Wonders of Exoplanets: Theoretical perspective of exploring Exoplanet

Thousands of exoplanets have been identified, and astronomers continue to discover more each year. These incredible planets holds a path for future life, making them a crucial study area for modern astronomy.

Introduction

Studying these planets provides valuable insights into the formation and evolution of planetary systems and will shed light on the possibility of finding habitable worlds beyond our solar system. Exoplanets could and will significantly shape the future of humanity’s exploration of space. This article traces the fundamentals of exoplanets; section 1 will explore the basis of exoplanets and the basic needs for life, section 2 will cover why we search of exoplanets and the reasons behind it and finally section 3 examines the methods of finding them distant planets from earth and space.

Basic of exoplanets

Exoplanets, also called extrasolar planets, are celestial bodies that orbit stars other than the Sun. The detection of exoplanets has been a significant area of research in astronomy since their first discovery in the 1990's. Exoplanets exhibit diverse physical characteristics, such as size and composition. Some are rocky and similar to Earth, while others are gas giants like Jupiter. A large group of these exoplanets are inhabitable but a subset of them resides within their parent star’s habitable zone, known as the Goldilocks zone (Kenney, 2017). In this zone, a planet’s surface temperature stays between 32°F and 212°F (0°C and 100°C). This is the temperature at which water takes the form of liquid, thus creating basic needs for a planet (Kenney, 2017). But as well, an exoplanet needs to have enough mass, and enough gravity, to sustain an atmosphere, which creates a perfect environment for life (Kenney, 2017). This zone is different in every solar system due to the difference in mass and the life expectancy of the star (Kenney, 2017). Being too close to the sun, e.g. Mars, will burn the surface of the planet and destroy all the life on the planet. This also happens to a planet which is too far away from the Sun, e.g. Neptun. So, if an exoplanet is to hold life, it will need to be at a distance where the sun can grant the planet warmth and not be too close where the sun can emit its flares and damage the atmosphere of the planet (Kenney, 2017).

Some exoplanets are free-floating objects, most commonly known as rogue planets. This occurs when a planet lacks any binding association with a star. While these planets are presumed to be widespread throughout the universe, their detection remains challenging, as they do not emit detectable light and can only be detected from their gravitational influence on other celestial objects (Paul M. 2022 February 02). Despite the Goldilocks zone, there is a theory that an exoplanet, which is a rough planet, can still hold life without the need for the Sun (Paul M. 2022 February 02). While there is no Sun to heat the surface of the planet, there still is internal heat, as the magma inside the planet would still be hot, meaning if internal heat is still inside a planet, there is potential for liquid water, which means there is a potential for life on the exoplanet (Paul M. 2022 February 02). But rogue planets are not easy to find so the expectation of reaching one is only imaginable.

Why do we look for them?

As we gather more data on exoplanets and their potential for supporting extraterrestrial life, we can better understand our place as a minor planet within the vastness of our galaxy and universe. Furthermore, exploring exoplanets can offer valuable insights into the formation and evolution of planets and stars. By comparing the characteristics of exoplanets with those of planets within our solar system, researchers can obtain a deeper comprehension of planetary formation processes. Despite the challenges associated with detecting signs of life on exoplanets, such as the presence of biomarkers in atmospheres, astronomers have kept searching for exoplanets by using many methods to find a perfect earth-like planet. As the earth and its materials are decreasing, exoplanets are an opportunity to colonies and create new life on earth like exoplanets, but this exploration is difficult at the current level of technologies we currently possess. From exoplanets to stars, we gain a larger sense of the universe and how it was created and where it is headed. With thousands of exoplanets identified so far and more being discovered each year, it is clear that the study of exoplanets is a crucial part of our exploration of the cosmos.

Methods for Finding Exoplanets

Astronomers use a variety of techniques to detect these distant worlds, each with its advantages and limitations. But even though these methods do help find exoplanets, it still is difficult to accurately state whether it is an exoplanet or not. The methods include the transit method, radial velocity, direct imaging, gravitational microlensing, astrometry, and pulsar timing. But not all are used because some exoplanets can be found in such a way, e.g. a rough planet does not have a sun, so the transit method can’t be used.

Transit method

Thus far, 3795 planets have been found through this method (Exoplanet EU). The transit method refers to when an exoplanet passes directly through the observer, meaning the telescope, and the star it orbits (NASA: Exoplanet expiration Planets beyond our Solar System). This causes the starlight to be dimmer at times; this repeating movement shows us that there are exoplanets passing through, hence the name “transit” (NASA: Exoplanet expiration Planets beyond our Solar System). These changes in brightness are characterized to be very small, have fixed periods and are repeating. How much the star dims is up to the exoplanet, as the size of the planet will either make the planet more easily visible or not (NASA: Exoplanet expiration Planets beyond our Solar System). E.g., If there is a small planet transiting a giant star, the starlight will not be as dim as if more giant planets were orbiting a small star. The transit method can identify the size of the planets, but when it is combined with the Radial velocity, it can measure the mass of the planet, and we can fully understand the mass and size of the planet. This can lead us to understand the structure and characteristics of the planet, e.g. if the planet is a gas giant or a rocky planet, in which we can know if the planet is habitable or not.

