Gravitational Wave Detector Could Be Used To Study Comet Dust

Artist impression of LISA Pathfinder in space. ESA/C. Carreau

LISA Pathfinder is the successful precursor mission for the future European gravitational wave observatory in space. Last year it demonstrated that not only is the technology ready for the future observatory, but the instruments are even more sensitive than we thought.

This exquisite sensitivity has intrigued NASA scientists who want to use the European Space Agency (ESA) craft to study something slightly less exotic than gravitational waves: comet dust.

The Solar System is full of microscopic fragments of comets and asteroids, about the mass of a grain of sand. They might not seem important but they are moving at 36,000 kilometers (22,000 miles) per hour so they do have a quite the momentum.

The researchers have modeled how to use LISA Pathfinder to measure the dust direction and distribution. The probe was designed to keep two test cubes in a perfect freefall, responding only to gravity. It has a shield to protect it from external forces and it has micronewton thrusters to balance them out.

"Every time microscopic dust strikes LISA Pathfinder, its thrusters null out the small amount of momentum transferred to the spacecraft," co-investigator Diego Janches, from NASA’s Goddard Space Flight Center, said in a statement. "We can turn that around and use the thruster firings to learn more about the impacting particles. One team's noise becomes another team's data."

When the early results from LISA Pathfinder came in last year, the researchers were delighted that the spacecraft had a precision of almost five times better than expected. It is the most sensitive instrument to measure acceleration ever sent to space. The ingenuity of this project is utterly remarkable.

Micrometeoroids are not just leftovers of distant epochs. Comets and asteroids have always peppered the Solar System and continue to do so. These space grains have different velocities and orbits, and a deep space mission like LISA Pathfinder and its successor could provide a lot more clues to their origin.

"This is a proof of concept, but we'd hope to repeat this technique with a full gravitational wave observatory that ESA and NASA are currently studying for the future," said Ira Thorpe, who leads the team. "With multiple spacecraft in different orbits and a much longer observing time, the quality of the data should really improve."

The full-scale LISA – Laser Interferometer Space Antenna – will launch in the 2030s and will have three spacecraft stationed millions of kilometers apart, with lasers stretching between them. This will allow us to observe gravitational waves that we would not be able to observe on Earth – and now learn a lot more about dust, too.

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