What is an exoplanet?

An artist's representation of Kepler-11, a small, cool star around which six planets orbit. Credit: NASA/Tim Pyle
An artist's representation of Kepler-11, a small, cool star around which six planets orbit. Credit: NASA/Tim Pyle

In our solar system, every planet revolves around the Sun. Exoplanets are planets that revolve around other stars. Exoplanets are extremely difficult to directly observe using telescopes. The intense light from the stars they orbit obscures them. Therefore, astronomers use various techniques to find and research these far-off planets. By observing the impacts that these planets have on the stars they circle, astronomers seek exoplanets.

How can we find exoplanets?

Finding "wobbly" stars is one approach to seeking exoplanets. A planet-bearing star's orbit around its core is not a complete circle. From a distance, the star appears to be swaying due to its eccentric orbit. This technique has led to the discovery of hundreds of planets. Only massive planets, such as Jupiter or even larger, may be viewed in this fashion, though. Because they produce only minute wobbles that are difficult to detect, smaller Earth-like planets are tougher to identify.

How can we discover planets that are like Earth in other solar systems?

NASA launched the Kepler spacecraft in 2009 to search for exoplanets. Kepler searched for planets with a variety of sizes and trajectories. Additionally, these planets circled variously sized and hot stars. Some of the planets Kepler has found are rocky planets that are quite far from their star. The habitable zone, where life may be feasible, is this ideal region. Kepler used a technique known as the transit method to find exoplanets. A transit occurs when a planet crosses in front of its star. A little portion of the star's light is obstructed as the planet passes in front of it. This implies that when a planet moves in front of a star, the star will appear to be slightly less luminous.

Astronomers may watch as a star's brightness varies throughout a transit. They may use this to determine the size of the planet. Astronomers can determine a planet's distance from its star by observing the intervals between transits. This provides information on the temperature of the globe. A planet may have liquid water, a necessary component for life if the temperature is exactly perfect.

The Kepler mission has so far uncovered thousands of planets. Furthermore, more will be discovered by NASA's Transiting Exoplanet Survey Satellite (TESS) mission, which is scanning the whole sky for planets revolving around the closest and brightest stars. Exoplanets are widely distributed across the cosmos, as we now know. And more are expected to be discovered by NASA in future expeditions.

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