Collaborative Research: A gravitational inventory of the solar system using high precision minor planet astrometry

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The NSF's Legacy Survey of Space and Time (LSST) will use the Vera C. Rubin Observatory to image over half the sky during 2023-2033. The investigators will improve the accuracy of sky position measurements for minor planets, allowing them to be used as "test particles" for exploring the gravitational forces in the solar system. The highly precise positions of these bodies will be used to study the potential gravitational effects of “planet X,” which might exist in the outer solar system. This work will indirectly benefit other astronomers by substantially improving the accuracy of LSST measurements of the motions of stars and planets. The program will involve young scientists from under-represented groups in astrophysical research at both the University of Pennsylvania and the Harvard-Smithsonian Center for Astrophysics and will support one graduate student at each institution. It will expand participation in summer research for undergraduates at Penn through a program directed at bringing first-generation / low-income undergraduates into research. By combining millions of LSST observations of thousands of Trojans, the effective motion of these objects over 10 years can be measured to 10-meter accuracy. Combined with ranging data from spacecraft at Jupiter and Saturn, a more accurate and specific understanding of gravity in the outer solar system will be possible by watching the Trojans complete an orbit around the Sun over LSST's lifetime. Accuracy below 1 meter will be obtained from the 200,000 brightest main belt asteroids (MBAs). This collective measurement accuracy allows detection of the gravity of a "Planet X" lurking undiscovered in the outer solar system. Close passages between the test particles will allow determination of the masses of perhaps 10 Trojans and 150-250 MBAs. By combining the signals all the mutual encounters, it should be possible to measure the mean relation between mass and brightness for MBAs down to about 15 km diameter and Trojans down to about 50 km diameter.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.