![Petunia skylight](https://upload.wikimedia.org/wikipedia/commons/6/68/Petunia_skylight.jpg)
Martian lava tubes are
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates a ...
caverns on
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
that are believed to form as a result of fast-moving, basaltic lava flows associated with
shield volcanism.
Lava tubes usually form when the external surface of the lava channels cools more quickly and forms a hardened crust over subsurface lava flows.
The flow eventually ceases and drains out of the tube, leaving a conduit-shaped void space which is usually several meters below the surface. Lava tubes are typically associated with extremely fluid
pahoehoe lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...
.
Gravity on mars is about 38% that of Earth's, allowing Martian lava tubes to be much larger in comparison.
Detection and access
Lava tubes and related flow structures were first recognized upon examination of
Viking orbiter images, and later identified using orbiter imagery from
Mars Odyssey,
Mars Global Surveyor,
Mars Express, and
Mars Reconnaissance Orbiter.
[ Lava tubes can visually be detected two ways. The first is as long sinuous troughs known as rilles, which are believed to be the remains of collapsed lava tubes. The second method of possible identification is through observation of cave "skylights" or pit craters, which appear as dark, nearly circular features on the surface of Mars.][ In June, 2010, a group of seventh grade science students at Evergreen Middle School in Cottonwood, California, participating in the Mars Student Imaging Project, helped researchers discover a new series of lava tubes near ]Pavonis Mons
Pavonis Mons (Latin for "peacock mountain") is a large shield volcano located in the Tharsis region of the planet Mars. It is the middle member of a chain of three volcanic mountains (collectively known as the Tharsis Montes) that straddle the M ...
through identification of a skylight estimated to be 190×160 meters wide and at least 115 meters deep.[ It is only the second skylight known to be associated with this volcano.] In addition to orbital imagery, lava tubes could be detected through the use of:
* Ground-penetrating radar
*Gravimetry
Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest.
Units of measurement
Gr ...
*Magnetometry
A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...
*Seismography
A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, Types of volcanic eruptions, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to f ...
*Atmospheric effects
*Lidar
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
*Infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
*Human or robotic exploration[
There has been increased interest in the identification and investigation of lava tubes because they could present scientists with information regarding the geological, paleohydrological, and supposed biological histories of the planet.] When speaking about lunar lava tube
Lunar lava tubes are lava tubes on the Moon formed during the eruption of basaltic lava flows. When the surface of a lava flow cools, it hardens and the lava can channel beneath the surface in a tube-shaped passage. Once the flow of lava diminishe ...
s, Dr. William "Red" Whittaker, CEO of Astrobotic Technology
Astrobotic Technology is an American privately held company that is developing space robotics technology for lunar and planetary missions. It was founded in 2007 by Carnegie Mellon professor Red Whittaker and his associates with the goal of w ...
, states that "something so unique about the lava tubes is that they are the one destination that combines the trifecta of science, exploration, and resources." Access to uncollapsed sections of lava tubes can be done by entering at the end of rille, through skylights, or by drilling or blasting through the roof of a lava tube.[ Initial exploration of lava tubes may involve rovers, but with difficult challenges. Traditional skylights have large rubble piles directly below them (as seen in the first figure) which would be an obstacle for the rover. The vertical drop that the rover would have to perform would also have to be taken into consideration, as well as the ability of the rover to remain in communication with assets at the surface or in orbit.]
Lava tube conditions
Gravity on Mars is about 38% that of Earth, allowing Martian lava tubes to be much larger in comparison. Lava tubes represent prime locations for direct observation of pristine bedrock where keys to the geological, paleohydrological, and possible biological history of Mars could be found. The surface of Mars experiences extreme temperature fluctuations and receives a high amount of Ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
due to the lack of a magnetic field and the planet's thin atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, which is about one one-hundredth (or 1 percent) the thickness of Earth's. The thin atmosphere allows Mars to radiate heat energy away more easily, so temperatures near the equator can get up to during a summer day, and then drop down to at night. Subsurface conditions on Mars are dramatically more benign than those on the surface, which lead researchers to believe that if life did (or does) exist on Mars, it would most likely be found in these more hospitable environments. Life forms would not only be protected from the high surface temperatures and ultraviolet radiation, but also from wind storms and regolith dust.[ Martian lava tubes could possibly trap ]volatiles
Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.
On planet Earth, the term ' ...
such as water which is considered essential for life, and may also contain reservoirs of ancient ice since cold air can pool in lava tubes and temperatures remain stable.[ The ability to tap into these reservoirs may provide dramatic insight into the paleoclimatology and astrobiological histories of Mars.][
]
Possibilities for life on Mars
The discovery of Martian lava tubes has implications for the possibility of past or present life on Mars.
The magnetic and climatic histories of Mars and Earth are extremely different, and would have greatly dictated the evolution of both biospheres. Around four billion years ago, the Martian dynamo shut down following a proposed period when a long-lasting Noachian ocean existed, and when life may have existed at the surface. A sudden and intense increase of solar particles eliminated the atmospheric and hydrological protection, causing the atmosphere to thin and water to retreat from the surface. At this point, life may have sought refuge in subterranean environments such as lava tubes.[
A wide range of organisms may have survived in the subsurface, such as chemolithotrophs and ]lithoautotroph A lithoautotroph is an organism which derives energy from reactions of reduced compounds of mineral (inorganic) origin. Two types of lithoautotrophs are distinguished by their energy source; photolithoautotrophs derive their energy from light while ...
s, and certain extremophiles
An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme temper ...
like halophiles
The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...
or psychrophiles.[ Microbes found on Earth have been discovered thriving in near-freezing temperatures and very low-oxygen air. This allows researchers to believe that organisms can live in similar extreme situations such as those on Mars where temperatures are colder and less oxygen is available.] Volcanic minerals found in lava tubes could provide a rich source of nutrients to chemosynthetic
In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydro ...
organisms.[ Scientists are also interested in gaining access to Martian lava tubes because they could give insight into the processes that led to life on Earth since the geologic rock record is better preserved on Mars.]
Future human habitation
The interior of lava tubes, along with other subsurface cavities, could prove to be prime locations for future crewed missions to Mars by providing shelter for habitats.[ These natural caverns have roofs estimated to be tens of meters thick which would provide protection from the extreme conditions that would be experienced on the surface.][ The habitat would be protected from ]solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
, micrometeorites, extreme temperature fluctuations (ambient temperature is believed to be stable in lava tubes), winds, and regolith dust storms which could pose a threat to human health and technology. These natural shelters would also reduce the landed payload mass for crewed missions which would be economically advantageous.[
]
See also
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References
{{Geography of Mars, geology
Geology of Mars
Lava tubes