In our solar system the shortest-lived planet ever known to exist in the universe existed until recently..... A planet that appeared and disappeared in just 76 years.
Well... it all depends on how you look at planetary classification. If you're older than 30, you'll remember that Pluto became the ninth planet in our solar system after its discovery in 1930, but that it ceased to be so when in 2006 the International Astronomical Union withdrew that title because it did not meet the minimum requirements for a planet. It then became just one of thousands of objects orbiting our star.
We know that there are millions of planets beyond our Solar System, but current technology does not allow us to verify the existence of more than a few thousand.
Similarly, you may also recall that until relatively recently the only planets that existed outside our solar system were those in science fiction films.
Officially, the first confirmation of a planet detected outside our solar system was in 1992, and since then we have found more and more exoplanets, reaching the current figure of almost 4,000 planets confirmed and catalogued. Only in the last 25 years have we been able to state with certainty that they exist, and the term exoplanet has been coined for them.
In the last 25 years, a real revolution has taken place in increasing our knowledge about these celestial bodies. Our eagerness to know more and more about these planets is unstoppable and is fuelled by our human need to be curious, especially when it comes to finding life outside our planet.
There are many ways to detect exoplanets, but the two most common are indirect methods: the transit method, which allows the diameter of the planet to be calculated by means of the decrease in luminous intensity of its star as it orbits just in front of it; or the radial velocity method, which makes it possible to calculate the mass of the planet by means of the interference it produces with the mass of its star, since its remoteness and lack of its own light make it unlikely to be detected and observed directly.
The transit method requires that the planet passes in front of its star and is therefore aligned with the plane of view of the observer, making it undetectable in 90% of cases. Nevertheless, while the radial velocity method has allowed us to detect 677 planets, the transit method has allowed us to discover 2,951. But this only means that we have missed 90% of planets by this method and that there is still a lot more to look for.
It has just been announced that one of the tools that has contributed the most records to the exoplanet catalogue so far will soon be completed. It is the Kepler mission (part of NASA's Discovery programme), which in 2009 put into orbit around the Sun the first satellite capable of the specific activity of finding exoplanets the size of our Earth in habitable environments.
The Kepler satellite was launched with an estimated working life of 3.5 years and, therefore, its mission should have ended in 2012. But as with almost all missions where the spacecraft is not expected to be recovered, it was decided to continue the mission as long as the satellite responded, and so far it has, after two of its four reactive gyroscopes have failed and it is estimated that it has practically run out of fuel (because no... it does not have a remaining hydrazine gauge).
The first nominal working phase of 3.5 years is called the Kepler mission, but from then on it is called K2. This new phase has been opened in its configuration to the observing community, where all formal proposals submitted to NASA are open for consideration. The seventh (and possibly last) cycle of the phase K2 will open in just one week (16 August 2018). So you know, there's still time. If you want to show off this summer, prepare a project and find your own exoplanet!
To the credit of the Kepler mission so far, an extraordinary 2,327 exoplanets, 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 therefore fuels the long-sought possibility of life), but it also confirms that there are more planets than stars in our Milky Way galaxy at a ratio of about 8 to 10 planets per star. and that it is quite likely that in the rest of the galaxies in the universe with ages similar to ours, this ratio is very similar.
We'll have to say goodbye to Kepler, but we say hello to TESS - Transitioning Exoplanet Survey Satellite (you now know which main methodology this satellite will use to discover exoplanets).
TESS is the next step forward in the identification and classification of exoplanets. It was just launched in April this year on a Space X Falcon 9 rocket, which will inject it into a highly stable, fuel-saving Earth orbit and will have a nominal lifetime of two years, although it is likely to last up to ten.
TESS will cover an area 400 times larger than Kepler's and equivalent to 85% of space visible from Earth, monitoring some 200,000 stars in which approximately 20,000 new exoplanets are expected to be found to add to the nearly 4,000 already known.
We will wait to see what TESS brings us and, in the meantime, we can delight ourselves with exoplanets of such curious characteristics as:
Proxima b. It is the exoplanet with the most social "followers". Being "only" 4 light years away and within the habitable zone of its star, it has unwittingly become another media star.
2Mass J2126. Its star is more than 7,000 times the distance between the Earth and the Sun, making it the largest known solar system.
J1407b. It has a ring similar to Saturn's, but 200 times larger.
Wasp 12b. This exoplanet is so close to its star that it has an orbit of little more than a day. Due to the gravity and accelerations exerted by this proximity it has an oblong rather than a spherical shape and is slowly being devoured by its star.
Kepler 16b. It is a planet orbiting two stars orbiting each other (binary star system).
PSR B 1620-26b. It is the oldest known planet at nearly 13 billion years old (the universe is 13.8 billion years old) and orbits a white dwarf and a pulsar.
