Goldilocks and the Three Planets

The recent NASA confirmations of liquid water on Mars and the cause of a stripping atmosphere on Mars have brought a lot of attention to Mars. Since we are on simulated Mars, we have gotten a lot of questions regarding our reaction to the news.

There are three planets in the habitable zone of our Sun: Venus, Earth, and Mars. Venus is wicked close to the Sun and does not have an internal magnetic field because of its really slow rotation. So it is very hot and has a very dense atmosphere that is made up mostly of CO2, and is dramatically affected by solar winds.

An artist’s impression of how solar winds are affected by Venus’ (top) and Earth’s (lower) magnetic fields. Source: ESA

Mars isn’t that much further away from the Sun than Earth. It is at the edge of the habitable zone. It could be habitable, but it isn’t, because of its atmospheric loss cause by the Sun. The Sun can only get away with this because Mars doesn’t have an internal magnetic field. Mars has many hundreds of very small magnetic fields (indicating prior plate tectonics), but none of them have the effect of Earth’s large one magnetic field.

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The crustal magnetic fields of Mars measured by the Mars Global Surveyor. Red indicates positive magnetic fields and blue denote negative magnetic fields. Source: NOAA
The Van Allen Belt layer of energetic charged particles is held in place around the Earth by the our magnetic field. Source: Johns Hopkins University Applied Physics Laboratory
The Van Allen Belt layer of energetic charged particles is held in place around the Earth by our magnetic field. Source: Johns Hopkins University Applied Physics Laboratory

Mars lacks the one major requirement that we understand for an internal magnetic field… the spinning magnetic core (dynamo) that converts the kinetic energy of the fluid core into electrical and magnetic field energy. Mars is believed to have had a dynamo that died – stopping spinning, cooled off – hundreds of millions of years ago. Prior to that, it may have been much more Earth-like (atmosphere, water, temperature) because it was protected from solar stripping. As an aside, all of the large gas giants also have spinning cores, and by virtue of that are able to keep their atmospheres. The important point is that because Mars’ dynamo died, all the factors that we associate with life and habitability have gone away as well.

Speaking of life, last winter, NASA confirmed that the Curiosity rover found a localized source of methane on Mars. This is super cool because methane is created either biogenically or geothermally- meaning that either life created it or it was created in a place that could possibly support life. The short rate of decay of methane also tells us that it was formed recently rather than being an ancient artifact. So…life on Mars? Possibly.

A couple weeks ago, things got even more exciting as NASA confirmed the suspicions of liquid water with HiRISE photos. Those photos indicate that water ice under the surface of Mars melts and flows downhill. This is super cool. Water is life! If you want to read about our crewmate Andrzej taking photos of it back in 2011 check out his blog post:

So, there is water on Mars – liquid water – and it isn’t all frozen in the ice caps as previously thought.

Subsurface flows on the slopes of Newton Crater, imaged by HiRISE. Source: NASA/JPL-Caltech/Univ. of Arizona

So, does life exist on Mars? We don’t know yet, but this is a great moment to remember why studying Mars and planetary science in general is so important: it teaches us about our own world. We are so fortunate that we still have a spinning dynamo, and that we have not have been blown off the face of the planet with a vortex of solar wind. Looking backward in time, without the dynamo, life would never have been able to evolve in the first place. Looking forward, Mars and Venus are a window into our own possible future if we are not cautious about what we do while we are here. We live in the same vicinity of space, are about the same size, and have the exact same sun. We are one wrong step away from turning into a planet that is either way to hot or way too cold, so we need to be conscience of our habitat and protect this planet while we are here.