Confirmed: An exoplanet with three Suns

Image credit: Caltech/R. Hurt

Astronomers have confirmed the presence of KOI-5Ab, an exoplanet first identified by NASA’s now retired Kepler Space Telescope in 2009. In fact, the exoplanet was second ever identified by Kepler telescope.

Kepler looked for extrasolar planets during its 9 years, 7 months, 23 days mission (2009–2018). The telescope used transit method to hunt for alien worlds.

During its two different missions, Kepler telescope discovered about two-thirds of the roughly 4,300 known exoplanets. Scientists are still scanning through the huge Kepler data to look for potential exoplanets.

About 1,800 light years away from us, in the constellation of Cygnus lies a system called KOI-5. It is a triple star system with one of the star orbited by the gas giant exoplanet KOI-5Ab.

Despite being second exoplanet candidate detected by Kepler, it was left behind because of the system’s complications.

While going through Kepler data, astronomers spotted a transit signal of a gas giant orbiting a Sun like star.

Follow up research revealed that the host star is not alone, it had a companion star. This made the research further more difficult.

There was already huge amount of Kepler data waiting to be decoded, and also there were easier picks than KOI-5Ab. All these factors prompted astronomers to abandon the system KOI-5 at that time.

By 2014, astronomers had identified the KOI-5 as a triple star system. But it still wasn’t clear if exoplanet KOI-5Ab indeed was there.

As 2009 transit signals could also have been generated by one of the companion stars. This further complicated the research.

Then came Kepler’s successor NASA’s Transiting Exoplanet Survey Satellite (TESS). Launched in 2018, TESS also detected a transit signal in the KOI-5 system- possibly generated by an exoplanet with an orbital period of five Earth days.

So scientists re-analysed all the previous data collected by TESS and Kepler, and various other ground based observatories. The re-analysis confirmed the presence of an exoplanet KOI-5Ab.

The three stars of the system are: KOI-5A, KOI-5B and KOI-5C.

Main star KOI-5A has a close partner star KOI-5B. They both orbit each other once in every thirty Earth years. The third star of the system KOI-5C lies much way out from first two stars, and orbits the pair in every four hundred Earth years.

The exoplanet KOI-5Ab orbits around KOI-5A in a very close five Earth day orbit. The exoplanet is probably a gas giant with about half the mass of Saturn and seven times the size of Earth.

Exoplanet’s orbital plane is misaligned with star KOI-5B. This may be due to KOI-5B’s gravitational push on the planet back in the system’s history when the exoplanet was forming.

Image credit: Caltech/R. Hurt

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