All About Space pays homage to the amazing achievements that have shaped humanity’s understanding of the universe around us.
Water on Mars. Discovered: 1975.
Percival Lowell had claimed in the 19th Century that he could see ‘canals’ on Mars. Alas, they were a figment of his imagination and water on Mars seemed like science fiction, at least until the launch of the Mariner 9 orbiter in 1971. This gave astronomers their first evidence that water might exist on the Red Planet. Ancient river beds and canyons along with weather fronts and fogs were all signs that water had once resided on Mars.
The Viking 1 and 2 missions, both consisting of a lander and orbiter, arrived at Mars in 1975. What they found confirmed that water had once run on Mars, but long, long ago. The Vikings sent back ‘postcards’ of dried-up floodplains and deep valleys carved out of the Martian landscape as well as evidence of erosion in soil and rocks, suggesting that rain once graced the surface.
In the 2000s, the European Space Agency’s Mars Express discovered water-ice buried just a few metres underground. The rovers Spirit and Opportunity trundled over terrain that had been chemically altered by flowing water millions of years ago.
It seems that for some periods in its history, Mars has been warmer and wetter than it is now, caused by changes in climate instigated by its wobbly axis. However, this is all evidence from the past; are there any signs of liquid water on Mars today? Indeed there are. NASA’s now-defunct Mars Global Surveyor spacecraft recorded changes in gullies in crater walls that seemed to show flows of water. Debate still rages as to the veracity of the findings but one thing is for sure: although Mars is known as the Red Planet now, it may have once been more blue.
William Herschel discovers Uranus. Discovered: 1781.
Originally thought to be a star, Uranus was observed many times by other astronomers as early as 1690; years before its groundbreaking discovery in 1781. Born in Germany, British astronomer William Herschel made history when he discovered the gaseous world, along with two of its largest moons, Titania and Oberon, six years later.
During his search for double stars using his reflector telescope, Herschel chanced upon Uranus in the constellation of Gemini but initially dismissed it as a comet due to its unusual motion across the night sky and cast aside the general consensus that, what he saw on that chilly night during mid-March, was a pale blue star. Not entirely convinced by his first identification of the mysterious object, the astronomer tirelessly made many observations to check out his suspicions that the distant object was a nonstellar disc. If it was not a star nor a comet, then what could it be?
Elsewhere, Swedish-born Russian astronomer and mathematician Anders Johan Lexell was also watching this mysterious ‘star’ and got to work on his own measurements, computing its orbit and later finding it likely to be planetary. Determining that what he had hit upon was a planet, Herschel figured out that the distant world must be beyond the orbit of the famously ringed planet Saturn and added it to the already discovered five planets of our Solar System — Mercury, Venus, Mars, Jupiter and Saturn.
Uranus’s discovery marked an important point in astronomy proving that our Solar System was larger than once thought. Around 65 years later, Uranus had almost completed one full orbit since being found by Herschel and, during its path across the sky, Lexell was the first to notice that its orbit around the Sun had irregularities that could not be explained by Newton’s laws of planetary motion and gravitation. However, the oddness of the planet’s tango around the Sun could be explained by the presence of a further, unknown world tugging at Uranus’s orbit with its gravity. It was then that Neptune was uncovered.
First exoplanet around a Sun-like star. Discovered 1995.
While 51 Pegasi b might not have been the first exoplanet to ever be discovered, it was the first distant world to be pinpointed around a star like our Sun, which makes finding this 50 light year distant world a fascinating discovery in itself.
It was found with the helping hand of the radial velocity method on a telescope located at Observatoire de Haute-Provence in France by astrophysicist Michel Mayor and PhD student Didier Queloz.
Despite orbiting a Sun-like star, 51 Pegasi b was completely different to our perfectly balanced planet; no water flowed on its surface and no life as we know it is likely to exist on it. Teams of astronomers found this distant world to not only be gaseous, beginning the family of what we now know as ‘hot Jupiters’, but also to be incredibly hot, suffering temperatures of some1,000 degrees Celsius (1,800 degrees Fahrenheit). It has a mass of some 150 times that of Earth. The exoplanet is also tidally locked, forever stuck in a position where only one side gets a treatment of searing heat splashed on to its surface from its star, 51 Pegasi.
The discovery of 51 Pegasi b threw a curve ball as it went against the then accepted theories of planet formation, leaving astronomers the task of finding somewhere where this mysterious new finding — of a huge world so close to its star — would fit in their models of planetary creation and evolution.
The discovery of similar exoplanets around the binary system 55 Cancri, which consists of a Sun-like star and a red dwarf as well as yellow-white dwarf Tau Bootis, added more fuel to the fire — experts needed to find a compatible theory for the making of these superheated worlds.
Einstein’s theory of relativity Albert Einstein caused quite a stir with the introduction of his theory of special relativity in 1905, which was followed swiftly by his general theory of relativity in 1916. Both theories shook the very foundations of physics, immediately bringing Isaac Newton’s three laws of motion into question. Newton’s laws, which were first compiled in 1687 and combined with the law of universal gravitation, helped to explain Kepler’s three laws of planetary motion.
