Our sun is a single star system, but using new technology, scientists are discovering double – and even triple! – star systems

The planets of the sun revolve around a single star, just like the planets in many systems. Revolving around a single star is the general principle, but scientists have recently discovered planets that revolve around two stars, without causing any irregularities. Planets that revolve around two stars are accepted as a new class of planets and according to calculations their numbers in the Milky Way galaxy are estimated to reach at least ten million.

How can this be possible? A planet traveling around two stars enters the gravitational field of each star during its motion, and its velocity and orbit constantly changes.

If stars can shade (eclipse) each other, it is possible for one planet to shade one or two stars. When this event takes place, the planet and stars orbit on the same plane. This intersection on the same orbital plane means that the planet and star have passed in front of each other; we can measure this due to a reduction in the amount of light emitted by the star. If the distance between the two stars is too long, these stars act as if they are isolated from each other. In that moment, the planet that is moving on one of the star’s orbits does not feel the effect of the other star. These are called S-type planets and dozens of them have been discovered in the last decade.

Interesting events take place when stars get close to each other. In such cases, the time required for stars to make a complete revolution around each other is described in days or weeks. The ability of a planet to move in “braided pathways”^[1] that will allow a stable orbit around two stars that are so close to each other cannot be a coincidental event without fine adjustments.

S-type systems are only one type of double-star systems. In P-type systems, the planet revolves around the two stars simultaneously. For this type of planet to travel in a stable orbit, the orbital distance from the stars must be longer than a critical distance. If it is closer than this critical distance, the planet’s orbit becomes progressively unstable, and it is either pulled towards one of the two stars and collides, or gets thrown into outer space. This critical distance is 2/3 of the star’s magnitude.

In a system of a single star and planet, the transit of the planet occurs as if the light makes a periodic movement, such as when a light house rotates around itself. These passes allow us to detect stars. Double-star planet systems are another example of this. It is not easy to estimate the movement of an object consisting of three elements. In a single-star system, the star’s movements are stable; thus, it is easy to estimate the movement of a planet. Yet in a double-star system, the distance between the two stars is much shorter than their distances to the planet; for this reason, these stars revolve at a higher speed around each other than the planet revolves around them. This means that the planet’s rotation is difficult to predict.

As a result, the planetary movement of a double-star system will not be periodical; different than that of a single-star system, the time of transit passes will vary according to the relative motion of the planet to the star. If the planet and the star it revolves around are moving in the same direction, the transit pass time will be longer; but if the star is located at the other half portion of the orbit and traveling in the opposite direction, the transit passing time will be much shorter.

The Kepler spacecraft and telescope that NASA launched in March 2009 is designed for detecting planets that cause reductions in the light of stars when they are passing in front of them. Today, more than two thousand twin star systems that display eclipses have been discovered. Two planets that revolve around stars eclipsing each other every 7.5 days were discovered and called the Kepler-47 system. Along with these double star systems, a triple-star system has been discovered through the Kepler telescope; the properties of this system are extraordinary.

Among these, planet Kepler-47b of the inner region completes its voyage around its stars in less than 50 days. In addition, this planet, which is not visible directly, is predicted to be a very hot planet. Since a foggy layer inhibiting its visualization is found to have formed as the result of methane gas combusting in its hot atmosphere. Kepler-47b, which is three times bigger than the Earth’s radius, is the smallest planet among those that have been discovered in two-star systems.

The planet Kepler-47c of the outer region completes its one full tour around its twin stars in 303 days and it moves in a region that is described as the habitable zone in the Milky Way galaxy. There can be liquid water present on the surface of a planet in the habitable zone. However, just being in this zone does not totally mean that the place is suitable for life. Kepler-47c is predicted to be slightly bigger than Neptune and to have an atmosphere composed of thin and bright water-vapor cloud.

Reference

William F. Welsh, Laurance R. Doyle, “Worlds with Two Suns,” Scientific American, October 2013, pp. 40-47.

S- And P- type planets traveling around two stars

Kepler-47c exists in the habitable zone and liquid water is predicted to be present on its surface.

A representative image of the Kepler 16a/b based on acquired data.

^[1] The Qur’anic verse “By the heaven full of braided pathways, surely you are in contradicting views”(Adh-Dhariyat, 51:7-8) sounds like pointing to this phenomenon.

a

Astronomers have discovered a planet with the longest known orbital period. Exoplanet Kepler-421b has been identified through the Kepler observatory, a space-based telescope. It circles its star once every 704 days. More than 1800 exoplanets have been discovered so far, but compared to Kepler-421b, those had much shorter orbital periods, like a few weeks or even a few days. The host star for Kepler-421b is much like the sun, but it is little bit smaller and relatively cooler. With an orbital distance of 177 million kilometers, Kepler-421b gets about one-fourth the light from the host star as the Earth receives from the sun, which makes the exoplanet as cold as -100 °C. The unusual orbit places Kepler-421b beyond the “snow line,” which is accepted as the dividing line between rocky and gaseous planets. Outside of the snow line, water condenses into ice grains that stick together to build planets known as “gas giants.” Since gas giant planets are very close to their stars, theorists believe that many exoplanets migrate inward early in their history. However, Kepler-421b is the first example of why such migration may not be necessary.

