James Webb targets intriguing exoplanets to train spectrographs

It has already set an unprecedented record for the Large Magellanic Cloud and even managed to observe an asteroid, proving that it is also capable of capturing moving objects. And look, the James Webb Space Telescope (JWST) hasn’t started working yet, being in the final stages of calibrating its instruments.

Launched on December 25, 2021, the James Webb Telescope hasn’t even begun to practice science, in fact, and has already recorded amazing images of the universe. Photo: Muratart – Shutterstock

It is estimated that the Next Generation Observatory will begin to provide science, in fact, from the second half of the year. Among the planned investigations are studies of two hot exoplanets that have been classified as “super-Earths” due to their size and rock composition.

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One of them is 55 Cancri-e, also known as Janssen, which orbits around the star 55 Cancri, similar to our Sun. The other, “LHS 3844 b,” is an exoplanet orbiting the red dwarf LHS 3844.

The researchers will train the telescope’s high-resolution spectrometers on these targets to understand the geological diversity of planets across the galaxy and the evolution of rocky planets like Earth.

Illustration comparing the rocky exoplanets LHS 3844 b and 55 Cancri e with Earth and Neptune. Credit: NASA, ESA, CSA, Danny Player (STScI)

Orbiting less than 2.4 million kilometers from its host star (one-twenty-five the distance between Mercury and the Sun), 55 Cancri-e completes a circle in less than 18 hours. With surface temperatures well above the typical melting point of rock-forming minerals, today’s side of the planet is supposed to be covered in oceans of lava.

Planets that orbit near their star are thought to have one side permanently facing the host. As a result, the hottest points should be those directly facing the star, and the amount of heat coming from the day should not change much over time.

Exoplanet 55 Cancri-e Has Unexpected Behavior

But that does not seem to be the case. Observations from NASA’s retired Spitzer Space Telescope indicate that the hottest region is transferred from the portion directly facing the star, while the total amount of detected heat varies.

One explanation for these observations is that the planet has a dynamic atmosphere that moves heat around it. “55 Cancree E may have a dense atmosphere dominated by oxygen or nitrogen,” explained Regno Ho of NASA’s Jet Propulsion Laboratory (JPL), who is leading a team that will use the near-infrared camera (NIRCam) and infrared instrument. ) from Webb to capture the spectrum of heat emissions by planet days.

“If it has an atmosphere, Webb has the sensitivity and wavelength to detect it and identify its components,” Hu said.

Yet another interesting possibility is that 55 Cancri-e does not have this behavior of keeping a closed face facing its star. Alternatively, it could be like Mercury, rotating three times per two orbits (what is known as a 3:2 resonance). As a result, the planet will have a day cycle.

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“This may explain why the hotter part of the planet is turning,” explained Alexis Brandecker, a researcher at Stockholm University who leads another team studying the planet. “Just like on Earth, it will take time for the surface to heat up. The hottest time of the day will be in the afternoon, not quite midday.”

Brandeker’s team plans to test this hypothesis using NIRCam to measure heat emitted from the bright side of this exoplanet during four different orbits. If it had a 3:2 resonance, the scientists would scan both hemispheres twice and should be able to detect any differences between the two hemispheres.

In such a scenario, the surface would heat up, melt, and even evaporate during the day, forming an extremely thin atmosphere that Webb could detect. At night, the steam cools and condenses to form lava droplets that would float to the surface, becoming solid again by nightfall.

The James Webb Telescope will give new perspectives on Earth-like planets

Like 55 Cancri-e, LHS 3844 b orbits very close to its star, completing its orbit in 11 hours. However, because its star is small and relatively cold, the planet is not hot enough for its surface to melt. Moreover, observations indicate that the planet is unlikely to have a large atmosphere.

Although it is not possible to directly record the surface of LHS 3844 b with Webb, the lack of an atmosphere makes it possible to study the surface using spectroscopy.

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

The team will use MIRI to capture the LHS 3844 b-days thermal emission spectrum, then compare it with spectra of known rocks such as basalt and granite to determine its composition. If the planet is volcanically active, the spectrum may also reveal traces of volcanic gases.

The significance of these observations goes beyond just two of the more than 5,000 confirmed exoplanets. “They will give us wonderful new perspectives on Earth-like planets in general, helping us see what early Earths would have looked like when it was as hot as these planets are today,” Kreidberg said.

These observations will be made for 55 Cancri-e and LHS 3844b as part of Webb’s first cycle public observations programme, expected to begin in June.

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