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Steve B. Howell DOING THE GROUND WORK Physical Sciences︱ Dr Howell’s research focuses in - quite literally - on candidates which may one in a system. This work involves ground-based observational research, using a method called high-resolution speckle imaging. Twinkle, twinkle The need for this type of follow-up How astronomers investigate alien research was identified even before was launched. Howell has spent the last decade studying what he refers The NASA Kepler Space o you believe in aliens? More during its mission than all other to as ‘-like’ events. That is, since revolutionised our than one in two people in the discovery methods combined. some of the exoplanet discoveries by understanding of the . UK, Germany and the US believe transit observations may be false, the D Standing below the Gemini telescope 8m there is intelligent life out there in the Of particular interest to Kepler were remain candidates until By continuously observing over mirror, Howell examines his high-resolution half a million during its four- universe, meaning that - whether your discoveries of -like planets. These imaging instrument mounted to the telescope. scrutinised in more detail. year mission, Kepler discovered belief is rooted in crop circles, statistics ‘rocky’ planets have a similar size to thousands of exoplanets. Many or gut feeling - ‘you are not alone’. Earth, and are within the ‘habitable Exoplanet transit searches from space hundreds of these are Earth-like zone’, usually defined as having a The K2 programme, with Dr Steve time implying that a is regularly such as Kepler or TESS, in size and composition, and tens 100 years ago the hunt for alien life was temperature in which liquid could Howell as lead scientist, gave new life orbiting that star. The intrinsic brightness which gather information for many of them reside in the habitable limited to speculations about and reside on the planet’s surface. to Kepler until it retired in 2018 when of the star is used as an indication of the stars at once but over a broad area ‘Goldilocks’ zone. Kepler and the . Nowadays we can look further the telescope finally ran out of fuel. star’s size; the amount the brightness of the sky, have relatively low spatial similar space-based telescopes afield, to planets which orbit stars outside TWINKLE TWINKLE - K2 discovered many new exoplanets dips is used to determine the relative resolution. Each pixel of their cameras like TESS discover planets purely our own system: exoplanets. SPOTTING EXOPLANETS and extended the search for four size of the planet. may contain multiple stars, making it by infererence, never actually Directly viewing exoplanets is not quite additional years. The data collected by hard to identify which star is responsible ‘seeing’ these planets. Instead Unquestionably, the game-changer in so easy. The Kepler these missions is expected to continue However, there are several reasons why for the observed transit-like regular dip they watch for tell-tale periodic the field of exoplanets was the Kepler used photometric data to infer the revealing new exoplanets for several the data might not give the full story. in brightness. dips in brightness. When a star space telescope. Johnannes Kepler existence of an exoplanet. This method more years. Especially problematic is the existence of twinkles, suggesting an alien (1571-1630) was a mathematician, is known as the transit method. It binary star systems. This two star system To solve this problem, and to validate planet has been detected, Dr astrologer, and astronomer. He used involves observing a star (or groups of affects the brightness readings in the and characterise the exoplanets and Steve B. Howell at NASA’s Ames THE NEED FOR Research Centre has the job of observations of the planets in our solar stars) over time and monitoring their EXOPLANET FOLLOW-UP photometric data, and leads to incorrect their host stars, high spatial resolution determining what it is. Using system to develop his famous laws of brightness very precisely. If an orbiting A new wave of exoplanet space estimates of planetary size, density, and images are required. Speckle imaging some of the largest ground- planetary motion. Kepler also worked planet passes directly in front of - that telescope missions is well underway, therefore possibilities of habitability. is a technique used by ground-based based telescopes on Earth on optics and invented an improved is, it transits - a star, the light level will including NASA’s telescopes to and a technique called speckle version of ’s astronomical dip slightly and then return to normal. Transiting Exoplanet remove the interferometry, the