Scientists can map subtle shifts in Earth's gravity using atoms

NASA is preparing to send a quantum sensor into orbit to measure subtle shifts in Earth’s gravity. The implications of this effort reach far beyond academic curiosity because these measurements could reveal hidden phenomena, from changes in global water availability to pockets of oil and gas beneath the surface.

After two decades of planning, a group of researchers is set to integrate this sensor with a satellite and launch it by the end of the decade.

The team includes private companies, academic partners, and NASA’s Jet Propulsion Laboratory, where Jason Hyon serves as chief technologist for Earth Science and also directs the Quantum Space Innovation Center.

Detecting hidden gravity shifts

A gravity gradiometer is a tool that picks up tiny variations in how hard gravity pulls on objects. These changes are often invisible to everyday perception, yet they help paint a detailed picture of what lies under land or ocean.

Experts who track Earth’s shifting mass rely on high-precision satellites for data on water supplies, ice sheets, and other large systems.

This mission, called Quantum Gravity Gradiometer Pathfinder (QGGPf), could be a major step toward refining those measurements and making them more accurate. A more precise view of our planet’s gravity may benefit efforts to manage natural resources on a global scale.

Measuring Earth’s gravity with frozen atoms

The heart of the mission relies on rubidium atoms that are chilled to extremely low temperatures. They are placed in free fall within the instrument, creating test masses that respond to gravity’s pull in ways that the device can measure with fine precision. 

By monitoring the difference in how two atomic clouds accelerate, the team gains insights into subtle gravity shifts.

Chilling atoms to near absolute zero is tricky to do on Earth because they need sustained free fall conditions. In space, these atoms remain in microgravity, offering a longer window to track tiny shifts in their movements.

Using atoms to track Earth’s gravity

Today’s space-based gravity missions rely on multiple satellites that track their positions relative to each other. The QGGPf mission proposes a compact, single-satellite approach.

The sensor takes up about 0.3 cubic yards (0.2 cubic meters) and weighs roughly 275 pounds (125 kilograms). That size is manageable for launch yet still big enough to house complex laser and vacuum systems.

The ability to see variations at smaller scales may assist with identifying underground aquifers or regions where geological shifts threaten infrastructure. This is especially significant for communities that need to track freshwater availability.

“We could determine the mass of the Himalayas using atoms,” noted Hyon.

Testing the instrument’s sensitivity

NASA’s Earth Science Technology Office supports QGGPf, which highlights how agencies sometimes partner with smaller businesses and laboratories to advance the development of cutting-edge instruments.

Key roles in this project come from companies that develop the compact laser systems for cooling and trapping atoms. The synergy between government and private enterprise speeds up innovation.

“We need to fly it so that we can figure out how well it will operate,” said Ben Stray, a postdoctoral researcher at JPL. He and others anticipate that the data collected will confirm whether the instrument truly achieves the sensitivity required for future missions.

Atoms reveal secrets of Earth’s gravity

Gravity is stronger where there is more mass. A system able to detect even minor mass differences could deliver maps of rock density or water distribution beneath the surface. By comparing local gravity over time, scientists can also spot changes linked to melting glaciers or draining groundwater basins.

Much of this detail is absent from current measurements, which are already beneficial for climate scientists and geologists. QGGPf aims to build on that success and produce data at a higher resolution.

Keeping the data accurate

The sensor depends on lasers that cool atoms until they behave like overlapping waves. If any vibration or misalignment disrupts this setup, the data may lose accuracy.

The team has focused on stabilizing optical components and ensuring that the vacuum system holding the atoms remains in the best possible condition.

A robust spacecraft attitude control system will keep the device oriented so that random movements in orbit don’t blur the results. Plans also include methods to guard against minor temperature fluctuations that could shift laser alignment or disturb the sensor’s vacuum chamber.

Gravitational fields of other planets

Knowing exactly how gravity changes can help with more than resource management. These measurements could enhance the understanding of fault lines and the structure of Earth’s crust.

The approach could also be applied to studies of gravitational fields on other planets, where future missions might carry versions of the same sensor to help map the inner layers.

“The QGGPf instrument will lead to planetary science applications and fundamental physics applications,” said Hyon. Teams worldwide are watching to see if QGGPf’s technology can move quantum sensing from laboratory floors into reliable, orbit-based instruments.

New generation of quantum sensors

If this project meets its goals, it will open the door to more sensitive tools that may someday detect subtle gravitational signals from even smaller hidden features.

There is growing hope that a new generation of quantum sensors will transform how we explore everything from mining and energy reserves to the biggest questions about planetary formation.

Scientists from many disciplines are eager to see how a single craft can gather detailed insight into Earth’s gravitational puzzle. That data could indicate both risks and resources that might otherwise be missed.

The study was published in EPJ Quantum Technology.

Image Credit: NASA

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