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  • richardmitnick 12:05 pm on August 18, 2019 Permalink | Reply
    Tags: , , , , , , , Transit method   

    From Ethan Siegel: “Ask Ethan: What Has TESS Accomplished In Its First Year Of Science Operations?” 

    From Ethan Siegel
    Aug 17, 2019

    An illustration of NASA’s TESS satellite and its capabilities of imaging transiting exoplanets. Kepler has given us more exoplanets than any other mission, and it revealed them all through the transit method.

    Planet transit. NASA/Ames

    NASA/Kepler Telescope, and K2 March 7, 2009 until November 15, 2018

    With TESS, we are looking to extend our capabilities even farther, using the same method with superior equipment and techniques. (NASA)

    After Kepler but before James Webb, TESS is preparing astronomers for the coming exoplanet revolution.

    There are always new discoveries and achievements occurring in science, and certain fields have experienced recent advances that are nothing short of revolutionary. A generation ago, humanity didn’t know if stars beyond our Sun had planets around them; today, we’ve discovered thousands of star systems with planets orbiting them. Planets of varying masses orbit all types of star at a vast range of distances, and astronomers are preparing for the day where we can image Earth-sized exoplanets directly to seek signs of extraterrestrial life. Today, in a post-Kepler but pre-James Webb world, TESS is the leading exoplanet-finding mission. A year into its mission, what has it accomplished? That’s what Patreon supporter Tim Graham wants to know, asking:

    With TESS completing [the] first year of its mission, surveying the southern sky, how does it compare to Kepler?

    TESS is fundamentally different than Kepler, but what it’s found should give us all incredible hope for the 2020s.

    Kepler was designed to look for planetary transits, where a large planet orbiting a star could block a tiny fraction of its light, reducing its brightness by ‘up to’ 1%. The smaller a world is relative to its parent star, the more transits you need to build up a robust signal, and the longer its orbital period, the longer you need to observe to get a detection signal that rises above the noise. Kepler successfully accomplished this for thousands of planets around stars beyond our own. (MATT OF THE ZOONIVERSE/PLANET HUNTERS TEAM)

    There are some similarities between TESS and Kepler in how both missions work.

    Both TESS and Kepler measure the light coming from a target star (or a set of target stars),
    they monitor the total light output over relatively long periods of time,
    they search for periodic dips in the overall flux from the star,
    and if the dips repeat in frequency and magnitude, both extract the radius and orbital distance for a potential candidate planet.

    This is the essence of the transit method in searching for exoplanetary candidates, and it was famously employed by Kepler over its recently-ended mission, beginning in 2009. Thanks largely to Kepler, the number of known exoplanets skyrocketed from a few dozen to many thousands in under a decade.

    Today, we know of over 4,000 confirmed exoplanets, with more than 2,500 of those found in the Kepler data. These planets range in size from larger than Jupiter to smaller than Earth. Yet because of the limitations on the size of Kepler and the duration of the mission, the majority of planets are very hot and close to their star, at small angular separations. TESS has the same issue with the first planets it’s discovering: they’re preferentially hot and in close orbits. Only through dedicates, long-period observations (or direct imaging) will we be able to detect planets with longer period (i.e., multi-year) orbits. (NASA/AMES RESEARCH CENTER/JESSIE DOTSON AND WENDY STENZEL; MISSING EARTH-LIKE WORLDS BY E. SIEGEL)

    The primary mission of Kepler, however, was fundamentally different from the primary mission of TESS. While Kepler’s goal was to characterize the planetary systems of as many stars as possible in as great detail as possible, TESS is particularly concerned with finding and characterizing exoplanetary systems around the closest stars to Earth. Both of these ambitions are scientifically useful and important, but what TESS is doing doesn’t compare to Kepler at all.

    In order to accomplish the goal, Kepler’s primary mission involved the continuous observation of a small region of the sky, along one of the Milky Way’s spiral arms. These observations spanned three years, encapsulating over 100,000 stars located up to some 3,000 light-years away. Thousands of these stars were discovered to exhibit these transits: the same number you’d expect if every star possessed planets that were randomly aligned relative to our line-of-sight.

