In hunt for Planet Nine, citizen scientist finds something truly unexpected

20 Feb 2019

Illustration of J0207 with two distinct components, which scientists think best explain the system’s infrared signal. Image: NASA Goddard Space Flight Center/Scott Wiessinger

While the hunt continues for a potential ninth planet in our solar system, a citizen scientist has discovered something very different.

German citizen scientist and member of the NASA-led Backyard Worlds: Planet 9 project Melina Thévenot was recently observing the heavens when she spotted something strange. Along with the project’s mission to find proof of the existence of a so-called ‘Planet Nine’ in our solar system, it also aims to locate new brown dwarfs further out into the cosmos.

However, what she spotted looked nothing like either a planet or a brown dwarf. As it turns out, it was a white dwarf that could potentially change our understanding of how planetary systems evolve. The star, called LSPM J0207+3331 (J0207), is the oldest and coldest known white dwarf found to date and may be the first to have been found with multiple dust rings.

Operating on billion-year timescales

A white dwarf is an Earth-sized remnant of a sun-like star that has long since died. While they are typically ringed by dust and debris, Thévenot originally thought J0207 may have been a brown dwarf that was too big to be a planet, but too small to be a star. After further investigation, the brown dwarf theory was ruled out because it was found to have significant infrared brightness.

This excess was thought to be radiating from a warm, dusty circumstellar disc, which form from the continual break-up of small rocky planetesimals orbiting the white dwarf. Yet what puzzled astronomers from Arizona State University who followed up on the discovery was the fact that the white dwarf is three times older than any other white dwarf known to harbour such a disc.

“This white dwarf is so old that whatever process is feeding material into its rings must operate on billion-year timescales,” said John Debes of the Space Telescope Science Institute who was later brought into the research.

“Most of the models scientists have created to explain rings around white dwarfs only work well up to around 100m years, so this star is really challenging our assumptions of how planetary systems evolve.”

Another puzzling fact is that the J0207 disk may be composed of more than one distinct ring-like component, something never seen before in circumstellar material surrounding a white dwarf. Scientists are now left with the challenge of figuring out how the white dwarf fits in with existing formation models.

The researchers’ findings have been published to The Astrophysical Journal Letters.

Colm Gorey was a senior journalist with Silicon Republic