The space agencies of the US, Europe, Russia, and China are all launching rovers to Mars this year. From a report: The 2010s saw Mars welcome NASA's Curiosity rover, which landed on the red planet in 2012, and bid farewell to the Opportunity rover, which was declared dead in February after 14 years on the Martian surface. Curiosity is now the only working rover on the planet, signaling the end of a decadal era in the exploration of Mars. But even as this older generation of Mars-cars winds down, a flurry of new rover missions is gearing up to redefine Martian road trips for a new decade. Three different rovers are scheduled to launch to Mars during the summer of 2020: NASA's Mars 2020 rover, Europe and Russia's Rosalind Franklin, and China's Huoxing-1. If this trio manages to successfully land on Mars in 2021, it would mark the first time that the planet has ever hosted three operational rovers (or even four, assuming that Curiosity is still rolling). The presence of two rovers from agencies other than NASA would also diversify Martian surface operations after decades of American dominance on the planet.

The "endgame" in the decadeslong campaign to eradicate polio suffered major setbacks in 2019. From a report: While the effort lost ground in Afghanistan and Pakistan, which recorded 116 cases of wild polio -- four times the number in 2018 -- an especially alarming situation developed in Africa. In 12 countries, 196 children were paralyzed not by the wild virus, but by a strain derived from a live vaccine that has regained its virulence and ability to spread. Fighting these flare-ups will mean difficult decisions in the coming year. The culprit in Africa is vaccine-derived polio virus type 2, and the fear is that it will jump continents and reseed outbreaks across the globe. A brand new vaccine is now being rushed through development to quash type 2 outbreaks. Mass production has already begun, even though the vaccine is still in clinical trials; it could be rolled out for emergency use as early as mid-2020. At the same time, the Global Polio Eradication Initiative (GPEI) is debating whether to combat the resurgent virus by re-enlisting a triple-whammy vaccine pulled from global use in 2016. That would be a controversial move, setting back the initiative several years, as well as a potential public relations disaster -- an admission that the carefully crafted endgame strategy has failed. "All options are on the table," says viro-logist Mark Pallansch of the U.S. Centers for Disease Control and Prevention, one of the five partner organizations in GPEI. "We are clearly in the most serious situation we have been in with the program," adds Roland Sutter, who recently stepped down as the director of polio research at the World Health Organization (WHO). The heart of the problem is the live oral polio vaccine (OPV), the workhorse of the eradication program -- the only polio vaccine powerful enough to stop viral circulation. Given as two drops into a child's mouth, OPV for decades contained a mix of three weakened polio viruses, one for each of the three wild serotypes that have long plagued humanity. All three serotypes in the vaccine have the potential to revert to more dangerous versions; that's why the endgame strategy calls for deploying OPV in massive campaigns to eradicate the wild virus, then ending its use entirely.

Basic extrapolations suggest that if there are other spacefaring civilizations in the Milky Way, they could spread across the entire galaxy with surprising speed. Why, then, have we found no irrefutable evidence of aliens visiting Earth? Popular answers to this puzzle -- that we are alone, that interstellar travel is impossible, that aliens are hiding from us -- all rest on assumptions that verge on implausibility.

What scientists can see and measure, in the garbage patches and on beaches, accounts for only a tiny fraction of the total plastic entering the water. From a report: Every year, 8m tons of plastic enters the ocean. Images of common household waste swirling in vast garbage patches in the open sea, or tangled up with whales and seabirds, have turned plastic pollution into one of the most popular environmental issues in the world. But for at least a decade, the biggest question among scientists who study marine plastic hasn't been why plastic in the ocean is so abundant, but why it isn't. What scientists can see and measure, in the garbage patches and on beaches, accounts for only a tiny fraction of the total plastic entering the water. So where is the other 99% of ocean plastic? Unsettling answers have recently begun to emerge. What we commonly see accumulating at the sea surface is "less than the tip of the iceberg, maybe a half of 1% of the total," says Erik Van Sebille, an oceanographer at Utrecht University in the Netherlands.

India has approved its third lunar mission months after its last one failed to successfully land on the moon, its space agency said on Wednesday, the latest effort in its ambitions to become a low-cost space power. From a report: The Chandrayaan-3 mission will have a lander and a rover, but not an orbiter, Indian Space Research Organisation (ISRO) Chairman K. Sivan told reporters at its headquarters in Bengaluru, according to an official telecast. The Chandrayaan-2 mission in September successfully deployed a lunar orbiter that relays scientific data back to earth, but was unable to place a rover on the lunar surface after a "hard" landing. That mission had aimed to land on the south pole of the moon, where no other lunar mission had gone before. The region is believed to contain water as craters in the region are largely unaffected by the high temperatures of the sun.