Friday, December 14, 2012

Curiosity On Mars

The Curiosity Rover on Mars, shown below, made headlines in the last few days.


The image above is a mosaic self-portrait taken by the rover's imager at Rocknest, an area in Gale Crater on Mars, taken in October 2012.

What we know about Earth, Mars, other planets in our solar system and even other planets in our universe is increasing every day but deep mysteries remain. Mars offers a tremendously valuable natural laboratory in which scientists can explore fundamental questions about how life on Earth came to exist.


The image above compares the size of Earth and Mars in true colour.

Understanding Mars (and Earth) will help researchers figure out what to look for as they look for signs of life in the universe. I doubt there is a human alive that hasn't wondered, are we alone? We are asking not only if there is life elsewhere but also how life got its start here on Earth.

Humans have been listening to the cosmos for decades and we haven't heard a peep from anyone or anything, leaving the question of whether we're alone or not unanswered. Meanwhile, there are many questions about the nature of life that might have answers here on our own planet or in our own solar system. What defines life? What does life need to exist in terms of environment, nutrients, energy, and basic bodily building blocks or molecules? Is liquid water or oxygen necessary for life? What about radiation? What chemical reactions are absolutely required for life? Must it be based on DNA, protein, or even carbon, like life on Earth? These questions help astronomers look for possible signs of life in the universe. And they help scientists know what questions to ask and what to look for on Mars. Mars is a rocky planet similar to Earth, and it seems very likely to have had liquid water during some period in its past. The image below is an artist's impression of what a wetter Mars might have looked like billions of years ago, based on geological data.


(Ittiz;Wikipedia)

Mars should have had many of the same raw materials that Earth once did when the first simple unicellular organisms began to evolve here. Figuring out what the raw ingredients for life were on Earth and then looking for signs they once existed, or still exist, on Mars is a logical step in answering the question, are we alone, and it is exactly what Curiosity is designed to do.

What Curiosity Should Look For On Mars

Scientists are using what we know about life on Earth as the starting point, so they are looking for signs of organic (carbon-based) life. That search began with looking for obvious signs of life on Mars such as fossilized organisms like bacteria, as well as atmospheric and geological signatures of living organisms. For example, oxygen in our atmosphere is a signature of abundant photosynthetic plant life on Earth. Molecular oxygen (O2) gas is highly reactive. It quickly disappears from the atmosphere by reacting with other gas molecules and oxidizing rock. If all photosynthesis suddenly stopped, almost all the free atmospheric oxygen on Earth would gradually be depleted. Although oxygen is necessary for multicellular life on Earth, Mars could have harboured life even though it has an oxygen-deficient atmosphere. The first simple organisms on Earth, called anaerobes, evolved when Earth had almost no oxygen in its atmosphere. In fact, a gradual oxygen build-up in the atmosphere by cyanobacteria colonizing at the time was toxic to them, causing Earth's first major extinction event.

No obvious signs of life on Mars have been found but that doesn't mean that some pre-life organic molecules didn't form. Biochemists have made progress toward understanding how very simple life can evolve from the right mix of complex organic molecules in a favourable environment, but no one has yet been able to replicate the millions of years of natural and spontaneous organic chemistry that led to the first life on Earth.

Any sign of organic molecules that could be building blocks of life on Mars might give us a clue that life can and will form given the right ingredients, environment and time. Current geological evidence suggests that billions of years ago, Earth was a tumultuous place where volcanoes raged, filling the sky with lightning. It was almost completely covered by a shallow warm sea, rich in dissolved carbon dioxide, methane, ammonia, hydrogen sulphide and hydrogen cyanide. Most researchers believe the environment began to stabilize quickly and nucleotides, which are basic components of RNA (shown below right), formed and replicated spontaneously followed by ribosomes and proteins. These complex organic structures were eventually enclosed in a primitive membrane and developed a way to reproduce themselves, forming the first simple unicellular organisms.

