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James Webb Telescope eyes exoplanet with oceans of lava

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The James Webb Space Telescope is about to start peering into deep space in one of the most highly anticipated missions of recent years.

Five months after launch, and following a million-mile voyage to a spot that put it in orbit around our sun, the most powerful space telescope ever built is currently performing final calibrations of its onboard scientific instruments. Then, in just a few weeks’ time, it will begin the exciting work of trying to unlock the mysteries of our universe.

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This week, NASA disclosed that the James Webb Space Telescope team has already identified two celestial bodies that it wants to explore with the space-based observatory: The lava-covered 55 Cancri e and the airless LHS 3844 b.

Both of these exoplanets (a planet outside our solar system) are classified as “super-Earths” for their size and rocky composition. The Webb team will train the telescope’s high-precision spectrographs on both in the hope of finding out more about the “geologic diversity of planets across the galaxy, and the evolution of rocky planets like Earth,” NASA said.

55 Cancri e

55 Cancri e is a mere 1.5 million miles from its sun (we’re 93 million miles from ours) and therefore features surface temperatures far above the melting point of typical rock-forming minerals. It means that parts of its surface are likely to be covered in oceans of lava.

The Webb team is keen to find out if 55 Cancri e is tidally locked, resulting in one side always facing its star. Such a state would be usual for planets that orbit this close to a star, but earlier observations carried out by NASA’s Spitzer Space Telescope suggest the hottest part of the planet is away from the area that directly faces the star and that the heat on the day side varies.

This has left scientists wondering if 55 Cancri e has a dynamic atmosphere that shifts heat around. It’s a question that Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) should be able to answer by capturing the thermal emission spectrum of the day side of the planet.

Alternatively, it’s also possible that the planet is not tidally locked and is actually rotating. In this case, the surface would “heat up, melt, and even vaporize during the day, forming a very thin atmosphere that Webb could detect,” NASA said, adding that, in the evening, the vapor would then cool and condense to form “droplets of lava that would rain back to the surface, turning solid again as night falls.” Again, the team plans to use Webb’s NIRCam to determine if this is the case.

LHS 3844 b

The much smaller and cooler LHS 3844 b offers Webb scientists a chance to closely analyze the solid rock on an exoplanet’s surface. Different types of rock have different spectra, so the Webb team plans to use MIRI to learn more about the planet’s composition.

MIRI will capture the thermal emission spectrum of the day side of LHS 3844 b and compare it to spectra of known rocks, like basalt and granite, to determine its composition, NASA said.

Webb’s observations of the two exoplanets are expected to help scientists in much broader ways. “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 Laura Kreidberg of the Max Planck Institute for Astronomy.

The James Webb Space Telescope mission is also aiming to track down the first galaxies formed after the Big Bang, find out how galaxies evolved from formation to now, and measure the physical and chemical properties of planetary systems — among other goals.

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Trevor Mogg
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