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Proxima b was added to the Habitable Exoplanets Catalog
An international team of astronomers from the Pale Red Dot campaign have found evidence of a potentially habitable world orbiting the closest star to Earth, Proxima Centauri, a cool red-dwarf slightly older than the Sun . The planet, named Proxima b, has a minimum mass of 1.3 times that of Earth and orbits its parent star every 11.2 days, receiving about 70% the energy Earth receives from the Sun.
A potentially habitable world is a planet around another star that might support liquid water on its surface and therefore lies within the so-called habitable zone. Though currently we cannot tell exactly how habitable such planets are because we can not investigate their geologic or atmospheric composition, it is believed that small planets located in the habitable zone, just like Earth and now Proxima b, would be more likely to have the right conditions for life as we know it.
Proxima b was added to the Habitable Exoplanets Catalog (HEC)  as one of the best objects of interest for the search for life in the universe. The planet orbits well within the conservative habitable zone of Proxima Centauri. Additionally, Proxima b is now not only the closest potentially habitable planet to Earth (4.2 light years away), but it is also the most similar to Earth (ESI = 0.87) , with respect to Earth’s mass and insolation.
Other factors, though, make Proxima b quite different from Earth. It is probably tidally-locked, always giving the same face to its star. The illuminated side might be too hot, while the dark side too cold for liquid water or life. A thick atmosphere or a large ocean, though, could regulate the temperatures across the planet, but we do not know if this is the case .
Probably the most detrimental factor for the habitability of Proxima b is the activity of its parent star, which produces strong magnetic fields, flares, and high UV and X-ray fluxes as most red-dwarf stars do. These factors may lead to the atmospheric and water loss of the planet, but would not necessarily preclude habitable conditions , , . Should Proxima b have a magnetic field, much like Earth does, it would potentially be shielded from such devastating forces.
The mass of Proxima b suggests a rocky composition, but we do not know its radius to evaluate its bulk density . The planet could be between 0.8 to 1.4 Earth radii depending on composition  and if rocky should be about 10% larger than Earth. However, Proxima b could be larger given that we only know its minimum mass.
Statistically, it is not expected to have a potentially habitable world so close to Earth due to their expected low occurrence in the galaxy. It is estimated that 24% of red-dwarf stars have an Earth-sized planet (1 to 1.5 RE) in the optimistic habitable zone . This corresponds to an average separation of eight light years between them in the Solar Neighborhood (248 red-dwarfs within 10 parsecs) . Therefore, the probability of having a potentially habitable world orbiting our nearest star is less than 10%. Either Proxima b was a lucky find or these worlds are more common than previously thought.
The most exciting aspect of this discovery is that Proxima b is relatively close enough to Earth for detailed studies in the next years by current and future observatories. Other known potentially habitable worlds, especially those from the NASA Kepler primary mission, are too far away to get any information about their atmosphere or composition with current technology. Projects like StarShot are even considering the possibility of reaching the stars with miniaturized space probes, but this exciting approach might take many decades.
Proxima b is an excellent object for future characterization via transit or direct imaging in search for biosignatures . There is a 1.5% chance that Proxima b transits its parent star . Such transits will take 53 minutes as seen from Earth and will produce a notable 0.5% decrease on the brightness of Proxima Centauri . Direct imaging in the next decades might even provide information about the surface and weather of Proxima b .
In any case, Proxima b is now one of the prime targets to understand the extension of our habitable universe in years to come. Red-dwarf stars are the most common star in our galaxy, comprising about 75% of the stars. If we find out that planets around red-dwarf stars, such as Proxima b, are in fact not habitable then the ‘real estate’ for life in the universe will be instead very small. The answer lies 4.2 light years away waiting for us.References
 Anglada-Escudé, Guillem , Amado, Pedro J., Barnes, John,
Butler, R. Paul, Coleman, Gavin A. L., de la Cueva, Ignacio,
Dreizler, Stefan, Endl, Michael, Giesers, Benjamin,
Jeffers, Sandra V., Jenkins, James S., Jones, Hugh R. A., Kiraga, Marcin, Kürster, Martin, López-González, María J., Marvin, Christopher J., Berdiñas, Zaira M., Morales, Nicolás,
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Zechmeister, Mathias. (2016). A terrestrial planet candidate in a temperate orbit around Proxima Centauri. Nature XX, XX.
 The Earth Similarity Index (ESI) is a measure of Earth-likeness from zero (no similarity) to one (identical to Earth) given some known planetary properties. For exoplanets the ESI is based on stellar flux and either the mass or radius of the planets. Since habitability depends on many other factors it is not known if planets with similar mass and stellar flux to Earth (i.e., ESI values closer to one) are also in general more habitable.
