Illustration showing what the exoplanet 55 Cancri e might look like, based on current understanding of the planet. 55 Cancri e is 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). Spectroscopic observations using Webb’s Near Infrared Camera (NIRCam) and Medium Infrared Instrument (MIRI) will help determine whether or not the planet has an atmosphere and, if so, what that atmosphere is made of. Observations will also help determine if the planet is blocked or not. Credits: NASA, ESA, CSA, Dani Player (STScI)
Astronomers will train Webb’s high-precision spectrographs on two intriguing rocky exoplanets.
Imagine if the Earth were much, much closer to the Sun. So close that a whole year would only last a few hours. So close that gravity has closed one hemisphere in the light of the permanent burning day and the other in the eternal darkness. So close that the oceans boil, the rocks begin to melt and the clouds rain lava.
Although there is nothing like our own solar system, planets like this, rocky, about the size of Earth, extremely hot and close to their stars, are not strange in the Milky Way galaxy.
What are the surfaces and atmospheres of these planets really like? NASA’s James Webb Space Telescope is about to give some answers.
Illustration showing what the exoplanet LHS 3844 b might look like, according to current understanding of the planet. LHS 3844 b is a rocky planet 1.3 times the diameter of Earth that orbits 0.006 astronomical units of its cool red dwarf star. The planet is hot, with daytime temperatures estimated to be above 1,000 degrees Fahrenheit (over 525 degrees Celsius). Observations of the planet’s thermal emission spectrum using Webb’s Medium Infrared Instrument (MIRI) will provide further evidence to help determine what the surface is made of. Credits: NASA, ESA, CSA, Dani Player (STScI)
Geology from light years: Webb prepares to study rocky worlds
With its beautifully aligned mirror segments and scientific instruments in the process of being calibrated, NASA’s James Webb (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.
Studies planned for the first year include 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. Scientists will train Webb’s high-precision spectrographs on these planets in order to understand the geological diversity of the galaxy’s planets, as well as the evolution of rocky planets like Earth.
Super-Hot Super-Earth 55 Cancer 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.
Illustration comparing rocky exoplanets LHS 3844 bi 55 Cancri e with Earth and Neptune. Both 55 Cancri e and LHS 3844 b lie between the Earth and Neptune in size and mass, but are more Earth-like in composition. The planets are arranged from left to right in ascending radius order. Deep Earth Climate Observatory Earth Image: Earth is a warm, rocky planet with a solid surface, oceans of water, and a dynamic atmosphere. Illustration of LHS 3844 b: LHS 3844 b is a hot, rocky exoplanet with a solid, rocky surface. The planet is too hot for the oceans to exist and does not appear to have any significant atmosphere. Illustration of 55 Cancri e: 55 Cancri e is a rocky exoplanet whose daytime temperature is high enough for the surface to melt. The planet may or may not have an atmosphere. Image of Neptune from Voyager 2: Neptune is a cold ice giant with a thick, dense atmosphere. The illustration shows the planets to scale in terms of radius, but not the location in space or the distance of their stars. As Earth and Neptune orbit the Sun, LHS 3844 b orbits a small, cool red dwarf star about 49 light-years from Earth, and 55 Cancer orbits a Sun-like star about 41 light-years away. Both are very close to their stars, completing an orbit in less than one Earth day. Credits: NASA, ESA, CSA, Dani Player (STScI)
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.
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 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 is it raining 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.”
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. This particular simulation assumes that LHS 3844 b has no atmosphere. and the diurnal side is covered by dark volcanic basaltic rock. (Basalt is the most common volcanic rock in our solar system, forming volcanic islands like Hawaii and most of the Earth’s ocean floor, as well as large portions of the surfaces of the Moon and Mars.) For comparison, the gray line represents a spectral model of basaltic rock based on laboratory measurements. The pink line is the spectrum of granite, the most common igneous rock found on the continents of the Earth. The two types of rocks have very different spectra because they are made of different minerals, which absorb and emit different amounts of different wavelengths of light. After Webb observes the planet, researchers will compare the actual spectrum with modeled spectra of various types of rocks like these. to find out what the surface of the planet is made of. Credits: NASA, ESA, CSA, Dani Player (STScI), Laura Kreidberg (MPI-A), Renyu Hu (NASA-JPL)
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.
Slightly colder Super-Earth LHS 3844 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. “
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 prospects …