太陽系外惑星の大気(ジェームズ・ウエッブ宇宙望遠鏡3) (No. 739)
date 2022 09 21 --------------------------- 最強の天体望遠鏡の地位を誇るものといえば、 それはジェームズ・ウェッブ宇宙望遠鏡でしょう。 これまでに少しづつその観測装置と結果を紹介してきましたが、 今回は３つ目、近赤外スリットレス分光装置(NISS, Near-Infrared Slitless Spectrograph)です。 と言われても何のことやら、わからないと思いますので、 まずは、このNISSという観測装置で調べた結果を紹介します。 それは「ほうおう座」にあるWASP-96という星の周りを回っている惑星の観測です。 WASP-96は太陽と似た感じの星ですが、 その周りを回る惑星の方はちょっと変わっていて、 木星より大きいのに木星より軽くて、つまり、ふわふわした惑星です。 公転半径は地球・太陽間の20分の1ほどです。 ということは、太陽系で言うと水星軌道よりずっと近い位置で回っています。 公転周期はたった3日ほどです。 図1のように、 惑星が星を横切るように運動するため、 ミニ日食のように星の明るさが暗くなるのでこの惑星の存在がわかります。 ここからが重要です。 惑星が光を遮る時、光の波長によって遮る効果が変わるのです。 ふわふわした惑星の中に水があると水がよく吸収する波長では惑星による遮る効果が高くなります。 どの波長で星の光が遮られるかを見ていると、 惑星の大気の中にどんな分子があるかがわかります。 冒頭に紹介した近赤外スリットレス分光装置(NISS)を通して惑星が横切る様子を見ていればこのことを観測できます。 例えば、水のよく吸収する波長(複数ある)で星の光が大きく遮られれば、 「おっ、この惑星大気には水があるな」と気がつくわけです。 図2は実際に水のあることを示すジェームズ・ウェッブ宇宙望遠鏡のNISSのデータです。
図1 惑星が起こす「食」よる惑星大気の分析の原理 http://www.shibatashinpei.jp/lib/yamashin/739-fig1.jpg
図2 WASP-96の惑星に水があることを示すデータ(提供：NASA, STScI). http://www.shibatashinpei.jp/lib/yamashin/739-fig2.jpg
本文終わり
パワポ http://www.shibatashinpei.jp/lib/yamashin/739-fig.pptx What are the capabilities of NIRISS? The Near-Infrared Imager and Slitless Spectrograph provides three unique scientific capabilities over a field of view of 2.2 by 2.2 arcmin2. It conducts R ~ 150 slitless spectroscopy at 0.8 to 2.25 microns optimized for Lyman alpha emission-line galaxy surveys. It conducts defocused R ~ 700 slitless spectroscopy at 0.7 to 2.5 microns optimized for exoplanet transit spectroscopy of bright host stars. It uses a 7-aperture non-redundant mask to provide sparse-aperture interferometric imaging at 3.8, 4.3 and 4.8 microns, optimized for studying exoplanets. The NIRISS dectector is a single 2048 by 2048 pixel detector array with 65 milliarcsec pixels. NIRISS R ~ 150 slitless spectroscopy will reach 5.5 x 10-18 ergs s-1cm-2 line sensitivity at 1.4 microns, 10 sigma in 10,000 seconds.
