GRAZIL

Starting point / motivation

The Moon - the only natural satellite orbiting our home planet – is one of the most fascinating extraterrestrial objects. Owing to its low geological activity, knowledge about the physical nature of the Moon helps to unlock secrets of the evolution of the Earth and the solar system.

One of the most striking examples are the large positive gravity anomalies (so-called mascons) on the lunar surface, which originate from large impacts and provide a window into the crustal structure of terrestrial planets (terrestrial planets in the solar system include Mercury, Venus, Earth, and Mars).

Due to its closeness to the Earth, the Moon is not solely of particular interest in planetary science from the evolutionary point of view, but also with regard to human landing, or attempts for human settlement. For the time being, many questions in lunar research are still open; therefore, space agencies all over the globe advocate continuing investment in lunar science.

One key quantity in lunar science is the Moon's gravity field. Gravity is sensitive to a body's composition, density structure and rotation. Furthermore, gravity dominates the force on a test mass in the body's exterior, and hence is of crucial relevance for satellite orbit design and spacecraft navigation.

With the Gravity Recovery And Interior Laboratory (GRAIL) mission, for the first time ever, a planetary satellite project exclusively dedicated to the recovery of the gravity field has been realized ("one-sensor mission").

The data collected by the twin-satellite mission allows deriving the lunar gravity field with unprecedented accuracy and resolution. Geophysical parameters, such as the deformation Love numbers, can be estimated together with the gravity field. Due to the lack of appropriate seismic data, these geophysical quantities act as fundamental constraints to determine the state and size of the lunar core.

Contents and goals

Our goal is to derive high-accuracy gravity field information from the data collected by GRAIL. For this purpose, we make use of dynamic precise orbit determination in combination with a novel inference technique in lunar sciences.

The approach is an adapted version of a method that has been developed and very successfully applied for the recovery of the gravity field of the Earth. We pay particular attention on the long-to-medium-wavelength gravitational spectrum with special view on the separation of gravity field parameters from the deformation Love numbers. We expect to find answers to pending questions in lunar research, especially as far as the state and size of the lunar core is concerned.

Coordinator

Austrian Academy of Sciences

Project partner

University of Technology Graz

Austrian Academy of Sciences
Dr. Ignaz Seipel-Platz 2
A-1010 Vienna
Web: www.oeaw.ac.at