A huge comet almost hit Mars … and then missed. It passed just 87,000 miles from the martian surface. That might seem far away, but remember our moon is about 240,000 miles from Earth’s surface.
As astronomer Phil Plait, who writes the Bad Astronomy blog for Slate, notes:
The NASA comet page says the coma (the big fuzzy cloud of gas surrounding the solid nucleus of the comet) is about 20,000 km across. At closest approach, that means that if you were standing on Mars, the comet would appear to be over 8° across! That means that if you have a big hand, you could just barely block it with your upraised fist.
Again — our Moon appears only about 0.5°. This was huge.
And human probes orbiting mars had a front row seat. They recorded the comet’s approach, and then quickly swung around behind Mars to avoid potentially harmful debris in the comet’s tail. The data from their close encounter will be trickling in over the next couple weeks.