Organic Material And Mysterious Methane On Mars
By Judith E Braffman-Miller
Human observations of Mars go all the way back to an ancient era when Egyptian astronomers discovered it in the 2nd millennium B.C., at a time when the Pharaoh Khakhaure Senusret III ruled over this Bronze Age civilization. Since then, perhaps no other planet in our Sun’s family has intrigued our species as much as Mars, probably because our collective imagination has made this small rusty-red world the most probable abode of life beyond Earth. Mars still captivates our fantasies–and yet, outlandish tales of “little green Martian men” may not be completely off target. In June 2018, astronomers announced that NASA’s plucky little rover Opportunity has discovered new evidence preserved in Martian rocks that sings a tantalizing Sirens’ song that the planet could have supported ancient life–as well as new evidence in the Martian atmosphere that relates to the search for current life on the Red Planet. While by no means powerful evidence for the existence of life itself on Mars, these findings are a promising sign for future missions sent from Earth to explore the Martian surface and subsurface.
The new findings, that include the detection of “tough” organic molecules in 3-billion-year-old sedimentary rocks near the Martian surface, as well seasonal variations in the levels of methane in the atmosphere of Mars, are published in two separate papers in the June 8, 2018 issue of the journal Science.
An organic molecule contains carbon and hydrogen–and may also possess nitrogen and oxygen, as well as other elements. Even though they are frequently associated with life, organic molecules can also form as a result of non-biologic processes, and are not necessarily indicators of the presence of life.
“With these new findings, Mars is telling us to stay the course and keep searching for evidence of life. I’m confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet,” Dr. Thomas Zurbuchen commented in a June 7, 2018 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Zurbuchen is associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. The JPL is in Pasadena, California.
Dr. Jen Eigenbrode of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is lead author of one of the two research papers published in Science, noted in the same JPL Press Release that “Curiosity has not determined the source of the organic molecules. Whether it holds a record of ancient life, was food for life, or has existed in the absence of life, organic matter in Martian materials holds chemical clues to planetary conditions and processes.”
In February 2018, Opportunity witnessed its 5,000th Martian dawn. A Martian day, called a sol, is about 40 minutes longer than a day on Earth, and a year on Mars is equivalent to nearly two Earth-years. Opportunity landed on the Red Planet January 25, 2004, Universal Time (UT), and its primary mission was planned to last about 90 sols–however, it greatly exceeded expectations. Indeed, NASA scientists did not expect this amazingly sturdy little rover to last through one entire, bitterly cold, Martian winter–let alone last for longer than 5,000 Martian dawns.
Singing A Sweet Sirens’ Song Since The Bronze Age
In addition to Bronze Age Egyptian astronomers, Mars was detected by observers living in other civilizations throughout the ancient world. For example, Chinese documents recording the movements of Mars appeared before the founding of the Zhou Dynasty (1045 B.C.). More detailed observations of the Red Planet were conducted by Babylonian astronomers who developed arithmetic techniques in order to predict the future positions of the planet.
Ancient Greek philosophers, as well as Hellenistic astronomers, devised a geocentric model in their efforts to explain the Red Planet’s motions. Measurements of Mars’ angular diameter were recorded in ancient Greek and Indian documents. In the 16th century, Nicolaus Copernicus (1473-1543) proposed his heliocentric model for our Solar System in which the planets travel circular orbits around our Star, the Sun. This was later revised by Johannes Kepler (1571-1630), who proposed an elliptic orbit for Mars that more accurately fit observations.
Galileo Galilei (1564-1642) made the first telescopic observation of Mars in 1610, using his primitive little “spyglass”–one of the first telescopes used for astronomical purposes. During that same century, other astronomers observed the dark patch dubbed Syrtis Major Planum, as well as polar ice caps on Mars, using the tiny telescopes of that era. These early astronomers also determined the Martian rotation period and axial tilt. These observations were primarily conducted during the time intervals when Mars was situated in opposition to the Sun–that is, at the points when the Red Planet was making its closest approaches to Earth.
