Until recently, our solar system had a planet with the shortest known lifespan in the universe… a planet that appeared and disappeared in just 76 years.

Well… it all depends on what planetary classification criteria you look at. If you are more than 30 years old, you will remember that Pluto became the ninth planet in our solar system after being discovered in 1930, but that it ceased to be a planet in 2006, when the International Astronomical Union revoked that status, as it did not meet the minimum requirements for being a planet. It then became just one more object in the thousands that orbit around our star.

The existence of almost 4.000 extra solar planets (exoplanets) have recently been verified with our actual technology. And many more will soon be discovered with new technology under deployment…

You may also recall that until relatively recently, the only planets that existed outside our solar system were those that appeared in science fiction films.

Officially, the first confirmation of a planet detected outside our solar system was in 1992, and since then we have continued to find more and more extra solar planets. Currently, there are nearly 4,000 confirmed and catalogued planets. It is only in the last 25 years that we have been able to say with complete certainty that these planets exist, so the term “exoplanet” was coined to describe them.

During these 25 years, a true revolution has arisen, increasing our knowledge about these celestial bodies. Our thirst to know ever more about these planets is unquenchable and is fed by the human need to be curious, especially when it comes to anything related to finding life outside our planet.

There are many ways to detect exoplanets, but the two most common are indirect methods (obviously, the huge distances involved and the fact that planets lack their own light means that direct detection and observation are unlikely) Among the most used indirect methods are: the transit method, which allows to calculate the diameter of a planet by using the decrease in the light intensity of its star when the planet orbits directly in front of the star; and the radial velocity method, which allows to calculate the mass of a planet by the interference it produces on the mass of its star.

The transit method requires the planet to pass in front of its star, and it must therefore be aligned with the field of view of the observer, which makes planets undetectable in 90% of cases. Despite this, while the radial velocity method has made it possible to detect 677 planets, the transit method has led to the discovery of 2,951. But since 90% of planets can’t be discovered through this method, there are many more to look for.

The impending termination of one of the tools that has contributed most to the exoplanet catalogue to date has just been announced. The Kepler mission (framed within the NASA’s Discovery Program), which was launched into orbit around the Sun in 2009, was the first satellite with the ability to carry out the specific activity of finding exoplanets of a similar size to our Earth in potentially habitable environments.

The Kepler satellite was launched with an estimated lifespan of 3.5 years, and its mission should therefore have finished in 2012. But as is the case for almost all missions in which the spacecraft is not expected to be recovered, they decided to continue with the mission while the satellite remained responsive, which it has done ever since, even after two of the four reaction wheels failed and it was estimated to be practically out of fuel (funny enough …it did not have any device for measuring remaining hydrazine).

The first phase of its nominal mission, lasting 3.5 years, was called the Kepler mission, but from then on it was called K2. This new phase has been made open to the community of observers, accepting and evaluating all formal proposals made to NASA. The seventh cycle (possibly the last) of the K2 phase began in August this year (2018). So, be advised: …you still have time …if you want to brag about it, prepare a project and find your own exoplanet!

To date, the Kepler mission is credited with the extraordinary figure of 2,327 exoplanets and 4,500 exoplanet candidates detected, and more than 13 million objects studied.

The relevance of this mission is not only the accumulation of data on exoplanets and the probability of their being in a habitable zone with respect to their star (which feeds the much sought-after possibility of them harbouring life), but also that it confirms that in our Milky Way, there are more planets than stars, in a ratio of about 8 to 10 planets per star. It is also likely that other galaxies in the universe that are comparable in age to the Milky Way have similar ratios.

We will have to say goodbye to Kepler, but we can say hello to TESS – Transiting Exoplanet Survey Satellite (now you can make an educated guess on what main methodology for discovering exoplanets it is going to use!).

TESS is the next step forward in the identification and classification of exoplanets. It was launched in April of this year, in a Falcon 9 rocket by Space X, which will insert it into a highly stable Earth orbit in order to save fuel. It will have a nominal duration of two years, although it is likely that it can last up to ten years. 

TESS will cover an area 400 times bigger than Kepler, equivalent to 85% of space visible from Earth, monitoring around 200,000 stars, around which we expect to find approximately 20,000 new exoplanets, to be added to the nearly 4,000 that have already been confirmed.

We will have to wait to see what TESS brings us. In the meantime, we can enjoy ourselves with the exotic characteristics of some exoplanets such as:

Proxima Centauri b. The exoplanet with the highest number of social “followers”. Due to being “only” 4 light years away and within the habitable zone of its star, it has unwittingly become another media star.

2Mass J2126-8140. Its star is more than 7,000 times further away than the distance between the Earth and the Sun, making it the largest known solar system.

J1407b. It has a ring similar to that of Saturn, but 200 times bigger!

Wasp-12b. This exoplanet is so close to its star that its orbit lasts a little more than one Earth day. Due to gravity and the acceleration imposed by this proximity, it has an elongated shape instead of a spherical one, and bit by bit it is being devoured by its star.

Kepler-16b. This is a planet that orbits around two stars that orbit around each other (binary star system).

PSR B1620-26 b. This is the oldest known planet, being almost 13 billion years old (the universe is 13.8 billion years old). In addition, it orbits around a white dwarf and a pulsar.



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