The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star named LHS 1140, in the constellation of Cetus (The Sea Monster). Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth and lies in the middle of the habitable zone. The orbit is seen almost edge-on from Earth and as the exoplanet passes in front of the star once per orbit it blocks a little of its light every 25 days.
This artist's impression shows the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth and may be the new holder of the title 'best place to look for signs of life beyond the Solar System' [Credit: ESO/spaceengine.org]
"This is the most exciting exoplanet I've seen in the past decade," said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). "We could hardly hope for a better target to perform one of the biggest quests in science—searching for evidence of life beyond Earth."
"The present conditions of the red dwarf are particularly favourable—LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars," explains team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland.
For life as we know it to exist, a planet must have liquid surface water and retain an atmosphere. When red dwarf stars are young, they are known to emit radiation that can be damaging for the atmospheres of the planets that orbit them. In this case, the planet's large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.
Using ESO's HARPS instrument at La Silla, and other telescopes around the world, an international team of astronomers discovered this super-Earth orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth and has likely retained most of its atmosphere [Credit: M. Weiss/CfA]
The discovery was initially made with the MEarth facility, which detected the first telltale, characteristic dips in light as the exoplanet passed in front of the star. ESO's HARPS instrument, the High Accuracy Radial velocity Planet Searcher, then made crucial follow-up observations which confirmed the presence of the super-Earth. HARPS also helped pin down the orbital period and allowed the exoplanet's mass and density to be deduced.
The astronomers estimate the age of the planet to be at least five billion years. They also deduced that it has a diameter 1.4 times larger than the Earth—almost 18 000 kilometres. But with a mass around seven times greater than the Earth, and hence a much higher density, it implies that the exoplanet is probably made of rock with a dense iron core.
This super-Earth may be the best candidate yet for future observations to study and characterise its atmosphere, if one exists. Two of the European members of the team, Xavier Delfosse and Xavier Bonfils both at the CNRS and IPAG in Grenoble, France, conclude: "The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries!".
In particular, observations coming up soon with the NASA/ESA Hubble Space Telescope will be able to assess exactly how much high-energy radiation is showered upon LHS 1140b, so that its capacity to support life can be further constrained.
Further into the future—when new telescopes like ESO's Extremely Large Telescope are operating—it is likely that we will be able to make detailed observations of the atmospheres of exoplanets, and LHS 1140b is an exceptional candidate for such studies.
Two veteran NASA missions are providing new details about icy, ocean-bearing moons of Jupiter and Saturn, further heightening the scientific interest of these and other "ocean worlds" in our solar system and beyond. The findings are presented in papers published Thursday by researchers with NASA's Cassini mission to Saturn and Hubble Space Telescope.
This illustration shows Cassini diving through the Enceladus plume in 2015. New ocean world discoveries from Cassini and Hubble will help inform future exploration and the broader search for life beyond Earth [Credit: NASA/JPL-Caltech]
In the papers, Cassini scientists announce that a form of chemical energy that life can feed on appears to exist on Saturn's moon Enceladus, and Hubble researchers report additional evidence of plumes erupting from Jupiter's moon Europa.
"This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at Headquarters in Washington. "These results demonstrate the interconnected nature of NASA's science missions that are getting us closer to answering whether we are indeed alone or not."
The paper from researchers with the Cassini mission, published in the journal Science, indicates hydrogen gas, which could potentially provide a chemical energy source for life, is pouring into the subsurface ocean of Enceladus from hydrothermal activity on the seafloor.
The presence of ample hydrogen in the moon's ocean means that microbes -- if any exist there -- could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water. This chemical reaction, known as "methanogenesis" because it produces methane as a byproduct, is at the root of the tree of life on Earth, and could even have been critical to the origin of life on our planet.
Life as we know it requires three primary ingredients: liquid water; a source of energy for metabolism; and the right chemical ingredients, primarily carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. With this finding, Cassini has shown that Enceladus -- a small, icy moon a billion miles farther from the sun than Earth -- has nearly all of these ingredients for habitability. Cassini has not yet shown phosphorus and sulfur are present in the ocean, but scientists suspect them to be, since the rocky core of Enceladus is thought to be chemically similar to meteorites that contain the two elements.
"Confirmation that the chemical energy for life exists within the ocean of a small moon of Saturn is an important milestone in our search for habitable worlds beyond Earth," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.