researchers telescope – a refracting type or a This will happen repeatedly, once for Survey Satellite Unquestionably, the game-changer in distortions caused by are identifying the planets Keplerian telescope. every orbit of the exoplanet. This is by (TESS). TESS disturbances in the which might be best-suited to no means the only way exoplanets can searches for transit the field of exoplanets was the Kepler Earth’s atmosphere. habouring life. Launched in 2009, armed with a be detected. Another method, ‘direct signals across the space telescope. By re-constructing photometer as its only scientific imaging’ looks at the thermal emissions whole sky, and is an image from instrument, the Kepler space telescope of young, large planets. The radial expected to lead to several thousand many short exposures with specialised began surveying one field of view in the velocity method can identify exoplanet- more exoplanet discoveries. PLATO will software, very high-resolution images sky. Kepler discovered more exoplanets hosting stars from the ‘wobble’ as their also look for transits deeper in space can be produced with the ability to see planets orbit them. Finally, gravitational than Kepler could. In addition, the deep into the alien . microlensing observes the lensing effect James Webb Space Telescope and the of when a solar system passes Nancy Grace Roman Space Telescope ULTRA-HIGH RESOLUTION directly behind another (unrelated) star. will join the European Space Agency’s As a result of Howell’s research into CHEOPS, collecting information to ultra-high spatial resolution images, None of these other methods, however, help characterise existing exoplanets in three new instruments have been built. have discovered as many exoplanets the search for life. These are installed at some of the as transit . Over its years largest ground-based telescopes in the of service, the Kepler space telescope For each transit signal and new world. Essentially, Howell and his team observed a staggering 530,506 stars exoplanet discovered, it is important to produce the highest-resolution images every 30 minutes for four years and perform detailed follow-up observations yet achieved. detected over 4,000 exoplanets. After of the host stars. This crucial work has two of its three reaction wheels failed in become Dr Steve Howell’s domain. So far, the team has observed over 2014, an ingenious proposal to repurpose 1,000 exoplanet hosting stars from Kepler as ‘K2’ led to an adaptation of Every star which shows a transit Gemini North Telescope, one of a pair Kepler and K2, and more than 500 of giant observatories (one in each spacecraft balance by using sunlight with signature yields an exoplanet candidate, hemisphere), providing full sky coverage. from TESS. This has resulted in 65 precise positioning using thruster fuel. with the measured starlight viewed over published papers in the last year and a vector punch/Shutterstock.com www.researchoutreach.org www.researchoutreach.org apart, and fall into a narrow range of possible inter-stellar distances.

Given that planets and their stars tend Behind the Research to be formed at the same time, Howell’s discovery changes our understanding of planetary formation. His work suggests Dr Steve B. Howell that many planets were formed under the same conditions which lead to E: steve.b.howell@.gov W: https://www.nasa.gov/mission_pages/kepler/overview/index.html binary , a very different mechanism than our own single-star solar system.

This isn’t the only big discovery made Research Objectives References Mauna Kea (Hawai’i) is the site of many major telescopes, including Gemini-North. Its viewing conditions are the finest of any Earth-based observatory. through speckle imaging. Howell and Steve Howell currently works to understand the Howell SB, Scott NJ, Matson RA, Everett ME, Furlan E, his team also use their research to characteristics and true of exoplanets – that is Gnilka CL, Ciardi DR, Lester KV. (2021). The NASA High- answer important questions about the planets that orbit alien . Over 4,000 exoplanets Resolution Speckle Interferometric Imaging Program: half alone. One of the important Exoplanet-hosting binaries are more exoplanets themselves. Which star in are currently known, and Dr Howell’s research aims Validation and Characterization of Exoplanets and Their learning points from this work is the likely to orbit further from each other, the binary is the one hosting the planet? to provide detailed knowledge of their formation, Stellar Hosts. Front. . Space Sci. 8:635864. value of community understanding of typically around 100 astronomical units If two stars appear very close in space, dynamics and evolution. Making