Einstein’s theory of relativity predicts many features of the Solar System and Mercury’s peculiar nimble orbit around the Sun became one of Einstein’s primary targets in proving his theories. The pint-sized world’s odd path around our star involves its point of closest approach not always occurring at the same place and, as a result it slowly moves around the Sun in a crazy orbital dance -engaging in, what is known as, a perihelion precession. Einstein found that Mercury’s perihelion altered by 43 seconds of arc (one second of arc is 1/3,600 of an angular degree) every century and, while the effect is extremely small, Newton’s theory could not fully account for it.
In Newton’s workings, he did not account for the light that emanates from a strong gravitational field resulting in the shift in the light’s wavelength, creating an effect that we dub redshift. Einstein’s calculations not only revealed the shift in a larger wavelength, but his theory also predicted that the direction of light changes in a gravitational field — something that was proved with the advent of gravitational lensing.
A galaxy cluster can be so massive and compact that light rays passing through it are deflected by its gigantic gravitational field, causing a lensing effect similar to an optical lens and an image is formed.
Perhaps the most famous of all equations that Einstein produced was the mass-energy equivalence formula, also known as E=mc2 and, from this concept, the great scientist described the fabric of space-time as a medium that could be distorted by the presence of mass and energy. Additionally, he stated that the speed of light was the greatest speed that a mass-less object could travel at.
The Sun is the centre of the Solar System. Discovered: 1532.
As early as the 3rd Century, observations by astronomers from old civilisations such as ancient Greece placed the Earth at the centre of the universe. Back in the days of Aristotle and Ptolemy it was easy to see why both astronomers supported this geocentric model as they watched the Sun, Moon, naked eye planets and stars, wheel across the night sky appearing to circle our planet.
However, not everyone was convinced and during the 16th Century, polymath astronomer Nicolaus Copernicus dismissed the idea, favouring a completely different model altogether; what if the Sun was at the centre of the universe?
The shift from the Ptolemaic geocentric model to the Copernican Revolution of a heliocentric model was a successful one. However, while putting together his theory, Copernicus failed to realise that the orbits of the planets around the Sun were not circular. It was here that his model failed to address the details of planetary motion. In addition, while he was relatively confident in his workings, he feared ridicule by fellow astronomers as well as the Church, who, by this point, were invested in a geocentric universe. As a result he kept his ideas secret, but long after his lifetime, a chain of events were set into motion with the next generation of scientists picking up from where Copernicus had left off.
One such individual was Johannes Kepler, who far from put off by the partially inaccurate model, was intrigued by the very idea of a Sun-centred universe and, during the following century, it was his calculations that revealed the orbits of our Solar System’s planets as we know them; spinning on their elliptical paths around our star.
Building on the heliocentric model further, Galileo Galilei later set to his telescope, making observations of the heavens, which included the discovery that Venus has phases like the Moon, that added more ammunition to Copernicus’s model and completely obliterated Aristotle’s theory in the process.
Further observations highlighted another important detail; the Sun was not the centrepiece of the universe and by the Twenties Edwin Hubble illustrated that our star was one of many billions that make up our Milky Way Galaxy. The Sun might not be at the centre of our universe, but it is nestled at the centre of our Solar System surrounded by eight planets including our Earth.
The laws of. planetary motion. Discovered: 1609-1619.
Astronomer Johannes Kepler certainly gave a huge chunk of science to add to our understanding of astronomy when he brought us the three laws of planetary motion.
Kepler was an assistant to Danish astronomer Tycho Brahe but, unlike Brahe, he believed in the Copernican principle. Under Brahe’s supervision, he was tasked with understanding Mars’s troublesome orbit and it was by solving this mystery that Kepler struck gold. Contemplating Copernicus’s theory that the planets orbit the Sun, Kepler realised that both astronomers assumed that planets travelled in circular orbits rather than ellipses, which he figured explained the Martian orbit. He commandeered more of Tycho’s data after his death and got to work on disproving the geocentric model by devising Kepler’s First Law, Second Law and Third Law.
In his first law, Kepler suggested that planets moved in elliptical orbits around the Sun, which rests at one focus of the ellipse. This means that the distance between the planet and the Sun is changing as it orbits.
His second law states that, if you draw an imaginary line joining the Sun to a planet, then an equal area is swept out in an equal time meaning that when the planet is closest to the Sun it moves much faster with the world in question completing its elliptical motion with a constantly changing angular speed.
His third law implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit. This explains why Mercury completes its orbit in 88 days compared to Neptune, which takes 165 years.
The expansion of the universe. Discovered: 1929.
Today we think of the universe as expanding but it is thanks to astronomer Edwin Hubble that we’ve got some idea about the current behaviour of the universe.
Hubble’s arrival at Mount Wilson Observatory in 1919 marked a turning point in the history of astronomy.
At this time, astronomers concerned themselves with cloudy patches called nebulae (now known as galaxies) that splattered the night sky. While many astronomers believed that these fuzzy objects hung inside our galaxy, Hubble was convinced there could be more located outside of the Milky Way.
Taking photos of these distant nebulas, he proved his own theory.
