University of Maryland astronomer Michael A'Hearn has won the 2008 Kuiper Prize in recognition of his seminal contributions to, and leadership of, the study of comets.

Awarded by the American Astronomical Society's Division of Planetary Science (DPS) the Kuiper Prize is given "to scientists whose achievements have most advanced our understanding of the planetary system."

The prize is named for Gerard P. Kuiper who is widely regarded as the father of planetary science. A'Hearn is receiving his award and will deliver a Kuiper Prize lecture at the DPS annual meeting that runs from October 10 through October 15 in Ithaca, New York.

This is the second major space science award A'Hearn has received in 2008. In August, the American Institute of Aeronautics and Astronautics awarded him its Space Science Award "for his leadership of the 'Deep Impact' mission, which delivered the first man-made object to impact the nucleus of a comet and study its composition."

At the Nucleus of Comet Discovery
"Mike A'Hearn is, in my opinion, the undisputed intellectual leader in the field of cometary physics and a contributor of international renown," says Michael Belton, emeritus astronomer, National Optical Astronomy Observatory and president of Belton Space Exploration Initiatives.

"His contributions are characterized by both observational virtuosity and insightful physical analysis."

Belton and other planetary scientists cite A'Hearn's work as a scientist and teacher and point to his origination of three paradigm shifts that have occurred in recent decades in scientists' understanding of the physical nature of cometary nuclei. The nucleus is the solid body of the comet.

It is surrounded by a cloud of gas and dust given off by the nucleus that forms the comet's tail. In lay terms, comets, and their nuclei, often have been described as either dirty snowballs or icy dirtballs, but A'Hearn and other researchers are showing that they are much more complex, mysterious and perhaps more varied objects than these simple descriptions imply.

The first A'Hearn-led shift in the view of comet nuclei was the product of papers he authored with colleagues and students in the late 1980s.

This work for the first time combined thermal and visual observations together to show something definitive and quantitative about the nature of cometary nuclei; indicating they are irregular dark objects that sport a largely inactive surface. In 1986, asteroid 3192 A'Hearn was named in honor of his contributions to cometary science.

A second major shift in scientists' understanding of comets resulted from an exhaustive 17-year survey of comet observations led by A'Hearn. Its results, published in 1995 as "Ensemble properties of comets, compiled results of photometry of 85 comets," showed that comets are largely very similar in composition.

The most recent and best known paradigm shift led by A'Hearn actually is still underway, and it comes in large part as a result of his leadership of the Deep Impact mission, which produced a wealth of new comet data and made world-wide headlines when it smashed a probe into comet Tempel 1 on July 4, 2005.

Among the surprising findings of Deep Impact was the fluffiness of structure of the nucleus and previously unseen surface features, like craters, indicating processes actively changing the comet's surface.

Many of the surface findings from Tempel 1 were very different from the findings of the two other space missions to comets: Deep Space 1 and Stardust, leaving A'Hearn and other cometary scientists questioning anew some of what they thought they knew about these fascinating objects.

DI and its Leader Just Keep Going and Going
A'Hearn and the Deep Impact spacecraft are now involved in a new comet mission called EPOXI. The name EPOXI is a combination of EPOCh and DIXI, the acronyms for the two components of the extended mission.

The Extrasolar Planet Observations and Characterization or EPOCh component is a search for Earth-like planets around stars selected as likely candidates for such planets. EPOCh observations began in January 2008 and completed in August.

The Deep Impact eXtended Investigation or DIXI is the cometary investigation portion of the mission. The spacecraft is expected to fly by comet Hartley 2 on Nov. 4, 2010, allowing scientists to compare findings for this comet with those from other comet missions.

Although in recent years A'Hearn has studied comets through the use of space missions, he has said he is a traditional astronomer by disposition and training. He studied physics at Boston College, and then earned his PhD in astronomy from the University of Wisconsin. From there he went to the University of Maryland where much of his early work was based on telescopic observations. But, whether by telescope or spacecraft, A'Hearn has been expanding human understanding of comets for 42 years with many new discoveries still in store.

"I'm trying to solve the mystery of what conditions were like in the early solar system, how things formed," he said in a profile posted on the Deep Impact mission website prior to the mission's 2005 encounter with Tempel 1. "My tools are comets and asteroids."