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When I was a kid, I was hoping that there are other planets in the universe beyond our solar system. But no planets were detected around other stars until the January 9th, 1992 when the first discovery of two planets orbiting the Pulsar type star PSR 1257+12 was announced by two radio astronomers- Aleksander Wolszczan and Dale Frail. The discovery was confirmed, and it is now in history as the first detection of the exoplanet outside our solar system.
The era of hunting the exoplanets have started, and many methods were developed to help detect another alien world in our galaxy. Since then, thousands of exoplanets were confirmed using different detection methods. You may ask how scientists find planets outside our solar system? There are a few methods of how they do it. But if you are interested only in how you can help with the detection of exoplanets, you can skip to the end of this article to find out.
Methods of Detecting Exoplanets
There are two main categories of methods for how scientists find planets. There are direct methods where we directly observe the exoplanets near the stars with the telescope. It is extremely tough to do, but possible with big ground telescopes or telescopes in space.
And the second, more popular, are indirect methods, which means that we have to collect and analyze different data from the star and determine if the data show us the presence of the exoplanet.
Direct Imaging Method To Detect Exoplanets
The issue with the direct imaging method is that the planets are very faint, and the stars are too bright. So it is hard to see any planets around the stars only by pointing the telescope at it. However, we have direct images of the exoplanets, and the first one was released in 2004.
The image was taken by Very Large Telescope array (VLT), and it is a composite image of brown dwarf 2M1207 and his planet 2M1207b. This star is 230 light-years away from us. It is the first image of the exoplanet and the first discovery of an exoplanet orbiting a brown dwarf. The planet is 5 times more massive than Jupiter. The system is young, so the planet is still glowing hot, which makes it appears brighter in the infrared spectrum. The brown dwarf is a low mass star, so the conditions were ideal for photographing this system.
We photographed many other exoplanets since then. Mostly, big gas giants that are larger than Jupiter. The method that scientists use to image the exoplanets around the stars is called the coronograph method. Coronograph is using a mask called an occulting disk that is in the telescope, and it is blocking out the light from the star. In this case, you see only the corona of the star, so that’s why it’s called coronograph. By blocking the light from the star, we are able to see faint planets orbiting the star. It is very similar to the Solar eclipse when the moon is blocking light from the Sun, and you see only the thin disk of light around the moon.
But there is still a problem for ground telescopes because of the Earths atmosphere, which basically means that discoveries with this method are limited even with the advanced adaptive optics. Adaptive optics are compensating for the light distortion traveling through the atmosphere, but it is not ideal. The best way is to have a telescope on the Earth’s orbit.
StarShade Exoplanet Mission
Starshade is a proposed mission by NASA to launch a space telescope with large occulter flying in formation. This flower shaped occulter will be able to position itself between the targeted star and the space telescope blocking the light of that star allowing the telescope to see exoplanets. Something like huge coronograph in space. This mission will enable to directly image Earth-like planets, which is impossible to do for us now from the ground telescopes.
Observing Exoplanets With Optical Interferometry
Even with the challenges to observe the exoplanets with a ground-based telescope, the scientists have still one trick up the sleeve. It is called optical interferometry. In March of 2019, the ESO (European Southern Observatory) announced a successful observing of the exoplanet HR8799e with VLT using optical interferometry. HR8799e is one of the few exoplanets where the movement was confirmed by direct imaging.
Optical interferometry is a method of combining data from multiple different telescopes to achieve better resolution of the observed object. Four separate telescopes of the VLT array in Chile were used to observe this exoplanet. The same technique was used to make the first photograph of the black hole in the center of the M878 galaxy by using a network of radio telescopes around the world.
Optical interferometry will allow us to collect more information about exoplanets, especially about their atmospheres.
Indirect Methods To Detect Exoplanets
The direct methods to detect exoplanets are exciting, but the indirect methods are still more efficient, and we have found many more exoplanets using them. Also, indirect methods allow even amateur astronomers and citizen scientists to help detect exoplanets from home. So even you can do it without expensive equipment and contribute to science in your free time. But let me explain first all the indirect methods used to detect exoplanets, and you will see what you can do.
Reflexive Motion Detection Method
The reflexive motion is the method of detection which measures the motion of the star. Imagine two objects, the star and the planet that orbits the star. Because of the gravitational pull of the planet, the star is not stationary. It wobbles a little bit. The gravitational pull of the planet is minimal, so the movement of the star is very small. The star is making tiny circles that are hard to measure, but they can be detected with Doppler spectroscopy.
