Illustration of exoplanet 55 Cancri e, a rocky planet almost twice the diameter of Earth, orbiting only 0.015 astronomical units from its sun-like star. Due to its narrow orbit, the planet is extremely hot, with daily temperatures reaching 4,400 degrees Fahrenheit (about 2,400 degrees Celsius). Credit: NASA, ESA, CSA, Dani Player (STScI)
With its mirror segments beautifully aligned and its scientific instruments calibrated, NASA’s James Webb Space Telescope is just weeks away from full operation. Soon after the first observations are revealed this summer, Web’s in-depth science will begin.
Among the studies planned for the first year are studies of two hot exoplanets classified as “super-Earth” because of their size and rocky composition: the lava-covered 55 Cancri e and the airless LHS 3844 b. Researchers will train Webb’s high-precision spectrographs on these planets to understand the geological diversity of planets throughout the galaxy and the evolution of rocky planets such as Earth.
Super hot superland 55 Cancri e
55 Cancri 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 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.
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.
Illustration comparing the rocky exoplanets LHS 3844 b and 55 Cancri e with Earth and Neptune. Credit: NASA, ESA, CSA, Dani Player (STScI)
55 Cancri e is there a dense atmosphere?
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 the thermal emission spectrum from the diurnal side of the planet. “If there is an atmosphere, [Webb] it has sensitivity and a wavelength range to detect it and determine what it is made of, “Hu added.
Or is it raining in the evening on 55 Cancri e?
Another intriguing possibility, however, is that the 55 Cancri e is not tidal locked. Instead, it may be like Mercury rotating three times for every two orbits (this is known as 3: 2 resonance). As a result, the planet will have a day-night cycle.
“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 warm up. The hottest time of the day will be in the afternoon, not exactly 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 four different orbits. If the planet has a 3: 2 resonance, they will observe each hemisphere twice and must be able to detect any difference between the hemispheres.
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 would cool and condense to form lava droplets that would fall back to the surface, becoming solid again as night fell.
Possible heat emission spectrum of the hot extraterrestrial exoplanet LHS 3844 b, measured by the Webb medium infrared instrument. The spectrum of heat radiation shows the amount of light with different infrared wavelengths (colors) that are emitted from the planet. Researchers are using computer models to predict what the planet’s heat emission spectrum will look like, assuming certain conditions, such as whether there is an atmosphere and what the planet’s surface is made of. Credit: NASA, ESA, CSA, Dani Player (STScI)
Slightly cooler super-terrestrial LHS 3844 b
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.
What is the surface of LHS 3844 b made of?
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.”
Illustration of the exoplanet LHS 3844 b, a rocky planet 1.3 times the diameter of Earth, orbiting about 0.006 astronomical units from its cool red dwarf star. The planet is hot, with daily temperatures estimated at more than 1,000 degrees Fahrenheit (more than about 525 degrees Celsius). Credit: NASA, ESA, CSA, Dani Player (STScI)
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.
The significance of these observations exceeds 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 was like when it was as hot as it is today,” Kreidberg said.
These observations of 55 Cancri e and LHS 3844 b will be conducted as part of the Webb Cycle 1 general observer program. General Observers’ programs were competitively selected using a dual anonymous review system, the same system used to distribute time in Hubble.
Lava or not, the exoplanet 55 Cancri will probably have an atmosphere
Provided by the Space Telescope Science Institute
Citation: Astronomers will train James Webb Telescope’s high-precision spectrographs on two intriguing rocky exoplanets (2022, May 27) extracted on May 27, 2022.
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