August 13, 2022

First hints of a planet orbiting in a white dwarf’s habitable zone

First hints of a planet orbiting in a white dwarf’s habitable zone
First hints of a planet orbiting in a white dwarf’s habitable zoneFirst hints of a planet orbiting in a white dwarf’s habitable zone

Astronomers have found 65 evenly spaced rocks orbiting a white dwarf star in its habitable zone, hinting that a planet’s gravity may be holding them there

Space 11 February 2022

Illustration of the white dwarf star WD 1054-226 orbited by clouds of planetary debris and a major planet in the habitable zone

Mark A. Garlck/MarkGarlick.com

A distant white dwarf is surrounded by space rocks marching in perfect time. Based on this observation, astronomers have spotted the first hints of what may be a planet in the habitable zone of one of these stellar corpses, hinting that they might be just as good for life as bigger, younger stars.

“A lot of people think of a white dwarf as a dead system or a dead end, but this tells us that there is a lot of stuff going on around white dwarfs,” says Jay Farihi at University College London.

He and his colleagues spotted these hints while observing a star called WD 1054-226 about 118 light years away, using several powerful telescopes. They found that something appeared to be regularly passing in front of the star, causing dips in its light. The biggest of these dips happened every 23.1 minutes, in a pattern which repeated itself every 25 hours.

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The data indicates that the star is surrounded by a ring of 65 comet-sized or moon-sized objects, remarkably evenly spaced in their orbits. “The structures that are transiting are so highly regular that you can’t really do that accidentally,” says Farihi. That doesn’t mean it’s aliens, though. “Regular structures in space do invoke this idea of planetary engineering, but I favour the more mundane explanation,” he says.

The more mundane explanation is that the bits of cosmic debris are kept in order by the gravitational pull of a planet orbiting slightly further away from the star. “If we’re correct that there is a planet causing this order, my guess would be that it would be around the size of Mercury or Mars,” says Farihi.

The researchers calculated that the objects orbiting it are about 2.6 million kilometres from the star – about one fifth of the distance between Mercury and the sun – putting their temperatures at around 50°C, which is right in the middle of the range for liquid water oceans. This means that if there is a planet there, it could have the right temperature for oceans and maybe even life.

Journal reference: Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/stab3475

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