Sunflowers’ internal clock

Plants are known to grow toward the sun to maximize the amount of energy they absorb. Sunflowers (Helianthus annuus) show the most fascinating behavior during summer, when they follow the sun as it rises in the east every morning and sets in the west every evening. In a recent study, scientists challenged the obvious explanation for this plant’s behavior: are flowers solely responding to sunlight or are there other unknown mechanisms at work? They designed a clever yet simple experiment where they grew sunflowers in chambers with a fixed overhead light that was continuously on. Surprisingly, for several days, the sunflowers under constant light kept moving as if the sun were rising in the east and setting in the west. This unexpected result suggests that sunflowers were not responding only to the direction of the light but also to an internal biological clock. Furthermore, they discovered that sunflowers bend when one side of the stem grows faster than the other. For example, the west side of the stem seems to grow faster to bend the plant towards the east in the morning. Scientists now hope to understand how an internal biological clock in sunflowers has the opposite effects on opposite sides of the stem. Sunflowers are not the only plants performing this diurnal dance; other agriculturally important crops such as soybeans and cotton exhibit the very same behavior. Solar tracking is known to boost plant yield and discovering the mechanisms of how plants track the sunlight might have important implications for improving global agricultural yields.

Friends linked by genes

It is a common observation that close friends look alike. Even centuries ago, Plato noted the tendency that good friends usually have similar appearances. Recently, a group of geneticists took this idea even further and suggest that people on average tend to choose friends who are genetically similar. The study provided convincing evidence that we have more DNA sequences in common with the people we pick as friends than we do with strangers in the same population. Researchers performed a genome-wide analysis of approximately 1.5 million markers of gene variations from 1,932 subjects of the Framingham Heart Study, which is one of the most comprehensive genetic databases. They identified 1300 pairs of non-relative friends and compared their genetic information to each other. The analyses showed that friends share similar genetic variations (around 1% genomewide), to the degree that it is as if they have the same great-great-great-grandparent – in other words, as if they were fourth cousins. Notably, friend pairs seem to have the greatest similarity in the genes that are responsible for a sense of smell and they show the most difference in immunity-related genes. Friendship entails spending a lot of time together and looking out for each other. Odors are strong behavioral cues in human psychology and people with similar olfactory preferences might like to prefer living or hanging out in similar environments. Likewise, it is potentially a big advantage that friends don’t get infected from the same microbes at the same times, so that one of them can take care of the other. As much as these anthropological implications are merely speculations with many caveats – and despite there being many obvious social, ethnical, and cultural factors that help determine friendships – the genetic basis of friendship and other social interactions may hold answers to at least some of the mysteries of human behavior.

A planet that revolves around another star outside our solar system is called an Exoplanet or Extra solar planet. Ongoing studies involving this field are carried out via simultaneous ground and space based missions and observations. Scientists are searching a small portion of the Milky Way galaxy, approximately 3000 light years away, by using ground and space telescopes, along with various other astronomic methods (1). Despite all this technology, the observation area is too big when compared to the size of the object of interest.

It has been calculated that the Milky Way, a disc shaped galaxy, consists of 200 billion stars spread over a diameter of nearly 100,000 light years and a thickness of 1000 light years. When we consider the amount of stars in a single galaxy, and the fact that there are between a hundred billion and one trillion galaxies in the universe, the number of possible exoplanets is likely much larger than those we currently know of.

Classification of exoplanets

Exoplanets are classified according to their physical, chemical, and other characteristics, along with their diameter and mass: Jupiter like; greater than Jupiter; Earth like; greater than Earth

Classifications according to surface and atmospheric temperatures are as follows: Hotter than Jupiter; colder than Neptune; colder than Jupiter; small blue dots or twin Earths.

The presences of free-floating planets which have lost their parent stars because of different formation processes or other factors have also been discovered.

One of the common features of the exoplanets currently discovered is their short distance to the star they revolve around, which is usually less than half the distance between the Earth and the Sun. The known exoplanets are also defined by their faster revolutions in much shorter periods. Therefore, larger planets that are closer to their stars can be observed easily. When these planets are passing in front of their stars, a decrease in the brightness of the star is detected via spectrometers (Figure 1).

Figure 1. Passing of a planet in front of a star and a spectrum of this event.

