A German volunteer scientist working with a NASA-led project has found the oldest and coldest-known white dwarf, which significantly is also ringed by debris and dust, the space administration says.

Melina Thevenot, one of the volunteers sorting through data from NASA's Wide-field Infrared Survey Explorer space telescope as part of the Backyard Worlds project, discovered the earth-sized remnant of a dead star while in the European Space Agency's archives.

The German scientist had been searching for brown dwarfs - objects larger than planets but smaller than stars - when she found something much brighter and farther away.

The information was given to NASA's Goddard Space Flight Center in Maryland, which then used one of the world's largest telescopes at Hawaii's Keck Observatory to study the white dwarf.

Being able to call on such impressive resources was a "really motivating aspect" of the project, said Thevenot, one of 150,000 volunteer scientists working for Backward Worlds.

Named J0207, the white dwarf is about 145 light years away in the Capricornus constellation, and has been around for three billion years based on its temperature of 5800 degrees Celsius, NASA said.

Scientists think it could be the first white dwarf with multiple dust rings, with the find forcing astronomers to "reconsider models of planetary systems and it could help us learn about the distant future of our solar system," a NASA spokesperson said.

A paper on the project's latest findings was published on Tuesday in The Astrophysical Journal Letters, with Thevenot one of two citizen scientist co-authors.