What is an exoplanet? Planets beyond our solar system, explained
By the WhyCosmos team · Last updated:
An exoplanet is a planet that orbits a star other than our Sun. The first ones were confirmed in the 1990s; today more than 6,000 are known, from rocky worlds the size of Earth to giants bigger than Jupiter. Most are found indirectly, by the tiny effects they have on the light of the star they orbit.
Until the 1990s, nobody knew for certain whether planets existed around other stars. Today more than 6,000 are confirmed, and Indian scientists have discovered some of them. The question has moved on from "are there other planets?" to "could any of them have life?", which is exactly the kind of open question that turns a curious child into a scientist.
How to explain it to your child
Explain it to an 8-year-old
Our Sun is one lamp in a gigantic neighbourhood, and Earth is one of the planets going around it. Now imagine another lamp very far away, with its own planets going around it. Those faraway planets are exoplanets. They are so far away and so dim that scientists usually find them by noticing how they change their star's light.
Explain it to a 13-year-old
An exoplanet is a planet outside our solar system that orbits another star. Astronomers rarely see one directly, because its star is millions or billions of times brighter. Instead they measure the planet's effect on the star: a tiny regular dip in brightness when the planet passes in front of it (the transit method), or a slight wobble in the star's motion caused by the planet's gravity (the radial velocity method). An Earth-size planet crossing a Sun-like star dims it by only about one hundredth of one percent.
Key facts
| What it is | A planet orbiting a star outside our solar system |
|---|---|
| Also called | Extrasolar planet |
| Confirmed so far | More than 6,000; NASA's Exoplanet Archive passed 6,000 in September 2025 |
| First confirmed | 1992, around a pulsar; the first around a Sun-like star, 51 Pegasi b, in 1995 |
| Most successful detection method | The transit method: a tiny dip in starlight |
| Closest known | Proxima Centauri b, about 4.2 light-years away |
| India's discovery | K2-236b, announced in 2018 by PRL Ahmedabad using the PARAS spectrograph at Mount Abu |
| Life found? | Not yet; there is no confirmed evidence of life beyond Earth |
How do scientists find exoplanets?
| Method | How it works | Best at finding |
|---|---|---|
| Transit | The planet passes in front of its star, which dims slightly and regularly | Planets close to their stars; used by NASA's Kepler and TESS missions, and behind most known exoplanets |
| Radial velocity | The planet's gravity makes the star wobble, shifting its light slightly towards blue and then red | Massive planets; this method also gives a minimum mass for the planet |
| Direct imaging | The star's glare is blocked so the planet itself can be photographed | Young, hot giant planets far from their stars |
| Microlensing | A star with a planet passes in front of a more distant star and briefly magnifies its light | Planets far from Earth and far from their own stars |
Combining two methods tells scientists the most: a transit gives a planet's size, radial velocity gives its mass, and together they give its density, which shows whether it is rocky or gassy.
Has India discovered an exoplanet?
Yes. In 2018, scientists at the Physical Research Laboratory (PRL) in Ahmedabad announced K2-236b, a planet about 27 times Earth's mass and six times its size, orbiting a Sun-like star roughly 600 light-years away. They measured it with PARAS, a spectrograph designed in India, on a 1.2-metre telescope at Gurushikhar near Mount Abu. With that discovery India joined the small group of countries that have found planets around other stars, and PRL teams have reported more since.
What is the habitable zone?
The habitable zone, sometimes called the Goldilocks zone, is the range of distances from a star where a planet's surface could be neither too hot nor too cold for liquid water. Several planets orbit inside their star's habitable zone, including some of the seven Earth-size planets around the star TRAPPIST-1, about 40 light-years away. Kepler-186f, announced in 2014, was the first Earth-size planet found in the habitable zone of another star.
Being in the habitable zone does not mean a planet has life, or even water. It also needs the right atmosphere and conditions, and most of those details are still unknown.
Could there be life on an exoplanet?
Scientists have not confirmed life anywhere beyond Earth, but exoplanets give them places to look. Large telescopes can now study starlight that passes through a planet's atmosphere and work out which gases are present. In 2022 NASA's James Webb Space Telescope made the first clear detection of carbon dioxide in an exoplanet's atmosphere, on the giant planet WASP-39b.
In 2025 a research team reported a possible hint of a gas linked to living things in the atmosphere of K2-18b. Other scientists have not confirmed it, and the claim remains disputed. That honest uncertainty is a good example for children of how science actually works: a claim is tested by others before it is accepted.
Are exoplanets like Earth?
Most are not. Astronomers have found "hot Jupiters", gas giants orbiting so close to their stars that a year lasts a few days, and "super-Earths" and "mini-Neptunes", sizes between Earth and Neptune that are common in the galaxy but missing from our own solar system. The very first exoplanets ever confirmed, in 1992, orbit a pulsar, a rapidly spinning neutron star left behind by a supernova.
The telescopes and techniques behind these discoveries, from optics to the electromagnetic spectrum and space telescopes, are lessons 4 to 7 of Astronomy 201, the WhyCosmos course that follows Astronomy 101.
Questions parents and kids ask
An exoplanet is a planet that goes around a star other than our Sun, far outside our solar system.
No. Earth orbits the Sun, so it is one of the eight planets of our own solar system. Exoplanets orbit other stars.
More than 6,000 have been confirmed. NASA's Exoplanet Archive passed the 6,000 mark in September 2025, and thousands more candidates are waiting to be confirmed.
Proxima Centauri b, about 4.2 light-years away. It orbits Proxima Centauri, the nearest star to the Sun, inside that star's habitable zone.
Yes. In 2018 scientists at the Physical Research Laboratory, Ahmedabad, announced K2-236b, found with the Indian-built PARAS spectrograph at Mount Abu.
Possibly, but no life beyond Earth has been confirmed. Telescopes such as the James Webb Space Telescope are now studying exoplanet atmospheres for gases that could be signs of life.
Your child asks questions like this every week.WhyCosmos runs live online astronomy classes for ages 8–16, taught by real astrophysicists — where questions like these are the curriculum.
Related terms in this glossary
Sources and further reading
NASA: Exoplanets · NASA Exoplanet Archive · ISRO: PRL scientists discover a sub-Saturn exoplanet (2018)