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韋伯太空望遠鏡將提供銀河系中兩顆有趣的“超級地球行星”的詳細信息

韋伯太空望遠鏡將提供銀河系中兩顆有趣的“超級地球行星”的詳細信息

系外行星 55 Cancri E 及其恆星

根據目前對該行星的了解,插圖顯示了 55 Cancri E 行星的外觀。 巨蟹座 55 是一顆岩石行星,其直徑大約是地球的兩倍,距離它的類太陽恆星約 0.015 天文單位。 由於其狹窄的軌道,這顆行星非常熱,全天溫度達到 4,400 華氏度(約 2,400 攝氏度)。 使用網絡攝像頭近紅外 (NIRCam) 和中紅外 (MIRI) 儀器進行光譜觀測將有助於確定這顆行星是否有大氣層,如果有,那麼大氣層是由什麼組成的。 這些觀察還將有助於確定地球是否正在逐漸關閉。 圖片來源:NASA、ESA、CSA、Dani Player (STScI)

天文學家將在兩顆有趣的岩石系外行星上訓練高分辨率韋伯光譜儀。

想像一下,如果地球離太陽更近。 如此接近,以至於一整年只會持續幾個小時。 如此接近以至於重力將一個半球鎖定在灼熱的日光中,而將另一個半球鎖定在永恆的黑暗中。 如此接近,以至於海洋沸騰了,岩石開始融化,熔岩從雲層中傾瀉而下。

雖然在我們的太陽系中沒有這樣的行星,但像這樣的行星——岩石般的、地球大小的、極熱的、靠近恆星的行星——在我們的太陽系中並不少見。[{” attribute=””>Milky Way galaxy.

What are the surfaces and atmospheres of these planets really like? Exoplanet LHS 3844 b and Its Star

Illustration showing what exoplanet LHS 3844 b could look like, based on current understanding of the planet.
LHS 3844 b is a rocky planet with a diameter 1.3 times that of Earth orbiting 0.006 astronomical units from its cool red dwarf star. The planet is hot, with dayside temperatures calculated to be greater than 1,000 degrees Fahrenheit (greater than about 525 degrees Celsius). Observations of the planet’s thermal emission spectrum using Webb’s Mid-Infrared Instrument (MIRI) will provide more evidence to help determine what the surface is made of. Credit: NASA, ESA, CSA, Dani Player (STScI)

Geology from 50 Light-Years: Webb Gets Ready to Study Rocky Worlds

With its mirror segments beautifully aligned and its scientific instruments undergoing calibration, NASA’s James Webb Space Telescope (Webb) is just weeks away from full operation. Soon after the first observations are revealed this summer, Webb’s in-depth science will begin.

Included in the investigations planned for the first year are studies of two hot exoplanets classified as “super-Earths” for their size and rocky composition: the lava-covered 55 Cancri e and the airless LHS 3844 b. Scientists will train Webb’s high-precision spectrographs on these planets with a view to understanding the geologic diversity of planets across the galaxy, as well as the evolution of rocky planets like Earth.

Super-Hot Super-Earth 55 Cancri e

55 Cancri e orbits less than 1.5 million miles from its Sun-like star (one twenty-fifth of the distance between Mercury and the Sun), completing one circuit in less than 18 hours. With surface temperatures far above the melting point of typical rock-forming minerals, the day side of the planet is thought to be covered in oceans of lava.

Comparison of Exoplanets 55 Cancri e and LHS 3844 b to Earth and Neptune

Illustration comparing rocky exoplanets LHS 3844 b and 55 Cancri e to Earth and Neptune. Both 55 Cancri e and LHS 3844 b are between Earth and Neptune in terms of size and mass, but they are more similar to Earth in terms of composition.
The planets are arranged from left to right in order of increasing radius.
Image of Earth from the Deep Space Climate Observatory: Earth is a warm, rocky planet with a solid surface, water oceans, and a dynamic atmosphere.
Illustration of LHS 3844 b: LHS 3844 b is a hot, rocky exoplanet with a solid, rocky surface. The planet is too hot for oceans to exist and does not appear to have any significant atmosphere.
Illustration of 55 Cancri e: 55 Cancri e is a rocky exoplanet whose dayside temperature is high enough for the surface to be molten. The planet may or may not have an atmosphere.
Image of Neptune from Voyager 2: Neptune is a cold ice giant with a thick, dense atmosphere.
The illustration shows the planets to scale in terms of radius, but not location in space or distance from their stars. While Earth and Neptune orbit the Sun, LHS 3844 b orbits a small, cool red dwarf star about 49 light-years from Earth, and 55 Cancri e orbits a Sun-like star roughly 41 light-years away. Both are extremely close to their stars, completing one orbit in less than a single Earth day.
Credit: NASA, ESA, CSA, Dani Player (STScI)

Planets that orbit this close to their star are assumed to be tidally locked, with one side facing the star at all times. As a result, the hottest spot on the planet should be the one that faces the star most directly, and the amount of heat coming from the day side should not change much over time.

