A Step Closer to Finding Signs of Life in Alien Atmospheres

The discovery of the first?exoplanets?in the early 1990s was another pivotal moment in our understanding of Earth's place in the vast, visible universe. Although we can imagine and predict the existence of worlds orbiting other Sun-like stars that may be larger, smaller, hotter, or colder than ours, detecting exoplanets is now possible. Stars are planets that do not orbit our Sun as part of our solar system.

PSR B1257+12 was interesting as it is a member of a particular group of pulsars, called a millisecond pulsar, making an incredible 161 rotations per second. Pulsars are the remanences of a massive star after exploding, called a supernova explosion, at the end of its life. The first two exoplanets were officially announced in 1992 by astronomer Alex Wolszczan orbiting the millisecond pulsar PSR B1257+12. The two discovered planets were both at 4 Earth masses and orbiting the pulsar on slightly elliptical orbits lasting 65 and 98 days.?

The first exoplanet around a Sun-like star was discovered in 1995 by astronomer Michael Mayor and Didier Queloz. The planet Pegasi 51 is fifty light years away from Earth and is famously recognised as the first discovery of a 'proper' exoplanet. Planet?51 Pegasi b?is a giant gas planet with a minimum mass of approximately one-half the size of Jupiter. What makes this planet very interesting is its proximity to its host star. 51 Pegasi b orbits the star at 0.05 AU (Earth orbits), bringing it closer to its star than Mercury is to our Sun. It makes 51 Pegasi b a?hot Jupiter?with blistering temperatures around 1000 °C in its outer atmosphere. Heat increases the radius of this planet to ca. 25% larger radius since the high temperatures expand its atmosphere.

According to?Wikipedia, as of August 1st, 2022, we have 5,125 confirmed exoplanets in 3,794 planetary systems, with 829 systems having more than one planet. The planets can be grouped roughly into four major classes:

1. 30% Gas Giants: the size of Saturn or Jupiter or many times bigger
2. 35% Neptune-like: these can be ice giants or much warmer with sizes around Neptune or Uranus
3. 31% Super-Earth: planets the size between Earth and Neptune, which might be rocky worlds like Earth or more like a mini-Neptune likely to be shrouded in an extended atmosphere
4. 4% terrestrial planets: minor, rocky planets around the size of Earth.

The search for atmospheres around planets makes planet hunting even more enjoyable. The composition of a planet's atmosphere is an important indicator of whether a planet could support life as we know it. The most important components are oxygen, water, carbon dioxide, and methane. The latter is likely, but not restricted, to be produced by living systems due to its short shelf life if not replenished frequently.?Life would do that.

One primary technique to analyse exoplanet atmospheres is to observe the planet's transit in different wavelengths of light. Starlight is composed of different wavelengths ranging from low to high energy waves. During the planet's transit through the star's light, small amounts of it pass through the planet's atmosphere on the way to Earth. If such light passes to different molecules in the planet's atmosphere, particular wavelengths with different energies are absorbed. It gives each molecule an 'absorption fingerprint', and the atmosphere viewed at these wavelengths turns opaque, allowing the atmosphere to appear slightly larger. The technique of recording these 'fingerprints' is called?transmission spectroscopy.

NASA's?James Webb Space Telescope?captured the first clear evidence of carbon dioxide outside the solar system in a planet's atmosphere. The planet is named?WASP-39 b?and is a hot gas giant with a mass roughly one-quarter that of Jupiter, which makes it closer to the size of Saturn, with a diameter 1.3 times greater than Jupiter's. The gas giant is orbiting a Sun-like star, WASP-39, 700 light-years away. This observation provides essential insights into the composition and formation of the planet. It offers evidence that in the future, Webb may be able to detect and measure carbon dioxide in the thinner atmospheres of smaller, rocky planets.

What do you think: will we detect a biosignature of an exoplanet soon, even before we find it in our solar system? What are the implications?

To read more: https://www.jpl.nasa.gov/news/nasas-webb-detects-carbon-dioxide-in-exoplanet-atmosphere