The universe is brimming with orphaned, orbitless planets, according to a landmark study published today in the journal Nature. An international team of scientists report that hundreds of billions of these free-floating planets are scattered throughout deep space, apparently ejected from the solar systems where they were born. The discovery of such rogue planets isn't a surprise — planetary formation theory predicted they should exist, says lead author Takahiro Sumi — but the sheer number of them is. According to Sumi's calculations, planets outnumber stars in the Milky Way by 2 to 1, a possibility astronomers are calling "shocking," "astounding" and "exciting," among other superlatives.
"The implications of this discovery are profound," writes Joachim Wambsganss of Germany's Heidelberg University in an accompanying commentary in Nature. Astronomers have identified some 500 planets circling distant stars over the past two decades, and earlier this year NASA's Kepler satellite helped reveal 1,235 more so-called "exoplanets." But these were all detected using techniques that favor planets clustered near stars, spotting them by looking for how they bend their home star's light. The newly discovered rogue planets, on the other hand, were found using a method known as gravitational microlensing, which relies on a similar principle but is more sensitive to starless planets. In this method, scientists look at "background stars" to see if their light is bent and magnified by a massive object's gravitational field, even if that object is far from the star and merely passing by. As it turns out, there are hordes of massive gas giants drifting far from the nearest star, roughly the distance at which Uranus or Neptune orbits our sun.
There is a possibility that many of these free-floating planets actually are orbiting a star, the study's authors say, just at a much greater distance than most previously detected exoplanets. "Either there is a large population of Jupiter-mass planets far from their star, or, yes, there are a lot of lonely planets out there," MIT planetary theorist Sara Seager tells the New York Times. Either way, the findings are groundbreaking because they suggest planets, once thought to be relatively rare, are even more common than stars, practically littering the universe. This, adds Alan Boss of the Carnegie Institution, is "pretty exciting in telling what is out there in the night sky. ... Lots of theories will grow in this environment."
The swollen Mississippi River has crested at 57.1 feet in Vicksburg, Miss., more than a foot over its record level set in 1927, CNN reports, and 14 feet above flood stage. But while the historic flooding continues to threaten people throughout the Mississippi Delta, and likely will for weeks to come, PBS NewsHour reports on a less obvious effect of the river's wrath: a supersized "dead zone" in the Gulf of Mexico. The oxygen-deprived zone is already about the size of New Jersey, and experts say it could grow to record size this summer.
"We're expecting probably the largest-ever amount of hypoxia," says Louisiana marine scientist Nancy Rabalais, referring to the low-oxygen conditions that create aquatic dead zones. "That's the prediction based on the amount of nitrogen coming down the river." The Gulf normally suffers some amount of hypoxia every summer, as the Mississippi dumps out all the nutrients it has collected during its 2,320-mile journey south from Minnesota. Those nutrients — especially artificial fertilizers from Midwestern farms, but also animal waste, pesticides and various other chemicals — become fuel for huge algae blooms, which grow larger and larger as they gobble them up. The algae later die and sink, where bacteria eat them, consuming dissolved oxygen in the process. That can quickly deplete oxygen from the water, making it difficult or impossible for marine life to survive. While this has become common in the Gulf, the huge amounts of water flowing down the Mississippi this year are carrying far more nutrients than usual, potentially fueling one of the largest dead zones the Gulf has ever seen.
With both people and wildlife in the Gulf still weakened by last year's BP oil spill, the prospect of such a large dead zone is troubling, Rabalais says. Fish and other free-swimming animals typically flee dead zones for more breathable waters, while less mobile creatures often simply suffocate and die. If this summer's dead zone triggers a mass exodus and/or die-off of economically important shrimp, crabs and snapper, it could ruin a badly needed fishing season. "A lot of the Louisiana shrimp fisheries use smaller vessels," Rabalais says. "With the price of fuel and the distance they have to go, they might opt not to go offshore."
The mysterious red-crested tree rat has returned after a 113-year absence, PhysOrg reports, waltzing up to a Colombian eco-lodge as if to announce that rumors of its extinction were greatly exaggerated. The species hadn't previously been seen since 1898, despite several organized searches, and had long been considered extinct. But the perfectly alive specimen (pictured) revealed itself at the nature reserve earlier this month, hanging around for two hours as excited research volunteers took its photo for the first time in history.
"He just shuffled up the handrail near where we were sitting and seemed totally unperturbed by all the excitement he was causing," says Lizzie Noble, one of two researchers who encountered the rodent. "We are absolutely delighted to have rediscovered such a wonderful creature ... Clearly the El Dorado Reserve has many more exciting discoveries waiting." The meeting took place at the El Dorado Nature Reserve in far northern Colombia, around 9:30 on the night of May 4, and lasted two hours before the tree rat calmly wandered back into the forest, offering no clues why he chose that moment to reveal himself.
"The El Dorado Nature Reserve represents the ultimate Noah's Ark, protecting the last populations of many critically endangered and endemic flora and fauna; a living treasure trove like no other on Earth," says Paul Salaman from the World Land Trust U.S., who confirmed the species' identity. As American Bird Conservancy President George Fenwick adds, "Had we not worked with our partners to establish this reserve, it is reasonable to believe this species would still remain something that was only talked about in science journals. Now we need to work with our partners to take steps to see that this species continues to be a part of our world." The red-crested tree rat will likely now be classified at "Critically Endangered" by the International Union for Conservation of Nature, PhysOrg reports. That's not just because of its rarity — unfortunately, its range has recently been invaded by feral house cats that prey on native fauna.
The six-man crew of NASA's Endeavour space shuttle has already completed its mission's No. 1 objective, the AP reports, installing a $2 billion cosmic-ray detector on the International Space Station this morning. The Alpha Magnetic Spectrometer (pictured) is designed to scour waves of high-energy rays gushing through space, looking for evidence of dark matter, antimatter and other weird phenomena that traditional telescopes can't see.
Endeavour, which is currently on its final mission before retirement, docked with the space station Wednesday, and its crew used robotic arms this morning to lift the 7.5-ton instrument out of the shuttle's cargo hold and install it onto the space station's metal truss, where it's expected to remain for the rest of the space station's life. "AMS looks absolutely fantastic on the truss," shuttle commander Mark Kelly radioed to the program's lead scientist, MIT Nobel laureate Samuel Ting, back on Earth. Ting has worked on the project for 17 years, fighting to have AMS placed back on the shuttle after its flight was suspended several years ago, and he personally thanked the shuttle crew for their work. "This has been a very difficult experiment, and I think in the next 20 to 30 years, nobody will be able to do such a thing again," Ting told the astronauts. "I hope together with you, we will try to make a contribution to a better understanding of our universe."
Meanwhile, engineers at Mission Control are still analyzing several damaged areas on the underside of Endeavour, the AP reports. Some thermal tiles were apparently dented and dinged during liftoff Monday morning, with some gashes up to 6 inches long and 2 inches wide. Mission Control may ask Kelly and his crew to investigate the damage this weekend, but Kelly tells Reuters in an in-flight interview. "There's three areas that are a little bit of a concern," he says. "The team on the ground will decide in the next couple of days if we have to take a closer look at it, but we've seen this kind of stuff before and it's not too much of a concern for us." Endeavour is scheduled to return to Earth June 1.
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Image (artist's rendering of an isolated planet): R. Hurt/JPL-Caltech/NASA
Image (color-coded map of Gulf dead zone): NASA Visible Earth
Photo (red-crested tree rat): Lizzie Noble/ProAves/Conservation International
Image (Alpha Magnetic Spectrometer on space station): NASA