Earth’s Twins Found! – Yet Another Exoplanet Milestone!

Image of Habitable Zone

There are three fundamental ingredients that a planet must have if LAKI (Life As we Know It) should exist on it and they are organic molecules, sufficient energy for these molecules to react and liquid water as a medium for these reactions. Though it sounds simple, only planets with very close resemblance to Earth in all aspects might harbor these three ingredients. The planets closer to their start are too hot for liquid water and the ones farther are too cold. Similarly the ones too large are gaseous and the ones too small cannot have an atmosphere. That is where finding Earth-like planets become very important.

Liquid water is the main component of the primordial soup where organic molecules react and form complex self replicating structures like our DNA which eventually lead to formation of LAKI. There is of course a remote possibility of formation of exotic life forms in planets with extreme conditions like the extremophiles we observe in certain areas on Earth but generally we are on the lookout for planets where normal life forms like our own can exist and flourish. This is in the light of possible colonization of future worlds by humans.

Image of Kepler Space Telescope

After years of hunting, astronomers have finally detected, the first Earth-sized exoplanets orbiting a star quite similar to our Sun, located 950 light years from Earth thereby taking exoplanet research to the next level. These two planets are among five orbiting the G-type parent star Kepler-20. Entitled “Earth-Twins”, they are by far the most important exoplanets discovered. Scientist at the Harvard-Smithsonian Center for Astrophysics, Dr. François Fressin led the research and according to him, this marks the dawn of an exciting new era of planetary discovery.

NASA’s Kepler space telescope used the transit method to detect these planets in which it notices tiny dips in the parent star apparent brightness when planets passed in front of it. The scientists then use ground based observatories to confirm that they have found a planet by measuring the minute wobbles of the parent star’s position caused by gravitational tugs from its planets.

Image of Planets size comparison

The larger of the two planets named Kepler 20f, is 1.03 times the size of Earth while Kepler 20e is slightly smaller with 0.87 times the radius of Earth and orbits closer to its parent star. Their masses are 3 times and 1.7 times the mass of Earth respectively. Their orbital periods are 6.1 Earth days for 20e and 19.6 Earth days for 20f at distances of days at a distance of 7.6 million kilometers and 16.6 million kilometers respectively. These sizes are gravitationally good enough to form rocky interiors. According to Dr. Fressin’s team, the planets have Earth-like compositions consisting of a third of iron core with a silicate mantle. The outer planet, Kepler 20f might have a thicker, water vapor atmosphere according to Dr. Fressin.

Due to their current close proximity to their parent star, both planets could be too hot to support life. 20e is at 760 degrees Celsius while 20f is at 430 degrees Celsius. Dr. Fressin noted that in the past, they may have had favorable conditions similar to Earth before they drifted closer to their star. The reason he says is that the rocky materials required to form the planets this close to the star is scarce. Hence, they could have been formed farther out and later migrated in. Another curious aspect of the system is that the rocky planets alternate between their gaseous sisters unlike our solar system where terrestrial planets are inside and gas giants are out.

Though we have discovered over 700 exoplanets since 1996, this particular discovery is important since this is the first time we received positive confirmation that Earth sized and smaller planets exist outside our solar system. It also is a demonstration of the capability of the Kepler Space Telescope in detecting small planets located at extreme distances. Since its launch in 2009, Kepler alone has discovered 28 definite planets and 2,326 planet candidates. Of these, all are larger than Earth except 20e and 20f.

So far the most significant discovery in planet hunting, also made by Dr. Fressin’s team was a planet named Kepler 22b, 2.4 times the size of Earth, located within the habitable zone (the region of space around a star that is neither too cold nor too hot) of its parent star, which implies the planet could harbor liquid water and probably life. According to Dr. Fressin the discovery of Kepler 20f and 20e is the latest most significant of all planet discoveries.

This discovery will cause planetary scientists to revise their existing theories on planet formation. Other planets in the system are Kepler 20b, 20c, and 20d with diameters of 24,000 km, 40,000 km, and 35,000 km respectively with orbital periods of 3.7, 10.9, and 77.6 Earth days. Kepler-20d, weighs roughly 20 times Earth’s mass, while 20c and 20b weigh 16.1 and 8.7 times Earth.

We live in an era where it is impossible to say whether we are alone in the universe or not. The telescope is currently scanning 150,000 stars and one of the greatest dreams of planet hunters is to discover and Earth sized planet residing in the habitable zone of its star. That would be marked one of the greatest discoveries in all history where we know that an exact replica of our planet exists that could possibly support life. It is only a matter of time before this “holy grail” in exoplanet research is found.


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  2. Moskowitz, C. “Found! 2 Earth-Size Alien Planets, the Smallest Exoplanets Yet.” Space. Dec 20, 2011. (accessed Dec 21, 2011).
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New planet discovered in trinary system – Another milestone in exoplanet research!

Image of Hot Jupiter
Most exoplanets are Hot Jupiters

Though the number of extrasolar planets continued to grow over the years, exoplanet researchers were sceptical about existence of planets around multiple star systems since it was suspected that if the stars are not sufficiently farther apart, the constantly varying gravitational force would eventually tug the planet out of orbit. However, recent discoveries of planets in such star systems have proven this hypothesis otherwise.

Planetary scientists last week announced the discovery of a new planet in the HD 132563 trinary star system in the constellation Auriga after a 10-year long study of the system which also made several other discoveries. The system consists of two stars with masses equivalent to the mass of our sun orbiting around each other at 400 AU. The main star of the system called HD 132563A is itself a binary star making it a trinary star system. According to the team led by Silvano Desidera of the Astronomical Observatory in Padova, Italy, this fact was not previously known about the system which was initially considered to be a binary.

Image of HD188753 Orbit
Orbit of HD188753 – Courtesy NASA

This new planet orbits the secondary star in the system called HD 132563B and was discovered spectroscopically using the SARG (Spettrografo Alta Risoluzione Galileo) at Italian Telescopio Nazionale Galileo or TNG. It is estimated that the planet is at least 1.3 times the mass of Jupiter and orbits around its parent star at a mean distance of 2.6 AU with a moderately high eccentricity of 0.22. The team has tried to image the planet directly using adaptive optics  since they could not initially rule out the detection as an instrument effect in the star’s glare.

This discovery brings the total number of planets discovered in multiple star systems to eight. Though the number is small, it seems planets can be commonly found orbiting around more remote members of trinary star systems for good periods of time. The age of the H132563 system is estimated to be between 1-3 billion years in the shorter end and up to 5 billion years. The two estimates have been drawn by measuring the amount of stellar activity and lithium (which decreases with time) and fitting the mass and luminosity onto isochrones respectively. Either way, the planetary system is dynamically stable.

Image of Gliese 667 C
The “Super-Earth” Gliese 667 C – Artist’s Impression

The team has suggested that based on these eight discoveries, it is possible that the occurrence of planets on remote members of multiple star systems may be just as common as planets around wide binaries or even single stars. The Extrasolar Planets Encyclopaedia thus received its 565th member. The HARPS (High Accuracy Radial Velocity Planet Searcher), the spectrographic component of the European Southern Observatory’s 3.6 meter telescope in 2009 discovered a “Super-Earth” in orbit around Gliese 667C, the third star in multiple system located in the constellation Scorpius. This earthlike planet is 5.7 times the mass of Earth and revolves around its parent star, a red dwarf, every seven days.