Rosetta sniffs oxygen around Comet 67P

Scientists have detected molecules of oxygen in the hazy halo of comet 67P/Churyumov–Gerasimenko — an unexpected discovery that may challenge theories about the formation of the Solar System. The detection was made by an instrument on board the European Space Agency’s Rosetta spacecraft.

“As soon as we got close enough to the comet, we actually found it right away,” says Andre Bieler, a physicist at the University of Michigan in Ann Arbor and lead author of the paper. Andre says that he was surprised by both the presence and abundance of molecular oxygen (O2) because it is usually quick to react with other chemicals.

From September 2014 to March 2015, as 67P made its way closer to the Sun, Andre and his colleagues used a mass spectrometer on Rosetta to sniff the molecules swirling around the comet and identify their chemical composition. They found on average that O2 makes up 3.8 per cent of the cloud relative to the most abundant substance, water.

“It’s a tour de force,” says Paul Feldman, an astronomer at Johns Hopkins University in Baltimore, Maryland, who is a co-investigator on another Rosetta spectrometer, Alice. It was not immediately clear where the oxygen came from.

The team discovered that water and oxygen were often found together — an indication that similar processes released both molecules. But Andre and his colleagues ruled out many scenarios in which oxygen arises as a by-product when energetic particles such as photons and electrons split apart water.

Instead, the researchers argue that the oxygen is a remnant from when 67P formed billions of years ago, a process that may have trapped the gas in small grains of ice and rock that coalesced to create the comet’s solid core.

But many models of the early Solar System rule this out because most oxygen tends to pair off with hydrogen. Given this affinity, it is tricky to adjust models of the early Solar System to allow for the survival of gaseous O2, says Mike A’Hearn, an astronomer at the University of Maryland in College Park and a co-investigator on Alice. But he adds that it may be possible with the right chemical abundances and temperature conditions.

Andre acknowledges that more experiments will be needed to determine what the detection of oxygen really means. “We think this result is of interest beyond the cometary community because it forces us to rethink all of these models,” he says.
Chris Cesare

Why do muscles ache after exercise?
After rigorous exercise, muscle pain is more acute a day or two later rather than immediately. Ever wondered why? Welcome to the equivocal effects of Delayed Onset Muscle Soreness (DOMS), the scientific term for aches that accumulate and intensify a day or two after a strenuous workout.

Usually, DOMS involves not just pain but also “loss of strength and range of motion in the affected area,” said Scott Sailor, a professor of kinesiology at Fresno State University in Fresno, California, and the president of the National Athletic Trainers’ Association.

DOMS commonly occurs after exercise that involves lengthening muscles while they contract, Scott said, such as running downhill. But it can develop after any exertion that is more intense or prolonged than is normal for you. Such strenuous workouts can cause multiple slight tears to the muscle tissue, after which a variety of cells and substances migrate to these muscles to help them start healing.

Interestingly, these substances are not necessarily the same as those that arrive after a more severe muscle injury. Molecules that promote inflammation and swelling, for instance, tend to predominate in tissues affected by a serious injury, but can be absent in tissue affected by DOMS, recent studies show.

Similarly, “there was a time when we attributed the muscle soreness to lactic acid,” Scott said. “We have now learned that lactic acid leaves the muscle so quickly” that it cannot be involved in causing DOMS. In essence, researchers remain puzzled about what cellular reactions cause DOMS.

There is also controversy about how to treat it. “Various treatments have been attempted over the years,” said Scott, including massage, icing and anti-inflammatory painkillers. “At best, they have decreased the perception of pain,” he said, but only temporarily.

So if you do develop DOMS, accept that, for the next five to seven days, you are going to be sore. Refrain from strenuous exercise during this time, Scott said, although gentle walking is fine. And, if it is any consolation, your muscles should be stronger after they recover. In your future workouts, Scott said, increasing the duration or intensity gradually should increase strength and fitness to limit the potential of experiencing the effects of DOMS.

Gretchen Reynolds