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Seeing the invisible: visible-light metamaterial superlens made from nanobeads

(a) Conceptual drawing of nanoparticle-based metamaterial solid immersion lens (mSIL) (b) Lab-made mSIL using titanium dioxide nanoparticles (c) SEM image of 60 nm size imaging sample (d) corresponding superlens imaging of the 60 nm sample by the developed mSIL. (credit: BangorUniversity/Fudan University)

A team of British and Chinese scientists has developed a new “metamaterial-based solid immersion lens” (mSIL) microscope lens design that can extend the magnification of an optical microscope to see objects smaller than the approximately 200 nanometers Abbe diffraction limit, the smallest size of bacteria.

Led by Zengbo Wang, PhD, at Bangor University UK and Prof Limin Wu at Fudan University, China, the team created minute droplet-like lens structures on the surface to be examined. These act as an additional lens to magnify the surface features previously invisible to a normal microscope lens, adding 5x magnification to existing microscopes.

Schematic illustration of the assembly of the all-dielectric TiO2 mSIL. (A) Anatase TiO2 nanoparticles (15 nm) were centrifuged into a tightly packed precipitate. (B) The supernatant was replaced by an organic solvent mixture consisting of hexane and tetrachloroethylene to form a TiO2 nano–solid-fluid. (C) To prepare a hemispherical mSIL, the nano–solid-fluid was directly sprayed onto the sample surface. (D) To prepare a super-hemispherical mSIL, the nano–solid-fluid was sprayed onto the sample surface covered by a thin layer of organic solvent mixture. (E and F) After evaporation of the solvents, the nanoparticles underwent a phase transition to form a more densely packed structure. (credit: Wen Fan et al./Science Advances)

Made of millions of nanobeads, the spheres break up the light beam. Acting as individual minute beams, each bead refracts the light. “We’ve used high-index titanium dioxide (TiO2) nanoparticles as the building element of the lens,” Wang says. “These nanoparticles are able to bend light to a higher degree than water.”

“Each sphere bends the light to a high magnitude and splits the light beam, creating millions of individual beams of light. It is these tiny light beams which enable us to view previously unseen detail.”

Wang believes that the results will be easily replicable and that other labs will soon be adopting the technology and using it for themselves. Titanium dioxide is cheap and readily available, so rather than buying a new microscope, the lenses are applied to the material to be viewed, rather than to the microscope.

“The next challenge is to adapt the technology for use in biology and medicine. This would not require the current use of a combination of dyes and stains and laser light, which change the samples being viewed,” he says.

The lens is described in a paper in the open-access journal Science Advances today (August 12).

Abstract of Three-dimensional all-dielectric metamaterial solid immersion lens for subwavelength imaging at visible frequencies

Although all-dielectric metamaterials offer a low-loss alternative to current metal-based metamaterials to manipulate light at the nanoscale and may have important applications, very few have been reported to date owing to the current nanofabrication technologies. We develop a new “nano–solid-fluid assembly” method using 15-nm TiO2 nanoparticles as building blocks to fabricate the first three-dimensional (3D) all-dielectric metamaterial at visible frequencies. Because of its optical transparency, high refractive index, and deep-subwavelength structures, this 3D all-dielectric metamaterial-based solid immersion lens (mSIL) can produce a sharp image with a super-resolution of at least 45 nm under a white-light optical microscope, significantly exceeding the classical diffraction limit and previous near-field imaging techniques. Theoretical analysis reveals that electric field enhancement can be formed between contacting TiO2 nanoparticles, which causes effective confinement and propagation of visible light at the deep-subwavelength scale. This endows the mSIL with unusual abilities to illuminate object surfaces with large-area nanoscale near-field evanescent spots and to collect and convert the evanescent information into propagating waves. Our all-dielectric metamaterial design strategy demonstrates the potential to develop low-loss nanophotonic devices at visible frequencies.

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Dark energy measured with record-breaking map of 1.2 million galaxies

One slice through the map of the large-scale structure of the Universe from the Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey. Each dot in this picture indicates the position of a galaxy 6 billion years into the past. The image covers about 1/20th of the sky, a slice of the Universe 6 billion light-years wide, 4.5 billion light-years high, and 500 million light-years thick. Color indicates distance from Earth, ranging from yellow on the near side of the slice to purple on the far side. Galaxies are highly clustered, revealing superclusters and voids whose presence is seeded in the first fraction of a second after the Big Bang. This image contains 48,741 galaxies, about 3% of the full survey dataset. Gray patches are small regions without survey data. (credit: Daniel Eisenstein and SDSS-III)

A team of hundreds of physicists and astronomers have announced results from the largest-ever, three-dimensional map of distant galaxies, created to make one of the most precise measurements yet of the dark energy currently driving the accelerated expansion of the Universe.

“We have spent five years collecting measurements of 1.2 million galaxies over one quarter of the sky to map out the structure of the Universe over a volume of 650 cubic billion light years,” says Jeremy Tinker of New York University, a co-leader of the scientific team carrying out this effort. “This map has allowed us to make the best measurements yet of the effects of dark energy in the expansion of the Universe.”