Improved telescopes developed in the 19th century helped astronomers map permanent albedo features on Mars in detail. The earliest crude map of Mars was published in 1840, and this first map was followed by a series of improved maps from 1877 onward.
The intriguing fantasy of “little green Martian men” emerged when astronomers mistakenly believed that they had spotted the spectroscopic signature of water in the Martian atmosphere. This Sirens’ song of Martian life became popular among the general public. Indeed, the American astronomer Perceval Lowell (1855-1916) thought that he had detected a network of artificial canals on the Red Planet’s surface. However, these interesting linear features were later determined to be mere optical illusions. In addition, the Martian atmosphere was found to be too thin to support an Earth-like environment that could indicate the presence of life as we know it.
During the 1920s, the range of the Red Planet’s surface temperature was measured. It was determined to range from a chilly -121 degrees to 45 degrees Fahrenheit. The atmosphere of this rusty-red world was shown to be arid with only scanty quantities of oxygen and water. In 1947, the Dutch-American astronomer Gerard Kuiper (1905-1973) demonstrated that the thin Martian atmosphere harbored extensive carbon dioxide that amounted to about twice the amount found in Earth’s atmosphere.
Mars, like Earth and the other solid planets (Mercury and Venus), dwells close to our Star in the brightly lit and toasty inner realm of our Sun’s kingdom. Even though Mars is the fourth major planet from our Star, as well as Earth’s near-neighbor in the Solar System, it has still managed to keep its secrets well-hidden from the prying eyes of curious observers. For example, in March 2016, a team of astronomers announced they had discovered that the Martian surface had been tilted by 20 to 25 degrees about 3 to 3.5 billion years ago. This catastrophe occurred when our Solar System was still young, since our Star and its family were born about 4.56 billion years ago. The culprit behind this tattle-tale tilt is generally thought to be an enormous volcanic structure. This behemoth volcano, called the Tharsis volcanic dome, is the largest of its erupting kind in our entire Solar System. Because of the enormous mass of the Tharsis volcanic dome, it resulted in the outer layers of Mars (crust and mantle) to rotate around its core.
This terrible shift is thought to have unfortunately happened right at the time life may have first emerged out of a primeval Martian stew composed of non-living substances. It also provides an answer to three of the Red Planet’s most well-kept secrets: why rivers on Mars formed and where they are currently located; why the Tharsis dome is located at the Martian equator; and why underground reservoirs of water ice are situated very far from the Martian poles.
Mars is commonly referred to as the “Red Planet” because it is abundantly coated with iron oxide on its surface. This bestows upon the planet its signature rusty-red color. The surface of Mars is pockmarked with numerous impact craters that resemble the impact craters seen on Earth’s Moon. Mars also shows polar ice caps, deserts, and volcanoes akin to those on Earth. This outermost of the inner quartet of terrestrial planets (Mercury, Venus, Earth and Mars, in that order), the Red Planet displays a rotational period and changing seasons, resembling those of Earth.
Unlike Earth’s large and lovely lunar companion, the duo of tiny Martian moons are deformed, and resemble potatoes. The two moons, dubbed Phobos and Deimos, are often considered to be captured asteroids that escaped from the Main Asteroid Belt between Mars and Jupiter, only to be gravitationally snared by the Red Planet during their unfortunate wanderings. As a result, the two tiny moons experienced a dramatic alteration from lost and lonely asteroids to the moons of one of our Solar System’s major planets.
Since 2000, cameras in orbit around Mars have dispatched back to astronomers on Earth a treasure chest filled with tattle-tale images. These images reveal that the Martian surface is etched by small valleys sculpted into slopes, that are hauntingly similar in shape to gullies that were created by floods of rushing water on Earth. The Red Planet’s gullies are probably less than a few million years old, and some of them may be younger than that. A few million years is considered to be a brief period on geological time scales. These observations provide intriguing clues that large amounts of water, in its life-sustaining liquid phase, may still be bubbling beautifully on Mars today. This flowing Martian water might be responsible for sculpting the surface gullies.
