The Andromeda Galaxy, M31, is encircled by dozens of satellites – smaller galaxies in orbit around it. One of the larger satellites is something of an oddball. Of the three-dozen brightest, it’s the only one that lines up on the far side of Andromeda as seen from our home galaxy, the Milky Way.

M31 is the closest giant galaxy to the Milky Way – just two-and-a-half million light-years away. Messier 110 is a couple of hundred thousand light-years farther. It’s a few thousand light-years in diameter, and contains about 10 billion stars – a tiny fraction the size of Andromeda.

Astronomers have spent years watching M31’s entourage with Hubble Space Telescope. They recently reported that 36 of the 37 brightest members line up on the side of M31 that faces the Milky Way. And that’s hard to explain.

The study said there’s only a tiny chance that the alignment is a coincidence – there must be a reason for it. But no one knows what that reason might be.

It’s not a result of the Milky Way’s gravitational pull – it’s not strong enough. So there’s no obvious explanation for why M110 is an oddball – lurking on the far side of M31.

M31 is low in the northeast at nightfall. Under dark skies, it looks like a hazy slash of light about as wide as the Moon. Through a small telescope, M110 looks like a bright star close by.

Script by Damond Benningfield