These new measurements were carried out by the Baryon Oscillation Spectroscopic Survey (BOSS) program of the Sloan Digital Sky Survey-III. Shaped by a continuous tug-of-war between dark matter and dark energy, the map revealed by BOSS allows scientists to measure the expansion rate of the Universe and thus determine the amount of matter and dark energy that make up the present-day Universe. A collection of papers describing these results was submitted this week to the Monthly Notices of the Royal Astronomical Society.

Measuring the expansion rate of the Universe

BOSS measures the expansion rate of the Universe by determining the size of the baryonic acoustic oscillations (BAO) in the three-dimensional distribution of galaxies. The original BAO size is determined by pressure waves that traveled through the young Universe up to when it was only 400,000 years old (the Universe is presently 13.8 billion years old), at which point they became frozen in the matter distribution of the Universe.

The end result is that galaxies have a slight preference to be separated by a characteristic distance that astronomers call the acoustic scale. The size of the acoustic scale at 13.7996 billion years ago has been exquisitely determined from observations of the cosmic microwave background from the light emitted when the pressure waves became frozen. Measuring the distribution of galaxies since that time allows astronomers to measure how dark matter and dark energy have competed to govern the rate of expansion of the Universe.

“We’ve made the largest map for studying the 95% of the universe that is dark,” noted David Schlegel, an astrophysicist at Lawrence Berkeley National Laboratory (Berkeley Lab) and principal investigator for BOSS. “In this map, we can see galaxies being gravitationally pulled towards other galaxies by dark matter. And on much larger scales, we see the effect of dark energy ripping the universe apart.”

The Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey has transformed a two-dimensional image of the sky (left panel) into a three-dimensional map spanning distances of billions of light years, shown here from two perspectives (middle and right panels). This map includes 120,000 galaxies over 10% of the survey area. The brighter regions correspond to the regions of the Universe with more galaxies and therefore more dark matter. (credit: Jeremy Tinker and SDSS-III)

Ariel Sanchez of the Max-Planck Institute of Extraterrestrial Physics led the effort to estimate the exact amount of dark matter and dark energy based on the BOSS data and explains: “Measuring the acoustic scale across cosmic history gives a direct ruler with which to measure the Universe’s expansion rate. With BOSS, we have traced the BAO’s subtle imprint on the distribution of galaxies spanning a range of time from 2 to 7 billion years ago.”

To measure the size of these ancient giant waves to such sharp precision, BOSS had to make an unprecedented and ambitious galaxy map, many times larger than previous surveys. At the time the BOSS program was planned, dark energy had been previously determined to significantly influence the expansion of the Universe starting about 5 billion years ago. BOSS was thus designed to measure the BAO feature from before this point (7 billion years ago) out to near the present day (2 billion years ago).

Jose Vazquez of Brookhaven National Laboratory combined the BOSS results with other surveys and searched for any evidence of unexplained physical phenomena in the results. “Our latest results tie into a clean cosmological picture, giving strength to the standard cosmological model that has emerged over the last eighteen years.”

Rita Tojeiro of the University of St. Andrews is the other co-leader of the BOSS galaxy clustering working group along with Tinker. “We see a dramatic connection between the sound wave imprints seen in the cosmic microwave background 400,000 years after the Big Bang to the clustering of galaxies 7-12 billion years later. The ability to observe a single well-modeled physical effect from recombination until today is a great boon for cosmology.”

The map also reveals the distinctive signature of the coherent movement of galaxies toward regions of the Universe with more matter, due to the attractive force of gravity. Crucially, the observed amount of infall is explained well by the predictions of general relativity.

“The results from BOSS provide a solid foundation for even more precise future BAO measurements, such as those we expect from the Dark Energy Spectroscopic Instrument (DESI),” says Natalie Roe, Physics Division director at Berkeley Lab. “DESI will construct a more detailed 3-dimensional map in a volume of space ten times larger to precisely characterize dark energy — and ultimately the future of our universe.”

Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science.

Abstract of The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample

We present cosmological results from the final galaxy clustering data set of the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. Our combined galaxy sample comprises 1.2 million massive galaxies over an effective area of 9329 deg^2 and volume of 18.7 Gpc^3, divided into three partially overlapping redshift slices centred at effective redshifts 0.38, 0.51, and 0.61. We measure the angular diameter distance DM and Hubble parameter H from the baryon acoustic oscillation (BAO) method after applying reconstruction to reduce non-linear effects on the BAO feature. Using the anisotropic clustering of the pre-reconstruction density field, we measure the product DM*H from the Alcock-Paczynski (AP) effect and the growth of structure, quantified by f{sigma}8(z), from redshift-space distortions (RSD). We combine measurements presented in seven companion papers into a set of consensus values and likelihoods, obtaining constraints that are tighter and more robust than those from any one method. Combined with Planck 2015 cosmic microwave background measurements, our distance scale measurements simultaneously imply curvature {Omega}_K =0.0003+/-0.0026 and a dark energy equation of state parameter w = -1.01+/-0.06, in strong affirmation of the spatially flat cold dark matter model with a cosmological constant ({Lambda}CDM). Our RSD measurements of f{sigma}_8, at 6 per cent precision, are similarly consistent with this model. When combined with supernova Ia data, we find H0 = 67.3+/-1.0 km/s/Mpc even for our most general dark energy model, in tension with some direct measurements. Adding extra relativistic species as a degree of freedom loosens the constraint only slightly, to H0 = 67.8+/-1.2 km/s/Mpc. Assuming flat {Lambda}CDM we find {Omega}_m = 0.310+/-0.005 and H0 = 67.6+/-0.5 km/s/Mpc, and we find a 95% upper limit of 0.16 eV/c^2 on the neutrino mass sum.

