# Exoplanets

Exploring the universe

## Earth-like planets around G-type stars

Kepler telescope was launched by NASA on 7 mars 2009 to monitoring a large number of stars in the constellations Cygnus, Lyra, and Draco. The telescope was placed in orbit around the sun. The main goal was to look for planets that were similar to Earth. The ideal Earth 2.0 will have the same size as Earth and orbiting a Sun similar as our and is in the so-called Goldilocks zone of its star, those planets could harbor life if the planet has the correct atmospheric conditions and liquid water. The thought was also by monitoring approximately 100 000 stars we will be able to get statistics on how many Earth-similar planets that orbit sun-like stars it is in our galaxy.

Kepler-22 is a star in the northern constellation of Cygnus 600 light years away. It is a sun-like G-type main-sequence star a so-called yellow dwarf. Kepler 22 is just is slightly smaller and cooler than our Sun. The first transit of a planet orbiting Kepler 22 was observed already on the third day after Kepler's service begun on 12 mars 2009. The third transit was observed on 15 December 2010. These measurements were confirmed by observations made by the Spitzer telescope and from Earth-based telescopes. On 5 December 2011, the announcement about the first potentially habitable exoplanet has been discovered was released.

Kepler 22 b is more than twice the size of Earth it has a radius of 2.35 times Earth's radius and 20 times more massive. As gravity is proportional to the mass of the planet divided with radius squared.

$$g\propto \frac{1}{r^{2}}\Rightarrow \frac{20.36}{2.35^{2}} =3.68$$

It will have about 3.6 times the gravity than Earth. Kepler 22 b has a similar orbit as Earth a year on Kepler 22 b, is 290 days long. Kepler 22 b is a so-called Super Earth. It could have oceans but it could have an environment that is closer to Neptune.

Image credit: NASA/Ames/JPL-Caltech

The first-ever exoplanet found around a G2V star as our sun and at the same distance from its star as Earth is Kepler-452b. The planet is often quoted Earth 2.0 or Earth’s cousin. It is 1.63 times larger in radius than Earth and is 4.7 times more massive than Earth. The planet is a Super-earth. There are also indications that the planet has water on the surface, which increase the possibility of life. A year on Kepler-452b is 380 days long just 15 days longer than Earth. The planet is about 1,400 light-years away from the Solar System. The star 1.4 billion years older than the Sun so the aliens there should have a much longer time than us to evolve their civilization. As the planet has twice the gravity than Earth the aliens would be twice as strong as we are.

$$g\propto \frac{1}{r^{2}}\Rightarrow \frac{4.7}{1.63^{2}} =1.77$$

The planet was discovered on 23 July in 2015 by the Kepler telescope.

The closest star that has exoplanets and that is similar to our own Sun (G-type star) is called Tau Ceti it is only just 12 light years away. Tau Ceti mass is 78 percent of our Sun. Tau Ceti has 7 confirmed exoplanets. Tau Ceti e is on the inner border to the habitable zone where it might be too hot and Tau Ceti f is on the outer border to the habitable zone where it might be too cold, but it is still a very interesting object with high Earth similarity index.

The farthest potentially habitable exoplanet discovered is Kepler-1638 b at approximately 2,900 light-years from Earth and it orbits a G-type star. With similar size and age as our Sun. Kepler-1638 b has a mass 8 times earth and its radius is 1.87 times Earth radius and 2.26 times the gravity

$$\frac{8}{1.87^{2}} =2.28$$

it was discovered in 2016. Two similar planets were also discovered the same year Kepler-1606 b and Kepler-1090 b

These are all the potentially habitable planets that been discovered around G-type stars so far and Kepler-452 b is the most Earth-like planet discovered yet. Planets that have the same size as Earth has been discovered around red dwarfs stars, but those stars could have dangerous for life radiation and their planets have tidally locked orbits. The new space telescope TESS will now continue the search for Earth 2.0 now when the Kepler telescope has retired.

