Mars Curiosity ........................Search for Life
The Mars Science Laboratory and its rover centerpiece, Curiosity, is the most ambitious Mars mission yet flown by NASA. The rover landed on Mars in 2012 with a primary mission to find out if Mars is, or was, suitable for life. Another objective is to learn more about the Red Planet's environment.
In March 2018, it celebrated 2,000 sols (Mars days) on the planet, making its way from Gale Crater to Aeolis Mons (colloquially called Mount Sharp), where it has looked at geological information embedded in the mountain's layers. Along the way, it also has found extensive evidence of past water and geological change.
As big as an SUV
One thing that makes Curiosity stand out is its sheer size: Curiosity is about the size of a small SUV. It is 9 feet 10 inches long by 9 feet 1 inch wide (3 m by 2.8 m) and about 7 feet high (2.1 m). It weighs 2,000 lbs. (900 kilograms). Curiosity's wheels have a 20-inch (50.8 cm) diameter.
Engineers at NASA's Jet Propulsion Laboratory designed the rover to roll over obstacles up to 25 inches (65 centimeters) high and to travel about 660 feet (200 m) per day. The rover's power comes from a multi-mission radioisotope thermoelectric generator, which produces electricity from the heat of plutonium-238's radioactive decay.
Science goals
According to NASA, Curiosity has four main science goals in support of the agency's Mars exploration program:
- Determine whether life ever arose on Mars.
- Characterize the climate of Mars.
- Characterize the geology of Mars.
- Prepare for human exploration.
The goals are closely interlinked. For example, understanding the current climate of Mars will also help determine whether humans can safely explore its surface. Studying the geology of Mars will help scientists better understand if the region near Curiosity's landing site was habitable. To assist with better meeting these large goals, NASA broke down the science goals into eight smaller objectives, ranging from biology to geology to planetary processes.
In support of the science, Curiosity has a suite of instruments on board to better examine the environment. This includes:
- Cameras that can take pictures of the landscape or of minerals close-up: Mast Camera (Mastcam), Mars Hand Lens Imager (MAHLI) and Mars Descent Imager (MARDI).
- Spectrometers to better characterize the composition of minerals on the Martian surface: Alpha Particle X-Ray Spectrometer (APXS), Chemistry & Camera (ChemCam), Chemistry & Mineralogy X-Ray Diffraction/X-Ray Fluorescence Instrument (CheMin), and Sample Analysis at Mars (SAM) Instrument Suite.
- Radiation detectors to get a sense of how much radiation bathes the surface, which helps scientists understand if humans can explore there – and if microbes could survive there. These are Radiation Assessment Detector (RAD) and Dynamic Albedo of Neutrons (DAN).
- Environmental sensors to look at the current weather. This is the Rover Environmental Monitoring Station (REMS).
- An atmospheric sensor that was primarily used during landing, called Mars Science Laboratory Entry Descent and Landing Instrument (MEDLI).
A complicated landing
The spacecraft launched from Cape Canaveral, Florida, on Nov. 26, 2011, and arrived on Mars on Aug. 6, 2012, after a daring landing sequence that NASA dubbed "Seven Minutes of Terror." Because of Curiosity's weight, NASA determined that the past method of using a rolling method with land bags would probably not work. Instead, the rover went through an extremely complicated sequence of maneuvers to land.
From a fiery entry into the atmosphere, a supersonic parachute needed to deploy to slow the spacecraft. NASA officials said the parachute would need to withstand 65,000 lbs. (29,480 kg) to break the spacecraft's fall to the surface.
Under the parachute, MSL let go of the bottom of its heat shield so that it could get a radar fix on the surface and figure out its altitude. The parachute could only slow MSL to 200 mph (322 kph), far too fast for landing. To solve the problem, engineers designed the assembly to cut off the parachute, and use rockets for the final part of the landing sequence.
About 60 feet (18 m) above the surface, MSL's "skycrane" deployed. The landing assembly dangled the rover below the rockets using a 20-foot (6 m) tether. Falling at 1.5 mph (2.4 kph), MSL gently touched the ground in Gale Crater about the same moment the skycrane severed the link and flew away, crashing into the surface.