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How birds unlock their ultraviolet vision super-sense

Some birds have been found to be as intelligent as mammals. And some that can see ultraviolet (UV) light live in a super-sensory world apart, able to transmit and receive signals between each other in a way that is invisible to many other species.

Now the ability of finches, sparrows, and many other birds to see ultraviolet (UV) light is explained in a study published in the journal eLife by scientists at the Washington University School of Medicine in St. Louis.

Carotenoid pigments determine bird’s UV perception or not

The study reveals two essential adaptions that enable birds to expand their vision into the UV range: chemical changes in light-filtering pigments called carotenoids (such as carotene, found in carrots, associated with vitamin A) and the tuning of light-sensitive proteins called opsins (light-sensitive proteins), some of which are also used in optogenetics research.

Birds acquire carotenoids through their diets and process them in a variety of ways to shift their light absorption toward longer (visible light) or shorter (UV) wavelengths.

“There are two types of light-sensitive cells, called photoreceptors, in the eye: rods and cones. Cone photoreceptors are responsible for color vision. While humans have blue, green, and red-sensitive cones only, birds have a fourth cone type which is either violet or UV-sensitive, depending on the species,” says senior author Joseph Corbo, MD, PhD, Associate Professor of Pathology and Immunology.

UV vs visual perception by cones in the eye is fine-tuned by evolution

“Our approach showed that blue-cone sensitivity is fine-tuned through a change in the chemical structure of carotenoid pigments within the photoreceptor, allowing both violet and UV-sighted birds to maximize how many colors they can see.”

The study also revealed that sensitivity of the violet/UV cone and the blue cone in birds must move in sync to allow for optimum vision. Among bird species, there is a strong relationship between the light sensitivity of opsins within the violet/UV cone and mechanisms within the blue cone, which coordinate to ensure even UV vision.

Taken together, these results suggest that both blue and violet cone cells have adapted during evolution to enhance color vision in birds.

Birds have achieved UV vision by use of a specialized optical organelle, the pigmented cone oil droplet. These oil droplets are located in the path of light through the receptor and act as cutoff filters matched to the visual pigment sensitivity of each cone subtype.

Spectral filtering in bird cones. a) A flat-mounted chicken retina under brightfield illumination that shows the distinctive pigmentation of the cone oil droplets. (b) A diagram of the avian single cone photoreceptors showing the relative position of the oil droplet within the cells (top) and a representation of the spectral filtering cutoff effects of the droplet (bottom). (credit: Matthew B Toomey et al./eLife)

“The majority of bird species rely on vision as their primary sense, and color discrimination plays a crucial role in their essential behaviors, such as choosing mates and foraging for food. This explains why birds have evolved one of the most richly endowed color vision systems among vertebrates,” says first author Matthew Toomey, a postdoctoral fellow at the Washington University School of Medicine.

“The precise coordination of sensitivity and filtering in the visual system may, for example, help female birds discriminate very fine differences in the elaborate coloration of their suitors and choose the fittest mates. This refinement of visual sensitivity could also facilitate the search for hidden seeds, fruits, and other food items in the environment.”

The team now plans to investigate the underlying molecular mechanisms that help modify the carotenoid pigments and light-sensitive protein tuning in a wide range of bird species, to gather further insights into the evolution of UV vision.

Abstract of Complementary shifts in photoreceptor spectral tuning unlock the full adaptive potential of ultraviolet vision in birds

Color vision in birds is mediated by four types of cone photoreceptors whose maximal sensitivities (λmax) are evenly spaced across the light spectrum. In the course of avian evolution, the λmax of the most shortwave-sensitive cone, SWS1, has switched between violet (λmax > 400 nm) and ultraviolet (λmax < 380 nm) multiple times. This shift of the SWS1 opsin is accompanied by a corresponding short-wavelength shift in the spectrally adjacent SWS2 cone. Here, we show that SWS2 cone spectral tuning is mediated by modulating the ratio of two apocarotenoids, galloxanthin and 11’,12’-dihydrogalloxanthin, which act as intracellular spectral filters in this cell type. We propose an enzymatic pathway that mediates the differential production of these apocarotenoids in the avian retina, and we use color vision modeling to demonstrate how correlated evolution of spectral tuning is necessary to achieve even sampling of the light spectrum and thereby maintain near-optimal color discrimination.

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A spectacular survey of the distant universe

An image of a small section (0.4 percent) of the Ultra-Deep Survey field. Most of the objects in the image are very distant galaxies, observed as they were more than 9 billion years ago. In the full image, 250,000 galaxies have been detected over an area of sky four times the size of the full moon. (credit: Omar Almaini, University of Nottingham)

Astronomers at The University of Nottingham have released spectacular new infrared images of the distant Universe, providing the deepest view ever obtained over a large area of sky — showing more than 250,000 galaxies, including several hundred observed within the first billion years after the Big Bang.