Kepler-1638 b Kepler-1606 b Kepler-1090 b Kepler-452 b tau Cet e tau Cet f Kepler 22 b

## The Weird! signal

Arecibo Observatory in Puerto Rico is a very large radio telescope build inside an abandoned sinkhole in May 2017 the telescope was looking for exoplanets around red dwarfs. A red dwarf is much smaller than our Sun and small earth size objects are easier to spot around small dim stars. These are so-called quiet stars its ultraviolet radiation would not strap the potential orbiting exoplanets from its life-supporting atmosphere. The stars that were examined was Ross 128, Gliese 398, Gliese 436, Wolf 359, HD 95735, BD +202465, and K2-18). The telescope detected a new kind of signal never seen before from Ross 128, 11 light-years from Earth. The signal lasted for around 10 min and was in frequencies between 4.6 and 4.8 GHz. The uniqueness of this signal gave rise to some speculation it could be alien in origin.

The Arecibo scientists worked with researchers from the SETI Institute reach and ruled out that the signal is from an alien civilization. It was probably coming from our own satellites It would explain why the signals have the same frequencies interval as our satellites, and Ross 128 was close to the celestial equator where many of the satellites are stationed. Astronomers call this the Weird! signal in honor of the Wow! signal from 1977 that still remains as one of the strongest candidates for alien transmission. The PHL also conducted a survey with almost 800 participants to find out what people thought was causing the Weird! Signal. The Weird! Signal was never heard of again.

Here is the press release at PHL about the Weird! Signal /press-releases/theweirdsignal

Credit: ESO/M. Kornmesser

An exoplanet orbiting Ross 128 was discovered in July 2017 by the HARPS instrument at the La Silla Observatory in Chile using the radial velocity method. Its existence was confirmed on 15 November 2017 and was given the name Ross 128 b. The planet is in the habitable zone of its star in the so-called Goldilocks zone. Ross 128 b is one the best candidate for a potentially habitable exoplanet confirmed so far. It has the mass 1.35 of Earth. If it has an atmosphere and if it has the right chemical balance for life it could be an earth 2.0. That is not proven it could have the same condition as Venus depending on the greenhouse effect. Ross 128 b is just like Trappist-1 planets and Proxima b tidally locked in its orbit around the star. Eternal night on one side and eternal day on one side. Its year is only 9.9 days long. As Ross 128 is twice the age of our Sun the potential aliens of that planet would have billions of years more than us to evolve their civilization.

Visit Ross 128 b here: Ross 128

Ross 128 b

## Can Exoplanets have habitable moons

Titan that is the largest moon of Saturn is the only moon in our solar system that has a dense atmosphere. Titan is also the only object in our solar system except for earth that has liquids on the surface. Titan has just like earth a landscape with rivers and lakes it has a variating climate with wind and rain. The river and lakes are liquid methane and the atmosphere consists of nitrogen. The average surface temperature in -179 C or -290 F. Not even the most resistant living organisms that are known on Earth would ever survive on Titan and many scientists find it very unlikely that life could exist on Titan. However, it would not be theoretically impossible for life on Titan. Perhaps organisms that been developed on Titan differs from the one developed on Earth. Perhaps those lifeforms like freezing liquid methane just like we like water. Huygens probe that landed successfully on Titan in 2005 was not equipped to provide evidence for biosignatures. More probes to investigate Saturn’s moons has been proposed in the future, though.

credit  NASA/JPL-Caltech

In our solar system, the inner planets are terrestrial and the outer planets are gas giants and according to the theory of solar system formation, massive Jovians can only form in the cold outer regions of the system.

But still, it is very common that exosolar systems have so-called hot Jovians. A hot jovian is a gas giant that is orbiting close to its sun. The first one orbiting a sun-like star was discovered In 1995 by Michel Mayor and Didier Queloz around the star 51 Pegasi. One explanation could be that young large Jovians formed in the outer regions of their solar system gains enough gravitational force that it reduces the planet's orbital energy causing the planet to migrate inward. 827 hot Jovians and 139 warm Jovians have been discovered so far. If a jovian is in the habitable zone of its star it could have moons. Just like Titan the moon could have atmosphere and oceans and those oceans could be water instead of methane and the temperature could be similar to earth. Perhaps an alien civilization exists on a moon instead of a planet. The science fiction movie Avatar from 2009 takes place on the moon Pandora orbiting the gas giant Polyphemus in the Alpha Centauri A system. Alpha Centauri A does look like a pleasant home for exoplanets the star emits far less radiation than our sun, but no one is found so far.