 Kopparapu, R. kumar, Wolf, E. T., Haqq-Misra, J., Yang, J., Kasting, J. F., Meadows, V., … Mahadevan. (2016). The Inner Edge of the Habitable Zone for Synchronously Rotating Planets around Low-mass Stars Using General Circulation Models. The Astrophysical Journal, 819(1), 84. http://doi.org/10.3847/0004-637X/819/1/84
 Vidotto, A. A., Jardine, M., Morin, J., Donati, J.-F., Lang, P., & Russell, A. J. B. (2013). Effects of M dwarf magnetic fields on potentially habitable planets. Astronomy & Astrophysics, 557, A67. http://doi.org/10.1051/0004-6361/201321504
 Zuluaga, J. I., Bustamante, S., Cuartas, P. A., & Hoyos, J. H. (2013). The Influence of Thermal Evolution in the Magnetic Protection of Terrestrial Planets. The Astrophysical Journal, 770(1), 23. http://doi.org/10.1088/0004-637X/770/1/23
 Bolmont, E., Selsis, F., Owen, J. E., Ribas, I., Raymond, S. N., Leconte, J., & Gillon, M. (2016). Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: Implications for the planets of TRAPPIST-1. arXiv:1605.00616 [astro-Ph]. Retrieved from http://arxiv.org/abs/1605.00616
 Dressing, C. D., & Charbonneau, D. (2015). The Occurrence of Potentially Habitable Planets Orbiting M Dwarfs Estimated from the Full Kepler Dataset and an Empirical Measurement of the Detection Sensitivity. The Astrophysical Journal, 807(1), 45. http://doi.org/10.1088/0004-637X/807/1/45
 Seager, S., Bains, W., & Petkowski, J. j. (2016). Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry. Astrobiology, 16(6), 465–485. http://doi.org/10.1089/ast.2015.1404
 Burke, C. J., & McCullough, P. R. (2014). Transit and Radial Velocity Survey Efficiency Comparison for a Habitable Zone Earth. The Astrophysical Journal, 792(1), 79. http://doi.org/10.1088/0004-637X/792/1/79
Note: The PHL @ UPR Arecibo created an independent assessment, and produced multimedia content for ESO and the general public as part of the announcement of the Proxima b discovery. We acknowledge the collaboration of Guillem Anglada-Escudé from Queen Mary University of London (lead scientist of the discovery), the ESO Public Information Office, Edgard Rivera-Valentín from the Arecibo Observatory (USRA), the computational resources of the HPCf of the University of Puerto Rico, the University of Puerto Rico at Arecibo, and the music of Lyford Rome.
Video 01. The Pale Red Dot campaign aimed to find a planet orbiting our nearest stellar neighbor, Proxima Centauri. Incredibly, the quest succeeded and the team did indeed find a planet. Even more exciting, the planet, Proxima b, falls within the habitable zone of its host star. The newly discovered Proxima b is by far the closest potential abode for alien life. Credit: ESO.
Video 02. This is an artistic interpretation of the potentially habitable planet around our nearest star, Proxima Centauri. The planet is represented here as a mostly desert-like, tidally-locked world with shallow oceans and a strong atmospheric circulation allowing heat exchange between the light and dark hemispheres. The star and orbit are to scale, but the planet was enlarged (x30) for visibility. Video was rendered by the PHL’s SER software. Additional versions of this video are available here. Credit: PHL @ UPR Arecibo, ESO. Background music ‘Atmospherics Final’ by Lyford Rome.
Video 03. This is a one-minute real-time simulation showing a close encounter with Proxima b at 20% the speed of light. The StarShot Initiative is planning a mission to the Alpha Centauri stellar systems at such speed. The same animation would take over two days to complete at the speed of NASA's New Horizons (~16 km/s). Video was rendered by the PHL’s SER software. Additional versions of this video are available here. Credit: PHL @ UPR Arecibo, ESO. Background music ‘Into the Black’ by Lyford Rome.
Video 04. This is a simulation of the possible surface temperatures of a tidally-locked Proxima b, always giving the same face to its star. The simulations show the large temperature differences between the permanent daylight and nightside hemispheres. This assumes that an ocean and atmosphere transfers heat effectively around the planet, but we do not know yet if this is the case. The temperature range includes habitable conditions, even for complex life (0-50°C). However, Proxima b may also be exposed to high UV and X-ray fluxes that could challenge any presence of life. Proxima b seems to be an extreme, but very interesting planet by terrestrial standards. Additional versions of this video are available here. Credit: M. Turbet/I. Ribas/ESO.
Figure 01. Summary of the properties of the Proxima Centauri System. The size of the red-dwarf star Proxima Centauri and its planet Proxima b are approximately to scale in this diagram. The planet is at a distance of almost 20 times the Earth-Moon distance (74 star radii) from its star. For comparison, Earth is at 407 times the Earth-moon distance from the Sun. Credit: PHL @ UPR Arecibo.
Figure 02. Size comparison of Earth and Proxima b. Proxima b might be about 10% larger than Earth given its minimum mass (1.3 Earth masses) and assuming a rocky composition. This particular artistic representation depicts Proxima b as a mostly desert-like, tidally-locked world with shallow oceans maintained by heat-exchange in a dense atmosphere. Credit: PHL @ UPR Arecibo, NASA EPIC Team.
Figure 03. Size comparison of the red-dwarf star Proxima Centauri and its planet Proxima b with some Solar System bodies, including Earth, Jupiter, Saturn, and the Sun. The color of Proxima Centauri and the Sun were enhanced. Credit: PHL @ UPR Arecibo.