    Kepler’s field-of-view contains approximately 150,000 stars, but transits have only been observed for a few thousand. In theory, nearly all of these stars should have planets, but only a small percentage of planetary systems should have good enough alignments from our perspective for a transit to be observed. (PAINTING BY JON LOMBERG, KEPLER MISSION DIAGRAM ADDED BY NASA)

    Once its primary mission ended [Kepler’s reaction wheels had failed], however, Kepler switched to an alternate goal: the K2 mission. Instead of pointing at one region of the sky for a long period of time, Kepler would observe a different region of the sky for approximately 30 days, search for transits there, and then move on to another region of sky. This led to some incredible discoveries, particularly around the smallest, coolest stars in the Universe: the M-class red dwarfs.

    The lowest-mass stars are also the smallest in physical size, meaning that even a terrestrial-like, rocky planet can block a significant fraction of the star’s light during a transit: enough to have its flux dip detected by Kepler. In addition, these exoplanets can possess very short periods, meaning that to have Earth-like temperatures on them, they’ll need to be so close that they complete a full orbit in less than a month. Many fascinating systems have been discovered and/or measured precisely by the K2 mission.

    This image montage shows the Maunakea Observatories, the Kepler Space Telescope, and the night sky with various K2 fields-of-view highlighted. Inside each field-of-view there are dots inside, which point out the various planetary systems discovered and measured by the K2 mission. (KAREN TERAMURA (UHIFA); NASA/KEPLER; MILOSLAV DRUCKMÜLLER AND SHADIA HABBAL)

    The K2 mission, perhaps, could be viewed as the best testing ground for TESS, but is still fundamentally different. The Kepler telescope was designed to have a narrow field-of-view but to go relatively deep: measuring flux dips around stars up to thousands of light-years away.

    TESS, on the other hand, was designed to survey practically the entire sky, with a much wider field-of-view. It doesn’t need to go as deep, because its goal is to seek planets around the closest stars to Earth: those within just 200 light-years of us. If there’s a planet orbiting a star with the right orientation to exhibit a transit as viewed from our perspective, TESS will not only find it, but will enable scientists to determine the planet’s orbital distance and physical radius.

    NASA’s TESS satellite will survey the entire sky in 16 chunks-at-a-time that are approximately 12 degrees across apiece, ranging from the galactic poles down to near the galactic equator. As a result of this surveying strategy, the polar regions see more observing time, making TESS more sensitive to smaller and more distant planets in those systems. (NASA/MIT/TESS)

    Every system where an exoplanet is found by TESS will be remarkable, regardless of what type of star it is or what types of planets are found around it. You see, the goal of TESS is not, contrary to what many people think, to find an Earth-like world at the right distance from its parent star to have liquid water (and maybe life) on its surface. Sure, that would be awfully nice, but that’s not the purpose of TESS.

    Instead, the science goal of TESS is to find candidate exoplanets and candidate exoplanetary systems where future observatories ⁠ — like the James Webb Space Telescope ⁠ — can try to take detailed measurements of the planets themselves. This would include the capacity for measuring the atmospheric contents during transit, searching for potential biosignatures, or even, if we get lucky, the possibility of direct exoplanet imaging.

    Hundreds of candidate planets have been discovered so far in the data collected and released by NASA’s Transiting Exoplanet Survey Satellite (TESS). Some of the closest worlds to be discovered by TESS will be candidates for being Earth-like and within the reach of direct imaging. (NASA/MIT/TESS)

    TESS was launched in April of 2018, and began taking its first scientific data in July of last year. It’s now been more than 12 months, which means that half of the sky (13 separate sets of observations of 27 days each) has now been observed by TESS. This coverage of the entire southern sky is unprecedented in terms of searches for nearby exoplanets, and while TESS now is turning to the northern hemisphere, let’s take a look at TESS’s discoveries so far:

    21 new exoplanets have been discovered, already confirmed by ground-based telescopes,

    ranging in size from as small as 0.80 times the size of Earth to larger than Jupiter,

    with an additional 850 candidate exoplanets that have been identified, awaiting ground-based confirmation,
    one system, Beta Pictoris, where exocomets (!) have been observed,

    and a small, super-Earth class planet orbiting very close to a Sun-like star that also possesses an enormous super- Jupiter on an extremely elliptical trajectory.

