At 117 light years away from us, the white dwarf WD1054-226 glows towards its end. But a ring of planetary ruins with moon -sized structures now excited about this star: it indicates a nearby planet in the habitable zone around the star, which could have potentially liquid water and thus the prerequisite for life. Jay Farihi from University College London and his team write to the "Monthly Notices of the Royal Astronomical Society".
The working group observed the system with various telescopes and regularly observed a darkening of the white dwarf – a difficult undertaking, since such stars are relatively faint due to lack of fuel. Farihi and Co attribute these light fluctuations to 65 evenly distributed clouds of planetary debris orbiting the star every 25 hours and dimming its light every 23 minutes. Such regularity suggests that the structures are precisely arranged by a nearby planet, the team writes. "The moon-sized structures we observed are irregular and dusty, similar to comets, rather than solid, spherical bodies. Their absolute regularity is a mystery that we cannot explain at present," says Farihi.
Without the gravity of a nearby planet, however, these structures would rub and destroy them through collisions. Farihi and Co refer to the attraction of the small German Shepherd's moons in the rings around Neptune and Saturn, which help to create stable structures that circle these planets.
The orbit around the white dwarf was most likely emptied during a period in which the star had inflated into a giant. Each planet in its habitable zone is therefore relatively young. The area would still be habitable for at least two billion years, including at least one billion years in the future, the scientists said. "Since our Sun will become a white dwarf in a few billion years, the study offers a glimpse into the future of our own solar system," says Farihi. This will be the case in four to five billion years and will mean the end at least for Mercury and Venus. Compared to a star like the Sun, the habitable zone of a white dwarf is smaller and much closer to the star because white dwarfs emit less light and thus heat.
