# Exoplanets

Exploring the universe

## K2-18 b a water world

K2-18, also known as EPIC 201912552, is a red dwarf star located 124 light-years from Earth, in the constellation of Leo.
Visit the planet here K2-18 b

The star has an Exoplanet K2-18 b in its so-called goldilocks zone. The planet that was discovered by the Kepler telescope in 2015 is 8 times more massive than Earth and has a 33 days orbit.
It is the first Super earth exoplanet in the habitable zone of its star where we have been able to discover water in its atmosphere. Water has previously been discovered on Jovians outside the habitable zone of its star. See our previous article: Atmosphere on exoplanets

The measurements were done with the Hubble telescope and were confirmed by two separate analyses by researchers at Université de Montréal and University College London (UCL) The result was published just a month ago on September 2019. This is very exciting news K2-18 b is cool enough to have liquid water and models suggest that its atmosphere has sufficient pressure that will form clouds and have rainfall just like earth. But some analysis suggests that planets this size could lack solid surface and could be more similar to Neptune than earth. It is not possible from the Hubble data to see how much water there is in the atmosphere.

Credit:AP/M. Kornmesser/ESA/Hubbl­e

K2-18 b is now expected to be observed with the James Webb Space Telescope that will be launched and for the ARIEL space telescope which mission is to study the atmospheres of Exoplanets in great details that will be launched in 2028. These telescopes have the instruments to look for gases in the planet's atmosphere that could only be produced by living organisms. It would be hard to imagine any human-like creatures would be able to live in that environment but may be possible for microorganisms. Even if there is no sign of life. The atmosphere on K2-18 b will tell us a lot about how planets in the habitable zone are formed around red dwarf stars

K2-18 b

## Will we ever be able to travel to the stars

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 that 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 are 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

Proxima Cen b Alcubierre drive

## Atmosphere on exoplanets

The chemical composition of an exoplanet atmosphere can tell us much about conditions on the planet and if it is potentially life bearing. Many planets it's discovered using the transit method. When a planet passes in front of its star a small drop of light will occur. By looking at the transit with different wavelength of the light scientists can find out the chemical composition of the atmosphere. Let's say if the planet does not have an atmosphere all colors (wavelengths) of the light will be blocked equally at the transit. But if the planet does have an atmosphere some atoms will absorb light better at certain wavelengths making the light not equally blocked. If the depth of the blocked light from the star is larger when being looked at a certain color with a spectrograph then the atmosphere will contain the element that is absorbing that color. This method is called transmission spectroscopy and to be able to find molecules like water scientist need to look at the longer wavelength in the infrared spectrum. Most of the discoveries of atmospheres are of hot Jupiters or hot Neptunes as the heated atoms or molecules will absorb light better at high temperatures.

The first detection of an atmosphere around an exoplanet was in 2001 when sodium was detected on the hot Jovian named HD 209458 b that is also known under the nickname Osiris.
Osiris that is located in the constellation Pegasus 159 light-years from us is known for several first discoveries in exoplanet research.
It was the first transiting exoplanet and the first planet to have its orbital speed and mass measured. The planet has an evaporating hydrogen atmosphere and containing oxygen and carbon. In 2013 water vapor was detected in the atmosphere of Osiris and several other hot Jovians like  XO-1b, WASP-12b, WASP-17b, and WASP-19b. Water vapor was also reported on  HAT-P-11 b in September 2014. HAT-P-11b is a Neptune sized exoplanet and that was also the first time any molecules was discovered on such a small planet.

In February 2016, it was announced that Hubble Space Telescope had detected hydrogen and helium in the atmosphere of 55 Cancri e. 55 Cancri e is a super-Earth exoplanet with a diameter just twice as Earth. 55 Cancri e is a very hot planet with an average temperature of 2,300 °C on the dayside. No water vapor was discovered on the planet. In 2018 iron and titanium was found in the atmosphere of a super-hot Jovian Kelt-9 b

The most recent discovery of an atmosphere was on GJ 3470 b. It is a Super-Earth about 14 earth masses. But it’s atmosphere contains hydrogen and helium and seems to lack heavier elements like methane and ammonia.