LIke DNA, RNA is a remarkable biological molecule that codes and decodes information and regulates the expression of genes. The molecule itself is an enzyme and a chemical catalyst, which means it can self-duplicate and it can  enhance the creation of other molecules such as helping to build peptides from amino acids, both important properties of life. Unlike DNA, RNA is a single strand, like the hairpin strand shown right. It's used as a messenger molecule in our bodies, helping to turn the genetic information in our DNA into proteins. Because RNA is simpler than DNA it may have predated it, being the first genetic material to be function inside simple virus-like and bacteria-like organisms.

If scientists could find signs that a similar process at least began on Mars, we could begin to answer a fundamental question about the universe - is life inevitable? This very human question makes the current Curiosity Mission so compelling.

Past Rover Missons To Mars Found Evidence Of Liquid Water

The Curiosity rover is a car-size robotic rover that was launched in November, 2011 It landed in Gale Crater on Mars in August this year (2012). It was originally on a two-year mission but that mission was extended indefinitely just a few days ago. Curiosity (the one to the right) is the latest of three generations of Mars rovers, shown below.


The examples above are test rovers, all from NASA's Jet Propulsion Laboratory. The smallest rover, front center, is the flight spare of the Sojourner, which landed on Mars in 1997. To the left is the test rover for Spirit and Opportunity, which both landed on Mars in 2004 for a planned 90-(Martian) day mission. Spirit became stuck in 2009 and ceased communications in 2010 but Opportunity is still active on Mars, moving, gathering information and reporting back to Earth. Whereas Opportunity is a solar-powered rover, Curiosity is fueled by a radioisotope thermoelectric generator. It converts the heat generated by radioactive plutonium into electricity. The plutonium decays slowly (half-life of 87.7 years) so the electricity available 14 years from now will be only slightly reduced from 125 watts of power to 100 watts, its minimum expected lifetime.

All the rovers were designed to test the rocks, soil (also called sand but properly called regolith) and atmosphere of Mars in a hands-on way. After seeing what looked like dry riverbeds and other large water-related structures on the surface of Mars (shown below), scientists wanted to look for signs of past water activity such as precipitation, evaporation and sedimentation and to look for minerals that are known to be created only in the presence of water.

The image left shows streamline islands in Maja Vallis on Mars, taken by Viking. The image bottom left shows intricately branched channels, also taken by Viking. For more Viking images and information, try the online publication by the Viking Orbiter Imaging Team.

The identical Viking 1 and Viking 2 landers carried out the first experiments to look for signs of life on Mars in the late 1970's. They carried out gas chromatography, a gas exchange experiment, a labelled release experiment and a pyrolytic release experiment (all described in the preceding link). Organic compounds are common on asteroids, meteorites and comets so researchers expected to find them on the surface of Mars too, but they didn't find anything organic except chloromethane and dichloromethane. One theoretical explanation is that the surface of Mars, exposed to strong ultraviolet (UV) radiation, has built up a strongly oxidizing layer of regolith. One of these oxidants is perchlorate which breaks organic molecules apart, leaving chloromethane and dichloromethane as products. Perchlorate was later discovered on Mars in 2008 by the Wet Chemistry Lab onboard the Phoenix Mars Lander. Most researchers found the Viking organic molecule findings inconclusive, spurring the beginning of Mars rover exploration, where samples can be taken from a variety of geological sites.




All life as we know it requires liquid water, at least at some stage. If direct evidence of past liquid water was found, researchers could focus on determining if there was ever a life-conducive environment on Mars. Meanwhile, the Sojourner rover along with the Pathfinder lander, shown below, was launched in 1996 to test the idea of sending a robotic rover and to explore the Martian atmosphere and surface. It had cameras, a meteorological station to investigate the Martian atmosphere and an X-ray spectrometer to analyze soils and rocks.