Figure 04. The Alpha Centauri family is composed of three stars. The G-star Alpha Centauri A and its K-star companion B orbit each other in a very eccentric orbit separated from 11 to 36 astronomical units (AU). Proxima Centauri is believed to be also bound to this system, but at a distance of 15,000 AU. Our G-star Sun is shown for scale. The color of the stars were adjusted to approximately imitate the human eye perception. Credit: PHL @ UPR Arecibo.
Figure 05. Simulated comparison of a sunset on Earth and Proxima b. The red-dwarf star Proxima Centauri appears almost three times bigger than the Sun in a redder and darker sky. Red-dwarf stars appear bigger in the sky than sun-like stars, even though they are smaller. This is because they are cooler and the planets have to be closer to them to maintain temperate conditions. The original photo of the beach was taken at Playa Puerto Nuevo in Vega Baja, Puerto Rico. Credit: PHL @ UPR Arecibo.
Figure 06. Simulated comparison of a sunset on Earth with that of four known potentially habitable worlds. The sunset from the planets with red-dwarf stars (Proxima b, Gliese 667C c, and Wolf 1061 c) appear darker, but with a bigger star than those with K-stars (Kepler-442 b) or sun-like stars. Red-dwarf stars appear bigger in the sky than sun-like stars, even though they are smaller, because they are cooler and the planets have to be closer to them to maintain temperate conditions. The original photo of the beach was taken at Playa Puerto Nuevo in Vega Baja, Puerto Rico. Credit: PHL @ UPR Arecibo.
Figure 07. Comparison of the visual appearance of Earth illuminated by the Sun (left) and a red-dwarf star (right). The light from a red-dwarf star, such as Proxima Centauri, makes Earth look darker and with a pale green-yellow tone instead of the familiar pale blue. Credit: PHL @ UPR Arecibo, NASA EPIC Team.
Figure 08. Artistic representations of the top 10 potentially habitable worlds in the Habitable Exoplanets Catalog, now including Proxima b. They are sorted in this image by the Earth Similarity Index (ESI), a measure of how similar a planet is in size (given by radius or mass) and stellar flux (insolation) to Earth. Planetary habitability depends on many factors and it is not known if planets with a similar size and insolation as Earth are generally habitable. Earth, Mars, Jupiter, and Neptune for scale. Planet candidates indicated with asterisks. Credit: PHL @ UPR Arecibo.
Figure 09. Artistic representations of the top 10 potentially habitable worlds in the Habitable Exoplanets Catalog, now including Proxima b. They are sorted in this image by distance from Earth in light years. Earth, Mars, Jupiter, and Neptune for scale. Planet candidates indicated with asterisks. Credit: PHL @ UPR Arecibo.
Figure 10. Orbit of Proxima b assuming a maximum eccentricity of 0.350, but its actual orbit might be less eccentric (closer to the red dotted circle). The size of the habitable zone is shown in a green shade and the ice-line with a blue dotted circle. The orbit is well within the tidal-lock radius (outside of the frame). Credit: PHL @ UPR Arecibo.
Figure 11. This figure shows all planets near the habitable zone, now including Proxima b (darker green shade is the conservative habitable zone and the lighter green shade is the optimistic habitable zone). Only those planets less than 10 Earth masses or 2.5 Earth radii are labeled. Some are still unconfirmed (* = unconfirmed). Size of the circles corresponds to the radius of the planets (estimated from a mass-radius relationship when not available). Credit: PHL @ UPR Arecibo.
Figure 12. Sky map with all the stars with known potentially habitable planets (yellow circles). The star Proxima Centauri is close to the center bottom of the figure. Click image to enlarge. Credit: PHL @ UPR Arecibo, Jim Cornmell.
What does it take to consider a planet potentially habitable? If a planet is suitable for life, could life be present? Is life on other planets inevitable? Even though there is no scientific evidence of extraterrestrial life, scientists continue to gather and analyze astronomical data, leading to a better understanding of what it takes to find such life and where are the best planets to find it.
Scientists Prof. Abel Méndez (Associate Professor of Physics and Director of the Planetary Habitability Laboratory, University of Puerto Rico at Arecibo) and Dr. Wilson González-Espada (Associate Professor of Physics and Science Education, Morehead State University, Kentucky) just published a book describing the search for potentially habitable extrasolar planets and what are the best candidates so far.
Searching for Habitable Worlds: An Introduction, is a fun and accessible book for everyone, from school students and the general public to amateur astronomers of all ages. The use of non-technical language and abundant illustrations make this a quick read to inform everyone about the latest news in the search for other planets that we might be able to inhabit. The book is part of the Institute of Physics/Morgan & Claypool Publishers book series called “IOP Concise Physics”, whose main goal is to make available shorter texts in rapidly advancing areas or topics where an introductory text is more appropriate.
After a brief discussion on why humans are hard-wired to be curious and to explore the unknown, Searching for Habitable Worlds: An Introduction describes what extrasolar planets are, how to detect them, and how to pin down potentially habitable ones. In addition, a data-driven list of the best candidates for habitability is profiled, and the next generation of scientific instruments and probes to detect extrasolar planets are identified.
According to Prof. Méndez, “detecting extrasolar planets is a complex process, but it is becoming easier as instrumentation and technologies evolve. Current methods allow scientists to determine their size, mass, temperature, orbital parameters and possible chemical composition. Only extrasolar planets with a unique combination of physical and chemical properties are classified as potentially habitable. It is also important to consider that, even if an extrasolar planet is not habitable today, it could have been habitable in the past or might potentially be habitable in the future. Earth, for instance, was not habitable nearly five billion years ago but it is now.”
