
Large stationary gravity wave in the atmosphere of Venus - bcaulfield
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2873.html
======
bahro
To be clear, this article is about gravity waves
([https://en.wikipedia.org/wiki/Gravity_wave](https://en.wikipedia.org/wiki/Gravity_wave)),
or ripples at the interface of two media of different densities caused by
gravity, such as waves on the ocean or ridges of clouds, not gravitational
waves
([https://en.wikipedia.org/wiki/Gravitational_wave](https://en.wikipedia.org/wiki/Gravitational_wave)),
the propagating ripples in spacetime.

~~~
greglindahl
Gravity waves aren't _caused_ by gravity, they are in the _direction_ of the
gravitational force.

~~~
OscarCunningham
Sure they are. Some of the denser fluid is above the average level of the
surface, and gravity pulls it back down again. That's what makes the wave.

~~~
greglindahl
Gravity is one of several forces that may act on what's going on, but the
cause of the wave is the initial perturbation, which isn't gravity. Put
another way, if I have a steady-state hydrostatic system, gravity waves won't
just spring into existence. You need that initial push.

In this case, the initial push seems to be wind hitting a mountain and being
forced up.

~~~
contravariant
You need the medium, gravity, and 'push' to get a wave. Calling them
<medium>-wave, or 'push'-wave doesn't really tell you anything useful, so
they're called gravity-waves. An alternative would have been buoyancy-wave,
but apparently this didn't catch on (buoyancy and gravity are really two sides
of the same coin, anyway).

~~~
Godel_unicode
Buoyancy is related to density, which is independent of gravity. Check:
buoyancy can exist in a non-inertial reference frame provided acceleration in
a "downward" direction.

Also, you don't need gravity to be the force being acted against in order to
form a wave. You can get impact waves in water at 0g because of surface
tension.

[https://en.m.wikipedia.org/wiki/Buoyancy](https://en.m.wikipedia.org/wiki/Buoyancy)

------
autocorr
It's really something that Akatsuki is doing amazing science after the trials
and tribulations that satellite has been through. After failing orbital
insertion around Venus, it went five years in heliocentric orbit to reposition
itself for insertion around Venus again. The team ended up macguyvering its
secondary attitude control jets[1] for a long burn (~20 min) that they weren't
designed for, but it worked and allowed for a successful insertion--albeit in
a non-ideal orbit with a 9 day period instead of the originally planned 1.25
days.

[1] [https://spaceflightnow.com/2015/12/06/japanese-space-
probe-t...](https://spaceflightnow.com/2015/12/06/japanese-space-probe-to-
steer-into-orbit-around-venus/)

~~~
zymhan
I think any space-related MacGuyvering should be termed Kerballing.

~~~
chipaca
Seconded.

------
JumpCrisscross
Fun fact: spiral galaxies' galactic arms are stationary waves. They don't spin
like spokes on a wheel. Stars in the arms don't remain in them - every star
traverses through the arms and the regions between them [1]. Indeed,
correlations have been hypothesised between Earth's extinction events and our
Sun's predicted passage through these arms [2].

[1] [https://m.youtube.com/watch?v=c5Us-
jonCLA](https://m.youtube.com/watch?v=c5Us-jonCLA)

[2] [https://arxiv.org/pdf/1309.4838.pdf](https://arxiv.org/pdf/1309.4838.pdf)

------
WalterBright
> thick clouds of sulfuric acid

Given how reactive sulfuric acid is, how does this concentration remain
stable?

~~~
56678tytyu
Oxygen is one of the most corrosive gases. How do we remain stable? But
reducing ourselves to ash...of Hydrogen.

~~~
mirimir
How? Lack of activation energy.

And indeed, metabolism is basically catalyzed combustion.

------
CydeWeys
> The planet Venus is covered by thick clouds of sulfuric acid that move
> westwards because the entire upper atmosphere rotates much faster than the
> planet itself.

How the hell?! I get that the length of a Venus day is really long (243 Earth
days), but why would the wind be rotating in the same direction but faster?

~~~
JumpCrisscross
And they're speeding up!

"Already travelling at super-hurricane speeds, winds on Venus...accelerated by
an astonishing one-third" between 2006 and 2012 [1].

[1]
[http://www.abc.net.au/science/articles/2013/06/19/3784975.ht...](http://www.abc.net.au/science/articles/2013/06/19/3784975.htm)

------
LyalinDotCom
as someone who isn't a scientist I found this link to be a bit easier to
consume: [http://gizmodo.com/an-enormous-atmospheric-anomaly-has-
been-...](http://gizmodo.com/an-enormous-atmospheric-anomaly-has-been-spotted-
on-ven-1791172483)

------
andy_ppp
Here is a picture (I think) of this phenomena; it's _much_ larger than I
thought!

~~~
delinka
Did you forget to link to the picture?

~~~
andy_ppp
[http://www.skyandtelescope.com/wp-content/uploads/GW-
Venus.j...](http://www.skyandtelescope.com/wp-content/uploads/GW-Venus.jpg)

Oops :-(

