Dr. Dimitra Atri is a computational physicist working on various aspects of astroparticle physics, radiation biophysics, and astrobiology at the Blue Marble Space Institute of Science (BMSIS). Prior to that, he was a postdoctoral fellow at the Tata Institute of Fundamental Research in Mumbai, India. He earned his Ph.D. in Physics from the University of Kansas in May 2011. He has written a number of articles on topics like effects of ionizing radiation on human health, observation of muon excess due to gamma ray bursts detected from space etc. For a full list of his publications, go to http://kusmos.phsx.ku.edu/~dimitra/Publications.html
Some of his current projects include, modeling the impact of hard solar events and galactic cosmic rays on astronaut health in long-term space missions, exploring the impact of particle interaction models tuned with LHC data on gamma-ray and neutrino production in our galaxy, modeling the background flux of protons, antiprotons, neutrinos and gamma-rays using updated particle interaction models with GALPROP (galprop.stanford.edu) and modeling the impact of high-energy astrophysical events on the Earth’s atmosphere (ionization) and biosphere (radiation dose). Most recently, he is one of the founding members of Astrobiology India, an initiative dedicated to encouraging the growth of astrobiology research and education in India. He is one of panel experts of our website’s Ask An Astrobiologist column. Let’s meet Dr. Dimitra Atri:
Interviewed by Benu Atri, Baylor College of Medicine, Houston, Texas.
Tell us about your journey to becoming a computational physicist. What was your Ph.D. about and what is its influence in astrophysics? Do you recall some particularly memorable moments or achievements that you’d like to share with us?
While growing up, I was always fascinated by the night sky. I was a passionate amateur astronomer with a 3-inch refractor telescope. As I began studying astronomy, I quickly found myself more interested in the physics powering the stars and everything around us. Growing up in rural India, there were no opportunities around me to study astrophysics and we are talking pre-internet age here. So I enrolled to study engineering with the goal of switching to astrophysics whenever possible. During college, the Internet revolution happened in India and I came to know about the doctoral program in Physics at the University of Kansas who had accepted engineering students for Ph.D. As an undergrad, I read a lot of popular science articles and found new research at the interface of astrophysics and particle physics, also known as astroparticle physics very fascinating. While studying physics at KU, I developed an interest in astrobiology and my research so far has been to combine astrobiology with astroparticle physics. I quickly realized that there has been virtually no work in this area so I decided to work on it for my dissertation. The scale of the phenomena I was studying was beyond what can be studied in a laboratory both in terms of size and energy scales. However, it is possible to simulate such environment on a computer and thus began my journey as a computational physicist. I used a supercomputer to model the effects of high-energy cosmic rays on the Earth’s atmosphere and biosphere.When I started this project, I would use certain keywords during literature review, to see if I can find some similar work in the literature to cite, but most attempts did not result in any related papers. By the time I was graduating, the same keywords would point to my papers! I would say, for me, that was the most memorable moment during graduate school. Also, the year 2012 was the centenary of the discovery of cosmic rays by Victor Hess, the Austrian physicist who was awarded the Nobel Prize in Physics in 1936 for the discovery. There were two major conferences in 2012 celebrating the discovery; one was in Innsbruck (Austria), home of Victor Hess, and the other one in Bad Saarow (Germany) where his balloon landed that lead to this discovery. I was an invited speaker in both these conferences and speaking in front of the legends in the field was another of the most memorable moments of my life.
Your work has involved studying cosmic rays extensively. What is the source of cosmic rays and what are its effects on terrestrial life? How does one study them and their effects? Are there any underlying assumptions in such studies?
Cosmic rays are basically energetic charged particles of astrophysical origin traveling with speeds close to the speed of light. These charged particles are produced either in the sun, which are of lower energy, and also from supernovae or exploding stars, beyond the solar system, also known as Galactic Cosmic Rays. Then, there are ultra-high energy cosmic rays whose energy rivals that of a pitched baseball, but their production mechanism is not known. Cosmic rays interact with the atmosphere and initiate photochemical changes leading to the depletion of ozone, which gives way to solar UVB on the ground level. They also produce secondary particles, which reach the surface and directly damage the DNA. They increase mutation rates and are potentially carcinogenic. Increased mutation rates from cosmic ray exposure during Earth’s history could also have affected the evolution of life on the Earth. The effects can be studied by a combination of theoretical tools and laboratory studies. Astronauts are also exposed to these particles in outer space and a major challenge for space agencies is to protect astronauts from this hazardous radiation. Currently, astronaut Scott Kelly is on board the International Space Station where he will be spending a year exposed to this radiation. One of the objectives of this year long mission is to study the impact of solar and cosmic radiation on his health.
