No water on Mars. Maybe.

Around this time two years ago, flowing water on Mars was all the rage. According to a new study, however, it might not have been water at all. Just sand.

What the eff?!

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Cassini: the end of a legend

20 years after it launched, the NASA spacecraft Cassini ends its mission today. Its 13 years in orbit culminate in one last mission: to dive into the planet’s atmosphere, while still measuring and transmitting data.

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Enceladus: a song of ice and tides

An artist impression of Cassini diving into Enceladus water plumes. credit: NASA/JPL

Cassini will terminate its 20-odd-years-long mission in September. But it’s determined to go out with a bang. In yesterday’s press conference, NASA announced that the probe, during a 2015 flyby of Saturn’s moon Enceladus, found clues that the ocean within the icy moon has almost all we think it needs to spark life. Continue reading

Why galaxies are flat (and Earth isn’t)

The universe teems with flat stuff. Most galaxies, including the Milky Way, are quite flat and (relatively) thin pancakes of stars. All planets of the solar system (real planets, not Pluto) orbit pretty much on the same plane. Unsurprisingly, it’s no coincidence.

The plane along which all (real) planets orbit around the Sun. credit:

The plane along which all (real) planets orbit around the Sun. credit:

Galaxies and star systems form the same way: coagulating clouds of gas—though at obviously different scales.

Imagine throwing a plume of gas or atoms in space. Push them in random directions: some one way, some another, some up, some down. Unless you cheated, they bump into each other and, because of gravity, clump together. When the atoms didn’t collide head-on (ie, most of the times), these clumps spin. Clumps themselves attract each other and collide into bigger spinning blobs.

After each collision, the atoms and chunks of atoms align, canceling out all of their opposing motion, but keep spinning (in fancy physics terms, it’s called angular momentum conservation). You can see the blobs in the video up here as a forming galaxy seen from “above”.

Slowly but surely, the whole cloud flattens to a plane. If it’s a galaxy, it forms stars on that plane, whereas in the Solar System it became that begot the orbital plane.

Other planetary systems and galaxies spin too, but each inclined its own way, because they formed from different clouds of gas.

A lot of galaxies, photographed by the Hubble Space Telescope. They’re spinning in every which way. Credit: NASA/wikimedia

But if planets and stars also form by congealing gas, why aren’t they flat as well?

The reason is that planets and stars are much denser than galaxies. Being closer to each other, their clumps of gas feel a stronger gravitational pull to the center of the blob, that wins over the mechanism that would keep them flat. So planets and stars become spheres.

Saturn formed across all the stages: most matter coalesced in the huge (clearly spherical) planet, but a little formed some of its many more or less round moons, finally the last faint leftovers ended up as the iconic, extremely flat rings.

Round, flat, round: Saturn, its rings, and four of its many moons. Credit: NASA/wikimedia

If you want more
  • A long but excellent post on planets, galaxies, and roundness by the great Neil DeGrasse Tyson
  • Minutephysics has a cool video that explains this more technically, and shows why it can only happen in a 3D universe


Cover photo: CC0 WikiImages/pixabay

Water on Mars! Sometimes!

A long time ago Mars had water on its surface, and maybe even oceans–we knew that. But now we‘re sure think that a little water still flows there. Sometimes. Kinda.

On September 28, NASA gave a big-time press conference, with a public livestream, to announce they found proof of something people suspected for a while: water flows on Mars.

The Mars Reconnaissance Orbiter probe collected pictures of slopes, where long streaks stretch and shrink seasonally.

Because they conspicuously resemble small water streams, scientists studied them combining the great images from the HiRISE telescope on board the probe with spectroscopic measurements (which measure different light wavelengths to determine the chemical composition of a material).

The result is that these streaks (called Recurring Slope Lineae, or RSL) have all the makings of being caused by water flowing.

But RSLs are likely more similar to mud than water. Since Mars is really cold (-63 Celsius on average), the only way for water to prevent freezing is to have enormous concentrations of salt. The most probable candidate is perchlorate, which is almost everywhere on the planet surface. And it’s very toxic.

So don’t quite picture these as happy little mountain streams. They’re more like small avalanches of killer mud.

It’s also totally unclear where the water comes from. One possibility is that a thick layer of ice just below the surface thaws in the summer. Another is that there are actual underground waterbeds on Mars. Or maybe the water comes from the atmosphere, and the perchlorate captures it to the ground.

It may not look like much, but until now Earth was the only planet we knew with liquid surface water. This is a big step to figure how water works in the solar system.