The images are from the final data release from the Ultra-Deep Survey (UDS), which maps an area four times the size of the full Moon to unprecedented depth. Astronomers will use the new images to study the early stages of galaxy formation and evolution.

The release of the final UDS images represents the culmination of a project that began taking data in 2005. The scientists used the United Kingdom Infrared Telescope (UKIRT) on Hawaii to observe the same patch of sky repeatedly, building up more than 1000 hours of exposure time.

Understanding how galaxies evolved

Observing in the infrared is required for studying the distant Universe, since ordinary starlight is “redshifted” to longer wavelengths due to the cosmological expansion of the Universe.

Earlier releases of data from the UDS have already produced a wide range of scientific advances, including studies of the earliest galaxies in the first billion years after the Big Bang, measurements of the buildup of galaxies through cosmic time, and studies of the large-scale distribution of galaxies to weigh the mysterious “dark matter” that pervades the cosmos.

David Maltby, PhD, a postdoctoral research fellow at The University of Nottingham, said the scientists are aiming to understand how galaxies evolved to produce the rich diversity we see today.

“For example, we still don’t understand why the most massive galaxies are usually elliptical in shape, while less massive galaxies tend to be disk-shaped with spiral arms. By looking back in time to the early Universe we can catch these galaxies in their infancy, and observe them as they change and evolve over many billions of years.”

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Universe’s first life might have been born on diamond planets

In this artist’s conception, a carbon planet orbits a sunlike star in the early universe. Young planetary systems lacking heavy chemical elements but relatively rich in carbon could form worlds made of graphite, carbides, and diamond rather than Earth-like silicate rocks. Blue patches show where water has pooled on the planet’s surface, forming potential habitats for alien life. (credit: Christine Pulliam (CfA), Sun image: NASA/SDO)

New findings by scientists at the Harvard-Smithsonian Center for Astrophysics (CfA) suggest that planet formation in the early universe might have created carbon planets consisting of graphite, carbides, and diamond and that astronomers might find these diamond worlds by searching a rare class of stars.

“This work shows that even stars with a tiny fraction of the carbon in our solar system can host planets,” says lead author and Harvard University graduate student Natalie Mashian. “We have good reason to believe that alien life will be carbon-based, like life on Earth, so this also bodes well for the possibility of life in the early universe.”

The primordial universe consisted mostly of hydrogen and helium, and lacked chemical elements like carbon and oxygen necessary for life as we know it. Only after the first stars exploded as supernovae and seeded the second generation did planet formation and life become possible.

Clues to how life got started in the universe

Mashian and her PhD thesis advisor Avi Loeb examined a particular class of old stars known as carbon-enhanced metal-poor (CEMP) stars. These “anemic” stars contain only one hundred-thousandth as much iron as our Sun, meaning they formed before interstellar space had been widely seeded with heavy elements.

“These stars are fossils from the young universe,” explains Loeb. “By studying them, we can look at how planets, and possibly life in the universe, got started.”

CEMP stars have more carbon than would be expected, given their age. This relative abundance would influence planet formation as fluffy carbon dust grains (from supernovae) clump together to form tar-black worlds.

From a distance, these carbon planets would be difficult to tell apart from more Earth-like worlds. Their masses and physical sizes would be similar. Astronomers would have to examine their atmospheres for signs of their true nature. Gases like carbon monoxide and methane would envelop these unusual worlds.

The transit technique for detecting carbon planets

When a planet crosses in front of its star as viewed by an observer, the event is called a transit. The relative change in flux caused by a carbon-based planet transiting across its host CEMP star would range from ~0.0001% to ~0.01%.
(credit: NASA Ames)

But a dedicated search for planets around CEMP stars can be done using the transit technique, the scientists suggest. We encountered the transit technique on KurzweilAI in “How to use laser cloaking to hide Earth from remote detection by aliens” — in which we noted we two Columbia University astronomers suggested that we could cloak our Earth from aliens by shining a laser during transits so they couldn’t see the tiny giveaway changes in brightness — or that we could modify the light from our Sun during a transit to make it obviously artificial, sending a message to ET: “we’re here.”

In the new CfA paper, published in the Monthly Notices of the Royal Astronomical Society*, the scientists note that the relative change in flux caused by a carbon-based planet transiting across its host CEMP star ranges from ~0.0001% to ~0.01% — too weak to be detected by ground telescopes. That means it would require “space-based transit surveys that continuously monitor a large number of potential host stars over several years and measure their respective transit light curves.”

Fortunately, “there are a number of ongoing, planned, and proposed space missions committed to this cause,” the CfA scientists note. No word if the space-based transit surveys will also watch for artificial messages.

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

* The CfA study is also available (open-access) on arXiv.

Abstract of CEMP stars: possible hosts to carbon planets in the early universe

We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] ≥ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance rmax from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star’s [C/H] abundance. We then use our linear relation between rmax and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational program to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the Big Bang.