ジェームズ・ウエッブ望遠鏡シリーズ
系外惑星, No.739
遠方銀河,NIRSpec No.732
深宇宙,NIRC No.731
打ち上げ,Orbit No.708
webb ダイジェストガイド.pdf
NISS説明.pptx
webb telescope 著作権関係
note: NASA’s James Webb Space Telescope has captured the distinct signature of water, along with evidence for clouds and haze, in the atmosphere surrounding a hot, puffy gas giant planet orbiting a distant Sun-like star. The observation, which reveals the presence of specific gas molecules based on tiny decreases in the brightness of precise colors of light, is the most detailed of its kind to date, demonstrating Webb’s unprecedented ability to analyze atmospheres hundreds of light-years away. While the Hubble Space Telescope has analyzed numerous exoplanet atmospheres over the past two decades, capturing the first clear detection of water in 2013, Webb’s immediate and more detailed observation marks a giant leap forward in the quest to characterize potentially habitable planets beyond Earth. WASP-96 b is one of more than 5,000 confirmed exoplanets in the Milky Way. Located roughly 1,150 light-years away in the southern-sky constellation Phoenix, it represents a type of gas giant that has no direct analog in our solar system. With a mass less than half that of Jupiter and a diameter 1.2 times greater, WASP-96 b is much puffier than any planet orbiting our Sun. And with a temperature greater than 1000°F, it is significantly hotter. WASP-96 b orbits extremely close to its Sun-like star, just one-ninth of the distance between Mercury and the Sun, completing one circuit every 3½ Earth-days. The combination of large size, short orbital period, puffy atmosphere, and lack of contaminating light from objects nearby in the sky makes WASP-96 b an ideal target for atmospheric observations. On June 21, Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) measured light from the WASP-96 system for 6.4 hours as the planet moved across the star. The result is a light curve showing the overall dimming of starlight during the transit, and a transmission spectrum revealing the brightness change of individual wavelengths of infrared light between 0.6 and 2.8 microns. While the light curve confirms properties of the planet that had already been determined from other observations – the existence, size, and orbit of the planet – the transmission spectrum reveals previously hidden details of the atmosphere: the unambiguous signature of water, indications of haze, and evidence of clouds that were thought not to exist based on prior observations. A transmission spectrum is made by comparing starlight filtered through a planet’s atmosphere as it moves across the star to the unfiltered starlight detected when the planet is beside the star. Researchers are able to detect and measure the abundances of key gases in a planet’s atmosphere based on the absorption pattern – the locations and heights of peaks on the graph. In the same way that people have distinctive fingerprints and DNA sequences, atoms and molecules have characteristic patterns of wavelengths that they absorb. The spectrum of WASP-96 b captured by NIRISS is not only the most detailed near-infrared transmission spectrum of an exoplanet atmosphere captured to date, but it also covers a remarkably wide range of wavelengths, including visible red light and a portion of the spectrum that has not previously been accessible from other telescopes (wavelengths longer than 1.6 microns). This part of the spectrum is particularly sensitive to water as well as other key molecules like oxygen, methane, and carbon dioxide, which are not immediately obvious in the WASP-96 b spectrum but which should be detectable in other exoplanets planned for observation by Webb. Researchers will be able to use the spectrum to measure the amount of water vapor in the atmosphere, constrain the abundance of various elements like carbon and oxygen, and estimate the temperature of the atmosphere with depth. They can then use this information to make inferences about the overall make-up of the planet, as well as how, when, and where it formed. The blue line on the graph is a best-fit model that takes into account the data, the known properties of WASP-96 b and its star (e.g., size, mass, temperature), and assumed characteristics of the atmosphere. The exceptional detail and clarity of these measurements is possible because of Webb’s state-of-the-art design. Its 270-square-foot gold-coated mirror collects infrared light efficiently. Its precision spectrographs spread light out into rainbows of thousands of infrared colors. And its sensitive infrared detectors measure extremely subtle differences in brightness. NIRISS is able to detect color differences of only about one thousandth of a micron (the difference between green and yellow is about 50 thousandths of a micron), and differences in the brightness between those colors of a few hundred parts per million. In addition, Webb’s extreme stability and its orbital location around Lagrange Point 2 roughly a million miles away from the contaminating effects of Earth’s atmosphere makes for an uninterrupted view and clean data that can be analyzed relatively quickly. The extraordinarily detailed spectrum – made by simultaneously analyzing 280 individual spectra captured over the observation – provides just a hint of what Webb has in store for exoplanet research. Over the coming year, researchers will use spectroscopy to analyze the surfaces and atmospheres of several dozen exoplanets, from small rocky planets to gas- and ice-rich giants. Nearly one-quarter of Webb’s Cycle 1 observation time is allocated to studying exoplanets and the materials that form them. This NIRISS observation demonstrates that Webb has the power to characterize the atmospheres of exoplanets—including those of potentially habitable planets—in exquisite detail. Image credit: NASA, ESA, CSA, and STScI The James Webb Space Telescope is the world's premier space science observatory. 