Pluto hogs the spotlight in the continuing scientific debate over what is and what is not a planet, but a less conspicuous argument rages on about the planetary status of massive objects outside our solar system. The dispute is not just about semantics, as it is closely related to how giant planets like Jupiter form.
Dim objects called brown dwarfs, less massive than the Sun but more massive than Jupiter, have powerful winds and clouds — specifically, hot patchy clouds made of iron droplets and silicate dust. Scientists recently realised these giant clouds can move and thicken or thin surprisingly rapidly, in less than an Earth day, but did not understand why.
Brown dwarfs are sometimes called failed stars as they are too small to sustain the hydrogen fusion process that powers stars. Their temperatures can range from nearly as hot as a star to as cool as a planet and their masses also range between star-like and giant-planet-like. A near-infrared survey has discovered several ultracool brown dwarfs in the Sun’s vicinity.
The European Southern Observatory’s HAWK-I infrared instrument on the Very Large Telescope (VLT) in Chile has been used to peer deeper into the heart of Orion Nebula than ever before. The spectacular picture reveals about ten times as many brown dwarfs and isolated planetary-mass objects than were previously known.
Contradicting the long-standing idea that large Jupiter-mass planets take a minimum of 10 million years to form, astronomers have just announced the discovery of a giant planet in close orbit around a 2 million-year-old star that still retains a disc of circumstellar gas and dust. CI Tau b is at least eight times larger than Jupiter and 450 light-years from Earth.
Brown dwarfs are objects that are too large to be called planets, yet too small to shine by nuclear fusion. Two German researchers have taken a careful look at the distribution of nearby examples of these “failed stars” and to their surprise discovered a significant asymmetry in their spatial arrangement.