Dr. González-Espada noted that although the book’s contents might sound complex or intimidating, it was carefully written to use accessible language and a lively narrative style that will motivate young people to study astronomy and other physical sciences. “Searching for Habitable Worlds: An Introduction presents topics in a very interesting way, with a minimum of technical jargon and plenty of visuals. At the same time, it highlights the fact that the search and characterization of extrasolar planets is an emerging discipline, and that plenty of breathtaking discoveries are yet to be made.”
Searching for Habitable Worlds: An Introduction is available at the Morgan & Claypool Publishers Bookstore, Amazon (Kindle), and other online book retailers.
Aunque no existe evidencia científica de la existencia de seres extraterrestres, sí se está acumulando evidencia sólida de la existencia de muchos otros planetas en otras estrellas, también conocidos como exoplanetas. Unos pocos de éstos parecen tener el tamaño y la órbita correcta para ser posiblemente habitables. ¿Cuántos de estos mundos pudieran ser habitables? ¿Dónde están? ¿Tendrán esos planetas vida similar a la nuestra o habitarán en ellos organismos jamás soñados por la imaginación humana?
Los científicos boricuas Prof. Abel Méndez (Catedrático Asociado en Física y Director del Laboratorio de Habitabilidad Planetaria, Universidad de Puerto Rico en Arecibo) y el Dr. Wilson González Espada (Catedrático Asociado en Física y Educación Científica, Morehead State University, Kentucky) acaban de publicar el libro Searching for Habitable Worlds. Esta publicación discute la información más reciente sobre los planetas posiblemente habitables, cómo se identifican y cuáles existen hasta el presente.
El libro está dividido en seis ideas principales: (1) Cómo y por qué la curiosidad humana nos ha llevado a explorar las maravillas del espacio; (2) Qué son los exoplanetas y qué técnicas se usan para encontrarlos; (3) Qué es la habitabilidad planetaria y cómo se mide; (4) Qué es la "tabla periodica" de los exoplanetas y cómo ayuda a clasificar exoplanetas similares a la Tierra; (5) Cuántos exoplanetas se han descubierto hasta el presente y cúales son sus características astrofísicas principales; y (6) Qué misiones de exploración espacial están en planes para descubrir aún más mundos posiblemente habitables.
El libro Searching for Habitable Worlds es parte de la serie Libros Concisos del Instituto de Física (IOP, en inglés), una organización científica británica, sin fines de lucro, cuya meta es el avance de la física, su didáctica, investigación y aplicaciones. IOP colabora con la casa editorial norteamericana Morgan & Claypool Publishers. La serie Libros Concisos IOP incluye libros cortos en temas de rápido avance y alta relevancia a la comunidad científica.
Según el Prof. Méndez, “detectar exoplanetas es un proceso complejo, pero que que se hace cada vez más fácil con el uso de tecnologías modernas. Una vez se confirma que un exoplaneta existe, hay que determinar su tamaño, órbita y posible composición química. Para que un mundo sea habitable tiene que tener una combinación poco común de ingredientes.”
“También hay que considerar que, si un planeta no es habitable hoy, pudo haberlo sido en el pasado o serlo en el futuro. Por ejemplo, hace casi cinco billones de años nuestro planeta no era tan habitable, pero cambios geológicos y astronómicos han logrado que hoy día sí lo sea,” añadió el astrobiologo vegabajeño.
Por su parte, el cagüeño Dr. González Espada indicó que, aunque el contenido del libro parecería complicado, el mismo está escrito en un lenguaje sencillo y accessible para jóvenes, astrónomos principiantes y el público en general. “El libro presenta los temas con la menor cantidad de palabras técnicas, y con muchísimas ilustraciones y fotos a color. La idea es que si alguien quiere conocer sobre exoplanetas y habitabilidad de una manera rápida y actualizada, nuestro libro sea una excelente consulta inicial.”
Una de las metas principales del libro es que sirva de inspiración a nuevas generaciones de jóvenes científicos. “Sólo se ha examinado a profundidad una cantidad minúscula del cielo nocturno que vemos, así que existen muchas oportunidades de estudio e investigación. Necesitamos jóvenes que lean nuestro libro y eso los motive a estudiar astronomía y otras ciencias físicas para que hagan los descubrimientos del futuro.”
El libro Searching for Habitable Worlds está disponible en la página web de Morgan & Claypool Publishers y en otras librerías electrónicas, incluyendo Amazon Kindle.
Contacto de Prensa: Viviana Tirado <firstname.lastname@example.org>
Goldilocks (www.goldilocks.info) is an interactive space data visualization providing new ways to see & learn about the planets that fall within the “Circumstellar Habitable Zone (CHZ),” also known as the “Goldilocks Zone.” These are the planets that are believed to have the basic required conditions to support possible life.
Commissioned by, and created for, Visualized, the creative data visualization conference which took place in New York in October 2015, Goldilocks was designed by Data Experience Designer, Jan Willem Tulp with guidance from members of the European Space Agency (ESA) & American History Museum's Earth & Planetary Science Division.
