Telescópio Espacial Webb para fornecer detalhes de dois intrigantes “planetas super-Terras” na Via Láctea

Os astrônomos treinarão um espectrômetro Webb de alta resolução em dois exoplanetas rochosos interessantes.

Imagine se a Terra estivesse muito mais perto do sol. Tão perto que um ano inteiro duraria apenas algumas horas. Tão perto que a gravidade trancou um hemisfério na luz do dia escaldante e o outro na escuridão eterna. Tão perto que os oceanos fervem, as rochas começam a derreter e lava está chovendo nuvens.

Embora não haja nada parecido em nosso sistema solar, planetas como esse – rochosos, do tamanho da Terra, extremamente quentes e próximos de suas estrelas – não são incomuns em nosso sistema solar.[{” attribute=””>Milky Way galaxy.

What are the surfaces and atmospheres of these planets really like? NASA’s James Webb Space Telescope is about to provide some answers.

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.

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] Ele tem a sensibilidade e a faixa de comprimento de onda para detectar e identificar seus componentes.”

Ou está chovendo lava à noite em 55 Cancri E?

No entanto, outra possibilidade interessante é que o 55 Cancri e não seja travado no painel. Alternativamente, pode ser como Mercúrio, girando três vezes por duas órbitas (o que é conhecido como ressonância 3:2). Como resultado, o planeta terá um ciclo de dia e noite.

“Isso pode explicar por que a parte mais quente do planeta está girando”, explicou Alexis Brandecker, pesquisador da Universidade de Estocolmo que lidera outra equipe que estuda o planeta. “Assim como na Terra, levará tempo para a superfície aquecer. A hora mais quente do dia será à tarde, não ao meio-dia.”

O espectro de emissão do potencial de calor do exoplaneta super-Terra quente LHS 3844 b, medido pelo instrumento de infravermelho médio de Webb. O espectro de emissão térmica mostra a quantidade de luz de diferentes comprimentos de onda infravermelhos (cores) emitidas pelo planeta. Os pesquisadores usam modelos de computador para prever como será o espectro de emissão de calor de um planeta assumindo certas condições, como se existe ou não uma atmosfera e do que é feita a superfície do planeta.
Esta simulação particular assume que LHS 3844 b não tem atmosfera e que o lado diurno está coberto por rochas ígneas ígneas escuras. (O basalto é a rocha ígnea mais comum em nosso sistema solar, formando ilhas vulcânicas como o Havaí e a maior parte do fundo do oceano da Terra, bem como grandes porções das superfícies da Lua e de Marte.)
Para comparação, a linha cinza representa um espectro típico de rochas basálticas com base em medições de laboratório. A linha rosa é o espectro do granito, que é a rocha ígnea mais comum encontrada nos continentes da Terra. Esses dois tipos de rochas têm espectros muito diferentes porque são feitos de diferentes minerais que absorvem e emitem diferentes quantidades de diferentes comprimentos de onda de luz.
Depois que Webb observar o planeta, os pesquisadores compararão os espectros reais do modelo de diferentes tipos de rochas como essa para ver do que é feita a superfície do planeta.
Fonte: NASA, ESA, CSA, Dani Player (STScI), Laura Kreidberg (MPI-A), Renyu Hu (NASA-JPL)

A equipe de Brandeker planeja testar essa hipótese usando o NIRCam para medir o calor emitido do lado iluminado de 55 Cancri e através de quatro órbitas diferentes. Se um planeta tivesse um eco de 3:2, eles observariam cada hemisfério duas vezes e seriam capazes de detectar qualquer diferença entre os dois hemisférios.

Nesse cenário, a superfície aqueceria, derreteria e até evaporaria durante o dia, formando uma atmosfera extremamente fina que Webb poderia detectar. À noite, o vapor esfria e se condensa para formar gotas de lava que choverão de volta à superfície, tornando-se sólidas novamente à medida que a noite cai.

Mais frio que LHS 3844 B. super-Terra

Enquanto 55 Cancri e fornecerá informações sobre a estranha geologia de um mundo coberto de lava, LHS 3844 B Oferece uma oportunidade única para analisar rochas duras em[{” 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.