201 Allison Laboratory
Auburn, AL 36849
dennis (at) auburn.edu
I am a planetary scientist at Auburn University working on the exploration and observation of comets and asteroids.
My research centers on the physical and chemical behavior of comets. What processes affect the observable gas surrounding comets? How are they connected to the formation of our solar system? How do they evolve through atomic and molecular reactions? I try to answer these questions by combining telescopic observations (Hubble, Chandra, Swift), laboratory experiments, and in-situ exploration by planetary missions (Rosetta, EPOXI, and Stardust NExT).
The gas around comets is altered by sun light, by the interaction with the solar wind, and by physical and chemical reactions. Planets and comets emit X-rays through charge exchange between the solar wind and the neutral molecules in their atmospheres. I have studied the underlying charge exchange reactions in the lab and use telescopes like XMM-Newton and the Chandra X-ray Observatory to remotely study the plasma environments of comets.
Rosetta observations of comet 67P/Churyumov-Gerasimenko revealed that under certain conditions, electron impact reactions can be the most important reactions in the coma. I collaborate with the Comenius University in Bratislava (Slovakia) to characterize these reactions. A major goal of our project is to determine how to use the emission from electron collisions to study gases in comets and the atmospheres of other small bodies, such as Europa.
Cometary activity changes as active areas on the surface rotate in and out of sunlight. This variability is caused by changes in the distribution of sunlight as the comet rotates (diurnal variation) and orbits the sun (seasonal variation and evolution). Using telescopes such as the Discovery Channel Telescope, the Neil Gehrels-Swift observatory, and Spitzer, I study the variability of cometary activity to explore the chemical heterogeneity of their nuclei.
Comet outburst can be spectacular, turning a modestly active comet into a naked eye object. Rosetta observations suggest mini-outburst may occur on a daily basis. I use the Zwicky Transient Facility (ZTF) to systematically monitor all observable comets in the Northern sky. ZTF will be an early warning system for comet outbursts. Using rapid-follow up telescopes such as the Las Cumbres Observatory and the Neil Gehrels-Swift observatory I investigate where in comets’ orbits outbursts occur, the frequency and duration of outbursts, and determine the composition of the ejected material.
I have been involved in three missions to comets: Deep Impact/EPOXI, which flew by comet 103P/Hartley 2; Stardust-NExT to comet 9P/Tempel 1; and Rosetta, which orbited 67P/Churyumov-Gerasimenko for over two years. I am a co-investigator on Rosetta's OSIRIS camera system and lead the investigation of the gases imaged in its coma.
I am also a co-investigator on the CAESAR mission study, which NASA recently selected for further development for its New Frontiers Program. We hope to return over 100 grams of comet material from the surface of 67P to Earth by 2038.
Two new papers on charge exchange reactions in comets
Jan 3, 2019 | I wrote a guest blog about cometary X-ray observations for the website of the Chandra X-ray observatory.
Close approach of Comet 46P/Wirtanen: a space mission in reverse!
Dec 7, 2018 | On December 16th, comet 46P/Wirtanen will make an historically close approach to Earth passing within 30 Lunar distances (11.5 million km). We have organized a large observing campaign that includes Chandra, Hubble , the Neil Gehrels-Swift Telescopeand the Las Cumbres Observatory. These telescopes will study the comet's rotation, chemical composition, and its interaction with the solar wind.
Hubble Space Telescope observations of Comet 46P/Wirtanen
Nov. 12, 2018 | Our team of Rosetta scientists have been awarded over two days on the Hubble Space Telescope to study the chemical composition of Comet 46P/Wirtanen, and atomic and molecular reactions near its nucleus and to use the comet as a natural laboratory to study plasma processes.
The unique close proximity of 46P allows us to study the inner part of the coma (within 150 km of the nucleus), a region rarely accessible to remote observations. These observations will allow us to detect the emission of short-lived species (such as S2, O2), of molecules not accessible from the ground (CO2), and to investigate the transitions between regions where either electrons or photons drive most of the chemistry in the coma. Because the comet is so close to Earth, we can compare the HST observations directly with the results of the Rosetta and Deep Impact missions to comets.