    The Pi Mensae system was discovered to house an exoplanet way back in 2001: Pi Mensae b, with more than 10 Jupiter masses, and a huge difference between its closest approach (1.21 AU) and farthest distance (5.54 AU) from its parent star. TESS uncovered Pi Mensae c: a super-Earth with an orbital period of just 6.3 days. This marks the first time a nearby and distant planet with such different properties and orbits have been discovered around the same star. (NASA / MIT / TESS)

    But my favorite exoplanetary system investigated by TESS (so far) has to be the one around the nearby star HD 21749. It’s located 53 light-years away, it’s slightly smaller and less massive than our Sun (about 70% the mass and radius), and it now has two known planets around it.

    The first one discovered was HD 21749b, with 2.8 times the radius of Earth and 23.2 times the Earth’s mass. With a 36-day orbit, it should be on the warm side (about 300 °F/150 °C), slightly smaller but significantly denser than Uranus or Neptune. It is the longest-period exoplanet known within 100 light-years of Earth, and one of the best candidates in the TESS field for direct imaging.

    But the second planet, announced in April, is even better: HD 21749c was the first Earth-sized planet discovered by TESS, with Mercury-like temperatures, 90% the radius of Earth, and an orbital period of just 7.8 days.

    An artist’s conception of HD 21749c, the first Earth-sized planet found by NASA’s Transiting Exoplanets Survey Satellite (TESS), as well as its sibling, HD 21749b, a warm sub-Neptune-sized world. (ROBIN DIENEL / CARNEGIE INSTITUTION FOR SCIENCE)

    There are huge advantages to what TESS is doing over what either Kepler or K2 did. Because TESS is preferentially measuring the nearest stars to us, identifying planets and planetary systems where follow-up observations will matter the most. The reason why is simple.

    1.When a planet orbits its star, it will be physically separated from it by some knowable, measurable distance.
    2.Depending on how far away the star is from us, that will correspond to an angular scale, with the planet achieving the largest angular separations from its star when it’s ¼ and ¾ of the way through its orbit relative to the moment of transit.
    3.Therefore, if you can identify the closest exoplanets with well-measured orbital parameters, you can use a high-resolution telescope equipped with a coronagraph to directly image the planet in question.

    As you may have guessed, the James Webb Space Telescope will have exactly the instrumentation and capabilities necessary to directly image many of these worlds.

    The Near Infrared Camera (NIRCam) is Webb’s primary imager that will cover the infrared wavelength range 0.6 to 5 microns. NIRCam is equipped with coronagraphs, instruments that allow astronomers to take pictures of very faint objects around a central bright object, like stellar systems. NIRCam’s coronagraphs work by blocking a brighter object’s light, making it possible to view the dimmer object nearby. (LOCKHEED MARTIN)

    When it’s a bright, sunny day and you want to see an object in the sky that’s very close to the Sun, what do you do? You hold up a finger (or your whole hand) and block out the Sun, and then look for the nearby object that’s much intrinsically fainter than the Sun. This is exactly what telescopes equipped with coronagraphs do.

    With the next generation of telescopes, this will enable us to finally directly-image planets around the closest stars to us, but only if we know where, when, and how to look. This is exactly the type of information that astronomers are gaining from TESS. By the time the James Webb Space Telescope launches in 2021, TESS will have completed its first sweep of the entire sky, providing a rich suite of tantalizing targets suitable for direct imaging. Our first picture of an Earth-like world may well be close on the horizon. Thanks to TESS, we’ll know exactly where to look.

    There are four known exoplanets orbiting the star HR 8799, all of which are more massive than the planet Jupiter. These planets were all detected by direct imaging taken over a period of seven years, with the periods of these worlds ranging from decades to centuries.

