Hubble detects tiny 'lost' planets

Astronomers using the Hubble space telescope may have found the smallest 'free-floating' objects detected.

The six planet-sized masses are too small to be seen directly but were noticed when they passed in front of a distant star.

Their gravitational fields acted like a lens, brightening the star behind them for a short time.

The effect, known as micro-lensing, was so brief in each case that astronomers who observed it reckon they may be only 80 times the mass of the Earth.

Objects this small have never before been detected by micro-lensing observations and if the results are confirmed the bodies would be the smallest objects seen that are not orbiting any star.

The six masses, all inside the globular cluster M22, may be planets torn away from parent stars in the cluster.

The work was carried out by a team led by Kailash Sahu of the Space Telescope Science Institute in Maryland and published in the journal Nature.

He said: "Hubble's excellent sharpness allowed us to make this remarkable new type of observation, successfully demonstrating our ability to see very small objects."

In April two astronomers revealed they had found 13 "free-floating" objects in the Orion Nebula which don't orbit any star.