His discovery of these other galaxies led to the universe being inflated to a size 100 times larger than first thought. He immediately got to work on measuring the distances to these galactic structures. Poring over his images, Hubble noticed a number of novae, as well as other dim stars brightening over a period of frames.
He also identified a star that would help him determine the distance to the Andromeda Galaxy — a Cepheid variable. Comparing the star’s apparent brightness with its actual brightness, he determined that Andromeda was 900,000 light years away. However, astronomers have found that Hubble made an error and Andromeda is, in fact, about 2 million light years away!
Hubble was aware of a few galaxies approaching the Milky Way, but there were also several moving away at what he believed were high speeds. This apparent moving towards and away from the Milky Way is known as Doppler shifting. Hubble measured the distance and Doppler shift for as many galaxies as he could but his discovery that some galaxies were moving away from us led to his realisation that the universe was expanding. This amazing discovery impressed the likes of Albert Einstein and allowed later astronomers to measure the age of the universe.
Jupiter’s moons. Discovered: 1610.
Taking a look through a good pair of binoculars or a telescope at the bright star in the night sky that represents Jupiter, you are very likely to spot the gas giant’s most prominent moons -Europa, Io, Ganymede and Callisto.
The quartet of satellites didn’t go unnoticed, not even in the early 1600s, as Galileo Galilei pointed his telescope at the planet. Writing down his observations, the Italian astronomer didn’t see all of the moons, but only three which he, at the time, believed were stars fixed in positions close to what we now know as a great gas giant striped with belts of angry swirling storms.
Galileo’s observations between December 1609 and January 1610 saw the fourth moon make its appearance from behind Jupiter and caused him to rethink his original thoughts as to what the four points of light were. Watching them further, he realised they were orbiting as moons and as their discoverer, Jupiter’s four largest satellites of many were named after the astronomer and dubbed the Galilean moons.
Galileo’s finding not only spelt out the turning point in which the telescope was seen as an invaluable instrument for uncovering the cosmos outside the atmospheric confines of our planet, but also had its part in the debunking of Ptolemy’s idea of our Earth being at the centre of everything with the stars, Sun and planets revolving around it.
Cosmic Microwave Background Radiation. Discovered: 1965.
Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in New Jersey never imagined that they would find damming evidence for the Big Bang — which occurred some 13.7 billion years ago — along with support for an expanding universe previously postulated by Edwin Hubble while experimenting with the Holmdel Horn Antenna. The super sensitivity of the antenna, which was built to detect radio waves ricocheting off echo balloon satellites, unintentionally encountered the readings for Cosmic Microwave Background (CMB) radiation, thermal radiation left over from the Big Bang, as a low yet steady interference. This noise, which they found had an intensity 100 times more powerful than the physicists were expecting, seeped into every corner of the sky and was present from day through to night.
Could this finding have been a mistake? Fortunately not for the duo, who in 1978 received a Nobel Prize for Physics for their joint discovery.
Clearing away pigeons nesting in the antenna as possible sources of interference, Penzias and Wilson found that the noise did not disappear. The CMB that permeates the universe had been found and the physicists had measured it at an average temperature of -270.15 degrees Celsius (-450 degrees Fahrenheit).
Liquid on Titan. Discovered: 1995.
Although seas of liquid on the surface of Saturn’s largest moon, Titan, were suspected as early as the days of the Voyager 1 and 2 spacecrafts, it wasn’t until 1995, after the launch of the Hubble Space Telescope, that astronomers grabbed a clearer picture of what was really lurking on the moon’s surface. The suspicions of scientists were proven correct in what they believed was an atmosphere that held moisture, however, getting snaps of any expanses of liquid proved tricky
Enter the Cassini-Huygens orbiter-probe in 2004, which spied its first lake, Ontario Lacus, at the moon’s southern pole. A couple of years after the mission’s arrival at Saturn, radar pictures of the north pole in winter showed expanses of smooth lakes filled with methane. This marked an important point in the history of space exploration, a landmark for the discovery of the first lakes outside Earth.
By early 2005, the Huygens lander had separated from the Cassini probe and descended through the thick atmosphere before touching down on Titan’s surface, immediately getting to work transmitting a radio link from itself to Cassini, which thenbeamed new information back to Earth. However, pebbles scattered over the surface were not the only thing that Huygens found as it fell through the smog. Contradicting previous evidence, the probe spotted no great lakes but dried up river beds. Scientists suggested that the probe’s penetrometer had landed on a huge pebble thought to be made of water ice and, as it landed, had found wet clay as well as many rounded pebbles, indicating running fluids. Infrared pictures of abundant chemicals covering the surface of Titan taken in late-2007 saw the Cassini-Huygens take a closer look at Titan as it edged in closer to the limb of the large moon, revealing more possible lakes as well as ethane. In February 2008, Titan’s polar lakes were found to contain hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Earth.
Finding lakes on Saturn’s largest moon not only provided evidence of the first world other than Earth to harbour liquid and organic materials on its surface, but Titan’s lakes make it an important planet for studying weather as scientists watch the liquids, gases and temperatures at play.