Exoplanet Detection

Exoplanet Detection

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Exoplanets, also known as extrasolar planets, are planets located outside our solar system. Detecting exoplanets using telescopes is a challenging task since they are concealed by the brightness of the star they orbit. Howeveroplan the they orbit. These effects are crucial in discovering exoplanets.

What are the methods for exoplanetdetection?

There are various methods for exoplanet detection, including direct imaging, radial velocity/Doppler spectroscopy, transit photometric, astrometry, and pulsar timing.

Direct imaging

The direct imaging technique is a process of using large telescopes equipped with adaptive optics and coronagraphs to capture images of exoplanets by measuring their luminosity. However, it's only useful for detecting exoplanets located far from their orbiting star, where the exoplanet's thermal emission is visible.

This detection method is best suited for larger exoplanets with warmer temperatures and eccentric orbits, as they have higher thermal energy and, as a result, higher temperatures. The temperature of an exoplanet is also related to its radius and brightness, so this method can determine the size of the detected exoplanets. It can even detect brown dwarfs by measuring their thermal emission.

Brown dwarfs are objects in the sky that are too small to generate nuclear fusion but emit infrared radiation due to their high temperatures. They are an intermediate between a star and a planet and have masses less than 0.075 solar masses. Brown dwarfs are too small to undergo nuclear fusion but are hot enough to radiate energy, particularly at infrared wavelengths.

Radial velocity/Doppler spectroscopy

Observing the elliptical motion of a star from a distance can cause changes in the light spectrum of the star. When a star moves closer to the observer, its light wavelength shortens and shifts towards the blue end of the spectrum. Conversely, when the star moves away from the observer, the light wavelength lengthens and appears to be shifted to the red.

Electromagnetic spectrum
Electromagnetic spectrum

The radial velocity method, also known as Doppler spectroscopy, detects exoplanets by observing the Doppler shift of a star and its small deviations in its orbit over time. This suggests that an orbiting mass has gravitational effects on this star. When an exoplanet is detected, its minimum mass can be calculated using the radial velocity method by measuring the amplitude of the sun’s radial velocity over time.

Transit photometry

The transit photometry technique detects exoplanets by observing a star's brightness over time. If there is a periodic decrease in brightness, it indicates that an exoplanet is in transit in front of the star, causing a decrease in brightness proportionate to the sizes of the star and the planet. This method can measure the radius of an exoplanet relative to its orbiting star. Additionally, transit photometry can be used to determine the atmospheric elements of a planet by observing the "transit" that occurs when a planet passes in front of the star. By analyzing the light that passes through the planet's atmosphere, scientists can identify the presence of certain gases or elements. This method has been used to detect elements like water and methane in exoplanet atmospheres.


Astrometry, the oldest recorded method of exoplanet detection, involves precise measurements of a star's coordinates in the sky as a reference point. Deviations from this reference point are recorded over time. If an exoplanet is orbiting a star, its gravitational pull will cause the star to shift slightly from its orbit. Both the star and the exoplanet have gravitational effects on each other, causing them to orbit around a mutual center of mass called the barycenter. Since the star has greater mass, the barycenter will be closer to the star's radius. As a result, it is easier to find exoplanets orbiting lower-mass stars or other low-mass objects like brown dwarfs using astrometry.

Pulsar timing

Pulsar is a neutron star, which is a very dense residue of a supernova. These emit radio waves as they periodically rotate intrinsically. The motion of a pulsar is recorded from the slight changes in its radio pulses’ timing, which can be used to estimate the characteristics of its orbit.

Pulsar and its companion star.Source: NASA Goddard Space Flight Center

This method was first used to study themotion of pulsars but was later found to be very accurate in detecting verysmall planets. However, this method is not used frequently, as pulsars arerelatively rare.

What are the advantages of exoplanetdetection?

Detecting exoplanets has various advantages they can help answer some questions about our origins as humans or whether intelligent life exists beyond the earth. Studying exoplanets:

Detecting Exoplanets - Key takeaways There are several methods for exoplanet detection. Direct imaging uses luminosity and thermal emission measurements. Radial velocity uses the Doppler effect. Thetransit photometry method studies the reduction of the luminosity of stars due to planet transit. The astrometry method observes the position of a star overtime. The pulsar timing method records the timings of pulsar radio wave emission. Detecting exoplanets has several advantages, including the potential detection of life on exoplanets and thus increasing our chances of finding earth-like planets for future human colonisation.

Exoplanet Detection

How do we detect exoplanets?  
There are various methods, including to measure the luminosity, thermalemissions, doppler shifts and radio wave timing of the planet and their parentstar.
Can we detect earth-size exoplanets?
Yes, but they can only be detected in small orbits of low-mass stars.
What are the 5 methods to detect exoplanets?
The 5 methods to detect exoplanets are direct imaging, radial velocity, transitphotometry, astrometry, and pulsar/variable star timing.
Does lidar detect exoplanets?  
Yes, lidar detects exoplanets.
How can astronomers detect exoplanets?  
Astronomers detect exoplanets by observing and using various indications inorbits, luminosity, thermal emission and motion of stars and their orbitingplanets.

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