The Cassini spacecraft detected the hydrogen in the plume of gas and icy material spraying from Enceladus during its last, and deepest, dive through the plume on Oct. 28, 2015. Cassini also sampled the plume's composition during flybys earlier in the mission. From these observations scientists have determined that nearly 98 percent of the gas in the plume is water, about 1 percent is hydrogen and the rest is a mixture of other molecules including carbon dioxide, methane and ammonia.
The measurement was made using Cassini's Ion and Neutral Mass Spectrometer (INMS) instrument, which sniffs gases to determine their composition. INMS was designed to sample the upper atmosphere of Saturn's moon Titan. After Cassini's surprising discovery of a towering plume of icy spray in 2005, emanating from hot cracks near the south pole, scientists turned its detectors toward the small moon.
This graphic illustrates how Cassini scientists think water interacts with rock at the bottom of the ocean of Saturn's icy moon Enceladus, producing hydrogen gas [Credit: NASA/JPL-Caltech]
Cassini wasn't designed to detect signs of life in the Enceladus plume -- indeed, scientists didn't know the plume existed until after the spacecraft arrived at Saturn.
"Although we can't detect life, we've found that there's a food source there for it. It would be like a candy store for microbes," said Hunter Waite, lead author of the Cassini study.
The new findings are an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean. Previous results, published in March 2015, suggested hot water is interacting with rock beneath the sea; the new findings support that conclusion and add that the rock appears to be reacting chemically to produce the hydrogen.
The paper detailing new Hubble Space Telescope findings, published in The Astrophysical Journal Letters, reports on observations of Europa from 2016 in which a probable plume of material was seen erupting from the moon's surface at the same location where Hubble saw evidence of a plume in 2014. These images bolster evidence that the Europa plumes could be a real phenomenon, flaring up intermittently in the same region on the moon's surface.
These composite images show a suspected plume of material erupting two years apart from the same location on Jupiter's icy moon Europa. Both plumes, photographed in UV light by Hubble, were seen in silhouette as the moon passed in front of Jupiter [Credit: NASA/ESA/STScI/USGS]
The newly imaged plume rises about 62 miles (100 kilometers) above Europa's surface, while the one observed in 2014 was estimated to be about 30 miles (50 kilometers) high. Both correspond to the location of an unusually warm region that contains features that appear to be cracks in the moon's icy crust, seen in the late 1990s by NASA's Galileo spacecraft. Researchers speculate that, like Enceladus, this could be evidence of water erupting from the moon's interior.
"The plumes on Enceladus are associated with hotter regions, so after Hubble imaged this new plume-like feature on Europa, we looked at that location on the Galileo thermal map. We discovered that Europa's plume candidate is sitting right on the thermal anomaly," said William Sparks of the Space Telescope Science Institute in Baltimore. Sparks led the Hubble plume studies in both 2014 and 2016.
The researchers say if the plumes and the warm spot are linked, it could mean water being vented from beneath the moon's icy crust is warming the surrounding surface. Another idea is that water ejected by the plume falls onto the surface as a fine mist, changing the structure of the surface grains and allowing them to retain heat longer than the surrounding landscape.
For both the 2014 and 2016 observations, the team used Hubble's Space Telescope Imaging Spectrograph (STIS) to spot the plumes in ultraviolet light. As Europa passes in front of Jupiter, any atmospheric features around the edge of the moon block some of Jupiter's light, allowing STIS to see the features in silhouette. Sparks and his team are continuing to use Hubble to monitor Europa for additional examples of plume candidates and hope to determine the frequency with which they appear.
The green oval highlights the plumes Hubble observed on Europa. The area also corresponds to a warm region on Europa's surface. The map is based on observations by the Galileo spacecraft [Credit: NASA/ESA/STScI/USGS]
NASA's future exploration of ocean worlds is enabled by Hubble's monitoring of Europa's putative plume activity and Cassini's long-term investigation of the Enceladus plume. In particular, both investigations are laying the groundwork for NASA's Europa Clipper mission, which is planned for launch in the 2020s.
"If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them," said Jim Green, Director of Planetary Science, at NASA Headquarters.
Hubble's identification of a site which appears to have persistent, intermittent plume activity provides a tempting target for the Europa mission to investigate with its powerful suite of science instruments. In addition, some of Sparks' co-authors on the Hubble Europa studies are preparing a powerful ultraviolet camera to fly on Europa Clipper that will make similar measurements to Hubble's, but from thousands of times closer. And several members of the Cassini INMS team are developing an exquisitely sensitive, next-generation version of their instrument for flight on Europa Clipper.
