Tagged: Coronagraphs Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 2:41 pm on May 29, 2019 Permalink | Reply
    Tags: , , , Coronagraphs, , Infrared vision, ,   

    Fom James Webb Space Telescope: “A New View of Exoplanets With NASA’s Upcoming Webb Telescope” 

    NASA Webb Header

    NASA Webb Telescope
    NASA/ESA/CSA

    Fom James Webb Space Telescope

    May 29, 2019

    Contact:
    Ann Jenkins /
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4488 /
    jenkins@stsci.edu

    Christine Pulliam
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4366
    cpulliam@stsci.edu

    1
    About This Image

    One of the targets Webb will study is the well-known, giant ring of dust and planetesimals orbiting a young star called HR 4796A. This Hubble Space Telescope photo shows a vast, complex dust structure, about 150 billion miles across, enveloping the young star HR 4796A. (The light from HR 4796A and its binary companion, HR 4796B, have been blocked to reveal the much dimmer dust structure.) A bright, narrow inner ring of dust encircling the star may have been corralled by the gravitational pull of an unseen giant planet. Credits: NASA/ESA and G. Schneider (University of Arizona)

    How Do We Find Exoplanets?

    The James Webb Space Telescope will open a new window on exoplanets, planets around other suns. With its keen infrared vision, Webb will observe them in wavelengths where they have never been studied before. One of the telescope’s first observation programs is to look at young, newly formed exoplanets and the systems they inhabit. Scientists will use all four of Webb’s instruments to observe three targets: A recently discovered exoplanet; an object that is either an exoplanet or a brown dwarf; and a well-studied ring of dust and planetesimals orbiting a young star. Webb will be vital for understanding how these objects form, and what these systems are like. These observations are part of a program that allows the astronomical community to quickly learn how best to use Webb’s capabilities, while also yielding robust science.

    While we now know of thousands of exoplanets — planets around other stars — the vast majority of our knowledge is indirect. That is, scientists have not actually taken many pictures of exoplanets, and because of the limits of current technology, we can only see these worlds as points of light. However, the number of exoplanets that have been directly imaged is growing over time. When NASA’s James Webb Space Telescope launches in 2021, it will open a new window on these exoplanets, observing them in wavelengths at which they have never been seen before and gaining new insights about their nature.

    Exoplanets are close to much brighter stars, so their light is generally overwhelmed by the light of the host stars. Astronomers usually find an exoplanet by inferring its presence based on the dimming of its host star’s light as the planet passes in front of the star—an event called a “transit.” Sometimes a planet tugs on its star, causing the star to wobble slightly.

    In a few cases, scientists have captured pictures of exoplanets by using instruments called coronagraphs. These devices block the glare of the star in much the same way you might use your hand to block the light of the Sun. However, finding exoplanets with this technique has proven to be very difficult. All that will change with the sensitivity of Webb. Its onboard coronagraphs will allow scientists to view exoplanets at infrared wavelengths they’ve never seen them in before.

    Webb’s Unique Capabilities

    Coronagraphs have something important in common with eclipses. During an eclipse, the Moon blocks the light of the Sun, allowing us to view stars that would normally be overwhelmed by the Sun’s glare. Astronomers took advantage of this during the 1919 eclipse, 100 years ago on May 29, in order to test Albert Einstein’s theory of general relativity. Similarly, a coronagraph acts as an “artificial eclipse” to block the light from a star, allowing planets that would otherwise be lost in the star’s glare to be seen.

    “Most of the planets that we have detected so far are roughly 10,000 to 1 million times fainter than their host star,” explained Sasha Hinkley of the University of Exeter. Hinkley is the principal investigator on one of Webb’s first observation programs to study exoplanets and exoplanetary systems.

    “There is, no doubt, a population of planets that are fainter than that, that have higher contrast ratios, and are possibly farther out from their stars,” Hinkley said. “With Webb, we will be able to see planets that are more like 10 million, or optimistically, 100 million times fainter.” To observe their targets, the team will use high-contrast imaging, which discerns this large difference in brightness between the planet and the star.

