“Discovering Rare Elements in the Atmosphere of Hot Jupiter KELT-9b”

2023-05-12 12:00:05

The type of planet discovered for the first time in the history of observation as an exoplanet revolving around a star other than the sun is “hot jupiter“is. The gas planets in the solar system are farther from the sun than the earth, so they are in a cold environment, but it is not uncommon for hot Jupiters, which orbit very close to their stars, to have surface temperatures of over 1000 degrees Celsius. . As the name suggests, hot Jupiters are exposed to extreme temperatures, and the environment is considered to be quite extreme.

Gas giants like Jupiter and Saturn are thought to have rocky cores, which are hidden deep in their thick atmospheres. As such, the atmospheric constituents of gas giants are mostly hydrogen and helium, and no rocky or metallic elements are usually found.

However, in the case of hot Jupiters, which are heated to high temperatures, extremely strong atmospheric circulation occurs, so rocks and metal elements also appear on the surface. The heavier the element, the smaller the amount originally contained in the planet, and the less likely it is to rise from the core to the sky, making it difficult for it to appear on the surface.

【▲ Figure: Imaginary image of the hot Jupiter KELT-9b (left) orbiting the star KELT-9 (right) (Credit: Bibiana Prinoth)】

A research team such as NWB Borsato of Lund University, one of the hot Jupiters “KELT-9band searched for metallic elements contained in the atmosphere.

KELT-9b, located about 670 light-years from Earth,One of the hottest exoplanets with a maximum surface temperature of 4300°Cis. It is known from previous observations that the atmosphere of KELT-9b, which has been heated to a temperature higher than the surface temperature of a cold star, has very unusual characteristics as a hot Jupiter. For example, molecules such as water and carbon dioxide do not exist because they are broken down by intense radiation from stars. On the other hand, metallic elements such as iron and titanium have already been discovered. A closer look at KELT-9b’s atmosphere may also reveal other metallic elements.

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Borsato et al. Observed KELT-9b using the spectroscope “HARPS-N” installed at the Roque de los Muchachos Observatory and the spectroscope “CARMENES” installed at the Caral Alto Observatory. (both Spanish observatories). Both spectrometers specialize in spectral analysis corresponding to the Doppler effect caused by planetary motion, and have excellent performance in investigating the atmospheric composition of hot Jupiters.

As a result of observation, 8 kinds of metallic elements (※1) was found, but the most interesting discovery among them was “terbium」 (※2) and”barium」 (※3) is. Terbium was first discovered in the atmosphere of an exoplanet. This is the third case of barium, but both the first and second cases (WASP-76b and WASP-121b) were just discovered in 2022 and are extremely rare cases.

Terbium is element 65 and barium is element 56, the two top heavy elements found in the atmospheres of extrasolar planets. It is currently unknown whether the mechanism that lifts such heavy elements from the depths of the planet can be explained by simple atmospheric circulation alone, or whether other mechanisms are at work.

Working on the composition of the hot Jupiter’s atmosphere provides clues for exploring the normally inaccessible regions of the deep interior of the gas giant. Mechanisms that lift heavy elements will also provide clues to the details of material cycles inside planets. Observations by KELT-9b may not only discover rare elements in the atmosphere, but also provide important clues to learn the details of the planet as a whole.

*1…Calcium, titanium, vanadium, chromium, nickel, strontium, barium, terbium

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*2: One of the elements belonging to a group of similar elements called rare earths. It is used as a crystal stabilizer for fuel cells that operate at high temperatures, as a special alloy that expands and contracts with magnetism, and as a green fluorescent agent.

*3: One of the alkaline earth metals. The most prominent application is a contrast agent (so-called “barium porridge”) that makes use of the properties of X-rays that are difficult to pass through. In addition, it has appeared in materials that are expected to be put into practical use in the future, such as fireworks that use the green flame reaction, ceramics that exhibit piezoelectric effects, and high-temperature superconductors.

Source

• NWB Borsato, et al. “The Mantis Network. III. Expanding the limits of chemical searches within ultra-hot Jupiters: New detections of Ca I, VI, Ti I, Cr I, Ni I, Sr II, Ba II, and Tb II in KELT-9 b”. (Astronomy & Astrophysics) (arXiv)
• Nicholas Borsato. “Scientists discover rare element in exoplanet’s atmosphere”. (Lund University)
• T. Azevedo Silva, et.al. “Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b”. (Astronomy & Astrophysics)

Text: Riri Ayae

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