Exploring the universe

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.

Where are they?

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: 

  • When civilizations envolve enough advanced technology the inhabitants could create a kind of virtual reality and no longer care about the actual reality. 
  • We won the lottery. The probability of life developing and last so long is so low that it only happened once, on earth.  
  • Civilizations destroy them self before they invent interstellar space travel. By war or by environmental pollution or natural disasters.
  •  Aliens are too different from humans perhaps they see us as to primitive species and does not contact us to avoid interfering with our natural development   
  • The civilization on Earth has not been around long. We started transmitting radio waves in 1906 to short of a timespan to extraterrestrial to notice us. And we have not been looking enough for signals in space to notice them.

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* fnfffL  
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 fand 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.

Breakthrough Starshot

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.


Proxima Cen b

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