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 CSA (Canadian Space Agency). NASA Headquarters oversees the mission for the agency’s Science Mission Directorate. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency’s Johnson Space Center in Houston; Jet Propulsion Laboratory (JPL) in Southern California; Marshall Space Flight Center in Huntsville, Alabama; Ames Research Center in California’s Silicon Valley; and others. NIRISS was contributed by the Canadian Space Agency. The instrument was designed and built by Honeywell in collaboration with the Université de Montréal and the National Research Council Canada. Download full-resolution, uncompressed versions and supporting visuals of this and other "Webb First Images" from the Space Telescope Science Institute: https://webbtelescope.org/contents/news-releases/2022/news-2022-032 Last Updated: Jul 14, 2022 Editor: Rob Garner Tags: Exoplanets, Goddard Space Flight Center, James Webb Space Telescope, Universe https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-reveals-steamy-atmosphere-of-distant-planet-in-detail ---------- Filtered Starlight Transiting planets like WASP-39 b, whose orbits we observe edge-on rather than from above, can provide researchers with ideal opportunities to probe planetary atmospheres. During a transit, some of the starlight is eclipsed by the planet completely (causing the overall dimming) and some is transmitted through the planet’s atmosphere. Because different gases absorb different combinations of colors, researchers can analyze small differences in brightness of the transmitted light across a spectrum of wavelengths to determine exactly what an atmosphere is made of. With its combination of inflated atmosphere and frequent transits, WASP-39 b is an ideal target for transmission spectroscopy. First Clear Detection of Carbon Dioxide The research team used Webb’s Near-Infrared Spectrograph (NIRSpec) for its observations of WASP-39b. In the resulting spectrum of the exoplanet’s atmosphere, a small hill between 4.1 and 4.6 microns presents the first clear, detailed evidence for carbon dioxide ever detected in a planet outside the solar system. "As soon as the data appeared on my screen, the whopping carbon dioxide feature grabbed me,” said Zafar Rustamkulov, a graduate student at Johns Hopkins University and member of the JWST Transiting Exoplanet Community Early Release Science team, which undertook this investigation. “It was a special moment, crossing an important threshold in exoplanet sciences.” No observatory has ever measured such subtle differences in brightness of so many individual colors across the 3 to 5.5-micron range in an exoplanet transmission spectrum before. Access to this part of the spectrum is crucial for measuring abundances of gases like water and methane, as well as carbon dioxide, which are thought to exist in many different types of exoplanets. “Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets,” said Natalie Batalha of the University of California at Santa Cruz, who leads the team. Understanding the composition of a planet’s atmosphere is important because it tells us something about the origin of the planet and how it evolved. “Carbon dioxide molecules are sensitive tracers of the story of planet formation,” said Mike Line of Arizona State University, another member of this research team. “By measuring this carbon dioxide feature, we can determine how much solid versus how much gaseous material was used to form this gas giant planet. In the coming decade, JWST will make this measurement for a variety of planets, providing insight into the details of how planets form and the uniqueness of our own solar system.” 図の説明 A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by Webb’s Near-Infrared Spectrograph (NIRSpec) July 10, 2022, reveals the first clear evidence for carbon dioxide in a planet outside the solar system. This is also the first detailed exoplanet transmission spectrum ever captured that covers wavelengths between 3 and 5.5 microns. Credits: Illustration: NASA, ESA, CSA, and L. Hustak (STScI); Science: The JWST Transiting Exoplanet Community Early Release Science Team Download the full-resolution, uncompressed version and supporting visuals from the Space Telescope Science Institute Media Contacts: Laura Betz Goddard Space Flight Center, Greenbelt, Md. 301-286-9030 laura.e.betz@nasa.gov Christine Pulliam Space Telescope Science Institute, Baltimore, Md. 410-338-4366 cpulliam@stsci.edu Last Updated: Aug 27, 2022 Editor: Jamie Adkins