Neutrino Geoscience: Geoneutrinos and heat production in the Earth

The PI seeks to understand the power driving the Earth’s engine and how long the fuel, which powers its engine, will last and keep the planet active and habitable. There are two sources of energy within the Earth: the primordial energy and radiogenic energy. Primordial energy is the kinetic energy that comes from heating during a collision: particle to particle, small planet to small planet, and big planet to big planet collisions.

A simple estimate of this energy, derived from the velocity of meteorites and the mass of the earth, gives 1032 joules, or more than a trillion, trillion times the power of all nuclear power plants in existence. Unfortunately, we lack a fuel gauge for either energy source and consequently we do not know how much power is left to drive the earth's engine, nor how much energy (and time) is left to keep it habitable.

Geoneutrinos are naturally occurring electron antineutrinos produced during beta-decays of these heat producing elements. These neutrinos are tiny fundamental particles that are almost impossible to detect, because they are about a billion times smaller than a proton, near-massless and chargeless. In 2005, particle physicists first detected the earth's emission of geoneutrinos with large underground detectors and are now telling us about the amount of radiogenic heat inside the earth.

Reading the earth's fuel gauge by counting geoneutrinos, however, requires that geologists understand the abundance and distribution of these heat producing elements in the continents and the mantle.By quantifying the planet’s geoneutrino flux we can establish precisely its composition and define the meteoritic building blocks used to construct the Earth. Competing theoretical models of the Earth’s composition will be unbiasedly interrogated by neutrino technology and tell us which of the competing chemical models of the Earth is the right one.

New results from geoneutrino detectors in Japan and Italy present contrasting stories as to how much fuel is left in the earth's engine. Geologists are addressing these complexities by building 3-D physical and chemical models of the earth’s continents. We seek to resolve these complexities. This award will fund the research of a graduate student and the outreach efforts of the PI.

Debate continues regarding the convective power of earth's mantle and the abundances of radiogenic elements in the earth. The earth has a nonuniform 3D physical and compositional structure. Consequently, there is minimal consistency between heat production models. Data from current and planned geoneutrino detectors (major 100’s of million dollars particle physics experiments) can bring resolution to several major issues in earth sciences which we seek to answer:

1. what are the building blocks used to make the planet; 2. what is the proportion of radiogenic heat relative to the residual heat of accretion and core formation; 3. what is the fraction of radiogenic heat in the continental crust relative to that in the mantle; and 4. what is the composition of the bulk silicate earth, and its present upper and lower mantle?

Answers to these questions will, in turn, define the power that drives plate tectonics, mantle convection and the geodynamo. From this we will also get insights into the structure of mantle convection. Neutrino geoscience offers a potential to address broad interdisciplinary issues over conventional methods.

Geoneutrino measurements sample the globe and are not confounded by mantle melting processes. The current debate about the mantle's Urey ratio (values ranging from 0.1 to 0.8; where UR = (radiogenic mantle power)/(total - crustal radiogenic power)) confound predictions for the Earth's abundances of chondritic refractory elements (36 elements, including Ca, Al, Th, & U), its cooling rate, and the onset of plate tectonics.

Having geoscientists working with physicists to determine the crustal model for the geoneutrino signal and the mantle's contribution to heat production will promote mutually beneficial interdisciplinary collaborations.

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.