Go to www.goldilocks.info for a full screen view.
For press related quotes from the team involved behind the project, please contact:
Visualized hosts creative data visualization conferences around the world, bringing together the most innovative minds that are changing the way we communicate, understand, and interact with data. The Visualized annual flagship conference takes place in October in New York City.
TULP interactive is an award winning Data Experience Design studio, run by Jan Willem Tulp. TULP interactive helps organizations by creating data visualizations that communicate and find insights in data. TULP interactive works for clients such as Scientific American, Nature, Unicef, UNESCO, World Economic Forum and Amsterdam Airport.
Additional Notes About the Visualizations
New collaboration to study star-planet magnetic interactions.
Caption: Artistic representation of the magnetic field (red lines) around a potentially habitable world (Credit: PHL @ UPR Arecibo).
The Planetary Habitability Laboratory of the University of Puerto Rico at Arecibo (PHL @ UPR Arecibo) is starting a new collaboration with Rice University and the Arecibo Observatory to study the magnetic interactions of stars and planets, focusing on potentially habitable worlds.
There are up to thirty potentially habitable worlds out of the nearly two thousand known confirmed planets around other stars (exoplanets). We understand that these worlds might have the right size and distance from their star to sustain surface liquid water, but little else is known.
Exoplanets similar to Earth could end up dry and unsuitable for life depending on how they evolve with their star. Therefore, it is necessary to understand the long-term interactions between planets and their star to recognize and characterize habitable worlds.
The Sun produces the energy to maintain a temperate environment and sustain life on Earth. It also emits harmful energy that could strip our atmosphere or damage life at a cellular level, but Earth’s magnetic field gives us some protection from the damaging effects of the Sun.
Scientists keep monitoring and understanding how our Sun and Earth interact, maintaining a global habitable environment. However, many stars are much more active than the Sun or suitable planets might lack the protection of a magnetic field, thus limiting their potential for life.
The study as part of this collaboration will model star and planet magnetic interactions using the Sun’s interactions with the Earth, Saturn and Jupiter as calibration points. Such models might help not only to better understand the diversity of habitable worlds out there but also to create new strategies for their search and detection.
The PHL will contribute with its expertise on habitable exoplanets, the creation of educational visualizations, and a summer astronomy academy. The academy will be held at the Integrated Science Multi-use Laboratory (ISMuL) of the UPR Arecibo, and the Arecibo Observatory.
This five-years collaboration, Modeling the Magnetic Interactions between Stars and Planets, is led by members of the Laboratory for Space and Astrophysical Plasmas from the Rice Space Institute and funded by a NSF INSPIRE grant.
— Spanish Version —
Mundos Extraños Alrededor de Estrellas Extrañas
Nueva colaboración para el estudio de las interacciones magnéticas entre estrellas y planetas.
El Laboratorio de Habitabilidad Planetaria de la Universidad de Puerto Rico en Arecibo (PHL @ UPR Arecibo) está comenzando una nueva colaboración con la Universidad de Rice y el Observatorio de Arecibo para estudiar las interacciones de las estrellas con los planetas, centrándose en mundos potencialmente habitables.
Ya hay un máximo de treinta mundos potencialmente habitables entre los casi dos mil planetas conocidos y confirmados alrededor de otras estrellas (exoplanetas). Entendemos que estos mundos pueden tener el tamaño y la distancia a su estrella para mantener agua líquida en su superficie, pero muy poco más se sabe.
Los exoplanetas similares a la Tierra podrían terminar áridos y no aptos para la vida dependiendo de la evolución con su estrella. Por lo tanto, es necesario entender las interacciones a largo plazo entre los planetas y sus estrellas para reconocer y caracterizar mundos habitables.
El Sol produce la energía necesaria para mantener un ambiente templado y sostener la vida en la Tierra. También emite energía dañina que nos podría despojar de nuestra atmósfera o dañar la vida a nivel celular, pero el campo magnético de la Tierra nos da una cierta protección contra los efectos dañinos del Sol.
Los científicos monitorean y estudian cómo el Sol y la Tierra interactúan, manteniendo un ambiente habitable globalmente. Sin embargo, muchas estrellas son mucho más activas que el Sol o los planetas adecuados pudieran carecer de la protección de un campo magnético, lo que limita su potencial para la vida.
El estudio en esta colaboración pretende modelar las interacciones magnéticas de las estrellas y planetas utilizando las interacciones del Sol con la Tierra, Saturno y Júpiter como puntos de calibración. Tales modelos pueden ayudar no sólo para comprender mejor la diversidad de mundos habitables en el universo, sino también para crear nuevas estrategias para su búsqueda y detección.
El PHL contribuirá en este estudio con su experiencia en exoplanetas habitables, creando visualizaciones educativos y ofreciendo una academia de astronomía en verano. La academia se llevará a cabo en el Laboratorio de Multiusos de Ciencias Integradas (ISMuL) de la UPR de Arecibo y el Observatorio de Arecibo.
Scientists from Puerto Rico get together to study habitable planets.
One of the main goals of exoplanet science is the detection and characterization of Earth-like planets. So far, there are about 30 exoplanets considered potentially habitable out of the nearly two thousands already confirmed. However, some or all of these planets might turn out not suitable for life depending on their bulk composition and atmospheric properties.
