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Science has found over 5,000 alien worlds, but what do we know about these exoplanets?

In the vast expanse of our universe, with its billions of stars and galaxies, the discovery of over 5,000 exoplanets has led scientists to a compelling realization: there is no such thing as an “ordinary” planet. These distant worlds, far removed from our own, challenge our understanding of outer space.

First exoplanet with a Sun-like star 

It was 1995 when astronomers Michel Mayor and Didier Queloz stumbled upon 51 Pegasi b, the first exoplanet found orbiting a Sun-like star. “The discovery rocked the astronomical world as its characteristics did not fit into the theory of planetary formation at the time,” recalls the European Space Agency

This “hot Jupiter” orbits its star in a mere four days. The planet is tidally locked, forever showing its same face to its star. Adding to the allure, water particles were detected in its atmosphere by 2017.

First with an atmosphere

The art of exoplanet detection evolved, and by 1999, HD 209458 b was discovered using the transit method. As a planet transits or passes in front of its star, the starlight gets absorbed by particles in the atmosphere. 

The historical moment came when the NASA/ESA Hubble Space Telescope measured the atmosphere’s composition, marking it the first of its kind. This exoplanet, later revisited by ESA’s Cheops mission in 2020, has a remarkably dark and cloudless atmosphere.

First exoplanet to be photographed

Direct imaging, another method of detecting exoplanets, introduced us to the enigmatic 2M1207b. This heavyweight, boasting five times the mass of Jupiter, orbits a brown dwarf at a staggering distance, equivalent to 55 times that from Earth to the Sun. 

This exoplanet proudly claimed its title as the first directly imaged planet, courtesy of the European Southern Observatory’s Very Large Telescope in 2004.

First orbiting two stars

Our universe thrives on variety. Some exoplanets, like Kepler 16b, orbit not one, but two stars. This gaseous entity, slightly smaller than Saturn, revolves around a binary star system. Each star is less massive than our Sun, one significantly more so than the other.

First exoplanet with a deformed shape

WASP-103b defies our understanding of planetary shapes. With a mass 1.5 times that of Jupiter, it’s squeezed into an elongated, rugby ball-like form due to intense gravitational interactions with its star. As it whirls around its star in less than a day, it appears to be gradually distancing itself.

First terrestrial exoplanet 

CoRoT-7b is an example of terrestrial planets, but it is a far cry from Earth. Larger by half and six times heavier, its days are molten, and nights, bitterly cold. An unforgiving landscape with no discovered atmosphere to buffer the heat.

First with traces of CO2

The advent of the NASA/ESA/CSA James Webb Space Telescope escalated exoplanet studies. Its keen eyes discerned traces of carbon dioxide in the atmosphere of WASP-39 b – the first-ever confirmation of this molecule on an exoplanet.

First exoplanets orbiting a pulsar 

The pulsar PSR B1257+12 revealed a surprise – two planets in its vicinity. Pulsars, magnetized neutron stars emitting strong radiation, are incredibly precise in their rotations. However, discrepancies in this pulsar’s emission led scientists to its planetary companions.

First synchronized exoplanets 

Diversity reigns supreme in the universe, even in planetary systems. A rhythmic dance is on display around the star TOI-178. Five of its six planets have synchronized orbits, moving in a captivating 18:9:6:4:3 pattern. To an observer, they align at regular intervals, presenting a celestial ballet.

These discoveries highlight the boundless mysteries of our universe. Each exoplanet, with its unique story, pushes the boundaries of our knowledge. As the European Space Agency notes, the exoplanet realm continually challenges our comprehension of the cosmos.

More about the search for exoplanets

Exoplanets, or planets outside our solar system, have intrigued astronomers and the public alike for decades. But how do scientists find these distant worlds, and why does their discovery matter? Let’s dive into the dynamic realm of exoplanet exploration.

Why hunt for exoplanets?

The search for exoplanets isn’t just about finding new worlds; it’s about seeking answers to fundamental questions. Are we alone in the universe? What kinds of planetary systems exist out there? Is there another Earth-like planet? Discovering exoplanets expands our understanding of the universe and the potential for life beyond our solar system.

The tools of the trade: Telescopes and techniques

Transit method

The most successful technique, the transit method, involves monitoring stars for small, regular dips in brightness. When a planet crosses in front of its star from our viewpoint, it blocks a tiny fraction of the star’s light. This event, known as a ‘transit’, gives away the planet’s presence. NASA’s Kepler Space Telescope, launched in 2009, utilized this method and identified thousands of exoplanet candidates.

Radial velocity or doppler method

As a planet orbits its star, it exerts a gravitational tug, causing the star to wobble slightly. Astronomers detect this wobble by observing shifts in the star’s spectrum of light. The European Southern Observatory’s HARPS instrument stands out as a champion in this method, having confirmed dozens of exoplanets.

Direct imaging

Here, astronomers try to capture images of planets directly. Though challenging due to the brightness of stars, advancements in technology have made a few direct images possible, especially for large planets far from their stars.

Gravitational microlensing

This method takes advantage of the gravitational force of stars and planets. When a distant star aligns perfectly with a nearer star, the closer star’s gravity can magnify and brighten the distant star’s light. If the closer star has a planet, it too can act as a lens, producing a noticeable effect in the light curve.

Looking forward

The search for exoplanets has undergone rapid advancements over the past few decades. Future and current missions, like the James Webb Space Telescope and the European Space Agency’s PLATO mission, promise to revolutionize our understanding even further. These telescopes will offer greater sensitivity and precision, enabling the detection of smaller, Earth-like planets in the habitable zones of their host stars.

The search for exoplanets challenges our understanding of the cosmos. Every discovery offers a chance to contemplate our place in the universe and to dream of worlds yet unseen. As technology advances and our gaze deepens, we inch closer to answering some of life’s most profound questions.

Image Credit: ESA

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