This artist’s impression shows a sunset (speculated and hypothetical) as seen from an exoplanet in another solar system – super-Earth Gliese 667 Cc, in a triple star system. Image Credit: ESO/L. Calçada. Source: http://www.eso.org/public/images/eso1214a/.
While candidates beckon even within our Solar System (particularly moons of other planets), so do the stars at night … and their potential planets and moons.
In this last regard, evidence continues to mount that some such star systems do indeed include planets (known as exoplanets), and that some of those planets host natural satellites, or moons (known as exomoons).
While there are many factors speculated to potentially influence planet and moon habitability, some key ones boil down to an assessment of the presence, or likely presence, of stable liquid water, the availability of energy accessible for life, and likely presence or potential formation of organic compounds.
An Artist’s hypothetical impression of suspected exoplanet Gliese 667 Cb with the the stars Gliese 667 A and Gliese 667 B in the background. Source: http://www.eso.org/public/images/eso0939a/, Image Credit: Credit: ESO/L. Calçada.
Image: public domain, available at http://en.wikipedia.org/wiki/Titan_(moon)
Huygens Probe replica, by David Monniaux, available at http://commons.wikimedia.org/wiki/File:Huygens_probe_dsc03686.jpg
The above image, taken from the surface of Titan, moon of Saturn, is the only image from a moon other than the moon (of Earth). It was taken by the Huygens probe, which landed on Titan in 2005.
While the portion of the surface of Titan shown in the surface image appears bare, Titan is in fact strongly evidenced as elsewhere having surface bodies of liquid hydrocarbons (as well as an atmosphere with which such liquids may chemically interact). These surface liquids represent the first stable bodies of liquid found beyond Earth. In addition, Titan is evidenced to have a subsurface liquid water/ammonia ocean.
It has been (very speculatively) theorized (including by astrobiologist Chris McKay) that methanogenic (methane-producing) microbes may live in the surface lakes of Titan, using, as a solvent, not water as all Earth-based life does, but liquid hydrocarbons, such as methane, in the lakes of Titan (for some more overview information on this, see the Fosdick’s Astrobiology Series article on this subject).
Image: public domain, http://photojournal.jpl.nasa.gov/catalog/PIA00502
In the above image, the dark orange lines crisscrossing Europa’s
Mosaic of images of the surface of Europa taken by the Galileo spacecraft, including the Conamara region, and showing surface features including lineae. Public domain image, http://photojournal.jpl.nasa.gov/catalog/PIA01092
surface are called lineae, and may result from fracturing of the surface crust of Europa from tidal flexing, a force related to the gravity exerted on Europa by Jupiter.
Europa is strongly evidenced as having subsurface oceans of liquid water, with tidal flexing believed to provide the heat that keeps its oceans from freezing.
Possible hydrothermal vents in the subsurface oceans of Europa (which could be caused by tidal flexing) could hypothetically provide a habitat for life, just as life clusters around hydrothermal vents in the oceans of Earth.
The on the above image, actress Jodie Foster’s character shows
From the 1997 movie, “Contact”
the flash of excitement and amazement at the recognition of what seems to be non-“naturally”, non-randomly occurring radio signals from a distant star system – not merely signals, but, in fact a communication – a repeating pattern, a structure, bespeaking an intelligent formulation, and thus an intelligent source.
One area of astrobiology includes
The Very Large Array (VLA) Radio Astronomy Observatory in New Mexico, USA. Source: http://en.wikipedia.org/wiki/Radio_astronomy#mediaviewer/File:USA.NM.VeryLargeArray.02.jpg
the search for intelligent life beyond earth (and generally beyond the solar system), often including the use of radio astronomy in attempting to receive, identify and interpret hypothetical radio frequency communications from such intelligent life (a large part of the activities collectively known as SETI – the Search for ExtraTerrestrial Intelligence).
The ultimate homerun of astrobiology, success in this effort would not only affirmatively answer the massive question of whetherlifeexists beyond Earth (and indeed beyond the Solar System), but also the exponentially more massive question of whether intelligent life exists beyond Earth and in another star system.
Radio communications (that is, radio frequency electromagnetic communications) would seem the most promising form of communication for potential interstellar communications.
Just as visible electomagnetic signals (i.e., light) can be received from sources very close by (look up and see light with the source being a ceiling light fixture a few feet away) or incredibly far away (look into the night sky and see light from a star a hundred light years away, or even a thousand), so can radio electromagnetic signals.
Like light, radio signals can be received from sources very close by (such as by a receiver in radio controlled car, the source being the radio controller held by a child across the room), or from not as close by (such as by a person’s car stereo receiver from an FM broadcasting tower), or, in fact, from incredibly far away, such as by a radio telescope, from a distant star or another galaxy.
Radio astronomy generally, and radio SETI, can use telescopes with large “dish”-like receivers, or arrays of many such telescopes essentially working together (called radio interferometry), to receive, in the strongest and clearest fashion practical, radio signals from distant star systems and celestial bodies.
Image: public domain, http://mars.nasa.gov/mer/gallery/press/spirit/20050420a.html
The above strikingly detailed image shows a region of Mars called
Artist’s concept of a Mars Rover, public domain image, http://photojournal.jpl.nasa.gov/catalog/PIA04413
Gusev Crater. It was taken by the Mars Spirit rover in 2005.
Mars, today, can be described as appearing similar to a harsh desert on Earth. It is indeed mostly void of liquid water – essential to all life as known on Earth.
Yet, abundant evidence, including present-day Martian landforms, strongly suggests that, during some times in its extremely ancient history, Mars flowed with water over large portions of its surface – a wet world truly different than the Mars of today.
Did life perhaps thrive in the waters of ancient Mars? Conditions may have been too salty or acidic, at least for life as known on Earth, but perhaps not.
Mars echos, but moons in the Solar System – Europa, Titan, Enceladus – ring out, now, with the real possibility of harboring life.
Archaea are a type of microorganism – a relatively simple, ancient form of life, and yet intriguing.
Extant since early in the history of life on Earth, and still widely
Archaea, in high magnification, public domain image, available at http://en.wikipedia.org/wiki/Archaea
distributed on Earth today, archaea include extremophiles: microorganisms that thrive in extreme environmental conditions. For example, certain extremophiles live in highly saline water environments (halophiles), extremely hot water environments such as the hot spring depicted above (thermophiles) and extremely cold water environments (cryophiles or psychrophiles).
Extremophiles are particularly interesting to astrobiologists, who attempt to identify environments beyond earth that may harbor life – environments that are often extreme by Earth standards.
As an important example, microorganisms, including archaea, have been found to thrive around hydrothermal vents, which are essentially underwater volcanoes. These microbes use chemicals in the heated, mineral rich water for energy (leading to entire ecosystems there). Yet hydrothermal vents are evidently not unique to Earth, even in the Solar System; they are thought to likely exist, for example, on Europa, moon of Jupiter, as well as Titan and Enceladus, moons of Saturn. If archaea can thrive around earth’s hydrothermal vents, could microorganisms thrive around hydrothermal vents on Europa, Titan, Enceladus and elsewhere beyond Earth?
