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Maitreyi Sanadhya

The Search for a Second Earth




As long as we have remembered, Earth has been a unique planet. There is a very specific set of conditions that must be in place in order for life to exist; the planet/astronomical body must exist in what is known as a ‘Goldilocks Zone,’ a zone a certain distance away from the solar system’s star where water can be liquid, an atmosphere that does not consist of toxic gases, slow interplanetary winds, a magnetic field to hold the atmosphere in place, and dozens more prerequisite conditions. The probability of these conditions to exist simultaneously is a very slim one. Life is carbon-based, so organic hydrocarbons need to exist. Theoretically, a silicone-based life form could exist somewhere, but the ratio of carbon to silicon atoms within the universe makes it more probable that alien life will also be carbon-based, however, germanium-based life is also a probability, but since it is rarer than even silicon, the chances remain slim.


Nonetheless, Earth possesses all of these conditions; many scientists and philosophers have believed for centuries that we are alone in the universe. However, due to developing technology, our telescopes are now able to see further and further into the night sky, putting Galilean observations to shame. Satellites have been launched into space, the most recent being TESS (Transiting Exoplanet Survey Satellite) and based on predictions, by the end of its two-year mission, around 3,000 more exoplanets will have been discovered. Furthermore, missions here on Earth to search for these masked exoplanets are being conducted, the most notorious being the TRAPPIST project, which discovered three Earth-sized planets orbiting a star. Two are tidally locked, mimicking the motions of the moon around the Earth, rendering them less optimal for life, but there is a third that is just on the brink of the habitable “Goldilocks” zone. Due to the rate of technological development, by 2020, we will be able to simply observe a planet and deduce its atmospheric composition.


How? It all begins with transit photometry. The term transit photometry may be wordy, but the concept is rather simple; the brightness of a star is observed, and any periodic dimmings are recorded. If the star dims at a regular interval, then we may infer that a planet in orbit is blocking it, hence the regular time intervals between dimmings. This method may be painstaking, as some planets have very long orbit times - take Pluto, for example; its orbit is no lesser than 248 Earth years. Since its discovery, it has not even completed one complete orbit of the sun. - As the planet is passing, we can observe the light filtering in through the atmosphere, which helps us deduce its composition. The method is based on the principle of absorption of light by certain compounds. For example, carbon dioxide in gas form absorbs light at a wavelength of 15 nanometers. By mapping out the exoplanet’s entire spectrum of light emission, we can find the gaps in the light emitted and cross-reference the elements present within the atmosphere. Even our sun does not emit the full spectrum of light, as its composition of hydrogen results in the absorption of light emitted at certain wavelengths. A diagram showing hydrogen absorption bands is displayed below:


What does this all imply? Due to new scientific processes, we can now observe an exoplanet and know to a high degree of certainty what its atmosphere is composed of. The relative uncertainty remains low despite the redshift that occurs when light travels long distances, as shifts in light spectrum are always factored in and calculated using the principles of the Doppler effect. Research conducted into this field is crucial, especially now, as our planet is facing a global warming crisis, and if action is not taken within the next couple of decades, the harm done to our world will be irreversible. We are still many stages away from actually reaching these exoplanets, as progression in space transport has slowed since the Cold War due to funding being allocated elsewhere. For us to reach these planets in a reasonable time frame, we would have to travel almost at the speed of light; the nearest star to our sun is 4.22 light years away, virtually impossible for us to reach as of now. If our solar system’s sun had been in a globular cluster (a group of stars locked together with their gravity), then it would have been easier to travel between systems, as stars in globular clusters have distances between them of only 1 lightyear at times, but remain isolated for now, on the outer edges of the Perseus galactic arm. For now, all we can do is point our telescopes into the vast cosmos and search for a planet that our descendants may one day call ‘home.’


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