    Webb will have the capability of observing its targets in the mid-infrared, which is invisible to the human eye, but with sensitivity that is vastly superior to any other observatory ever built. This means that Webb will be sensitive to a class of planet not yet detected. Specifically, Saturn-like planets at very wide orbital separations from their host star may be within reach of Webb.

    “Our program is looking at young, newly formed planets and the systems they inhabit,” explained co-principal investigator Beth Biller of the University of Edinburgh. “Webb is going to allow us to do this in much more detail and at wavelengths we’ve never explored before. So it’s going to be vital for understanding how these objects form, and what these systems are like.”

    Testing the Waters

    The team’s observations will be part of the Director’s Discretionary-Early Release Science program, which provides time to selected projects early in the telescope’s mission. This program allows the astronomical community to quickly learn how best to use Webb’s capabilities, while also yielding robust science.

    “With our ERS program, we will really be ‘testing the waters’ to get an understanding of how Webb performs,” said Hinkley. “We really need the best understanding of the instruments, of the stability, of the most effective way to post-process the data. Our observations are going to tell our community the most efficient way to use Webb.”

    The Targets

    Hinkley’s team will use all four of Webb’s instruments to observe three targets: A recently discovered exoplanet; an object that is either an exoplanet or a brown dwarf; and a well-studied ring of dust and planetesimals orbiting a young star.

    Exoplanet HIP 65426b: This newly discovered, directly imaged exoplanet has a mass between six and 12 times that of Jupiter and is orbiting a star that is hotter than and about twice as massive as our Sun.

    Direct imaging-This false-color composite image traces the motion of the planet Fomalhaut b, a world captured by direct imaging. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute

    The exoplanet is roughly 92 times farther from its star than Earth is from the Sun. The wide separation of this young planet from its star means that the team’s observations will be much less affected by the bright glare of the host star. Hinkley and his team plan to use Webb’s full suite of coronagraphs to view this target.

    Planetary-mass companion VHS 1256b: An object somewhere around the planet/brown dwarf boundary, VHS 1256b also is widely separated from its red dwarf host star—about 100 times the distance that the Earth is from the Sun. Because of its wide separation, observations of this object are much less likely to be affected by unwanted light from the host star. In addition to high-contrast imaging, the team expects to get one of the first “uncorrupted” spectra of a planet-like body at wavelengths where these objects have never before been studied.

    Circumstellar debris disk: For more than 20 years, scientists have been studying a ring of dust and planetesimals orbiting a young star called HR 4796A, which is about twice as massive as our own Sun. Astronomers think that most planetary systems probably looked a lot like HR 4796A and its debris ring at their earliest ages, making this a particularly interesting target to study. The team will use the high-contrast imaging of Webb’s coronagraphs to view the disk in different wavelengths. Their goal is to see if the structures of the disk look different from wavelength to wavelength.

    Planning the Program

    To plan this Early Release Science program, Hinkley asked as many members of the astronomical community as possible the simple question: If you want to plan a survey to search for exoplanets, what are the questions that you need the answers to for planning your surveys?

    “What we came up with was a set of observations that we think is going to answer those questions. We are going to tell the community that this is the way Webb performs in this mode, this is the kind of sensitivity we get, and this is the kind of contrast we achieve. And we need to rapidly turn that around and inform the community so that they can prepare their proposals really, really quickly.”

    The team is excited to view their targets in wavelengths never before detected, and to share their knowledge. According to Biller, “We could see years ago that for some of the planets we’ve already discovered, Webb would be really transformational.”

    The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The James Webb Space Telescope will be a large infrared telescope with a 6.5-meter primary mirror. Launch is planned for later in the decade.

    Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

    Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.

    Webb is an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center is managing the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

    Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.

    There will be four science instruments on Webb: the Near InfraRed Camera (NIRCam), the Near InfraRed Spectrograph (NIRspec), the Mid-InfraRed Instrument (MIRI), and the Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). Webb’s instruments will be designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.

