Hubble Space Telescope observations used to answer key questions about exoplanets

Archival Hubble Space Telescope observations of 25 hot Jupiters have been analyzed by an international team of astronomers, allowing them to answer five open questions important to our understanding of exoplanet atmospheres. Among other findings, the team found that the presence of metal oxides and hydrides in the atmospheres of the hottest exoplanets was clearly correlated with the thermal inversion of the atmospheres. Credit: ESA/Hubble, N. Bartmann; DC BY 4.0

A global team of astronomers studied the records The Hubble Space Telescope observations of 25 hot Jupiters, allowing them to answer five important unresolved questions for our understanding of exoplanet atmospheres. The researchers discovered, among other things, that the existence of metal oxides and hydrides in the hottest atmospheres of exoplanets was clearly linked to the thermal inversion of the atmospheres.

The field of exoplanet science has long since shifted from simple detection to characterization, although characterization remains extremely difficult. So far, the majority of characterization research has focused on modeling or studying one or a few exoplanets. This new research study, led by researchers based at University College London (UCL), used the largest amount of archival data ever examined in a single exoplanet atmospheric study to assess the atmospheres of 25 exoplanets. Most of the data comes from observations made with the " data-gt-translate-attributes="[{" attribute="">Nasa/ESA Hubble Space Telescope.

Hot Jupiters are a class of gas giant exoplanets that are thought to be physically similar to Jupiter but which have very short orbital periods (P

Lead author Quentin Changeat explains: “Hubble has enabled the in-depth characterization of 25 exoplanets, and the amount of information we have learned about their chemistry and formation – thanks to a decade of intense observing campaigns – is incredible.”

The science team set out to find answers to five open-ended questions about exoplanet atmospheres – an ambitious goal they managed to achieve. Their questions probed what H– and certain metals can tell us about the chemistry and circulation of exoplanet atmospheres, and about planet formation. They chose to study a wide range of hot Jupiters, with the aim of identifying patterns within their sample population that could provide more general insight into exoplanet atmospheres.

Study co-leader Billy Edwards of UCL and the French Alternative Energies and Atomic Energy Commission (CEA) said: “Our paper marks a turning point for the field: we are now moving from characterizing from the atmospheres of individual exoplanets to the characterization of atmospheric populations.

In order to investigate their sample of 25 exoplanets, the team reanalyzed a huge amount of archival data, consisting of 600 hours of Hubble observations, which they supplemented with more than 400 hours of space telescope observations. Spitzer. Their data contained eclipses for all 25 exoplanets and transits for 17 of them. An eclipse occurs when an exoplanet passes behind its star as seen from Earth, and a transit occurs when a planet passes in front of its star. Both eclipse and transit data can provide crucial information about an exoplanet’s atmosphere.

The large-scale survey yielded results, with the team able to identify clear trends and correlations between exoplanet atmospheric constitutions and observed behavior. Some of their key findings concerned the presence or absence of thermal inversions in the atmospheres of their sample of exoplanets. They found that almost all exoplanets with thermally inverted atmospheres were extremely hot, with temperatures above 2000 Kelvins. Importantly, it is hot enough for the metal species TiO (titanium oxide), VO (vanadium oxide), and FeH (iron hydride) to be stable in one atmosphere. Of the exoplanets exhibiting thermal inversions, almost all were found to have H–, TiO, VO, or FeH in their atmosphere.

It is always difficult to draw conclusions from such results because correlation does not necessarily equal causation. However, the team was able to come up with a compelling argument why the presence of H–, TiO, VO or FeH could lead to thermal inversion, namely that all of these metallic species are very efficient absorbers of starlight. It could be that the atmospheres of exoplanets hot enough to harbor these species tend to thermally invert because they then absorb so much starlight that their upper atmospheres heat up even more. Conversely, the team also found that colder hot Jupiters (with temperatures below 2000 Kelvins, and therefore no H–, TiO, VO, or FeH in their atmospheres) almost never had thermally reversed.

An important aspect of this research was that the team was able to use a large sample of exoplanets and a very large amount of data to determine trends, which can be used to predict the behavior of other exoplanets. This is extremely useful, as it gives insight into how planets can form, and also because it allows other astronomers to plan future observations more efficiently. Conversely, if a paper studies a single exoplanet in great detail, while valuable, it is much more difficult to extrapolate trends. A better understanding of exoplanet populations could also bring us closer to solving open mysteries about our own solar system.

As Changeat puts it: “Many questions such as the origins of water on Earth, the formation of the Moon and the different evolutionary histories of Earth and " data-gt-translate-attributes="[{" attribute="">March, are still unresolved despite our ability to obtain in-situ measurements. Large studies of exoplanet populations, such as the one we present here, aim to understand these general processes.

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