The James Webb Telescope explores deep space against the backdrop of alien planets. JWST launches art. Items … [+] of this image provided by NASA.
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According to a NASA report, with beautifully aligned mirror segments and calibration of its scientific instruments, the James Webb Space Telescope is just weeks away from conducting its first research.
In the first year of operations, researchers will focus on two exoplanets: 55 Cancri e and LHS 3844 b. The two exoplanets will be used to calibrate telescope instruments and to study the geological diversity and evolution of rocky planets in our galaxy.
55 Cancri orbits less than 1.5 million kilometers from its sun-like star (one-twenty-fifth of the distance between Mercury and our Sun), completing one orbit in less than 18 hours. With surface temperatures well above the melting point of typical rock-forming minerals, the daily side of the planet is thought to be covered with lava oceans.
Although nothing like this exists in our own solar system, planets like this – rocky, about the size of Earth, extremely hot and close to their stars – are thought to be quite common.
It is believed that the planets that orbit so close to their star are tidal locked, with one side facing the star all the time. As a result, the hottest spot on the planet should be the one most directly facing the star, and the amount of heat coming from the day should not change much over time.
But this does not seem to be the case. Observations by NASA’s 55-year-old Spitzer Space Telescope show that the hottest region has been displaced by the part that faces the star most directly, while the total amount of heat detected by the day varies.
One explanation for these observations is that the planet has a dynamic atmosphere that moves heat around.
“55 Cancri e may have a dense atmosphere dominated by oxygen or nitrogen,” said Renyu Hu of NASA’s Southern California Jet Propulsion Laboratory, who is leading a team that will use Webb’s Near Infrared Camera (NIRCam) and a medium-infrared instrument. (MIRI) to capture heat emissions from the daily side of the planet.
Another intriguing possibility, however, is that the 55 Cancri e is not tidal locked. Instead, it may be like Mercury, rotating very slowly with a day-night cycle lasting more than one orbit.
“This may explain why the hottest part of the planet has been displaced,” said 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 exactly at noon. Brandecker’s team plans to test this hypothesis using NIRCam to measure the heat emitted by the illuminated side of the 55 Cancri e during different orbits.
In this scenario, the surface will heat up, melt and even evaporate during the day, creating a very thin atmosphere that Webb can detect. In the evening, the steam will cool and condense to form lava droplets that will fall back to the surface, solidifying again as night falls.
While 55 Cancri e will give an idea of the exotic geology of a lava-covered world, LHS 3844 b provides a unique opportunity to analyze hard rock on the surface of an exoplanet.
Like the 55 Cancri e, the LHS 3844 b orbits extremely close to its star, making one revolution in 11 hours. However, because its star is relatively small and cool, the planet is not hot enough to melt the surface. In addition, Spitzer’s observations show that the planet is very unlikely to have a significant atmosphere.
Although we will not be able to map the surface of LHS 3844 b directly with Webb, the lack of a darkening atmosphere makes it possible to study the surface with 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 with your own eyes that granite is lighter in color than basalt. There are similar differences in the infrared light that rocks emit. “
The Kreidberg team will use MIRI to capture the heat emission spectrum of the day side of LHS 3844 b and then compare it with the 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.
Illustration comparing LHS 3844 b and 55 Cancri e with the Earth.
NASA / ESA / CSA / Days Player
The significance of these observations exceeds only two of the more than 5,000 confirmed exoplanets. “They will give us fantastic new perspectives on Earth-like planets in general, helping us learn what the early Earth was like when it was as hot as it is today,” Kreidberg said.
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