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This article originally appeared on The conversation. The post contributed to the article at Space.com’s Expert Voices: Op-Ed & Insights.
Quentin Changeat, Postdoctoral researcher in astronomy, UCL
Billy edwards, Scientist of the Twinkle Space Mission Project, Researcher in Astronomy, UCL
Until the early 2000s, the only known planets were in our own neighborhood, the solar system. They generally form two categories: the small rocky planets of the inner solar system and the cold gas planets located in the outer part. With the discovery of exoplanets, of planets orbiting stars other than the Sun, additional classes of planets were discovered and a new image began to emerge. Our solar system is by no means typical.
For example, data from the Kepler mission showed that large gaseous exoplanets can orbit very close to their star – rather than far from it, as is the case in our solar system, causing them to reach temperatures in excess of 1000. Kelvin (727 degrees Celsius). These have been nicknamed the “hot” or “ultra-hot” Jupiters. And while most of the other exoplanets are smaller, between the size of Neptune and Earth, we don’t know much about their makeup.
Related: Hottest Alien Planet Ever Discovered Is A Real Scorcher
But how can hot, gaseous planets form and exist so close to their star? What kinds of extreme physical processes are happening here? The answers to these questions have big implications for our understanding of exoplanets and planets in the solar system. In our recent study, published in The Astrophysical Journal Letters, we added another piece to the puzzle of planetary formation and evolution.
Dated-9b
In essence, hot Jupiters are a window into extreme physical and chemical processes. They provide an incredible opportunity to study physics under environmental conditions almost impossible to replicate on Earth. Their study improves our understanding of chemical and thermal processes, atmospheric dynamics and cloud formation. Understanding their origins can also help us improve planetary formation and patterns of evolution.
We still struggle to explain how the planets form and how elements, such as water, were delivered to our own solar system. To find out, we need to know more about the compositions of exoplanets by observing their atmospheres.
Observe the atmospheres
There are two main methods for studying the atmospheres of exoplanets. In the transit method, we can pick up starlight that is filtered through the atmosphere of the exoplanet as it passes in front of its star, revealing the fingerprints of all the chemical elements that exist there.
The other method of investigating a planet is during an “eclipse”, when it passes behind its host star. The planets also emit and reflect a small fraction of light, so by comparing the small changes in total light when the planet is hidden and visible, we can extract the light from the planet.
Both types of observations are made at different wavelengths, or colors, and because chemicals and compounds absorb and emit at very specific wavelengths, a spectrum (light broken down by wavelength) can be produced so that the planet can deduce the composition of its atmosphere.
Secrets of Kelt-9b
In our study, we used publicly available data taken by the Hubble Space Telescope to obtain the eclipse spectrum for this planet.
We then used open source software to extract the presence of molecules and found that there were a lot of metals (made from molecules). This finding is interesting because it was previously believed that these molecules would not be present at such extreme temperatures – they would be broken down into smaller compounds.
Subject to the strong gravitational pull of its host star, Kelt-9b is “locked”, which means that the same face of the planet is constantly facing the star. This results in a large temperature difference between the day and night sides of the planet. As eclipse observations probe the warmer side of the day, we have suggested that the molecules observed may in fact be driven by dynamic processes from colder regions, such as at night, or deeper in the sky. interior of the planet. These observations suggest that the atmospheres of these extreme worlds are governed by complex, poorly understood processes.
Kelt-9b is interesting because of its orbit inclined by about 80 degrees. This suggests a violent past, with possible collisions, which is in fact also observed for many other planets in this class. It is very likely that this planet formed far from its mother star and that the collisions occurred during its inward migration to the star. This supports the theory that large planets tend to form far from their host star in protostellar disks – which give rise to solar systems – capturing gaseous and solid materials as they migrate to their star.
But we don’t know how it happens. It is therefore crucial to characterize many of these worlds to confirm various scenarios and better understand their history as a whole.
Future missions
Observatories, like the Hubble Space Telescope, were not designed to study the atmospheres of exoplanets. The next generation of space telescopes, like the James Webb Space Telescope and the Ariel mission, will have much better capabilities and instruments specifically designed for rigorous observation of exoplanet atmospheres. They will allow us to answer many fundamental questions raised by Jupiter’s class of extremely hot planets, but they will not stop there.
This new generation of telescopes will also probe the atmosphere of small worlds, a category that current instruments are struggling to achieve. In particular, Ariel, which is slated to launch in 2029, will observe around 1,000 exoplanets to tackle some of the most fundamental questions in exoplanet science.
Ariel will also be the first space mission to examine in detail the atmosphere of these worlds. He should finally tell us what these exoplanets are made of and how they were formed and evolved. It will be a real revolution.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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