Working Across Many Scales - Letter from the Directors - July 2020

Working Across Many Scales
Thursday, July 30, 2020 

An atom has a diameter of a fraction of a billionth of a meter. Earth’s diameter at the equator is about 12.7 million meters. The most distant object seen in Scott Sheppard’s continuing search for planet X orbits as far as 345 billion meters from the Sun.  We are sticking with meters for the distance unit here to make the point about the range of scales of our research.  For those of you not familiar with metric units, a meter is about half the six-feet we are supposed to be socially distancing from one another, or if you are from Pittsburgh, a meter is twelve pierogis laid side by side. The research reported in this month’s newsletter covers these 21 orders of magnitude range in spatial scale.

Small things with big impact

At the atomic level, EPL’s Banting Fellow, Olivier Gagné, examined the factors that control the length of bonds within crystal made of oxygen and various transition metals, which in turn determines a number of properties of these crystals. Although the atoms in the materials around us are largely unseen—except by very special microscopes—the way they arrange themselves ultimately determines their properties, for example, whether a substance is soft or hard, whether it is an electrical conductor or insulator, as well as the many other properties essential to our technology-reliant society.

Using a microscope to study planets

Earth's magnetic field protects our atmosphere from solar radiation.
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles from the solar wind and cosmic rays.

Working with sample sizes some five orders of magnitude larger than single atoms—though still smaller than the diameter of a human hair—EPL scientists Alex Goncharov, Nicholas Holtgrewe, Sergey Lobanov, and Irina Chuvashova found that the addition of silicon to iron metal can affect the thermal conductivity of the alloy at the pressure and temperature conditions found in Earth’s core. This is important because Earth’s magnetic field is generated by convective flow of the liquid iron in the outer core.  The primary energy source driving that convection is heat loss from the core to the rocky mantle above.  Think of the sinking plumes of liquid in your favorite beverage when you float an ice cube on its surface.  The more thermally conductive the material is in Earth’s core, the more quickly it will transfer its heat to the mantle. When the temperature of the core gets close to that of the base of the mantle, there is no longer any excess heat to exchange, so the driving force of core convection stops, which would cause Earth’s magnetic field to vanish in the absence of other driving forces like compositional buoyancy.

Earth’s magnetic field has been with our planet for at least 3 billion years, though observations described by EPL Staff Scientist Peter Driscoll in his neighborhood lecture in 2018 suggest that its strength has varied substantially over Earth history. Earth’s magnetic field extends well into the space around the planet.  In the Sun’s direction, pressure from the Solar wind limits the extent of the field to about 60 million meters, but the field extends some 1.2 billion meters away from Earth on the other side. This deflection of the Solar wind, along with other high-energy charged particles like cosmic rays, by Earth’s magnetic field is essential for the survival of life on Earth’s surface.  

As a historical side note, a good deal of our understanding of the ways that cosmic rays interact with Earth’s upper atmosphere derives from fundamental studies made at DTM in the 1930s using balloon-borne cosmic ray detectors like that shown in the picture below.

Beyond Earth’s, but not the Sun’s, influence

Scott Sheppard talked to The Guardian about the search for Planet X. Illustration: Carnegie Institution for Science | Roberto Molar

The measurements by Goncharov and colleagues, done on samples about ten-millionths of a meter in diameter, connect phenomena occurring deep in Earth’s interior with those extending billions of meters into space. 

Yet, the extent of Earth’s influence on its surroundings pales with respect to the gravitational reach of the Sun. The searches conducted by Sheppard and colleague Chad Trujillo of Northern Arizona University for distant objects orbiting the Sun continue to provide evidence for the gravitational influence of outer Solar System bodies from a still unseen massive planet that could be in an orbit that takes it over 200 trillion meters from the Sun.

Making the tools for discovery

The new Okuma lathe works on four axes, which will allow the machine to turn and mill materials at the same time. Photo credit: Victor Lugo

From atomic structures to the outer reaches of our Solar System and beyond, Carnegie scientists’ work depends on access to a wide variety of highly specialized tools

For instance, our astronomers depend on access to large ground-based telescopes like those at Carnegie’s Las Campanas Observatory and large-scale national and international facilities like the Suburu Telescope in Hawaii and the newly renamed Vera Rubin Observatory. 

In contrast, work like that reported by Goncharov and colleagues depends on devices made in-house at EPL, for example, the diamond anvil cell. Our campus has long maintained excellent machine shop facilities and employed skilled instrument makers that allow our scientists to design and build new cutting-edge instrumentation that can make measurements on previously impossible scales.

This month, our shop expanded its instrument-making capabilities through the delivery of a 4-axis computer-controlled lathe. The lathe will further expand our skilled instrument makers' ability to precisely machine the many types of scientific tools essential to discovery.

Welcoming the next generation of world-leading scientists

The BBR campus welcomes our new class of postdoctoral fellows. This campus photo was taken in 2019.

Every year, Carnegie departments conduct international searches for the best early-career scientists to join our research programs. The postdocs bring fresh expertise, ideas, and abundant energy to campus.  In return, we provide them access to the excellent facilities on campus and mentoring that expands their expertise and prepares them for their future careers.

We are pleased to report that this year’s class of postdocs is the first for the combined Earth and Planets Laboratory in which the selection was done by the scientific staff of both the former DTM and Geophysical Laboratory. We will be welcoming this group to campus over the next few months.  While maintaining appropriate PPE and social distancing (two meters – 24 pierogis) protocols, we look forward to helping them start on their research programs at EPL.

Rick Carlson and Michael Walter

Director and Deputy Director
Earth and Planets Laboratory