But this doesn’t seem to be the case. Observations of 55 Cancri e from NASA’s Spitzer Space Telescope suggest that the hottest region is offset from the part that faces the star most directly, while the total amount of heat detected from the day side does vary.

Does 55 Cancri e Have a Thick Atmosphere?

One explanation for these observations is that the planet has a dynamic atmosphere that moves heat around. “55 Cancri e could have a thick atmosphere dominated by oxygen or nitrogen,” explained Renyu Hu of NASA’s Jet Propulsion Laboratory in Southern California, who leads a team that will use Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) to capture the thermal emission spectrum of the day side of the planet. “If it has an atmosphere, [Webb] 它具有檢測和識別其成分的靈敏度和波長范圍。”

還是在 55 Cancri E 的晚上下雨熔岩?

不過,還有一個有趣的可能性,就是 55 Cancri e 並沒有逐步解鎖。 或者,它可能像水星一樣,每兩個軌道自轉三圈(即所謂的 3:2 共振)。 因此,地球將有一個晝夜循環。

領導另一個研究地球的團隊的斯德哥爾摩大學研究員亞歷克西斯·布蘭德克解釋說:“這可以解釋為什麼地球上最熱的部分會變成這樣。就像在地球上一樣,地表升溫需要時間。最熱的部分一天中的時間將在下午。不是中午。

系外行星 LHS 3844 b 的熱發射光譜

由韋伯中紅外儀器測量的超級地球熱系外行星 LHS 3844 b 的熱勢發射光譜。 熱發射光譜顯示了行星發射的各种红外波長(顏色)的光量。 研究人員使用計算機模型來預測假設某些條件下行星的熱發射光譜會是什麼樣子,例如是否存在大氣層以及行星表面是由什麼構成的。
這個特殊的模擬假設 LHS 3844 b 沒有大氣層,並且白天覆蓋著深色火成岩玄武岩(玄武岩是我們太陽系中最常見的火成岩,它構成了夏威夷等火山島和大部分海底在地球上,以及月球和火星的大部分錶面。)
為了比較,灰線代表基於實驗室測量的典型玄武岩光譜。粉紅色線是花崗岩的光譜,花崗岩是地球大陸上發現的最常見的火成岩。因為這兩種岩石的光譜非常不同,因為它們是它們由不同的礦物質製成,它們吸收和發射不同長度、不同波長的光。
在韋伯發現這顆行星後,研究人員將比較像這樣的不同類型岩石的實際模型光譜,以了解這顆行星的表面是由什麼構成的。
資料來源:NASA、ESA、CSA、Dani Player (STScI)、Laura Kreidberg (MPI-A)、Renyu Hu (NASA-JPL)

Brandeker 的團隊計劃使用 NIRCam 來測試這一假設,以測量從 55 Cancri e 的照明側通過四個不同軌道發出的熱量。 如果一顆行星有 3:2 的回波,他們將觀察每個半球兩次,並且應該能夠檢測到兩個半球之間的任何差異。

在這種情況下,表面會在白天升溫、融化甚至蒸發,形成韋伯可以探測到的極薄大氣層。 到了晚上,蒸汽會冷卻並凝結成熔岩滴,這些熔岩會像雨點一樣落回地表,隨著夜幕降臨,再次變成固體。

稍涼的超級地球 LHS 3844b

雖然 55 Cancri e 將提供對熔岩覆蓋世界的特殊地質的洞察,但 LHS 3844 b 提供了一個獨特的機會來分析[{” attribute=””>exoplanet surface.

Like 55 Cancri e, LHS 3844 b orbits extremely close to its star, completing one revolution in 11 hours. However, because its star is relatively small and cool, the planet is not hot enough for the surface to be molten. Additionally, Spitzer observations indicate that the planet is very unlikely to have a substantial atmosphere.

What Is the Surface of LHS 3844 b Made of?

While we won’t be able to image the surface of LHS 3844 b directly with Webb, the lack of an obscuring atmosphere makes it possible to study the surface with spectroscopy.

“It turns out that different types of rock have different spectra,” explained Laura Kreidberg at the Max Planck Institute for Astronomy. “You can see with your eyes that granite is lighter in color than basalt. There are similar differences in the infrared light that rocks give off.”

Kreidberg’s team will use MIRI to capture the thermal emission spectrum of the day side of LHS 3844 b, and then compare it to spectra of known rocks, like basalt and granite, to determine its composition. If the planet is volcanically active, the spectrum could also reveal the presence of trace amounts of volcanic gases.

The importance of these observations goes far beyond just two of the more than 5,000 confirmed exoplanets in the galaxy. “They will give us fantastic new perspectives on Earth-like planets in general, helping us learn what the early Earth might have been like when it was hot like these planets are today,” said Kreidberg.

These observations of 55 Cancri e and LHS 3844 b will be conducted as part of Webb’s Cycle 1 General Observers program. General Observers programs were competitively selected using a dual-anonymous review system, the same system used to allocate time on Hubble.

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 the Canadian Space Agency.

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