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What do you think of when it comes to extra terrestrial life? Most popular sci-fi books and TV shows suggest humanoid beings could live on other planets. But when astronomers are searching for extra-terrestrial life, it is usually in the form of emissions from bacteria or other tiny organisms.<\/p>\n
A new research paper in the Astrophysical Journal suggests that Cambridge scientists have\u00a0managed to find this type of emission<\/a>\u00a0with a certainty of 99.7% from a planet called K2-18b, 124 light years away. They used Nasa\u2019s\u00a0James Webb Space Telescope<\/a>\u00a0to analyse the chemical composition of the planet\u2019s atmosphere and say they found\u00a0promising evidence<\/a>\u00a0K2-18b could host life.<\/p>\n It\u2019s an exciting breakthrough but it doesn\u2019t confirm alien life.<\/p>\n Let\u2019s look at why scientists largely do not accept the paper as proof of alien life.<\/p>\n Exoplanet hunting fell out of public interest quickly due to the staggering number of planets scientists are discovering. The first convincing exoplanet around a sun-like star was\u00a0discovered in 1995<\/a>\u00a0via\u00a0radial velocity<\/a>, where you don\u2019t look at the planet but instead observe its effect on its nearest star. As the star wobbles back and forth it causes a tiny shift in the wavelength of the light it emits, which we can measure. We already know of\u00a0roughly 7,500 planets<\/a>.<\/p>\n Only\u00a043 (to date)<\/a>\u00a0have been observed directly (about 0.5% of them). Most are discovered through indirect means, such as radial velocity or the\u00a0transit method<\/a>. The transit method is where you look at how the brightness of the star decreases as the planet passes in front of it. It will block a tiny amount of the light.<\/p>\n Looking at the atmosphere of an exoplanet is even more difficult. Scientists use\u00a0spectroscopy<\/a>\u00a0to do this. The light coming out of the star can be observed directly and a small amount of it will also pass through the atmosphere of the planet. Researchers can estimate what an exoplanet\u2019s atmosphere is made of by studying\u00a0which light from the star is emitted or absorbed<\/a>\u00a0in the atmosphere.<\/p>\n Let\u2019s try an analogy. You have a desk lamp at one end of a long table and you are standing at the other end, looking at the lamp. There is a glass of liquid in between you and the lamp. In very simple terms, the glass of liquid acting as the exoplanet and atmosphere, looks slightly blue, which allows you to identify it as water. In reality for scientists though, it\u2019s more like the glass of water is a tiny glass bead which is rolling around while someone is messing around with a dimmer switch on the lamp. Then, freak weather results in a gentle mist forming on the table. The liquid is 99% pure water and 1% mineral water and the scientist is trying to see what minerals are in the water.<\/p>\n You can see that the expertise required to be perform this work is incredible. They observed molecules with a 99.7% confidence rate, which is a remarkable achievement.<\/p>\n The key data in this study is in a graph fitting light absorption rates to which kind of molecules could be there and working out how abundant they are. It features in this short film about the discovery.<\/p>\nWhy it\u2019s so hard to detect to alien life<\/strong><\/h4>\n
An exoplanet atmosphere<\/strong><\/h4>\n
The data from JWST and K2-18b<\/strong><\/h4>\n