Workers at the Jet Propulsion Laboratory are shown above closing up the metal petals of the Pathfinder Lander, enclosing the Sojourner rover inside, visible on the nearest "petal" before its launch.

The Sojourner data suggested that Mars did in fact have a warmer wetter past with a thicker atmosphere and liquid water. The Spirit and Opportunity rovers were then designed to expand on the successful Sojourner rover prototype and test the hypothesis of a once wet and warm Mars further. Below, one of the rovers is shown inside its lander's petals.


These rovers have a robotic arm, panoramic cameras, three different spectrometers to test rock and soil, a rock abrasion tool to remove dust and examine fresh material underneath, and a microscopic imager. The rovers were designed to travel widely and test many different geological sites. They found that most of Mars' rock appeared to be volcanic in origin and its soil, or regolith, comes from the weathering of these rocks. They found significant nickel in some soils, suggesting that the regolith came from meteoric impacts as well. Chemical analysis showed that the volcanic rocks have been slightly altered by tiny amounts of water and that coatings and cracks in the rocks contain water-deposited minerals. They also found that dust on the planet, which covers all surfaces, is magnetic because it was shown to contain the mineral magnetite. Some component in the dust, possibly sulphate minerals, also contains chemically bound water. They found additional chemical confirmation of water in water-specific minerals such as goethite and carbonates. In a region called the Columbia Hills, they found clear evidence of weathering caused by liquid water.

Knowing that liquid water was once present on Mars, the Curiosity mission is designed to go one step further by looking specifically for evidence of chemistry linked to, or a possible precursor of, organic life on Mars.

How To Get A Big Robotic Science Lab To Mars

This rover is big (the size of a small car and weighing about 900 kg), so it could not be placed in a lander. Instead, it had to be put directly inside its aeroshell (the protective container on the spaceship that protects the unit from space). It also couldn't be slowed down and cushioned upon landing on Mars using airbags, like the Pathfinder mission and the Mars Exploration Rover mission used. This landing had to be precisely guided and soft, and it had to be pre-programmed in advance because of the time delay between Earth and Mars.

First, the aeroshell containing the rover separated from the cruise stage of the rocket, which provided power, communications and propulsion during the long flight to Mars. Thrusters on the aeroshell then fired to place it within a 20 by 7 km landing ellipse and align its heat shield. A supersonic parachute deployed when the aeroshell slowed down enough by friction with the Martian atmosphere. All the previous rover landings used similar parachutes but the Martian atmosphere is so thin these parachutes are not enough to slow the aeroshell sufficiently. The returning command module used in the Apollo missions could rely on atmospheric braking and parachutes alone because Earth's atmosphere is much thicker. The aeroshell's heat shield separated and fell away and the rover (attached to a descent stage platform) dropped out of the aeroshell. Variable thrust rockets on the descent stage platform above the rover further slowed the descent, using a radar altimeter feeding data to the rover's flight computer as it navigated itself down. Soon afterward, a sky crane lowered Curiosity under the descent stage while Curiosity transformed from its stowed configuration to its landing configuration, locking its wheels in place. The sky crane slowed to a complete stop as Curiosity touched down and soon after freed itself and flew away to crash land elsewhere. This new procedure, shown below, is an important advance in lander technology, allowing more delicate testing lab equipment to get to far-off planets and study them.
Curiosity's landing, coined "the seven minutes of terror," is discussed by NASA engineers this five-minute video:


             
Curiosity Is A Complete Geological Testing Lab

Curiosity needs to be able to obtain various kinds of surface and internal rock and soil samples from various regions and test them in various ways. What really sets Curiosity apart from its predecessors is its instruments. It is essentially a mobile geologic testing lab. First it uses high-resolution cameras to look for geological features of interest. Gale Crater is a good place to look. Curiosity's landing site is marked by the tiny green dot in the image (created by combining data from three Mars orbiters) below.