    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

    As in our Solar System, the inner planets revolve around their star more rapidly, and the outer planets revolve more slowly, as predicted by the law of gravity. With the next generation of telescopes like JWST, we may be able to measure Earth-like or super-Earth-like planets around the nearest stars to us. (JASON WANG / CHRISTIAN MAROIS)

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 10:59 am on December 26, 2018 Permalink | Reply
    Tags: Aliens? Or Alien Impostors? Finding Oxygen Might Not Mean Life After All, , , , , , , Transit method   

    From Ethan Siegel: “Aliens? Or Alien Impostors? Finding Oxygen Might Not Mean Life, After All” 

    From Ethan Siegel
    Dec 25, 2018

    Both reflected sunlight on a planet and absorbed sunlight filtered through an atmosphere are two techniques humanity is presently developing to measure the atmospheric content and surface properties of distant worlds. In the future, this could include the search for organic signatures as well. (MELMAK / PIXABAY)

    The most surefire, easily-seen signature of life on Earth might be a cosmic red herring around other worlds.

    In our quest for life beyond the Solar System, it makes sense to look for a world like our own. We’ve long hoped to find an Earth-sized world around a Sun-like star at the right distance for liquid water as our first step, and with thousands of planets in our coffers already, we’re extremely close. But not every world with the right physical properties is going to have life; we need additional information to know whether a potentially habitable world is actually inhabited.

    The follow-up would be to analyze the planet’s atmosphere for Earth-like signatures: potential signs of life. Earth’s combination of atmospheric gases — nitrogen, oxygen, water vapor, carbon dioxide and more — has been assumed to be a dead giveaway for a planet with life on it. But a new study by planetary scientist Dr. Sarah Hörst’s team throws that into doubt [see paper below]. Even worlds rich in oxygen might not harbor aliens, but an impostor process that could fool us all.

    Most of the planets we know of that are comparable to Earth in size have been found around cooler, smaller stars than the Sun. This makes sense with the limits of our instruments; these systems have larger planet-to-star size ratios than our Earth does with respect to the Sun. (NASA / AMES / JPL-CALTECH)

    The scientific story of how to even reach that point is fascinating, and closer to becoming a reality than ever before. We can understand how this happens by imagining we were aliens, looking at our Sun from a large distance away, trying to determine if it possessed an inhabited world.

    By measuring the slight variations in the frequency of the Sun’s light over long periods of time, we’d be able to deduce the gravitational influence of the planets on them. This detection method is known either the radial velocity or the stellar wobble method, and can tell us information about a planet’s mass and orbital period. Most of the early (pre-Kepler) exoplanets were discovered with this technique, and it’s still the best method we have for both determining planetary masses and confirming the existence of candidate exoplanets.

    Radial Velocity Method-Las Cumbres Observatory

    Radial velocity Image via SuperWasp http:// http://www.superwasp.org/exoplanets.htm

    Veloce Rosso, Australia’s next premier astronomical instrument. On the the Anglo-Australian Telescope (AAT). a precision radial velocity spectrograph, capable of detecting Earth-like planets

    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    Today, we know of over 3,500 confirmed exoplanets, with more than 2,500 of those found in the Kepler data. These planets range in size from larger than Jupiter to smaller than Earth. Yet because of the limitations on the size of Kepler and the duration of the mission, there have been zero Earth-sized planets found around Sun-like stars that fall into Earth-like orbits. (NASA/AMES RESEARCH CENTER/JESSIE DOTSON AND WENDY STENZEL; MISSING EARTH-LIKE WORLDS BY E. SIEGEL)

    We also need to know the size of the planet. With the stellar wobble alone, we’ll only know what the mass of the world is relative to the angle-of-inclination of its orbit. A world that’s the mass of Earth could be well-suited to life if it’s got an Earth-like atmosphere, but it could be disastrous for life if it’s an iron-like world with no atmosphere at all, or a low-density, puffy world with a large gaseous envelope.

    The transit method, where a planet passes in front of its parent star, is our most prolific method for measuring a planet’s radius.

    Planet transit. NASA/Ames

    By calculating how much of the parent star’s light it blocks when it crosses our line-of-sight, we can determine its size. For an alien civilization whose line-of-sight was properly aligned with Earth orbiting the Sun, we’d be able to detect it with technology only about 20% more sensitive than Kepler was.