Radial velocity, one of the methods used to discover exoplanets, relies on the observations of a star’s kinetic fluctuations. The proximity and size of a revolving planet leads to slight changes in location and velocity of a host star. As a result of this, the star gets closer to earth and then becomes more distant, which is observed as the Doppler shift of spectral line color waves. 75 % of all known planets have been discovered using this method (Figure 2).

Figure 2. Doppler shift – radial velocity

Earth-like planets or habitable places

In an official NASA report in December 2011, the discovery of an Earth-like planet was announced for the first time. This planet, named Kepler 22b, is 600 light years away and remains the most similar one to Earth among the known heavenly bodies. The distance of Kepler 22b to its star shows a high possibility for the presence of a habitable zone.

So what does this mean?

Earth is such a special home for us humans that everything here has been assigned to serve us with delicate calculations. Factors such as the Earth’s mass, gravity, distance to the Sun, rotational and revolution velocity, chemistry, thickness of the atmosphere, magnetic shield, hydrosphere/land ratio, ecological balances, and average temperature are all perfect for biological life.

Earth revolves in such a region and position that a majority of the planetary water is in a liquid state and is not ice or vapor.Thedistance of the habitable zone to our Sun is between 135,000,000 – 225,000,000 km. Earth revolves at a 150,000,000 km distance to the Sun. The value of a habitable zone for each planet depends on the diameter, mass, heat and radiation strength of the host star. In other words, aside from the similarity of an exoplanet to Earth, a classification of its host star with in terms of size and age is also important.

Kepler 22b owns the title as the first planet to match the criteria above with its following features:

• Has a radius 2.4 times bigger than Earth
• Revolution time is 290 days (365 for Earth)
• 15% closer to its star compared to the Earth-Sun distance
• The size and surface temperature of Kepler 22b’s host star is very similar to that of the Sun’s
• The surface temperature of the planet is 22 C
• The size of the habitable zone for Kepler 22bis 133,500,000 – 240,000,000 km (Figure 3).

Figure 3. Comparison of the solar systems of Kepler 22b and Earth.

Aside from these similarities, it is noteworthy to report the problems that scientists encountered regarding Kepler 22b:

• The unknown presence of water on the surface
• No information on the gaseous contents of the atmosphere.
• The gravitational force is 2.5 times greater than on Earth.
• Rocks constitute the surface instead of soil.

The hardest part is that Kepler 22bremains 600 light years away from us. This means it would take us 11 billions years to get there with today’s fastest spacecrafts. Who knows when we will be able to decrease this time with the advent of superior technology.

What do religious scholar say about life in outer space?

Among His manifest signs is the creation of the heavens and the earth, and that He has dispersed in both of them living creatures. And He has full power to gather them together when He wills. (Ash-Shura 42:29)

While interpreting the Qur’anic verse above, Fethullah Gülen notes the following:

“Since the earliest times, this verse has been taken as a proof for the view that there are living creatures, whether resembling human beings or not, in the places other than the earth. This view may be true. The second part of the verse, ‘He has full power to gather them together when He wills,’ has been understood that these creatures and human beings will possibly come together either in this world or in that of the other creatures. … there may be earth-like globes in the heaven where creatures resembling earthly ones live.” (Gülen 2012, 272-273)

“Perhaps people will not be able to reach those places individually or as a whole generation, but this can be achieved by mankind as a species. In other words, when the Divine Will manifests itself in that direction, humans here can encounter those other life forms.” (Gülen 2007, 232)

This commentary reflects what Bediuzzaman Said Nursi had said decades ago:

“The earth, although much smaller than other heavenly bodies, is so densely inhabited by living creatures that even its grossest and most rotten parts are full of living things, such as micro-organisms. This shows that those infinite firmaments, with their numerous stars and constellations, are inhabited by conscious, living beings …” (Nursi 2010, 530-531) 29th Word, First Aim, First Fundamental)

Nebiyev is a professor of physics in Azerbaijan.

References

• http://kepler.nasa.gov/
• http://planetquest.jpl.nasa.gov/
• http://en.wikipedia.org/wiki/Habitable_zone
• Gülen, M. Fethullah. 2007. Kendi iklimimiz, Istanbul, Nil Yayinlari.
• Gülen. M. Fethullah. 2012. Reflections on the Qur’an: Commentaries on Selected Verses, NJ: Tughra Books.
• Nursi, Bediuzzaman Said. 2010. The Words, (29th Word) NJ: The Light, Inc.
• Chris Kitchin Exoplanets: Finding, Exploring, and Understanding Alien Worlds- (www.springer.com/series/6960)-2012
• Mercy, G., P. Butler et al. 2005. “Observed Properties of Exoplanets: Masses, Orbits, and Metallicitie”.. Progress of Theoretical Physics Supplement, Vol. 158, No. 24-42.