In the crater's center is a huge mountain informally called Mount Sharp and from it large outflow channels, possibly carved by once-flowing water, extend into the plains below. This is where researchers hope to find signs of organic material and possibly even signs of extinct primitive life, which might have had a chance to evolve in this once-wet environment. When Curiosity finds a feature of interest here, it vaporizes a tiny part of it's surface with a laser and examines the emission spectrum from it, telling it what elements are present. If the composition is interesting, the rover can swing over a microscope and an X-ray spectrometer to examine it more closely. An X-ray spectrometer uses an X-ray to excite the electrons in the atoms of the material. The spectrum given off by the excited electrons is specific to each element present and provides a confirmation and better detail of the elemental makeup of the material. Finally, Curiosity can drill into the material and place a powdered sample into one of two mobile labs, the SAM or the CheMin.

SAM (Sample Analysis at Mars), shown below, is a suite of instruments - a mass spectrometer, a gas chromatograph and a tuneable laser spectrometer.


These instruments can identify gases present in the rock as well as any organic material present. The tuneable laser spectrometer can precisely measure isotope ratios in carbon and oxygen in any carbon dioxide or methane present in the sample. This can tell the researchers if the organic material has a biological or geochemical origin. Carbon has two stable isotopes, carbon-12 and carbon-13. Carbon-12 makes up 99% of all the carbon on Earth but it is even more concentrated in biological material because biochemical reactions favour carbon-12 over carbon-13, so an overabundance of carbon-12 in a material suggests it has a biological origin, at least a biology familiar to us on Earth.

CheMin (Chemistry and Minerology Instrument) consists of an X-ray powder diffraction instrument and an X-ray fluorescence instrument. It is shown below being installed into Curiosity. The inlet funnel for samples is sticking out at the bottom.

These instruments can identify and quantify minerals present in rock samples and by doing so they can assess whether water was involved in their formation or deposition or whether water has altered the rock at any point in its history. CheMin is especially focused on looking for any possible bio-signature minerals in rock samples. These include minerals that are created only through biological processes. Examples here on Earth are coal, oil, chalk, limestone, pearls and amber. While scientists don't expect to find these materials, they can look at the abundance and isotopic composition of various metals involved in redox reactions common in biology such as iron, chromium, and some rare earth elements as well as sulphur and oxygen isotope ratios in minerals that suggest biological activity. Of course researchers are also on the lookout for any microfossils such as tiny microscopic objects that resemble spores or bacteria. Such a find could be a definitive sign of past life on Mars.

Using these instruments, Curiosity is focused on looking for additional geological signs of past or present liquid water on or near Mars' surface as well as geological signs of past or present life in an area of Mars (Gale Crater) that is most likely to have harboured it. Right off the mark, Curiosity has kept researchers busy, sending back evidence of an ancient riverbed in Gale Crater, monitoring dust storms, measuring radiation levels and, most importantly, analyzing its first sample of Martian soil. Below is an image of the results of the first analysis of soil from the CheMin's X-ray powder diffraction instrument.

This X-ray diffraction image reveals the presence of crystalline minerals such as feldspar, pyroxenes and olivine mixed with amorphous material likely to be volcanic glass. X-rays beamed at the sample are scattered by the atoms in it. Each mineral shows up as a unique scattering pattern, a set of rings. The colours, right, represent the intensity of the X-ray beam, red being most intense in the center. X-ray diffraction gives scientists not only the chemical composition of rocks and sand but it also reads the mineral's internal structure, how its crystals are arranged. It tells them much more about what's present. For example, the presence of carbon could mean diamond or graphite and they have very different structures (and properties), which this X-ray diffraction instrument can distinguish. Knowing what minerals are present can reveal much about the geological evolution of the rocks and sand, and scientists suspect they will be able to piece together a collection of younger and older mineral samples, which could show a gradual transition from a wet environment to a very dry one. Olivine is especially interesting because, in the presence of water, it weathers into a material called iddingsite, which is a combination of clay minerals, iron oxides and ferrihydrites. Comparing the presence of iddingsite with olivine could tell researchers how much water was once present and the rate at which it disappeared.