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With two suns in its sky, Luke Skywalker's home planet Tatooine in "Star Wars" looks like a parched, sandy desert world. In real life, thanks to observatories such as NASA's Kepler space telescope, we know that two-star systems can indeed support planets, although planets discovered so far around double-star systems are large and gaseous. Scientists wondered: If an Earth-size planet were orbiting two suns, could it support life?
This artist's concept shows a hypothetical planet covered in water around the binary star system of Kepler-35A and B [Credit: NASA/JPL-Caltech]
It turns out, such a planet could be quite hospitable if located at the right distance from its two stars, and wouldn't necessarily even have deserts. In a particular range of distances from two sun-like host stars, a planet covered in water would remain habitable and retain its water for a long time, according to a new study in the journal Nature Communications.
"This means that double-star systems of the type studied here are excellent candidates to host habitable planets, despite the large variations in the amount of starlight hypothetical planets in such a system would receive," said Max Popp, associate research scholar at Princeton University in New Jersey, and the Max Planck Institute of Meteorology in Hamburg, Germany.
Popp and Siegfried Eggl, a Caltech postdoctoral scholar at NASA's Jet Propulsion Laboratory, Pasadena, California, created a model for a planet in the Kepler 35 system. In reality, the stellar pair Kepler 35A and B host a planet called Kepler 35b, a giant planet about eight times the size of Earth, with an orbit of 131.5 Earth days. For their study, researchers neglected the gravitational influence of this planet and added a hypothetical water-covered, Earth-size planet around the Kepler 35 AB stars. They examined how this planet's climate would behave as it orbited the host stars with periods between 341 and 380 days.
"Our research is motivated by the fact that searching for potentially habitable planets requires a lot of effort, so it is good to know in advance where to look," Eggl said. "We show that it's worth targeting double-star systems."
In exoplanet research, scientists speak of a region called the "habitable zone," the range of distances around a star where a terrestrial planet is most likely to have liquid water on its surface. In this case, because two stars are orbiting each other, the habitable zone depends on the distance from the center of mass that both stars are orbiting. To make things even more complicated, a planet around two stars would not travel in a circle; instead, its orbit would wobble through the gravitational interaction with the two stars.
Popp and Eggl found that on the far edge of the habitable zone in the Kepler 35 double-star system, the hypothetical water-covered planet would have a lot of variation in its surface temperatures. Because such a cold planet would have only a small amount of water vapor in its atmosphere, global average surface temperatures would swing up and down by as much as 3.6 degrees Fahrenheit (2 degrees Celsius) in the course of a year.
"This is analogous to how, on Earth, in arid climates like deserts, we experience huge temperature variations from day to night," Eggl said. "The amount of water in the air makes a big difference."
But, closer to the stars, near the inner edge of the habitable zone, the global average surface temperatures on the same planet stay almost constant. That is because more water vapor would be able to persist in the atmosphere of the hypothetical planet and act as a buffer to keep surface conditions comfortable.
As with single-star systems, a planet beyond the outer edge of the habitable zone of its two suns would eventually end up in a so-called "snowball" state, completely covered with ice. Closer than the inner edge of the habitable zone, an atmosphere would insulate the planet too much, creating a runaway greenhouse effect and turning the planet into a Venus-like world inhospitable to life as we know it.
Another feature of the study's climate model is that, compared to Earth, a water-covered planet around two stars would have less cloud coverage. That would mean clearer skies for viewing double sunsets on these exotic worlds.
Author: Elizabeth Landau | Source: NASA [April 12, 2017]
What chemical processes in space could have created the building blocks of life is being researched by chemists at Ruhr-Universität Bochum (RUB) in Prof Dr Wolfram Sander's team. In their experiments, the scientists are simulating the conditions in space to understand in detail how certain chemical reactions occur.
How the building blocks of life came to Earth is an unsolved puzzle. Maybe comets had something to do with it [Credit: NASA/JPL-Caltech]
One theory says that the building blocks of life were not created on Earth. Cometary impacts may have brought amino acids, the basic units of proteins, to our planet. How such complex molecules could have formed in space is a question being investigated by Sander's team. The scientists are interested in processes in a condensed phase, i.e. in liquids, solids or on surfaces, into which there has been little research.
