Searching for Aliens from our Backyard

Copernicus removed Earth from the centre of the Universe, and by placing it in orbit around an ordinary star, our Sun (and consequently later astronomers placing that star one among hundreds of billions in an ordinary galaxy in a universe that has hundreds of billions of galaxies) has made the biggest revolution in the history of natural philosophy. Darwinian evolution has dethroned humans from special creation and showed us to be a ‘beast’ like any other species originating in the African savanna whose fossils anthropologists discover all the time. Now we sit lonely at the 3rd rock from the Sun and think that are we the only thinking and sapient in the heartbreakingly large Universe that started about 13.8 billion years ago? Are there other sapient aliens thinking the same, sitting at a waterhole of a planet orbiting some faraway star?

For many years, the SETI project has been trying even to drop radio messages sent by extraterrestrial intelligent civilisations. But to date, there is absolute radio silence, with our radio telescope natural humming and hiss emitted by ionised hydrogen recapturing their lone electrons, not an SOS by a galactic hitchhiker or a love letter by an alien to his GF to a galaxy far, far away. There are three possibilities. One technologically advanced ET is absent or very rare, or there is a protocol not to disturb or interfere with backward species like us, so they are hiding their messages in disguise of natural radio signals. Second, their communication technology uses exotic science that we have yet to discover. The third possibility is that no technologically advanced intelligent ET has yet evolved in our galaxy’s backyard.

Our galaxy is a large place if a star goes supernova on the other side of the galaxy. Its light will reach us only after about 80 thousand years. Suppose there is a technologically advanced civilisation evolved on the other side of our galaxy. A lakh years back, their automated reconnaissance mission landed on a continent that we call Africa. The mission found a species of ape that had just invented firemaking. A report was sent using a radio transmitter stating that a species of ape is evolving and has the potential to become a technologically advanced species. It is only now they must have received the report and if they have sent the typical handshake message ‘Hello Earthlings’! We will get this message in the year 102023 AD!

Another popular approach among astrobiologists is looking for signs of basic life in the Universe. This bottom-up quest for life in the Universe has led to success in the last few decades. First, it started with searching for planets orbiting around other stars. Kepler and other missions have found about 6140 planets in 4527 planetary systems. 85% of these planets are too close to their stars to have life because they are tidally locked to their ‘Sun’ like our Moon is to Earth. Such planets will have one side burnt out and the other permanently frozen. About one in five Sun-like stars have an earth-size planet in the habitable zone. Assuming there are 400 billion stars in the Milky Way. This means that there are 22 billion Earth-like habitable planets out there. Soon, the James Webb space telescope will not only discover more such planets, but it will also be able to find the atmospheric composition of such planets.

Mercury and Venus were found to be inhospitable to life due to harsh conditions found on these inner planets. Mars initially showed lots of promise as an abode of microbial life. Initially, in the solar system’s history, Mars may have been suitable for life in the past as it had liquid water and still possessed lots of frozen water in polar regions and maybe a lot in other places. The lack of an earth-like strong global magnetic field brings hard radiation of solar storms to its surface, and additionally, the Martian surface is made sterile by UV radiation. But many icy moons of Jupiter and Saturn hold a substantial subsurface ocean. Ganymede, Callisto, Europa of Jupiter and Titan and Enceladus of Saturn are moons that have the potential to support microbial life. The source of energy in such hypothetical ocean worlds would not be the Sun but the partial tidal melting of these Moon by their host planets. Organic compounds that are precursors to life have been found on some of these moons.

In the coming decades, NASA and the European Space Agency have meticulously planned and are set to execute many missions to these moons, aiming to find aliens in our backyards.

Europa Clipper: Europa Clipper will explore Europa, investigate its habitability and aid in selecting a landing site for the future Europa Lander. This exploration focuses on understanding life’s three main requirements: liquid water, chemistry, and energy.

Europa Lander: to be launched in 2027 to complement Europa Clipper mission. The mission’s objectives are to search for biosignatures at the subsurface ≈10 cm, characterise the composition of non-ice near-subsurface material, and determine the proximity of liquid water and recently erupted material near the lander’s location.

Dragonfly mission to Titan: A robotic rotorcraft mission to the Largest Moon of Saturn with an atmosphere thicker than the Earth. It will be launched in 2028. It will study the prebiotic atmosphere of the Titan, which is quite similar to the Earth before the origin of life.

Future Astrobiology mission concepts under consideration to water worlds in the outer Solar System:

• Enceladus Explorer (EnEx)
• Enceladus Life Finder (ELF)
• Enceladus Life Signatures and Habitability (ELSAH)
• Explorer of Enceladus and Titan (E2T)
• Journey to Enceladus and Titan (JET)
• Jupiter Icy Moons Explorer (JUICE)
• Life Investigation For Enceladus (LIFE)
• Neptune Odyssey
• Titan Lake In-situ Sampling Propelled Explorer (TALISE)
• Titan Mare Explorer (TiME)
• Trident for Triton