Illustration of the exoplanet 55 Cancri e, a rocky planet almost twice the diameter of Earth that orbits only 0.015 astronomical units of its Sun-like star. Due to its narrow orbit, the planet is extremely hot, with daytime temperatures reaching 4,400 degrees Fahrenheit (about 2,400 degrees Celsius). Credits: NASA, ESA, CSA, Dani Player (STScI)
With its well-aligned mirror segments and scientific instruments in the process of being calibrated, NASA’s James Webb Space Telescope is just weeks away from full operation. Shortly after the first observations are revealed this summer, Webb’s in-depth science will begin.
Among the research planned for the first year are studies of two hot exoplanets classified as “super-Earths” for their size and rock composition: the 55 Cancri e covered with lava and the LHS 3844 b without air. Researchers will train Webb’s high-precision spectrographs on these planets with the goal of understanding the geological diversity of the galaxy’s planets and the evolution of rocky planets like Earth.
Super hot earth 55 Cancri e
55 Cancer orbits less than 1.5 million miles from its sun-like star (one-fifth of the distance between Mercury and the Sun), completing a circuit in less than 18 hours. With surface temperatures well above the melting point of typical rock-forming minerals, the diurnal part of the planet is believed to be covered in lava oceans.
Planets orbiting so close to their star are supposed to be blocked by the tide, with one side facing the star at all times. As a result, the hottest spot on the planet should be the one directly facing the star, and the amount of heat from the day should not change much over time.
But that doesn’t seem to be the case. 55 Cancri e observations from NASA’s Spitzer Space Telescope suggest that the warmer region is offset by the part that faces the star most directly, while the total amount of heat detected from the side of the day varies.
Illustration comparing rocky exoplanets LHS 3844 bi 55 Cancri e with Earth and Neptune. Credits: NASA, ESA, CSA, Dani Player (STScI)
55 Cancer and has a thick atmosphere?
One explanation for these observations is that the planet has a dynamic atmosphere that moves heat. “55 Cancers could have a thick atmosphere dominated by oxygen or nitrogen,” said Renyu Hu of NASA’s Jet Propulsion Laboratory in Southern California, who leads a team that will use the nearby infrared camera (NIRCam) and Webb’s Infrared Medium Instrument (MIRI). ) to capture the spectrum of thermal emission from the diurnal side of the planet. “If it has an atmosphere, [Webb] it has the sensitivity and wavelength range to detect it and determine what it’s made of, “Hu added.
Or lava rain in the evening at 55 Cancri e?
Another intriguing possibility, however, is that 55 Cancri e is not blocked in a dizzy way. Instead, it can be like Mercury, rotating three times every two orbits (what is known as 3: 2 resonance). As a result, the planet would have a day-night cycle.
“This could explain why the hottest part of the planet is moving,” said Alexis Brandeker, a researcher at Stockholm University who leads another team studying the planet. “Just like on Earth, the surface would take time to warm up. The hottest hour of the day would be in the afternoon, not just at noon.”
Brandeker’s team plans to test this hypothesis using NIRCam to measure the heat emitted from the illuminated side of 55 Cancri e over four different orbits. If the planet has a 3: 2 resonance, they will observe each hemisphere twice and should be able to detect any differences between the hemispheres.
In this scenario, the surface would heat up, melt, and even vaporize during the day, forming a very fine atmosphere that Webb could detect. In the evening, the steam would cool and condense to form lava drops that would rain on the surface again, becoming solid again as night fell.
Possible thermal emission spectrum of the hot super-terrestrial exoplanet LHS 3844 b, measured by Webb’s medium-infrared instrument. A thermal emission spectrum shows the amount of light from different infrared wavelengths (colors) emitted by the planet. Researchers use computer models to predict what a planet’s thermal emission spectrum will look like under certain conditions, such as whether or not there is an atmosphere and what the planet’s surface is made of. Credits: NASA, ESA, CSA, Dani Player (STScI)
Super-ground LHS 3844 slightly colder b
While 55 Cancri e will provide an insight into the exotic geology of a lava-covered world, LHS 3844 b offers a unique opportunity to analyze solid rock on the surface of an exoplanet.
Like 55 Cancri e, LHS 3844 b orbits very close to its star, completing a revolution in 11 hours. However, because its star is relatively small and cool, the planet is not hot enough for the surface to melt. In addition, Spitzer’s observations indicate that the planet is very unlikely to have a substantial atmosphere.
What is the surface of LHS 3844 b made of?
Although we cannot imagine 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 rock have different spectra,” said 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 emitted by rocks.”
Illustration of the exoplanet LHS 3844 b, a rocky planet 1.3 times the diameter of Earth orbiting 0.006 astronomical units from its cool red dwarf star. The planet is hot, with daytime temperatures estimated to be above 1,000 degrees Fahrenheit (over 525 degrees Celsius). Credits: NASA, ESA, CSA, Dani Player (STScI)
The Kreidberg team will use MIRI to capture the diurnal side heat emission spectrum of LHS 3844 b and then compare it with known rock spectra, such as basalt and granite, to determine its composition. If the planet is volcanically active, the spectrum could also reveal the presence of traces of volcanic gases.
The significance 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 primitive Earth might have been like when it was hot like these planets today,” Kreidberg said.
These observations from 55 Cancri ei LHS 3844 b will be made as part of Webb’s Cycle 1 general observer program. General observer programs were competitively selected using a dual anonymous review system, the same system used to allocate time to Hubble.
Lava or not, the exoplanet 55 Cancri is likely to have an atmosphere
Provided by Space Telescope Science Institute
Citation: Astronomers will train high-precision spectrographs of the James Webb Telescope on two intriguing rocky exoplanets (2022, May 27) recovered on May 27, 2022
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