Academic Reading — Test 118

Reading passage

For more than two centuries, observers have watched Mars with a mixture of curiosity and unease, and two of its most puzzling atmospheric phenomena continue to occupy researchers today: the intermittent appearance of methane and the planet's vast, swirling dust storms. Although these two features arise from very different processes, both reveal how dynamic and surprisingly active the apparently dead red planet remains. Understanding them has become a central goal of the orbiters and rovers that now study the Martian environment, partly because each may carry clues about whether the planet could ever have supported, or might still support, simple forms of life. Methane is of particular interest because, on Earth, the gas is produced largely by living organisms, although it can also form through purely geological reactions between rock and water. The molecule does not survive long in the Martian atmosphere; sunlight breaks it apart within a few hundred years, which is a brief interval in planetary terms. Any methane detected today must therefore have been released comparatively recently, implying that some active source is still at work beneath the surface. Several instruments have reported faint, fluctuating traces of the gas, and these readings appear to rise and fall with the Martian seasons. The Curiosity rover, operating inside Gale Crater, has measured a gentle background level that climbs during the warmer months and falls again as temperatures drop, a pattern that hints at gas seeping from the soil when conditions allow. Yet the methane story remains deeply contested. Orbiting spacecraft designed specifically to hunt for the gas have frequently failed to confirm the surface measurements, detecting almost none in the wider atmosphere even when the rover below reported a clear signal. This apparent contradiction has produced a long-running debate. One proposal suggests that methane may be released in small, localised puffs that are quickly destroyed or scattered before they can spread high enough to be seen from orbit. Another holds that the gas accumulates near the ground overnight and is dispersed by daytime winds, so that an orbiter scanning the upper atmosphere during daylight would naturally miss it. Until the measurements can be reconciled, scientists remain cautious about claiming that the methane has any biological origin at all. Dust storms present a more visible, though no less complex, challenge. The Martian surface is covered with fine reddish particles that are easily lifted by wind, and because the atmosphere is extremely thin, even modest gusts can raise enormous clouds of dust. Most storms are small and short-lived, but on rare occasions they expand until they envelop the entire planet. Such global events are not annual; they occur only every few Martian years and tend to develop when Mars is closest to the Sun and the southern hemisphere is experiencing summer. At that point the extra warmth drives stronger winds, and once dust begins to rise it absorbs sunlight, heats the surrounding air and generates yet more wind, creating a self-reinforcing cycle that can be difficult to halt. The consequences of these storms are considerable. A planet-wide dust event can block so much sunlight that the surface grows noticeably colder, while the upper atmosphere warms as the suspended particles trap heat. For solar-powered machines the effect can be severe: one long-serving rover fell silent during a particularly fierce global storm in 2018, when the sky darkened so completely that its panels could no longer gather enough energy to keep its systems alive. Engineers planning future missions, especially those that might one day carry human crews, must therefore treat dust as a serious hazard rather than a mere inconvenience. Fine grains can also work their way into machinery and instruments, gradually degrading equipment that is meant to operate for years. Intriguingly, the two phenomena may not be entirely separate. Some researchers have wondered whether the churning of the surface during large storms could expose buried material or alter the way gases escape from the ground, potentially influencing when and where methane appears. The connection is far from proven and remains speculative, but it illustrates how interconnected the Martian system can be. What is clear is that Mars, long imagined as a frozen and inert world, possesses an atmosphere capable of dramatic change. Each new measurement, whether of a faint chemical trace or a towering wall of dust, adds another piece to a puzzle that scientists are still very far from solving, and that continues to shape the design of every spacecraft sent to explore the planet.