When I was a little kid, I was very interested in the planets of our solar system, at that time no exoplanets had been discovered yet. I had memorized the order and the name of the nine planets. Mercury, Venus, Tellus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
Wait now there are only eight planets in our solar system. Is what I learned as a kid no longer correct? Yes Pluto is no longer considered a planet by science it is a dwarf planet. But astronomers still thinks there is a ninth planet out there somewhere.
Urbain Le Verrier was an nineteenth-century mathematician and physicist that with help of Newtonian mechanics made calculations on Uranus orbit to predict the position of the undiscovered planet Neptune. Later observations of Neptune's orbit led to the speculations that it is another undiscovered planet outside Neptune.
Pluto and Charon Courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Percival Lowell was a businessman. He founded the Lowell Observatory in flagstaff, Arizona in the beginning of the twentieth century. He started a project of finding the mysterious ninth planet that was given the code name Planet X. In 1930 the planet (sorry the dwarf planet) Pluto was discovered by Clyde Tombaugh. From the outside of the Neptune orbit and 20 AU (1 AU is the distance between Earth and Sun) out in space is the region called the Kuiper Belt. Kuiper Belt is an asteroid belt that probably has over 70 000 object with a diameter of 100 kilometers. Outside this belt the whole solar system is surrounded by Oort's cloud the origin of comets. Pluto was the first Kuiper belt object to be discovered. Pluto has a diameter 2 377 kilometers comparing with the moon 3 474 kilometers and the smallest planet Mercury has an diameter of 4 879 km. For almost 50 years Pluto was thought to be larger than Mercury, it was first when detecting Pluto's moon Charon in 1978 that it was possible to measure Pluto's mass.
in 1987 the Astronomer David Jewitt encouraged Jane Luu that was graduate student at the time to look for objects outside Pluto with the words "If we don't, nobody will." They discovered after five years work in 1992 several larger object in the Kuiper Belt that confirmed that there is an asteroid belt in that region. In 2003 the dwarf planet Sedna was discovered at 80 AU three times as far as Neptune from Sun. Sedna has a diameter of 995 km. In 2005 Eris (first know as Xena) was discovered Eris has a diameter of 2 326 km which is almost the same size as Pluto, but Eris is more massive than Pluto and many astronomers considered Eris as the tenth planet in our solar system. International Astronomical Union come to another conclusion in 2006 and downgraded Pluto to not be an planet.
Following five objects in our solar system has been classified as dwarf planets by IAU so far
Estimates suggest that it will be hundreds of dwarf planets in the Kuiper belt. The objects found so far has strange orbits. Mathematical models has shown that these orbits could be explained if there is an undiscovered planet which gravity is effecting these objects. The hypothetical planet that have a mass about 10 times that of Earth and orbit about 600 AU from Sun. The planet is thought to be gaseous or it could be rocky a so called super earth. It may take between 10 000 and 20 000 years for the planet to make one full orbit around the Sun.
The search for Planet X has intensified and has led to more recent discoveries that give more proof that the planet actually is out there. One of the big announcements in astronomy this year October 2018 was the discovery of the dwarf planet nicknamed goblin. Goblin is as far out as 80 AU from the Sun but when it is at the most distant point in the orbit, it will be 2 300 AU from the Sun, which would be what was predicted if Planet X is out there. Goblin is a smaller object 300 km diameter. Also recently a new Object was announced on 17 december 2018 under the nickname Farout. The object is 120 AU from the Sun. The search for Planet X continues and hopefully our solar system soon has nine Planets again.
Where are they? That question asked the famous physicist and genius Enrico Fermi during a discussion with his colleagues when having a lunch break from their daily work with developing the nuclear bomb at Los Alamos National Laboratory in 1950.
There are billions of stars in the milky way that are similar to our sun and many of them are billions of years older than our sun.
Some of these stars should with high probability have Earth-like planets and some may have civilizations with more advanced technology than us. Should not this life has been able to spread all over the galaxy at this time? So why can we not see any trace of aliens here? This paradox is called Fermi's paradox. Some popular explanations to the paradox are:
Image Credit: The digital artist
Search for extraterrestrial intelligence SETI is a term for scientific searches for intelligent extraterrestrial life. And several SETI program and initiatives have in decades been monitoring space in search for signals from other civilizations on exoplanets.
In the previous article, I wrote about Breakthrough Starshot that is founded by Russian billionaire Yuri Milner. He also found the project called Breakthrough Listen that are using large radio telescopes for listening for signals. One of the founders of SETI is the American astronomer and astrophysicist Frank Drake.
Frank Drake is well known for the equation from 1961 that bears his name. Drake’s Equation is a probabilistic equation that could be used to estimate the number of active communicative extraterrestrial civilizations in our galaxy.
The Drake equation is: N=R* fp ne fl fi fc L
N = number of advanced technological civilizations that could communicate
R* = The yearly rate of formation of stars suitable for developing life in our galaxy
fp = The fraction that has exoplanets
ne = The average number of habitable planets per planet system
fl =The fraction that will develop life
fi = The fraction that will develop intelligent life
fc = The fraction that will develop advanced technological civilizations
L = The average life length of advanced technological civilization
We cannot use Drake's equation to make estimates. Because we don’t have enough data/knowledge yet to give any values or really good guesses for these terms.
