The MIRI instrument aboard JWST helps study a particularly interesting star system, HR 8799. The observations provided data to analyze the chemical composition of the atmospheres of four exoplanets in this young star system. When the JWST space telescope first saw daylight in July 2022, it was the subject of a major research program established by members of the International Astronomical Union. This list includes the first distant galaxies, the formation of planets in protoplanetary disks of gas and dust, as well as the end of the “dark ages of the Universe” and the first light. Among the many targets, exoplanets cannot be absent from the list.
One distant star system has especially fascinated scientists. Fifteen years ago, astronomers discovered three exoplanets orbiting the star HR 8799, located about 133 light-years from Earth. Then a fourth exoplanet was discovered, all of which were found by direct detection. These are giant planets with wide orbits, which is very rare. In addition, the HR 8799 system is attractive to observe because it belongs to a young star system.
This is why JWST recently observed this system. Thanks to its instruments, including the MIRI and rotary infrared instruments, it can provide data that allows studying the star system in more detail. The mass of HR 8799 exceeds 1.5 solar masses, and the star’s luminosity is nearly five times that of the Sun. A dust disk has formed around it, and this is a fairly young star – its age is only about 30 million years. Young solar systems are of particular interest because they reveal details about planet formation. A new study by Anthony Bocaletti of the Paris Observatory aims to investigate these details.
The HR 8799 system includes four planets: HR 8799 b, c, d and e. They are all giant stars with masses ranging from 5.7 to 9.1 times the mass of Jupiter – the mass limit for brown dwarfs – objects with characteristics between planets and stars. The planets’ orbits range from 16 to 71 astronomical units, and their orbital periods range from 45 to 460 years. The fact that they were discovered 15 years ago is also significant because astronomers have accumulated a history of observing the HR 8799 system. The discovery of massive giant planets with orbits larger than 5 astronomical units is rare. Therefore, any discoveries about such systems are important. Using the capabilities provided by the MIRI tool, JWST can shed light on unknown aspects of such systems and allow scientists to describe them more fully. Until recently, technical difficulties associated with mid-infrared observations have made detailed study of the HR 8799 system difficult
.With JWST, scientists can refine information obtained from previous observations and better understand different aspects of the system. Emphasis on more precise characterization of the atmospheres of exoplanets. Despite some uncertainty about their composition and the open question of whether they are brown dwarfs, the JWST observations have cleared up doubts. With planetary temperatures ranging from 900 K to 1300 K, new measurements show that the temperature of planet HR 8799 b is lower than previous measurements suggested. In addition, the MIRI instrument can clearly detect the presence of two chemical compounds in the atmospheres of exoplanets: water and carbon monoxide. In addition, according to the data, scientists also have controversial evidence of the detection of methane, which is further evidence that these objects are planets and not brown dwarfs, why? Brown dwarf still shows clear methane content at such temperatures.
Mid-infrared (MIRI) devices are designed with the ability to apply a variety of filters. Some of them are specifically designed to detect ammonia, as this could be an indication of the presence of precursor life on exoplanets. However, data from four planets in the HR 8799 system show that they are slightly warmer than the temperatures at which ammonia is expected to be present. In addition, the HR 8799 system stands out thanks to the presence of a dust disc with two belts. Researchers wondered whether the inner edge of the outer ring might indicate the presence of a fifth planet whose mass lies between Jupiter and Saturn, or whether it was simply a plume of dust. This led to a debate that was resolved by JWST’s observations. The researchers concluded that the inner edge of the outer ring is a background object unrelated to HR 8799. This is the first opportunity for JWST to study a young exoplanet system using the MIRI instrument, its filters and coronagraph. JWST’s MIRI instrument opens new opportunities for high-contrast mid-infrared imaging and opens new avenues for the study of young exoplanetary systems. The main objective of the work is to carry out observations and test different algorithms to determine the best scenario for using the instruments and interpreting the results of future observations.