A huge galaxy seems to appear out of nowhere and surround our own. Now, scientists have found a completely new moon on the edge of our own Solar System.

The moon, which is about 161 km (100 miles) in diameter, has been found orbiting Makemake, the second brightest frozen minor planet, way out in the Kuiper belt past Pluto. So, what’s going on exactly? And why did it take us so long to notice these important things in our own galaxy?

Because it is so small, the newly found moon, which is temporarily called “S/2015 (136472) 1” or “MK 2” for short, was able to stay hidden for so long.

The moon, like the new galaxy that was found earlier this month, reflects so little light that it has been hard to see in the brightness of Makemake.

It’s more than 1,300 times dimmer than the planet it orbits, and it’s so dim that Makemake was once thought to be the only distant dwarf planet without a moon, but it no longer has that title.

Astronomers couldn’t see the moon until April of last year, when they pointed the Hubble Space Telescope at Makemake for more than two hours. Astronomer Alex Parker from the Southwest Research Institute in Texas was looking at the data when he saw a faint point of light moving around Makemake about 20,900 km (13,000 miles) away.

Parker told National Geographic, “I was sure someone had already seen it.” He asked another scientist, Marc Buie, about it, and Buie said, “There’s a moon in the Makemake data?”

“At that point, everything got exciting and went into high gear,” Parker said.

Now, the researchers want to use Hubble to learn more about MK2 and figure out its orbit. They want to learn more about the dwarf planet’s make-up and density.

“Makemake is a rare object like Pluto, so finding a friend for it is important,” said Parker. “The discovery of this moon has given us a chance to learn a lot more about Makemake than we could have without the companion.”

The Kuiper belt is a huge pool of frozen leftovers from when our Solar System formed about 4.5 billion years ago. Many dwarf planets are in this pool. Scientists still don’t know much about these icy planets, though.

One of Makemake’s mysteries is why it looked like it had different patches of dark and bright, reflective material all over it. But the planet rotates once every 7.7 hours, so if that were true, the brightness of the planet should change, which it doesn’t.

But Parker said on Twitter that this could be because the old infrared data picked up not only Makemake, but also MK2:

The new information also shows how much Pluto and Makemake are alike. Pluto’s mass wasn’t known until 1978, when its moon Charon was found. Parker said, “That’s the kind of measurement that having a satellite can make possible.”

In addition to the observations from Hubble, he is now hoping that the NASA probe New Horizons will pass by Makemake on its way out of the Solar System.

It’s amazing to think that there is still a lot of space we haven’t found yet. Who knows, maybe this is also the year we find Planet Nine. People, keep your eyes on the sky.

The research has been sent out for peer review, and it has been posted on the pre-print site arXiv.org so that other people in the field can comment.

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