Therefore, even though the Martian surface isn’t especially inviting today, there is sufficient evidence indicating that long ago its climate allowed life-sustaining liquid water to pool at the surface.
Searching For Life As We Know It
Data derived from Curiosity show that billions of years ago, a lake of water existed within Gale Crater that contained all of the precious ingredients necessary for life as we know it to exist–including both chemical building blocks and energy sources.
“The Martian surface is exposed to radiation from space. Both radiation and harsh chemicals break down organic matter. Finding ancient organic molecules in the top five centimeters of rock that was deposited when Mars may have been habitable, bodes well for us to learn the story of organic molecules on Mars with future missions that will drill deeper,”explained Dr. Eigenbrode in the June 7, 2018 JPL Press Release.
In the second research paper, published in the June 8, 2018 issue of Science, astronomers describe the discovery of seasonal variations in methane in the Martian atmosphere over the course of nearly three Martian years–which are the equivalent of almost six Earth years. This variation was spotted by Curiosity’s Sample Analysis at Mars (SAM) instrument suite.
Astronomers cannot rule out the possibility that this methane has biological origins. However, water-rock chemistry might also be responsible for the methane. Earlier observations detected the presence of methane in the Martian atmosphere, mostly in large, unpredictable plumes. This later result reveals that low levels of methane within Gale Crater repeatedly peak during the warm, summer months, only to plummet during the winter each year.
“This is the first time we’ve seen something repeatable in the methane story, so it offers us a handle in understanding it. This is all possible because of Curiosity’s longevity. The long duration has allowed us to see the patterns in this seasonal ‘breathing’,” explained Dr. Chris Webster in the June 7, 2018 JPL Press Release. Dr. Webster is of the JPL, and is the lead author of the second paper.
The Quest To Find Organic Molecules On Mars
In order to detect organic molecules in the Martian soil, Curiosity drilled deep down into a type of sedimentary rock called mudstone that is found in four regions of Gale Crater. This mudstone formed very slowly billions of years ago from silt that had collected at the bottom of the ancient lake. The samples of rock were analyzed by SAM, which used an oven to heat the samples (in excess of 900 degrees Fahrenheit), in order to liberate organic molecules from the powdered rock.
SAM measured small organic molecules that emerged from the mudstone sample. These small molecules are really fragments of larger organic molecules that do not vaporize as easily as their smaller counterparts. Some of the fragments were found to contain sulfur, which may be responsible for preserving them. This is the same way that sulfur is used on Earth to make car tires more durable, Dr. Eigenbrode explained in the June 7, 2018 JPL Press Release.
The results of the new research also suggest that organic carbon concentrations are on the order of 10 parts per million. This is close to the amount detected in Martian meteorites that plunged down to Earth, and approximately 100 times more than earlier detection of organic carbon on the Martian surface. Some of the molecules detected include benzene, toluene, thiophenes, and small carbon chains, such as propane or butane.
In 2013, SAM identified some organic molecules containing chlorine in rocks at the deepest regions of the crater. This latest discovery adds to the inventory of molecules detected in the ancient Martian lake sediments, and helps to shed light on why they were preserved.
Discovery the presence of methane in the Martian atmosphere and ancient carbon preserved on the surface gives planetary scientists confidence that NASA’s Mars 2020 rover and the European Space Agency’s (ESA’s) ExoMars rover will detect even more organics, both on the surface of the Red Planet, as well as in its shallow subsurface.
These latest results also help planetary scientists make some important decisions as they work to find answers to questions about the possibility of life on Mars.
As Dr. Michael Meyer, lead scientist for NASA’s Mars Exploration Program at NASA Headquarters, noted in the June 7, 2018 JPL Press Release: “Are there signs of life on Mars? We don’t know, but these results tell us we are on the right track.”
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, journals, and newspapers. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others some of the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.
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