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Explainer: What are exoplanets?


Exoplanets remain one of the most significant discoveries astronomers have made, and the knowledge of their existence has broadened our understanding of the universe.

The year 2022 will mark 30 years since the first exoplanet was discovered, and while over 4,000 have been detected since, they still remain somewhat of a mystery.

What are exoplanets?

To put it simply, while all planets in the solar system orbit around the sun, planets that orbit around stars are called exoplanets.


While there are many still yet to be found, the first was discovered later in space exploration as they are extremely difficult to detect due to the brightness of the stars they orbit.

The Greek translation of exo means outside’ or outer and in regard to these particular planets, they are extremely far away.

However, over 2,000 exoplanets discovered have been found to only be 50 light years away, and even closer than that is Earth’s nearest neighbor, the Alpha Centauri, just 4.2 light years in distance.  

How and when was the first exoplanet discovered?


The first exoplanet was found in 1992, by astronomers Alexander Wolszczan and Dale Frail.

According to Astronomy.com, the discovery was an accident, as the astronomers were originally researching a neutron star. But it led to one of the most significant breakthroughs in space history.  

A neutron star is the second densest object in the universe – just after blackholes – and are formed when a giant star dies.

However, some of these neutron stars are called pulsars, because they regularly give off pulses detected by their radio frequency. In this scenario, the astronomers saw that this particular pulsar, PSR B1257+12, 2300 light-years away, had an irregular pulse, which was highly unusual.

This led to Wolszczan and Frail concluding the pulsar had two planets surrounding it, and as they orbited the neutron star, its pulse became inconsistent.

How do astronomers find exoplanets?

As mentioned above, exoplanets are difficult to detect, but astronomers have found multiple methods to assist in the hunt.

The first is called the “wobble method, or scientifically known as the “radial velocity method.

According to NASA, stars that have planets around them will not perfectly orbit around their centre, therefore the star will appear like its wobbling.

Through this, hundreds of planets have been discovered, however the method falls short when looking for smaller Earth-like planets that create small wobbles that are even harder to detect.

Therefore, the “transit method was established, and this has been the benchmark upon thousands of exoplanet discoveries.

A transit occurs when a planet passes between a star and its observer, NASA says.

“Transits reveal an exoplanet not because we directly see it from many light-years away, but because the planet passing in front of its star ever so slightly dims its light,” the American agency explains.

“This dimming can be seen in light curves – graphs showing light received over a period of time. When the exoplanet passes in front of the star, the light curve will show a dip in brightness.”

While the transit method has underpinned many discoveries, the change of brightness during a transit can be insignificant, depending on the size of the planet.

According to the University of Montreal, for a star the scope of the sun, the transit of a Jupiter-size planet will cause a decrease in radiance of about one percent, and an Earth-like planet will only show a decrease of brightness of about 0.001 per cent.

Despite that, transits have enabled astronomers to not only detect exoplanets’ existence, but also their size, how long they take to orbit, and even their atmosphere.

Last year, astronomers discovered an extreme ultra-hot Jupiter that orbits its star in only 16 hours, the shortest time ever noted.

Exoplanets typically orbit their stars in around 10 days or less, compared to Jupiter’s 12-year orbit.

NASA’s Kepler mission

Almost 20 years after the discovery of exoplanets, NASA launched a spacecraft called Kepler into space to look for more of these star-orbiting planets.

It blasted off on 7 March 2009 and remained in space for 9.6 years.

It left a legacy of more than 2,600 exoplanets discovered outside of our solar system, and many were noted to be promising places for life.

While Kepler retired in 2018, its successor, NASA and MIT’s Transitioning Exoplanet Survey Satellite (TESS) launched in April the same year to continue its work.

It is still in orbit now, and its catalog of planet candidates passed 5,000 TESS Objects of Interests in December 2021.

Australia and the search for exoplanets

Searching for exoplanets is a worldwide mission, as they provide invaluable data about planets that could sustain life.

The Anglo-Australian Planet Search (AAPS) is a long-term astronomical survey beginning in 1998 to present and continues to catalogue 240 nearby stars in the Southern Hemisphere.

As of 2015, the AAPS had achieved the highest search in the Southern Hemisphere, after identifying over 40 exoplanets using the telescope.

Last November, Australian professor Peter Tuthill announced he was leading a collaboration with the US to locate a planet that could be orbiting around one of Earth’s nearest stars, the Alpha Centauri.

Dubbed the Telescope for Orbit Locus Interferometric Monitoring of our Astronomical Neighborhood (TOLIMAN), it will use a diffractive pupil lens that makes it easier to detect star movements which could lead to “telltale signs” for orbiting planets.

Earlier this year, the University of Southern Queensland joined a UK-based project to analyse the atmospheres of exoplanets.

The lightweight Twinkle satellite will launch in 2024, and it’s hoped the seven-year mission will provide new insights into the formation and evolution of our solar system.

Australia, in collaboration with TESS, was instrumental in discovering Alpha Draconis in 2020, a Thuban that lies about 270 light years away in the northern constellation Draco. Despite its “alpha” designation, it shines as Draco’s fourth-brightest star.

Isabella Richards

Isabella Richards

Bella Richards is a journalist who has written for several local newspapers, her university newspaper and a tech magazine, and completed her Bachelor of Communications (Journalism) at the University of Technology Sydney in 2020. She joined Momentum Media in 2021, and has since written breaking news stories across Space Connect, Australian Aviation and World of Aviation.

You can email Bella on: [email protected]

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