    Kepler was designed to look for planetary transits, where a large planet orbiting a star could block a tiny fraction of its light, reducing its brightness by ‘up to’ 1%. The smaller a world is relative to its parent star, the more transits you need to build up a robust signal, and the longer its orbital period, the longer you need to observe to get a detection signal that rises above the noise. (MATT OF THE ZOONIVERSE/PLANET HUNTERS TEAM)

    This is roughly where we are today. We’ve found hundreds of worlds that we suspect are rocky orbiting their stars, many of them right around Earth-sized. For a large fraction of them, we’ve measured their mass, radius, and orbital period, with a small percentage being at the right orbital distance to have Earth-like temperatures.

    Most of them orbit red dwarf stars — the most common class of star in the Universe — which means the forces should tidally lock them: the same side should always face the star. These stars flare often, posing a danger to any potential atmospheres on these worlds.

    But a significant fraction will orbit K, G, or F-class stars, where they can rotate on their axes, maintain an atmosphere, and have the potential for Earth-like life. That’s where we want to look.

    When a planet transits in front of its parent star, some of the light is not only blocked, but if an atmosphere is present, filters through it, creating absorption or emission lines that a sophisticated-enough observatory could detect. If there are organic molecules or large amounts of molecular oxygen, we might be able to find that, too. (ESA / DAVID SING)

    And that’s where future technology is hoping to take us. If a larger Kepler-like telescope were equipped with the right instruments, we could break up the light passing through an exoplanet’s atmosphere during a transit, and determine its atomic and molecular contents. If we were looking at Earth, we could determine that it was composed of nitrogen, oxygen, argon, water vapor, and carbon dioxide, along with other trace signatures.

    Even without an ideal alignment, direct imaging will still be possible.

    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

    Potential NASA flagship missions, such as HabEx or LUVOIR (with either a starshade or a coronagraph), could block the light of the parent star and detect the light from an orbiting planet directly. This light could again be broken up into its individual wavelengths, determining its molecular content.

    NASA Habitable Exoplanet Imaging Mission (HabEx) The Planet Hunter

    NASA Large UV Optical Infrared Surveyor (LUVOIR)

    Whether from absorption (transit) or emission (direct imaging), we could learn what a potential Earth-twin’s atmosphere is composed of.

    The Starshade concept could enable direct exoplanet imaging as early as the 2020s. This concept drawing illustrates a telescope using a star shade, enabling us to image the planets that orbit a star while blocking the star’s light to better than one part in 10 billion. (NASA AND NORTHROP GRUMMAN)

    So what if we find an oxygen-rich world? No other planets, dwarf planets, moons, or other objects contain even 1% oxygen that we know of. Earth’s atmosphere transformed over nearly 2 billion years before it had an oxygen content comparable to what it does today, and it was anaerobic life processes that created our modern atmosphere that’s rich in molecular oxygen. Because of how easily oxygen is destroyed by ultraviolet light and how difficult it is to produce in large quantities via inorganic, chemical processes, oxygen has long been taken as the one biosignature we could rely on to indicate a living world.

    If organic molecules were found there as well, it would seem like a surefire indicator that life, indeed, must have taken hold on such a planet.

    And that’s where the Hörst lab’s new findings come into play. In a paper just published in ACS Earth and Space Chemistry, a specially-designed chamber to mimic the environment of a hazy exoplanet atmosphere showed that molecular oxygen (O2) could be created in a number of environmental conditions likely to occur naturally, with no life necessary to create it.

    The ingenious method was to create a gas mixture that would be consistent with what we expect an Earth-like or super-Earth-like environment might hold. That mixture was then inserted into a specially-designed chamber and subjected to a variety of temperature, pressure, and energy-injection conditions that would likely mimic the activity that could occur on actual exoplanets.