    NASA Webb NIRCam

    NASA Webb NIRspec

    NASA Webb MIRI

    CSA Webb Fine Guidance Sensor-Near InfraRed Imager and Slitless Spectrograph FGS/NIRISS


    Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.

    Launch is scheduled for later in the decade on an Ariane 5 rocket. The launch will be from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb will be located at the second Lagrange point, about a million miles from the Earth.

    NASA image

    ESA50 Logo large

    Canadian Space Agency

     
  • richardmitnick 6:27 am on November 2, 2017 Permalink | Reply
    Tags: , , , , Coronagraphs, , Earth-sized alien worlds are out there. Now astronomers are figuring out how to detect life on them, Exobiology, , , NASA Deep Space Climate Observatory, NASA HabEx, , , ,   

    From Science: “Earth-sized alien worlds are out there. Now, astronomers are figuring out how to detect life on them” 

    ScienceMag
    Science Magazine

    Nov. 1, 2017
    Daniel Clery

    Stephen Kane spends a lot of time staring at bad pictures of a planet. The images are just a few pixels across and nearly featureless. Yet Kane, an astronomer at the University of California, Riverside, has tracked subtle changes in the pixels over time. They are enough for him and his colleagues to conclude that the planet has oceans, continents, and clouds. That it has seasons. And that it rotates once every 24 hours.

    He knows his findings are correct because the planet in question is Earth.

    1
    An image from the Deep Space Climate Observatory satellite (left), degraded to a handful of pixels (right), is a stand-in for how an Earth-like planet around another star might look through a future space telescope.
    (LEFT TO RIGHT) NASA EPIC TEAM; STEPHEN KANE

    Kane took images from the Deep Space Climate Observatory satellite, which has a camera pointing constantly at Earth from a vantage partway to the sun, and intentionally degraded them from 4 million pixels to just a handful.

    2
    NASA Deep Space Climate Observatory

    The images are a glimpse into a future when telescopes will be able to just make out rocky, Earth-sized planets around other stars. Kane says he and his colleagues are trying to figure out “what we can expect to see when we can finally directly image an exoplanet.” Their exercise shows that even a precious few pixels can help scientists make the ultimate diagnosis: Does a planet harbor life?

    Finding conclusive evidence of life, or biosignatures, on a planet light-years away might seem impossible, given that space agencies have spent billions of dollars sending robot probes to much closer bodies that might be habitable, such as Mars and the moons of Saturn, without detecting even a whiff of life. But astronomers hope that a true Earth twin, bursting with flora and fauna, would reveal its secrets to even a distant observer.

    Detecting them won’t be easy, considering the meager harvest of photons astronomers are likely to get from such a tiny, distant world, its signal almost swamped by its much brighter nearby star. The new generation of space telescopes heading toward the launch pad, including NASA’s mammoth James Webb Space Telescope (JWST), have only an outside chance of probing an Earth twin in sufficient detail.

    NASA/ESA/CSA Webb Telescope annotated

    But they will be able to sample light from a range of other planets, and astronomers are already dreaming of a space telescope that might produce an image of an Earth-like planet as good as Kane’s pixelated views of Earth. To prepare for the coming flood of exoplanet data, and help telescope designers know what to look for, researchers are now compiling lists of possible biosignatures, from spectral hints of gases that might emanate from living things to pigments that could reside in alien plants or microbes.

    There is unlikely to be a single smoking gun. Instead, context and multiple lines of evidence will be key to a detection of alien life. Finding a specific gas—oxygen, say—in an alien atmosphere isn’t enough without figuring out how the gas could have gotten there. Knowing that the planet’s average temperature supports liquid water is a start, but the length of the planet’s day and seasons and its temperature extremes count, too. Even an understanding of the planet’s star is imperative, to know whether it provides steady, nourishing light or unpredictable blasts of harmful radiation.

