For some of us, August 24, 2006, feels like just yesterday – the day Pluto was ousted from the exclusive 'planets club.

Pluto's Demotion: Reflections from Sara and Rebecca

Similarly, my friend Rebecca vividly recalls Pluto's re-designation to dwarf status. For her, it wasn't merely about the celestial body's reclassification; after all, science evolves with new knowledge. What struck her was the way the astronomy community handled the PR surrounding this cosmic adjustment.

At the tender age of 11, I (Sara) found my entire class passionately chanting "Pluto is a planet" during lunch break in protest of the recent news. It was a heartfelt display, and my 11-year-old self was outraged and somewhat inconsolable. Now, as a much older me, I wholeheartedly accept the reality: Pluto is not a planet.

A Missed Opportunity in Pluto's Demotion

Renowned astronomers, usually celebrated for their public presence, stumbled through explanations of Pluto's reclassification, mostly remaining unapologetic. However, what was poorly communicated as a demotion was, in fact, the exciting discovery of new members in our Solar System, with Pluto leading the way. Fortunately, astronomers now benefit from improved media support, and there's a wealth of fascinating science to catch up on. Let's delve into what you might have missed.

Pluto's Demise: Unveiling the Dwarf Planet Reality

Pluto's destiny was likely sealed when Eris was discovered in 2005, sharing the outskirts of our Solar System with similar characteristics. Despite Eris having a smaller radius but more mass than Pluto, astronomers predicted the increasing discovery of such objects with advancing telescopic capabilities. Today, the Solar System boasts five known dwarf planets.

The distinction between "planet" and "dwarf planet" criteria was established by the International Astronomical Union. In short, Pluto's reclassification in 2006 was not a deliberate targeting; it simply didn't meet all three criteria for a full-fledged planet:

• It must orbit a star (in our Solar System, the Sun).
• It must be large enough for gravity to shape it into a spherical form.
• It must be sizable enough for its gravity to clear neighboring objects of similar size from its orbit.
  

Pluto's failure to fulfill the third criterion led to its reclassification. However, the question remains: Is our Solar System destined to have only eight planets? Not necessarily—another discovery might be waiting to unfold.

Hunting for Planet Nine
The quest for a possible ninth planet in our Solar System began when astronomers, puzzled by the movements of newly discovered dwarf planets, turned to complex simulations on supercomputers. In 2016, California Institute of Technology astronomers Konstantin Batygin and Mike Brown, after meticulous modelling, theorized the existence of a ninth planet, approximately ten times Earth's mass and positioned a staggering 90 billion kilometres from the Sun—15 times farther than Pluto. While a bold claim, skepticism persists.
Determining the planet's existence isn't as straightforward as pointing a telescope in its presumed direction. The theoretical planet is estimated to be exceptionally dim, potentially 600 times fainter than Pluto, posing a challenge for Earth's largest telescopes. Moreover, the vastness of our Solar System and the limited window for optimal search conditions complicate the exploration.

Despite these challenges, efforts persist. In 2021, a team utilizing the Atacama Cosmology Telescope revealed results from their search for the elusive ninth planet's movements in the Solar System's outskirts. While confirmation remains elusive, they identified ten candidates for further investigation, hinting that answers about the mysteries at our planetary fringe may emerge in the coming years.

Unveiling Distant Worlds

Despite possessing telescopes capable of revealing galaxies from the universe's infancy, directly imaging planets outside our Solar System, known as exoplanets, remains a formidable task.

The difficulty lies in fundamental physics. Planets primarily emit dim red wavelengths of light, making them most visible when reflecting their star's light. The farther a planet is from its star, the more challenging it becomes to observe. Recognizing this challenge, astronomers sought alternative methods to explore planets in foreign star systems. Before Pluto's reclassification, they had already identified the first exoplanet, 51 Pegasi B, using the radial velocity method. This technique involves detecting the gravitational interaction between a gas giant and its star, but it proves tedious and challenging from Earth's surface.

To overcome these limitations, astronomers devised the transit method. Similar to how Mercury or Venus briefly block a portion of the Sun's light during transit, powerful telescopes can detect this phenomenon in distant star systems, providing a novel approach to explore the mysteries of exoplanets.

Through the use of the Kepler space telescope and the Transiting Exoplanet Survey Satellite (TESS), we have surveyed tens of thousands of stars, unveiling thousands of new planets, including dozens similar in size to Earth. However, while these observatories provide information about a planet's size and distance from its star, they cannot inform us about the potential habitability or presence of life. To delve into these aspects, the James Webb Space Telescope is essential.

James Webb Space Telescope Unveils Exoplanetary Secrets

The James Webb Space Telescope (JWST) has completed its initial year and a half of scientific exploration, showcasing numerous accomplishments, including the detection of molecules in the atmospheres of exoplanets using the transit method. Among the fascinating findings, WASP-17, identified as a "hot Jupiter," stands out. This exoplanet, reminiscent of science fiction, reveals evidence of quartz nanocrystals in its clouds, adding an intriguing dimension to our understanding of distant worlds.

In the realm of exoplanets, K2-18b, a super-Earth discovered by Kepler, reveals traces of methane and carbon dioxide. Although these findings are remarkable, the crucial element for sustaining life, water vapor, remains elusive.

As we advance in the field of planetary studies, the prospects for 2024 appear promising. Perhaps, with the capabilities of the James Webb Space Telescope (JWST), we may witness the revelation of water vapor in the atmosphere of an exoplanet. Additionally, there's a chance that an unexpected ninth planet could emerge, potentially filling the cosmic void left by Pluto.