A precursor of amino acids
Besides hydrogen and oxygen, the icy core of comets usually also contains nitrogen and carbon -- all the elements needed for an amino acid. A possible precursor of amino acids in space could be the molecule hydroxylamine (NH2-OH), which consists of one nitrogen, one oxygen and three hydrogen atoms. However, it has not yet been possible to verify this in space.
RUB PhD student Yetsedaw Tsegaw investigated in an experiment whether the conditions in space would actually allow this molecule to form. He adjusted the conditions in the comet ice in the lab, brought ammonia (NH3) and oxygen (O2) together in this environment and treated the mixture with high-energy radiation, such as that found in space. He observed the reactions that occurred with a special form of infrared spectroscopy.
Hidden molecule
Tsegaw took the measurements as a guest researcher in the working group of Prof Dr Ralf Kaiser at "WM Keck Research Laboratory in Astrochemistry" in Hawaii. He then analysed the data at RUB. The result: hydroxylamine was actually created in the experiment. However, it was not visible at first sight. The bands of hydroxylamine were overlaid in the infrared spectrum by the bands of other molecules. Only when Tsegaw gradually warmed the sample and the interfering substances evaporated was he able to identify hydroxylamine.
In theory, the molecule could thus form in comet ice. The chemist presumes that people had not been searching for it using the right methods until now.
You can find more information in a detailed article in the science magazine Rubin at Ruhr-Universität Bochum.
Astronomers have detected an atmosphere around the super-Earth planet GJ 1132b. This marks the first detection of an atmosphere around an Earth-like planet other than Earth itself, and thus is a significant step on the path towards the detection of life outside our Solar System. The team that made the discovery, led by Keele University's Dr John Southworth, used the 2.2 m ESO/MPG telescope in Chile to take images of the planet's host star GJ 1132. They were able to measure the slight decrease in brightness as the planet and its atmosphere absorbed some of the starlight while transiting (passing in front of) the host star.
Artist's impression of super-Earth planet GJ 1132b [Credit: Max Planck Society]
Dr John Southworth explains, "While this is not the detection of life on another planet, it's an important step in the right direction: the detection of an atmosphere around the super-Earth GJ 1132b marks the first time that an atmosphere has been detected around an Earth-like planet other than Earth itself."
Is there life out there?
Astronomers' current strategy for finding life on another planet is to detect the chemical composition of that planet's atmosphere, on the look-out for chemical imbalances which could be caused by living organisms. In the case of our own Earth, the presence of large amounts of oxygen is a tell-tale sign of life.
Until these findings by Dr Southworth's team, the only previous detections of exoplanet atmospheres all involved gas giants reminiscent of a high-temperature Jupiter.
Dr Southworth says that whilst we're still a long way from detecting life on exoplanets, this discovery is the first step:
"With this research, we have taken the first tentative step into studying the atmospheres of smaller, Earth-like, planets. We simulated a range of possible atmospheres for this planet, finding that those rich in water and/or methane would explain the observations of GJ 1132b. The planet is significantly hotter and a bit larger than Earth, so one possibility is that it is a "water world" with an atmosphere of hot steam."
Studying atmospheres
The planet in question, GJ 1132b, orbits the very low-mass star GJ 1132 in the Southern constellation Vela, at a distance of 39 light-years from Earth. The system was studied by a team led by John Southworth (Keele University, UK) and Luigi Mancini (currently at the University of Rome Tor Vergata), and including researchers from the Max Planck Institute for Astronomy (MPIA, Germany) and the University of Cambridge.
The team used the GROND imager at the 2.2 m ESO/MPG telescope of the European Southern Observatory in Chile to observe the planet simultaneously at seven different wavelength bands spanning the optical and near-infrared. As GJ 1132b is a transiting planet, it passes directly between Earth and its host star every 1.6 days, blocking a small fraction of the star's light. From the amount of light lost, astronomers can deduce the planet's size -- in this case only 1.4 times that of Earth.
Crucially, the new observations showed the planet to be larger in one of the seven wavelength bands. This suggests the presence of an atmosphere that is opaque to this specific light (making the planet appear larger), but transparent to all the others.
The discovery of this atmosphere is encouraging. Very low-mass stars are extremely common (much more so that Sun-like stars), and are known to host lots of small planets. But they also show a lot of magnetic activity, causing high levels of X-rays and ultraviolet light to be produced which might completely evaporate the planets' atmospheres. However, the properties of GJ 1132b show that an atmosphere can endure this for billion of years without being destroyed. Given the huge number of very low-mass stars and planets, this could mean that the conditions suitable for life are common in the Universe.
