In case you didn’t know, a huge — like, on a galactic scale — cloud of gas is currently speeding toward our galaxy at 700,000 mph. It’s full of sulfur, over 11,000 light-years long and 2,500 light-years wide, contains as much mass as a million suns… and was very likely spat out of the Milky Way while T. rex was walking the Earth.

(The dinosaur, not the British rock band.)

And it’s a case of “what goes up must come down” — the cloud is on a ballistic trajectory after being blown out from our own galaxy, 70 million years ago.

Weirdest Space Stories of 2015

Known about since 1963, the “Smith Cloud” — so-called after its discoverer Gail P. Smith — was first detected at the Dwingeloo Radio Observatory in the Netherlands. It’s since been repeatedly observed in radio wavelengths with the NRAO’s Green Bank Observatory in West Virginia and recently with the Hubble Space Telescope, which determined that it does in fact contain heavy elements like sulfur (contrary to some earlier analyses). This, along with its arcing trajectory, strongly indicates an origin from the star-enriched region along the outermost edges of our galaxy.

“The cloud is an example of how the galaxy is changing with time,” said Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland, leader of the research team. “It’s telling us that the Milky Way is a bubbling, very active place where gas can be thrown out of one part of the disk and then return back down into another.”

ANALYSIS: Black Hole’s Rejected Snack Becomes Science Goldmine

Diagram of the 100-million-year “boomerang” trajectory of the Smith Cloud. NASA, ESA, A. Field and A. Fox (STScI).

The comet-shaped Smith Cloud contains no stars and so it’s not visible in optical wavelengths. But, if it were, it would span an area of night sky as large as the constellation Orion.

When the high-velocity cloud does impact the disc of the galaxy — in about another 30 million years or so — it will be on a different (albeit neighboring) arm than the one in which our solar system resides.

The collision will likely ignite an explosion of star formation around the impact site, perhaps with enough matter and energy to create two million new solar-mass stars.

NEWS: Eerie Dark Cloud Blocks Distant Starlight from View

“Our galaxy is recycling its gas through clouds, the Smith Cloud being one example, and will form stars in different places than before,” said Fox. ”Hubble’s measurements of the Smith Cloud are helping us to visualize how active the disks of galaxies are.”

What actually caused the ejection of the cloud is not yet known. One intriguing suggestion is that it’s a region of dark matter that collided with the Milky Way and somehow captured a clump of gas as it went.

“There are theoretical calculations suggesting that a dark matter satellite could capture gas as is passes through the Milky Way disk and that may be the amazing circumstance we are witnessing,” said research co-author and long-time Smith Cloud fan Jay Lockman, an astronomer with the National Radio Astronomy Observatory (NRAO).

The findings were published in the Jan. 1, 2016 issue of The Astrophysical Journal Letters.

Sources: NASA and NRAO