This is a guest article by Abha Vishwakarma
Half a century has passed since humankind stepped onto the Moon. ‘One step for a man, one giant leap for mankind’, in the words of Armstrong. Yet so hostile did it prove to be for life, that we had to turn our gaze further away into the darkness. We wandered around Venus, who with the cloud veil of hers has always been unwelcome to a stranger. Little did we know, we would be welcomed by our most unexpected neighbour, the God of War, Mars.
The Retrograde motion of Mars:
For centuries humankind has questioned the nature of its existence, whether it is unique to us or does it also linger in the darkness that sweeps our sky. In that quest, Mars has been the most intriguing place to look at. It’s peculiar motion sets it apart from every other visible planet. With careful observation, one can notice a significant change in its position relative to the background of stars almost every other day. About once every two years, early Egyptian astronomers noticed a change in the direction of its motion as opposed to its normal progression, a phenomena now understood as Retrograde Motion.
Yet more intriguing is the fact that this retrograde path traced by Mars in the sky is always distinct than before. Much later, using Tycho Brahe’s detailed observations of the planet’s positions, in an attempt to explain this peculiar phenomenon, Kepler discovered that the orbit of Mars must be elliptical with the sun being at one of its foci and that the closer a planet is to the sun, the faster it should move, eventually leading to the formulation of Kepler’s Laws.
The telescope era and presence of life on Mars:
The advent of telescopes escalated Mars’ observation. Cassini calculated the length of a Mars day by noticing fuzzy dark areas (albedo features) on the planet which disappeared and reappeared at the same point every 24 hours and 40 minutes. The albedo features also indicated a misalignment of its axis with that of Earth’s, its obliquity (axis tilt angle) later measured to be about 25 degrees, slightly greater than the 23.5 degree obliquity of Earth. But a striking observation, something that convinced the American astronomer Percival Lowell about the presence of life on Mars, were the polar caps. White fuzzy patches seen at the north and sometimes south poles of the planet, these were widely believed to be water ice.
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Lowell did a comprehensive study and claimed to have seen long dark lines on the surface of Mars. He believed they were canals, built by an alien civilization, bringing water from the polar caps. Such was people’s liking of a possibility of life elsewhere, perhaps triggered by a wish for peaceful living around the nearing World War 1, that a series of science fiction books and movies were released illustrating green Martians with their huge black eyes living at the intersections of these canals. Of course, as we know now, there are no such things as canals on Mars and what Lowell saw were perhaps just optical illusions triggered by wishful thinking.
It is also important to mention that, interestingly, ancient Indian astronomers were able to give a fairly accurate estimate of the diameter of Mars without the use of any telescope, a fact that becomes believable once one is aware of other such estimates given by them, without a telescope, for many objects further beyond our solar system.
Life demands certain elements for its existence, one of them being a liquid medium to carry out the metabolic processes, like water on our planet. By the 1960s astronomers and scientists were trying to figure out a way to find the amount of water vapor in the atmosphere of Mars. A planet’s atmosphere absorbs and emits certain wavelengths of light depending on its composition, imparting its signature on the light that travels through it. But observing this signature from beneath the atmospheric blanket of Earth was difficult. Our atmosphere affects the light coming off Mars, especially those wavelengths of light corresponding to water vapour.
This is because water vapour on Earth absorbs a wide range of wavelengths and only some narrow regions within this range, about a few microns across, will provide an opening for any observation of water vapor on Mars. But even so, all the light from Mars corresponding to water vapor would get absorbed back by the water vapour on our planet. The elegant solution to this problem was the use of the phenomena of Doppler shifting.
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Due to the relative motion between both planets, at certain times in their course when the planets move directly towards or away from each other, the wavelength corresponding to water vapor on Mars is doppler shifted by a few microns and the clever selection of a wavelength region for the observation made it possible to detect some water vapor in the atmosphere of Mars. It turns out, there is in fact not a lot of it there.
