Two studies say the LISA observatory could detect planets orbiting pairs of white dwarfs

Two papers published on November 10, 2026, in The Astrophysical Journal describe how LISA, the Laser Interferometer Space Antenna, could find planets orbiting pairs of white dwarfs, the Earth-sized remnants of stars like the Sun. No planet is yet known around such a pair, the authors note, so detections would add a new population of worlds. NASA, which announced the work the same day, is a partner in the gravitational-wave observatory, which the European Space Agency leads and which is planned for launch in the mid-2030s.

Both papers are led by Casey McGrath, a postdoctoral researcher at the University of Maryland, Baltimore County, and NASA's Goddard Space Flight Center. They model what the observatory could detect: LISA is still in development, and no planet has yet been found this way.

A wobble in the waves

The method borrows from radial velocity, a technique already used with light to find planets around nearby stars. A planet's gravity tugs its star back and forth, and the Doppler effect shifts the star's spectral lines toward redder and bluer wavelengths in turn. Double white dwarfs in tight orbits are expected to be LISA's most common sources, according to McGrath. On their own they emit gravitational waves at a nearly steady frequency, explained Scott Noble, a NASA Goddard astrophysicist and co-author of the second paper. A massive enough planet would make the pair wobble as well, adding a Doppler modulation that LISA would register as sidebands, secondary signals at frequencies above and below the main one. McGrath likens them to the sidebands of a radio carrier wave, which carry voices or music.

“If an exoplanet also orbits within one of these systems, its presence becomes imprinted on the gravitational wave signal in a way we’ll be able to uncover,” McGrath said in NASA's announcement. In the first paper, of which McGrath is the sole author, the method turns on what the paper calls the phase modulation index, a parameter more sensitive to heavy planets on long orbits. The paper finds that the index grows between the frequency band where LISA will work and the higher band of the current LIGO, Virgo and KAGRA observatories, by a factor of roughly 10,000 to 1 million in our reading of the abstract's order-of-magnitude notation. It also explores how an undetected planet could bias estimates of a source's properties.

Checking with Webb

The second paper, by McGrath with Mary Anne Limbach of the University of Michigan, Noble and Vincent Kofman, asks how a detection could be confirmed with light. The team took a known double white dwarf, ZTF J2243+5242, and placed it for the exercise at 150 parsecs, about 490 light-years by our conversion. A planet would show up as extra infrared light beyond what the two white dwarfs are expected to emit, and the authors describe their study as the first to explore this infrared excess as a way to find planets around white dwarf pairs. NASA says Webb could detect the excess out to at least 500 light-years. In the test case, Webb could spot a planet of about five Jupiter masses, while LISA could detect one smaller than Jupiter under ideal circumstances. Precise position measurements, by Gaia or the Habitable Worlds Observatory, offer a second check, the abstract says.

“These joint detections will allow us to establish that the gravitational signals correspond to genuine planets rather than false positives,” said Limbach, an assistant research scientist at Michigan.

How many targets

Astronomers estimate that the Milky Way holds 10 million pairs of white dwarfs that circle each other in less than an hour, systems that emit gravitational waves in the range LISA is built to detect, according to NASA. They expect LISA to pick out about 10,000 of them individually, plus around 100 mixed pairs involving white dwarfs, neutron stars or black holes. NASA says LISA could pick up a planet of Jupiter's mass around such pairs at distances of up to thousands of light-years.

The mission

LISA will consist of three spacecraft flying in a triangle with sides of 2.5 million kilometers (1.6 million miles) that follows Earth around the Sun. Laser beams between the spacecraft will monitor the distances between free-floating cubes inside them, looking for the minute changes caused by passing gravitational waves. NASA is contributing the telescopes, the laser system, devices that manage electric charge on the cubes and data analysis, and OHB-System AG in Germany will build the satellites, according to NASA. Gravitational waves were predicted by Albert Einstein's general theory of relativity in 1916 and first detected by ground-based observatories in 2015. The idea of spotting planets around double white dwarfs with a space detector was first proposed in 2008 by the Japanese astronomer Naoki Seto.