Faces of the Foundation: Sean Solomon
posted: 4/16/2018
listed in Faces of the Foundation
For
a geophysicist, Hertz Fellow Sean Solomon spends a lot of time looking up
instead of down. Though much of his career has been spent probing beneath the
ocean floor and deep within the Earth to understand how the surface of our planet
is formed and moves, he has also sent instruments to the Moon, and to our three
nearest neighbors in the solar system – Mercury, Venus, and Mars. The other
three rocky planets, he says, are “nature’s experiments in how a planet like
Earth became the planet it is today.” As the director of Columbia University’s
Lamont-Doherty Earth Observatory, he is now applying a lifetime of experience studying
these planets to the vital task of understanding and preserving our own.
Studying
structures deep beneath the surface, or on other planets, requires the application
of many different measurement systems – seismology, gravimetry, magnetometry –
and different disciplines, says Solomon. “The roots of my work go back to when
I was a Hertz Fellow,” Solomon adds.
He entered
MIT at the right time to participate in two different geological revolutions. As
the 1960s came to a close, the theory of plate tectonics was taking shape. As
the scientific community was growing to understand how one plate sinking
beneath another created the great trenches and deep earthquakes in the Western
Pacific, Solomon was on a ship in that very region, operating a gravimeter to
map the moving rock beneath him.
The
second revolution was equally historic. With advisor M. Nafi Toksöz, Solomon
helped interpret data from the seismometers that the Apollo astronauts took to
the Moon, helping to probe the interior of a world other than Earth for the
first time. (One of his papers with Toksöz and others drawing on these data is
titled, simply, “Structure of the Moon.”)
“The
Hertz Fellowship enabled my exploration,” he says. “Rather than focus on one
narrow question, I could do research on geophysics, planetary seismology, and
more.”
Since
earning his PhD, much of Solomon’s terrestrial career has been devoted to
seismology – at its simplest, measuring vibrations propagating through the
Earth (or, occasionally, other planets). If you know enough about the vibrations’
source, you can tell a lot about the portion of the Earth or planet through
which they have traveled to reach a detector. Solomon used this tool, alongside
other sensing methods, to track how molten rock cools as it erupts along
divergent plate boundaries such as the Mid-Atlantic Ridge. "We were able
to learn how the crust forms and characterize the earthquakes that occur
there," he says.
Different
sensing methods were important for terrestrial research, but they were
indispensable for the research Solomon has conducted about other planets “In
exploring other planets, seismology has not, by and large, been one of the
tools we use,” he says. Seismometers must make physical contact with the
surface of a planet, creating design challenges and competing with other
scientific equipment for valuable space, even on planetary lander and rover
missions.
Solomon’s
interdisciplinary thinking has allowed him to take leadership roles in missions
to other worlds, including as principal investigator for NASA’s recently
completed MESSENGER mission to orbit and characterize Mercury. It was through neutron
spectrometry, laser altimetry, and imaging, not seismology, that MESSENGER confirmed
that even Mercury – the closest planet to the Sun – has water ice hiding in the
permanent shadows of its cratered surface. This and other MESSENGER discoveries
were cited as among Solomon’s key contributions when President Barack Obama
awarded him the National Medal of Science in the physical sciences in 2014.
Solomon
says exploring the inner planets is fascinating because they provide a very diverse
range of outcomes for how rocky planets like ours evolve. "In some
respects, they don't look like they came from the same family, and yet they
did."
These
differences illustrate just how lucky we are that Earth’s surface environment can
support life, he says. From the magnetic field generated in the molten core
providing magnetic shielding to tectonic activity providing nutrient cycling
that could have been especially important for early life in the ocean,
"Earth is a good place for life's experiment to work out."
As
director of Lamont, Solomon sees his role as working across disciplines to help
understand and protect “life’s experiment.” “I was attracted by the passion of
the scientists here,” he says. As the geologists, biogeochemists, atmospheric
scientists, and others at Lamont learn more about the challenges facing Earth’s
changing climate and the response of biological systems to those changes, Solomon
says "the work Lamont scientists are doing is really at the core of how to
grapple with some of society’s most pressing issues.”