This discovery makes GJ 1132b one of the highest-priority targets for further study by the current top facilities, such as the Hubble Space Telescope and ESO's Very Large Telescope, as well as the James Webb Space Telescope which is slated for launch in 2018.
Griffith University archaeologists Associate Professor Adam Brumm, who with Indonesian colleagues led the excavations that yielded the new findings, and Dr Michelle Langley, who analysed the recovered ornaments and art objects.
Excavations at the limestone cave of Leang Bulu Bettue on the Indonesian island of Sulawesi [Credit: Justin Mott]
Griffith University archaeologists are part of a joint Indonesian-Australian team that has unearthed a rare collection of prehistoric art and ‘jewellery’ objects from the Indonesian island of Sulawesi, dating in some instances to as early as 30,000 years ago.
The Australian Research Centre for Human Evolution (ARCHE) team, based in Griffith’s Environmental Futures Research Institute, together with Indonesian colleagues, have shed new light on ‘Ice Age’ human culture and symbolism in a paper published today in Proceedings of the National Academy of Sciences.
Dated to between 26,000 to 22,000 years ago, this humanly modified artefact consists of a drilled and perforated finger bone from an endemic bear cuscus. The hole at one end formerly bore a string, while wear marks on the ornament show that it repeatedly rubbed against human skin or clothing during the period of its use. These facts suggest the perforated bone was suspended for use as a 'pendant' or similar jewelry object [Credit: Griffith University]
The study was co-led by Associate Professor Adam Brumm, an Australian Research Council (ARC) Future Fellow, and Dr Michelle Langley , who also holds a fellowship from the ARC, analysed the recovered artefacts, and is the country’s leading expert in the study of ancient ornaments and bone technology.
“Scientists have long been curious about the cultural lives of the first Homo sapiens to inhabit the lands to the immediate north of Australia sometime prior to 50,000 years ago — part of the great movement of our species out of Africa,” Associate Professor Brumm says.
Prehistoric ornaments excavated from the Sulawesi cave site Leang Bulu Bettue [Credit: Michelle Langley/Adam Brumm/Bear/Luke Marsden]
“Some have argued that Pleistocene human culture declined in sophistication as Homo sapiens ventured beyond India into the Southeast Asian tropics and the island chains east of continental Eurasia, known as ‘Wallacea’. “However, the onset of new research programs in Wallacea is steadily dismantling this view.”
Adding to the 2014 breakthrough discovery of 40,000-year-old cave art on the Wallacean island of Sulawesi, which is said to be some of the world’s oldest, is a unique assemblage of previously unknown symbolic objects excavated from a Sulawesi cave site called Leang Bulu Bettue.
Hollow bone tube with red and black pigments, made from the long bone of a bear cuscus, may have been used as an ‘air-brush’ to create human hand stencils on rock surfaces [Credit: Michelle Langley]
The recovered artefacts, dated to between 30,000 to 22,000 years ago, consist of disc-shaped beads made from a babirusa (‘pig-deer’) tooth and a pendant fashioned from the bone of a bear cuscus (a large and primitive possum-like marsupial found only on Sulawesi), as well as ‘portable’ art objects: stones incised with geometric patterns, the meaning of which is unknown.
Dr Langley’s analysis also revealed extensive evidence for rock art production at the site, including discarded ochre pieces, ochre stains on tools, and a bone tube that may have been a ‘blow-pipe’ for creating hand stencil motifs, the earliest of which date to at least 40,000 years ago on Sulawesi.
Hand stencils may have been created using pigments and a bone 'air-brush' [Credit: Yinika Perston]
“Previously, assemblages of multiple and diverse types of Pleistocene ‘symbolic’ artifacts were entirely undocumented from Wallacea,” she said.
“It was also unknown if or how Sulawesi cave artists adorned their bodies or whether their artistic repertoire even extended beyond rock paintings. Our understanding of the symbolic lives of these people is now much richer.”
Wallacea, the zone of oceanic islands positioned east of the Wallace Line, one of the world’s major biogeographical boundaries, and lying between the continental regions of Asia and Australia-New Guinea [Credit: Adam Brumm]
The team says these early examples of art and ‘jewellery’ imply that the spiritual beliefs of modern humans may have transformed as they encountered new forms of animal life on the journey from Asia to Australia.