observations with new https://doi.org/10.3389/fspas.2021.635864 the host star or stars in an exoplanet- technology instrumentation, Howell performs research hosting system. on exoplanets, and in particular detailed study of the Howell SB, Matson RA, Ciardi DR, Everett ME, Livingston stars that they orbit. A new wave of exoplanet telescope JH, Scott NJ, Horch EP, Winn JN. (2021). Speckle TWO STARS ARE BETTER THAN ONE missions is well underway, including Observations of TESS Exoplanet Host Stars: Understanding (FOR PLANET FORMATION) Detail the Binary Exoplanet Host Star Distribution. Recent research led by Howell on TESS Nasa’s Transiting Exoplanet Survey [Accepted, Astronomical Journal]. exoplanet stars finds that almost half of Bio all exoplanet-hosting stars are actually Satellite (TESS) which searches for transit Dr Steve B. Howell is a research scientist at NASA and was Howell SB, Sobeck C, Haas M, Still M, Barclay T, Mullally F, part of a binary or multiple star system. the project scientist for the Kepler and K2 missions. Steve Troeltzsch J, Aigrain S, Bryson ST, Caldwell D. (2014). The K2 This has important implications for the signals across the whole sky. has worked in many aspects of astronomy: pioneering the Mission: Characterization and Early Results. Publications of way we interpret the transit signals. For use of charge-coupled devices (CCDs), building innovative the Astronomical Society of the Pacific.126 398. example, ‘contamination’ light from are they really close, or do they just instruments, and involvement in many STEM activities. doi: 10.1086/676406. the second star can reduce the dip in line up well with the view from Earth? Howell has written over 800 scientific papers, nine books brightness when the exoplanet transits Which planets are the best candidates on astronomy, and two fiction books. He enjoys its host star. for further investigation by telescopes scientific challenges, the great outdoors, vegetarian Personal Response

Steve B. Howell that can perform spectroscopy to gourmet cooking, and playing blues music. The exoplanet will then be predicted determine the composition of the Can you briefly detail the part speckle imaging has to play amongst the ‘new generation’ of space telescopes to be smaller than it really is, meaning exoplanet’s atmosphere and search for Funding like the James Webb and Nancy Grace Roman space the planet is incorrectly characterised. signatures of life? NASA Exoplanet Program Office and NASA Headquarters telescopes? What may look Earth-like from TESS data may actually more likely be an High-resolution speckle imaging Collaborators One of the most fundamental questions of humanity -like ice giant! gives us new ways of understanding • Crystal L. Gnilka is, Are we alone? Since humans looked up at the lights in the night sky the question of where we came from and who the increasing number of candidate • David R. Ciardi else is out there has been a fundamental driving force for Recent research from Howell’s team Typical ground-based image of a star field, exoplanets and their environments, • Kathryn V. Lester showing a bright red star near the centre. A high- exploration and discovery. also details an interesting discrepancy resolution image of this star (inset) reveals that it including identifying those which might • Elise Furlan between binary star pairs with is really a close binary pair. be best-suited to harbour life. • Rachel A. Matson Speckle imaging and the research it enables is one and without exoplanets. This was • Mark E. Everett aspect of the larger picture that someday will lead to discovered in a survey of 186 exoplanet • Nicholas J. Scott the discovery of life on an alien world. My current work NASA host stars from the TESS mission. provides detailed information on many exoplanets and the stars which they orbit in order to help all of us in astronomy produce a list of the best exoplanets to STELLAR WORK observe in the future. These exoplanets will provide the The most up-to-date estimates suggest greatest for science to discover signatures pairs of stars in binary systems are, on that life exists elsewhere in the Galaxy. average, 40 astronomical units from each other (the distance between our and the planet Pluto). These estimates are based on observations of binary stars without regard to exoplanets. Howell’s survey of TESS data - looking specifically Artist’s concept of five relatively small exoplanets discovered by Kepler, all of which orbit in the habitable zone of their host star. at 45 binary systems with exoplanets, Kepler-186f is the most Earth-like planet Kepler discovered (NASA). provides a different result.

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