The Milky Way, our Galaxy, is thought to be 13.7 billion years old and contains around 300 billion of stars. Could somewhere out there be a planetary system similar to ours? Perhaps a planet that followed the same evolutionary path? Where to look for it/them?
If life begun by a coincidental assembly of elements in a favourable environment, there has been enough time and plenty of opportunities for similar circumstances to take place anywhere else in our galaxy or further away.
“Our solar system was formed about ten billion years after the Big Bang, from gas contaminated with the remains of earlier stars. The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, some of these atoms came to be arranged in the form of molecules of DNA.
We do not know how DNA molecules first appeared. The chances against a DNA molecule arising by random fluctuations are very small. Some people have therefore suggested that life came to Earth from elsewhere, and that there are seeds of life floating around in the galaxy. However, it seems unlikely that DNA could survive for long in the radiation in space. And even if it could, it would not really help explain the origin of life, because the time available since the formation of carbon is only just over double the age of the Earth.
One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated” (Hawking, S. No date).
It is accepted by many astrophysicists that there is a high probability of there being life elsewhere in the universe, if not on other planets or on moons within our own solar system (deGrasse Tyson, N. No date). Astronomers are constantly looking for evidence of planetary arrangements similar to ours because they might have provided the opportunity for the development of life.
Planets found outside our Solar System are called Exoplanets or Extra Solar Planets, thought to revolve around their own star. Only the star is directly visible from Earth because it produces light. Planets illuminated by their star are too small and dim to be visible. Their presence is only deducted by indirect methods, which have improved with advances in astronomy.
One of the first reports of the discovery of planets orbiting a star (pulsar PSR B1257+12) was made by radio astronomers Wolszczan and Frail in 1992. Later, in 1995, a planet was found orbiting a star (51 Pegasi) by Mayor and Queloz. This time the planet had a 4.2-day orbital period and seemed to be too close to the star to have earth-like temperatures. Since then, other similar arrangements were described and those planets were commonly named “Hot Jupiters” or “Roaster Planets” because only giants are large enough to be detected.
In the last 18 years, 859 exoplanets were identified, including 128 multiple planetary systems. The majority of them falling into the category of Hot Jupiters. Stellar imaging technology is still unable to detect smaller and dimmer planets.
METHODS OF DETECTION
The first method of detection is Radial Velocity, which relies on the detection of changes in spectral characteristics of the star as it moves away and towards us. These changes are presumed to be a response to the gravitational pull of the giant exoplanet. This deduction method cannot apply to smaller planets with larger orbits as they would hardly cause any change on the star they are orbiting.
The second method of detection is Photometric Transit, where changes in brightness of the star are assumed to be caused by a large planet crossing between the star and our observation point. The larger the planet, the more it will obscure the star as it travels in front of it, an effect also known as Primary Eclipse. A Secondary Eclipse occurs when the planet’s signal disappears as it travels behind the star (Harvey, S. 2011). This is also an indirect method and its biggest problem is that it only works if the plane of the planetary orbit is close to our observation line of sight, which is thought to account only for 10% of the cases. Other factors affecting luminosity result in around 35% of false-positive reports.
Even combining both methods, it may take the better part of this century to find the perfect alignment to confirm at least 3 orbits.
SEARCH EFFORTS AND NEW TECHNOLOGIES
The Search for Extraterrestrial Intelligence Institute (SETI) has been looking for evidence of life in the universe since 1984. Although it has not yet confirmed a signal from an alien civilization, optimists say that it is only a matter of time. The SETI Institute is comprised by three centres, the Centre for SETI Research, the Carl Sagan Centre for the Study of Life in the Universe and the Centre for Education and Public Outreach.
NASA is also looking further away than our solar system, they have plans to build a telescope called the Terrestrial Planet Finder to search for Earth-like planets (Achenbach, J. No date).
Among the new efforts to detect minute changes in spectral characteristics of stars, is that proposed by Danish astronomers from the Stellar Observation Network Group (SONG) at Aarhus University. The plan is to build a network of 8 robotic telescopes orbiting our planet in 2 rings: one in the northern and another one in the southern hemisphere. Thanks to their separation, data collected from their different points of view would make it possible to detect positional changes and optical effects like Microlensing, which occurs as the light from a star is deviated by the gravitational field of a nearby object like a planet. Although the planet cannot be seen, its presence can be deducted by the deviation of light it produces when it is in close alignment to its star.
Other technological developments involve advances in telescope light sensors with increasing resolution and reduced noise at low light levels. Coupled with high speed acquisition of images, modern devices are essentially photon counting as most frames in dark areas will contain zero photons.
An example of new technology is the Electron Multiplying Charge-Coupled Device (EMCCD), a light sensor recently installed on the 1.54m Danish Telescope at “La Silla” Observatory in Chile. This famous site offers minimal light pollution thanks to its high altitude at 2400m and its location, surrounded by the Atacama desert, far from urban areas. The new light sensor technology is also being adopted by the Stellar Observation Network Group (SONG) for their observatories: “Teide” in Tenerife and “Qinhai” on the Tibetan Plateau.
By January 2013, from less than 1000 exoplanets discovered, 4 planets ranging between 1.5 and 2 times the size of Earth have been found to be orbiting a star similar to our own.
The closest exoplanet under scrutiny is Alpha Centauri Bb. Having a mass similar to Earth’s, it is thought to be in orbit around the star Alpha Centauri B, located 4.37 light-years away. The planet was discovered using Doppler Spectroscopy in 2008, and after more than 450 observations and data analysis to remove sources of error, scientists were able to announce the finding in October 2012. In June 2013, other scientists found evidence of activity noise in the data, which played against the confirmation of the discovery (Hatzes, A. 2013). The case is therefore inconclusive and requires further research.
THE POSSIBILITY OF LIFE
Behind all these efforts is the idea of the possibility of life existing somewhere in the universe. If life evolved by chance on this planet, why wouldn’t it have also evolved somewhere else? Given the vast number of planetary systems being found only in our vicinity and the time that elapsed since the creation of those systems, it would be too egocentric to think that our situation is unique.
Scientist use our own evolution and the changes happening to our society to predict what could happen in the future. A path that could be applicable to life forms developing in similar systems somewhere else in the universe.
One of those scientists is Astrophysicist Prof Michio Kaku, who has dedicated part of his life to the promotion of science, making it accessible to the public and expressing his view of the future of humanity.
In his book “Physics of the Future: How scientists will shape human destiny and our daily lives by the year 2100,” Dr Kaku predicts changes from the perspective of an “insider” who, after interviewing more than 300 scientists, has first-hand look at novelty products. The prototypes of all technologies already exist, giving his forecast a solid base.
“We are witnessing the birth of a new era, in which we will become masters of nature as our civilisation evolves to type-1” (Kaku, 2011).
The first video below features CBS News interview of Prof Michio Kaku in February 2017, shortly after NASA’s discovery of the Trappist-1 Solar System, which contains 7 planets, 3 of which lie in the “habitable zone” (3 min).
The second video features Prof Kaku in his “Science Fantastic” podcast from March 2017, where he talks about exoplanets and interviews Prof Michael Summers, Professor of Physics and Astronomy at George Mason University, who wrote a book about Exoplanets (1:48 hr).
UNPRECEDENTED PROGRESS
Technology is advancing at an unprecedented rate. In the field of computing, a modern pocket mobile device has thousands of more calculation power than the IBM 1401, one of the most powerful computers built only 50 years ago, which occupied an entire room and weighted 4 tons.
At a price of £1 million, that computer was a distant relative of our current £50 mobile devices.
With ever increasing numbers of research centres, advances in technology are leading the way of society. We can hardly keep up with the pace of change. By the time we learn how to use our new devices, they have already become obsolete. The same goes for the search of exoplanets, improvements in resolution will increase the chances of finding hundreds or perhaps thousands of planets with the potential of sustaining life.
By June 2018, NASA confirmed 3,700 exoplanets in our galaxy with 2,724 candidate findings that need to be analysed before confirmation (Brennan 2018). These observations were possible thanks to NASA’s Kepler Space Telescope, which was launched in 2009 and follows an Earth-trailing orbit around the sun (heliocentric). The mission is bound to finish in 2019 as the spacecraft’s fuel is depleted but beginning in 2018, the data collected will be examined by the astronomical community and not only by the Kepler mission team, which will result in an accelerated confirmation of exoplanets (Hawkes 2018).
Additional recent findings were provided by the Hubble Telescope observations. The analysis of the infrared spectrum of the atmosphere of exoplanet WASP-107b, a gas giant orbiting its own star, revealed the presence of Helium. This is the first time Helium is detected on any exoplanet; in our solar system, this gas is one of the main constituents of Jupiter and Saturn.
The image on the right shows samples of the silhouette of exoplanets against the light spots of their own stars, and an artist interpretation of the atmosphere surrounding the exoplanet, which interferes with the light of the star as it travels in front of it. The spectroscopic analysis of this interference provided the signature distortion produced by Helium (NASA 2018).
References
§ Achenbach, J (No date) "Life Beyond Earth." National Geographic Magazine [Online]. Available here. (Accessed: 02 August 2013).
§ "Alpha Centauri Bb" (2013). Wikipedia. [Online]. Available here. (Accessed: 13 August 2013).
§ deGrasse Tyson, N (No date) "The Search for Life in the Universe." NASA's Astrobiology Magazine [Online]. Available here. (Accessed: 02 August 2013).
§ "Extrasolar Planet" (2013). Wikipedia. [Online]. Available here. (Accessed: 13 August 2013).
§ Harvey, S (2011) "The Exotic Atmospheres of Hot Jupiter-like Planets." NASA's Solar System Exploration [Online]. Available here. (Accessed: 09 August 2013).
§ Harpsoe, K (2013) "The search for Earth-like Exoplanets." Labnews magazine, March, pp 24-25.
§ Hatzes, A (2013) "Radial Velocity Detection of Earth-mass Planets in the Presence of Activity Noise: The Case of Alpha Centauri Bb." The Astrophysical Journal at Cornell University Library [Online]. Available here. (Accessed: 13 September 2013).
§ Hawking, S (No date) "Life in the Universe." [Online]. Available here. (Accessed: 02 August 2013).
§ Kaku, M (2011) Physics of the Future: How scientists will shape human destiny and our daily lives by the year 2100. 1st ed. New York: Doubleday.
§ "Milky Way" (2013). Wikipedia. [Online]. Available here. (Accessed: 02 August 2013).
§ "SETI 101" (2013). SETI Institute. [Online]. Available here. (Accessed: 02 August 2013).
§ Brennan, P (2018) Exoplanet in the corner pocket: a recount for thousands of worlds. [Online]. Available here. (Accessed: 10 August 2018).
§ Hawkes, A (2018) NASA’s Kepler Spacecraft Nearing the End as Fuel Runs Low. [Online]. Available here. (Accessed: 10 August 2018).
§ NASA (2018) Hubble detects helium in the atmosphere of an exoplanet for the first time. [Online]. Available here. (Accessed: 10 August 2018).
Images
§ All images edited by ren@rt. Source: NASA, Scribd, SETI, YouTube and others.