    “Each [observation] will provide crucial evidence to piece together to say if there is life,” says Mary Voytek, head of NASA’s astrobiology program in Washington, D.C.

    In the heady early days following the discovery of the first exoplanet around a normal star in 1995, space agencies drew up plans for extremely ambitious—and expensive—missions to study Earth twins that could harbor life. Some concepts for NASA’s Terrestrial Planet Finder and the European Space Agency’s Darwin mission envisaged multiple giant telescopes flying in precise formation and combining their light to increase resolution. But neither mission got off the drawing board. “It was too soon,” Voytek says. “We didn’t have the data to plan it or build it.”

    Instead, efforts focused on exploring the diversity of exoplanets, using both ground-based telescopes and missions such as NASA’s Kepler spacecraft.

    NASA/Kepler Telescope

    Altogether they have identified more than 3500 confirmed exoplanets, including about 30 roughly Earth-sized worlds capable of retaining liquid water. But such surveys give researchers only the most basic physical information about the planets: their orbits, size, and mass. In order to find out what the planets are like, researchers need spectra: light that has passed through the planet’s atmosphere or been reflected from its surface, broken into its component wavelengths.

    Most telescopes don’t have the resolution to separate a tiny, dim planet from its star, which is at least a billion times brighter. But even if astronomers can’t see a planet directly, they can still get a spectrum if the planet transits, or passes in front of the star, in the course of its orbit. As the planet transits, starlight shines through its atmosphere; gases there absorb particular wavelengths and leave characteristic dips in the star’s spectrum.

    Astronomers can also study a transiting planet by observing the star’s light as the planet’s orbit carries it behind the star.

    Planet transit. NASA/Ames

    Before the planet is eclipsed, the spectrum will include both starlight and light reflected from the planet; afterward, the planet’s contribution will disappear. Subtracting the two spectra should reveal traces of the planet.

    Teasing a recognizable signal from the data is far from easy. Because only a tiny fraction of the star’s light probes the atmosphere, the spectral signal is minuscule, and hard to distinguish from irregularities in the starlight itself and from absorption by Earth’s own atmosphere. Most scientists would be “surprised at how horrible the data is,” says exoplanet researcher Sara Seager of the Massachusetts Institute of Technology in Cambridge.

    In spite of those hurdles, the Hubble and Spitzer space telescopes, plus a few others, have used these methods to detect atmospheric gases, including sodium, water, carbon monoxide and dioxide, and methane, from a handful of the easiest targets.

    NASA/ESA Hubble Telescope

    NASA/Spitzer Infrared Telescope

    Most are “hot Jupiters”—big planets in close-in orbits, their atmospheres puffed up by the heat of their star.

    3
    In an artist’s concept, a petaled starshade flying at a distance of tens of thousands of kilometers from a space telescope blocks a star’s light, opening a clear view of its planets. NASA/JPL.

    The approach will pay much greater dividends after the launch of the JWST in 2019. Its 6.5-meter mirror will collect far more light from candidate stars than existing telescopes can, allowing it to tease out fainter exoplanet signatures, and its spectrographs will produce much better data.

    4
    https://jwst.nasa.gov/mirrors.html

    And it will be sensitive to the infrared wavelengths where the absorption lines of molecules such as water, methane, and carbon monoxide and dioxide are most prominent.

    Once astronomers have such spectra, one of the main gases that they hope to find is oxygen. Not only does it have strong and distinctive absorption lines, but many believe its presence is the strongest sign that life exists on a planet.

    Oxygen-producing photosynthesis made Earth what it is today. First cyanobacteria in the oceans and then other microbes and plants have pumped out oxygen for billions of years, so that it now makes up 21% of the atmosphere—an abundance that would be easily detectable from afar. Photosynthesis is evolution’s “killer app,” says Victoria Meadows, head of the NASA-sponsored Virtual Planet Laboratory (VPL) at the University of Washington in Seattle. It uses a prolific source of energy, sunlight, to transform two molecules thought to be common on most terrestrial planets—water and carbon dioxide—into sugary fuel for multicellular life. Meadows reckons it is a safe bet that something similar has evolved elsewhere. “Oxygen is still the first thing to go after,” she says.

