Did you know that the force that keeps you on the ground changes from place to place? This force is known as gravity and describes why apples fall from trees as well as why planets orbit the sun. On the Earth, the strength of gravity at your location is related to the mass around you. I use gravity to measure the mass of the Earth’s great ice sheets, which are as large as continents and thicker than our tallest skyscrapers. The ice sheets are currently changing, losing mass into the oceans and causing the seas to rise. My research looks at smaller regions of the Greenland and Antarctic ice sheets, measuring their mass month-by-month. These smaller regions are like river systems, flowing ice from their interiors to the coasts. Minute changes in snowfall, ice melt, and iceberg production can change how much mass is in each of these regions year to year. With gravity, we are getting a better picture of these regions, as well as other glaciers thoughout the world.
So! How do we measure the Earth’s gravity? Well, in 2002 as twin pair of satellites was launched. These satellites are named GRACE (Gravity Recovery and Climate Experiment), and they chase each other in their orbits around our planet. When one satellite approaches a region with more mass, it speeds up, attracted by the gravity of that mass. We measure when and where the satellites speed up and slow down by measuring the distance between them. When the leading satellite speeds up it will gain distance on the trailing satellite, just as a fast runner will beat a slow runner in a race. The trailing satellite will speed up when it approaches the same region of mass, creating a game of cat-and-mouse with the leading satellite. With GRACE, we can create maps of how the Earth’s mass shifts around the globe due to water cycles, ocean circulation, ice sheet melt and more. It is almost like putting regions of the Earth on gigantic scales.
In my research I’ve spent the most time monitoring Greenland. With GRACE we can see that Greenland is losing a lot of ice, but we don’t know why right away. With other datasets we can try to get a better picture of what is causing the mass to change. We look at how much snow falls, how much ice melts, and how much ice is put out into the sea. Putting everything together helps us understand what is happening. We can see that Greenland overall is both melting and losing additional ice by creating more icebergs. This is not good news. Greenland is big and Antarctica is much larger. So I continue to monitor Greenland as well as Antarctica to try to determine their overall health, which may help us understand how our sea levels and our climate will change into the future.
– Tyler, University of California Irvine, USA