Telescopio espacial Webb para proporcionar detalles de dos intrigantes «planetas súper-Tierra» en la Vía Láctea

Los astrónomos entrenarán un espectrómetro Webb de alta resolución en dos interesantes exoplanetas rocosos.

Imagina si la Tierra estuviera mucho más cerca del sol. Tan cerca que un año entero duraría solo unas pocas horas. Tan cerca que la gravedad ha encerrado un hemisferio en la abrasadora luz del día y el otro en la oscuridad eterna. Tan cerca que los océanos se evaporan, las rocas comienzan a derretirse y la lava llueve sobre las nubes.

Si bien no hay nada como esto en nuestro sistema solar, los planetas como este, rocosos, del tamaño de la Tierra, extremadamente calientes y cerca de sus estrellas, no son infrecuentes en nuestro 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] Tiene la sensibilidad y el rango de longitud de onda para detectar e identificar sus componentes”.

¿O está lloviendo lava por la noche en 55 Cancri E?

Sin embargo, otra posibilidad interesante es que el 55 Cancri e no tenga bloqueo de bisel. Alternativamente, podría ser como Mercurio, girando tres veces en dos órbitas (lo que se conoce como resonancia 3:2). Como resultado, el planeta tendrá un ciclo diurno y nocturno.

«Esto puede explicar por qué la parte más caliente del planeta está girando», explicó Alexis Brandecker, investigador de la Universidad de Estocolmo que dirige otro equipo que estudia el planeta. «Al igual que en la Tierra, la superficie tardará un tiempo en calentarse. El momento más caluroso del día será por la tarde, no al mediodía».

El espectro de emisión de potencial de calor del exoplaneta caliente LHS 3844 b de la supertierra, medido por el instrumento de infrarrojo medio de Webb. El espectro de emisión térmica muestra la cantidad de luz de diferentes longitudes de onda infrarrojas (colores) emitida por el planeta. Los investigadores utilizan modelos informáticos para predecir cómo se verá el espectro de emisión de calor de un planeta asumiendo ciertas condiciones, como si hay o no una atmósfera y de qué está hecha la superficie del planeta.
Esta simulación en particular asume que LHS 3844 b no tiene atmósfera y que el lado diurno está cubierto de rocas ígneas ígneas oscuras. (El basalto es la roca ígnea más común en nuestro sistema solar y forma islas volcánicas como Hawái y la mayor parte del suelo oceánico de la Tierra, así como grandes porciones de las superficies de la Luna y Marte).
A modo de comparación, la línea gris representa un espectro típico de rocas basálticas basado en mediciones de laboratorio. La línea rosa es el espectro del granito, la roca ígnea más común que se encuentra en los continentes de la Tierra. Estos dos tipos de rocas tienen espectros muy diferentes porque están hechos de diferentes minerales que absorben y emiten diferentes cantidades de diferentes longitudes de onda de luz.
Después de que Webb detecte el planeta, los investigadores compararán los espectros del modelo real de diferentes tipos de rocas como esta para ver de qué está hecha la superficie del planeta.
Fuente: NASA, ESA, CSA, Dani Player (STScI), Laura Kreidberg (MPI-A), Renyu Hu (NASA-JPL)

El equipo de Brandeker planea probar esta hipótesis usando NIRCam para medir el calor emitido desde el lado iluminado de 55 Cancri e a través de cuatro órbitas diferentes. Si un planeta tuviera un eco de 3:2, observarían cada hemisferio dos veces y deberían poder detectar cualquier diferencia entre los dos hemisferios.

En este escenario, la superficie se calentaría, se derretiría e incluso se evaporaría durante el día, formando una atmósfera extremadamente delgada que Webb podría detectar. Por la noche, el vapor se enfría y se condensa para formar gotas de lava que lloverán de regreso a la superficie, volviéndose sólidas nuevamente cuando caiga la noche.

Algo más fresco Super Earth LHS 3844 b

Mientras que 55 Cancri e proporcionará información sobre la extraña geología de un mundo cubierto de lava, LHS 3844 B Brinda una oportunidad única para analizar rocas duras en[{» 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.