Later, using the known information about Mars and the law of conservation of energy, computer simulations deduced the composition of the polar caps to be mostly dry ice. Discoveries like these were a huge disappointment for people expecting the possibility of life there. But with hope, attempts were made to send something out there to get a closer look. After many unsuccessful attempts by the Soviet Union and NASA, Mariner 4 by NASA was the first successful flyby mission to Mars.
Eager to see the first picture of our extraterrestrial neighbor, the team couldn’t wait for the processed image and drew it on a paper, pixel by pixel, using the data received. And thus the first-ever picture of Mars was a hand-drawn image. Although the team was somewhat unlucky because the regions captured by Mariner 4 had no features distinct from those on the moon.
The Mariner 9 spacecraft reached Mars in 1971, although by then the planet was covered in its periodic dust storms, a phenomenon previously marked by the appearance and disappearance of the polar caps at regular intervals. Mars was shy, but not for long. The dust storm cooled and the first clear pictures of Mars were taken.
For the first time, features that resemble river valleys here on earth were seen on another planet, a clear indication of water having flown on the surface. Valles Marineris, that huge crack on the surface of Mars, closely resembled some canyons on our planet, like Escalante Canyon at Utah.
Following missions like the Viking landers and orbiters, Mars Global Surveyor, Pathfinder, and Curiosity have further enhanced our understanding of Mars. Mangalyaan by India, launched with the prime objective of developing algorithms and methods for optimizing the use of resources in the spacecraft and the secondary objective of studying the red planet, has achieved great success by successfully making it into Martian orbit with a budget of just about 60 million US dollars. To put things into perspective, the budget of the movie Gravity was 100 million US dollars.
One of the most important findings of Mangalyaan is that the Martian atmosphere stretches much higher than anticipated, up to hundreds of kilometers high. This is extremely crucial information for landing purposes and to study the weather conditions on Mars.
The polar ice caps:
Some surface features on Mars, like the layers in its icy polar caps, have always indicated a history of drastic climate change every thousands of years. One of the lesser-known facts about Mars is its axis. The obliquity of Mars changes every few thousands to millions of years. The extent to which the poles point towards or away from the sun determines the amount of ice in them and consequently the composition of the atmosphere and the rest of the planet.
Ice forms, dust accumulates, some ice disappears, dust accumulates again, creating these beautiful layers over the course of millions of years. One might then ask why such obliquity variation is not observed here on earth, the answer to which is the moon, which provides stability to Earth’s rotational motion by acting as it’s large lever arm.
But what about water on Mars right now? Without having to dig the surface, orbiters have used Gamma-Ray Spectroscopy methods to detect subsurface water on Mars, and they found a lot of it, not surprisingly in the polar caps but unexpectedly even in low latitude regions around the equator(although not as much as in the former).
It can be clearly seen in fresh crater impacts on Mars which eventually get covered by dust. The polar caps are covered with dry ice but beneath them lies in huge amounts, water ice. In fact, another piece of evidence for water on Mars are structures that represent glaciers here on Earth.
A while ago, the successful launch of yet another milestone was achieved, the Perseverance rover equipped with a technology demonstration, the Mars Helicopter, or Ingenuity. Its prime objective will be to find signatures of past life on Mars. It is very similar to the rover Curiosity except for some features, like the instrument MOXIE, which will test a method to generate oxygen from atmospheric carbon dioxide on Mars. Why?
Because we want to go there and we certainly cannot breathe carbon dioxide! Also using something called depot caching, it will collect rock samples and preserve them at safe places in the Martian surface so that future manned missions can make use of these samples.
It is remarkable how our curiosity has enabled us to reach places further beyond the capabilities of a physical body and study them in detail. But it is the consequence of this curiosity that once one is aware of a possibility of being at those places, one is ready to take the risk to explore. Yet the usefulness of such exploration has always been questioned when there are things yet to be taken care of here on Earth, although the global budget for space exploration is below 4%. But globalization itself is a consequence of exploration.
Had Vasco da Gama never set out of Europe, he would have never discovered India. Earth is a beautiful place, but we are capable of places that are further beyond. Imagine sitting at the terrace of your home on Mars, gazing at the stars, fun right?
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