Exploring the universe has always been one of humanity's greatest desires. Among the most fascinating areas of study is the search for and observation of exoplanets, planets that orbit stars other than the Sun.

This research has expanded our understanding of the cosmos and raised fundamental questions about life beyond Earth. Below, we'll explore exoplanets, how they were discovered, methods for detecting them, and whether amateur astronomers can observe them.

What are exoplanets and how were they discovered?

Exoplanets are planets located outside the solar system that orbit other stars. Unlike planets in our solar system, such as Earth or Jupiter, exoplanets do not revolve around the Sun, making them significantly more complicated to observe and study.

The existence of these celestial bodies was a long-debated theory for centuries, but it was not confirmed until the end of the 20th century.

Astronomers Aleksander Wolszczan and Dale Frail announced the first confirmed discovery of an exoplanet in 1992. They detected planets orbiting a pulsar, a rapidly rotating neutron star called PSR B1257+12.

These planets didn't look like planets in our solar system due to their location in an extreme environment, but their discovery marked a milestone. It made us realize that exoplanets not only existed but could exist even in more violent environments than we had imagined.

Subsequently, in 1995, scientists Michel Mayor and Didier Queloz confirmed the first exoplanet orbiting a star similar to the Sun, 51 Pegasi b. This finding revolutionized astronomy and opened the doors to an ever-growing field of study.

Today, thanks to advanced technologies and space missions such as the Kepler telescope and the James Webb telescope, more than 5,000 exoplanets have been identified, each with unique characteristics that reveal the diversity and complexity of planetary systems.

How are exoplanets detected?

Detecting exoplanets is challenging because of their distance and the brightness of the stars they orbit, which often overshadows them. Despite these difficulties, astronomers have developed several effective methods to locate them.

First, let’s clarify one important point: Exoplanets cannot be directly observed. They are too small and faint to be seen, and their proximity to the bright stars they orbit makes observation even more challenging, as the starlight overwhelms any attempt to detect them directly.

So, how do astronomers see exoplanets?

The answer is that they don't. Astronomers can't photograph exoplanets directly since that's impossible. What they do is detect them indirectly with interference methods that allow them to decipher whether or not a star has exoplanets around it.

Below, we'll explore the four principal or most commonly used methods in modern astronomy:

TRANSIT METHOD

The transit method is one of the most effective and popular for detecting exoplanets. This method is based on observing the passage of a planet in front of its host star, which causes a small decrease in the brightness of the star. This decrease in the brightness of a star is known as a transit.

This is where the tricky thing about observing exoplanets lies, as the decrease in a star's brightness can be due to many things, such as dust, asteroids, accretion disks, etc.

Defining whether or not a star's decrease in brightness is an exoplanet is extremely difficult. It requires observing the same star for many hours, days, and sometimes years.

This is because to observe a transit, you must wait for the planet to pass in front of its star, which can take a long time. Do you remember when it took the Earth to orbit the Sun? Exactly 365 days.

This is how long an extraterrestrial civilization would have to wait to see Earth pass in front of the sun only once. It's wild, isn't it?

How does it work?

When a planet transits before its star, it blocks a fraction of its light. By monitoring this periodic decline, astronomers can infer the presence of a planet. This method also makes it possible to determine key characteristics of the exoplanet, such as its size, orbit, and, in some cases, its atmospheric composition.

Of course, before that, astronomers must make hundreds of hours of observations before ruling out that the transit is due to something else.

Tools Needed

Space telescopes like Kepler and TESS are specifically designed to record this brightness dimming. Ground-based telescopes equipped with sensitive photometers are also used.

This method has been responsible for most of the exoplanets discovered to date. More than 3,000 planets have been identified by transits, including some in the "habitable zone," where conditions could allow liquid water to exist.

Wobble method (astrometry)

The wobble method, also known as astrometry, detects exoplanets by observing subtle motions in a star's position caused by the gravitational pull of an orbiting planet.

How does it work?

