Alessandro Massarotti

Biography

The main focus of my current research is the study of the structure and evolution of rocky planets. These include bodies such as the Earth, Mars, Venus, Mercury and the many exoplanets currently being discovered orbiting stars other than our Sun.  I have been working on this long-term project for almost three years, assembling a state-of-the-art computer code that describes rocky planets using the best information available about the Earth and the behavior of materials under the enormous pressures and temperatures of planetary interiors.

One of the aims of my research is to better explain processes that have taken place on our planet since its formation, such as the continuous formation of new continental crust, the cycling of water between the oceans and the Earth’s interior, and the onset and strength of the Earth’s magnetic field. The code is also built to predict the strength of various kinds of volcanism and the rate of continental drift as a function of time.

A further goal of this research is the understanding of the grand geophysical features of both Mars and Venus, planets that appear to have taken a very different evolutionary path when compared to the Earth: Venus has a very thick and extremely hot atmosphere but no water on its surface; it is very volcanic but shows no evidence of plate tectonics, or even the presence of continents; Mars, instead, has a very thin atmosphere but possesses considerable water reserves in the form of ice under its surface; huge volcanoes are present but inactive; Mars also displays no evidence of plate tectonics or continents. My theoretical model predicts the possible presence and the strength of tectonic processes throughout the history of planets whose masses range between the 0.1 and 10 times the Earth’s mass (including Mars and Venus) under a variety of conditions, such as the overall composition of the planet and its temperature at formation.

Another line of my research is in the field of astronomy. In recent years I published work on red giant stars and the likelihood that these old Sun-like stars may have gobbled up nearby planets as they expanded during this final stage of their evolution. In an ongoing project I am studying the process of orbit circularization and change of rotation rate due to tidal interactions between red giant binary stars in close orbits.  The same data where used in already completed research, described below.

Massarotti et al. (2008) is an investigation of 761 red giants within 100 pc from Earth. These stars are close enough to the Earth that their distance was found with great accuracy using parallax methods by the Hipparcos satellite in the 1990’s. Knowing their distance within 10% allowed me to find their luminosity and other physical parameters (e.g. the stellar radius) with accuracy.  Using these results I was able to use stellar models to determine the exact age of these stars and their evolutionary phase. The analysis of the stellar spectra allowed me to find the rate of rotation of these red giants. At this point I was very surprised to find out that stars acquire surface rotation from a rapidly spinning core when the outer their layers briefly become coupled with the core by the process of stellar convection. This finding corroborates the notion that stars like our own Sun initially rotate fast, but soon lose surface rotation because of stellar winds; the stellar core however keeps its high rotation rate and divulges some of its rotation to the stellar surface during the red giant phase.

The same paper, together with the follow-up publication Massarotti (2008), explores the issue of planetary ingestion by old stars. Of the 761 stars we investigated, three display rotation rates higher than their evolutionary phase would grant. The most reasonable explanation of these observations is the spin-up that stars undergo as they swallow and destroy Jupiter-size planets in their vicinity while they grow in size with age. In Massarotti (2008) I showed the consistency of this hypothesis with the current statistics of the distribution of giant planets as a function of distance for Sun-like stars.

I am also interested in a totally separate field of physics, namely high-energy particle physics and quantum gravity. I am fascinated by the conceptual difference between the angular momentum related to particle motion and the ‘spin’ possessed by fundamental particles such as electrons. According to the standard view of fundamental particles these are truly points of mass and charge, without dimension. If that is true it is hard to conceive the presence of an intrinsic spin associated with them.

While the solution of this puzzle may rest in abandoning the idea of point particles, another way to proceed is to make spin a fundamental quantity describing particles and explain motion in terms of spin and its evolution instead (see Massarotti & Chakravorty (1997)). This is a radical approach, since it aims at explaining space itself in terms of the evolution of spin in a discretized version of time. We are not be aware of the ‘digital’ nature of space and time because of the tiny scales at which the discretization is supposed to occur. As a corollary, this way of approaching particle physics promises to use spin in order to also explain the nature of charges (such as electric charge among others) and the way particles associate themselves in families according to the way they interact with each other.

Earlier in my career, I published other papers in astronomy and early cosmology (a branch of astrophysics).  My interests ranged from the direct detection of giant planets around newly born stars in IR images taken by the Hubble Space Telescope (see Massarotti et al. (2005)) to unorthodox models for galaxy formation due to high energy phase transitions in the early universe Massarotti & Quashnock (1993), Massarotti  (1991) and Griest et al. (1989).

Education

  • B.S. Physics, University Of Rome ‘La Sapienza’
  • Ph.D. Physics, University of Chicago

Research Interests

  • Plate tectonics
  • Atmospheres of terrestrial planets

Courses Taught

  • The Universe
  • Planets, Moons & the Search for Alien Life
  • Physics III
  • Physics II
  • Physics I