    Chao He explaining how the study’s PHAZER setup works, where PHAZER is the specially-designed Planetary HAZE chamber found in the Hörst lab at Johns Hopkins University. (CHANAPA TANTIBANCHACHAI / JOHNS HOPKINS UNIVERSITY)

    A total of nine different gas mixtures were used at temperatures ranging from 27 °C (80 °F) up to approximately 370 °C (700 °F), representing the temperature range expected to naturally occur. The energy injection came in two different forms: from ultraviolet light and from plasma discharges, which represent natural conditions likely to be caused by sunlight or lightning-like activity.

    The results? There were multiple scenarios that resulted in the production of both organic molecules (like sugar and amino acid precursors) and oxygen, yet didn’t require any life at all to get them. According to first author Chao He,

    People used to suggest that oxygen and organics being present together indicates life, but we produced them abiotically in multiple simulations. This suggests that even the co-presence of commonly accepted biosignatures could be a false positive for life.

    By heating atmospheric gases thought to mimic exoplanet atmospheres to various temperatures and subjecting them to ultraviolet and plasma-based energy injections, organic molecules and oxygen can be produced. We must be careful that we don’t mistake an abiotic signature of coincidence oxygen and organics for life. (C. HE ET AL., ‘GAS PHASE CHEMISTRY OF COOL EXOPLANET ATMOSPHERES: INSIGHT FROM LABORATORY SIMULATIONS,’ ACS EARTH SPACE CHEM. (2018))

    The experiment wasn’t some cherry-picked design to attempt to produce this false-positive result, either. The gases inside the chamber were designed to mimic the contents of known exoplanetary atmospheres, with the ultraviolet energy injection designed to simulate sunlight. The experiments simulated a variety of atmospheric (hydrogen-rich, water-rich, and carbon dioxide-rich) environments, and all of them created haze particles and yielded organic molecules such as hydrogen cyanide, acetylene, and methanimine.

    Multiple environments generated organic molecules, prebiotic precursor molecules, and oxygen all at once, at Earth-like temperatures and much hotter temperatures as well. The paper itself states the main conclusion very succinctly:

    Our laboratory results indicate that complex atmospheric photochemistry can happen in diverse exoplanet atmospheres and lead to the formation of new gas products and haze particles, including compounds (O2 and organics) that could be falsely identified as biosignatures.

    The amount of molecular oxygen produced in these experiments was relatively small by some metrics; Hörst herself wouldn’t call the atmospheres created in the lab “oxygen-rich.” But it’s nevertheless possible that these processes would translate into an oxygen-rich atmosphere on an exoplanet, given the right conditions and enough time. At this point, it appears possible that finding the presence of both organics and molecular oxygen could be due to abiotic, non-life processes exclusively.

    Signatures of organic, life-giving molecules are found all over the cosmos, including in the largest, nearby star-forming region: the Orion Nebula. Someday soon, we may be able to look for biosignatures in the atmospheres of Earth-sized worlds around other stars, or we may detect simple life directly on another world in our Solar System. (ESA, HEXOS AND THE HIFI CONSORTIUM; E. BERGIN)

    This doesn’t mean that finding an Earth-like world with an oxygen-rich atmosphere won’t be incredibly interesting; it absolutely will be. It doesn’t mean that finding organic molecules coincident with the oxygen won’t be compelling; it will be a finding worth getting excited over. It doesn’t even mean that it won’t be indicative of life; a world with oxygen and organic molecules may well be overflowing with living organisms. But it does mean that we have to be careful.

    Historically, when we’ve looked to the skies for evidence of life beyond Earth, we’ve been biased by hope and what we know on Earth. Theories of dinosaurs on Venus or canals on Mars still linger in our memories, and we must be careful that extraterrestial oxygen signatures don’t lead us to falsely optimistic conclusions. We now know that both abiotic processes and life-dependent ones can create an oxygen-rich atmosphere.

    The hard problem, then, will be disentangling the potential causes when we actually find our first oxygen-rich, Earth-like exoplanet. Our reward, if we’re successful, will be the knowledge of whether or not we’ve actually found life around another star.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 9:33 am on September 22, 2018 Permalink | Reply
    Tags: , , , , , , NASA/MIT TESS finds 1st two exoplanet candidates during first science orbit, , TESS in excellent health, Transit method   

    From NASA Spaceflight: “TESS in excellent health, finds 1st two exoplanet candidates during first science orbit” 

    NASA Spaceflight

    From NASA Spaceflight

    September 20, 2018
    Chris Gebhardt

    The joint NASA / Massachusetts Institute of Technology (MIT) Transiting Exoplanet Survey Satellite, or TESS, has completed its first science orbit after launch and orbital activations/checkouts. Unsurprisingly given TESS’s wide range of view, a team of scientists have already identified the planet-hunting telescope’s first two exoplanet candidates.
    No image credit.