The Planetary Habitability Laboratory of the UPR Arecibo is organizing a workshop to work on present and future problems on the characterization of Earth-like worlds. The purpose of this workshop is to initiate new multidisciplinary research collaborations on the chemical and biological constraints for simple and complex life on Earth-like planets.
Scientists and graduate students from Puerto Rico interested in the search for life in the universe, especially those with a biology or chemistry background, are invited to this two-hour workshop. The workshop will be held on Thursday, April 30, 2015 from 10AM to 12 Noon at the ISMuL Conference Room of the University of Puerto Rico at Arecibo.
The workshop is sponsored by the Planetary Habitability Laboratory (PHL), the NASA Astrobiology Institute (NAI), the Integrated Science Multi-use Laboratory (ISMuL), and the Center for Research and Creation (CIC) at the University of Puerto Rico at Arecibo (UPR Arecibo).
More information is available on phl.upr.edu/press-releases/ew2. Register online or send an email to email@example.com or call ISMuL at (787) 815-0000 x3680/3690 or (787) 817-4611. Spaces are limited.
10:00 AM Welcome and Introductions
10:10 AM Introduction to Potentially Habitable Worlds
11:10 AM Discussion
12:00 PM Adjourn
Artistic representation of the potentially habitable Super-Earth Gliese 832 c against a stellar nebula background. Credit: PHL @ UPR Arecibo, NASA Hubble, Stellarium.
UPDATE: Check figure 5 for an alternative version.
Gliese 832 c is the nearest best habitable world candidate so far
An international team of astronomers, led by Robert A. Wittenmyer from UNSW Australia, report the discovery of a new potentially habitable Super-Earth around the nearby red-dwarf star Gliese 832, sixteen light years away. This star is already known to harbour a cold Jupiter-like planet, Gliese 832 b, discovered on 2009. The new planet, Gliese 832 c, was added to the Habitable Exoplanets Catalog along with a total of 23 objects of interest. The number of planets in the catalog has almost doubled this year alone.
Gliese 832 c has an orbital period of 36 days and a mass at least five times that of Earth's (≥ 5.4 Earth masses). It receives about the same average energy as Earth does from the Sun. The planet might have Earth-like temperatures, albeit with large seasonal shifts, given a similar terrestrial atmosphere. A denser atmosphere, something expected for Super-Earths, could easily make this planet too hot for life and a "Super-Venus" instead.
The Earth Similarity Index (ESI) of Gliese 832 c (ESI = 0.81) is comparable to Gliese 667C c (ESI = 0.84) and Kepler-62 e (ESI = 0.83). This makes Gliese 832 c one of the top three most Earth-like planets according to the ESI (i.e. with respect to Earth's stellar flux and mass) and the closest one to Earth of all three, a prime object for follow-up observations. However, other unknowns such as the bulk composition and atmosphere of the planet could make this world quite different to Earth and non-habitable.
So far, the two planets of Gliese 832 are a scaled-down version of our own Solar System, with an inner potentially Earth-like planet and an outer Jupiter-like giant planet. The giant planet may well have played a similar dynamical role in the Gliese 832 system to that played by Jupiter in our Solar System. It will be interesting to know if any additional objects in the Gliese 832 system (e.g. planets and dust) follow this familiar Solar System configuration, but this architecture remains rare among the known exoplanet systems.
Figure 1. Artistic representation of the potentially habitable exoplanet Gliese 832 c as compared with Earth. Gliese 832 c is represented here as a temperate world covered in clouds. The relative size of the planet in the figure assumes a rocky composition but could be larger for a ice/gas composition. Credit: PHL @ UPR Arecibo.
Figure 2. Orbital analysis of Gliese 832 c, a potentially habitable world around the nearby red-dwarf star Gliese 832. Gliese 832 c orbits near the inner edge of the conservative habitable zone. Its average equilibrium temperature (253 K) is similar to Earth (255 K) but with large shifts (up to 25K) due to its high eccentricity (assuming a similar 0.3 albedo). Credit: PHL @ UPR Arecibo.
Figure 3. The Habitable Exoplanets Catalog now has 23 objects of interest including Gliese 832 c, the closest to Earth of the top three most Earth-like worlds in the catalog. Credit: PHL @ UPR Arecibo.
Figure 4. Stellar map with the position of all the stars with potentially habitable exoplanets including now Gliese 832 (lower left). Credit: PHL @ UPR Arecibo, Jim Cornmell.
Figure 5. Artistic representation of the potentially habitable Super-Earth Gliese 832 c with an actual photo of its parent star (center) taken on June 25, 2014 from Aguadilla, Puerto Rico by Efrain Morales Rivera of the Astronomical Society of the Caribbean. Original annotated image available here. Credit: Efraín Morales Rivera, Astronomical Society of the Caribbean, PHL @ UPR Arecibo.
Artistic representation of the potentially habitable world Kapteyn b with the globular cluster Omega Centauri in the background. It is believed that the Omega Centauri is the remaining core of a dwarf galaxy that merged with our own galaxy billions of years ago bringing Kapteyn's star along. Credit: PHL @ UPR Arecibo, Aladin Sky Atlas.