    Fifteen years ago, when exoplanets were new and researchers started thinking about how to scan them for life, “Champagne would have flowed” if oxygen had been detected, Meadows recalls. But since then, researchers have realized that things are not that simple: Lifeless planets can have atmospheres full of oxygen, and life can proliferate without ever producing the gas. That was the case on Earth, where, for 2 billion years, microbes practiced a form of photosynthesis that did not produce oxygen or many other gases. “We’ve had to make ourselves more aware of how we could be fooled,” Meadows says.

    To learn what a genuine biosignature might look like, and what might be a false alarm, Meadows and her colleagues at the VPL explore computer models of exoplanet atmospheres, based on data from exoplanets as well as observations of more familiar planets, including Earth. They also do physical experiments in vacuum chambers. They recreate the gaseous cocktails that may surround exoplanets, illuminate them with simulated starlight of various kinds, and see what can be measured.

    Over the past few years, VPL researchers have used such models to identify nonbiological processes that could make oxygen and produce a “false positive” signal. For example, a planet with abundant surface water might form around a star that, in its early years, surges in brightness, perhaps heating the young planet enough to boil off its oceans. Intense ultraviolet light from the star would bombard the resulting water vapor, perhaps splitting it into hydrogen and oxygen. The lighter hydrogen could escape into space, leaving an atmosphere rich in oxygen around a planet devoid of life. “Know thy star, know thy planet,” recites Siddharth Hegde of Cornell University’s Carl Sagan Institute.

    Discovering methane in the same place as oxygen, however, would strengthen the case for life. Although geological processes can produce methane, without any need for life, most methane on Earth comes from microbes that live in landfill sites and in the guts of ruminants. Methane and oxygen together make a redox pair: two molecules that will readily react by exchanging electrons. If they both existed in the same atmosphere, they would quickly combine to produce carbon dioxide and water. But if they persist at levels high enough to be detectable, something must be replenishing them. “It’s largely accepted that if you have redox molecules in large abundance they must be produced by life,” Hegde says.

    Some argue that by focusing on oxygen and methane—typical of life on Earth—researchers are ignoring other possibilities. If there is one thing astronomers have learned about exoplanets so far, it is that familiar planets are a poor guide to exoplanets’ huge diversity of size and nature. And studies of extremophiles, microbes that thrive in inhospitable environments on Earth, suggest life can spring up in unlikely places. Exobiology may be entirely unlike its counterpart on Earth, and so its gaseous byproducts might be radically different, too.

    But what gases to look for? Seager and her colleagues compiled a list of 14,000 compounds that might exist as a gas at “habitable” temperatures, between the freezing and boiling points of water; to keep the list manageable they restricted it to small molecules, with no more than six nonhydrogen atoms. About 2500 are made of the biogenic atoms carbon, nitrogen, oxygen, phosphorus, sulfur, and hydrogen, and about 600 are actually produced by life on Earth. Detecting high levels of any of these gases, if they can’t be explained by nonbiological processes, could be a sign of alien biology, Seager and her colleagues argue.


    A. CUADRA/SCIENCE

    Light shining through the atmospheres of transiting exoplanets is likely to be the mainstay of biosignature searches for years to come. But the technique tends to sample the thin upper reaches of a planet’s atmosphere; far less starlight may penetrate the thick gases that hug the surface, where most biological activity is likely to occur. The transit technique also works best for hot Jupiters, which by nature are less likely to host life than small rocky planets with thinner atmospheres. The JWST may be able to tease out atmospheric spectra from small planets if they orbit small, dim stars like red dwarfs, which won’t swamp the planet’s spectrum. But these red dwarfs have a habit of spewing out flares that would make it hard for life to establish itself on a nearby planet.