“Sulawesi, in particular, is renowned among biogeographers for its extremely high rate of species endemism – essentially all of the island’s land mammals, except for bats, occur nowhere else on earth,” Associate Professor Brumm says.
“The discovery of ornaments manufactured from the bones and teeth of two of Sulawesi’s flagship endemics – babirusas and bear cuscuses – and a previously recorded painting of a babirusa dated to at least 35,400 years ago, shows that humans were drawn to these dramatically new faunal species. This may indicate that the conceptual world of these people changed to incorporate exotic animals.”
The researchers think that this ‘symbolic negotiation’ with novel species might have been fundamental to the later settlement of Australia, which harboured unprecedentedly rich communities of endemic faunas and floras.
They speculate that the human journey through the biogeographically unique zone of Wallacea might have prompted new ways of thinking about the natural world, suggesting elements of the complex human-animal spiritual relationships that define Aboriginal cultures may actually pre-date the initial colonization of Australia.
The work reported in PNAS was conducted in collaboration with scientists from a range of Indonesian academic institutes, including the National Research Centre for Archaeology (ARKENAS), as well as a large team of Sulawesi-based archaeologists. Other Griffith University scientists involved were Associate Professor Maxime Aubert, Dr Jillian Huntley and Professor Rainer Grün. Associate Professor Aubert and Dr Huntley are also members of members of the Place, Evolution and Rock Art Heritage Unit (PERAHU) within the Griffith Centre for Social and Cultural Research.
Proxima Centauri, the closest star to the Earth (only 4.28 light-years away) is getting a lot of attention these days. It hosts a planet, Proxima Cen b, whose mass is about 1.3 Earth-mass (though it could be larger, depending on the angle at which we are viewing it). Moreover, Proxima Cen b orbits the star in its habitable zone.
An artist's impression of the surface of the planet Proxima Cen b orbiting the M dwarf star Proxima Centauri, the closest star to the solar system. The double star Alpha Centauri AB also appears in the image [Credit: ESO/M. Kornmesser]
Proxima Cen itself is an M-dwarf star with a mass only about one-tenth the Sun's mass and a luminosity about one-thousandths of the Sun's; because the star is dim, the planet's habitable zone is twenty times closer to the star than the Earth's is to the Sun, and the planet orbits in 11.3 days. M dwarfs are the most abundant type of stars, and their small radii make them easier targets (relatively speaking) to spot transiting exoplanet signatures.
Recent statistical estimates have concluded that half of M dwarf stars probably host an exoplanet between about 0.5–1.4 Earth-radii orbiting in or near their "habitable zone." Proxima Cen and its exoplanet, therefore, are important benchmark objects for understanding low-mass stars, their planets, and the planetary environments.
M dwarf stars pose a particular hazard to their planets: A large proportion of their radiation, much more than in Sun-like stars, is in the form of UV, extreme UV, and X-rays. This radiation can evaporate a planet's atmosphere, especially when those planets orbit nearby in the habitable zone. Indeed, the question astronomers ask is whether planets like Proxima Cen b can retain any atmosphere at all, at least over a long enough time for the planet to be "habitable" from any practical point-of-view. An addition danger is posed by the star's magnetic activity, which is not only responsible for the corrosive radiation but which also drives stellar winds and coronal mass ejections that could be even more perilous to atmospheric survival.
The photoevaporation of planetary atmospheres due to stellar radiation has been studied in limited situations, but not much effort has been devoted to the case of active M-dwarf stars and their magnetic activity. CfA astronomers Cecilia Garraffo, Jeremy Drake and Ofer Cohen have begun a program to model the stellar winds and magnetic field for active M-dwarf stars, and to investigate the impact on the atmospheres of planets in habitable zones. Proxima Cen is their first specific example.
They found that the pressure of the stellar wind at the exoplanet was a thousand to ten thousand times higher than the solar wind pressure at Earth. Moreover, the pressure is highly nonuniform, and Proxima b will pass through these extreme pressure variations twice each orbit leading to the compression and expansion of its atmosphere by factors of up to 3 every day. The atmosphere of Proxima Cen b is also likely to experience supersonic wind conditions.
All these phenomena will have a significant negative effect on any atmosphere that might exist on Proxima b. The extent to which similar hostile conditions prevail on other M-dwarf exoplanets is a subject of further studies.
