Hydrothermal Vents: The Origin of Life?

Astrobiology is becoming an increasingly discussed topic as new exoplanets are being found and we discover more about the worlds of our own solar system. Of course, for there to be life on other planets, it first needs to come into existence on its own through abiogenesis, or the creation of life through non-biological sources. Perhaps our best way to learn about how abiogenesis might occur on other worlds is to consider how it occurred on ours. While we can never be entirely sure as to the causes of life on Earth, one of the leading candidates for the catalyst behind abiogenesis is the humble hydrothermal vent.

A hydrothermal vent at the bottom of the Pacific Ocean, fumin’ away

Hydrothermal vents are the result of water underneath the seafloor being heated by the mantle and erupting out of the ground in sustained streams, sometimes at temperatures of over 300 degrees Celsius (although the water is still liquid due to the extreme pressures of the deep ocean). At the depths that they are found, no sunlight at all reaches the seabed, so you might think hydrothermal vents would be barren of life…

But you would be wrong. Behold, a hydrothermal vent colony of tubeworms

Hydrothermal vents actually have many times the biological density of the surrounding seafloor, primarily due to extremophile bacteria which get their energy by processing chemicals in the hydrothermal vent fluid. This is significant because these bacteria due not rely on the sun for energy, even indirectly (unlike most other deep-sea creatures, which feed on detritus further up in the water column). And because they are in the deep sea, they are shielded from events which occur further up, such as asteroid impacts or extreme solar radiation. This makes hydrothermal vents, which would have been much more common in Earth’s early life due to increased geological activity, ideal places for life to develop, providing a safe harbour from the outside chaos. Besides this, there are many chemicals present in hydrothermal vent fluid important for biological activity that were not present in the ancient atmosphere, such as methane and ammonia. Finally, the oldest known life that has been discovered are bacteria fossilized in hydrothermal vent chimneys, and this life appeared almost as soon as the Earth’s surface had cooler sufficiently to support an ocean.

Europa, a candidate for extraterrestrial life with possible hydrothermal vent activity

This all goes to show that other worlds, which have surface conditions very averse to life, may still be able to harbour it. Take Europa, whose surface is extremely cold and which has virtually no atmosphere. Any yet, it is known to be geologically active, with a subsurface ocean. So it is very possible that Europa is home to hydrothermal vents and if this is the case, it may present
the very same conditions that spawned life on Earth.

The Star-Crossed Fates of Phobos and Deimos

The planet Mars was named after Mars, who to the Romans was the God of War. Its two moons, Phobos and Deimos, carry the names of the Greek Gods of fear (from which we get phobia) and terror, respectively.

However, despite the naming scheme that seems to be inspired by Death Metal, Phobos and Deimos are not very intimidating. The look much less like something menacing and much more like two misshapen, cosmic potatoes of especially low quality.

But we really shouldn’t be making too much fun of Phobos and Deimos. After all, they are doomed. “How can a moon be doomed?” viewers at home may be wondering. Here is how:

The Death of Phobos

From what we have observed about Phobos, it appears to be formed of many segments of rock weakly held together by gravity, coated by a thin crust. This loose conglomeration of rock does not fare well when tidal forces are applied. And unfortunately for Phobos, it is being subjected quite strong tidal forces, as it is much closer to Mars than Deimos. Moreover, it is being pulled in closer to Mars at a rate of 2 meters every hundreds years. At this rate, scientists expect that Phobos will either collide directly with Mars, or break up into a fancy planetary ring.

Neither of these options are very appealing for Phobos.

The Rejection of Deimos

Deimos is suffering (or will be suffering, at any rate) from the opposite problem that is afflicting Phobos. Tidal acceleration is slowly but surely increasing Deimos’ orbit, and eventually Mars will lose gravitational hold on Deimos. Deimos will then be sent to drift about the Solar System indefinitely, or until it crashes into something. It is thought (though there is not a consensus) that Deimos and Phobos are asteroids that were captured by Mars at some point in the past, so perhaps it would be fitting for Deimos to rejoin its friends in the asteroid belt. Still, one can’t help but feel for Deimos’ impending loss of glory, falling from the status of moon to lowly space rock.

MAGNETAR

As you know, neutron stars are the result of massive stars (many times more massive the the sun) collapsing inward on themselves, leaving behind an extremely dense and energetic core. As you might expect these stars are extremely energetic — what you might not know is that sometimes as a result of the in-falling star materials angular momentum, neutron stars can spin. Sometimes they end up spinning very fast. These are magnetars. And as a result of their extremely rapid periods of rotation, they exhibit egregiously large magnetic fields. These fields are millions of times stronger than any man-made magnet. In fact, the magnetic field is so high around a magnetar that the field itself has an energy density 10,000 greater than that of lead, and distorts the orbit clouds of atoms into cylinders. I.e., you do not want to be close to a magnetar. Fortunately, they are so energetic that after around 10,000 years they effectively die, leaving behind a magnetized husk. Beware

The OORT CLOUD and You

You might find yourself looking at a (to-scale) diagram of the planets of the solar system (and Pluto), such as the following:

A solar system model that suspiciously does not include earth…

and think to yourself “Wow, Pluto is so much farther out from the sun than the Earth is. The solar system is so massive!”. And while you would be correct in your statement, the orbits of the sun’s outer planets (and dwarf planets) pale in comparison to the true extent of our solar system. Enter: the OORT CLOUD.

Actually, the Oort Cloud is going to have to wait. First, we’re going to have to cover comets. For a comet to show its characteristic tail, it has to pass (relatively) close to the sun. This implies that its orbit must be highly elliptical so that it can be near the sun for a short period of time before moving far enough away that it reverts to its less aesthetic ball-of-ice-and-rock form.

Everyone knows about Halley’s comet, which becomes visible from Earth every 76 years. Combining this lengthy period with the above fact that comet orbits must be very elliptical, one can imagine that Halley’s comet is, at its furthest extent away from the sun, far away. An in fact it manages to reach a bit farther than the orbit of Neptune before crashing back toward the sun.

But, in the grand scheme of things, Halley’s comet actually has a fairly short period. The famous Hale-Bopp comet has a period of over 2500 years and, as you might guess, reaches much farther away from the sun than Halley’s comet: 183 AU, or roughly 6 times farther than Neptune’s Aphelion.

But wait, there’s more! This unassuming ball of rock:

is Sedna, a minor planet whose aphelion is 936 AU, or 30 times Neptune’s aphelion.

But even beyond Sedna, there is the Oort Cloud. The Oort Cloud is a theoretical cloud of gas and icy bodies which exists at the very edge of the Sun’s gravitational influence. This cloud is conjectured to exist at up to 200,000 AU away from the sun. In other words, the outer reaches of the Oort Cloud, should it exists according to these projected specifications, would be over six thousand times farther away from from the sun is than Neptune. This is the true extent of our solar system, beyond which point the sun’s gravity is no longer sufficient to pull bodies along with it as it wanders through the galaxy.