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Recent Progress: Researchers Characterize Exoplanet Atmospheres Using a 4-meter Ground-based Telescope and Achieve Significant Advancements

In recent times, researchers from the National Astronomical Observatory utilized a 4-meter aperture ground-based telescope located in Chile to obtain optical wavelength transmission spectra of two hot Jupiters, namely WASP-69b and WASP-121b. Through model analysis, they were able to provide important constraints on the atmospheric properties of these planets. The research findings were published in the Monthly Notices of the Royal Astronomical Society and Astronomy and Astrophysics Research, respectively.

Hot Jupiters are a type of extreme exoplanets that orbit very close to their host stars, with orbital periods generally less than 10 days. Due to long-term and intense stellar radiation, the dayside temperature of these planets typically exceeds 1000K. As a result, their atmospheres are relatively inflated, exhibiting strong spectral signals, making them one of the most important targets for atmospheric studies. Transmission spectra are crucial data used to investigate exoplanet atmospheres. They represent the difference between the spectra during planetary transits and the out-of-transit spectra, carrying information about the temperature structure and chemical composition of the planetary atmospheres. Therefore, transmission spectra can be utilized to characterize the atmospheric properties of these planets.

WASP-69b has a radius of 1.057±0.047 RJup, a mass of 0.260±0.017 MJup, and an orbital period of approximately 3.868 days. In the transmission spectrum, the researchers, including authors Ouyang Qinglin and Wang Wei, observed a slope caused by Rayleigh scattering, inferring that the atmosphere of this planet is primarily composed of hydrogen. Additionally, the transmission spectrum of WASP-69b exhibits significant oscillation signals in the range of 700-900 nm. Combining atmospheric models, the authors suggest that this may be attributed to titanium oxide absorption. Titanium oxide is commonly considered as the main component responsible for generating temperature inversions in hot Jupiter atmospheres. However, its presence has previously only been detected in the atmospheres of ultra-hot Jupiters (Teq > 2000K), as maintaining a gaseous state for titanium oxide requires sufficiently high temperatures (> 1500K). Thus, this is the first evidence of titanium oxide’s existence in a classical hot Jupiter.

Figure 1: Transmission spectrum of WASP-69b and the corresponding best-fit inversion models. The blue and red lines represent the best-fit inversion models for optical transmission spectrum and combined optical + near-infrared transmission spectrum, respectively. The lower panels show the posterior distributions of the parameters for the two inversion models. Both inversion models exhibit relatively high metallicity.

WASP-121b has a radius of 1.865±0.065 RJup, a mass of 1.183±0.064 MJup, and an orbital period of approximately 1.275 days. The authors found that the transmission spectrum they obtained differs from previous spectra, and there are also significant differences among the spectra obtained by different researchers. Through literature research and reanalysis of previous data, they believe that these differences are likely to be real and unlikely to be attributed to data processing procedures or stellar activity. In other words, the atmospheric composition of this planet may vary over time. Inversion analysis reveals the presence of absorption signals from titanium oxide and vanadium oxide in the atmosphere of WASP-121b. However, the abundances of these components are inconsistent with previous results, further supporting the possibility of temporal variations in the atmosphere of this planet.

Figure 2: Similar to Figure 1, the transmission spectrum of WASP-121b and the corresponding best-fit inversion models are shown. The lower panels display clear posterior distributions of the inversion parameters, depicting the posterior distributions of titanium oxide and vanadium oxide abundances, corresponding to the absorption of these components in the atmosphere.

Both studies represent the first observational research on exoplanet atmospheres using the SOAR telescope. The SOAR telescope, whose full name is Southern Astrophysical Research Telescope, is operated jointly by astronomical institutions from Brazil, Chile, and the United States. The relevant observational data were obtained through the application of the lead author, Wang Wei, during their tenure at the South American Astronomical Observatory of the Chinese Academy of Sciences. The authors of the studies point out that, compared to the current mainstream large-aperture ground-based telescopes and space telescopes, 4-meter telescopes such as SOAR have slightly lower precision. However, they can still provide important constraints on the atmospheric properties of exoplanets. Therefore, 4-meter ground-based telescopes like SOAR can be a cost-effective yet reliable option for studying exoplanet atmospheres, facilitating future research on a larger sample of planetary atmospheres.

Figure 3: The SOAR telescope located in Chile, with an aperture of 4.1 meters.

Paper 1 link: https://academic.oup.com/mnras/article/521/4/5860/7091929

Paper 2 link: https://doi.org/10.1088/1674-4527/accbb2

Based on the principles established in a 2013 Memorandum of Understanding (MoU) between the Chinese Academy of Sciences (CAS) and the National Commission of Scientific and Technological Research of the Republic of Chile (CONICYT), and the more specific guidelines described in a recent (2015) Agreement between the National Astronomical Observatories of China (NAOC), the Chinese Astronomical Society, the Chilean Astronomical Society (SOCHIAS) and CONICYT (pdf), we are now inviting research proposals that involve China-Chile collaboration in astronomical research, to promote astronomical research collaborations between China and Chile, to advance astronomy in both countries.

These funds are for research projects based on a collaboration between astronomers from China and Chile, and the subject can be in areas such as astronomical research, observations, instrumental development, theory, etc. 

The duration of each project should be two years at maximum, and can request up to 75,000 USD/year. We are aiming to support 3 or 4 projects in this call.


The deadline for applications is now extended to May,31st 2022. Inquiries can be sent to Dr. Jiasheng Huang (Chief Scientist of CASSACA; jhuang#@#nao.cas.cn), or Dr. Lei Zhu (Deputy Director of CASSACA; lzhu#@#nao.cas.cn).

For more details, please read the attached announcement (pdf).

On October 20, 2021, the Joint Council Meeting of the Chinese Academy of Sciences South America Center for Astronomy (CASSACA) and the China-Brazil Joint Laboratory for Space Weather of CAS (hereinafter referred to as CBJLSW) was held at the headquarter of National Astronomical Observatories, Chinese Academy of Sciences (NAOC). Prof. Zhang Yaping, Vice President of the Chinese Academy of Sciences and the Chairman of CASSACA & CBJLSW Council, attended the meeting. The representatives of the Council members of both centers attended the meeting as well.

The Council reviewed and approved the annual work reports, funding implementations of the year 2021, as well as the work plans and budget arrangements for the next year of both oversea centers. In the meeting, the Council discussed extensively and put forward suggestions on several issues, including the platform operation, scientific research deployment, resource allocation, and international cooperation in the frontier areas such as astronomy, space science, climate and remote sensing observation.

In his concluding speech, Zhang Yaping fully acknowledged the efforts and achievements made by CASSACA and CBJLSW under the current difficult circumstances of COVID-19 pandemic. He pointed out that new requirements should be placed for the oversea centers in the new stage.  “The oversea centers should further refine their work priorities, make full use of the unique advantages of the oversea platform, promote multilateral collaboration, and develop a more open and dynamic system”, said by Zhang Yaping. He also encouraged the scientists to propose major scientific ideas and plans in order to gain more and more influential scientific achievements based on the overseas centers. 

CASSACA and CBJLSW were two oversea centers of Chinese Academy of Sciences. They were set up in October 2013 in Chile and in August 2014 in Brazil separately. They have been playing an important role in the international collaborations in the areas of astronomy and space weather between China and South America countries.