I was born in London in 1958. My father worked on a factory assembly line producing industrial steel cutters, my mother was a telephone operator. My first memories are of a winter with very heavy snow, of having appendicitis and of the birth of my sister, Jenny, all in 1962. I first noticed the sky three years later when, one evening, several bright meteors flashed overhead within a short interval. My mother said they were “shooting stars”, which confused me and left me wondering what I had seen. I began to look upwards at night more carefully and to think about space in the daytime and when it was cloudy (which, in England, was most of the time). Later, my grandparents bought me a tiny refractor as a birthday gift. Through it I saw the Moon, the stars and the planets, all against the sodium glare of the big city. I was astonished. A few years later, my uncle built me a bigger telescope: the planets looked even better. But I was also fascinated by trees, writing, machines, animals, music, rocks and fossils.  

Later, I met “physics”, then a new word for me. I found that it included many of the topics I most loved. A teacher told me that physics was the most difficult of subjects: I decided immediately to try to become good at it. Others told me that human knowledge was so vast that I could never hope to get to the edge of it. For years I believed them, but through my telescopes I sometimes saw things that I was pretty sure nobody else could have seen. The thought of being close to the edge made me very happy.

I was the first from my family to go to university. My time at University College London was free (tax-payer supported) and gave me an unsurpassable grounding in physics, mathematics and astronomy for which I remain extremely grateful. While at UCL, I won my first prize. The $500 Viking Prize from NASA was by far the largest sum of money I had ever seen. Crucially, it solved the problem of how to pay for my airfare to California, where I had been admitted as a graduate student at Caltech in 1979.

There, I worked closely with Ed Danielson, Gerry Neugebauer and his “infrared army” and I learned the importance of simplification from Peter Goldreich. I moved to MIT in 1983 as an assistant professor. Although not then equipped with good telescopes, MIT was where I first wondered “why is the outer solar system so empty compared to the inner solar system?”. This naive question was the key that later unlocked the door to the Kuiper belt. In 1988 I moved to the University of Hawaii, a place having unparalleled access to the world’s best telescopes and where, starting in 1992, we discovered and mapped the Kuiper belt.  

I liked Hawaii and stayed for 21 years. The decade of the 1990s was especially full of surprises, both personal and scientific. While observing on Mauna Kea I met Jing Li, a Chinese graduate student in solar physics visiting from the University of Paris. We were married in 1993. Our daughter, Suu Suu, was born in 2000. Scientifically, Jane Luu and I found that the Kuiper belt is thick, more like a doughnut than a sheet of paper, evidence of an unexpectedly violent past. We also found that the Kuiper belt is dynamically divided into regions. The Classical belt contains the most primordial bodies and has a still-unexplained sharp outer edge. We found many resonant objects (whose periods are related simply to Neptune’s), later shown by Renu Malhotra to be best explained if Neptune had migrated outwards, thus opening the door to wild new models of solar system evolution. Some resonant objects had Pluto-like orbits; we called them “plutinos” and concluded that Pluto was just another Kuiper belt object, albeit the brightest one. The Scattered belt, discovered in 1997, is the nursery of the comets. Joined by graduate student Chad Trujillo, we measured the mass of the belt and found too little material for the observed objects to grow – the current belt is probably a remnant of an original structure that was hundreds of times more massive.  Few of our observational results were predicted by dynamicists. Instead, increasingly elaborate models continue to emerge to account for what we have seen.  

I still like to be on the edge. At UCLA since 2009, I work on comets from the Kuiper belt and on a newly-found class of bodies that are half asteroid, half comet.  I suspect that similar objects once supplied water to the Earth’s oceans, as well as organic molecules that were the precursors to life.

17 September, 2012