Guest experiments at Comenius University (Slovakia) in support of Rosetta
Sep. 10, 2018 | Rosetta surprisinly found that collisions with electrons were the most important reaction in the gas surrounding comet 67P. These reactions provide a fingerprint of the gases in the coma but may also be used to detect faint traces of gas around comets, asteroids, and moons in the solar system.
Together with Juraj Orszagh and Stefan Matejcik from the Comenius University in Bratislava, Slovakia, I am characterizing the probability of these reactions and of the emission they produce in optical and far-ultraviolet wavelengths. Preliminary results will be presented at the meeting of the AAS' Division of Planetary Sciences meeting in Knoxville, TN.
May 23, 2018 | The atmosphere of Rosetta’s comet 67P/Churyumov-Gerasimenko is far from homogeneous. In addition to sudden outbursts of gas and dust, daily recurring phenomena at sunrise can be observed. In these, evaporating gas and entrained dust are concentrated to form jet-like structures.
A new study, led by the Max Planck Institute for Solar System Research (MPS) in Germany and published in the journal Nature Astronomy, now identifies the rugged, duck-shaped structure of the comet as the main cause of these jets. Not only do concave regions collimate gas and dust emissions similar to an optical lens, the complex topography also provide some areas of the surface with more sunlight than others.
Abrupt slow down in the rotation of comet 41P
Jan. 10, 2018 | Combining observations from Swift and Discovery Channel telescope we measured an unprecedented change in the rotation of a comet. Images taken in May 2017 reveal that comet 41P/Tuttle-Giacobini-Kresák was spinning three times slower than it was in March, when it was observed by the Discovery Channel Telescope at Lowell Observatory in Arizona. The results were published in Nature.
CAESAR comet sample return mission selected for Phase A development
If selected for deployment, the Comet Astrobiology Exploration Sample Return (CAESAR) mission will seek to retrieve primitive material from comet 67P/Churyumov-Gerasimenko. Comet 67P made headlines as the target of the European Space Agency’s Rosetta spacecraft mission, which orbited the comet from 2014 through 2016.
Dennis Bodewits and Michael Kelley, both associate research scientists in the UMD Department of Astronomy, will lead the Comet Environment Working Group for the CAESAR team. In this role, they will assess the risks that the comet’s harsh surface environment would pose to the spacecraft and will help define the technical requirements for the sample acquisition system (more) .
First light for Zwicky Transient Facility
Nov. 14, 2017 | A new robotic camera with the ability to capture dozens of comets and asteroids every night has taken its first image of the sky—an event astronomers refer to as "first light." The camera is the centerpiece of a new automated sky survey project called the Zwicky Transient Facility (ZTF), based at Caltech's Palomar Observatory near San Diego, California. I am part of a team that uses ZTF to monitor comet activity and looks for outbursts. (more).
Electrons make comet gas glow
Nov. 1, 2016 | The Rosetta spacecraft arrived at comet 67P/Churyumov-Gerasimenko in the summer of 2014. Using its OSIRIS cameras, we found that the comet was more than 100 times brighter than expected based on our models. It turns out that the conditions for 67P, far from the Sun, when the comet's activity was very low, were very different from those normally observed from Earth. In these conditions electron impact collisions produce much more light than reactions with Sun light. We published our results in the Astronomical Journal.
I am an associate professor of Physics at Auburn University. Born in Hoogezand-Sappemeer, the Netherlands, I studied experimental physics and astronomy at the University of Groningen. I got my Ph.D. after writing a dissertation on charge exchange emission from solar wind ions interacting with cometary atmospheres at the Center for Advanced Radiation Technology (KVI-CART) at the University of Groningen. Being awarded a NASA Postdoctoral Program grant I moved to Washington DC and started observing comets and asteroids with the Swift space telescope at the Goddard Space Flight Center. Between 2010 and 2018 I was a member of the Small Body Group at the University of Maryland, where I got involved in the comet fly-bys of the Deep Impact and Stardust-NEXT missions, and in the Rosetta mission that orbited comet 67P/Churyumov-Gerasimenko for over two years. I joined the Physics Department at Auburn University in 2018. The IAU honored me by assigning asteroid 10033 the formal name 'Bodewits' in 2017. I am one out of a dozen people who ever flew a man-powered helicopter (the University of Maryland’s Gamera II).