Discovered: Polar bears have been around for milions of years; the Big Rip gets moved up; a rat's heart becomes a jellyfish; JFK and LAX, hubs for the spread of infectious disease. 

Jellyrat? Rodentfish? Harvard bioengineers, playing god, have created an artificial jellyfish from the silicone and muscle cells salvaged from a rat’s heart. This "medusoid" comes to "life" when dropped into an electrically charged field, waving its eight flap-like appendages in a swimming motion. "Morphologically, we’ve built a jellyfish. Functionally, we’ve built a jellyfish. Genetically, this thing is a rat," said Kit Parker, who led the effort. Next, he hopes to build a similar jellyfish from human heart cells, which would be useful for testing prospective heart drugs.

[Nature]

Prehistoric polar bears. Evolutionary biologists at the University at Buffalo in New York now believe that the polar bear's origins date back much farther than anyone previously believed. Until quite recently, it was thought that polar bears emerged a mere 150,000 years ago. New DNA analysis of Ursus maritimus suggests that it forked off from the brown bear between 4 million and 5 million years ago. This was around the same time when thick sea ice first formed in the Arctic. Such longevity brings deeper resonance to the polar bear's present situation: teetering on the verge of extinction due to climate change. "Even if this species has for sure experienced dramatic climatic changes before, that does not mean it’s safe today," says Charlotte Lindqvist, one of the lead researchers. [Science News]

Modeling outbreak. West Nile virus, H1N1, avian flu... Many of the world's outbreaks of infectious disease cross borders, cropping up in distant countries around the world. Air travel may have a lot to do with that spread. Drawing on network theory to study contagion, researchers at MIT's Department of Civil and Environmental Engineering have constructed a new mathematical model to predict the role American airports might play in the spread of infectious disease. "Our work is the first to look at the spatial spreading of contagion processes at early times, and to propose a predictor for which 'nodes' — in this case, airports — will lead to more aggressive spatial spreading," says MIT professor Ruben Juanes. He predicts that the most influential spreaders of disease would include New York's JFK and Los Angeles' LAX airports. 

[Massachusetts Institute of Technology]

In seventeen billion years, the universe goes dark. We all know that the universe is expanding. Dark energy, a gravitationally repulsive force that may comprise up to 70 percent of space's content, is slowly making planets accelerate away from each other. Physicists seem to agree that the universe will eventually tear itself apart in an apocalyptic event dubbed the Big Rip. They typically cite a date over 20 billion years into the future as the universe's doomsday, but a recent study published in the Science in China Press says it could happen in 16.7 billion years. They reached this conclusion with 95.5 percent certainty by adjusting mathematical parameters they believe were flawed in previous calculations. [io9]