Scientists have discovered thousands of exoplanets, including many similar in size to our own that are potentially habitable. But to really gauge the possibility of life, how these planets formed and how they evolved, we need to know more about their chemistry. With its newly announced Ariel mission, the first dedicated to studying exoplanet atmospheres, the European Space Agency (ESA) is looking to fill in some of the gaps.
Ariel stands for Atmospheric Remote‐sensing Infrared Exoplanet Large‐survey, and the mission will launch a spacecraft into orbit with a set of advanced scientific instruments to peer beyond our Solar System. These include a telescope assembly, near-infrared spectrometers and near-infrared photometers.
Using these tools, ESA plans to survey a sample of around 1,000 exoplanets from gas giants to rocky worlds, with a particular focus on warm and hot planets. This is because warmer temperatures makes for atmospheres that are well mixed and with less condensation, making it easier to study their composition.
Scientists will do this using transit spectroscopy, much like NASA's James Webb Space Telescope and Transiting Exoplanet Survey Satellite set to launch over the next year. When exoplanets orbit their parent star too closely, the blinding light makes it impossible to image them directly. So scientists use what it is known as transiting instead, where the planet causes that starlight to flicker as it passes in front, giving them an indication of not just the exoplanet's presence, but also things like its mass and volume.
And by observing these transits through particular filters, scientists can draw conclusions about the makeup of the atmospheres. This is because the planet's atmosphere will block certain wavelengths of starlight depending on the molecules that are present within it, giving an indication of their chemical makeup.
The Ariel mission is billed as the first dedicated survey of exoplanet atmospheres, and by building a catalogue of observations gathered at a consistent range of wavelengths, it aims to explore questions like what are these planets made of? How did they and their planetary systems form and how do they continue to evolve? The answers could not just further our understanding of faraway worlds and chances of extraterrestrial life, but help put our own Solar System into context. It is scheduled to launch in mid-2028.
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