We have not discovered any Exomoons yet because as those are very hard to detect and confirm using current techniques. In July 2017 Hubble Space Telescope found signs of a Neptune-sized exomoon around the planet Kepler-1625b. Theoretical it could be possible with James Webb Space Telescope in the future to detect images of exomoons. Some scientists estimate that there are as many habitable exomoons as habitable exoplanets. There are several candidates with possible habitable exomoons in the PHL exoplanet catalog. It is possible both in the Android app and in this website catalog to filter for candidates with possible habitable exomoons.

Kepler-1625 b 51 Peg b Saturn

## Next generation space telescopes

Transiting Exoplanet Survey Satellite

A new telescope orbit our planet TESS and the old telescope Kepler has retired. TESS stands for Transiting Exoplanet Survey Satellite. TESS is designed to search for Exoplanets using the transit method and cover a 400 times larger area than Kepler telescope. I followed the launch online first it was planned to launch Monday 16 April 2018, but the weather conditions were not perfect so we had to wait until Wednesday 18 April 2018. TESS was launched from Cape Canaveral Air Force Station in Florida with SpaceX Falcon 9 rocket. SpaceX is a company run by the entrepreneur Elon Musk that also is famous for Tesla electric cars and Paypal.

The Kepler mission was launched on March 7, 2009, and ended on October 30, 2018, in that time it observed 530 506 stars and detected 2 662 planets. Kepler has a heliocentric orbit, which means that it is not orbiting the earth it orbiting the sun. The Kepler search range was between the constellations Cygnus and Lyra as you can see in our starmap that region has the most exoplanets

Credits: NASA's Goddard Space Flight Center/Chris Meaney

TESS has a unique elliptical orbit around the earth. TESS measure the star's brightness over time. When an exoplanet is transiting its star a small increase in the brightness occur. This data is sent back to earth at 10 billion pixels at the time. This data is washed using complex algorithms. The data is then analyzed using machine learning algorithms that find patterns matching a transit of a planet. The data should also be analyzed by humans that can detect patterns in the image that a machine might miss.

It is possible to volunteer on the research by registering on Zooniverse, perhaps you will discover an exoplanet. Hundreds of exoplanets have been discovered by volunteers during the Kepler mission.

Project can be found here: zooniverse.org

The James Webb Space Telescope

The Hubble Space Telescope that was launched in a low Earth orbit already in 1990 and has made discoveries that have increased our knowledge about the universe in three decades. Its successor, the James Webb Space Telescope (JWST), is currently scheduled to be launched in March 2021. JWST will be hundreds of times more powerful than the Hubble telescope. Its primary mirror is made of gold-coated beryllium and contains 18 hexagonal mirror segments.

James Webb will just like Kepler orbiting the sun on a far distance (1 500 000 km) from the Earth. In the so-called Lagrange point. The point in space where the Sun and Earth's gravitational fields take out each other and that will give the telescope the same orbit velocity as Earth. That will make the telescopes position in space stationery in relation to Earth. It is an IR-telescope that mean that it will register infrared radiation. Infrared is electromagnetic radiation with a longer wavelength than red visible light from 700 nm to 1 mm. Cold objects like brown dwarfs and exoplanets primary transmit infrared radiation and will be easier to investigate. This will also make objects far away from the young universe easier to investigate, the expansion of the universe makes the light increase in wavelength because of the Doppler effect it is known as redshift

The telescope is named after James E Webb. He run the space agency from 1961-1968 during the Apollo program. Even he was not scientist he did more for science than any other governmental official. He believed that the space agency had strike a balance between human spaceflight and science.

JWST will look closer at the exoplanets that TESS will discover. It will also study the light from the young universe approximately 400 million years after the big bang.

Article about next generation land based telescopes can be found here: Very Large Telescopes and Extremely Large Telescopes

## The hunt for Planet X

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

• Ceres was discovered in 1801 in the asteroid belt between Mars and Jupiter. Ceres was for decades considered being a Planet, but was downgraded to be an asteroid (Déjà vu anyone?), now it has been upgraded to be a dwarf planet. Ceres has a diameter of 946 km and is at a distance of 2.77 from the Sun
• Pluto at a distance 39.48 AU from Sun
• Haumea was discovered in 2004 and named after the Hawaiian goddess of childbirth Haumea has a diameter of 1 632 km at a distance 43.13 AU from Sun
• Makemake was discovered in 2005 and has a diameter of 1 430 km at a distance 45.79 AU from Sun
• Eris at a distance 67.67 AU from Sun

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.