Hubble confirms planets are made from dust

Don't tell Kim 'n' Aggie

Immanuel Kant was right: planets are formed from disks of dusty debris swirling around stars. NASA says images taken by the Hubble Space Telescope finally confirm Kant's prediction, made over 200 years ago.

The images, captured by Hubble back in 2000, show a planet orbiting in the same plane as its star's disk of dust. Over 200 examples of stars with extra solar planets have been found and there is no shortage of examples of young stars encircled by disks of debris. But prior to this Hubble image, there had been no evidence of both co-existing.

The planet orbits a Sun-like star called Epsilon Eridani, just 10.5 light-years from Earth in the constellation Eridanus. The planet's orbit is inclined 30 degrees to Earth, the same angle at which the star's disk is tilted.

In this, it is similar to our own solar system, where all the planetary orbits* are aligned. This has been interpreted as evidence that they all formed at the same time as the sun's disk. But Epsilon Eridani is much younger than our sun - only 800 million years old - so its disk has not yet dissipated, so both the planet and the Hubble confirm disks can co-exist.

The planet is the nearest extra-solar planet to Earth that has been found so far. It is now known to be around 1.5 times as massive as Jupiter, and it orbits its star every 6.9 years.

"Because of Hubble, we know for sure that it is a planet and not a failed star," Barbara McArthur of the University of Texas explained. She led the research along with her colleague G Fritz Benedict.

Making that deduction was not the work of five minutes. The team first identified the planet using the radial-velocity method. This measures tiny changes in a star's motion towards and away from Earth to infer the existence of unseen companions.

The team studied over a thousand astrometric observations from Hubble combined with other astrometric observations made at the University of Pittsburg's Allegheny Observatory. All this data was added to hundreds of ground-based radial-velocity measurements made over the past 25 years at various telescopes including the European Southern Observatory in Chile, and the McDonald Observatory at the University of Texas.

Their work is to be published in the November issue of the Astronomical Journal.

*Yes, all. See the demotion of Pluto for more details.

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