New worlds confuse astronomers

A pair of strange new worlds that blur the boundaries between planets and stars have been discovered beyond our Solar System, BBC News reports.

Dubbed "planemos", they circle each other rather than orbiting a star, the AP reports.

Their existence challenges current theories about the formation of planets and stars, astronomers report in the journal Science.

The pair belongs to what some astronomers believe is a new class of planet-like objects floating through space; so-called planetary mass objects, or "planemos", which are not bound to stars.

They appear to have been forged from a contracting gas cloud, in a similar way to stars, but are much too cool to be true stars.

And while they have similar masses to many of the giant planets discovered beyond our Solar System (the largest weighs in at 14 times the mass of Jupiter and the other is about seven times more massive), they are not thought to be true planets either.

The two objects have similar spectra and colours, suggesting that they formed at the same time about a million years ago.

The star known as Oph1622 is also called a brown dwarf. Its mass is equal to 14 Jupiters, or about one-seventy-fifth that of the Sun.

The two are separated by 22 billion miles, or about six times the distance between the Sun and Pluto. Both are young, about a million years old. Astronomers refer to them both by a recently coined word, planemo (pronounced PLAN-uh-mo), short for planetary mass object - planet-size bodies that may or may not be planets, New York Times reports.

Within the solar system, astronomers have been debating where to put the dividing line between planets and smaller clumps of rock and ice like comets and asteroids. The discovery of an object larger than Pluto in the outer solar system last year has rekindled debate on whether Pluto, by far the smallest among the current roster of nine planets, should be demoted.

In the past decade astronomers have found 200 planets around other stars . Almost all of these have been indirectly detected from a slight shift in the frequency of a star’s light caused by the gravitational pull of a planet.