Spies in space: scientists find stars masquerading as planets

Astronomers have discovered at least three small stars masquerading as exoplanets.

They were originally discovered by NASA's Kepler space telescope. Scientists classified them as exoplanets. However, a new study suggests a mistake may have crept in.

Scientists have revised their approach to determining the size of stars. This revealed three suspicious objects - Kepler-854b, Kepler-840b and Kepler-699b. They were about the size of two to four Jupiters - too big to be planets. Researchers say they should be classified as small stars.

The fourth suspicious object, known as Kepler-747b, is about 1.8 times the size of Jupiter, which is normal for an exoplanet. However, Kepler-747b is located relatively far from its star, meaning it probably doesn't receive enough light. It is also likely to be a star.