What happens if the retired space telescope and former spy satellite crash into each other?

Tonight

Leo Labs, a venture-based company that monitors satellites in Low Earth Orbit, tweeted yesterday that it was tracking two satellites that will come within 15 to 30 meters of each other January 29, just before 6:40 p.m. EST.

The two satellites are IRAS, a decommissioned NASA space telescope, and GGSE-4, a US Naval Research Lab intelligence satellite.

They're set to sweep past each other in the skies above Pittsburgh at an altitude of about 559 miles above Earth's surface.