Citizen science finds five planet system

Citizen science finds five planet system
Kepler K2-138 System (Artist's Concept) © NASA-JPL-Caltech

A discovery by citizen scientists has led to the confirmation of a system of five planets orbiting a far off star.

A mathematical relationship called ‘resonance chain’ shows how the planets’ orbits are linked with a pattern that is unique among the known planetary systems in our galaxy.

A study into the five-planet system could help understand the formation of other systems.

Since the discovery of four planets in this particular system was announced last year, Dr Jessie Christiansen, from Caltech in California, USA, has been working to shed further light on this planetary system, dubbed K2-138. This led to the discovery of the five planets, with the suggestion of a sixth.

The planets are all slightly bigger than Earth, ranging between 1.6 and 3.3 times its radius. The collected findings are to be published in the Astrophysical Journal.

The discovery was aided by using data from the Kepler space telescope, which identifies potential planets by looking for dips in nearby stars when planets cross their face, or transit them.

Resonance chain

Being in a resonance chain means that the orbiting planets exert a regular, period gravitational influence on each other, usually because the orbital periods are related by a ration of small integers.

Resonances are an important feature of any solar system. The newly found system has a resonance chain that means each planet takes almost 50% longer to orbit the star than the next planet.

Christiansen said: “If you keep going with the resonance chain, you skip 19 days, you skip 27 days and you end up at about 43 days,” adding: “That’s a tantalising clue that we may be missing more planets in this system.”

K2-138 could further knowledge around the process by which planets form and then migrate from their original positions. This is a particularly contested area, with several ideas surrounding it.

The star at the centre of the system is slightly smaller and cooler than our Sun. The innermost planet could potentially be rocky, like the Earth.

All of the five planets orbit around the star with periods shorter than 13 days. The close proximity suggests the planets have temperatures ranging from 800 to 1800°F (425 to 980°C), so even the planet with similarities to Earth would be inhabitable.

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