Exoplanets: All About them
When you look up at the sky, you can see thousands of stars lighting up the night sky. The stars that we see in the night sky make up only an extremely small fraction of the stars our galaxy contains, hundreds of billions of more stars exist in just our galaxy. By hearing this, a new question arises to your mind — Are there any planets orbiting these stars? Today, with modern technology, we are able to answer this question and the answer is YES!
Our star, the Sun itself is orbited by 8 planets, many dwarf planets and an infinite amount of space rocks. There are so many stars in the night sky that it is hard to believe that only our Sun is orbited by planets. Trying to find planets orbiting other stars is extremely hard but it is possible. The biggest problem is that any planet outside our Solar System would be very faint and far away. You might think that a telescope would solve this problem but again this does not solve the problem because the parent star would so bright and big that the planet would be completely outshined. So, spotting a planet orbiting a star directly with a telescope or any other type of instrument is not possible. However, you may be able to find a way to discover planets orbiting other stars.
As the planet orbits its parent star, it makes a big circle or an Ellipse. But the planet also has gravity and so it produces tugs on the star, which means that the star will make a small circle. This is known as Reflexive Motion. For a long time, this motion was very hard to find, even in nearby stars. So it turns out that indirect effects are also difficult to see.
In 1992, all of this changed. Astronomers Aleksander Wolsczan and Dale Frail made a shocking discovery. They had just found two planets orbiting a pulsar, the dead remnant of a massive star that had exploded. This was a very bizarre discovery. When a star explodes, the event is so powerful and catastrophic that it should have destabilized the orbit of any planet. However, follow up research confirmed that the planets did exist and in fact, a third one was found a few years later. These were the first planets discovered orbiting a star outside our Solar System. Any planet that orbits a star outside our Solar System is known as an Exoplanet or an Extrasolar Planet.
After this shocking discovery, another question arised — Are there any planets orbiting other Sun-like stars? In 1995, the Swiss astronomers Michel Mayor and Didier Queloz answered this question. They had found a planet orbiting the star 51 Peg, a Sun-like star located just 50 light-years away from us in the constellation of Pegasus. The Swiss astronomers discovered the planet by observing the Reflexive Motion of the star. So, discovering planets by observing the Reflexive Motion of the star is possible. Even though the back and forth motion of the star is too small, it is still detectable. Detecting this motion is very difficult and requires the use of some fancy and expensive equipment. However, the planet they had discovered called 51 Peg B was very very weird for many reasons. The planet had an orbital period of just 4 days, which means that this planet is extremely close to its parent star, just 8 million km away! In our Solar System, Mercury, the closest planet to the Sun, is about 55 million kilometres away from the Sun. The amount of tugs produced by the planet is dependent on the mass of the star — The more massive the planet, the harder it pulls on the parent star, making it move more quickly. They had found that 51 Peg B was about half the mass of Jupiter, and this was a problem. According to planetary formation models, this wasn’t possible. A planet couldn't form that big and that close to its parent star. It had probably formed farther out and then migrated inward, toward the star as it interacted with the surrounding disk of gas and dust. In our Solar System, Jupiter was formed in this process. Planets like 51 Peg B, which are extremely close to their parent star are known as Hot Jupiters. In the next few years, many other Hot Jupiters were found, just like 51 Peg B.
In 1999, a planet called HD 209458b had been discovered. It had a very short orbit around its star, so close that it took just 3.5 days to complete one orbit around its parent star. From our point of view on Earth, this planet’s orbit was edge-on. That means once per every orbit, we can see it pass directly in front of its parent star. This event is known as a transit. When a planet transits in front of its parent star, it blocks a little amount of the star’s light. That means we can detect the extremely small dip in the star’s brightness. That dip was found during the transit of HD 209458b. The amount of starlight blocked tells you how big the planet is — A bigger planet blocks more amount of starlight while a smaller planet blocks a lesser amount of starlight.
In 2009, NASA launched the Kepler Space Telescope, which is designed to detect transits around stars, therefore discovering new exoplanets. By early 2015, the Kepler Space Telescope had discovered the 1000th confirmed planet and 500 more were discovered by ground-based observatories and thousands more awaiting confirmation.
Can we take a photo of an exoplanet?
Taking a picture of an exoplanet is difficult because it is extremely faint but it is not impossible. In 2004, the first photo of an exoplanet was released. The planet that was photographed is known as 2M1207b.
A dozen more exoplanets have been photographed. Hot Jupiters are the easiest to photograph as they’re massive and fast, making them easily detectable. But as the technology has improved, we have been able to photograph exoplanets smaller than Mercury. We have also been able to see planets bigger than Earth but smaller than Neptune. Any exoplanet that is larger than Earth but smaller than Neptune is known as a Super-Earth.
Are there any habitable exoplanets just like Earth?
We have thousands of planets in just our own galaxy. But how many of them are habitable? Now, we have found many Earth-sized planets but Earth-like planets are totally different. For a planet to support life, it has to be at the right distance from its parent star to support Earth-like conditions and support the existence of liquid water on its surface. We’re just not sure. But from what we have studied so far, it looks like thousands of Earth-like planets might exist. Other things like an atmosphere and a magnetic field are also required for a planet to support life. But still, there are a lot of exoplanets and one of them could very well be a twin of Earth.