    The yet-to-be-confirmed exoplanets are located 59.5 light years from Earth in the Pi Mensae system and 49 light years away in the LHS 3844 system.

    TESS’s overall health:

    Following a successful launch on 18 April 2018 aboard a SpaceX Falcon 9 rocket from SLC-40 at the Cape Canaveral Air Force Station, Florida, TESS was injected into an orbit aligned for a gravity assist maneuver one month later with the Moon to send the telescope into its operational 13.65-day orbit of Earth.

    TESS’s orbit is highly unique, with the trajectory designed so the telescope is in a 2:1 resonance with the Moon at a 90° phase offset at apogee (meaning the telescope maintains a separation from the Moon so the lunar gravity field doesn’t perturb TESS’ orbit but at the same time keeps the orbit stable) to allow the spacecraft to use as little of its maneuvering fuel as possible to achieve a hoped-for 20 year life.

    At the time of launch, mission scientists and operators noted that first light images were expected from TESS in June 2018 following a 60-day commissioning phase.

    While it is not entirely clear what happened after launch, what is known is that the commissioning phase lasted 27 days longer than expected, stretching to the end of July. TESS’ first science and observational campaign began not in June but on 25 July 2018.

    By 7 August, the halfway point in the first science observation period, TESS took what NASA considers to be the ceremonial “first light” images of the telescope’s scientific ventures.

    TESS acquired the image using all four cameras during a 30-minute period on Tuesday, 7 August. The images include parts of a dozen constellations from Capricornus to Pictor, both the Large and Small Magellanic Clouds, and the galaxies nearest to our own.

    Ceremonial first light image captured by TESS on 7 August 2018 showing the full Sector 1 image (center) and close-ups of each of the four camera groups (left and right) Credit NASA/MIT/TESS

    “In a sea of stars brimming with new worlds, TESS is casting a wide net and will haul in a bounty of promising planets for further study,” said Paul Hertz, astrophysics division director at NASA Headquarters. “This first light science image shows the capabilities of TESS’ cameras and shows that the mission will realize its incredible potential in our search for another Earth.”

    George Ricker, TESS’ principal investigator at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, added, “This swath of the sky’s southern hemisphere includes more than a dozen stars we know have transiting planets based on previous studies from ground observatories.”

    While TESS orbits Earth every 13.65 days, its data collection phase for each of its 26-planned observation sectors of near-Earth sky lasts for two orbits so the telescope can collect light data from each section for a total of 27.4 days.

    With science operations formerly commencing on 25 July, the first observational campaign stretched to 22 August.

    Unlike some missions which only transmit data back to Earth after observational campaigns end, TESS transmits its data both in the middle and at the end of each campaign when the telescope swings past its perigee (closest orbital approach to Earth).

    On 22 August, after TESS completed its first observation campaign of a section of the Southern Hemisphere sky, the telescope transmitted the second batch of light data to Earth through the Deep Space Network.

    From there, the information was processed and analyzed at NASA’s Science Processing and Operations Center at the Ames Research Center in California – which provided calibrated images and refined light curves for scientists to analyze and find promising exoplanet transit candidates.

    NASA and MIT then made that data available to scientists as they search for the more than 22,000 exoplanets (most of those within a 300 light-year radius of Earth) that TESS is expected to find during the course of its two-year primary mission.

    First TESS exoplanet candidate:

    Given the sheer number of exoplanets TESS is expected to find in the near-Earth neighborhood, it is not surprising that the first observation campaign has already returned potential exoplanet candidates – the first of which was confirmed by NASA via a tweet on Wednesday, 19 September.