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Machine learning outperforms physicists in experiment

The experiment, featuring the small red glow of a BEC trapped in infrared laser beams (credit: Stuart Hay, ANU)

Australian physicists have used an online optimization process based on machine learning to produce effective Bose-Einstein condensates (BECs) in a fraction of the time it would normally take the researchers.

A BEC is a state of matter of a dilute gas of atoms trapped in a laser beam and cooled to temperatures just above absolute zero. BECs are extremely sensitive to external disturbances, which makes them ideal for research into quantum phenomena or for making very precise measurements such as tiny changes in the Earth’s magnetic field or gravity.

The experiment, developed by physicists from ANU, University of Adelaide and UNSW ADFA, demonstrated that “machine-learning online optimization” can discover optimized condensation methods “with less experiments than a competing optimization method and provide insight into which parameters are important in achieving condensation,” the physicists explain in an open-access paper in the Nature group journal Scientific Reports.

Faster, cheaper than a physicist

Optical dipole trap used in the experiment, showing the three laser beams and the condensate (red-yellow oval in blue square) (credit: P. B. Wigley et al./Scientific Reports)

The team cooled the gas to around 5 microkelvin. To further cool down the trapped gas (containing about 40 million rubidium atoms) to on the order of nanokelvin*, they then handed control of the three laser beams** over to the machine-learning program.

The physicists were surprised by the clever methods the system came up with to create a BEC, like changing one laser’s power up and down, and compensating with another laser.

“I didn’t expect the machine could learn to do the experiment itself, from scratch, in under an hour,” said co-lead researcher Paul Wigley from ANU Research School of Physics and Engineering. “A simple computer program would have taken longer than the age of the universe to run through all the combinations and work this out.”

Wigley suggested that one could make a working device to measure gravity that you could take in the back of a car, and the AI would automatically recalibrate and fix itself.

“It’s cheaper than taking a physicist everywhere with you,” he said.

* Billionth of a degree above absolute zero — where a phase transition occurs, and a macroscopic number of atoms start to occupy the same quantum state, called Bose-Einstein condensation.

** The 1064 nm beam is controlled by varying the current to the laser, while the 1090 nm beam is controlled using the current and a waveplate rotation stage combined with a polarizing beamsplitter to provide additional power attenuation while maintaining mode stability.

Abstract of Fast machine-learning online optimization of ultra-cold-atom experiments

We apply an online optimization process based on machine learning to the production of Bose-Einstein condensates (BEC). BEC is typically created with an exponential evaporation ramp that is optimal for ergodic dynamics with two-body s-wave interactions and no other loss rates, but likely sub-optimal for real experiments. Through repeated machine-controlled scientific experimentation and observations our ‘learner’ discovers an optimal evaporation ramp for BEC production. In contrast to previous work, our learner uses a Gaussian process to develop a statistical model of the relationship between the parameters it controls and the quality of the BEC produced. We demonstrate that the Gaussian process machine learner is able to discover a ramp that produces high quality BECs in 10 times fewer iterations than a previously used online optimization technique. Furthermore, we show the internal model developed can be used to determine which parameters are essential in BEC creation and which are unimportant, providing insight into the optimization process of the system.

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Astronomers discover potentially habitable planets just 40 light years from Earth

This artist’s rendering shows an imagined view of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. In this view, one of the inner planets is seen in transit (black dot) across the disc of its tiny and dim parent star. (credit: M. Kornmesser/ESO)

Astronomers have detected three exoplanets just 40 light years from Earth whose sizes and temperatures are comparable to those of Earth. The planets may be the best targets found so far for the search for life outside the solar system.

The results were published Monday (May 2) in the journal Nature.

Because the system is relatively close to Earth, co-author Julien de Wit, a postdoc at MIT, says scientists will soon be able to study the planets’ atmospheric compositions, as well as assess their habitability and whether life actually exists within this planetary system.

The scientists discovered the planets using TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope), a 60-centimeter telescope operated by the University of Liège, based in Chile. Built by lead authors Michael Gillon and Emmanuel Jehin of the University of Liège, TRAPPIST is designed to focus on 60 nearby small, ”ultracool” dwarf stars (those with effective temperatures of less than 2,700 kelvin) — stars that are so faint they are invisible to optical telescopes and are monitored at infrared wavelengths.

The team focused the telescope on the dwarf star, which they named TRAPPIST-1 — a Jupiter-sized star that is one-eighth the size of our sun and significantly cooler. Over several months, the scientists observed the star’s infrared signal fade slightly at regular intervals, suggesting that several objects were passing in front of the star.

Most exoplanetary missions have been focused on finding systems around bright, solar-like stars. These stars emit radiation in the visible band and can be seen with optical telescopes. However, because these stars are so bright, their light can overpower any signal coming from a planet. Ultracool stars emit radiation in the infrared band. Because they are so faint, these tiny red stars would not drown out the image of a planet crossing the star, giving scientists a better chance of detecting orbiting planets.

May be in the habitable zone

From their observations, the scientists determined that all three planets are likely tidally locked, with permanent day and night sides.

The two innermost planets orbit the star in 1.5 and 2.4 days and receive only four and two times, respectively, the amount of radiation the Earth receives from the sun. The third planet may orbit the star in anywhere from four to 73 days, and may receive even less radiation than Earth. But given their size and proximity to their star, all three planets may have regions with temperatures well below 127 degrees C (260 degrees F), within a range that is suitable for sustaining liquid water and life.

