How NASA’s Quantum Sensor Is Using Atoms To Measure Earth’s Gravity

Nasa Earth gravity

We all are familiar with the term gravity. In high school, we have been taught that Earth’s gravity pulls things toward its center at a rate of 9.8m/s^2. However it’s not entirely accurate. The Earth’s gravitational pull isn’t uniform, varying from one place to another and changes over time. Gravity is directly related to mass, more massive an object is, the more force it uses to pull on other objects.

Since 2000, scientists used satellites to map the Earth’s gravitational field. Recently, they have developed a new instrument which uses quantum phenomena for more accurate measurements. Altogether the mass of water is larger than any other component of the Earth. Therefore, the shifting mass of water is the biggest factor which contributes to a change in Earth’s gravity. Mass of a glacier or water trapped underground will be redistributed.

Measuring the minute changes in the gravitational field is a way to track what Earth’s water is doing and how the water cycle is being affected by the climate change. NASA missions like GRACE and GRACE-Follow On used twin satellites to map the field. The principle was one satellite would follow the other, and as they passed through fluctuations in the gravitational field, they would get closer or farther apart. Scientists can know how the gravity over the respective part of the world differed by measuring the distance. NASA is collaborating with the company AOSense.Inc for the project.

The new prototype sensor uses about 100million cesium atoms sealed in a vacuum near absolute zero, keeping the atoms insulated from the outside factors which may affect measurements. Gravity is the only force pulling on these atoms. These atoms are coaxed into behaving like light waves. Lasers can split and send these waves down different paths, interacting with gravity while travelling. When the waves finally met up, they form an interference pattern in which some sections of the waves have a higher amplitude while others have a lower amplitude.

The instrument can determine the effect on atoms by the gravity with unprecedented accuracy by studying the interference pattern. The past atom-based instruments required components of the size of a room, the new sensor is small enough to fit on a spacecraft. The device reported different gravitational measurements during testing after the scientists returned from lunch break because it was detecting the added mass from the food within their stomachs. In space, the sensor will map the Earth’s gravity 10 times more precisely than GRACE-Follow On at 4 times the spatial resolution. Gravity mapping satellites can also help us probe the Earth’s secrets like what’s happening under Antarctica.

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