    TESS’ first exoplanet candidate is Pi Mensae c – a super-Earth with an orbital period of 6.27 days. According to a draft of the paper announcing the discovery, several methods were used to eliminate the possibility of this being a false detection or the detection of a previously unknown companion star.

    The Pi Mensae system is located 59.5 light years from Earth, and the new exoplanet – if confirmed – would be officially classified Pi Mensae c, the second known exoplanet of the system.

    Exoplanet’s official classifications derive from the name of the star they orbit followed by a lowercase letter indicating the order in which they were discovered in a particular system.

    The order in which exoplanets are discovered does not necessarily match the order (distance from closest to farthest) in which they orbit their parent star.

    Moreover, the lowercase letter designation begins with the letter “b”, not the letter “a”. Thus, the first discovered exoplanet in a particular system will bear the name of its parent star followed by a lowercase “b”.

    Subsequent exoplanets orbiting the same start or stars (as the case may be), regardless of whether they orbit closer to or farther away from the parent star than the first discovered exoplanet will then bear the letters c, d, e, etc.

    NASA/Ames – Wendy Stenzel

    Therefore, confirmation of the new exoplanet candidate in the Pi Mensae system would make the planet Pi Mensae c.

    Pi Mensae b, a superjovian, was discovered on 15 October 2001 using the radial-velocity method of detection via the Anglo-Australian Telescope operated by the Australian Astronomical Observatory at Siding Spring Observatory.

    In the search for exoplanets, two general methods of detection are used – direct observation of a transiting exoplanet that passes between its star and the observation point on or near Earth (the method employed by TESS) and the radial-velocity, or doppler spectroscopy, method of detection which measures the wobble or gravitational tug on a parent star caused by an orbiting planet that does not pass between the star and the observation point on or near Earth.

    Overall, roughly 30% of the total number of known exoplanets have been discovered via the radial-velocity method, with the other 70% being discovered via the transiting method of detection.

    Radial Velocity Method-Las Cumbres Observatory

    Radial velocity Image via SuperWasp http:// http://www.superwasp.org/exoplanets.htm

    Planet transit. NASA/Ames

    Upon Pi Mensae b’s discovery in 2001, the planet was found to be in a highly eccentric 5.89 Earth-year (2,151 day) orbit – coming as close at 1.21 AU and passing as far as 5.54 AU from its star.

    Artist’s depiction of a Super-Juiter orbiting its host star

    With a 1.21 AU periastron, Pi Mensae b passes through its parent star’s habitable zone before arcing out to apastron (which lies farther out than Jupiter’s orbit of our Sun).

    Given the extreme eccentricity and the fact that the planet passes through the habitable zone during each orbit, it would likely have disrupted the orbit of any potentially Earth-like planet in that zone due to its extreme mass of more than 10 times that of Jupiter.

    As for Pi Mensae itself, the star is a 3.4 billion year old (roughly 730 million years younger than the Sun) yellow dwarf that is 1.11 times the mass of the Sun, 1.15 times the Sun’s radius, and 1.5 times the Sun’s luminosity.

    Due to its proximity to Earth and its high luminosity, the star has an apparent magnitude of 5.67 and is visible to the naked eye in dark, clear skies.

    The star’s brightness – unsurprisingly – gives a potential instant “win” for the TESS team, whose stated pre-mission goal was to find near-Earth transiting exoplanets around exceptionally bright stars.

    Pi Mensae is currently the second brightest star to host a confirmed transiting exoplanet, Pi Mensae b.

    As an even greater testament to TESS’ power, just hours before publication of this article, the TESS team confirmed a second exoplanet candidate from the first observation campaign.

    The second exoplanet candidate is LHS 3844 b. It orbits its parent star – an M dwarf – every 11 hours and is located 49 light years from Earth.

    The exoplanet candidate is described by NASA and the TESS team as a “hot Earth.”

    Given the wealth of light data for scientists to pour through from the now-completed first two of 26 observation sectors, it is highly likely that hundreds if not thousands of exoplanets candidates will be identified in the coming months and years — with tens of thousands of candidate planets to follow in the remaining 24 sectors of sky to be searched.

    See the full article here .


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