The rate of star formation is not a constant over time. When the universe was younger stars where being format at a higher rate. Today we could estimate R* to between 5-20 new stars per year in the Milky Way. We have when this article is written discovered 3875 exoplanets and that 55 could be habitable.
Even our closest star has exoplanets. Which give a higher estimate for fp and n e We don’t know anything about fl the only thing we know that is that life has developed on earth. If we find organisms on other celestial bodies in our solar- system like Mars or Jupiter/Saturn's moons it would indicate that life could be common on other solar systems.
Check out our interactive star map that shows the discovered exoplanets that have an earth-similarity index bigger than 0.7 and could possibly support life.
Our closest star is Alpha Centauri is just 4.37 light-years away. Alpha Centauri is not just a star it is a solar system that contains three stars Rigil Kentaurus, Toliman and Proxima Centauri. Rigil Kentaurus is just like our sun a spectral class type G star. Toliman is a class K star orange to red color. Together they form a binary star system, Proxima Centauri is a small and faint red dwarf and is closest to our sun. Proxima Centauri has an Earth-like exoplanet in the habitable zone Proxima Centauri b. The planet was discovered in August 2016 by ESO Very large telescopes. It was discovered by the wobble method. Just like other planets orbiting red dwarfs Proxima b is tidily looked. It is the eternal day on one side of the planet and night on the other side. The planet does not transit its star and that makes it difficult to get any reliable information about the planet atmosphere and composition. But there is a chance that the planet has an ocean and an atmosphere. Red dwarfs are known to have deadly radiation that could have a negative effect on life.
As the star is just around the corner 4.2 light-years away could we travel to the planet and look for aliens? The New Horizons probe, which lifted off in 2006 on a mission to Pluto and the Kuiper Belt moves at a speed of 84000 km / h it will only take us 54 thousand years to reach Proxima b at that speed.
A research and engineering project using solar sail will be capable of making that journey in just twenty-five years. So how does solar sail works? The sails are being pushed by the massless particles in light called photons. Due to the wave-particle duality of quantum particles, light could be described both as particles and waves and particles have momentum. Even though a photon has zero rest mass, it has energy. This could be derived from the relativistic equation E2 = (mc2)2 +(pc)2 if the mass is zero then E = pc. Most people would recognize the equation where the momentum is zero as Einsteins most famous equation E = mc2
The photoelectric effect that Einstein got his Nobel prize for in 1921 is also based on this phenomena. Where light shining on some material it will cause emission electrons. This effect is proportional to the frequency of the light f=c/λ.
Where the energy is E=hc/λ and the momentum p =h/λ, where λ is the wavelength of the light and h is a universal constant called Planck's constant 6.62607004 × 10-34 m2 kg / s and c the speed of light in a vacuum.
By using very tiny nano craft that just weights a gram and the sails would be four meters wide but just a couple 100 atoms thick. By then using high energy lasers blasting a 100-gigawatt beam on one solar sail from earth could accelerate the craft up to 20% of light speed within an hour. In space, there is no friction so the craft will keep its speed for the rest of the journey to Proxima b
Breakthrough Starshot initiative is planning to send hundreds or even thousands of nano crafts. The technology is not developed yet and it is very difficult to make the sails hold. Russian billionaire Yuri Milner and other investors have paid $100 million to cover the first 10 years of development. So it is not just science fiction it could be possible in a near future.
All data in this application comes from PHL's Exoplanets Catalog
Just now the in the Atacama desert, on the top of the mountain Cerro Armazones, north Chile. A new generation of land-based optical telescopes is being built.
It is built by the European Southern Observatory ESO that is a European astronomic organization with several telescopes already located on the southern hemisphere.
In north Chile they already have this generation optical telescopes in operation called Very Large Telescopes VLT. The new generation telescopes will be operational in 2024 and it is called Extremely Large Telescopes ELT. Astronomers imagination is not the best when it comes to the naming of their gadgets, but rest assured that these gadgets will live up to their name.
So how much better will ELT be than VLT?
Will we be able to make new discoveries about the universe?
Will we be able to find new Earth-like exoplanets with these telescopes?
VLT consist of four large telescopes width a diameter of 8.2 meters. The telescopes are located in a formation. They can work both independently and together. The total mirror surface has a diameter of a 16-meter telescope when they are coordinated. VLT is the largest Telescopes on earth.
Some important discoveries made by VLT telescopes so far has been:
ELT image credit:
ELT is an optical reflector telescope. The primary mirror will be 39.3 m in diameter composed of 798 hexagonal segments. The mirror will have a light absorption area of 978 m². Above this huge reflector, there is also a 4.2-meter diameter secondary mirror.
ELT will be much larger than VLT, it will gather 13 times more light. ELT will be able to correct for atmospheric distortions. The telescope will be able to take from earth 16 times sharper images than the Hubble Telescope that is in space.
Consider the impressive resume of VLT and Hubble we will have many existing reports about discoveries when ELT gets fully operational.
The main task of ELT will be to look for an exoplanet. By measurements of the wobbling movements, stars show because planets orbit around them, but also take direct images of large Jovians. Perhaps it will be possible for the telescope to characterize the atmospheres of the planets, and to take direct images of planets of Earth's size.
Read more at ESO