Analysis of gravity data collected through spacecraft orbiting other worlds reveals groundbreaking insights about planetary structures without having to land on the ground.

Although the moon and the asteroid Vesta are very different, the two NASA studies use the same technology to reveal new details about the interiors of the two.

In Moon Research, published on May 14 in the journal Nature, researchers have developed a new model of the lunar gravity that includes gravity changes in celestial bodies during an elliptical orbit around Earth. These fluctuations cause the moon to bend slightly due to the Earth's tidal forces, a process called tidal deformation - providing key insights into the deep internal structure of the moon.

The researchers used their models to create the most detailed map of the lunar gravity, providing an improved way to calculate the position and time of the moon for future missions. They achieved this by analyzing data on the motion of the NASA Grail (Grace Recovery and Internal Laboratory) mission, which spins the moon from December 31, 2011 to December 17, 2012.

In a second study published April 23 in the journal Nature Astronomy, the researchers focused on Vesta, an object in the main asteroid belt between Mars and Jupiter. They found that from July 16, 2011 to September 5, 2012, using NASA's deep space network radiation and imaging data, the spacecraft orbited asteroids from July 16, 2011 to September 5, 2012, instead of having unique layers as expected, but with a small iron core or no core at all, but that most of the internal structures might be unified.

Both studies, led by Ryan Park, director of the Solar System Dynamics Group at NASA's Jet Prosulsion Laboratory in Southern California, have gone through years of development due to its complexity. The team used the NASA supercomputer to build a detailed map, detailed map, how everyone's gravity changes. Thus, they can better understand the fabrication of the moon and Vesta and the formation of planetary bodies across the solar system.

“Grativity is a unique and fundamental property of a planetary mechanism that can be used to explore its deep interior,” Parker said. “Our technology does not require data from the surface; we just need to track the motion of the spacecraft very accurately in order to have a global perspective on the content inside.”

Moon studies have studied gravity changes near and far to the moon. While the proximity is a huge plain (called mare) formed by melting and solidifying billions of years ago, it is stronger in the distance, with almost no plains.

Some theories suggest that strong volcanoes on the near side may cause these differences. The process will result in radioactive, heat-producing elements accumulation within the proximal mantle, and the new study provides the strongest evidence that this may be the case.

"We found that the moon is more curved nearer than the distal end, which means that the internal structure of the nearer nearer than far is fundamentally different," Parker said. "When we first analyzed the data, we were very surprised by the results we didn't believe. So we did multiple calculations to verify the results found. Overall, it was a decade of work."

When comparing its results with other models, Parker's team found a small difference in the deformation of the two hemispherics, but larger than expected. The most likely explanation is that there is a warm mantle area proximally, indicating the presence of heat-producing radioactive elements, which is evidence of volcanic activity, which shapes the moon nearly 2 billion to 3 billion years ago.

Park's team took a similar approach to research, which focused on the rotational properties of Vesta to learn more about its internals.

"Our technology is sensitive to any change in the body's gravity field in space, whether that gravitational field changes over time, such as the tidal bending of the moon, or through space (such as a swaying asteroid)," Parker said. "Vista swings while spinning, so we can measure its moment of inertia, a feature that is highly sensitive to the internal structure of the asteroid."

The change in inertia can be seen when the skater rotates outward with his arms. As they pull their arms in, bringing more mass to the center of gravity, the inertia decreases and rotates at a speed. By measuring Vesta’s inertia, scientists can learn more about the distribution of mass inside an asteroid: if its inertia is low, it will be concentrated at its center; if it is high, the mass will be distributed more evenly.

Some theories show that Vesta has gradually formed onion-like layers and dense cores over the long period of time. However, new inertial measurements from Park's team show that Vesta is much more uniform in mass, its mass is evenly distributed throughout the process, and only has a small portion of dense material, or no core.

Over time, gravity pulls the heaviest element to the center of the planet, which is the end of Earth with dense liquid iron. Although Vesta has long been considered a differentiated asteroid, the more uniform structure suggests that it may not have a fully formed layer, or may have been formed by debris from another planetary body after a huge impact.

In 2016, Park used the same data type as the Vesta study, focusing on Dawn’s second goal, Dwarf Valley, and the results showed partial distinctions within.

Park and his team recently used NASA's Juno and Galileo spacecraft to use similar technologies to Jupiter's Volcano Moon IO in Jovian Satellite's Flybys and ground observations. By measuring how the gravity of IO changes as it orbits Jupiter (waves powerful tidal forces), they revealed that the blazing moon is unlikely to have a global magma ocean.

"Our technology is not limited to IO, Ceres, Vesta or the moon," Parker said. "There are many opportunities to use our technology to study the interiors of interesting planetary bodies throughout the solar system."

Ian J. O'Neill
Jet Propulsion Laboratory in Pasadena, California.
818-354-2649
ian.j.onel@jpl.nasa.gov

Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov