If There’s Life On Mars Why Have We Not Heard From ET?

Artists impression of the Curiosity Rover on Mars. In a paper published in the journal Science on 16 December 2014 NASA scientists revealed that this robot explorer has detected variable amounts of methane in the Martian atmosphere - a possible hint that life may be present. Courtesy: NASA/JPL

Artist’s impression of the Curiosity Rover on Mars. In a paper published in the journal Science on 16 December 2014 NASA scientists revealed that this robot explorer has detected variable amounts of methane in the Martian atmosphere – a possible hint that life may be present. Courtesy: NASA/JPL

NASA’s revelation that Mars burps methane gas has renewed speculation over the possibility that life exists on the red planet.

Most of the methane on Earth is due to biological processes and the US space agency’s research, published in the prestigious journal Science on 16 December, hints at the very real possibility that the momentous discovery of living organisms on another world could be just a few years away.

This is not the first time that we have heard reports of life on Mars. Results from one of the experiments on NASA’s Viking Mars landers hit the headlines back in 1976. Drops of nutrient tagged with radioactive carbon were deposited in a sample of Martian soil and evidence of metabolism was seen when radioactive carbon dioxide gas was emitted by the soil. Subsequently, the finding was dismissed.

In 1997 NASA revealed that an ancient meteorite that had come from Mars and that had been discovered on the ice of Antarctica had been found to contain structures that resembled fossils of very small bacteria. Since then a debate has raged over whether these are evidence for life having existed on Mars or whether they are some odd geological or crystalline feature of the rock.

Then a few years later, in 2003, NASA scientists announced that the Mars Odyssey probe had detected methane gas in the Martian atmosphere, a discovery that was confirmed by others at the time, although scientists were unable to determine whether it was biological or geological in origin. However, subsequent efforts have failed to detect any methane.

The latest finding from NASA’s Curiosity Rover, a small wheeled robot trundling around the surface of the planet, adds to the methane mystery. Curiosity has detected short-lived bursts of methane suggesting that something is actively producing the gas. The rover has already found evidence of complex organic chemistry in rock samples that it has studied.

The case for life on Mars is growing stronger with each new space probe. Confirmation that living microbes exist – or existed – on the surface of Mars would be an historic discovery. It could mean that life had evolved independently on two, separate, neighbouring worlds in orbit around the same star – albeit, there would remain a possibility that it developed on one planet and was somehow transported, perhaps by a meteorite, to the other.

This image illustrates possible ways methane might be added to Mars' atmosphere (sources) and removed from the atmosphere (sinks). NASA's Curiosity Mars rover has detected fluctuations in methane concentration in the atmosphere, implying both types of activity occur on modern Mars. A longer caption discusses which are sources and which are sinks. Image Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

This image illustrates possible ways methane might be added to Mars’ atmosphere (sources) and removed from the atmosphere (sinks). NASA’s Curiosity Mars rover has detected fluctuations in methane concentration in the atmosphere, implying both types of activity occur on modern Mars. Courtesy: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

Between 20 billion and 80 billion Earth-sized planets in the Milky Way

If the development of life is difficult in our universe then the chances of life appearing on two planets around the same sun would be very small. Thus the discovery of microbes on Mars would imply that the appearance of life is somehow natural and ubiquitous and, in the right conditions, may be inevitable.

The possibility that our universe could be teeming with life is made all the more likely by the fact that the Kepler space telescope tells us that many, many stars have planets orbiting them in exactly the same way that our local star – the Sun – has the Earth and Mars and a retinue of other worlds, large and small, going around it.

So far we have confirmed 1,523 planets orbiting alien suns with another 3,303 candidates spotted by the Kepler space telescope, according to records logged on a special database maintained by space scientists. Indeed, the data suggests that, on average, every star has at least one planet orbiting it and that around one in five of these stars have Earth-sized planets. There are between 100 billion and 400 billion stars in our Milky Way galaxy – and there are at least 100 billion galaxies in the observable universe. This suggests that there are between 20 billion and 80 billion Earth-sized planets in our galaxy alone. It also implies that there could be a lot of life out there.

Scientists have found a number of worlds of alien suns with orbits that are in the so called habitable zone – where surface temperatures should be just right for liquid water to freely exist, an important requirement for life as we understand it.

There are 10,000 detectable alien civilisations in our galaxy, according to veteran US radio astronomer Frank Drake, writing in a paper published by the Royal Society in 2011. Drake famously came up with an equation for calculating the number of alien civilisations back in the 1950s. It makes assumptions about the rate of star formation, the number of planets around stars and the probability that they will evolve life. Sixty years ago, most of the factors in this equation – such as how many stars have planets – were unknown. Today, there are fewer uncertainties and Drake used modern data to come up with the number 10,000. This sounds like a big number but in a galaxy of 100 billion suns it means that just one star in 10 million may support a civilisation.

But if Drake is right then this raises an interesting question: why have we not seen any evidence of extra terrestrial intelligence? The search for extra terrestrial intelligence (SETI) has been going on for over half a century since Drake first tuned into the stars looking for aliens on 8 April 1960 using a 26m radio telescope. That first search listened to two relatively nearby stars, Tau Ceti and Epsilon Eridani, on one single frequency of 1420MHz,the frequency that allows signals to travel with the least absorption by interstellar dust.

