[ad_1]
With more than 4,000 exoplanets – planets in orbit other than our sun – discoveries so far, it may seem like we are about to discover if we are alone in the universe. Unfortunately, we do not know much about these planets – in most cases, their mass and radius.
Understanding if a planet could host life requires a lot more information. At the present time, an extremely important piece of information is missing, namely the presence, composition and structure of their atmospheres. The signs of atmospheric water, oxygen and methane would all be signs that a planet could support life.
Now we have succeeded for the first time in detecting water vapor in the atmosphere of a potentially habitable exoplanet. Our results have been published in Nature Astronomy.
The atmosphere of a planet plays a vital role in the formation of conditions within it – or on its surface, as the case may be. Its composition, stability and structure all provide important insights into what it means to be there. Thanks to atmospheric studies, we can learn more about the history of the planet, study its habitability and, ultimately, discover signs of life.
Transit spectroscopy is the main method we use to examine exoplanets. This involves starlighting when a planet passes in front of its host star. As it transitions, starlight is filtered through the planet's atmosphere – light being absorbed or diverted depending on the components of the atmosphere.
The atmosphere therefore leaves a characteristic imprint in the starlight that we are trying to observe. Further analysis can then help us to match this fingerprint to known elements and molecules, such as water or methane.
For the moment, the study of atmospheres of exoplanets is limited, because this type of measurement requires a very high precision, for which the current instruments have not been designed. But molecular signatures of water have been found in the atmospheres of gaseous planets, similar to those of Jupiter or Neptune. This has never been seen before on small planets – until now.
K2-18b
K2-18b was discovered in 2015 and is one of hundreds of super-Earth-planets whose mass is between Earth and Neptune – discovered by NASA's Kepler probe. It's a planet with eight times the mass of the Earth that revolves around a so-called red dwarf star, much colder than the sun.
However, K2-18b is located in the habitable zone of its star, which means that it has the right temperature to support the liquid water. Given its mass and radius, K2-18b is not a gaseous planet but has a high probability of having a rocky surface.
We have developed algorithms to analyze starlight filtered by this planet using transit spectroscopy, using data from the Hubble Space Telescope.
This allowed us to realize the first successful detection of a water vapor atmosphere around a non-gas planet, also located in the habitable zone of its star.
For an exoplanet to be defined as livable, there is a long list of requirements to satisfy. The first is that the planet must be in the habitable zone where water can exist in liquid form. It is also necessary that the planet has an atmosphere allowing it to protect itself from any harmful radiation coming from its host star.
Another important element is the presence of water, vital for life as we know it. Although there are many other criteria of habitability, such as the presence of oxygen in the atmosphere, our research has made K2-18b the best candidate so far. It is the only exoplanet to fulfill the three conditions of habitability: the right temperatures, an atmosphere and the presence of water.
However, we can not say, with the current data, what is the probability that the planet supports life. Our data is limited to one area of the spectrum – this shows how much light is broken down by wavelength – where water dominates, so that other molecules can not unfortunately be confirmed.
First of many?
The next generation of telescopes, such as the James Webb Space Telescope and the ARIEL Space Mission, will allow us to find more information on the chemical composition, cloud cover and atmospheric structure of K2-18b. . This will help us understand how habitable it is.
These missions could also facilitate the detection of similar rock bodies in habitable areas of their parent stars.
It would certainly be exciting. K2-18b being 110 light-years away from the planet, it's not really a planet we could visit – even with tiny robotic probes – in the foreseeable future.
What's exciting is probably just a matter of time before we find similar planets closer. So perhaps we are on the right track to answer the age-old question of whether we are alone in the universe after all.
Angelos Tsiaras is a research associate in physics and astronomy at UCL.
This article first appeared in The Conversation.
[ad_2]
Source link