A simulated view of Europa's icy surface. NASA/JPL-Caltech

NASA on Tuesday issued a cryptic press announcement about Europa, an ice-encrusted moon of Jupiter that likely hides twice as much warm, liquid, and potentially habitable water as Earth.

The US space agency teased the discovery of some "surprising activity" out there, 390 million miles from Earth, citing the help of images from the Hubble Space Telescope.

Everyone will be filled in on the details via a live audio stream on Monday, Sept. 26, at 2 p.m. EDT, according to the release:

Astronomers will present results from a unique Europa observing campaign that resulted in surprising evidence of activity that may be related to the presence of a subsurface ocean on Europa.

Surprising evidence ... a subsurface ocean ... one of humanity's sharpest eyes in space ... could this be the discovery of extraterrestrial life?

We wouldn't count on it. In fact, NASA quickly squashed alien speculations on Twitter:

If history and how science works are any indication, what we'll like see on Monday are more Hubble images that look like this:

Hubble's long-distance (and pixelated) view of water vapor around Jupiter's icy moon Europa. NASA/ESA/L. Roth/SWRI/University of Cologne

No, computerized blue aliens are not floating above the south pole of Europa.

Back in 2012, Hubble used a special (yet very low-resolution) instrument called a spectrograph to sniff out normally invisible plumes of water vapor, shown as blue pixels above the moon.

The plumes it found likely rocketed more than 20 times the height of Mount Everest above Europa.

NASA announced that discovery in December 2013, ruling out a meteorite impact as the cause, since that could have sprayed water everywhere as it vaporized the moon's icy crust.

Researchers instead determined something huge was going on beneath Europa's surface (our emphasis added):

"By far the simplest explanation for this water vapor is that it erupted from plumes on the surface of Europa," said lead author Lorenz Roth of Southwest Research Institute in San Antonio. "If those plumes are connected with the subsurface water ocean we are confident exists under Europa's crust, then this means that future investigations can directly investigate the chemical makeup of Europa's potentially habitable environment without drilling through layers of ice. And that is tremendously exciting."

The announcement follows a growing line of research that increasingly shows Europa is not a cold, dead world.

It's surface is likely roiling with giant ice slabs that are cracking, breaking up, sinking, and melting:

NASA

And allowing ocean water hidden deep below to spray out into the vacuum of space around Jupiter:

A plume of subsurface ocean water vapor escapes through a crack in the icy crust of Europa, a moon of Jupiter. NASA/ESA/K. Retherford/SWRI

We contacted several Europa experts for their best guesses on what NASA's announcement might reveal.

Bill McKinnon, a planetary scientist at Washington University in St. Louis, wrote in an email to Business Insider that the discovery "has to be related" to the plumes, since the Hubble telescope "can't see shifting [ice] plates, or really any geology" on Europa from orbit around Earth.

"A plume confirmation would be a great thing," McKinnon added, "[b]ut I have no insider knowledge."

Beyond spotting a second plume, it stands to reason that we could move beyond "water is shooting out of Europa again" and learn something about what is hitching a ride inside those plumes.

Put another way, chemicals besides water could travel from deep within Europa's global ocean, through the icy crust, and out into space where Hubble can analyze them.

If the telescope saw something truly surprising — perhaps chemistry required for life, which we detailed earlier this year — researchers may push NASA to fast-track its Europa Clipper fly-by mission, and ultimately an ambitious scheme to sink a nuclear-powered robot below the ice to seek out signs of life:

The detection of life-friendly chemicals in Europa's plumes could be a long shot, though, since Hubble's aging instruments were never designed to do such a thing — it's incredibly impressive they could verify oxygen and hydrogen (the atoms in water) around Europa at all in 2012.

So we may need to wait until Monday to learn exactly what researchers have found.