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What makes Earth's atmosphere so special?

This photo of Earth and the moon was taken by an astronaut at the International Space Station in 2003.
This photo of Earth and the moon was taken by an astronaut at the International Space Station in 2003.
(Image: © NASA)

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

We Earthlings think we're oh-so-special. The abundance of oxygen in our atmosphere and the presence of liquid water on the surface of our planet makes our "Pale Blue Dot" stand out in contrast to the other planets in the solar system — a unique and fragile home for life. 

But for all the biological activity on our homeworld, we're not the only interesting planet orbiting the sun. There are some other equally amazing places in the solar system. Here is just a sampling.

Who asked for Venus?

Of all the rocky worlds in the solar system, Venus takes the cake — and then has some more. Its atmosphere is chokingly, toxically thick. At the surface, the air is almost a hundred times denser than it is on Earth, which makes "sea level" on Venus the pressure equivalent of an ear-crunching 3,000 feet (900 meters) under the water.

The miles upon relentless miles of air above Venus trap heat, a runaway greenhouse effect in full bloom. It makes the surface so hot that it's warmer there than on Mercury, despite the latter planet sitting closer to the sun.

Want to melt some lead? Just leave a lead bar sitting around on the surface of Venus, and wait. The atmosphere will do the rest of the work.

Related: Living on planet Venus: Why it would be hard (infographic) 

Japan's Akatsuki spacecraft captured this false-color image of Venus' dayside on March 30, 2018.

Japan's Akatsuki spacecraft captured this false-color image of Venus' dayside on March 30, 2018. (Image credit: JAXA/PLANET-C Project Team)

To make this hellish nightmare of a planet even worse (because why not), Venus' atmosphere hosts a substantial amount of sulfuric acid. The acid forms clouds in the upper atmosphere, and below that a pea-soup foggy haze, before condensing to produce acid rain.

But that acid rain doesn't even make it to the surface: the temperatures and pressures quickly evaporate it before it touches the ground.

Is Venus nasty? You bet. Is it special? Well, it's certainly one-of-a-kind.

Saturn's love for geometry

A high-res, colorful view of Saturn's Hexagon.

This colorful, high-resolution view of Saturn's hexagon was created using data from NASA's Cassini spacecraft.  (Image credit: NASA/JPL-Caltech/SSI/Hampton University)

So, Saturn has a hexagon on its north pole. No joke, we have pictures of it and everything. A real, legit geometric shape, staring at us like some sort of cosmic joke.

But it's no joke, just physics. The north pole of Saturn is dominated by a giant vortex-like hurricane, as winds whip around the planet at hundreds of miles per hour. But as you migrate farther south, the winds fade down to more sedate speeds. 

At a particular latitude, those winds become unstable, as faster-moving winds rub against their slower-moving cousins. The turbulent motion creates smaller, semi-permanent hurricanes, strung like beads on a necklace in Saturn's northern hemisphere. These hurricanes shape and sculpt the jet stream above them, forcing the winds to take on a distinctly six-sided appearance.

So, if you're a fan of geometry, there's no better planet than Saturn. Nobody else in our solar system sports such an arrangement of storms, making the ringed world an absolute standout.

A surprise from Titan

The hexagon isn't the only surprise to be found in the Saturnian system. Saturn's largest moon, Titan, is shrouded in dense, impenetrable fog.

And that fog hides a wonderful secret.

Titan's atmosphere is thick —by far, the thickest of any moon in the solar system, and even 50% thicker than the Earth's atmosphere. It's mostly nitrogen (just like the air of Earth) but also has a fair bit of methane and ethane. That gives Titan its characteristic yellow, ugly hue. And just above the surface, the methane bonds with hydrogen, sprinkling a few clouds in the smog.

And sometimes that methane forms droplets and falls to the ground, where it pools and collects to create streams, rivers, lakes, and even oceans of methane. And if it gets a little toasty, some of that methane evaporates back into the atmosphere, starting the cycle anew.

A complete cycle, akin to the water cycle on Earth, but at a temperature a few hundred degrees below zero. And with methane.

Besides the Earth itself, Titan is the only world in the solar system to boast liquids on its surface. Methane seas. Methane rain. A landscape dominated by liquid hydrocarbons. Life as we know it requires water, but it's not impossible for some form of life to arise in this methane oasis at the edge of the solar system.

And any place that could potentially host life is most certainly special.

Learn more by listening to the episode "AaS! 126: What's the wildest weather in the solar system?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Saul C. for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul on Twitter @PaulMattSutter and facebook.com/PaulMattSutter.

