Exoplanets

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: 

• The largest star ever R136A1 about 165000 light years away. It is over twice the size the scientists thought a star could have 
• For the first time revealed the effects predicted by Einstein's general relativity on the motion of a star passing closed to a black hole.
• That the young universe was much bluer than it is today and had fewer stars, 
• First direct image of an exoplanet. A five times Jupiter size planet orbiting a brown dwarf
• Earth-like planet in our closed star system Proxima Centauri b
• The discovery of TRAPPIST 1 system 
• The atmosphere around a super-Earth exoplanet called GJ 1214b, was analyzed mostly gaseous water 

ELT image credit:
ESO/L. Calçada

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

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.

Will humans ever be able to travel to the stars and colonize habitable exoplanets?
Closest habitable exoplanet Proxima Centauri b is 4.25 light-years away. The fastest spacecraft is NASA robotic spacecraft Parker Solar Probe that was launched in 2018 it has a max speed of 192 000 meters per second which is 0,0006 percent of light speed. With that speed, it will take 7000 years to reach Proxima Centauri b. We need to get to a speed at least 10 percent of light speed to reach Proxima Centauri in a reasonable time. A reasonable time is 50 years if we consider the wait dilemma. In 50 years we will be able to build space ships that can reach the target destination much faster, so it will be more beneficial to wait.
We will never reach the stars using rocket engines because we would need more fuel than it is mass in the observable universe to reach 10 percent of light speed.
The rocket equation is 
 
$$\Delta v =v_{e}\ln \frac{m+f}{n} $$
Where m is the mass of the vehicle, ve is the exhaust velocity of the rocket and f  is the mass of the fuel. If we solve f  from the rocket equation, we get:
$$f =me^{\frac{\Delta v }{v_{e}}}-m $$
If  we assume that the mass is equal to 1000 kg and exhaust velocity of 210,000 m/s which is the speed of our very best reaction engines, we get:
$$1000e^{\frac{3000}{21}}-1000 \approx 1*10^{65} $$
 Compare that with the total amount of mass in the observable universe that is  \(1.5*10^{53}\)kg. 

It would be theoretically possible to make the trip using nuclear fusion by detonating many nuclear bombs behind the spacecraft. Physicist Freeman Dyson and Ted Taylor at General Atomic worked with this idea in a project called Orion in 1958, but the Partial Test Ban Treaty of 1963 that forbid nuclear bombs in space ended the project. Another idea is to use a fusion rocket. Project Daedalus was a study conducted between 1973 and 1978 to design an unmanned interstellar spacecraft to reach Barnard's Star 5.9 light-years away. The trip was estimated to take 50 years, but the technology behind fusion rockets is complicated and we are not there yet. 

A more efficient method is to use antimatter rockets. When a subatomic particle collides with its respective antiparticle a large fraction of the rest mass is converted into energy. Depending on how much antimatter we could make it would be possible to reach a speed of 80 percent of light speed. The travelers on a ship with that speed only need to wait 3.2 years to arrive at Proxima Centauri b.
Because of time dilation from Einstein's special relativity :
$$t =\frac{t_{o}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$

$$\Rightarrow \frac{4.25}{0.8}*\sqrt{1-0.8^{2}}=3.2.$$
Antimatter is produced in many experiments at CERN, but far from the amount that is needed it takes a lot of energy and it is hard to contain. 

Credit Gerhard Janson pixabay

Another option is to travel faster than light. The Mexican theoretical physicist Miguel Alcubierre created an idea in 1994 which a spacecraft could travel at warp speed by using Albert Einstein's field equations in general relativity.
A signal in space cannot move faster than light, but the space itself can expand faster than light. The idea is that space is moving the ship just like a surfers board is moved by the water waves. This is mathematically possible, but one needs negative gravity. Negative gravity is produced by negative mass, not anti-matter which has positive gravity. Scientists have never observed negative gravity or mass, but there is nothing in the Einstein field equations that forbid it. Negative mass is equal to negative energy.  Dark energy is postulated to act in opposition to gravity and will perhaps work as negative energy. Dark energy explains why the universe is expanding at an accelerating rate and 72 percent of total energy in the universe consists of dark energy. If scientists figure out how to get this dark energy, perhaps warp drive like in Star-trek will be possible in the future.

The most promising option to travel to Proxima b is to use a solar sail read about the project here Breakthrough Starshot

It is extremely hard to get a direct image of an exoplanet because our instruments are completely blinded by the bright light from the star. For that reason exoplanets are mostly measured by indirect methods like the transit method or radial velocity or gravitational lensing. Direct imaging is the holy grail of exoplanet studies. When astronomers can study exoplanets in detail we can find out information about the planet's atmosphere and composition and even search for biosignature.

One way to solve it is to use an old technique coronagraph invented by the French astronomer Bernard Lyot in 1930 to study the sun's atmosphere. The coronagraph is a telescopic attachment that is designed to block the light from the star.

Some exoplanets have already been directly imaged by blocking the blinding light from the star. An image was taken of the multi-exoplanet system HR 8799 in September 2008. Three planets with masses of ten to seven times Jupiter were observed. The system is young 30 million years and the planets were still glowing from the formation. A fourth planet was discovered around the same system in 2010.

The very first direct image of an exoplanet was already taken in 2004 when a group of astronomers used the VLT telescope to take a picture of a planet (also this planet was several times the size of Jupiter) orbiting a brown dwarf called 2MASS J12073346-3932539 (don't forget the name).

Direct imaging has also been used on Proxima Centauri, our nearest star at 4.25 light-years away. In 2016 an Earth-like planet was discovered in the habitable zone of the system. Measurement by radial velocity in 2019 suggested that the system also has a larger planet Proxima c outside the habitable zone. The image was taken earlier this year by Raffaele Gratton and his colleagues using a VLT telescope and an instrument called SPHERE. The image has some noise and it could be a planet, but the point is brighter than expected. As the planet would not be that large if it exists. One explanation could be that the planet is surrounded by rings like Saturn but with a smaller planet and bigger rings.

One of the most recent news (May 20 2020) is that an image of an exoplanet being born around the star AB Aurigae 520 light-years from Earth has been taken by VLT using SPHERE.

Credit: ESO/Boccaletti et al.

The planet is formatting at the same distance as Neptune from the Sun.