A team of astronomers led by Queen Mary University of London has announced the discovery of a planet orbiting Proxima Centauri, the nearest star to our Sun.

Doppler spectroscopy
Image: ESO


It’s the latest of more than 3,500 exoplanets detected since the first confirmed discovery back in 1995.

Future generations of telescopes, such as the European Extremely Large Telescope currently under construction in Chile, should be able to image exoplanets directly. But for now, as they’re so faint, we have to rely on indirect methods.

One commonly used technique is to measure the brightness of a given star over time. If there are periodic dips in the amount of starlight we receive from it, then that suggests there’s something orbiting the star and repeatedly blocking out the light. The frequency of the dimming tells us how long it takes the planet to complete an orbit, and the amount by which the star’s brightness seems to dim gives us an idea of the planet’s radius.

Another way to detect exoplanets is by spotting the effect of their gravity on the star. When the planet is on the far side of the star as viewed from the Earth, it very slightly tugs the star towards it and away from us. The star’s light is Doppler shifted toward the blue end of the spectrum, to a longer wavelength. Half an orbit later, the star of pulled very slightly towards the Earth, and its light is redshifted. The amount by which the light is Doppler shifted indicates the gravitational force is experiences, and therefore the planet’s mass.

Studying exoplanets not only allows us to learn more about how planetary systems form and develop, but also has implications in the search for extraterrestrial life. Researchers think that the existence of life is dependent on liquid water, so a planet will have to be a distance from its host star such that its temperature is suitable for water to exist. This is known as the habitable zone, or, sometimes, the Goldilocks zone, as the conditions have to be just right.

The planet just announced is thought to be in the Goldilocks zone of Proxima Centauri – meaning there’s a potentially habitable planet right next door.

  • See the IOP’s schools resource about exoplanets on YouTube or read about other exoplanets potentially suitable for life on the IOP blog

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