Star revealed with seven Earth-sized planets in orbit

Trappist-1 is 40 light years away but scientists believe orbiting planets may support life

Thousands of exoplanets orbiting stars have been discovered but few are the Earth’s size. File photograph: Getty Images

Astronomers have discovered a nearby star that has seven Earth-sized planets in orbit around it.

At least six of them match Earth’s temperature, raising the possibility they may have liquid water that could support life.

The host star is called Trappist-1 and lies 40 light years away. It is known as an ultracool dwarf because it is no bigger than the planet Jupiter and gives off far less heat and light than our sun.

Its planets orbit right in close to the star and so receive more or less the same amounts of light and warmth as Earth does from our sun.


Scientists are very excited about the amazingly rich discovery not least because over time they will be able to learn all about the atmospheric and surface conditions of these planets and whether any of them carry liquid water.

“This is the first time so many Earth-sized planets have been found around a star,” said Prof Michaël Gillon of the University of Liége. “The most exciting thing is they are ideal for atmospheric study.”

Powerful stars

Thousands of exoplanets orbiting stars have been discovered but few are the Earth's size and density and most orbit large powerful stars.

The international research team decided to look at ultracool dwarf stars instead, and quickly found what they were looking for, planets.

They published their findings in the journal Nature.

“We got a clue something was going on with that star. We followed it continuously and accumulated months of data,” said Prof Gillon. They found three planets last May but the data from a collection of Earth-based and orbiting telescopes soon revealed the full count of seven planets.

Trappist-1’s planets were discovered by their transits, when they pass in front of the star and block some of its light.

“Choosing to look at a small star means we have 80 times the magnification,” said Dr Amaury Triaud based at the University of Cambridge. “That means we will be able to study the climate and chemical nature of the [planets’] atmospheres.”

Their success with Trappist-1 has encourage them to look at 1,000 small cool stars over the coming years using a dedicated telescope based at the European Southern Observatory.

Dick Ahlstrom

Dick Ahlstrom

Dick Ahlstrom, a contributor to The Irish Times, is the newspaper's former Science Editor.