HARPS are around stars close to the Sun. This makes them better targets for many kinds of additional follow-up observations.

[4] Neptune has about seventeen times the mass of Earth.

[5] This huge observing programme is led by Stéphane Udry (Geneva Observatory, Switzerland).

[6] Using the radial velocity method, astronomers can only estimate a minimum mass for a planet as the mass estimate also depends on the tilt of the orbital plane relative to the line of sight, which is unknown. From a statistical point of view, this minimum mass is however often close to the real mass of the planet.

[7] So far, HARPS has found two super-Earths that may lie within the habitable zone. The first one, Gliese 581 d, was discovered in 2007 (eso0722). HARPS was also recently used to demonstrate that the other candidate super-Earth in the habitable zone around the star Gliese 581 (Gliese 581 g) does not exist.

[8] With large numbers of measurements, the detection sensitivity of HARPS is close to 100% for super-Earths of ten Earth-masses with orbital periods of up to one year, and even when considering planets of three Earth masses with a one-year orbit, the probability of detection remains close to 20%.

[9] ESPRESSO, the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, is to be installed on the ESO Very Large Telescope. Currently undergoing preliminary design, it is scheduled to start operating in 2016. ESPRESSO will feature radial velocity precision of 0.35 km/h or less. For comparison, Earth induces a 0.32 km/h radial velocity on the Sun. This resolution should thus enable ESPRESSO to discover Earth-mass planets in the habitable zone of low-mass stars.
More information

The results are being presented on 12 September 2011 at the conference on Extreme Solar Systems held at the Grand Teton National Park, Wyoming, USA.

A summary is presented in the following paper (in preparation): “The HARPS search for southern extra-solar planets, XXXIV — Occurrence, mass distribution and orbital properties of super-Earths and Neptune-type planets” to appear in the journal Astronomy & Astrophysics.

The team is composed of M. Mayor (Observatoire de Genève [OAUG], Switzerland), M. Marmier (OAUG), C. Lovis (OAUG), S. Udry (OAUG), D. Ségransan (OAUG), F. Pepe (OAUG), W. Benz (Physikalisches Institut Universität Bern, Switzerland), J. L. Bertaux (Service d’Aéronomie, Paris, France), F. Bouchy (Institut d’Astrophysique de Paris, Université Pierre & Marie Curie, France and Observatoire de Haute-Provence/CNRS, France), X. Dumusque (OAUG), G. LoCurto (ESO, Germany), C. Mordasini (Max Planck Institute for Astronomy, Germany), D. Queloz (OAUG), N. C. Santos (Centro de Astrofísica da Universidade do Porto, Portugal and Departamento de Física de Astronomia, Faculdade de Ciências da Universidade do Porto, Portugal), D. Queloz (OAUG).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Science papers in Astronomy & Astrophysics:

“The HARPS search for Earth-like planets in the habitable zone, I — Very low-mass planets around HD20794, HD85512, HD192310” (Pepe et al., 2011)
"The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets" (Mayor et al., 2011)

HARPS
ESPRESSO
Gliese 581
Photos of La Silla Observatory

Contacts

Stéphane Udry
Observatoire de l’Université de Genève
Switzerland
Tel: +41 22 379 24 67
Email: stephane.udry@unige.ch

Francesco Pepe
Observatoire de l’Université de Genève
Switzerland
Tel: +41 223 792 396
Cell: +41 79 302 47 40
Email: francesco.pepe@unige.ch

Lisa Kaltenegger
Research Group Leader, Max Planck Institute for Astronomy
Heidelberg, Germany
Email: kaltenegger@mpia.de

Richard Hook
La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

More about → Fifty New Exoplanets Discovered by HARPS

Alien World is Blacker than Coal

The distant exoplanet TrES-2b, shown here in an artist's conception, is darker than the blackest coal. This Jupiter-sized world reflects less than one percent of the light that falls on it, making it blacker than any planet or moon in our solar system. Astronomers aren't sure what vapors in the planet's superheated atmosphere cloak it so effectively. Credit: David A. Aguilar (CfA)

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Cambridge, MA - 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 sunlight 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 Center 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.



TrES-2b orbits its star at a distance of only three million miles. The star's intense light heats TrES-2b to a temperature of more than 1,800° Fahrenheit - much too hot for ammonia clouds. Instead, its exotic atmosphere contains light-absorbing chemicals like vaporized 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."



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."



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 away in the direction of the constellation Draco. (One light-year is about 6 trillion miles.)



This research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available online.