HD 209458 b XO-1 b WASP-12 b WASP-17 b WASP-19 b HAT-P-11 b GJ 3470 b KELT-9 b 55 Cnc e

## Teegarden two new Earth like exoplanets has been discovered

Teegarden star that is a very faint M-type red dwarf star was discovered in 2003 and was named after Bonnard Teegarden that was working at NASA's Goddard Space Flight Center

The star is 12.5 light years away and has a mass of 0.08 solar masses and luminosity of 0.00073 of our sun. The parallax was initially measured wrong and gave it a distance of only 7.5 light years away that would be the third nearest star after Alpha Centauri and Bernard star. Teegarden is now ranked the 24th nearest star system. Observations by the ROPS survey in 2010 showed variation in the radial velocity of the star suggesting it has a planetary system.
CARMENES that stands for "Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs” at the Calar Alto Observatory announced evidence of two Earth-mass exoplanets orbiting the star within its habitable zone.

The news was announced a couple of days ago on June 18, 2019. The two planets have high earth similarity index and are located within its star habitable zone. Teegarden b is located in the optimistic habitable zone and Teegarden c is in the conservative zone. No transits of the planets have yet been seen by our astronomers. But because of the cosmic geometry, any alien astronomers living on Teegarden planets could use the transit method to discover Earth as we orbiting just in the right angle from their point of view. Teegarden b has the highest chance of having temperate surface environment.  However, as the planets are orbiting a red dwarf star their orbits are tidally locked and stellar activity from the star could be dangerous for life.

Here is a simulation of the solar system in our app here: Teegarden

Teegarden b Teegarden c

## European space agency upcoming exoplanet hunters

A new computer algorithm called Transit least squares has been tested on the old Kepler data. It resulted in the discovery of 18 Earth-sized exoplanets. Most of them are not good candidates for life as they are orbiting too close to their stars. But one of the new planets is in the habitable zone of its star. The planet is called EPIC 201238110.02 and is located on a distance at 522 light years from Earth.
Astronomers should now be able to find at least another 100 Earth-sized planets in the data from the Kepler mission with this method. Next generation land-based telescopes and space telescopes will also benefit from these algorithms in their search for Earth-like planets. This also bodes well for the upcoming missions planned by ESA.

When a planet transiting it star a small drop in brightness over time occur

Credit: NASA Ames

European space agency ESA is developing three space telescopes that will be used to study exoplanets. CHEOPS (CHaracterising ExOPlanets Satellite) and PLAnetary Transits and Oscillations of stars (PLATO) and Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL).

Cheops
Cheops will be measuring the size of known transiting exoplanets, and that data will be compared with ELT observations to find rocky planets like earth. It will lift off at Europe's spaceport in Kourou, located in in the northeast of South America in French Guiana, between 15 October to 14 November 2019. The mission will have a duration of 3.5 years It will be placed at low-Earth orbit at an altitude of 700 km. In a competition children between the age of 8 and 14 from several countries submitted drawings related to exoplanets. Of 8000 drawings 2700 drawings were selected to be engraved on two titanium plaques that will be placed on the telescope, see all the drawings here: childrens drawings

Plato
Plato will be a follow-up mission to the very successful Kepler it will search for planetary transits around one million stars. Plato will be focusing on Earth-like planets in the habitable zone around other G-type stars. It will carry 34 telescopes operating in the visible spectrum. Its observations will determine the age, orbit, and composition with the goal to establish if an Earth-like exoplanet has an atmosphere. A knowledge that could be used for more detailed categorization like scanning for biomarkers. The project is scheduled for launch in 2026 and has a 4 years mission duration. Just like James Webb and Kepler, it will be orbiting the sun in the so-called Lagrange point.

Ariel
Plato will be followed by Ariel, scheduled for launch in 2028. Ariel will study the atmospheres in great details of a sample 1000 exoplanets. Ariel will just like Plato orbiting the sun in the so-called Lagrange point.

EPIC 201238110.02 Plato Cheops Ariel