Doppler Spectroscopy – Radial Velocity Method
The reflexive motion can be detected with Doppler spectroscopy because the star is moving slightly from us and towards us. It is a pretty simple idea; all we need is to analyze the spectrum of the star and measure the Doppler shift of the star in the spectrum using highly sensitive spectrographs and search for periodic shifts. When the star is moving from us, the spectrum is red shifted, and when it is moving towards us, it is blue shifted.
The first exoplanet discovered with this method was 51 Pegasi b discovered on 5th of October 1995, by Michel Mayor and Didier Queloz from the University of Geneva. This is by far the most effective method for detecting exoplanets around other stars. The problem with this method is that we can not accurately determine the mass of the orbiting planet. It only provides the data to estimate the minimum mass of the planet.
Exoplanet Detection With Transit Photometry Method
Transit photometry is the last method I will describe in this article. This method of detecting exoplanets is the one where you can participate. So what is it? We are trying to find transit by using photometry. Photometry measures the light coming from the star. If something is orbiting the star and it is in our line of sight, the brightness of the star will dip. Depending on the duration of the orbit, it will dip periodically. The problem with this method is that if the planet orbiting the star is not in our line of sight, we are not able to detect it.
So, you may think that it is not a very useful method because the condition for observing the dip in the brightness will be rare. But surprisingly, it is not. The Kepler Space Telescope mission that was observing “only” 150 000 stars in Cygnus constellation revealed that there are thousands of possible exoplanets orbiting stars in our line of sight.
Kepler Space Telescope – Exoplanet Hunter
The Kepler Space Telescope was launched in March 2009, and his main mission was to search for exoplanets, especially Earth-like planets. The mission ended in November 2018; it was expected to last only a year. And the results? The Kepler discovered more than 2600 exoplanets and another 2900 are waiting for confirmation. Analyzing the data takes time and human resources. Kepler was able to detect brightness dip 10 000:1. It’s like having 10 000 lightbulbs, and you turn only one off.
TESS – Transiting Exoplanet Survey Satellite
The new NASA mission called TESS has bigger ambitions than Kepler. It was launched in April 2018 on top of the SpaceX rocket and mostly founded by Google. MIT manufactured TESS, and it will cover almost the whole night sky not only a small area like Kepler. The mission is planned to last for two years, but we will see. Kepler was also planned for one year and lasted almost 10 years.
Analyzing Photometry Data At Home
And here is the part where everyone can contribute to science by analyzing data from Kepler and TESS. The thing is that computers work well, but the human visual pattern recognition ability is still a big deal. Sometimes better than computers have. I will show you two sites where you can analyze and search for exoplanets.
Planet Hunters TESS
The TESS is up and already collecting a huge amount of data that have to be analyzed. You can participate in the project. All you need to do is to register an account on the Planet Hunters website and start to analyze the luminosity graphs coming from TESS. The short tutorial will guide you through the process. Even 5 minutes of your time here can significantly help to find Earth-like planets.
Project Discovery – EVE Online
EVE Online is MMORPG that is well known for the great community of players and past contribution to science through the Project Discovery. The Pas project was about the Human Protein Atlas (HPA), a Swedish-based program to map all of the proteins in human cells. Half a million players participated in the project, and the results were amazing.
The current Project Discovery is about searching for exoplanets. It is working in a similar way as the website Planet Hunters TESS, but in my opinion, the interface is much better and easier to understand. And it is pretty addictive and rewarding once you get into it. Watch the short video where a professor of University in Geneva Michel Mayor, who discovered exoplanet 51 Pegasi b, is explaining what it is about. And if you want to try it, create a free EVE Online account here, and you can start right away.
If you are space freak like me, you will probably end up playing the game. It is a very complex but rewarding space game. It is not for everyone, but at least give it a try for the Project Discovery.
How to Do Transit Photometry From Home
It is possible to do the transit photometry at home with your basic astrophotography equipment. You can try it to observe already discovered exoplanets. However, if you want to find new exoplanets, you will have to collect data from one star for a few days. This is theoretically possible but very challenging task to do from your backyard. Here is an amazing video tutorial from YouTube channel The Exoplanets Channel you have to watch if you want to detect exoplanets with your astrophotography equipment. It is quite cheap to do it too.
It is mindblowing how everything changed after the first discovery of exoplanet outside of our solar system. Before that, we were hoping for a few planets out there in the universe, but the reality is that if you look upon the night sky, almost every single star has at least one planet. It is possible that the number of planets in the universe vastly outnumbers the number of stars. But the most important planets for us are Earth-like planets orbiting in the habitable zone where the temperature allows liquid water to exist. We have found many so far, and we will find more in the future for sure.
We are already planning a mission to the closest star Proxima Centauri that also happens to have exoplanet called Proxima b in the habitable zone which discovery was the most surprising so far, I think.