Distant planet found with three daily sunrises and sunsets

8 Jul 2016

Artist's interpretation of a planet in a triple star system. Image via NASA/JPL-Caltech

Imagine living on a planet where every day you experience three sunrises and three sunsets. Well, that’s the case on a newly-discovered exoplanet that has rather strange seasons.

While planets with one or two local stars are plentiful in the vastness of space, every-so-often astronomers searching the cosmos find a real anomaly and, now, that anomaly is a distant planet that is influenced by three nearby stars.

Designated HD 131399Ab, the team from the University of Arizona in Tucson (UA) has published findings on the planet, which is at the mercy of the three suns, one of which the planet orbits while the other two smaller stars also orbit the parent star.

140 years of continuous daylight

While not the only planet discovered by astronomers that has three nearby stars, this particular world has been found to have an enormously wide orbit, which results in an orbit that’s 550-times that of our own Earth year.

Four-times larger than Jupiter, the planet is also 82 astronomical units (distance from the Earth to the sun) away from the largest star, and up to 400-times that from the other two smaller stars.

This peculiar arrangement results in a daily cycle that would likely drive Earth-dwellers insane as, depending on the season, the planet experiences three sunrises and sunsets.

Based on the astronomical readings, this very young planet – just 16m-years-old – would have experienced this cycle for the first few hundred years, then it would have settled into a second season where it would have been bathed in continuous daylight for around 140 years.

‘It can become unstable very quickly’

Despite this, the planet is believed to be one of the coldest and least massive directly-imaged exoplanets, with a temperature of just 580ºC.

The UA team will now need to monitor the planet to determine its prolonged trajectory and, based on early simulations, the slightest variation could send it on a doomed course outside of the star’s orbit.

“If the planet was further away from the most massive star in the system, it would be kicked out of the system,” said Daniel Apai, a senior researcher at UA dedicated to finding and observing exoplanets.

“Our computer simulations showed that this type of orbit can be stable, but if you change things around just a little bit, it can become unstable very quickly.”

As part of these future readings, the research team is particularly keen to find how the planet ended up on such a wide orbit of this less-than-normal star system.

Colm Gorey was a senior journalist with Silicon Republic