The past year in space science and astronomy was dominated by some debate and some tantalizing near-findings.

Among the highlights:

The 10th Planet?

You might think the discovery of an object larger than Pluto orbiting the Sun would automatically be hailed as the long-sought 10th planet. Caltech’s Mike Brown and his colleagues figured as much. Not so fast, many astronomers said. This new world is one of perhaps thousands out there that await discovery. Will we call them all planets? Should Pluto even be considered a planet? In a weird twist to the debate, Brown suggests we all ignore the scientific debate and let culture decide.

Signs of Life on Mars?

This story extends back to 2004 and looks like the sort of mystery that will keep scientists scratching their heads for years to come. The air of Mars seems to contain pockets of methane in doses that should not exist. Perhaps it is the belchings of subsurface microbes, European astronomers said early this year. They support that view with new evidence for blocks of underground ice in the same region as the methane, based on observations by the European Space Agency’s Mars Express. The ice could be supplying the precious liquid water needed to support the biology, they figure. Other astronomers think the reasoning is very speculative, however.

Birth of a Black Hole

An explosion 2.2 billion years ago, whose light just arrived at Earth this year, was detected and then monitored by an unprecedented array of telescopes on the ground and in space. The event prompted a furious exchange of e-mails. Within moments, the scientists, led by Neil Gehrels of NASA’s Goddard Space Flight Center, suspected they had seen the birth of a black hole as it happened (well, except for that previously mentioned time lag of 2.2 billion years). The event was triggered by the merger of two neutron stars, the thinking goes.

Protecting Ourselves

Some day, scientists have been telling us for some years now, we wi ll have to deal with an incoming asteroid or comet that would destroy civilization at worst or wipe out a city at least. Big impacts have occurred before, and there will be more. But we don’t know enough about space rocks and their composition to plan properly for deflecting or destroying such a menace. Turnabout proved to be fair play when NASA’s Deep Impact mission slammed a probe into Comet Tempel 1 on the 4th of July. The upshot? This comet was fluffy, unlike others that have been studied up close. Meanwhile, a group of scientists and astronauts, led by Russell Schweickart, a former Apollo astronaut, prodded NASA to visit asteroid Apophis, which has a slight chance of hitting us a few decades hence. NASA’s response: A purely scientific mission might be considered, but we have plenty of time to mount a diversion if further observations show this thing would really hit.