In this five-minute video, Curiosity chief scientist and geologist, John Grotzinger, describes how Curiosity took and analyzed its first sample:



The first mineral sample taken by Curiosity is similar to volcanic (basalt) soils in Hawaii. Feldspar is a very common mineral in Earth's crust (60% of it) that crystallizes from magma. Pyroxenes and olivine are also very common. Together they make up most of Earth's upper mantle (where olivine is protected from weathering by water). Seeing them on the plains of Gale Crater on Mars was not unexpected.

Life as we know it is built from carbon-based compounds called organic compounds. They make up proteins, carbohydrates and DNA, for example. Below are some very simple building blocks of these compounds. Below left is glucose, a simple sugar and part of many complex carbohydrates. Below right is an amino acid, part of a protein polymer. 20 different amino acids make up proteins in living organisms. "R" stands for a functional group that makes each amino acid unique. Far below left is adenosine, one of four nucleotides of DNA.


These kinds of molecules are especially important to scientists looking for signs of life on Mars. They all contain carbon backbones, as well as oxygen and hydrogen. These elements are present in most planetary atmospheres as well as in sand and rock. It is their distinct chemical arrangements that set them apart as organic compounds, something a good X-ray diffraction device can discern. Neither these molecules nor any organic molecules that are involved in their formation have been definitely discovered yet on Mars, a surprise to researchers. But that doesn't mean there aren't any on Mars.

While the chemical bonds in complex organic molecules, especially DNA, can be broken by ultraviolet (UV) radiation, UV radiation as well as the energy from lightning, likely to have been plentiful thanks to significant early volcanic activity on both planets, might have provided the energy needed to create the first simple amino acids and sugars.



Meteorites - A Bonus Sample Set From Mars

Scientists have a few tantalizing clues about what kind of environment ancient Mars might have been. Little bits of the planet have been raining down on Earth for millions of years, originating from ancient Martian impacts. Most known Martian meteorites have been radiometrically aged to be between 0.5 million and 1.5 billion years old. This is the time they were dislodged from the planet and shot into space. The rock inside them, however, can be much older, on the scale of billions of years old. One meteorite in particular caused a big stir in the scientific community when it was discovered in 1985. It was found in Alan Hills in Antarctica and it is called ALH 84001. This meteorite appears to have been ejected from Mars about 16 million years ago and arrived on Earth 13,000 years ago. Cracks in it are filled with carbonate materials that imply the presence of liquid water. These minerals have been aged to between 4 and 3.6 billion years old. They also found evidence for polycyclic aromatic hydrocarbons (PAHs) and tiny tubular and ovoid structures that some but not all researchers think could be microfossils of something called nanobacteria. Unfortunately this meteorite hasn't proved that ancient life existed on Mars. PAHs are atmospheric pollutants on Earth. Although the concentration of PAHs in the meteorite seems to be higher away from the surface that was exposed to air, it still could be of Earth origin. If the PAH's are of Mars origin, they might hold more promise. These complex organic compounds, detected in interstellar space, consist of multiple aromatic carbon rings that might be created in carbon/hydrogen rich cores of nebulae. They may be hydrogenated, oxygenated and hydroxylated into even more complex compounds such as amino acids and nucleotides when they are exposed to the conditions of interstellar space. Some researchers thinks fullerenes of these molecules created in nebulae might have seeded Earth with the raw materials of life. The idea that the tiny ovoid structures in the Martian meteorite might by nanobacteria is controversial. The existence of nanobacteria on Earth is widely disputed and many researchers think they may be too small to house RNA, DNA's smaller simpler cousin.

While the argument for ancient Martian life is ongoing, the argument for a once-wet Mars is very strong based on a variety of data that includes this meteorite. In 2011, researchers completed isotopic analysis on the rock that indicates its carbonates precipitated at a temperature of 18°C from water that contained dissolved carbon dioxide from the atmosphere. The isotopic ratios suggest a sequential deposition of carbonate from a gradually evaporating body of shallow water.