    To look for signs of life on a terrestrial planet around a sunlike star, astronomers will probably have to capture its light directly, to form a spectrum or even an actual image. That requires blocking the overwhelming glare of the star. Ground-based telescopes equipped with “coronagraphs,” which precisely mask a star so nearby objects can be seen, can now capture only the biggest exoplanets in the widest orbits. To see terrestrial planets will require a similarly equipped telescope in space, above the distorting effect of the atmosphere. NASA’s Wide Field Infrared Survey Telescope (WFIRST), expected to launch in the mid-2020s, is meant to fill that need.

    NASA/WFIRST

    Even better, WFIRST could be used in concert with a “starshade”—a separate spacecraft stationed 50,000 kilometers from the telescope that unfurls a circular mask tens of meters across to block out starlight. A starshade is more effective than a coronagraph at limiting the amount of light going into the telescope. It not only blocks the star directly, but also suppresses diffraction with an elaborate petaled edge. That reduces the stray scattered light that can make it hard to spot faint planets. A starshade is a much more expensive prospect than a coronagraph, however, and aligning telescope and starshade over huge distances will be a challenge.

    Direct imaging will provide much better spectra than transit observations because light will pass through the full depth of the planet’s atmosphere twice, rather than skimming through its outer edges. But it also opens up the possibility of detecting life directly, instead of through its waste gases in the atmosphere. If organisms, whether they are plants, algae, or other microbes, cover a large proportion of a planet’s surface, their pigments may leave a spectral imprint in the reflected light. Earthlight contains an obvious imprint of this sort. Known as the “red edge,” it is the dramatic change in the reflectance of green plants at a wavelength of about 720 nanometers. Below that wavelength, plants absorb as much light as possible for photosynthesis, reflecting only a few percent. At longer wavelengths, the reflectance jumps to almost 50%, and the brightness of the spectrum rises abruptly, like a cliff. “An alien observer could easily tell if there is life on Earth,” Hegde says.

    There’s no reason to assume that alien life will take the form of green plants. So Hegde and his colleagues are compiling a database of reflectance spectra for different types of microbes. Among the hundreds the team has logged are many extremophiles, which fill marginal niches on Earth but may be a dominant life form on an exoplanet. Many of the microbes on the list have not had their reflectance spectra measured, so the Cornell team is filling in those gaps. Detecting pigments on an exoplanet surface would be extremely challenging. But a tell-tale color in the faint light of a distant world could join other clues—spectral absorption lines from atmospheric gases, for example—to form “a jigsaw puzzle which overall gives us a picture of the planet,” Hegde says.

    None of the telescopes available now or in the next decade is designed specifically to directly image exoplanets, so biosignature searches must compete with other branches of astronomy for scarce observing time. What researchers really hanker after is a large space telescope purpose-built to image Earth-like alien worlds—a new incarnation of the idea behind NASA’s ill-fated Terrestrial Planet Finder.

    The Habitable Exoplanet Imaging Mission, or HabEx, a mission concept now being studied by NASA, could be the answer. Its telescope would have a mirror up to 6.5 meters across—as big as the JWST’s—but would be armed with instruments sensitive to a broader wavelength range, from the ultraviolet to the near-infrared, to capture the widest range of spectral biosignatures. The telescope would be designed to reduce scattered light and have a coronagraph and starshade to allow direct imaging of Earth-sized exoplanets.

    Such a mission would reveal Earth-like planets at a level of detail researchers can now only dream about—probing atmospheres, revealing any surface pigments, and even delivering the sort of blocky surface images that Kane has been simulating. But will that be enough to conclude we are not alone in the universe? “There’s a lot of uncertainty about what would be required to put the last nail in the coffin,” Kane says. “But if HabEx is built according to its current design, it should provide a pretty convincing case.”