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  • rod
    As space.com report said "We Earthlings think we're oh-so-special. The abundance of oxygen in our atmosphere and the presence of liquid water on the surface of our planet makes our "Pale Blue Dot" stand out in contrast to the other planets in the solar system — a unique and fragile home for life."

    Clearly there are some real differences between Earth's, mostly N2O2 atmosphere and other planets in our solar system documented. Perhaps, Earth is special :)

    Compare atmospheres found in exoplanet studies too, a small number have atmospheres measured out of an inventory larger than 4300. Example, 'Telescope Teamwork Reveals Gas Dwarf Planet's Atmosphere', https://www.space.com/nasa-telescopes-reveal-exoplanet-atmosphere.html, "The scientists predicted GJ 3470 b's atmosphere would be full of oxygen and carbon, the same elements that are at the root of the water vapor and methane gas observed at Neptune. "Instead, we found an atmosphere that is so poor in heavy elements that its composition resembles the hydrogen- helium-rich composition of the sun,"

    Accretion disks observed around young stars contain CO for much of the disk content. 'Modeling the Spatial Distribution and Origin of CO Gas in Debris Disks', https://ui.adsabs.harvard.edu/abs/2019ApJ...878..113H/abstract
    HINTS OF YOUNG SOLAR SYSTEMS, https://skyandtelescope.org/astronomy-news/hints-of-young-solar-systems/
    Reply
  • Catastrophe
    "We Earthlings think we're oh-so-special."

    Yes. We wonder at the miracles of how everything is just right for us when the reality is that we adapted to what was here -- not vice versa.
    Reply
  • rod
    Interesting comment by Cat in post #3. I note we have 4333 exoplanets now reported at this site, http://exoplanet.eu/catalog/, and 4276 exoplanets reported at this site, https://exoplanetarchive.ipac.caltech.edu/index.html
    *Adapted* is a very interesting word. At the moment, I am not aware of reports documenting that life adapted on any of the more than 4300 exoplanets documented. Somehow, here in our solar system, Earth is populated with life that *adapted* to the Earth while even planets like Mars or Venus in our solar system, life is not verified as living there today or for example, a fossil record from the past showing life evolved on those planets :)
    Reply
  • Catastrophe
    I am just a simple person. By "adapted" I just mean how we got here.
    Reply
  • Helio
    There's a real chance, IMO, that we won't find any planet like Earth in most of the galaxy, perhaps all the galaxy. But we can learn from all the rest on how it all works to better help us understand just what we have.

    As for CO, I think this is one of those molecules astronomers can locate in clouds and disks, so reports of finding it has a lot to do with the fact it's somewhat easy to identify.
    Reply
  • Catastrophe
    Hmmmmm . . . . . . . . . I always thought that probability was a bit iffy!
    Reply
  • Helio
    Catastrophe said:
    Hmmmmm . . . . . . . . . I always thought that probability was a bit iffy!
    Well, I would say you're probably right. ;)

    The topic of atmospheres is very important since it will likely be the next set of great astronomical data that comes our way in our search for both planets harboring life and ones we could have a summer home (winter home?) :)

    But what we've found so far is just a crude, albeit exciting, start. The confirmed number of a several thousand exoplanets comes from just detecting them -- a bump in the photon flux of the host star, a little regular wiggle in the spectral lines, etc. No image of any that would make a nice screen saver; when imaged directly (a handful only) they're just dim dots. We had to go to Pluto to get that one and we can't seem to even find the next one beyond it (i.e. Planet 9).

    Nevertheless, with improved spectroscopy from the near-future giant scopes, some of the composition of exoplanet atmospheres will be resolvable by subtracting out the host-star's spectrum. This limits the number since a transiting system is required, but they may be the leading number of observed exoplanets.
    Reply
  • Helio
    Helio said:
    The topic of atmospheres is very important since it will likely be the next set of great astronomical data that comes our way in our search for both planets harboring life and ones we could have a summer home (winter home?) :)

    Well, I suppose Venus would be easier to search. ;)
    Reply
  • RamanarayananSp
    For life to be in space, to sustain it Life force to be present. One of the main reason for Earth to have life is its position with respect to Sun.

    Also the thinking facility is very essential for Life. Each organ in our body functions because of its latent Intelligence.

    The observation reveals that looking from Earth the Sun and our Moon appear almost the same Angular size.

    The reason for this is the ratio of the distance from Earth to the diameter of the object (Sun and Moon respectively) is almost 107 to 110.

    Our search in the Space for this unique coincidence can be a factor to determine life in a planet.

    This may be a wild guess based on observation and perspective...
    Reply