Showing posts 1 - 40 of 40. View more »
Rocky planets in elliptical orbit experience hot and cold periods sometimes crossing the habitable zone. The new study provides a way to quantify whether these planets are able to support surface liquid water. Credit: PHL @ UPR Arecibo.
There Might be More Planets in the Habitable Zone
A common assumption in the search for habitable abodes beyond Earth is that the average temperature of planets always increases the more elliptical their orbit is. Now, scientists from the Planetary Habitability Laboratory (PHL) and the Arecibo Observatory in Puerto Rico have shown that planets in elliptical orbits are generally colder than previously believed.
Planets can move around their parent star in orbits that are not perfectly circular. These elliptical orbits put planets sometimes significantly closer or farther from their star, thus contributing to extreme temperature changes. This is not the case of Earth, and probably for the exoplanets orbiting the stars Proxima Centauri or TRAPPIST-1, but true for many known planets around other stars.
In the past, scientists assumed the average equilibrium temperature of a planet would increase with eccentricity because the average energy received from its star, the stellar flux, also increases with eccentricity. A new study, published in the Astrophysical Journal Letters, provides a new model that shows this is not always the case.
“A change in stellar flux does not translate accordingly to a change of temperature along elliptical orbits”, says Abel Méndez, a Planetary Astrobiologist from the PHL at the University of Puerto Rico at Arecibo and lead author of the study.
The equilibrium temperature is one of many important factors controlling the global climate of planets, from Mars-sized to Jupiter-sized worlds. The surface temperature of potentially habitable planets also depend on their equilibrium temperature and atmospheric greenhouse effect.
“We discovered this orbital cooling effect when we were not able to match the numerical models of our Habitable Exoplanet Catalog with current analytical models, so we derived a new analytical model that explains it,” says Méndez.
“If we followed some of the previous models, Mars, which is a planet with an eccentric orbit, should have an equilibrium temperature of -43 °C” , noted Edgard Rivera-Valentín, a Planetary Scientists at the Arecibo Observatory with the Universities Space Research Association and co-author of the study, “Now we’re getting -63 °C, which matches what we’ve observed.”
Hints to the orbital cooling effect described by Méndez & Rivera-Valentín appeared first in climate simulations of Earth-like planets in eccentric orbits. “Now we know that this is a universal effect not only caused by changes on the planet’s albedo, its ability to reflect stellar radiation,” says Méndez.
The study also suggests a new method to determine whether planets in elliptical orbits are within the habitable zone, the region around a star where rocky planets could support surface liquid water. This might have an impact on the number of planets considered potentially habitable, especially those initially considered too hot for life.
The effect described in the study is negligible for planets in nearly circular orbits, but strong enough to reevaluate the habitability of those in very elliptical orbits such as the planets of the red-dwarf star Wolf 1061 or even potential exomoons around warm jupiters.
Abel Méndez, PHL @ UPR Arecibo
Edgard Rivera-Valentín, Arecibo Observatory/USRA
Anilyn Diaz Hernandez, Press Officer, UPR Arecibo
Prof. Abel Méndez is a Planetary Astrobiologist and Associate Professor of Physics and Astrobiology at the University of Puerto Rico at Arecibo. He is the Director of the PHL, a laboratory dedicated to studies of the habitability of Earth, the Solar System, and extrasolar planets. He is also the co-author of the popular science book Searching for Habitable Worlds.
Dr. Edgard Rivera-Valentín is a Planetary Scientist at the Arecibo Observatory (AO) with the Universities Space Research Association (USRA). At AO he conducts observations of NEOs as part of NASA's Near-Earth Object Observations program. His research focuses on astrobiology and Solar System formation.
The Planetary Habitability Laboratory is a project of the University of Puerto Rico at Arecibo supported by the National Science Foundation, the NASA Astrobiology Institute, and the University of Puerto Rico. Computational resources are provided by the UPR’s High Performance Computing Facility.
The Arecibo Observatory is a facility of the National Science Foundation operated by SRI International in alliance with the Universities Space Research Association (USRA) and Ana G. Méndez-Universidad Metropolitana. The Planetary Radar Program at AO is fully funded by NASA through grants from the Near-Earth Object Observations program managed by USRA.
Artist concept of an Autonomous Active Sail (AAS) approaching the potentially habitable exoplanet Proxima b. The reflection of Proxima Centauri and background stars are seen on the mirror-like surface of the sail. Four communication lasers beams are shown firing from its corners to transmit information back to Earth. The lower right panels of the sail are in the process of becoming darker to change its direction and orientation from differences in radiation pressure. Credit: PHL @ UPR Arecibo.
Space travel visionaries solve the problem of interstellar slowdown at our stellar neighbour
In April last year, billionaire Yuri Milner announced the Breakthrough Starshot Initiative. He plans to invest 100 million US dollars in the development of an ultra-light light sail that can be accelerated to 20 percent of the speed of light to reach the Alpha Centauri star system within 20 years. The problem of how to slow down this projectile once it reaches its target remains a challenge. René Heller of the Max Planck Institute for Solar System Research in Göttingen and his colleague Michael Hippke propose to use the radiation and gravity of the Alpha Centauri stars to decelerate the craft. It could then even be rerouted to the red dwarf star Proxima Centauri and its potential Earth-like planet Proxima b.