    4
    NASA HabEx: The Planet Hunter

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 6:03 am on April 29, 2016 Permalink | Reply
    Tags: , , Coronagraphs,   

    From JPL-Caltech- “Hiding in the Sunshine: The Search for Other Earths” 

    NASA JPL Banner

    JPL-Caltech

    April 28, 2016
    Whitney Clavin
    Jet Propulsion Laboratory, Pasadena, California
    818-354-4673
    whitney.clavin@jpl.nasa.gov

    1
    The vacuum chamber at NASA’s Jet Propulsion Laboratory in Pasadena, California, used for testing WFIRST and other coronagraphs. A star is simulated inside the chamber using light brought in by an optical fiber, and the light of this “star” is suppressed in the testbed by coronagraph masks and deformable mirrors. Credits: NASA/JPL-Caltech

    We humans might not be the only ones to ponder our place in the universe. If intelligent aliens do roam the cosmos, they too might ask a question that has gripped humans for centuries: Are we alone? These aliens might even have giant space telescopes dedicated to studying distant planets and searching for life. Should one of those telescopes capture an image of our blue marble of a planet, evidence of forests and plentiful creatures would jump out as simple chemicals: oxygen, ozone, water and methane.

    Many earthlings at NASA are hoping to capture similar chemical clues for Earth-like planets beyond our solar system, also known as exo-Earths, where “exo” is Greek for “external.” Researchers are developing new technologies with the goal of building space missions that can capture not only images of these exo-Earths, but also detailed chemical portraits called spectra. Spectra separate light into its component colors in order to reveal secrets of planets’ atmospheres, climates and potential habitability.

    “Evidence for life is not going to look like little green people — it’s going to reveal itself in a spectrum,” said Nick Siegler, the chief technologist for NASA’s Exoplanet Exploration Program Office at the agency’s Jet Propulsion Laboratory in Pasadena, California. The program is helping to develop NASA’s plans for future exo-Earth imaging missions.

    Be gone starlight

    2
    Two different types of masks to be used in NASA’s upcoming Wide-Field Infrared Survey Telescope, or WFIRST, coronagraph instrument, are pictured. At left, the “hybrid Lyot” mask has carefully designed metal and “dielectric” layers, but without a microscope it looks like a barely visible pinprick of a dot on glass. At right is the “shaped pupil” mask, which is a few centimeters across and consists of highly reflective mirror regions interspersed with regions of black silicon. This silicon surface treatment absorbs nearly all incoming light. Credits: NASA/JPL-Caltech

    On the road to this goal, NASA is actively developing coronagraph technology in various laboratories, including JPL.

    4
    Technicians in the Optics Mitigation Facility

    2
    Coronagraph:An earlier image before the enclosure was installed showing what’s inside the enclosure

    Coronagraphs are instruments introduced in the early 20th century to study our sun. They use special masks to block out light from the circular disk of the sun, so that scientists can study its outer atmosphere, or corona.

    Now NASA is developing more sophisticated coronagraphs to block the glaring light of other stars and reveal faint planets that might be orbiting them. Stars far outshine their planets; for example, our sun is 10 billion times brighter than Earth. That’s similar to the flood of football stadium lights next to a tiny candle.

    “The search for Earth-like planets begins with the suppression of starlight,” said Rhonda Morgan of JPL, a coronagraph technologist for the Exoplanet Exploration Program Office. “It’s like blocking the sun with a sun visor while driving in order to see the road.”

    Telescopes on the ground have already used coronagraphs to take pictures of planets, but those planets are easier to photograph because they are large, bright, and orbit far from their host stars. To take a picture of Earth-size planets lying in the habitable zone of sun-like stars — the region where temperatures are just right for possible liquid oceans and lakes — will require a telescope in space. Out in space, the blurring effects of our blustery atmosphere can be avoided.

    ESO/SPHERE extreme adaptive optics system and coronagraphic facility on the extreme adaptive optics system and coronagraphic facility on The VLT
    ESO/SPHERE extreme adaptive optics system and coronagraphic facility on the VLT
    ESO/SPHERE extreme adaptive optics system and coronagraphic facility on the VLT.