The two planets closest to the star may have day sides that are too hot, and night sides too cold, to host any life forms. However, there may be a “sweet spot” — a region that still receives daylight, but with relatively cool temperatures — on the western side of both planets that may be temperate enough to sustain conditions suitable for life. The third planet, furthest from its star, may be entirely within the habitable zone.

“Now we have to investigate if they’re habitable,” de Wit says. “We will investigate what kind of atmosphere they have, and then will search for biomarkers and signs of life. We have facilities all over the globe and in space that are helping us, working from UV to radio, in all different wavelengths to tell us everything we want to know about this system.”

This research was funded, in part, by the Belgian Fund for Scientific Research, the European Research Council, and NASA.

Abstract of Temperate Earth-sized planets transiting a nearby ultracool dwarf star

Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them—ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.

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‘Breakthrough Starshot’ aims to reach Alpha Centauri 20 years after launch

Alpha Centauri (credit: ESO Online Digitized Sky Survey)

Internet investor and science philanthropist Yuri Milner and physicist Stephen Hawking announced Tuesday a $100 million research and engineering program, Breakthrough Starshot, aiming to demonstrate proof of concept for light-propelled “nanocrafts” that could travel to Alpha Centauri, our nearest star system.

The nanocrafts would fly at 20 percent of light speed and capture images of possible planets and other scientific data, arriving in just over 20 years after their launch.

“Earth is a wonderful place, but it might not last forever,” said Hawking. “Sooner or later, we must look to the stars. Breakthrough Starshot is a very exciting first step on that journey.”

Breakthrough Starshot program

L-R) Yuri Milner, Breakthrough Prize and DST Global Founder; Stephen Hawking, CH, CBE, FRS, Dennis Stanton Avery and Sally Tsui Wong-Avery Director of Research, University of Cambridge; Freeman Dyson, Emeritus Professor, Princeton Institute for Advanced Study; Ann Druyan, Producer, Co-Founder and CEO of Cosmos Studios; Avi Loeb, Frank B. Baird, Jr. Professor of Science at Harvard University; Mae Jamison, Nasa Astronaut, Principal 100 Year Starship Foundation; and Peter Worden, Chairman, Breaktrough Prize Foundation, Former NASA Director speak on stage as Yuri Milner And Stephen Hawking host press conference to announce Breakthrough Starshot, a new space exploration initiative, at One World Observatory on April 12, 2016 in New York City. (Photo by Bryan Bedder/Getty Images for Breakthrough Prize Foundation)

The Breakthrough Starshot program will be led by Pete Worden, the former director of NASA AMES Research Center, and advised by a committee of world-class scientists and engineers. The board will consist of Stephen Hawking, Yuri Milner, and Mark Zuckerberg.

Nanocrafts

Nanocraft, comprising Lightsail and StarChip powered by Light Beamer (credit: Breakthrough Initiatives)

The Alpha Centauri star system is 25 trillion miles (4.37 light years) away. With today’s fastest spacecraft, it would take about 30,000 years to get there. The program aims to establish whether a gram-scale nanocraft on a sail pushed by a light beam can fly more than 1,000 times faster.

Nanocrafts are gram-scale robotic spacecrafts, comprising:

Starchip (credit: Breakthrough Initiatives)

Starchip: a gram-scale wafer carrying cameras, photon thrusters, power supply, navigation, and communication equipment, and constituting a fully functional space probe.

Lightsail (credit: Breakthrough Initiatives)

Lightsail: Advances in nanotechnology are producing increasingly thin and lightweight materials, promising to enable the fabrication of meter-scale sails no more than a few hundred atoms thick and at gram-scale mass.

Light Beamer (credit: Breakthrough Initiatives)

Light Beamer. The rising power and falling cost of lasers has led to significant advances in light-beaming technology. Phased arrays of lasers (the “light beamer”) could potentially be scaled up to the 100 gigawatt level.

Breakthrough Starshot aims to bring economies of scale to the astronomical scale. The StarChip can be mass-produced at the cost of an iPhone and be sent on missions in large numbers to provide redundancy and coverage. The light beamer is modular and scalable. Once it is assembled and the technology matures, the cost of each launch is expected to fall to a few hundred thousand dollars.


Breakthrough Starshot

Path to the stars

The research and engineering phase is expected to last a number of years. Following that, development of the ultimate mission to Alpha Centauri would require a budget comparable to the largest current scientific experiments, and would involve building a ground-based kilometer-scale light beamer at high altitude in dry conditions, powered by a few gigawatt hours of energy per launch.

The plan is to launching a “mothership” carrying thousands of nanocrafts to a high-altitude orbit, taking advantage of adaptive optics technology in real time to compensate for atmospheric effects. Focusing the light beam on the lightsail would accelerate individual nanocrafts to the target speed within minutes.

The goal is to capture images of a planet and other scientific data and transmitting them back to Earth using a compact on-board laser communications system, using the same light beamer that launched the nanocrafts to receive data from them over 4 years later.

The organizers acknowledge that these and other system requirements represent significant engineering challenges, but are based on technology either already available or likely to be attainable in the near future under reasonable assumptions, the organizers say.

Kilometer-scale telescope

The proposed light propulsion system is at a scale that calls for global cooperation and support. Clearance for launches would be required from all the appropriate government and international organizations.

As the technology required for interstellar travel matures, a number of additional opportunities will emerge, including contributions to solar system exploration, using the light beamer as a kilometer-scale telescope for astronomical observations, and detection of Earth-crossing asteroids at large distances.

Astronomers estimate that there is a reasonable chance of an Earth-like planet existing in the “habitable zones” of Alpha Centauri’s three-star system. A number of scientific instruments, ground-based and space-based, are being developed and enhanced, which will soon identify and characterize planets around nearby stars. A separate Breakthrough Initiative will support some of these projects.

Getting it off the ground

The Breakthrough Starshot initiative is based entirely on research in the public domain. It will be dedicated to full transparency and open access, and open to experts in all relevant fields as well as the public to contribute ideas through its online forum.  The initiative will establish a research grant program, and will make available other funding to support relevant scientific and engineering research and development.

“We take inspiration from Vostok, Voyager, Apollo. and the other great missions,” said Pete Worden. “It’s time to open the era of interstellar flight, but we need to keep our feet on the ground to achieve this.”

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How to use laser cloaking to hide Earth from remote detection by aliens

A 22W laser used for adaptive optics on the Very Large Telescope in Chile. A suite of similar lasers could be used to cloak our planet’s transit around the Sun. (credit: ESO/G. Hüdepohl)

We could use lasers to conceal the Earth from observation by an advanced extraterrestrial civilization by shining massive  laser beams aimed at a specific star where aliens might be located — thus masking our planet during its transit of the Sun, suggest two astronomers at Columbia University in an open-access paper in Monthly Notices of the Royal Astronomical Society.

The idea comes from the NASA Kepler mission’s search method for exoplanets (planets around other stars), which looks for transits (a planet crossing in front a star) — identified by a tiny decrease in the star’s brightness.*

To detect exoplanets, NASA’s Kepler measures the light from a star. When a planet crosses in front of a star, the event is called a transit. The planet is usually too small to see, but it can produce a small change in a star’s brightness of about 1/10,000 (100 parts per million), lasting for 2 to 16 hours. (credit: NASA Ames)

Kepler has confirmed the existence of more than 1,000 planets using this technique, with tens of these worlds similar in size to the Earth. Kipping and Teachey speculate that alien scientists could use this approach to locate Earth, since it’s in the “habitable zone” of our Sun (a distance where the temperature is right for liquid water, so it may be a promising place for life), and may be of interest to aliens.*

How to cloak our Earth from aliens

Columbia Professor David Kipping and graduate student Alex Teachey suggest that transits could be masked by controlled laser emission, with the beam directed at the star where the suspected aliens might be located. When the planet’s transit takes place, the laser would be switched on to compensate for the dip in light.**

Illustration (not to scale) of the transit cloaking device. To cloak the Earth, a laser beam (orange) is fired from the night side of the Earth (blue circle) toward a target star (“receiver”) during the transit. (credit: David M. Kipping and Alex Teachey/MNRAS)

According to the authors, emitting a continuous 30 MW laser for about 10 hours, once a year, would be enough to eliminate the transit signal, at least in the visible-light range. The energy needed is comparable to that collected by the International Space Station solar array in a year. A chromatic (multi-wavelength) cloak, effective at all solar wavelengths, is more challenging, and would need a large array of tuneable lasers with a total power of 250 MW.***

“Alternatively, we could cloak only the atmospheric signatures associated with biological activity, such as oxygen, which is achievable with a peak laser power of just 160 kW per transit. To another civilization, this should make the Earth appear as if life never took hold on our world”, said Teachey.


Cool Worlds Lab/Columbia University | A Cloaking Device for Planets

Broadcasting our existence: the METI (message SETI) approach

The lasers could also be used to broadcast our existence by modifying the light from the Sun during a transit to make it obviously artificial, such as modifying the normal “U” transit light curve (the intensity vs. time pattern during transit). The authors suggest that we could even transmit information by modulating the laser beams at the same time, providing a way to send messages to aliens.

However, several prominent scientists, including Stephen Hawking, have cautioned against humanity broadcasting our presence to intelligent life on other planets. Hawking and others are concerned that extraterrestrials might wish to take advantage of the Earth’s resources, and that their visit, rather than being benign, could be as devastating as when Europeans first traveled to the Americas. (See Are you ready for contact with extraterrestrial intelligence? and METI: should we be shouting at the cosmos?)

Perhaps aliens have had the same thought. The two astronomers propose that the Search for Extraterrestrial Intelligence (SETI), which currently looks mailing for alien radio signals, could be broadened to search for artificial star transits. Such signatures could also be readily searched in the NASA archival data of Kepler transit surveys.

* Once detected, the planet’s orbital size can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star using Kepler’s Third Law of planetary motion. The size of the planet is found from the depth of the transit (how much the brightness of the star drops) and the size of the star. From the orbital size and the temperature of the star, the planet’s characteristic temperature can be calculated. From this, the question of whether or not the planet is habitable (not necessarily inhabited) can be answered. — Kepler and K2, NASA Mission Overview

** It’s not clear what indicators might lead to such a suspicion, aside from a confirmed SETI transmission detection. It would be interesting to calculate the required number and locations of lasers, their operational schedule, and their power requirements for a worst-case scenario — assuming potential threats from certain types of stars, or all stars — considering laser beam divergence angle, beam flux gradients, and maximum star distance within about one degree of a planet’s ecliptic plane can see it transit in the ecliptic plane, based on assumed maximum alien telescope resolving power.

[UPDATE 1/3/2016: Kipping correction: "within about one degree" and added "based on assumed maximum alien telescope resolving power"]

[UPDATE 1/3/2016: from Kipping regarding beam divergence angle, flux gradients, and primary focus of the paper]: “Beam shaping, through the use of multiple beams, can produce effectively isotropic radiation within the beam width. Unless the target is very close, the beam width typically encompasses the entire alien solar system by the time it reaches, due to beam divergence. So we don’t even really need to know the position of the target planet that well (although we likely do anyway thanks to our detection methods). A common misunderstanding of our paper is to erroneously assume that we are advocating that humanity should build this for the Earth, but actually we are pointing out that if even our current technology can pull off a pretty effective cloak then other more advanced civilizations may be able to hide from us perfectly.”]

*** For example, a chromatic cloak for the NIRSpec instrument planned for James Webb Space Telescope covering from 0.6 to 5 µm would require approximately 6000 monochromatic lasers in the array.

Abstract of A Cloaking Device for Transiting Planets

The transit method is presently the most successful planet discovery and characterization tool at our disposal. Other advanced civilizations would surely be aware of this technique and appreciate that their home planet’s existence and habitability is essentially broadcast to all stars lying along their ecliptic plane. We suggest that advanced civilizations could cloak their presence, or deliberately broadcast it, through controlled laser emission. Such emission could distort the apparent shape of their transit light curves with relatively little energy, due to the collimated beam and relatively infrequent nature of transits. We estimate that humanity could cloak the Earth from Kepler-like broadband surveys using an optical monochromatic laser array emitting a peak power of ∼30 MW for ∼10 hours per year. A chromatic cloak, effective at all wavelengths, is more challenging requiring a large array of tunable lasers with a total power of ∼250 MW. Alternatively, a civilization could cloak only the atmospheric signatures associated with biological activity on their world, such as oxygen, which is achievable with a peak laser power of just ∼160 kW per transit. Finally, we suggest that the time of transit for optical SETI is analogous to the water-hole in radio SETI, providing a clear window in which observers may expect to communicate. Accordingly, we propose that a civilization may deliberately broadcast their technological capabilities by distorting their transit to an artificial shape, which serves as both a SETI beacon and a medium for data transmission. Such signatures could be readily searched in the archival data of transit surveys.

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First detection of super-Earth atmosphere


ESA/Hubble, M. Kornmesser  | Transit of 55 Cancri e

Astronomers have analyzed the atmosphere of a “super-Earth” exoplanet for the first time, according to The Hubble Space Telescope project, an international cooperation between ESA and NASA. Result: it’s mostly hydrogen and helium.

The data gathered with the NASA/ESA Hubble Space Telescope and new analysis techniques also revealed that exoplanet 55 Cancri e has a dry atmosphere without any indications of water vapor.

The results will be published in the Astrophysical Journal (also available on open-source arXiv).

Exoplanet 55 Cancri e has a mass of eight Earth-masses* and is located in the planetary system of 55 Cancri, a star about 40 light-years from Earth.

This artist’s concept shows the NASA/ESA Hubble Space Telescope in orbit around the Earth. (credit: ESA/Hubble (M. Kornmesser))

“This is a very exciting result because it’s the first time that we have been able to find the spectral fingerprints that show the gases present in the atmosphere of a super-Earth,” explains Angelos Tsiaras, a PhD student at UCL, who developed the analysis technique along with his colleagues Ingo Waldmann and Marco Rocchetto.

“The observations of 55 Cancri e’s atmosphere suggest that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula from which it originally formed.”

Super-Earths like 55 Cancri e are thought to be the most common type of planet in our galaxy. They acquired the name ‘super-Earth’ because they have a mass larger than that of the Earth but are still much smaller than the gas giants in the Solar System.

55 Cancri e, however, is an unusual super-Earth as it orbits very close to its parent star. A year on the exoplanet lasts for only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. Because the exoplanet is orbiting its bright parent star at such a small distance, the team was able to use new analysis techniques to extract information about the planet, during its transits in front of the host star.

Observations were made by scanning the WFC3 very quickly across the star to create a number of spectra. By combining these observations and processing them through analytic software, the researchers were able to retrieve the spectrum of 55 Cancri e embedded in the light of its parent star.

* 55 Cancri e has previously been dubbed the “diamond planet” because models based on its mass and radius have led to the idea that its interior is carbon-rich.

Abstract of Detection of an atmosphere around the super-Earth 55 Cancri e

We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6σ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code, T-REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54μm. While additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the HCN detection, we discuss here the implications of such result. Our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic than previously thought.