Radial velocity

Radical velocity is very effective to use and one of the first methods which was used to find exoplanets. This method refers to the wobbling motion of a star, which can be seen from Earth and 1049 planets have been discovered to this day (Exoplanet EU). The method used to find exoplanets is called the “Doppler shift” which was founded by Christian Johann Doppler in the nineteenth century (Molecular Expressions: science Optics and you pioneers in optics). Doppler shift or the Doppler effect refers to changes in light frequency or wavelength caused by light source motion relative to observers. Changes in the wavelength change how we perceive the energy that we’re seeing or listening to. As sound waves scrunch together, they sound higher in pitch. And when visible light waves scrunch together, they look more blue in colour. When sound waves stretch out, they sound lower in pitch. And when visible light waves stretch out, they make an object look more red. This change in colour is called ‘redshift’, and this is how we identify if an object is getting closer to us or further away from us (NASA: Exoplanet expiration Planets beyond our Solar System). So by using this method we can understand if a star has a planet, how many and the exoplanets sizes (NASA: Exoplanet expiration Planets beyond our Solar System).

Direct imaging

This method does not allow astronomers to measure the mass of a planet directly, but they can use the spectrum and brightness to get information about its surface temperature and diameter. Thus far 228 planets have been found (Exoplanet EU). Direct imaging is one of the hardest to achieve, this is due to the difficulty of picturing planets when there are stars much brighter. Any of the light and radiation being reflected off the planet is, again cleared out as its sun creates more light and more radiation than the planet (NASA: Exoplanet expiration Planets beyond our Solar System). So due to this, Direct imaging uses infrared wavelengths to observe planets. Infrared wavelengths of a star like the Sun is only 100 times brighter than Jupiter, compared to a billion times brighter at visual wavelengths (Las Cumbres Observatory: Space book: 4.Exoplanets). As well as this astronomers have created two main methods to block out the light from the star, so a better image can be created of the planets. One is called coronagraphy, this device is inside a telescope, it blocks the light from the star before it reaches the telescope detector. This is used for ground based telescopes and it is built as an add-on for the telescope. Another is the “starshade”, this method uses a spacecraft which is designed to position itself at the right distance and angle so the starlight from the star will be blocked, leading to the starlight not reaching the telescope and a clear image being captured. As direct imaging is hard to achieve we can get a clear understanding of the surface temperature and diameter of an exoplanet. So this method is important to understand the overall habitability of the exoplanet.

Gravitational Microlensing

Thus far 253 planets have been found using this method. Gravitational microlensing is when one star passes in front of another star. The farther away star emits light to the observer in a direct line but when the other star goes in front of the distant star the light starts to bend due to the gravity of the other star. While the light bends we can see that the distant star is magnified from the point of the observer. While this is going on, if the distant star gets more magnified over time, that means there are more objects bending the light, thus we can identify that there are exoplanets orbiting the star. Astronomers can’t predict when or where these events will happen. So they have to watch the sky over a long period of time. When they record a star getting brighter and then dimming in the pattern of lensing objects, they can analyse the data to get information about the size of the star. Sometimes, rogue planets will cause quick events that astronomers can record. These events give us an idea of how common these rogue planets are in the galaxy.

Astormetery

Thus far only 20 planets have been found from astrometry (Exoplanet EU), due to the method needing precise measurements to a star’s position over time to detect a wobble. So in order to track the movement of the stars, scientists take a series of images of a star and some of the other stars that are near it. In each picture, they compare the distances between these reference stars and the star they’re checking for exoplanets. And if the star has moved in relation to the other star, there is a high possibility of exoplanets. But even though an exoplanet can be detected we can’t understand its size or components of the exoplanet (NASA: Exoplanet expiration Planets beyond our Solar System). So this method isn’t very effective to understand and learn about the features of exoplanets and instead identify where there are exoplanets.

Pulsar timing

Thus far 50 planets have been found using this method. This method uses a Pulsar, which is a rapidly rotating neutron star. But when an exoplanet orbits an neutron star, its chances of being a habitable planet is nothing as a neutron star is the extremely dense remnant of a star that exploded as a supernova so high-energy radiation emitted by the pulsars is very intense. pulsars emit intense electromagnetic radiation that is detected on Earth as regular and precisely timed pulses but depending on the speed of the rotation of the pulsar the timed pulses changes as well. So changes in the timing of the pulses indicate that the pulsar is moving back and forth, orbiting the centre of mass of a system with one or more planets. Astronomers can find out the orbit and the mass of the planets by precisely measuring irregularities in the timing of the pulsars. Even though we can find exoplanets, they are inhabitable so we have no chance of living there or even near it.

References

1. Kenney, K. L. (2017). Exoplanets: Worlds beyond our Solar System
2. Paul M. (2022 February 02). The Best Planets are Rogue Planets — https://www.discovery.com/space/the-best-planets-are-rogue-planets
3. NASA: Exoplanet expiration Planets beyond our Solar System: 5 Ways to Find a Planet — https://exoplanets.nasa.gov/alien-worlds/ways-to-find-a-planet/
4. Molecular Expressions: science Optics and you pioneers in optics — https://micro.magnet.fsu.edu/optics/timeline/people/doppler.html#:~:text=Christian%20Johann%20Doppler%20was%20a,conceptions%20of%20sound%20and%20light.
5. Las Cumbres Observatory: Space book: 4.Exoplanets -https://lco.global/spacebook/exoplanets/
6. Exoplanet EU — http://exoplanet.eu/catalog/