    To take a picture of Earth-size planets lying in the habitable zone of sun-like stars — the region where temperatures are just right for possible liquid oceans and lakes — will require a telescope in space. Out in space, the blurring effects of our blustery atmosphere can be avoided.

    Several types of coronagraphs are under development for proposed space missions. One mission, led by NASA’s Goddard Space Flight Center, Greenbelt, Maryland, is known as WFIRST.

    NASA/WFIRST
    NASA/WFIRST

    WFIRST stands for Wide-Field Infrared Survey Telescope. The WFIRST mission would be able to identify chemicals in the atmospheres of exoplanets as small as super-Earths, which are like Earth’s bigger cousins, such as Kepler-452b, a recent discovery by NASA’s Kepler mission.

    NASA/Kepler Telescope
    NASA/Kepler Telescope

    This would pave the way for future studies of the smaller exo-Earths. The WFIRST mission would also investigate other cosmic mysteries such as dark matter and dark energy.

    Tinkering with tiny masks

    Engineers and scientists at JPL are busily tinkering with different coronagraph technologies for WFIRST. Ilya Poberezhskiy, who manages the testbeds at JPL, explained two primary coronagraph designs while holding in his hand the tiny, starlight-blocking masks. One of them, the “shaped pupil” mask, is a few centimeters across, while the “hybrid Lyot” mask is a pinprick of a dot, barely visible at only one-tenth of a millimeter in size. Both technologies will fly together on the WFIRST mission as a part of one instrument — the occulting mask coronagraph.

    “A wheel-like mechanism will rotate to switch different masks inside the instrument and convert the coronagraph from one mode to another,” said Poberezhskiy.

    The main challenge for coronagraphs is controlling starlight, which has a tendency to stray. Just putting a circular mask in front of the star doesn’t obstruct the light completely; starlight bends around the mask like ocean waves curving around islands in a process called diffraction. Each coronagraph type deals with this challenge differently by using multiple masks as well as mirrors that can deform to sequentially suppress starlight in various stages.

    An animation explaining how the hybrid Lyot coronagraph works can be seen online at:

    https://exoplanets.jpl.nasa.gov/resources/1061/

    “The starlight likes to walk all over the place, and into the area where you want to image the planet,” said Wes Traub, the JPL project scientist for WFIRST. “The goal now is to get more practical with the kind of telescope we will use for WFIRST.”

    How to handle jitter

    Another challenge in designing coronagraphs is adjusting for a space telescope’s tiny vibrations, or jitter. The team at JPL is assessing how their coronagraphs handle jitter by simulating the effects in a vacuum chamber. They built a table-top-size telescope simulator for the tests.

    “In space, telescopes experience warping and vibrations that need to be measured and reduced inside the coronagraph,” said Poberezhskiy. “Our mock telescope will let us test the WFIRST coronagraph under realistic, space-like conditions.”

    As WFIRST development moves forward, mission planners are already thinking about a possible next step: a space telescope designed to image true Earth analogs. Such a mission may be more than a decade away, but development of the nuts and bolts of the technology is underway at a feverish pace.

    “It’s an exciting time for exoplanet research,” said Gary Blackwood, manager of the Exoplanet Exploration Program. “This is history in the making.”

    The hybrid Lyot coronagraph design team is led by John Trauger of JPL. The shaped pupil coronagraph is pioneered by Jeremy Kasdin of Princeton University, New Jersey. A third technology, called a phase-induced amplitude apodization complex mask coronagraph, is being developed by Olivier Guyon of the University of Arizona, Tucson; Brian Kern of JPL’ and Ruslan Belikov and Eduardo Bendek of NASA’s Ames Research Center, Moffett Field, California.

    WFIRST is managed at NASA’s Goddard, with participation by JPL, the Space Telescope Science Institute in Baltimore, the Infrared Processing and Analysis Center, also in Pasadena, and a science team comprised of members from U.S. research institutions across the country.

    For more information about NASA’s WFIRST mission, visit:

    http://www.nasa.gov/wfirst

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

    Caltech Logo
    jpl

    NASA image

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: