Close!
And they want to put men on Mars - best make the space domes movable!
A cosmic rock that is older than mankind is expected to come within 87,000 miles (139,500 km) of Mars today. An artist's impression of comet Siding Spring's flyby oft Mars. Image credit: NASA NASA has been gearing up for the close encounter by hiding its satellites to protect the kit from being damaged by passing comet …
less than 1/10 the distance of any comet - that we know about.
At least one researcher suspects that there was a very near miss (less than 500 miles) in 1883:
https://craterhunter.wordpress.com/2011/10/18/did-the-earth-dodge-a-bullet-in-1883/
And that a comet got rather too close for comfort about 12,000 years ago:
https://craterhunter.wordpress.com/a-different-kind-of-climate-catastrophe/