Other Martian meteorites also have what appear to some researchers to be microscopic fossilized life forms and most tested meteorites contain organic molecules. The latest testing comes from Andrew Steele et al., of the Carnegie Institution for Science. They showed that complex organic molecules containing reduced carbon - carbon bonded to hydrogen or itself - are present inside and throughout the meteorites they've tested and they are of Martian origin rather than from contamination in our biosphere. However, the formation of these particular organic molecules was most likely part of a volcanic process that traps carbon in crystals of cooling magma, a non-biological origin. Complex organic molecules are precursors to life on Earth and researchers have shown that Mars not only had warm shallow water at some point in the past but it was also doing some organic chemistry on its own, creating complex organic molecules, at least while water was present. Using this Martian meteor data, Curiosity will focus on finding and studying pools of reduced organic carbon on Mars to learn more about how it is created and how to distinguish it from organic molecules of biological origin.

What Curiosity Found So Far

The hunt for signs of life on Mars is not as easy as it might seem at first glance. Without obvious fossils or other evidence of life on Mars, researchers have to rely on the biochemistry and geology of all potential biomarkers on Mars, which makes up a complex list of what to look for. Added to that is uncertainty about how to extrapolate from Earth's almost-lost evidence of pre-life chemistry (and steps from non-life to life that still aren't understood) to what might be almost lost on Mars billions of years after the fact. What Curiosity found when it scooped up its first sample of Martian sand and tested it clearly excited the scientific community, but it left some of the rest of us feeling underwhelmed, partly because this sample is just a small piece of a huge and complex puzzle.

So far Curiosity's onboard lab is working very well and it has identified a complex chemistry in the first windblown sand samples it's tested, located in an area called Rocknest, a fairly flat part of Gale Crater. It found perchlorate, Ca(ClO4)2, an oxidizing molecule I mentioned earlier which the Phoenix Mars Lander identified. It is also an energy-rich molecule, a component of rocket fuel, and in theory it could be used as an energy source for microbes if they exist or existed. Curiosity has also found chlorinated methane compounds, which are organic molecules of non-biological origin. It identified four gases that were released when it heated its first Rocknest sample: water vapour, oxygen gas, sulfur dioxide gas and carbon dioxide gas. The oxygen gas could be from the breakdown of perchlorate in the sample. The water it detected does not mean the sample was damp at all. It is water molecules chemically bound to dust and sand grains. The levels of water, however, were higher than the researchers expected. So far, its analysis of Rocknest sand reveals several kinds of chlorinated methane compounds such as CH3CL, CH2CL2 and CHCl3, as well as sulfur compounds such as hydrogen sulfide. The carbon-containing compounds are technically organic molecules but they are not biological organic compounds in and of themselves. The presence of CH2Cl2 however is potentially interesting because it is an intermediate step involved in organic chain propagation, shown below, where carbon backbone chains can be created in the presence of UV radiation.

UV radiation (which bombards the surface of Mars and once bombarded Earth's surface before the ozone layer formed) cleaves chlorine gas into two free radicals. These radicals react with methane creating a longer carbon chain, shown right. This process can continue, creating long and complex carbon chains

It is possible, however, that the carbon detected may be from Earth and carried by Curiosity to Mars. The SAM detector is extremely sensitive. The chlorine, however, is almost certainly Martian. NASA now claims it has had no definitive detection of methane on Mars (yet). Methane (CH4) itself is an interesting molecule connected to life. 90% of the methane on Earth comes from the biological processes of life. It is not a stable compound, reacting quickly with other gases and breaking down in the presence of UV radiation. Methane is not expected to be present in any quantity on Mars if life does not exist there. Very trace amounts could come from comet impacts or chemical reactions underground between rocks and hot water. Volcanoes can pump out significant amounts of methane but none have been active on Mars for billions of years. Some experiments on Mars have detected higher than expected, but transient, methane levels in Mars' atmosphere, making researchers curious. Could there by a microbial source of methane, perhaps underground? On Earth, biologically produced methane tends to come with ethane while non-biological volcanic methane usually comes with sulfur dioxide. This might help provide some clues while exploring Mars's ongoing methane mystery.

