black and white image of a comet

The Philae probe recently landed on the surface of comet 67P/Churyumov-Gerasimenko. Its 10-year drilling expedition was hailed as a success. (Photo credit: European Space Agency)

European Space Agency

Comet Landing, Black Death

Graduate Division

Space Exploration: On Nov. 12, the European Space Agency landed a spacecraft on a comet. Watching the live streaming video and following the world’s excited Twitter updates, I wondered—not for the first time—if any kind of science or medicine event would ever draw this kind of hype.

Is biology inherently less flashy than space exploration? Certainly both probe the depths of the unknown, though space carries with it a romance that our inner anatomy typically does not. I’ve known that I wanted to be a biologist since before I knew how to pronounce it, but even so, when I stepped foot into the SpaceX facility at age 23, I felt a desire (fleeting, I promise) to be an aerospace engineer. Perhaps no one will ever glue themselves to the TV or Twitter feed waiting for updates on my tumor biology experiments. But then again, there is always the possibility of sending an experiment to space.

The Philae probe was released earlier on Nov. 12 from the Rosetta spacecraft that had carried it during the 10-year journey to comet 67P/Churyumov-Gerasimenko. Currently, the comet is located between Mars and Jupiter, closer to the latter. In a rather rocky landing, Philae bounced three times in the low gravity of the comet—the first bounce was a kilometer in height—before coming to rest in the comet’s frigid shadows approximately a kilometer from its target landing site. Unfortunately, this meant little sunlight for its solar panels, and thus only two days of battery life. The good news is that the ESA had contact with the lander during this period, allowing the Rosetta mission team to receive data and send commands.

Failing to fire its harpoon anchors, Philae is at risk of floating off the comet. This added risk to the planned drilling procedures aimed at analyzing the comet’s composition in search of clues of the primordial universe (did Earth’s oceans form from melted comets?). With the batteries running low, however, the probe gave it a try. The drilling was a success, and data from chemical analysis of the drilled sample was sent shortly before the probe went quiet.  

In spite of the mishaps, this mission has already taught us a lot about the comet—for example, that it stinks of ammonia, hydrogen sulfide, formaldehyde and methanol—and provided the first-ever close-up images. And there is plenty of additional transmitted data awaiting analysis. Scientists and engineers are celebrating the mission as a success.

References: NY Times, Reuters, Slate, Discovery, National Geographic, ESA.

History of Science of the Black Death: The current Ebola crisis in West Africa, like other modern disease outbreaks, is turning eyes back to the history of epidemics. The term “quarantine,” the isolation of people with potential exposure to a disease, dates back to Medieval Italy, referring to “quaranta” or “forty”—the number of days that incoming ships had to remain in port before crew could come ashore during the Black Death pandemic. One of the most devastating pandemics in history, the Black Death wiped out a third of Europe’s population in the mid-1300’s. While it is attributed to Yersinia pestis, the bacterium responsible for bubonic, septicemic and pneumonic plagues, the attribution relies on medical anthropology and paleomicrobiology, rather than the sophisticated and definitive methods of modern medicine.

My mother recently lent me her copy of “The Biology of Plagues: Evidence from Historical Populations,” in which the authors Susan Scott and Christopher Duncan argue that the discrepancies between the Black Death’s epidemiology and modern outbreaks of bubonic plague indicate that the Black Death was rather an Ebola-like hemorrhagic virus. For instance, written records of the Black Death indicate swift person-to-person transmission, whereas Y. pestis infection depends on a cycle of rodent, flea and human hosts. Furthermore, several Black Death outbreaks occurred in the winter, when rodents and fleas are less prevalent. Indeed, it is difficult to imagine any disease traveling 10 miles a day, particularly in the 14th century.

To address this controversy, scientists have since collected samples from known Black Death mass graves, and have successfully isolated Y. pestis DNA from many—but not allhuman skeleton teeth. In a 2011 publication in Nature, the groups of H.N. Poinar and J. Krause published a Y. pestis genome assembled from these samples, but surprisingly they could not identify any marked virulence genes that could explain the Black Death’s devastating spread and mortality. In the September 2014 issue of Immunity, A.L. St. John et al. reported that Y. pestis in mouse models spreads systemically between lymph nodes (where they cause the characteristic “buboes” of the bubonic plague) by infecting dendritic cells and monocytes. Furthermore, they could prevent the disease from spreading by administering a sphingosine-1-phosphate receptor (S1PR) inhibitor, which interferes with phagocyte migration.

With all this information, are we certain that Y. pestis was responsible for the Black Death? Was it perhaps a different sub-strain that has since become extinct? Is it less virulent today because the human population carries immunity selected during the pandemic? Or was the Black Death really caused by an unidentified pathogen? How many licks to the center of a Tootsie Pop? The world may never know.

References: The Biology of Plagues, Nature, Immunity