The European Space Agency's Laser Interferometer Space Antenna, scheduled to launch in 2035, could read the gravitational tug of near Earth asteroids, turning a noise source into a mass measurement for the thousands of objects other methods cannot weigh.
For most of the 41,000 known near-Earth asteroids, mass is a guess. The best determinations come from a narrow toolkit: watching a binary asteroid's two halves orbit each other, or catching a lucky gravitational encounter with a planet. Both tricks only work for a minority of objects. Fewer than 35% of near-Earth asteroids (NEAs) are known to within 10% of their true mass, according to a new peer-reviewed analysis of how the European Space Agency's planned Laser Interferometer Space Antenna (LISA) could fill that gap (Marques & Jennrich, A&A 2026).
LISA is built to listen for gravitational waves, the ripples in spacetime produced by colliding black holes and other extreme events. It is scheduled to launch in July 2035 and will fly three spacecraft in a triangular formation roughly 50 million kilometers behind Earth in heliocentric orbit. Inside each spacecraft sits a free-falling test mass, a shielded reference block whose position is tracked to picometer precision, sensitive enough to register the faintest gravitational tugs (Universe Today summary).
For LISA's primary science, those tugs are mostly noise. Asteroids and planets perturb the test masses, contaminating the gravitational-wave signal. The new paper, by S. Marques of the University of Bern and O. Jennrich of ESA's ESTEC facility and published in Astronomy & Astrophysics, argues that this "noise" is itself a usable measurement (paper). When a near-Earth asteroid passes inside the Minimum Orbital Intersection Distance (MOID) of LISA's orbit, its Newtonian gravity leaves a small, separable imprint on the test masses.
Separating that imprint from the gravitational-wave background is the central technical problem, and it is the same problem LISA already has to solve. The mission uses Time-Delay Interferometry (TDI) to synthesize an equal-arm interferometer and cancel laser frequency noise across the three spacecraft, the technique that lets it hear black-hole mergers in the first place. The same processing chain, the authors show, isolates the slower, longer-period tug of a passing asteroid.
The forecast yield is modest. Given current population models for NEAs and the assumed 10-year nominal mission, the paper estimates roughly three asteroid mass measurements over LISA's lifetime. Each one would be useful because of the long tail of objects other methods cannot weigh, not because LISA is a precision instrument on par with a flyby probe. Mass uncertainty scales inversely with the signal-to-noise ratio (SNR) of the encounter, and an SNR of five or better yields fractional mass uncertainty of about 20% at best. Recovering the asteroid's full state vector, meaning its position and velocity, is harder and depends strongly on flyby geometry.
The proposal lands against a known gap in planetary defense. Surveys have catalogued roughly 38% of near-Earth asteroids larger than 140 meters, the size threshold of most concern for impact hazard. Many of the asteroids LISA will encounter en route through its orbit have not yet been discovered, which is what makes the gravitational measurement valuable at all: it can, in principle, deliver mass for objects we are not currently tracking closely.
The honest constraints are several. LISA is not yet in space; the launch window is July 2035, and the asteroid-mass bonus would arrive years into the mission, not at first light. The measurement only triggers when an NEA passes close to LISA's orbit, so it is a sample, not a census. Dedicated in-situ probes remain the gold standard for mass determination when they fly, and optical and radar methods still win on precision where they apply. What LISA adds is coverage of the long tail: the thousands of known and not-yet-known NEAs that no probe will visit and that binary-orbit tricks cannot weigh.
What to watch next: the paper's yield estimate depends on the assumed NEA population, and improvements in survey completeness between now and 2035 will sharpen the prediction. A single high-SNR encounter during the mission's first years would be the first proof that the noise channel really is a signal channel.