Meanwhile we can be justified feeling a little let down that there are no definitive signs of any life or pre-life chemistry on Mars (yet). Scientific exploration can sometimes advance a rate much slower than we'd like it to. NASA and various other research teams around the world are successfully building a foundation for the future of Mars exploration that could get much more interesting when they eventually send humans to the planet. Also, Curiosity is just a few months into its two-year mission and it has not reached its main destination yet. Curiosity's main mission is to go to Mount Sharp, the huge mountain in the center of Gale crater. Mount Sharp, rising 5.5 km from the crater floor, appears to be an enormous mound of eroded sedimentary layered rock. These layers are especially interesting, considering that, being composed of sedimentary layers, they must come from a wet environment where they were sequentially deposited over a long period of time, about two billion years. This suggests that the crater may have once been filled with water, forming a large lake in the distant past. Sand and rock studies here will hopefully tell researchers whether it was once a lake or not.

Currently two rovers are operating on Mars - Curiosity and Opportunity - and three orbiters are surveying the planet - Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. NASA plans to send a new orbiter called MAVEN next year to analyze the atmosphere in greater detail, hoping to understand better Mars' dramatic climate change and its loss of water and most of its atmosphere. The European Space Agency (ESA) plans to send a Phoenix-like lander, called the ExoMars rover, to Mars in 2018. It will be equipped with drilling equipment that could drill about two metres deep into Martian rock for samples, looking for signs of bioorganic molecules using, among other instruments, an organic molecule analyzer. This instrument will have two operating modes - laser desorption mass spectrometry and gas chromatography mass spectrometry. Gas chromatography will identify all the volatile gases that are released as a sample is heated to 900°C. The gases will then be analyzed further in a mass spectrometer. In the other  mode, a special laser will ionize part of the sample surface and a mass spectrometer will analyze those ions. Researchers hope to determine the isotopic composition and the chirality of any organic molecules they identify, which will help determine if they come from a living or nonliving source. I mentioned the isotope connection to life earlier. Chirality is another interesting quality of all building blocks of living organisms. These molecules all have the same handedness. Amino acids are left-handed and the sugars in nucleotides are right-handed.  For example, below are two forms of alanine, an amino acid.


These two forms, called optical isomers, are mirror images of each other. Only one isomer is found in almost all living organisms - the L-isomer (some bacteria are a rare exception, having the mirror-image D-alanine in their cell walls). L-alanine is the one on the left, above. Why they are this way remains a mystery. Although Mars's surface is probably far too hostile for any life (too cold and dry with intense ultraviolet radiation), microbes might conceivably survive underground in protected rock crevices, for example, and this rover will be designed to find them if they are, or were, there.

NASA just announced it plans to send a new robotic science rover to Mars in 2020. It will utilize much of the successful technology developed for Curiosity, keeping costs and risks down. There will be an open competition for the payload and instruments on the new rover and a team will be set up to outline the new mission's scientific objectives.

The Curiosity mission was expensive. It cost NASA about 2.5 billion dollars. NASA, the ESA and other space agencies around the world are facing the pressure of tightening budgets and financially uncertain futures. Though NASA has plans to send a new rover, mentioned above, several future NASA Mars exploration mission plans have been cancelled or postponed. However, there still seems to be a healthy desire to explore Mars, to understand its evolution as a planet and to look for signs of life there. On the bright side, tight budgets and challenges often force ingenuity on researchers. The question, like a bright juicy carrot, remains - are we alone?

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