Also at the center is a mass concentration (mascon), or gravitational high. The Imbrium mascon is the largest on the moon. At the center of the Humboldtianum basin is a mascon, or gravitational high. Mare Serenitatis is an example of a mascon, an anomalous gravitational region on the moon. At the center of the basin is a mass concentration (mascon), or gravitational high. Examples of mascon basins on Mars include the Argyre, Isidis, and Utopia basins. The mascon was mapped at high resolution by GRAIL. The mascon was first identified by Doppler tracking of the Lunar Prospector spacecraft.