Archive for the ‘Astrobiology’ Category

“Where is everybody?” The Fermi Paradox

Sunday, September 7th, 2014

A paradox has been puzzling astronomers for decades.

In 1961 Frank Drake proposed his now famous Drake Equation, which is a thought experiment to simulate calculating the expected number of intelligent civilizations in the galaxy. It uses estimated values for things like the average number of planets around a star and how often life will form on a habitable planet. Though most of these values were complete guesses (some still are), we’re getting better at estimating the likelihood of extraterrestrial intelligence in our cosmic neighborhood.

As it turns out, we expect there to be thousands of civilizations on various planets throughout the Milky Way. Many of whom should have the ability to communicate and possibly even travel through the immense distances between solar systems. And yet, despite the Search for Extraterrestrial Intelligence (SETI) searching for signs of this life for many decades, we have no evidence of life anywhere else in the Galaxy. This is known as the Fermi Paradox after Enrico Fermi, the physicist who first proposed it.

Dozens of explanations for this paradox have been proposed over the years, but the true answer still eludes scientists. Let’s take a look at some of the common thoughts, as well as a few of the more curious solutions.

We are essentially alone

The most obvious explanation of this paradox is that the assumption of extraterrestrial intelligence currently existing in the galaxy is incorrect. This could be the case with a few different explanations:

  • Life is extremely rare to begin in the first place. Earth was a rare case where the necessary ingredients for life was a fluke, and is not a common occurrence on other planets.
  • Simple life is common on habitable planets, but rarely does it evolve into complex organisms, much less sentient, intelligent life that attempts communication.
  • Intelligent life does arise fairly often, however it destroys itself shortly after becoming spacefaring, thus the likelihood of another intelligent species currently able to communicate with us is low.

In any of these scenarios, the likelihood of finding evidence for complex life on other planets is extremely low. We may very well be the only sentient creatures in the galaxy.

We can’t find them

The Aricebo observatory in Peurto Rico

Alternative to the fact that we may be alone, is the idea that although intelligent life is relatively common in the universe, it difficult (or impossible) to find evidence of this. This assumes life, given the chance, will almost always evolve into more intelligent beings, eventually reaching a point where communication or space travel becomes possible. A number of explanations to this scenario have been proposed:

  • The distance between Earth and the nearest intelligent life is so far that communication is essentially impossible.
  • Even if a species possesses the technology to spread throughout the galaxy, it may not find it economical. Thus they remain in their local celestial neighborhood.
  • We have not been searching long enough, or looking for the right clues. Humans have been listening to only certain radio waves, and only for about 60 years. It is possible extraterrestrials are using something other than radio frequencies to communicate, such as gamma rays , or we do not understand how the information is formatted in their signals.
  • Earth is not as ideal for life as “superhabitable” planets, thus the effort of another species trying to communicate with us isn’t worthwhile.
  • Extra Terrestrials may not have any incentive to reach out to other species. This could be because they are solely interested in themselves, or perhaps because they don’t want to be found. In this scenario, a species may actually avoid detection for fear of a hostile engagement with another species.
  • Everybody is listening, and nobody is talking. SETI primarily focuses on listening to the airwaves for indications of intelligence, but does not actively transmit its own intelligent transmissions. The same could be happening for a majority of other beings.
  • Earth could be some sort of experiment, either by an extremely intelligent alien species, or entirely a computer simulation. This is known as the Planetarium Hypothesis.
  • Perhaps we have already been visited by aliens, and are either A) unknown to us, or B) occurred in the distant past, so we have no evidence.

Searching for Life in our Solar System

Tuesday, January 21st, 2014

Titan in Natural Color

Astrobiology is the study and search for extraterrestrial life – exotic life forms existing on other celestial bodies. While studies are underway searching for intelligent life throughout the galaxy such as SETI, there are a few places astrobiologists are looking in our own solar system.

Titan

Titan is the largest moon of Saturn, almost twice the size of our own moon. It is a unique celestial body in our solar system, in that it is the only satellite with a dense atmosphere, and has evidence of liquid on its surface.

Artist rendering of Titan’s Methane lakes

Titan’s atmosphere is primarily made up of Nitrogen, and is much thicker than Earth’s. This makes it extremely opaque, and for many years we had no idea what the surface looked like. In 1995 Hubble used its infrared instruments to image the surface of Titan, and discovered shallow lakes of liquid methane on the surface.

These lakes may support life, in a way that Earth’s oceans do. Instead of carbon based life, these creatures could be methane based, where they would inhale Hydrogen, and exhale methane. While no concrete evidence of these exotic life forms exists, the necessary building blocks are there. There are numerous plans to return to Titan (the Huygens probe landed on the surface in 2005), though none have been funded as of yet.