For more information on NASA’s Kepler mission, visit: http://www.nasa.gov/kepler. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:



David A. Aguilar

Director of Public Affairs

Harvard-Smithsonian Center for Astrophysics

617-495-7462

daguilar@cfa.harvard.edu



Christine Pulliam

Public Affairs Specialist

Harvard-Smithsonian Center for Astrophysics

617-495-7463

cpulliam@cfa.harvard.edu

Source: HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS

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Exoplanet Aurora: An Out-of-this-World Sight

This artist's conception shows a "hot Jupiter" and its two hypothetical moons with a sunlike star in the background. The planet is cloaked in brilliant aurorae triggered by the impact of a coronal mass ejection. Theoretical calculations suggest that those aurorae could be 100-1000 times brighter than Earth's. Credit: David A. Aguilar (CfA). High Resolution Image (jpg)

In this animation, stunning aurorae ripple around a "hot Jupiter." When a stellar eruption known as a coronal mass ejection hit the planet, it triggered these aurorae, which are the planetary equivalent of Earth's Northern and Southern Lights. However, this exoplanet's aurorae shine up to a thousand times brighter than Earth's, and extend from the equator to the poles. Animation created by Hyperspective Studios. Credit: CfA. Animation (mov)

Cambridge, MA - Earth's aurorae, or Northern and Southern Lights, provide a dazzling light show to people living in the polar regions. Shimmering curtains of green and red undulate across the sky like a living thing. New research shows that aurorae on distant "hot Jupiters" 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 Center for Astrophysics (CfA).

Earth's aurorae are created when energetic particles from the Sun slam into our planet's magnetic field. The field guides solar 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.

Particularly strong aurorae result when Earth is hit by a coronal mass ejection or CME - a gigantic blast that sends billions of tons 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.

Cohen and his colleagues used computer models to study what would happen if a gas giant in a close orbit, just a few million miles 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. A "hot Jupiter" would feel a stronger and more focused blast, like the difference between being 100 miles from an erupting volcano or one mile 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.

In the model, a CME hits the "hot Jupiter" and weakens its magnetic shield. Then CME particles reach the gas giant's atmosphere. Its aurora lights up in a ring around the equator, 100-1000 times more energetic than Earthly aurorae. Over the course of about 6 hours, the aurora then ripples up and down toward the planet's north and south poles before gradually fading away.

Despite the extreme forces involved, the exoplanet's magnetic field shields its atmosphere from erosion.

"Our calculations show how well the planet's protective mechanism works," explained Cohen. "Even a planet with a magnetic field much weaker than Jupiter's would stay relatively safe."

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 Earthlike 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 liquid water. 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.

This research has been accepted for publication in The Astrophysical Journal and is available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics

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NASA's Hubble Makes One Millionth Science Observation

Transiting Exoplanet HAT-P-7b
Credit: NASA, ESA, and G. Bacon (STScI)

All-Sky illustration of all Hubble observations as of June 27, 2011

Credit: NASA, ESA, and R. Thompson (CSC/STScI)

NASA's Hubble Space Telescope crossed another milestone in its space odyssey of exploration and discovery. On Monday, July 4, the Earth-orbiting observatory logged its one millionth science observation during a search for water in an exoplanet's atmosphere 1,000 light-years away.

"For 21 years Hubble has been the premier space science observatory, astounding us with deeply beautiful imagery and enabling ground-breaking science across a wide spectrum of astronomical disciplines," said NASA Administrator Charles Bolden. He piloted the space shuttle mission that carried Hubble to orbit. "The fact that Hubble met this milestone while studying a faraway planet is a remarkable reminder of its strength and legacy."

Although Hubble is best known for its stunning imagery of the cosmos, the millionth observation is a spectrocopic measurement, where light is divided its component colors. These color patterns can reveal the chemical composition of cosmic sources.

Hubble's millionth exposure is of the planet HAT-P-7b, a gas giant planet larger than Jupiter orbiting a star hotter than our Sun. HAT-P-7b, also known as Kepler 2b, has been studied by NASA's planet-hunting Kepler observatory after it was discovered by ground-based observations. Hubble now is being used to analyze the chemical composition of the planet's atmosphere.

"We are looking for the spectral signature of water vapor. This is an extremely precise observation and it will take months of analysis before we have an answer," said Drake Deming of the University of Maryland and NASA's Goddard Space Flight Center in Greenbelt, Md. "Hubble demonstrated it is ideally suited for characterizing the atmospheres of exoplanets, and we are excited to see what this latest targeted world will reveal."

"This exciting set of observations in search of water vapor on a planet orbiting another star is laying the foundation for how we plan to use the James Webb Space Telescope's more powerful vision to look for liquid water on nearby planets, the necessary precursor to extraterrestrial life," said Matt Mountain, STScI director.

Hubble was launched April 24, 1990, aboard space shuttle Discovery's STS-31 mission. Its discoveries revolutionized nearly all areas of astronomical research from planetary science to cosmology. The observatory has collected more than 50 terabytes of data to-date. The archive of that data is available to scientists and the public at: http://hla.stsci.edu/

Hubble's odometer reading includes every observation of astronomical targets since its launch and observations used to calibrate its suite of instruments. Hubble made the millionth observation using its Wide Field Camera 3, a visible- and infrared-light imager with an on-board spectrometer. It was installed by astronauts during Hubble Servicing Mission 4 in May 2009.

"The Hubble keeps amazing us with groundbreaking science," said Sen. Barbara Mikulski, the chairwoman of the Senate Commerce, Justice, Science and Related Agencies Appropriations Subcommittee that funds NASA. "I championed the mission to repair and renew Hubble not just to get one million science observations, but also to inspire millions of children across the planet to become our next generation of stargazers, scientists, astronauts and engineers."

CONTACT

Trent Perrotto
NASA Headquarters, Washington, D.C.
trent.j.perrotto@nasa.gov
202-358-0321

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

More about → NASA's Hubble Makes One Millionth Science Observation