NASA personnel tensely watched the rover's descent on live television. When they received confirmation that Curiosity was safe, engineers pumped fists and jumped up and down in jubilation.
News of the landing spread through traditional outlets, such as newspapers and television, as well as social media, such as Twitter and Facebook. One engineer became famous because of the Mohawk he sported on landing day.
Tools for finding clues to life
The rover has a few tools to search for habitability. Among them is an experiment that bombards the surface with neutrons, which would slow down if they encountered hydrogen atoms: one of the elements of water.
Curiosity's 7-foot arm can pick up samples from the surface and cook them inside the rover, sniffing the gases that come out of there and analyzing them for clues as to how the rocks and soil formed.
The Sample Analysis of Mars instrument, if it does pick up evidence of organic material, can double-check that. On Curiosity's front, under foil covers, are several ceramic blocks infused with artificial organic compounds. [Related: Curiosity Rover Finds Methane on Mars]
Curiosity can drill into each of these blocks and place a sample into its oven to measure its composition. Researchers will then see if organics appear that were not supposed to be in the block. If so, scientists will likely determine these are organisms hitchhiking from Earth.
High-resolution cameras surrounding the rover take pictures as it moves, providing visual information that can be compared to environments on Earth. This was used when Curiosity found evidence of a streambed, for example.
In September 2014, Curiosity arrived at its science destination, Mount Sharp (Aeolis Mons) shortly after a NASA science review said the rover should do less driving and more searching for habitable destinations. It is now carefully evaluating the layers on the slope as it moves uphill. The goal is to see how the climate of Mars changed from a wet past to the drier, acidic conditions of today.
"I think the principal recommendation of the panel is that we drive less and drill more," Curiosity project scientist John Grotzinger said during a news conference at the time. "The recommendations of the review and what we want to do as a science team are going to align because we have now arrived at Mount Sharp."
Evidence for life: Organic molecules and methane
Curiosity's prime mission is to determine if Mars is, or was, suitable for life. While it is not designed to find life itself, the rover carries a number of instruments on board that can bring back information about the surrounding environment.
Scientists hit something close to the jackpot in early 2013, when the rover beamed back information showing that Mars had habitable conditions in the past.
Powder from the first drill samples that Curiosity obtained included the elements of sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon, which are all considered "building blocks" or fundamental elements that could support life. While this is not evidence of life itself, the find was still exciting to the scientists involved in the mission.
"A fundamental question for this mission is whether Mars could have supported a habitable environment," stated Michael Meyer, lead scientist for NASA's Mars Exploration Program. "From what we know now, the answer is yes."
Scientists also detected a huge spike in methane levels on Mars in late 2013 and early 2014, at a level of about 7 parts per billion (compared to the usual 0.3 ppb to 0.8 ppb). This was a notable finding because in some circumstances, methane is an indicator of microbial life. But it can also point to geological processes. In 2016, however, the team determined the methane spike was not a seasonal event. There are smaller background changes in methane, however, that could be linked to the seasons.
Curiosity also made the first definitive identification of organics on Mars, as announced in December 2014. Organics are considered life's building blocks, but do not necessarily point to the existence of life as they can also be created through chemical reactions.
“While the team can't conclude that there was life at Gale Crater, the discovery shows that the ancient environment offered a supply of reduced organic molecules for use as building blocks for life and an energy source for life,” NASA stated at the time.
Initial results released at the Lunar and Planetary Science conference in 2015 showed scientists found complex organic molecules in Martian samplesstored inside the Curiosity rover, but using an unexpected method. In 2018, results based on Curiosity's work added more evidence that life was possible on Mars. One study described the discovery of more organic molecules in 3.5-billion-year-old rocks, while the other showed that methane concentrations in the atmosphere change seasonally. (The seasonal changes could mean that the gas is produced from living organisms, but there's no definitive proof of that yet.)
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