Space and planetary scientists are out in force this week at the annual meeting of the American Geophysical Union in San Francisco. The buzz centers on comets, especially on results from Rosetta, the first mission to orbit and land on a comet and Mars, where possible traces of methane-belching microbes have again been spotted. Here’s a round-up of some of this week’s science.

Still searching for Philae

Any hour, any day now, Rosetta-mission scientists expect to know where their lander is.

"The photos we need have been taken," says Matt Taylor, project scientist with the European Space Agency. "They’re in a pipeline, we’re just waiting for them to come down now."

So far the findings have been fascinating, says Kathrin Altwegg, the lead scientist for ROSINA, the sensor aboard Rosetta able to sniff out chemicals and molecules. "I think we picked a really good comet. Almost every day it surprises us with new results."

Altwegg and her team have begun to analyze the comet’s chemistry, which she says is more varied and richer in organic molecules than she expected. Other groups are analyzing its icy geology, with the suspicion that the lumpy comet is actually two comets melded together.

Why Comets Are Cool

Comets, and their drier compatriots asteroids, are holdovers from the ancient days of our solar system. Like a snapshot from the nursery, they might tell us what conditions were like in our planet’s early history.

Comets hold both water and carbon-based molecules. That makes them tempting targets for explaining how it was that life came to be — even though they also have wiped out a number of species. But the comet-as-nursery theory came under some pressure earlier this month, when Rosetta released its first results. The chemical signature from the comet’s water didn’t match the water on the Earth’s surface. Our planet’s water probably did not come from a comet — at least, not this type of comet.

Some space scientists think asteroids were a more likely delivery route or perhaps the water was made here all along. Two NASA missions, the already-launched Dawn and the upcoming OSIRIS-REx are hot on the pursuit of asteroids.

And we haven’t heard the last of Philae, according to Jean-Pierre Bibring, the lead lander scientist. Next February or March, as the lander gets just a little more light to power its solar panels, he expects it to wake up again. "I believe if we’re patient enough Philae will go beyond our expectations," he says.

Martian Methane Comes And Goes

Yesterday at the same meeting in San Francisco, NASA shared their latest findings from the Curiosity rover which has spent the last two years drilling, sniffing rocks and taking selfies on the surface of Mars.

Starting in late November 2013, Curiosity detected a spike in methane levels, nearly a 10-fold jump from low background levels. Methane remained abundant for about two months and disappeared as quickly as it arose. On Earth methane is usually a product of gas-burping microbes, so its presence raises hopes that Mars now or at one time hosted life.

"We knew that could happen, but you report what you find," says Grotzinger. "We don’t know when it might pop up again, but we’ll keep monitoring."

Although microbes would be most people’s favored source for the Martian methane, it isn’t a clear signal for life. It might also be the reaction product of water, rock-bound minerals, and ultraviolet radiation. At any rate, Grotzinger says he felt lucky to detect any methane at all.

"It’s not evidence that we’ve found life on Mars, but it is one of the few hypotheses we can propose and consider as we go forward," says Grotzinger. "The fact that we saw anything is amazing."

"Mars is turning the corner," Grotzinger says. It used to be a planet where space missions would explore and seek to explain. I think of it as the Star Trek mode — build a spacecraft, find cool things that no one has ever found before. Mars is now becoming a proving ground for a more deductive line of science."

As evidence he pointed toward NASA’s MAVEN mission. "They’re testing very specific hypotheses about how the atmosphere of Mars eroded," he said. "We’re doing the same for Curiosity with these ancient rocks."

The MAVEN of the Skies

NASA’s Mars Atmosphere and Volatile Evolution spacecraft has been orbiting the planet since September. Its mission is to study what happened in Mars’ once-abundant atmosphere. The loss of atmospheric gas, as solar wind gradually chewed it away, completely transformed Mars. It was once a relatively wet, warm pleasant place. Now, it is a frozen wasteland of dry rock.

In October MAVEN, and the other orbiters and rovers that make up the Mars flotilla, survived a close call. The planet was buzzed by wayward comet "Siding Spring," a visitor from the distant Oort Cloud. A Martian would have seen thousands of shooting stars per hour, researchers estimate. For the flyby Curiosity, which spends most of its time looking at the ground, glanced upward. It captured a few snapshots of its cometary visitor, much as an Earth-bound human might, staring in wonder at the night sky.