You recently sent an article to Arxiv.org on the possibility of cosmic ray-induced ionizing radiation powering life in subsurface environments in the Universe. Could you share with us the basic premise of this thought and the rationale behind your hypotheses? Will this change the way we look for life on other planets?
The idea came when I was reading about the discovery of Desulforudis audaxviator, in a 2-mile deep South African mine. This bacterium is completely cut off from the photosphere but uses radiation coming out of radioactive substances to power its metabolism. I also saw the flux of radiation present at the location and thought of comparing it with the flux of cosmic rays underground. I was surprised to see the numbers agreeing, so I thought – if subsurface life could be powered by radiation from radioactive substances, why not from a similar amount of radiation coming from cosmic rays? Since cosmic radiation is everywhere, it could power subsurface life anywhere in the galaxy, even on planets without stars, also known as rogue planets. When we talk about planetary habitability, studies are primarily focused on stellar photons and its effects on planet’s climate. This study extends the concept beyond photons to charged particles, which are ubiquitous in the Universe.
Earlier this year, there was an article on how solar events are unlikely triggers for birth defects on Earth. Could you tell our readers why we do or do not need to be worried about cosmic radiation causing damage on Earth?
In that study, we looked at the biological effects of large solar proton events or SPEs. These events have the potential to damage satellites and airplanes, therefore, disrupt modern telecommunication networks around the globe. Their biological effects were not studied, so we did thorough calculations. We found that even with the most intense SPE, the total radiation dose that you find at the ground level is very small. It is not enough to cause any biological damage and we shouldn’t worry about their direct health effects.
Could you comment on what the scenario was of ancient Earth compared to modern Earth and what, in your opinion, can be said about the Earth’s atmosphere – cosmic radiation in future?
There are other astrophysical events, which become relevant on geological timescales such as nearby supernovae. They occur at a rate of about 2 or 3 per century in our galaxy. They are also the primary source of Galactic Cosmic Rays. So, on timescales of millions of years, the radiation effects from these events become very important and it is most likely that they would have affected the evolution of life on Earth. However, unlike giant asteroid and comet impacts, these radiation bursts do not leave any trace behind. Even the radioactive substances they produce decay to stable particles in such long timescales, therefore, such events are almost impossible to trace.
What is your role as a Blue Marble Scientist?
I am in that phase where a scientist, after getting a Ph.D., has to spend several years in temporary research jobs before landing a permanent position. At present, I am collaborating with a number of groups around the globe, primarily in Europe, on various problems in astroparticle physics and astrobiology. Since my research is primarily theoretical in nature, the only resource I need is a computer with Internet access. With Blue Marble, I am able to do this while spending time with my family, which otherwise wouldn’t have been possible. The institute also helps me with research grants and disseminating my results to a wider audience. I am also mentoring a couple of graduate and undergraduate students and preparing them for a career in science.
What advice would you give to young students who want to work as an astrophysicist/astrobiology?
The Universe is a very exciting place packed with mysteries and it is very satisfying to find something new about it, no matter how insignificant it may be. Research can be tough and highly frustrating at times, but I find it very meaningful and would not trade it for anything else. My advice to young students would be to prepare for a very long journey, keep your mind open and find your own path to pursue. Astrobiology is highly interdisciplinary and you can contribute to the field from your own unique angle depending on your area of expertise. It is very important to build a solid foundation in basic subjects such as physics, biology and chemistry while pursuing undergraduate studies. At the Ph.D. level, you will need a lot of things from other disciplines you learned earlier.
How are you involved in outreach? What do you like most about it? Would you like to say a few words to encourage our readers to get more involved in outreach?
I enjoy communicating science to a broader audience and give a number of astrobiology-related talks in local high schools and colleges. I also contribute to an astrobiology blog, but I haven’t been active lately.
What do you do in your free time?
I like to travel and explore new places around the globe. I usually drive to new places and explore them on foot. That way I find small coffee shops and restaurants, and get the experience the place as a local, away from the typical tourist traps. Lately, I have gotten into hiking and photography and spend my weekends in state or national parks enjoying the outdoors.
Could you suggest some books, courses or online resources for beginners in astrophysics/astrobiology?
There are tons of online resources, which you can easily find. I am a big fan of review articles and I think they are the best way to get started on your subject of choice. For example, you can learn more about the effect on cosmic rays on planetary life here:
Atri, Dimitra, and Adrian L. Melott. “Cosmic rays and terrestrial life: a brief review.” Astroparticle Physics 53 (2014): 186-190.
Thank you so much, Dr. Atri. It is such a pleasure to have you in our team. Thank you so much for your time and such informative and inspiring Q & A!