In all that time since, no messages have been detected but there have been many false alarms. There has been just one tantalisingly brief, unrepeated and unexplained signal that was detected on 15 August 1977 by radio astronomer Jerry Ehman working on the Ohio State University Radio Observatory’s Big Ear telescope. It was a powerful spike of radio energy packed into a narrow range of frequencies – less than 10 kHz wide – around 1420MHz that climbed in intensity to reach a peak of 30 times the level of background noise. It was exactly the kind of signal you would expect to see from anyone sending a transmission across space. The signal was recorded over a period of 72 seconds and was never detected again.

On 15 August 1977, a signal was spotted by radio astronomer Jerry Ehman working on the Ohio State University Radio Observatory's Big Ear telescope located on the grounds of the Perkins Observatory, in Delaware, Ohio. It was a powerful spike of radio energy packed into a narrow range of frequencies - less than 10 kHz – exactly the kind of signal you would expect to see from anyone sending a transmission across space. Furthermore, the signal was at a frequency that many SETI scientists would expect aliens to use because signals at that frequency suffer from less absorption as they travel through space. In short, what the Big Ear recorded and what Ehman spotted was exactly what SETI scientists had been predicting. The Big Ear had an unusual design where the main antenna was fixed to the ground and could only scan across the sky as the Earth rotated. It could scan a very narrow slice of the sky at any one time as the rotation of the Earth dragged that patch across its field of view. Any given part of the sky took around 72 seconds to pass through this narrow antenna window which meant that signals from any particular spot of the sky would be detectable for just 72 seconds. Ehman was a professor at Franklin University in Columbus, Ohio, and he was doing voluntary work on the Big Ear SETI project. The work involved studying the hard copy printouts from the telescope's observations. Computers at the time were relatively primitive and the Observatory's machine had just one 1MB hard disk and 32KB of RAM memory chips. This meant that data could not be stored electronically and had to be continuously printed out to be analysed visually by a band of volunteers including Ehman who donated their time to the work. What Ehman saw that evening shocked him. In just one channel, over a 72 second period, the printout recorded a signal that was well above background noise levels and climbed in intensity to reach a peak of 30 times the level of background at exactly the mid-way point when the antenna would have been looking directly at the source and then the signal intensity steadily fell away. Using a red pen, Ehman circled the signal on the printout and scrawled the word “WOW!” in the left hand margin. Courtesy: North American Astrophysical Observatory/Big Ear Memorial Website

On 15 August 1977, a signal was spotted by radio astronomer Jerry Ehman working on the Ohio State University Radio Observatory’s Big Ear. It was a powerful spike of radio energy packed into a narrow range of frequencies – less than 10 kHz – exactly the kind of signal you would expect to see from anyone sending a transmission across space. Computers at the time were relatively primitive and the Observatory’s machine had just one 1MB hard disk and 32KB of RAM memory chips. This meant that data could not be stored electronically and had to be continuously printed out to be analysed visually by a band of volunteers including Ehman who donated their time to the work. What Ehman saw that evening shocked him. Using a red pen, Ehman circled the signal on the printout and scrawled the word “WOW!” in the left hand margin. But the signal was never seen again… Courtesy: North American Astrophysical Observatory/Big Ear Memorial Website

How near is ET?

So where is ET? The answer could lie in statistics, according to Italian astronomer Claudio Maccone. Back in 2008, Maccone discussed ideas about applying statistical methods to Drake’s equation. Maccone estimated that there were around 5,000 civilisations in our galaxy – each separated on average by around 28,000 light years. However, according to his statistical analysis there is a 75% chance we could find an alien civilisation between 1,361 and 3,979 light-years away. If anything, the most recent Kepler findings will have reduced those distances.

The trouble is that our technology is limited and signals from alien civilisations at distances of greater than around 500 light years may be undetectable. So the reason why we have not heard from ET may be very simple: our equipment is not up to the job yet.

There is a 75% chance we could find an alien civilisation between 1,361 and 3,979 light-years away, according to Italian astronomer Claudio Maccone. Courtesy: Clausio Maccone and Acta Astronautica.

There is a 75% chance we could find an alien civilisation between 1,361 and 3,979 light-years away, according to a statistical analysis by Italian astronomer Claudio Maccone. Courtesy: Claudio Maccone and Acta Astronautica.

But that may be changing and the statistics are on our side. Our ability to tune into the cosmos and scan many different frequencies while looking at many different stars is expanding with the exponential growth in computer power. Instead of scanning a few thousand stars we will soon be able to scan millions. Earlier this year, space scientist Seth Shostak, director for the US-based Center for SETI Research, told a NASA symposium at Stanford University that using sophisticated modern methods he thought we would detect an advanced alien civilisation “within two dozen years”.

So, expect to hear from ET by 2040.

References

Curiosity’s discovery of methane spikes on Mars: Read the NASA research paper on Curiosity’s discovery of methane burps on Mars here. See a NASA news release here.

The paper reporting the NASA Odyssey mission’s discovery of methane in the Martian atmosphere here.

This article has made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org. See this paper: The Exoplanet Orbit Database by Wright, J. T.; Fakhouri, O.; Marcy, G. W.; Han, E.; Feng, Y.; Johnson, John Asher; Howard, A. W.; Fischer, D. A.; Valenti, J. A.; Anderson, J.; Piskunov, N. published in Publications of the Astronomical Society of the Pacific, Volume 123, issue 902, pp.412-422 here.

For more on the Wow! Signal see the Big Ear Memorial Website here.

Frank Drake’s 2011 paper predicting 10,000 alien civilisations in our galaxy here.

A paper describing Claudio Maccone’s ideas about applying statistical methods to Drake’s equation here.

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