Although the stars appear fixed in the sky, they move slightly due to the planet's gravitational influence. This wobble can be measured by recording precise changes in the star's apparent position over time.

Although this seems simple, it is challenging since the wobbles of a star are barely perceptible by the most powerful telescopes, such as Hubble.

So, to detect this type of stellar wobble, very advanced measurement equipment is required, as well as many hours of direct observations of the star itself.

Tools Needed

This method requires telescopes with high-precision capability in position measurements, such as the Kepler Space Telescope. Although promising, the wobble is challenging to detect due to the stars' remoteness and the motions' small size.

Due to its technical challenges, this method has detected a limited number of exoplanets so far. However, advances in space observation technology promise to make it more effective in the future.

Radial velocity method

Radial velocity, also known as the Doppler method, measures a star's light change caused by a planet's gravitational pull. This change is detected as a Doppler effect in the star's light spectrum.

How does it work?

The Doppler effect is a phenomenon that occurs when a light source, such as a star, approaches or moves away from us, and that manifests itself in a change in the frequency of light.

When a planet orbits a star, the two experience a mutual gravitational pull. This causes the star to move slightly closer and further away from us. Astronomers analyze the star's light spectrum for variations that indicate this motion.

Tools Needed

Ground-based telescopes equipped with high-precision spectrographs, such as HARPS in Chile, are ideal.

This method was crucial for discovering the first exoplanets, including 51 Pegasi b. So far, hundreds of exoplanets have been identified with this technique, which is especially useful for detecting giant planets close to their stars.

Gravitational microlensing

Gravitational microlensing takes advantage of the effects of Einstein's general relativity to detect exoplanets. This method is based on the phenomenon by which the gravity of an intermediate star acts as a lens, amplifying the light of a more distant star and revealing the presence of planets.

How does it work?

When a star passes in front of another from our vantage point, its gravity can bend and focus the light from the farthest star. If a planet accompanies the intermediate star, its additional effect can be detected in light amplification.

Tools Needed

This method requires ground and space-based telescopes, such as the OGLE Observatory, to monitor microlensing events to monitor microlensing events.

Although less common, this method has detected dozens of exoplanets, especially in systems farther away from the Milky Way. It helps find planets at distances that are too great for other methods.

Can an amateur astronomer observe exoplanets?

As you have realized so far, detecting exoplanets is a technical challenge that can only be solved with large telescopes, such as those found in observatories or space telescopes like Hubble or James Webb.

This means that observing exoplanets is beyond the reach of the commercial telescopes that amateur astronomers usually use. This is due to several factors:

• Exoplanets are extremely faint objects close to bright stars.
• They require advanced tools such as spectrographs, photometers, and sophisticated data analysis algorithms.

To observe them, large aperture lenses, at least 1.5 meters in diameter, are required. This cannot be achieved in any commercial telescope, as it requires supports and motors only found in large astronomical observatories.

However, that doesn't mean amateur astronomy can't participate in exoplanet detection. In 2018, amateur astronomer Thomas Jacobs collaborated with professional scientists to analyze data from the Kepler telescope and discover a planetary system using the transit method.

Although Jacobs didn't use his telescope, his involvement shows that amateurs can contribute by analyzing public data.

Although observing exoplanets directly with home telescopes is virtually impossible, amateurs can participate in citizen science projects and contribute to this exciting area of research.

The importance of observing exoplanets

The study of exoplanets has profound implications for science and humanity. Some key reasons are:

Understanding the cosmos: By studying exoplanets, we can learn more about the formation and evolution of planetary systems, expanding our knowledge of the universe.

Searching for life: Identifying planets in the "habitable zone" and analyzing their atmospheres are crucial steps in looking for signs of life beyond Earth.

Technological impact: Research on exoplanets has driven the development of advanced optics, data analysis, and astronomy technologies.

Global inspiration and collaboration: This field has united scientists, institutions, and citizens worldwide in search for answers to fundamental questions about our existence.

In conclusion, exoplanets are fascinating and represent a window into our place in the universe, driving curiosity and innovation.