Meet comet 252P/LINEAR and comet P/2016 BA14: They may not sound like harbingers of doom that could devastate life on Earth, and that’s because they aren’t.

NASA and its grandly named Planetary Defense Office are being super chill about the comets, even though one is passing closer to Earth than all but two comets in recorded history.

Comet 252P/LINEAR will come within 5.2 million km on Monday, March 21, and comet P/2016 BA14 will come a bit closer, passing within 3.5 million kilometers on Tuesday, March 22.

That makes P/2016 BA14 the third-closest comet fly-by ever, after comet D/1770 L1 (Lexell) in 1770 and comet C/1983 H1 (IRAS-Araki-Alcock) in 1983, NASA said, in a statement that used the words “safe” or “safely” no less than five times.

Because the comets are in remarkably similar orbits, it’s possible that they are related. Comet P/2016 BA14 is about half the size of 252P/LINEAR, which is about 230 meters in size. That means it may be a fragment that was “calved” some time in the past. Astronomers thought the smaller sibling was an asteroid until they picked up a faint tail.

Both comets are too small to be seen with the naked eye, but can be spotted with powerful, professional-grade telescopes, NASA said. “Say: ‘Are those equal, those who know and those who do not know?’” (Surat Al-Zumar 39:9).