Enceladus

Enceladus’ icy surface

Enceladus is a small moon that orbits Saturn. It is only about 500km across, or about 13% the width of our moon. It exists about 238,000km away from the surface of Saturn, and takes 218 days to orbit.

Enceladus has recently been deemed the most habitable spot in the solar system beyond Earth. This is because Enceladus is covered in water ice, and is also extremely geologically active. At the southern end of the moon, giant plumes of liquid water spray out of the icy surface like geysers. These jets of water, known as cryovolcanoes, turn to vapor and give Enceladus the most notable atmosphere of any solar system moon outside of titan. The jets also indicate the core of the moon is warm due to tidal heating from Saturn’s gravity, which could allow for a water ocean underneath the ice. Fractures and a relatively low number of impact craters indicate the entire surface is tectonically active – another sign the moon is warm in its core.

Enceladus’ Cryovolcanoes

This warmth, along with water oceans, may lend itself towards the existence microbial extremophiles, if the hot rocky core is releasing its energy through hydrothermal vents. The existence of life using this method can be seen on Earth at extremely deep and geologically active points in the ocean, where no energy by means of sunlight can be utilized.

Europa

View of Europa’s Icy Surface

Europa is the fourth largest moon of Jupiter, only slightly smaller than our own moon. It is similar to Enceladus in that it is covered in water ice, and also believed to be warm at its core due to tidal heating from Jupiter’s gravitational pull. As with Enceladus, this could also harbor microbial life at or near hydrothermal vents. Additionally, it has been calculated cosmic radiation could convert some of the oxygen locked up in the surface ice into free oxygen in the oceans beneath. This could conceivably support larger life forms, such as small fish.

While Europa is thought to be one of the best chances for finding life in the solar system, the likelihood of a very thick ice shell makes it difficult to access the inner ocean. However, In December 2013 it was discovered that Europa also has large plumes of water, some as high as 200km, ejecting out of its surface, similarly to Enceladus. If these jets are releasing water from the subsurface oceans, it would be relatively easy for orbiting spacecraft to study the chemical makeup of the water vapor, and determine if life does in fact reside there.

Rendering of the proposed interior of Europa

Recently the US House Appropriations Committee has supplied $80 million in funding for the creation of future Europa exploration missions. These missions include Europan flybys, orbits, and eventually landing on the surface. These missions ultimately are intended to determine the likelihood of extra terrestrial life on Europa. Additionally, the Jupiter Icy Moons Explorer (JUICE), was recently approved by the European Space Agency, which will spend some time observing Europa. This mission is set to launch in 2022.

The Red Planet – pt. 2

Saturday, December 21st, 2013

This is part two of a three part series on Mars.

Decedents of Mars

The origin of life on Earth is a hotly debated topic throughout all facets of humanity. Both religiously and scientifically, there are dozens of explanations for how life began on our planet. While most focus on Earth being the cradle of life, there is a theory of the origin of life coming from another celestial body.

Note: This is a scientific theory, and has not been proven.

The Early Solar System

Our sun was formed approximately 4.6 billion years ago, and the planets formed shortly after that. In the early solar system, planets were extremely hot and constantly bombarded with asteroids. Because Mars is about 10 times less massive than the Earth, it was able to cool quicker. In doing so, it may have also formed liquid water earlier than Earth. As we saw in a previous article, water is the key to life, and thus Mars may have been habitable millions of years before Earth.

Extremophiles

Microscopic image of a Tardigrade

Although it is possible that Mars may have been habitable before Earth, it does not necessarily mean any life could travel between the two planets. Space is an extremely hostile environment, with frigid temperatures, fatal doses of radiation, and nearly a complete vacuum. To determine if life could exist in space, we must look at life on Earth today. Even in the harshest conditions on the planet, we find the Earth teeming with life. There is a classification of animals known as “extremophiles” that illustrate this survivability. One particular microscopic animal, known as the Tardigrade, can survive in almost any environment imaginable. They have been shown to live in temperatures a few degrees above absolute zero (−459.67°F), survive harmful doses of radiation, go without food for 10 years, and have even survived in the vacuum of space.

Transportation

Since it is plausible that a microscopic life form can exist in space, all that is needed is the vehicle to travel between planets. As mentioned earlier, the young universe was riddled with asteroids that would often collide into planets. A large enough impact will launch planetary matter with such velocity that it will escape the gravity of that planet and begin its journey into space. It is possible some of this matter on mars may have harbored some extremophiles, and perhaps that matter made its way to Earth, thus seeding life on our own planet. The origin of life on Earth is a hotly debated topic throughout all facets of humanity. Both religiously and scientifically, there are dozens of explanations for how life began on our planet. While most focus on Earth being the cradle of life, there is a theory of the origin of life coming from another celestial body.