In the night sky: Orion
In the night sky: Orion

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

In the night sky: Orion

4.3.1 Exoplanet encyclopedia

Described image
Figure 24 This chart shows artistic representations of all the known potentially habitable exoplanets ranked from best to worst by the Earth Similarity Index.

The Exoplanets Encyclopedia, run by the European exoplanet team, keeps an up-to-date list of how many exoplanets have been discovered – it now stands at more than 2000, including several systems where more than one exoplanet orbits its star.

Exoplanets are difficult to observe, partly because planets are very small compared with stars and partly because they don’t give out light of their own – planets ‘shine’ by reflecting light from the star they orbit. And this is the main reason why it is difficult to detect exoplanets – they are incredibly faint compared to a star. So how do you detect a faint planet-sized object orbiting a star many light years away?

The first exoplanet orbiting a main sequence star was observed in 1995. It has a mass much greater than that of the Earth – it is about half the mass of Jupiter – but orbits its star, 51 Pegasi, at a closer distance than Mercury orbits the Sun. For many years, the only exoplanets to be discovered were similar to this.

These hot Jupiters are gas giants that orbit very close to their stars and thus have a very high surface temperature. Hot Jupiters were, until the advent of spaceborne telescopes, the most common form of extrasolar planet known, because of the relative ease of detecting them from ground-based instruments.

In the next section, you will learn about the methods used to detect exoplanets.

INS_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371