The formation of planets over a long timescale naturally involves some events that are not good for the well-being of their potential inhabitants. These events include giant collisions with surrounding celestial bodies, which eventually merge with the planet after the impact, thus increasing its mass, or chop a part of its rocky crust off and eject it into space, like it might have happen with our Moon.

Although these events are definitely cataclysmic, they could still provide benefits for astronomy by pinpointing the exact location of their occurrence.

A team of astronomers from the United States proposed an idea to search for spectral signatures, which may indicate the atmosphere of an exoplanet disturbed by a giant impact event. A paper has recently appeared at arXiv.org. The authors claim that the method may be particularly suitable for detecting the Earth-like worlds, which chemical composition is identical or at least very similar to our home planet.

The arguments supporting this idea are based on the theoretical analysis of atmospheric chemistry, photochemistry and spectral signatures of different atmospheric mixtures, consisting predominantly of carbon dioxide (CO 2 ) and water vapor (H 2 O). During the study these hypothetical mixtures also included approximately 800 additional compounds (solid, liquid and gas), which are typical to the atmosphere and lithosphere of the Earth. These compounds were mixed in different proportions and combined with varied thermal conditions to resemble a post-giant-impact terrestrial planet.

A surviving post-giant-impact planet would be surely heated by the energy released during the impact. The heat would generate a dense and thick atmosphere layer, rich in steam and carbon dioxide. These environmental conditions may remain for millions of years, making the planet especially bright, visible and potentially easily detectable in the near-infrared range of spectrum. The aftereffects of the giant impact would make the terrestrial planets significantly easier to observe compared to their older, cold and stable counterparts, according to the team.

The computer simulation revealed that the post-impact atmosphere chemistry would definitely contain characteristic molecules, namely HCl, HF, alkali halides, SO 2 and other sulfur-bearing compounds, which are not expected in cooler atmospheres. The team suggests that the spectral signatures of these compounds could be used as markers for detection of post-giant impact Earth-like planets. The authors predict that one such planet may be discovered for every 10-50 stars surveyed in young stellar clusters, based on the expected frequency of terrestrial planets.

The scientists also note that these observations require equipment with higher level of spectral resolution and contrast than the currently available. However, some conclusions may be done by comparing spectrums of different exoplanets (e.g. post-impact terrestrial planets are expected to be notably redder than young giant planets), although more detailed studies would be accessible only with the largest modern telescopes.

By Alius Noreika, Source: www.technology.org