The planets around the nearby red-dwarf Kapteyn's star are over twice as old as Earth
An international team of astronomers, led by Guillem Anglada-Escude from Queen Mary University, reports two new planets orbiting a very old and nearby star to the Sun named Kapteyn's star. One of the newly-discovered planets, Kapteyn b, is potentially habitable as it has the right-size and orbit to support liquid water on its surface. What makes this discovery highly interesting is the peculiar story and age of the star. Kapteyn b is likely over twice the age of Earth and the oldest known potentially habitable planet listed in the Habitable Exoplanets Catalog.
The Super-Earth Kapteyn b orbits the star every 48 days and has a mass at least five times that of Earth's. The second planet, Kapteyn c, is a more massive Super-Earth with an orbit of 121 days and too cold to support liquid water. At the moment, only a few properties of the planets are known: minimum masses, orbital periods, and distances to the star. By measuring their atmospheres with future instruments, scientists will try to find out whether some of these planets are truly habitable worlds.
Kapteyn b is probably colder than Earth given a similar atmosphere. However a denser atmosphere could easily provide for equal or even higher temperatures. Based on its stellar flux (45% that of Earth's) and mass (≥ 4.8 Earth masses) the Earth Similarity Index (ESI) of Kapteyn b is comparable to Kepler-62f and Kepler-186f. Given its old age (~11.5 billion years), Kapteyn b has had plenty of time to develop life, as we know it.
The astronomers used new data from HARPS spectrometer at the ESO's La Silla observatory in Chile to measure tiny periodic changes in the motion of the star. Using the Doppler Effect, which shifts the star’s light spectrum depending on its velocity, the scientists worked out some properties of these planets, such as their masses and orbital periods.The study also combined data from two more high-precision spectrometers to secure the detection: HIRES at Keck Observatory and PFS at Magellan/Las Campanas Observatory.
About Kapteyn's Star
Discovered at the end of the 19th century and named after the Dutch astronomer who found it (Jacobus Kapteyn), Kapteyn's is the second fastest moving star in the sky and belongs to the galactic halo, an extended cloud of stars orbiting our Galaxy in very elliptic orbits. With a third of the mass of the Sun, this red-dwarf can be seen in the southern constellation of Pictor with an amateur telescope.
Typical planetary systems detected by NASA's Kepler mission are hundreds of light-years away. In contrast, Kapteyn's star is the 25th nearest star to the Sun and it is only 13 light years away from Earth. It was born in a dwarf Galaxy absorbed and disrupted by the Early Milky Way. Such a galactic disruption event put the star in its fast halo orbit. The likely remnant core of the original dwarf galaxy is Omega Centauri, an enigmatic globular cluster 16,000 light years from Earth which contains hundreds of thousands of similarly old suns. This sets the most likely age of its planets at 11.5 billion years; which is 2.5 times older than Earth and 'only' 2 billion years younger than the Universe itself (~13.7 billion years).
Original Research: Guillem Anglada-Escudé (firstname.lastname@example.org)
Habitable Exoplanets Catalog: Abel Méndez (email@example.com)
Figure 1. Artistic representation of the potentially habitable exoplanet Kapteyn b as compared with Earth. Kapteyn b is represented here as an old and cold ocean planet with a network of channels of flowing water under a thin cloud cover. The relative size of the planet in the figure assumes a rocky composition but could be larger for a ice/gas composition.
Figure 2. Comparison of the relative size of the orbits and the planets of Kapteyn's Star and the inner planets of our Solar System. The two planets of the Kapteyn's star fit within the orbit of Mercury. Planets are magnify x100 and stars x10 with respect to the orbit scale for clarity. The size of the corresponding optimistic (light green) and conservative (dark green) habitable zones are shown.
Figure 3. Details of the orbits of the two planets around the Kapteyn's star. Only one planet is shown in each diagram using a different orbital scale for clarity. The eccentricity of the planets correspond to the upper 99% confidence level, but they are more likely close to circular orbits.
Many Worlds with Complex Life (Credit: PHL @ UPR Arecibo, NASA, Richard Wheeler @Zephyris)
One Percent of All Exoplanets May Be Suitable for Complex Organisms
The number of planets on which complex life could exist in the Milky Way may be as high as 100 million, according to a study published this week by two former University of Texas at El Paso (UTEP) professors and their colleagues in the on-line journal, Challenges.
“This constitutes the first quantitative estimate of the number of worlds in our galaxy that could harbor life above the microbial level, based on objective data,” according to the lead author of the peer-reviewed study, Dr. Louis Irwin, Professor Emeritus and former Chair of Biological Sciences at UTEP.
Irwin and his colleagues surveyed the growing list of more than a thousand known exoplanets (planets in other solar systems). Using a formula that considers planetary density, temperature, substrate (liquid, solid, or gas), chemistry, distance from its central star, and age, Irwin’s team computed a “biological complexity index (BCI)”, which rates planets on a scale of 0 to 1.0 according to the number and degree of characteristics assumed to be important for supporting multiple forms of multicellular life.
The BCI calculation revealed that 1 to 2 percent of exoplanets showed a BCI rating higher than Europa, a moon of Jupiter thought to have a subsurface global ocean which could harbor different forms of life. Based on a very conservative estimate of 10 billion stars in the Milky Way Galaxy, and assuming an average of one planet per star, this yields the figure of 100 million. It could be over 10 times higher if we consider a larger number of stars in our galaxy.
