The James Webb Space Telescope (JWST) has already been hailed for providing information that was previously impossible to obtain. And now it has managed to determine the temperature of an exoplanet, writes Science News.
Astronomers consider the JWST to be the pinnacle of space telescopes. It is the largest and most powerful telescope ever launched into space and is the successor to the Hubble Space Telescope. Many believe that with JWST we will be able to observe the more distant regions of the universe. It consists of several cameras and spectrometers capable of detecting infrared radiation. These include the Near-Infrared Spectrograph (NIRSpec), the Mid-Infrared Instrument (MIRI), and the Near Infrared Camera (NIRCam).
Scientists hope to get information that will help them find out what the early universe looked like, how galaxies formed and evolved, and how stars were born inside gas and dust nebulae.
At the same time, another important mission of the JWST is to study the atmospheres of exoplanets and to find out if the observed planets contain the ingredients necessary for the emergence of life. On March 27 the JWST was able to measure the daytime temperature of the rocky exoplanet TRAPPIST-1 b.
In theory, we can measure the temperature of celestial bodies using the Stefan-Boltzmann law, which relates the temperature of a body to its flux—a measure of the amount of light it emits. Thus, to theoretically calculate the temperature of a planet, it is necessary to determine the flux of its host star—which can be measured, the distance between the planet and the star, and the "albedo" of the planet. Albedo is a quantity that takes into account the fraction of starlight that is reflected from a planet. A planet with an albedo of 1—unit—perfectly reflects all the light falling on it, while a planet with an albedo of 0 absorbs all the radiation falling on it. Astronomers then determine the planet's temperature using the magnitude of the planet's albedo and the total flux from the host star. This method of calculating the planet's temperature is simple and rather crude.
The JWST houses several cameras and spectrometers. Using the MIRI instrument, which consists of a camera and a spectrograph, the temperature of the day side of the TRAPPIST-1 b planet was measured. Photometric observations of TRAPPIST-1 b were made by MIRI just as its secondary eclipse began. A secondary eclipse is when an exoplanet begins to fall behind its host star, as seen by an “observer” like the JWST. The latter’s observations were made using the F1500W filter of the MIRI telescope. This filter enables detection of infrared radiation of a specific wavelength, similar to what scientists expect to see from exoplanets because TRAPPIST-1 b is a planet, and therefore it emits no light of its own. However, when viewed in the infrared range, it emits light. Therefore, MIRI is an ideal tool for observing exoplanets. By detecting it in the infrared range, we can determine its flux or brightness. MIRI, using the F1500W filter, observed TRAPPIST-1 b during five different secondary observation periods. The observational data consists of measuring the planet's brightness under infrared radiation. Scientists then reduce and optimize them using computer software and get the exoplanet's "light curve."
Computer models show that if TRAPPIST-1 b did not have a properly distributed heat atmosphere, its temperature would be just over 500 K. But if TRAPPIST-1 b had an atmosphere with uniform heat distribution, its daytime temperature would be close to 400 K. A comparison of these models suggests that TRAPPIST-1 b is most likely a rocky planet with no atmosphere. If it had an atmosphere, the heat would be distributed evenly over it, reducing the daytime temperature.
This JWST achievement is just the beginning. Its ability to detect a secondary eclipse is a huge achievement in itself. By measuring a planet's temperature, we can determine whether it has an atmosphere, which is an important step in determining whether life exists on the planet. As similar observations of other planets increase, we will learn more about the possibilities for life on other planets. Understanding the origin of life is also one of JWST's challenges. Scientists hope that these next-generation observations can provide more information about the properties of the atmospheres of other exoplanets in the universe.
