Some odd rock tracks in the sand - again.

originally posted by: signalfire
It's been surmised that there was a planet (Tiamat) that was where the asteroid belt is now; that it blew up

How does a planet blow up? No such possibility is allowed in any valid model of the Solar System, or indeed in physics in general.

It's the best explanation for the asteroid belt I can think of; it being an 'unformed planet' doesn't hold water IMHO.

The exploding planet hypothesis doesn't hold any water. The total mass of the asteroid belt is less than that of the Moon. There's just not enough stuff there to make up a planet. More likely, Jupiter's strong gravity (along with Mars' gravity) prevented a planet from forming properly. Or perhaps a planet was never going to be there, and the asteroids are just the remnants of the raw Solar System material (chunks of accreted material, etc.) that are being "sheperded" by Jupiter and Mars, just like Saturn's rings are being sheperded by its moons.

originally posted by: Bilk22
Yes but how do they know they're "sedimentary layers" and that they're "sedimentary layers" from a lake? What proof is there that water existed on Mars?

I guess you somehow missed countless articles and papers on past presence of water on Mars. From orbit, we have seen river channels and outflows, piles of sediments (such as Mt Sharp), spectroscopically identified hydrated minerals (such as clays and sulphates), and many other tell-tale signs. On the ground, Curiosity photographed sedimentary layers and pebbles that could only have formed or attained their shape in water.

So much science and analysis has been performed on this topic, especially during Curiosity's mission, that it puzzles me that people are still asking what evidence there is of past water.

Gale Crater
NASA Curiosity rover discovers evidence of freshwater Mars lake

a reply to: wildespace

So much science and analysis has been performed on this topic, especially during Curiosity's mission, that it puzzles me that people are still asking what evidence there is of past water.

Well it does take a lot of time looking for "anomalies".
It's hard to do that and keep track of the science.

originally posted by: wildespace

originally posted by: Bilk22
Yes but how do they know they're "sedimentary layers" and that they're "sedimentary layers" from a lake? What proof is there that water existed on Mars?

I guess you somehow missed countless articles and papers on past presence of water on Mars. From orbit, we have seen river channels and outflows, piles of sediments (such as Mt Sharp), spectroscopically identified hydrated minerals (such as clays and sulphates), and many other tell-tale signs. On the ground, Curiosity photographed sedimentary layers and pebbles that could only have formed or attained their shape in water.

So much science and analysis has been performed on this topic, especially during Curiosity's mission, that it puzzles me that people are still asking what evidence there is of past water.

Gale Crater
NASA Curiosity rover discovers evidence of freshwater Mars lake

So we know it was water and not some other liquid? I've read what is theorized about water having been present on Mars at one time, but where's the water now? What happened to it? That water represented a significant mass. Why didn't it effect Mars' orbit if it somehow vanished?

These are similar questions in understanding how ancient civilizations, with no known technology to see the stars and planets, having the ability to differentiate between the two. They're specs of light in the sky, using the naked eye. How did they know what was a planet vs a star? How did they understand the concept?

It appears that, lacking a substantial magnetic field to protect it, and rather weak gravity to hold it, Mars' atmosphere was gradually eroded by streams of solar particles. This would have carried away much of the water, which resided as vapor in the atmosphere. Lots of water is frozen in its polar caps, and a good deal lies frozen below the surface of the Red Planet.
Even the ancients were able to distinguish stars from planets. It is possible to easily observe, without optical aid, that the planets move in regular cycles, with respect to the stars, and in fairly short periods of time. The stars, by comparison are relatively fixed in position, moving so slowly that their movements can easily be overlooked.

originally posted by: Bilk22
So we know it was water and not some other liquid? I've read what is theorized about water having been present on Mars at one time, but where's the water now? What happened to it? That water represented a significant mass. Why didn't it effect Mars' orbit if it somehow vanished?

These are similar questions in understanding how ancient civilizations, with no known technology to see the stars and planets, having the ability to differentiate between the two. They're specs of light in the sky, using the naked eye. How did they know what was a planet vs a star? How did they understand the concept?

At some point, Mars' core cooled down and stopped spinning, which in turn stopped producing a global magnetic field (like we have one on Earth). Without the magnetic field, solar wind and radiation stripped most of the atmosphere molecule by molecule. With air pressure becoming very low, any water that didn't turn into ice was evaporated and eventually escaped into space, or got dissociated into oxygen and hydrogen.

A planet's orbit around the Sun doesn't depend on the planet's mass. It is only determined by the planet's distance from the Sun (planets closer to the Sun orbit faster, planets further away from the Sun orbit slower).

The way ancients differentiated between stars and planets, is that planets move with respect to stars over time. This is why the ancient Greeks called them planetes, which is Greek for "wanderers".

a reply to: Bilk22

What other liquid would you think it was?

Milk? Coke? Mercury?

Much too warm for it to have been any form of liquid gas: Nitrogen, Oxygen, Carbon Dioxide, Methane.

How sedimentary rocks form is pretty well understood science by geologists and scientists. Certain minerals present in those layers form while in water.

Mars has been loosing it's atmosphere for a very long time now. Not too long after if formed, it had a strong magnetic field like the Earth, and a much thicker atmosphere.

Having enough atmospheric pressure, and a high enough temperature, allows for the presence of liquid water. As the planet's core cooled, it's magnetic field began to weaken, enough to the point where the sun's solar wind started to strip away the atmosphere of Mars.

Once the pressure got low enough, water began to literally "boil" away (as you lower the air pressure, the temperature at which water boils goes down too). That water vapor was also carried away into space along with the atmosphere.

This process is gradual and not sudden. Loosing that mass will not change a planet's orbit. That's not how orbital mechanics work. In order to change a planet's (or anything else for that mater) orbit, it needs a change to it's orbital velocity, not mass.

As on Earth, a rocky planet that had water on it's surface, will most likely have water down in it's crust. That is where most of the water on Mars is now located.

The word "Planet" comes from ancient Greek and means "Wandering Star". They, along with other ancient cultures observed how certain "stars" seems brighter, did not seem to "twinkle" most of the time like all the other stars, were much brighter than the stars, and: They moved across the sky compared to all the other stars.

No one really understood what these "Planets" were back then, except that they moved fast, and that you could keep track of that movement, which would repeat itself.

It wasn't until the advent of the telescope at the beginning of the 1600s, that anyone was able to see the planets themselves in any detail.

ETA: oops, see Ross and Wildespace beat me too it.

originally posted by: eManym
I haven't seen many Mars surface images that don't have boulders scattered everywhere.

We've only seen a tiny portion of Mars from the surface. Who's to say that there aren't vast plains with no boulders?

By the way, latest images from Curiosity show a fairly boulder-less terrain:
mars.nasa.gov...
mars.nasa.gov...

Looks like the workmen have been out with their brushes. This is a very small patch of ground in front of the rover, isn't it?

However, the front hazcam on todays images do look like there are not many rocks about further out. Maybe it is a landing site cleared of rocks? :-)