Irwin emphasized that the study does not indicate that complex life exists on that many planets – only that the planetary conditions that could support it do. He also noted that complex life doesn't mean intelligent life (though it doesn't rule it out), or even animal life, but simply that organisms larger and more complex than microbes could exist in a number of different forms, quite likely forming stable food webs like those found in ecosystems on Earth.
“Other scientists have tried to make educated guesses about the frequency of life on other worlds based on hypothetical assumptions, but this is the first study that relies on observable data from actual planetary bodies beyond our solar system,” Irwin said.
Despite the large absolute number of planets that could harbor complex life, the Milky Way is so vast that, statistically, planets with high BCI values are very far apart. One of the closest and most promising extrasolar systems, known as Gliese 581, has possibly two planets with the apparent capacity to host complex biospheres, yet the distance from the sun to Gliese 581 is about 20 light years. One light year is the distance that light travels in one year.
Most planets with a high BCI are much further away. If the 100 million planets that Irwin’s team says have the theoretical capacity for hosting complex life were randomly distributed across the galaxy, they would average about 24 light years apart.
“On the one hand,” according to Irwin, “it seems highly unlikely that we are alone. On the other hand, we are likely so far away from life at our level of complexity, that a meeting with such alien forms is extremely improbable for the foreseeable future.”
Co-authors of the study include Dirk Schulze-Makuch, formerly an Associate Professor of Geological Sciences at UTEP, now at Washington State University, Alberto Fairén of Cornell University, and Abel Méndez, of the University of Puerto Rico at Arecibo.
Not surprisingly, higher BCI values tend to be correlated with higher ESI values, but there are some exceptions. “Planets with the highest BCI values tend to be larger, warmer, and older than Earth,” said Irwin, “so any search for complex or intelligent life that is restricted just to Earth-like planets, or to life as we know it on Earth, will probably be too restrictive.”Science Contacts
Louis Irwin, University of Texas at El Paso (firstname.lastname@example.org)
Figure 1. Biological complexity (BCIrel) relative to Earth similarity (ESI), as calculated in Schulze-Makuch et al. (2011), for Solar System planets (orange squares) and satellites (yellow squares), and for 365 exoplanets for which BCIrel > 0. The vast majority of exoplanets known to date are gas giants (green circles), but the ones with highest BCI values are likely rocky-water worlds (purple circles).
Kepler-186 is a stellar system of five planets with an Earth-size world in the habitable zone.
Simulated comparison of a sunset on Kepler-186f and Earth. On Kepler-186f the star looks dimmer but slightly larger.
All the known potentially habitable exoplanets so far are superterran worlds (aka super-Earths) somewhat larger than Earth. The potential of life of these worlds is difficult to relate to Earth since there are no planets in the Solar System of comparable size and we know very little of them. Now a team of scientists led by Elisa V. Quintana from the SETI Institute and NASA Ames report the discovery of Kepler-186f, the first terran world (Earth-size) in the habitable zone of a star.
Kepler-186f has a similar size to Earth and it is most likely a rocky world. It orbits the M-dwarf star Kepler-186 along with four other inner planets, which are as old as the Solar System (>4 Gyr), in the constellation Cygnus 500 light years away. Kepler-186f receives less stellar flux (~32%) than presently does Mars (~43%). It could have a temperate climate if it has an atmosphere much denser than Earth. Even Earth probably experienced at least one episode of global glaciation with just a slightly lower stellar flux than today, 650 million years ago. However, early Mars had running surface liquid water with a similar stellar flux as Kepler-186f.
Kepler-186f was added to the Habitable Exoplanets Catalog with a low Earth Similarity Index (ESI) of 0.64 due to its potential colder climate. Still, it could be a more Earth-like world if it is experiencing a much higher greenhouse effect than Earth. Nevertheless, Kepler-186f is also the best candidate now of a rocky world in the habitable zone compared to the other known potentially habitable worlds.
Figure 1. Artistic representation of Kepler-186f as a cold world with shallow oceans as compared to Earth. Other possible interpretations of Kepler-186f are as a snowball frozen world (Hoth-like) or a dry cold world (Mars-like).
Figure 2. Orbital distribution of planets in the stellar system Kepler-186 (top) compared to Kepler-62 (bottom). Both planets 'f' of Kepler-186 and Kepler-62 receive about the same stellar flux.
Figure 3. Analysis of the orbit of Kepler-186f. Its equilibrium temperature is around 192 K for a similar terrestrial albedo. For comparison, Mars has an equilibrium temperature of 210 K. Kepler-186f also orbits just in the outer stellar zone for tidally locked-planets but its rotational state is uncertain. The diagram does not show the orbits of the other inner planets of Kepler-186. More details about this figure are available in the Exoplanet Orbital Catalog.
Figure 4. The new lineup of up to 21 potentially habitable exoplanets according to the Habitable Exoplanets Catalog. Kepler-186f is the most Earth-size planet now but it also receives one third the energy from its star than Earth. This significantly lowers its observable similarities with Earth as compared with other planets in the catalog.
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