This star undergoes a long-term dimming that's so mysterious it was, at one time, proposed as possible evidence of an alien culture. Now, scientists say, a disk of debris - torn from a melting exomoon - might explain Tabby's Star.

Pulsars are the compact remnants of supernovae. They have strong magnetic fields and rotate rapidly. This one is spinning 707 times a second! Astronomers just discovered this pulsar is emitting high-energy gamma rays.

Could a collision between 2 asteroids millions of miles away cause an ice age on Earth, some 460 million years ago? A new study of earthly rocks and sediments - plus micrometeorites that fell in Antarctica - suggest it's possible.

Why is the internet so chock-full of stories about asteroids on a collision course with Earth? At this rate, we should have been obliterated many times over already. Here comes the newest scare story: asteroid 2007 FT3. No, it won't hit us, either.

Loki, the largest volcano on Jupiter's moon Io, erupts on a more or less regular schedule. Planetary scientists are predicting an eruption this month. Here's what we know.

Cassini data suggested that Saturn's rings were only 10 to 100 million years old. A new study suggests that a "ring rain" onto Saturn makes the rings look younger than they really are, and that in fact Saturn's rings date back billions of years.

What is ULX-4 - a mystery green blob of X-ray light that appeared in the Fireworks Galaxy - and then soon disappeared again? A black hole or neutron star are 2 possibilities.

"We have never seen anything like this in the 24 years we have studied the supermassive black hole. It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast."

It was exciting last week when scientists announced water vapor in a super-Earth's atmosphere. But, even as the announcement came, other scientists were cautioning that the planet - K2-18b - is probably less like a super-Earth and more like a mini-Neptune.

Astronomers now call recently-discovered flares from supermassive black holes in distant galaxies quasi-periodic eruptions. "Giant black holes regularly flicker like a candle but the rapid, repeating changes seen in GSN 069 from December onwards are something completely new," said one scientist.