In the recent science fiction film Passengers, a huge spaceship flies at half the speed of light on a 120-year-long journey toward the distant planet Homestead II, where its 5000 passengers are to set up a new home. This dream is impossible to realize at the current state of technology. “With today’s technology, even a small probe would have to travel nearly 100,000 years to reach its destination,” René Heller says.
Notwithstanding the technical challenges, Heller and his colleague Michael Hippke wondered, “How could you optimize the scientific yield of this type of a mission?” Such a fast probe would cover the distance from the Earth to the Moon in just six seconds. It would therefore hurtle past the stars and planets of the Alpha Centauri system in a flash.
The solution is for the probe’s sail to be redeployed upon arrival so that the spacecraft would be optimally decelerated by the incoming radiation from the stars in the Alpha Centauri system. René Heller, an astrophysicist working on preparations for the upcoming Exoplanet mission PLATO, found a congenial spirit in IT specialist Michael Hippke, who set up the computer simulations.
The two scientists based their calculations on a space probe weighing less than 100 grams in total, which is mounted to a 100,000-square-metre sail, equivalent to the area of 14 soccer fields. During the approach to Alpha Centauri, the braking force would increase. The stronger the braking force, the more effectively the spacecraft’s speed can be reduced upon arrival. Vice versa, the same physics could be used to accelerate the sail at departure from the solar system, using the sun as a photon cannon.
The tiny spacecraft would first need to approach the star Alpha Centauri A as close as around four million kilometres, corresponding to five stellar radii, at a maximum speed of 13,800 kilometres per second (4.6 per cent of the speed of light). At even higher speeds, the probe would simply overshoot the star.
During its stellar encounter, the probe would not only be repelled by the stellar radiation, but it would also be attracted by the star’s gravitational field. This effect could be used to deflect it around the star. These swing-by-manoeuvres have been performed numerous times by space probes in our solar system. “In our nominal mission scenario, the probe would take a little less than 100 years – or about twice as long as the Voyager probes have now been travelling. And these machines from the 1970s are still operational,” says Michael Hippke.
Theoretically, the autonomous, active light sail proposed by Heller and Hippke could settle into a bound orbit around Alpha Centauri A and possibly explore its planets. However, the two scientists are thinking even bigger. Alpha Centauri is a triple star system. The two binary stars A and B revolve around their common centre of mass in a relatively close orbit, while the third star, Proxima Centauri, is 0.22 light years away, more than 12,500 times the distance between the Sun and the Earth.
The sail could be configured so that the stellar pressure from star A brakes and deflects the probe toward Alpha Centauri B, where it would arrive after just a few days. The sail would then be slowed again and catapulted towards Proxima Centauri, where it would arrive after another 46 years − about 140 years after its launch from Earth.
An interstellar mission of an Autonomous Active Sail (AAS) to the nearest three stars. The sail uses an active reflective surface to change its direction and orientation from photogravitational assists from the stars, including the Sun. A light 90 grams sail could take nearly 100 years to reach Alpha Centauri A and another 50 years to Proxima Centauri. Many engineering challenges will need to be solved to pack enough communication and science instruments in such light but wide interstellar probes. Credit: PHL @ UPR Arecibo.
Proxima Centauri caused a sensation in August 2016 when astronomers at the European Southern Observatory (ESO) discovered an exoplanet companion that is about as massive as the Earth and that orbits the star in its so-called habitable zone. This makes it theoretically possible for liquid water to exist on its surface – water being a key prerequisite for life on Earth.
“This finding prompted us to think about the possibility of stopping a high-velocity interstellar lightsail at Proxima Centauri and its planet,” says René Heller. The Max Planck researcher and his colleague propose another change to the strategy for the Starshot project: instead of a huge energy-hungry laser, the Sun’s radiation could be used to accelerate a nanoprobe beyond the solar system. “It would have to approach the Sun to within about five solar radii to acquire the necessary momentum,” Heller says.
The two astronomers are now discussing their concept with the members of the Breakthrough Starshot Initiative, to whom they owe the inspiration for their study. “Our new mission concept could yield a high scientific return, but only the grandchildren of our grandchildren would receive it. Starshot, on the other hand, works on a timescale of decades and could be realized in one generation. So we might have identified a longterm, follow-up concept for Starshot,” Heller says.
Although the new scenario is based on a mathematical study and computer simulations, the proposed hardware of the sail is already being developed in laboratories today: “The sail could be made of graphene, an extremely thin and light but mega-tough carbon film,” René Heller says. The film would have to be blanketed by a highly reflective cover to endure the harsh conditions of deep space and the heat near the destination star.
The optical and electronic systems would have to be tiny. But if you were to remove all the unnecessary components from a modern smartphone, “only a few grams of functional technology would remain.” Moreover, the lightweight spacecraft would have to navigate independently and transmit its data to Earth by laser. To do so, it would need energy, which it could harness from the stellar radiation.
Breakthrough Starshot therefore poses daunting challenges that have so far only been solved theoretically. Nevertheless, “many great visions in the history of mankind had to struggle with seemingly insurmountable obstacles,” Heller says. “We could soon be entering an era in which humans can leave their own star system to explore exoplanets using fly-by missions.”
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,
Morin, Julien, Nelson, Richard P., Ortiz, José L.,
Ofir, Aviv, Paardekooper, Sijme-Jan, Reiners, Ansgar,
Rodríguez, Eloy, Rodríguez-López, Cristina, Sarmiento, Luis F.,
Strachan, John P., Tsapras, Yiannis, Tuomi, Mikko,
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.
1-10 of 40