There are billions of stars and planets just in our galaxy. These exoplanets like our earth revolve around their star(s). How many of them could contain life like on Earth? To answer this question, scientists are looking at distant planets for signs of life. For life as we know it to be sustainable on a planet, it should first be located in a region around it’s star called as the habitable zone.
What are exoplanets in a habitable zone?
Exoplanets are planets that are outside our Solar System. Our solar system has 8 planets orbiting the sun. Any planet outside this system will not orbit the sun but another star as part of another star system.
A habitable zone or the Goldilocks zone of a star system is a region around the star where an orbiting planet has conditions similar to that on earth. In our star system, the Solar System, Earth is the only planet that is located in the habitable zone. A planet in the habitable zone has the right temperature for liquid water to exist. Water is the most essential component of life. There are many more requirements for human life to be possible on an exoplanet but the first steps are habitable zone and water.
Water discovered in a new exoplanet
Scientists have discovered a new exoplanet with water vapour in its atmosphere. This exoplanet orbits a star that is 110 light years away from earth. It is so far away that even light, the fastest thing there is, takes 110 years to reach us from this planet.
The discovery, published in Nature Astronomy, is the first successful atmospheric detection for an exoplanet orbiting in its star’s habitable zone (1). This planet is named K2-18 b and is 8 times more massive than earth.
Scientists detected water in K2-18 b’s atmosphere by studying the light that passes through it. When light from a star passes through the atmosphere of a planet, it interacts with molecules in the atmosphere. The light exiting this atmosphere has a spectral signature of the atmosphere that it just passed through. This spectral signature can be analysed to identify the molecular properties of the atmosphere. The Hubble Space telescope captured the light from this planet a few years ago. Scientists then analysed this light and were surprised to find spectral signatures of water vapour in this light (1, 2). They also identified hydrogen and helium in this signature which are common for celestial objects.
Is there life on exoplanet K2-18 b?
There is currently no evidence supporting the presence of life on this exoplanet.
Discovery of water vapour in K2-18 b is certainly exciting news but it is just the beginning. Although water is the most essential component of life, there are other requirements that need to be satisfied for life, as we know it, to exist. The star that this exoplanet orbits, K2-18, is a cool but highly active dwarf star (it is not as hot as the sun). This means that radioactivity around this planet might be extremely high, making it unsuitable for life as we know it. The authors also write that other molecules including nitrogen and methane may be present in this planets atmosphere. However, current observations cannot confirm this. Moreover, further studies are required to estimate cloud coverage and the percentage of atmospheric water present. Therefore, at this
The next generation of space telescopes, including the NASA/ESA/CSA James Webb Space Telescope and ESA’s ARIEL mission, will be able to characterise atmospheres in more detail as they will carry more advanced instruments. ARIEL is expected to launch in 2028, and will observe 1,000 planets in detail to get a truly representative picture of what they are like.
“This study contributes to our understanding of habitable worlds beyond our Solar System and marks a new era in exoplanet research, crucial to ultimately place the Earth, our only home, into the greater picture of the Cosmos,” said Dr Angelos Tsiaras, lead author of the study.
- 1.A. Tsiaras, I. P. Waldmann, G. Tinetti, J. Tennyson, S. N. Yurchenko, Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b. Nat Astron (2019), doi:10.1038/s41550-019-0878-9.
- 2.Benneke et al., Water Vapor on the Habitable-Zone Exoplanet K2-18b. arXiv. 1909 (2019).